Staff Publications

Staff Publications

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    'Staff publications' is the digital repository of Wageningen University & Research

    'Staff publications' contains references to publications authored by Wageningen University staff from 1976 onward.

    Publications authored by the staff of the Research Institutes are available from 1995 onwards.

    Full text documents are added when available. The database is updated daily and currently holds about 240,000 items, of which 72,000 in open access.

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    pH-Controlled Coacervate-Membrane Interactions within Liposomes
    Last, Mart G.F. ; Deshpande, Siddharth ; Dekker, Cees - \ 2020
    ACS Nano 14 (2020)4. - ISSN 1936-0851 - p. 4487 - 4498.
    coacervates - liposomes - liquid−liquid phase separation - membranes - microfluidics

    Membraneless organelles formed by liquid-liquid phase separation are dynamic structures that are employed by cells to spatiotemporally regulate their interior. Indeed, complex coacervation-based phase separation is involved in a multitude of biological tasks ranging from photosynthesis to cell division to chromatin organization, and more. Here, we use an on-chip microfluidic method to control and study the formation of membraneless organelles within liposomes, using pH as the main control parameter. We show that a transmembrane proton flux that is created by a stepwise change in the external pH can readily bring about the coacervation of encapsulated components in a controlled manner. We employ this strategy to induce and study electrostatic as well as hydrophobic interactions between the coacervate and the lipid membrane. Electrostatic interactions using charged lipids efficiently recruit coacervates to the membrane and restrict their movement along the inner leaflet. Hydrophobic interactions via cholesterol-tagged RNA molecules provide even stronger interactions, causing coacervates to wet the membrane and affect the local lipid-membrane structure, reminiscent of coacervate-membrane interactions in cells. The presented technique of pH-triggered coacervation within cell-sized liposomes may find applications in synthetic cells and in studying biologically relevant phase separation reactions in a bottom-up manner.

    Melamine-Based Microporous Organic Framework Thin Films on an Alumina Membrane for High-Flux Organic Solvent Nanofiltration
    Amirilargani, Mohammad ; Yokota, Giovana N. ; Vermeij, Gijs H. ; Merlet, Renaud B. ; Delen, Guusje ; Mandemaker, Laurens D.B. ; Weckhuysen, Bert M. ; Winnubst, Louis ; Nijmeijer, Arian ; Smet, Louis C.P.M. de; Sudhölter, Ernst J.R. - \ 2020
    ChemSusChem 13 (2020)1. - ISSN 1864-5631 - p. 136 - 140.
    membranes - microporous materials - organic solvent nanofiltration - polymers - porous organic frameworks

    Microporous polymer frameworks have attracted considerable attention to make novel separation layers owing to their highly porous structure, high permeability, and excellent molecular separation. This study concerns the fabrication and properties of thin melamine-based microporous polymer networks with a layer thickness of around 400 nm, supported on an α-alumina support and their potential use in organic solvent nanofiltration. The modified membranes show excellent solvent purification performances, such as n-heptane permeability as high as 9.2 L m−2 h−1 bar −1 in combination with a very high rejection of approximately 99 % for organic dyes with molecular weight of ≥457 Da. These values are higher than for the majority of the state-of-the-art membranes. The membranes further exhibit outstanding long-term operation stability. This work significantly expands the possibilities of using ceramic membranes in organic solvent nanofiltration.

    In vivo 1H NMR methods to study dynamics of chloroplast water and thylakoid membrane lipids in leaves and in photosynthetic microorganisms
    Pagadala, Shanthi - \ 2017
    Wageningen University. Promotor(en): H. van Amerongen, co-promotor(en): H. van As. - Wageningen : Wageningen University - ISBN 9789463431569 - 130
    cell membranes - membranes - chloroplasts - thylakoids - photosynthesis - in vivo experimentation - stress conditions - stress - proteins - lipids - mobility - dynamics - celmembranen - membranen - chloroplasten - thylakoïden - fotosynthese - in vivo experimenten - stress omstandigheden - stress - eiwitten - lipiden - mobiliteit - dynamica

    Dynamics of thylakoid membranes and mobility of pigment-protein complexes therein are essential for survival of photosynthetic organisms under changing environmental conditions. The published approaches to probe mobility of the thylakoid membrane lipids and protein complexes are either dependent on the use of external labels or are used only for in vitro studies. Here, we present non-invasive 1H NMR methods (DOSY and DRCOSY) to study dynamics of water in chloroplasts, lipids in oil bodies and in thylakoid membranes and pigment-protein complexes under complete in vivo conditions in leaf disks of F. benjamina and A. platanoides and in suspensions of the green alga Chlamydomonas reinhardtii and blue-green alga Synechocystissp.PCC 6803.

    In leaf disks of Ficus benjamina and Acer platanoides, water in chloroplasts could be clearly discriminated from other pools. Both water in chloroplasts, and water in vacuoles of palisade and spongy cells showed resonances in the high field part of the spectra (with respect to pure water), in contrast to what has been reported in literature. Subepidermal cells (present only in F. benjamina but not in A. platanoides) may act as a water storage, buffer pool during drought. This pool prevented the fast loss of water from the chloroplasts. Nutrient stress and excess salt stress resulted in accumulated lipid bodies and in striking differences in the dynamics and spectra/composition of the different components. T2 values of the different components are compared with those observed in suspensions of Synechocystissp.PCC 6803. The differences in membrane composition (ratio of the different membrane lipids) were clearly observed in the DANS of the oil bodies and the (thylakoid) membranes, but the diffusion coefficients were quite comparable. Also the DANS of the component that is assigned to the pigment-protein complexes are quite different, reflecting the differed composition. The diffusion coefficients of this component in isolated spinach thylakoids and in C. reinhardtii are very comparable, but about a factor of 10 lower with respect to that of Synechocystis at short diffusion times. The dynamics of these complexes in these systems are thus quite different.

    Thermo-responsive block copolymers : synthesis, self-assembly and membrane development
    Mocan Cetintas, Merve - \ 2017
    Wageningen University. Promotor(en): F.A.M. Leermakers, co-promotor(en): M.M.G. Kamperman. - Wageningen : Wageningen University - ISBN 9789463431583 - 177
    polymer chemistry - polymers - membranes - synthesis - self assembly - thermal properties - polymeerchemie - polymeren - membranen - synthese - zelf-assemblage - thermische eigenschappen

    Block copolymers (BCPs) are remarkable materials because of their self-assembly behavior into nano-sized regular structures and high tunable properties. BCPs are in used various applications such as surfactants, nanolithography, biomedicine and nanoporous membranes. In these thesis, we aimed to fabricate thermo-responsive iso- and nanoporous membranes from BCPs.

    First, we optimized the synthesis of a thermo-responsive BCP, i.e. polystyrene-poly(N-isopropyl acrylamide) (PS-PNIPAM) with desired properties using controlled/living polymerization methods. We fabricated membranes using self-assembly and non-solvent induced phase separation (SNIPS) method. The membranes were nanoporous, thermo-responsive and exhibited an interconnected worm-like surface.

    We investigated the self-assembly behavior of BCPs using both theoretical and experimental approaches. The theoretical investigation involves self-consistent field modelling of Scheutjens and Fleer (SF-SCF) which is used for the first time for BCP self-assembly phenomena. Using SF-SCF, first, we found a chain length dependence on the critical point of BCP phase diagram which confirms well with the reported literature. Second, we worked on the stability of the common mesophases (e.g. single and double gyroids, double diamond, hexagonally perforated lamellae) that is observed between hexagonally ordered cylindrical (HEX) and lamellar (LAM) phases; at chain length, =300 and at intermediate segregation regime, =30. Among the mentioned mesophases double gyroid was the only phase dominant over HEX and LAM phases. At strong segregation regime of =120 with the same chain length, double gyroid was found as a metastable phase.

    The experimental approach of the BCP self-assembly was performed by solvent annealing of BCP thin films. For annealing, common laboratory solvents e.g. methanol, tetrahydrofuran, toluene were used with various ratios to tune the selectivity of the solvent mixtures to the blocks in the copolymer. A lamellar forming triblock copolymer using the solvent mixtures methanol: THF (v:v) 1:2 or methanol: toluene (v:v) 1:1 resulted in HEX phase. In contrast, no sustained long-range order was found when only one type of solvent was used.

    Next, we optimized the membrane fabrication parameters to obtain membranes with an isoporous surface. We investigated the effect of solvent selectivity, evaporation time and polymer concentration. For PS selective solvents, membranes exhibited a disordered surface whereas PNIPAM selective solvents resulted in membranes with an isoporous surface. For a large parameter space, isoporous membranes were attained which is not common for SNIPS method. Permeability tests at various temperatures proved fully reversible thermo-responsive behavior of these membranes.

    Finally, we concluded our work with future recommendations to obtain block copolymer membranes that have improved properties and suggested tests that will prove membranes’ suitability for industrial applications.

    Tuning for light and more : engineering phototrophy and membrane proteins in Escherichia coli
    Claassens, Nicolaas J.H.P. - \ 2017
    Wageningen University. Promotor(en): John van der Oost; Willem de Vos, co-promotor(en): Vitor Martins dos Santos. - Wageningen : Wageningen University - ISBN 9789463430920 - 328
    escherichia coli - phototropism - membranes - proteins - light - photosystem i - gene expression - escherichia coli - fototropie - membranen - eiwitten - licht - fotosysteem i - genexpressie

    The application of microbial and plant photosynthesis for biobased production on the one hand has a huge potential but on the other hand photosynthesis has serious limitations regarding its efficiency. Hence, studying both fundamental features of photosynthetic processes and engineering of photosystems is of paramount interest, exploring the engineering of photosystems is the overarching aim of this thesis. As described in Chapter 1, natural photosystems may be modified or transplanted to allow for more efficient conversion of solar light energy into biochemical energy. Hereto ambitious proposals to engineer photosystems have been made, and to realize those endeavors the disciplines of synthetic and systems biology are required. To explore how to apply and improve those disciplines hereto, the work described in this thesis has focused on the transplantation of simple photosystems (proton-pumping rhodopsins; PPRs) into the cell membrane of the heterotrophic model bacterium Escherichia coli. Both in silico analyses, including metabolic and thermodynamic modeling (Chapter 3) and a series of experimental studies on transplanting PPR photosystems (Chapters 4,6 and 7) were performed, which identified several challenges, limitations and most importantly opportunities. This thesis also describes the application of novel tools to substantially improve the functional production of PPRs and a variety of other membrane proteins in E. coli.

    Chapter 2 provides more details on previously reported examples of heterologous expression of PPRs in several hosts, and on the physiological impact of these transplanted photosystems. Based on this evaluation, some suggestions are made to improve and further exploit the transplantation of these photosystems.

    In Chapter 3 a systematic, integrated in silico analysis is made of anaerobic, photo-electro-autotrophic synthetic metabolism in E. coli, consisting of (i) a PPR photosystem for ATP regeneration, (ii) an electron uptake pathway, and (iii) a natural or synthetic carbon fixation pathway. Constraint-based metabolic modelling of E. coli central metabolism is used, in combination with kinetic and thermodynamic pathway analyses. The photo-electro-autotrophic designs are predicted to have a limited potential for anaerobic, autotrophic growth of E. coli, given the relatively low ATP regenerating capacity of the PPR photosystems, and the relatively high ATP consumption due to maintenance. In general these analyses illustrate the potential of in silico analyses to identify potential bottlenecks and solutions in complex designs for autotrophic and photosynthetic metabolism, as a basis for subsequent experimental implementation.

    To tackle a main bottleneck of PPR systems: their functional membrane-embedded production level, the heterologous production in E. coli of the proton-pumping rhodopsins from Gloeobacter violaceus (GR) and from Thermus thermophilus JL18 (TR) is quantified and experimentally optimized in Chapter 4. High constitutive production of both rhodopsin proteins is achieved by fine-tuning transcription and translation. Besides the canonical retinal pigment, the GR system has the ability to bind a light-harvesting antennae pigment, echinenone. After optimization of the heterologous pigment biosynthesis pathways for either retinal or echinenone production, appropriate quantities of retinal or echinenone for PPR reconstitution were detected in E. coli. Association of echinenone with GR broadens its absorption spectrum in E. coli, broadening the potential for light-harvesting also to blue light. Optimization of the branched pathway for simultaneous biosynthesis of both retinal and echinenone has been attempted by using a smart library of variable Ribosome Binding Sites (RBSs) with varying strengths (RedLibs). In general, the here described approaches towards improved functional production of rhodopsin photosystems in E. coli and their pigments may prove more widely applicable for heterologous production of more complex photosystems and other systems.

    In Chapter 5 an up-to-date overview is provided on how codon usage can influence functional protein production. The fact that all known organisms have an incomplete set of tRNAs, indicates that biased codon usage could act as a general mechanism that allows for fine-tuning the translation speed. Although translation initiation is the key control step in protein production, it is broadly accepted that codon bias, especially in regions further downstream of the start codon, can contribute to the translation efficiency by tuning the translation elongation rate. Modulation of the translation speed depends on a combination of factors, including the secondary structure of the transcript (more or less RNA hairpins), the codon usage landscape (frequent and more rare codons) and for bacteria also RBS-like sequences at which ribosomes can pause. The complex combination of interdependent factors related to codon usage that can influence translation initiation and elongation. This complexity makes that the design of synthetic genes for heterologous expression is still in its infancy, and despite the availability of some codon usage algorithms, it is often as well a matter of trial and error.

    In Chapter 6 the effect of different codon usage algorithms (optimization and harmonization) has been experimentally tested for heterologous production of membrane proteins. Apart from the codon usage algorithms also the combined effect of transcriptional fine-tuning in E. coli LEMO21(DE3) was assessed. The overproduction of 6 different membrane-embedded proteins, including 4 PPR variants (from bacteria, archaea and eukaryotes), was tested. For production of tested PPR variants, the different codon usage algorithms hardly influenced production, while transcriptional tuning had a large impact on production levels. Interestingly, for the other two tested non-PPR membrane proteins, some codon usage variants significantly improved production on top of transcriptional tuning. For both these proteins the codon-optimization algorithm reduced functional production below that of the wild-type codon variant, while the harmonization algorithm gave significantly higher production, equal or even higher than for the wild-type variant.

    In Chapter 7 it is demonstrated that a translational-tuning system can be used to successfully optimize the expression of several membrane proteins, based on initial findings presented in Chapter 4. The employed, recently developed Bicistronic Design (BCD) system is based on translational coupling of a gene encoding a short leader peptide and the gene of interest that is under control of a variable ribosome binding site. A standardized library of 22 RBSs allows for precise, gene context-independent, fine-tuning of expression of this second gene, here encoding a membrane protein. For all four membrane proteins tested in this study the BCD approach resulted in 3 to 7-fold higher protein levels than those obtained by two other recently developed methods for optimizing membrane protein production. The presented approach allows for inducer-free, constitutive, high-level production of membrane proteins in E. coli, which can be widely applicable for both membrane protein purification studies as well as for synthetic biology projects involving membrane proteins.

    In Chapter 8 a broad review and perspectives are provided on the potential of microbial autotrophs for the production of value-added compounds from CO2. Both photoautotrophic and chemolithoautotrophic production platforms are discussed, and recent progress in improving their efficiency and production potential is highlighted. Transplantation efforts for photosystems, but also for CO2 fixation pathways and electron uptake systems are discussed. An overview is provided on novel in silico and experimental approaches to engineer components related to autotrophy in heterotrophic and autotrophic model hosts, including approaches applied in this thesis. Future avenues are discussed for realizing more efficient autotrophic production platforms.

    Finally, in Chapter 9 and 10 the work in this thesis is summarized and a general discussion is provided on future avenues for engineering of PPR photosystems, photosystems in general and on the optimization of membrane protein production.

    Breaking down barriers: construction of a hybrid heterochiral membrane
    Siliakus, Melvin - \ 2016
    Wageningen University. Promotor(en): John van der Oost, co-promotor(en): Servé Kengen. - Wageningen : Wageningen University - ISBN 9789462579293 - 237
    membranes - engineering - escherichia coli - fatty acids - isoprenoids - archaea - thermococcus kodakarensis - polymerase chain reaction - gene knock-out - dna modification - membranen - engineering - escherichia coli - vetzuren - isoprenoïden - archaea - thermococcus kodakarensis - polymerase-kettingreactie - inactivering van genen - dna-modificatie

    Because of a chemical disparity between Archaeal and Bacterial membrane-lipids, these organisms thrive under distinct environmental conditions. Archaea are generally more resistant to extreme habitats like low pH, high temperature or presence of solvents. It has therefore long been hypothesized that the archaeal lipids provide archaeal cells with a higher robustness than bacterial lipids do for Bacteria. A recent study in which bacterial and archaeal lipids were mixed to form hybrid vesicles “lipid enclosed round structures”, for instance showed a higher temperature dependent stability than either the bacterial or archaeal lipid vesicles separately. In the present study, we therefore introduced the enzymatic machinery for assembly of archaeal lipids into the bacterium Escherichia coli. This engineering led to cells with a mixed membrane at a surprisingly high amount of 28% archaeal lipids. Although the intervention led to severe morphological malformations, the cells indeed showed an increased robustness to extreme cold and butanol.

    Preparation of polylactide microcapsules at a high throughput with a packed-bed premix emulsification system
    Sawalha, Hassan ; Sahin, Sami ; Schroën, Karin - \ 2016
    Journal of Applied Polymer Science 133 (2016)24. - ISSN 0021-8995
    biomedical applications - colloids - drug-delivery systems - membranes

    Core-shell polymer microcapsules are well known for their biomedical applications as drug carriers when they are filled with drugs and gas-filled microcapsules that can be used as ultrasound contrast agents. The properties of microcapsules are strongly dependent on their size (distribution); therefore, equipment that allows the preparation of small and well-defined microcapsules is of great practical relevance. In this study, we made polylactide microcapsules with a packed-bed premix emulsification system that previously gave good results for regular emulsions. Here, we tested it for applicability to a system in which droplets shrank and solidified to obtain capsules. The packed-bed column was loaded with glass beads of different sizes (30-90 μm) at various bed heights (2-20 mm), and coarse emulsions consisting of the polymer, a solvent, and a nonsolvent were pushed repeatedly through this system at selected applied pressures (1-4 bar). The obtained transmembrane fluxes (100-1000 m3 m-2 h-1) were much higher than those recorded for other membrane emulsification techniques. The average size of the obtained microcapsules ranged between 2 and 8 μm, with an average span of about 1; interestingly, the capsules were 2-10 times smaller than the interstitial voids of the beds. The droplets were larger when we used thicker beds and larger glass beads, and these effect correlated with the pore Reynolds number (Rep). Two breakup mechanisms were identified: spontaneous droplet snap-off dominated the system at low Reps, and localized shear forces dominated the system at higher Rep.

    Sensory quality of drinking water produced by reverse osmosis membrane filtration followed by remineralisation
    Vingerhoeds, M.H. ; Nijenhuis, M.A. ; Ruepert, N. ; Bredie, W.L.P. ; Kremer, S. - \ 2016
    Water Research 94 (2016). - ISSN 0043-1354 - p. 42 - 51.
    drinking water - water quality - sensory evaluation - taste research - reverse osmosis - membranes - filtration - drinkwater - waterkwaliteit - sensorische evaluatie - smaakonderzoek - omgekeerde osmose - membranen - filtratie
    Membrane filtration of ground, surface, or sea water by reverse osmosis results in permeate, which is almost free from minerals. Minerals may be added afterwards, not only to comply with (legal) standards and to enhance chemical stability, but also to improve the taste of drinking water made from permeate. Both the nature and the concentrations of added minerals affect the taste of the water and in turn its acceptance by consumers. The aim of this study was to examine differences in taste between various remineralised drinking waters. Samples selected varied in mineral composition, i.e. tap water, permeate, and permeate with added minerals (40 or 120 mg Ca/L, added as CaCO3, and 4 or 24 mg Mg/L added as MgCl2), as well as commercially available bottled drinking waters, to span a relevant product space in which the remineralised samples could be compared. All samples were analysed with respect to their physical–chemical properties. Sensory profiling was done by descriptive analysis using a trained panel. Significant attributes included taste intensity, the tastes bitter, sweet, salt, metal, fresh and dry mouthfeel, bitter and metal aftertaste, and rough afterfeel. Total dissolved solids (TDS) was a major determinant of the taste perception of water. In general, lowering mineral content in drinking water in the range examined (from <5 to 440 mg/L) shifted the sensory perception of water from fresh towards bitter, dry, and rough sensations. In addition, perceived freshness of the waters correlated positively with calcium concentration. The greatest fresh taste was found for water with a TDS between 190 and 350 mg/L. Remineralisation of water after reverse osmosis can improve drinking quality significantly.
    Lipid bilayer stability in relation to oxide nanoparticles
    Pera, H. - \ 2015
    Wageningen University. Promotor(en): Frans Leermakers, co-promotor(en): Mieke Kleijn. - Wageningen : Wageningen University - ISBN 9789462574670 - 144
    lipids - membranes - stability - nanotechnology - particles - analytical methods - models - modeling - lipiden - membranen - stabiliteit - nanotechnologie - deeltjes - analytische methoden - modellen - modelleren
    Lipid bilayer stability in relation to oxide nanoparticles

    All living organisms are composed of cells that are filled with a thick molecular soup. These molecules constitute a complex machinery that brings these cells to life. To contain these molecules, and to protect them from the hostile outer environment, a phospholipid bilayer envelopes the cell. It is essential that this lipid bilayer, also known as the cell membrane, should remain intact and form a perfect barrier at all times. Industrially manufactured nanoparticles are suspect to be able to penetrate this barrier, and thus endanger living organisms in the environment. This thesis deals with some aspects of the structural integrity of lipid bilayers, and especially how this integrity is affected by the interaction with nanoparticles.

    Experiments were performed with silica and titanium dioxide nanoparticles, interacting with lipid bilayers, using a variety of experimental techniques. In addition, a theoretical model was applied that is based on the Scheutjens-Fleer Self Consistent Field (SCF) theory. This model delivered detailed structural and thermodynamic information about the lipid bilayer. The modelling work helped us to improve our understanding of lipid bilayer stability, and showed the effect of the interaction with the nanoparticles on the phospholipid bilayer. These latter results could be related directly to our experiments.

    Let us first experimentally regard the interaction of lipid bilayers with synthetic oxide nanoparticles. We developed a protocol for high-throughput screening of the nanoparticle-bilayer interaction using a fluorescence technique. Results from this method were combined with reflectometry measurements and atomic force microscopy (AFM). The combination of these methods allowed us to relate lipid bilayer integrity to its interaction with nanoparticles and their adsorption onto the bilayer. In addition, the AFM results yielded detailed structural information at the nano-scale. We found that the interaction strongly depends on both lipid bilayer and nanoparticle charge. However, the specific interaction that depends on the nanoparticle type, starts to play a role when the charges are low. When the total interaction strength is regarded, a regime was found at which interaction is strong enough for the nanoparticles to adsorb onto the bilayer, but too weak to disrupt the bilayer. If, however, the bilayer is disrupted by the nanoparticles, the particle may steal away some lipid molecules from the bilayer, and leave again to disrupt the bilayer elsewhere.

    Let us now go into more detail on the SCF modelling. Bilayers are composed of phospholipids, which consist of a hydrophilic head group, and a hydrophobic tail. These bilayers were modelled using a single lipid molecule type, of which the head group structure and lipid tail length could be varied. We thus obtained bilayers that varied in their thickness, and the space that a single lipid takes within the bilayer. Changes in bilayer composition affect the bilayer mechanical properties, such as those constants that describe bilayer stretching or bending. This thesis shows how vesicles, which are bilayers in a globular shape, may become unstable if the bilayer lipid composition is changed. Under certain conditions, a vesicle would prefer to fall apart into many smaller vesicles, which is when highly charged head groups start to repel each other. Or the bilayer may form continuous cubic phases, which might occur if lipids with uncharged head groups but with very long tails are used to form the bilayer. Under very specific and finely tuned conditions, a lipid bilayer may become unstable to form stable pores in the membrane, or to fall apart into tiny lipid discs.

    Intracellular accommodation of rhizobia in legume host cell: the fine-tuning of the endomembrane system
    Gavrin, A.Y. - \ 2015
    Wageningen University. Promotor(en): Ton Bisseling, co-promotor(en): E. Federova. - Wageningen : Wageningen University - ISBN 9789462574182 - 160
    peulgewassen - rhizobium - bodembacteriën - endosymbiose - wortelknolletjes - membranen - waardplanten - legumes - rhizobium - soil bacteria - endosymbiosis - root nodules - membranes - host plants

    The symbiosis of legumes with rhizobia leads to the formation of root nodules. Rhizobia which are hosted inside specialized infected cells are surrounded by hostderived membranes, forming symbiosomes. Although it is known that symbiosome formation involves proliferation of membranes and changing of host cell architecture the mechanisms involved in these processes remain largely uncovered.

    In this thesis, I studied in more detail the adaptation of the endomembrane system of infected cells to intracellular rhizobia. I have shown that in the first cell layer of the nitrogen-fixing zone, the vacuole of the infected cells shrinks, creating space for the expanding symbiosomes. Here the expression of homotypic fusion and vacuole protein sorting complex (HOPS) genes VPS11 and VPS39 are switched off, whereas tonoplast proteins, like the vacuolar aquaporin TIP1g, are targeted to the symbiosome membrane. These observations suggest that tonoplast-targeted traffic in infected cells is altered. This retargeting is essential for the maturation of symbiosomes.

    Accommodation of intracellular rhizobia requires also the reorganization of the actin cytoskeleton. I have shown that during symbiosome development the symbiosomes become surrounded by a dense actin network and in this way, the actin configuration in infected cells is changed markedly. The actin nucleating factor ARP3 is operational in the rearrangement of actin around the symbiosome.

    It is known that the plasma membrane is inelastic; its capacity to stretch is only around 1-3%. Exocytosis of new membrane material is therefore involved in changes in the size of the membrane surface and in repair of damaged membrane loci. Membrane tension may create a vector for the fusion of membrane vesicles. To test this, the localization of proteins from the group of synaptotamin calcium sensors involved in membrane fusion, was studied. I have shown that the Medicago synaptotamins, MtSyt2 and MtSyt3, are localised on protrusions of the host plasma membrane created by expanding rhizobia (infection threads, cell wall-free unwalled droplets). Hence, at these sites of contact between symbionts membrane tension may create a vector for exocytosis.

    It is known that the host cell wall is modified during the development of infected cells. This process is mediated by the exocytotic pathway employing vesicle-associated membrane proteins (VAMPs) from the VAMP721 family. Previously it was shown in Medicago nodules, that cell-wall free interface membrane formation during bacterial release is dependent on these proteins. I have shown that the pectin modifying enzyme pectate lyase is delivered to the site of bacterial release in soybean nodules by VAMP721-positive vesicles.

    My study uncovered new mechanisms involved in the adaptation of host cells to intracellular rhizobia: defunctionalization of the vacuole, actin cytoskeleton rearrangement and the retargeting of host cell proteins to the interface membrane.

    Ion adsorption-induced wetting transition in oil-water-mineral systems
    Mugele, F. ; Bera, B. ; Cavalli, A. ; Siretanu, I. ; Maestro, A. ; Duits, M. ; Cohen Stuart, M.A. ; Ende, D. van den - \ 2015
    Scientific Reports 5 (2015). - ISSN 2045-2322 - 8 p.
    hydration forces - surfaces - recovery - wettability - interfaces - membranes - charge - layer
    The relative wettability of oil and water on solid surfaces is generally governed by a complex competition of molecular interaction forces acting in such three-phase systems. Herein, we experimentally demonstrate how the adsorption of in nature abundant divalent Ca2+ cations to solid-liquid interfaces induces a macroscopic wetting transition from finite contact angles (˜10°) with to near-zero contact angles without divalent cations. We developed a quantitative model based on DLVO theory to demonstrate that this transition, which is observed on model clay surfaces, mica, but not on silica surfaces nor for monovalent K+ and Na+ cations is driven by charge reversal of the solid-liquid interface. Small amounts of a polar hydrocarbon, stearic acid, added to the ambient decane synergistically enhance the effect and lead to water contact angles up to 70° in the presence of Ca2+. Our results imply that it is the removal of divalent cations that makes reservoir rocks more hydrophilic, suggesting a generalizable strategy to control wettability and an explanation for the success of so-called low salinity water flooding, a recent enhanced oil recovery technology.
    Listeria monocytogenes repellence by enzymatically modified PES surfaces
    Veen, S. van der; Nady, N. ; Franssen, M.C.R. ; Zuilhof, H. ; Boom, R.M. ; Abee, T. ; Schroën, C.G.P.H. - \ 2015
    Journal of Applied Polymer Science 132 (2015)10. - ISSN 0021-8995 - 6 p.
    stainless-steel - catalyzed modification - biofilm formation - attachment - growth - membranes - water - acid - functionalization - hydrophobicity
    : The effect of enzyme-catalyzed modification of poly(ethersulfone) (PES) on the adhesion and biofilm formation of two Listeria monocytogenes strains is evaluated under static and dynamic flow conditions. PES has been modified with gallic acid, ferulic acid and 4-hydroxybenzoic acid. The surfaces modified with any of these compounds show up to 70% reduced adhesion of L. mono-cytogenes under static conditions and up to 95% under dynamic flow conditions compared with unmodified surfaces. Also, under static conditions the formation of biofilms is reduced by 70%. These results indicate that the brush structures that are formed by the polymers on the PES surface directly influence the ability of microorganisms to interact with the surface, thereby reducing attachment and biofilm formation of L. monocytogenes. Based on these results, it is expected that enzyme-catalyzed surface modification is a promising tool to reduce microbial adhesion and biofilm formation
    Fluidized Capacitive Bioanode As a Novel Reactor Concept for the Microbial Fuel Cell
    Deeke, A. ; Sleutels, T.H.J.A. ; Donkers, T.F.W. ; Hamelers, B. ; Buisman, C.J.N. ; Heijne, A. ter - \ 2015
    Environmental Science and Technology 49 (2015)3. - ISSN 0013-936X - p. 1929 - 1935.
    waste-water treatment - electricity-generation - power-generation - iron reduction - scaled-up - performance - carbon - resistance - membranes - biofilms
    The use of granular electrodes in Microbial Fuel Cells (MFCs) is attractive because granules provide a cost-effective way to create a high electrode surface area, which is essential to achieve high current and power densities. Here, we show a novel reactor design based on capacitive granules: the fluidized capacitive bioanode. Activated carbon (AC) granules are colonized by electrochemically active microorganisms, which extract electrons from acetate and store the electrons in the granule. Electricity is harvested from the AC granules in an external discharge cell. We show a proof-of-principle of the fluidized capacitive system with a total anode volume of 2 L. After a start-up period of 100 days, the current increased from 0.56 A/m2 with 100 g AC granules, to 0.99 A/m2 with 150 g AC granules, to 1.3 A/m2 with 200 g AC granules. Contact between moving AC granules and current collector was confirmed in a control experiment without biofilm. Contribution of an electro-active biofilm to the current density with recirculation of AC granules was limited. SEM images confirmed that a biofilm was present on the AC granules after operation in the fluidized capacitive system. Although current densities reported here need further improvement, the high surface area of the AC granules in combination with external discharge offers new and promising opportunities for scaling up MFCs.
    Spatial constraints and the organization of the cytoskeleton
    Ga^rlea, I.C. - \ 2015
    Wageningen University. Promotor(en): Bela Mulder. - Wageningen : Wageningen University - ISBN 9789462572126 - 175
    celskelet - microtubuli - actine - eiwitten - celdeling - microvezels - membranen - cytoskeleton - microtubules - actin - proteins - cell division - microfilaments - membranes

    The shape of animal cells is in controlled by a network of filamentous polymers called the cytoskeleton. The two main components of the cytoskeleton are actin filaments and microtubules. These polymers continuously reorganize in order to performed their diverse cellular functions. For example, in processes such as cell migration actin filaments grow against the membrane, creating flat protrusions called lamellipodia. The lamellipodia enable the cells to move over surfaces. Microtubules are a key player in the cell division mechanism. There, the proper separation of the genetic material between the two daughter cells is controlled by two microtubule asters. The positioning of these two asters also determines the location where the cells will physically separate. Both migration and division are crucial processes for the cell, however the mechanisms underlying these processes are still poorly understood. The organization of the cytoskeleton in cells, and thus their functioning as cell shapers, is an interplay between mutual interaction, confinement and protein mediated interactions. Since cells are exquisitely complex systems, experimentally, the bottom-up approach proves useful in understanding the contribution of each of these interactions on the cytoskeleton organization. This approach is based on the idea of reconstructing a minimal system and adding more complexity to it as our understanding of this system increases.

    Starting by a bottom-up approach, as it is done in experimental systems, we study various aspects of confinement and mutual interactions on cytoskeleton organization. The simplest system in which these two interactions are expected to compete is when dense enough rigid cytoskeletal polymers are confined. Experimentally, this question is addressed by confining these polymers in microchambers which are small compared to the persistence length of the enclosed polymers. In Chapter 2, using Monte Carlo simulations, we investigate the organization of rigid polymers confined in shallow square containers, this geometry being simplified model of a lamellipodium. We find that, in the regime where the confinement effect, which causes wall alignment of the polymers, competes with the self-aligning tendency of the polymers, the organization is characterized by a nematic droplet aligned along a diagonal and wall aligned polymers. The pattern is stabilized by linear defect structures.

    By the same methods, in Chapter 3, we study rigid polymers in curved wall confinement, finding that the bipolar structure appearing in the disk geometry is drastically modified by the opening of a hole in the middle of the container. Unexpectedly, in this annular geometry, the organization is characterized by highly aligned domains separated by radial defect walls. The patterns observed are the result of the finite size of the particles.

    When the rigid polymers are small compared to the confining volume, their orientation is expected to vary over lengths which are much larger than the length of the polymer. In this regime the system is well described by continuum theories. Since currently employed continuum models either exclude the emergence of singularities by the way they are constructed (Oseen-Frank model) or are valid only in for a limited density range around the transition from an unordered to an ordered system (Landau-De Gennes model), in Chapter 4, we construct a mean-field model combining the virtues of these two models. We apply this model to a system of rigid small polymers enclosed in rectangular shallow container (geometry similar to the one in Chapter 2), finding that patterns which are minimizing the energy of the system are characterized by continuum variation of the orientation. However, our model also yields patterns containing point defects which have slightly higher energy.

    So far we have considered only rigid cytoskeletal polymers, however at the length scale of the cell the polymers are better described by an elastic rod. In Chapter 5 we study the configurations adopted by a cytoskeletal polymers when enclosed by a rigid ellipsoidal membrane. We find that, compared to the spherical confinement, the change in shape of the confining membrane leads to non-trivial organization of the enclosed polymers. Among the patters observed are single bundles, planar asters, circular and elliptical rings. In reconstructed systems such as emulsion droplets the cytoskeletal polymers push against the membrane, deforming it but, since the membrane is under tension, it also constrains them to bend. Determining the polymeric configurations as a function of the confining surface is the first step towards understanding this mechanical interplay between the cytoskeleton and the membrane.

    For proper cell division, a precise positioning of the two microtubule asters involved is required. The positioning of the two asters is based on pushing and pulling forces generated by the microtubule-membrane interaction. Experimental evidence shows that, in reconstructed systems, a spatial separation between the two asters in always present. Therefore, in Chapter 6, we investigate the steric repulsion between two asters finding that it indeed leads to a spatial separation.

    The models that we developed in this thesis are a starting point for understanding the cytoskeletal organization and its role in the cell. In the last Chapter of this thesis we give some directions that the present work opens.

    Effect of antimicrobial compounds on cut Gerbera flowers: Poor relation between stem bending and numbers of bacteria in the vase water
    Witte, Y. van de; Harkema, H. ; Doorn, W.G. van - \ 2014
    Postharvest Biology and Technology 91 (2014). - ISSN 0925-5214 - p. 78 - 83.
    jamesonii flowers - essential oils - rose flowers - membranes - longevity - stress - sugars - plants - life - acid
    Gerbera flowers (Gerbera jamesonii) often show stem bending. In four cultivars (Tamara, Liesbeth, Cora, and Mickey), we tested the effects on bending of antimicrobial compounds (chlorine bleach, a slow release chlorine compound, 8-hydroxyquinoline citrate [HQC], silver nitrate, carvacrol and thymol), some combined with sugars. At concentrations used for other cut flowers, inclusion in the vase solution of several of the antimicrobial compounds delayed bending, had no effect, or hastened bending. Hastening of bending was found at higher concentrations. It was accompanied with visible damage on the stem ends. Results with HQC indicated high toxicity as it did not delay bending at any of the concentration tested (100-400 mg L-1). At 200 mg L-1 HQC induced growth of bacteria that were not found in the controls. The number of bacteria in the vase water showed a low correlation with bending. Visible toxicity on the stem surface was often associated with a high bacteria count. However, at relatively high concentrations of the antimicrobial compounds stem bending was associated with a low count. This indicated an effect other than bacteria. Water uptake was low in stems that bent early. It is hypothesized that material from dead stem cells resulted in a xylem blockage which led to early bending. Sucrose at 15 g L-1 in combination with an antimicrobial compound (slow release chlorine, HQC) resulted in the absence of stem damage and produced much less bending than the same concentration of the antimicrobial compounds alone. Sucrose apparently counteracted the toxic effects of the antimicrobial chemicals. (C) 2014 Published by Elsevier B.V.
    KORRIGAN1 Interacts Specifically with Integral Components of the Cellulose Synthase Machinery
    Mansoori Zangir, N. ; Timmers, J.F.P. ; Desprez, T. ; Lessa Alvim Kamei, C. ; Dees, D.C.T. ; Vincken, J.P. ; Visser, R.G.F. ; Höfte, H. ; Vernhettes, S. ; Trindade, L.M. - \ 2014
    PLoS ONE 9 (2014)11. - ISSN 1932-6203
    secondary cell-wall - arabidopsis-thaliana - endo-1,4-beta-glucanase - expression - membranes - protein - system - plants - gene - endo-1,4-beta-d-glucanase
    Cellulose is synthesized by the so called rosette protein complex and the catalytic subunits of this complex are the cellulose synthases (CESAs). It is thought that the rosette complexes in the primary and secondary cell walls each contains at least three different non-redundant cellulose synthases. In addition to the CESA proteins, cellulose biosynthesis almost certainly requires the action of other proteins, although few have been identified and little is known about the biochemical role of those that have been identified. One of these proteins is KORRIGAN (KOR1). Mutant analysis of this protein in Arabidopsis thaliana showed altered cellulose content in both the primary and secondary cell wall. KOR1 is thought to be required for cellulose synthesis acting as a cellulase at the plasma membrane–cell wall interface. KOR1 has recently been shown to interact with the primary cellulose synthase rosette complex however direct interaction with that of the secondary cell wall has never been demonstrated. Using various methods, both in vitro and in planta, it was shown that KOR1 interacts specifically with only two of the secondary CESA proteins. The KOR1 protein domain(s) involved in the interaction with the CESA proteins were also identified by analyzing the interaction of truncated forms of KOR1 with CESA proteins. The KOR1 transmembrane domain has shown to be required for the interaction between KOR1 and the different CESAs, as well as for higher oligomer formation of KOR1.
    Linking lipid architecture to bilayer structure and mechanics using self-consistent field modelling
    Pera, H. ; Kleijn, J.M. ; Leermakers, F.A.M. - \ 2014
    Journal of Chemical Physics 140 (2014). - ISSN 0021-9606 - 23 p.
    interacting chain molecules - statistical thermodynamics - spontaneous curvature - bending moduli - association colloids - membranes - elasticity - adsorption - monolayers - vesicles
    To understand how lipid architecture determines the lipid bilayer structure and its mechanics, we implement a molecularly detailed model that uses the self-consistent field theory. This numerical model accurately predicts parameters such as Helfrichs mean and Gaussian bending modulus k c and k ¯ and the preferred monolayer curvature J m 0 , and also delivers structural membrane properties like the core thickness, and head group position and orientation. We studied how these mechanical parameters vary with system variations, such as lipid tail length, membrane composition, and those parameters that control the lipid tail and head group solvent quality. For the membrane composition, negatively charged phosphatidylglycerol (PG) or zwitterionic, phosphatidylcholine (PC), and -ethanolamine (PE) lipids were used. In line with experimental findings, we find that the values of k c and the area compression modulus k A are always positive. They respond similarly to parameters that affect the core thickness, but differently to parameters that affect the head group properties. We found that the trends for k ¯ and J m 0 can be rationalised by the concept of Israelachivili's surfactant packing parameter, and that both k ¯ and J m 0 change sign with relevant parameter changes. Although typically k ¯
    High loaded MBRs for organic matter recovery from sewage: Effect of solids retention time on bioflocculation and on the role of extracellular polymers
    Faust, L. ; Temmink, B.G. ; Zwijnenburg, A. ; Kemperman, A.J.B. ; Rijnaarts, H. - \ 2014
    Water Research 56 (2014). - ISSN 0043-1354 - p. 258 - 266.
    waterzuivering - membranen - biofilms - organische stof - water treatment - membranes - biofilms - organic matter - municipal waste-water - submerged membrane bioreactor - improved energy recovery - activated-sludge process - microbial community - surface-properties - substances eps - performance - extraction - constituents
    High loaded MBRs (HL-MBR) can concentrate sewage organic matter by aerobic bioflocculation for subsequent anaerobic conversion to methane or volatile fatty acids. In the range of very short solid retention times (SRT), the effect of SRT on bioflocculation and EPS production in HL-MBR was investigated. This short SRT range was selected to find an optimum SRT maximising recovery of organics by aerobic bioflocculation and minimizing losses of organics by aerobic mineralization. Bioflocculation was studied in five HL-MBRs operated at SRTs of 0.125, 0.25, 0.5, 1 and 5 d. The extent of flocculation, defined as the fraction of suspended COD in the concentrate, increased from 59% at an SRT of 0.125 d to 98% at an SRT of 5 d. The loss of sewage organic matter by biological oxidation was 1, 2, 4, 11 and 32% at SRT of 0.125–5 d. An SRT of 0.5–1 d gave best combination of bioflocculation and organic matter recovery. Bound extracellular polymeric substances (EPS) concentrations, in particular EPS-protein concentrations, increased when the SRT was prolonged from 0.125 to 1 d. This suggests that these EPS-proteins govern the bioflocculation process. A redistribution took place from free (supernatant) EPS to bound (floc associated) EPS when the SRT was prolonged from 0.125 to 1 d, further supporting the fact that the EPS play a dominant role in the flocculation process. Membrane fouling was most severe at the shortest SRTs of 0.125 d. No positive correlation was detected between the concentration of free EPS and membrane fouling, but the concentration of submicron (45–450 nm) particles proved to be a good indicator for this fouling.
    Charge-driven co-assembly of polyelectrolytes across oil-water interfaces
    Monteillet, H. ; Hagemans, F. ; Sprakel, J.H.B. - \ 2013
    Soft Matter 9 (2013)47. - ISSN 1744-683X - p. 11270 - 11275.
    controlled flocculation - opposite charge - small particles - emulsions - membranes
    We report a simple strategy to co-assemble oppositely charged polyelectrolytes across oil–water interfaces; this allows the accumulation of an electrostatic complex at the interface of species that are not surface active by themselves. To this end, we use a new, oil-soluble anionic polymer, poly-(fluorene-co-benzothiadiazole-co-benzoic acid), in combination with a cationic polyelectrolyte that is dissolved in the aqueous phase. When only one of the two charged components is present, no positive adsorption is observed in interfacial tension measurements; by contrast, when both polyelectrolytes are present, in the oil and water phases respectively, a rapid decrease of the interfacial tension is observed, indicating co-adsorption of the cationic and anionic polyelectrolytes. The complexation strength can be tuned through changes in both ionic strength and pH. Confocal microscopy and co-localization analysis further verifies the presence of both polyelectrolytes at the interface. With this approach, emulsions can be stabilized for several weeks; moreover, using the sensitivity of the complex to changes in pH, we are able to reversibly break and make the emulsions on demand.
    Bending rigidities of surfactant bilayers using self-consistent field theory
    Leermakers, F.A.M. - \ 2013
    Journal of Chemical Physics 138 (2013). - ISSN 0021-9606 - 11 p.
    interacting chain molecules - lipid-bilayers - curvature elasticity - statistical-theory - adsorption - membranes - size - thermodynamics - interface - relevance
    Self-consistent field (SCF) theory is used to find bending moduli of surfactant and lipid bilayers. Recently, we successfully applied low-memory search methods to solve the SCF equations. Using these we are now able to directly evaluate the Gaussian bending modulus for molecularly detailed models of bilayers by evaluating the excess Helmholtz energy of tensionless bilayers in a (part of the) Im3m cubic phase. The result prompted us to reconsider the protocol that has been used thus far to find the mean bending modulus k c and Gaussian bending modulus k¯. With respect to previous predictions, the value of k c is reduced by a factor of two and the Gaussian bending modulus is less negative and much closer to zero. In line with experimental data we now find that k¯can also become positive. In this paper we use the non-ionic surfactants series of the type C n E m for illustration.
    Chemodynamics of soft Charged nanoparticles in aquatic media: Fundamental concepts
    Town, R.M. ; Buffle, J. ; Duval, J.F.L. ; Leeuwen, H.P. van - \ 2013
    The Journal of Physical Chemistry Part A: Molecules, Spectroscopy, Kinetics, Environment, & General Theory 117 (2013)33. - ISSN 1089-5639 - p. 7643 - 7654.
    metal speciation dynamics - aqueous-solutions - solvent exchange - complexes - relaxation - nmr - ion - approximation - temperature - membranes
    Dehydration and thermal inactivation of Lactobacillus plantarum WCFS1: Comparing single droplet drying to spray and freeze drying
    Perdana, J.A. ; Bereschenko, L.A. ; Fox, M.B. ; Kuperus, J.H. ; Kleerebezem, M. ; Boom, R.M. ; Schutyser, M.A.I. - \ 2013
    Food Research International 54 (2013)2. - ISSN 0963-9969 - p. 1351 - 1359.
    desiccation tolerance - phase-transitions - probiotics - temperature - membranes - vitrification - survival - bacteria - injury - cells
    We demonstrated that viability loss during single droplet drying can be explained by the sum of dehydration and thermal inactivation. For Lactobacillus plantarum WCFS1, dehydration inactivation predominantly occurred at drying temperatures below 45 °C and only depended on the moisture content. Above 45 °C the inactivation was due to a combination of dehydration and thermal inactivation, which depended on the moisture content, temperature, and drying time. A Weibull model was successfully applied to describe the thermal and dehydration inactivation and enabled the prediction of residual viability of L. plantarum WCFS1 after single droplet drying. Subsequently, the model was evaluated to predict the viability loss during laboratory scale spray drying, showing a remarkable agreement if assumed that only thermal inactivation occurred. This indicated that very high drying rates in laboratory scale spray drying could induce instant fixation of the cell suspensions in a vitrified matrix and thereby preventing dehydration inactivation. Finally, the influence of drying rate on remaining viability was evaluated by comparing single droplet drying, freeze drying and laboratory scale spray drying of the same bacterial suspension. It was shown that slow drying leads to large dehydration inactivation, which diminished in fast drying processes such as laboratory scale spray drying where thermal inactivation appears to be the predominant mechanism of inactivation.
    Theory and operation of capacitive deionization systems
    Zhao, R. - \ 2013
    Wageningen University. Promotor(en): Bert van der Wal, co-promotor(en): Huub Rijnaarts; Maarten Biesheuvel. - S.l. : s.n. - ISBN 9789461736390 - 155
    waterzuivering - drinkwater - ontzilting - elektrodes - membranen - ionenuitwisseling - water treatment - drinking water - desalination - electrodes - membranes - ion exchange
    Bioelectrochemical production of caproate and caprylate from acetate by mixed cultures
    Eerten-Jansen, M.C.A.A. van; Heijne, A. ter; Grootscholten, T.I.M. ; Steinbusch, K.J.J. ; Sleutels, T.H.J.A. ; Hamelers, H.V.M. ; Buisman, C.J.N. - \ 2013
    ACS sustainable chemistry & engineering 1 (2013)5. - ISSN 2168-0485 - p. 513 - 518.
    microbial electrolysis cells - fuel-cells - hydrogen - biomass - conversion - ethanol - reduction - transport - membranes - butyrate
    The use of mixed cultures to convert waste biomass into medium chain fatty acids, precursors for renewable fuels or chemicals, is a promising route. To convert waste biomass into medium chain fatty acids, an external electron donor in the form of hydrogen or ethanol needs to be added. This study investigated whether the cathode of a bioelectrochemical system can be used as the electron donor for the conversion of acetate into medium chain fatty acids. We show that medium chain fatty acids were produced in a bioelectrochemical system at -0.9 V vs. NHE cathode potential, without addition of an external mediator. Caproate, butyrate and smaller fractions of caprylate were the main products formed from acetate. In-situ produced hydrogen was likely involved as an electron donor for the reduction of acetate. Electron and carbon balances revealed that 45% of the electrons in electric current and acetate, and 31% of the carbon from acetate were recovered in the formed products. This study showed for the first time production of medium chain fatty acids caproate and caprylate from acetate at the cathode of bioelectrochemical systems, and offers new opportunities for application of bioelectrochemical systems.
    Optimization of salt adsorption rate in membrane capacitive deionization
    Zhao, R. ; Satpradit, O.A. ; Rijnaarts, H. ; Biesheuvel, P.M. ; Wal, A. van der - \ 2013
    Water Research 47 (2013)5. - ISSN 0043-1354 - p. 1941 - 1952.
    waterkwaliteit - water - terugwinning - ontzilting - ionisatie - ionenuitwisselingsbehandeling - membranen - water quality - water - recovery - desalination - ionization - ion exchange treatment - membranes - ion-exchange membranes - porous-electrodes - water desalination - brackish-water - transport-properties - carbon - electrochemistry - performance - efficiency - anions
    Membrane capacitive deionization (MCDI) is a water desalination technique based on applying a cell voltage between two oppositely placed porous electrodes sandwiching a spacer channel that transports the water to be desalinated. In MCDI, ion-exchange membranes are positioned in front of each porous electrode to prevent co-ions from leaving the electrode region during ion adsorption, thereby enhancing the salt adsorption capacity. MCDI can be operated at constant cell voltage (CV), or at a constant electrical current (CC). In this paper, we present both experimental and theoretical results for desalination capacity and rate in MCDI (both in the CV- and the CC-mode) as function of adsorption/desorption time, salt feed concentration, electrical current, and cell voltage. We demonstrate how by varying each parameter individually, it is possible to systematically optimize the parameter settings of a given system to achieve the highest average salt adsorption rate and water recovery.
    Bioconjugation of Protein-Repellent Zwitterionic Polymer Brushes Grafted from Silicone Nitride
    Nguyen, A.T. ; Baggerman, J. ; Paulusse, J.M.J. ; Zuilhof, H. ; Rijn, C.J.M. van - \ 2012
    Langmuir 28 (2012)1. - ISSN 0743-7463 - p. 604 - 610.
    biosensor applications - poly(ethylene glycol) - antibody microarrays - surface - adsorption - well - membranes - plasma - immobilization - strategies
    A new method for attaching antibodies to protein-repellent zwitterionic polymer brushes aimed at recognizing microorganisms while preventing the nonspecific adsorption of proteins is presented. The poly(sulfobetaine methacrylate) (SBMA) brushes were grafted from a-bromo isobutyryl initiator-functionalized silicon nitride (SixN4, x = 3) surfaces via controlled atom-transfer radical polymerization (ATRP). A trifunctional tris(2-aminoethyl)amine linker was reacted with the terminal alkylbromide of polySBMA chains. N-Hydroxysuccinimide (NHS) functionalization was achieved by reacting the resultant amine-terminated polySBMA brush with bifunctional suberic acid bis(N-hydroxysuccinimide ester). Anti-Salmonella antibodies were subsequently immobilized onto polySBMA-grafted SixN4 surfaces through these NHS linkers. The protein-repellent properties of the polySBMA-grafted surface after antibody attachment were evaluated by exposing the surfaces to Alexa Fluor 488-labeled fibrinogen (FIB) solution (0.1 g·L–1) for 1 h at room temperature. Confocal laser scanning microscopy (CLSM) images revealed the minimal adsorption of FIB onto the antibody-coated polySBMA in comparison with that of antibody-coated epoxide monolayers and also bare SixN4 surfaces. Subsequently, the interaction of antibodies immobilized onto polySBMA with SYTO9-stained Salmonella solution without using blocking solution was examined by CLSM. The fluorescent images showed that antibody-coated polySBMA efficiently captured Salmonella with only low background noise as compared to antibody-coated monolayers lacking the polymer brush. Finally, the antibody-coated polySBMA surfaces were exposed to a mixture of Alexa Fluor 647-labeled FIB and Salmonella without the prior use of a blocking solution to evaluate the ability of the surfaces to capture bacteria while simultaneously repelling proteins. The fluorescent images showed the capture of Salmonella with no adsorption of FIB as compared to antibody-coated epoxide surfaces, demonstrating the potential of the zwitterionic layer in preventing the nonspecific adsorption of the proteins during the detection of bacteria in complex matrices.
    Mechanical Properties of Re-constituted Actin Networks at an Oil/Water Interface Determined by Microrheology
    Ershov, D.S. ; Cohen Stuart, M.A. ; Gucht, J. van der - \ 2012
    Soft Matter 8 (2012). - ISSN 1744-683X - p. 5896 - 5903.
    particle-tracking microrheology - cytoskeletal protein networks - micropipette aspiration - myosin-filaments - molecular motors - polymer networks - living cells - cortex - microscopy - membranes
    There have been various attempts to investigate the mechanical properties of the actin cortex in cells, but the factors that control them remain poorly understood. To make progress, we develop a reconstituted model of the actin cortex that mimics its structure. We attach actin filaments to lipids lining the surface of an oil droplet using biotin–streptavidin bonds. In this way we can form a thin actin network that can be visualized and studied by confocal microscopy. Our approach allows incorporation of different actin-binding and motor proteins into this 2D network and characterization of their effect on its mechanical properties in a quantitative way. To study the viscoelasticity of the network, we use passive particle tracking microrheology, which allows storage and loss moduli to be extracted from the mean square displacement of tracer particles. We show that adding cross-linkers to the cortex increases its elasticity by several orders of magnitude and addition of myosin in the presence of ATP results in a strong and rapid stiffening of the network. This approach opens up a variety of possibilities to study viscoelastic properties of the actin cortex in vitro, allowing incorporation of any protein of interest into the system.
    Effect of low dosages of powdered activated carbon on membrane bioreactor performance
    Remy, M.J.J. ; Temmink, H. ; Rulkens, W.H. - \ 2012
    Water Science and Technology 65 (2012)5. - ISSN 0273-1223 - p. 954 - 961.
    afvalwaterbehandeling - bioreactoren - membranen - actieve kool - poeders - dosering - vervuiling door afzetting - filtreerbaarheid - energiegehalte - waste water treatment - bioreactors - membranes - activated carbon - powders - dosage - fouling - filterability - energy content - polymeric substances eps - sludge - removal - water - mbrs - dewaterability
    Previous research has demonstrated that powdered activated carbon (PAC), when applied at very low dosages and long SRTs, reduces membrane fouling in membrane bioreactors (MBRs). This effect was related to the formation of stronger sludge flocs, which are less sensitive to shear. In this contribution the long-term effect of PAC addition was studied by running two parallel MBRs on sewage. To one of these, PAC was dosed and a lower fouling tendency of the sludge was verified, with a 70% longer sustainable filtration time. Low PAC dosages showed additional advantages with regard to oxygen transfer and dewaterability, which may provide savings on operational costs.
    Understanding flow-induced particle migration for improved microfiltration
    Dinther, A.M.C. van - \ 2012
    Wageningen University. Promotor(en): Remko Boom, co-promotor(en): Karin Schroen. - S.l. : s.n. - ISBN 9789461733498 - 207
    microfluidics - filtratie - migratie - deeltjes - stroming - suspensies - emulsies - membranen - microfluidics - filtration - migration - particles - flow - suspensions - emulsions - membranes

    Membrane microfiltration processes are used in for example the food, biotechnology, chemical and pharmaceutical industry, and more generally in e.g. wastewater treatment. Microfiltration is mostly used to separate components that are greatly different in size, e.g. micro-organisms from water, but rarely to fractionate components that are of similar size. This latter option would be interesting for many applications, since it would lead to enriched starting materials and possibly new products, but is hampered by accumulation of components in and on the membrane due to size exclusion by the pores. This leads to flux reduction and increased retention of components in time, basically the accumulated layer determines which components can pass the membrane (see Figure 1).

    Figure 1. Schematic representation of a cross-flow microfiltration process with a decrease in permeate flux over the length of the membrane due to pore blocking and particle adsorption in the pores and on the membrane walls.
    Most research focusses on accumulation mechanisms (concentration polarization, cake formation and adsorption) and concepts targeted at controlling particle accumulation. One example is back-pulsing, but this only gives a short term solution leading to extensive cleaning procedures given the way membranes are currently operated in practice. Clearly it would be beneficial if accumulation could be prevented, and through that, more stable operation could be achieved.

    This thesis presents how flow-induced particle migration can be used for stable membrane flux and retention of components in time. The particle migration mechanisms that are considered in this thesis, shear-induced diffusion, inertial lift, and fluid skimming, act on particles that are typically between 0.1 and 10 micron. They induce separation of components in the fluid moving (larger) particles away from the membrane, therewith facilitating separation; basically pore size no longer determines particle permeation. In the thesis it will be shown that these effects improve processing of dilute suspensions and make processing of highly concentrated systems possible, which is beyond the scope of current microfiltration processes.

    Before the design of these processes, methods to measure velocity and concentration profiles in microfluidic devices are described, compared and evaluated. The small dimensions of these devices will cause particles to migrate; as is used later in the thesis to facilitate segregation and separation. A drawback of the small dimensions is that they make measurement of velocity and concentration gradients difficult. Based on our evaluation, Nuclear Magnetic Resonance (NMR) and Confocal Scanning Laser Microscopy (CSLM), although expensive, are the most promising techniques to investigate flowing suspensions in microfluidic devices, where one may be preferred over the other depending on the size, concentration and nature of the suspension, the dimensions of the channel, and the information that has to be obtained.

    CSLM is used to study the behaviour of suspensions, between 9 and 38 volume%, at the particle level. Under Poiseuille flow in a closed microchannel, shear-induced diffusion causes migration in these suspensions. Under all measured process conditions, particles segregate on size within an entrance length of around 1000 times the channel height. Mostly, the larger particles migrate to the middle of the channel, while the small particles have high concentrations near the walls. This indicates that the small particles could be collected from their position close to the wall and that this principle can be applied to microfiltration (see Figure 2).

    Figure 2. Schematic representation of a cross-flow microfiltration process with a constant permeate flux over the length of the membrane due to shear-induced particle migration in combination with the use of a closed entrance length and large pores.
    Microfiltration of emulsions proves that the small particles can be removed without accumulation of particles in and on the membrane, as long as the process conditions are chosen appropriate. The membrane cross-flow module consists of a closed channel to allow particles to migrate due to shear-induced diffusion followed by a membrane with 20 micron pores, being much larger than the particles, where fractions of these emulsions can be removed. The emulsions consist of small droplets (~2.0 micron) and large droplets (~5.5 micron), with total concentrations between 10 and 47% and different ratios between small and large particles. As expected, the size of the emulsion droplets in the permeate is a function of trans-membrane pressure, membrane design and oil volume fraction (i.e., of the total, the small and the large particles). The guidelines for appropriate process conditions are described and application of the right process conditions leads to very high selectivity. This means that the permeate only consists of small droplets, and on top of that their concentration is higher than in the original emulsion. Especially at high droplet concentration (which is known to cause severe fouling in regular membrane filtration), these effects are occurring as a result of shear-induced diffusion. If only small particles are targeted in the permeate, the module can be operated at fluxes of 40 L/(h•m²); if fractionation is targeted the fluxes can be maintained considerably higher (2-10 fold higher).

    Separation of concentrated suspensions is currently done by dilution and since the process based on shear-induced diffusion works well at low velocities and high concentrations, industrial application could have major benefits in terms of energy and water use. An outlook is given on how current industrial processes can be designed and improved in terms of energy consumption by making use of particle migration. It is shown that return of investment of installation of these new membrane modules is short compared to the membrane life time, due to high energy savings. In order to reach this, it will be necessary to take unconventional process conditions that target particle migration and membrane designs as a starting point.

    Besides concentrated suspensions, also dilute suspensions benefit from particle migration. Migration phenomena can induce fractionation of yeast cells from water in dilute suspensions, using micro-engineered membranes having pores that are typically five times larger than the cells. The observed effects are similar to fluid skimming (in combination with inertial lift), and the separation performance can be linked to the ratio between cross-flow and trans-membrane flux, which is captured in a dimensionless number that can predict size of transmitted cells. For sufficiently high cross-flow velocity, the particles pass the pore and become part of the retentate; the separation factor can simply be changed by changing the ratio between cross-flow velocity and trans-membrane flux. Since the membranes have very large pores, fouling does not play a role and constant high trans-membrane flux values of 200–2200 L/(h•m2) are reached for trans-membrane pressures ranging from 0.02 to 0.4 bar.

    In conclusion, particle migration can improve (membrane) separation processes and even has the potential to lead to totally new separation processes. Particle migration can be advantageous in both dilute as well as concentrated systems, leading to reduced fouling, reduced energy and water consumption and a reduction in waste. This can all be achieved at production capacity similar or better than currently available in microfiltration processes.

    Enzyme-catalyzed modification of poly(ethersulfone) membranes
    Nady, N. - \ 2012
    Wageningen University. Promotor(en): Remko Boom; Han Zuilhof, co-promotor(en): Karin Schroen; Maurice Franssen. - S.l. : s.n. - ISBN 9789461731456 - 172
    membranen - oppervlakteverandering - laccase - enzymen - kunststoffen - membranes - surface modification - laccase - enzymes - plastics

    The robustness of a membrane is determined by the properties of the base polymer and the functionality of its surface. One of the most popular polymers used for membrane preparation is polyethersulfone (PES), which has excellent thermo-physical properties, but the surface properties are in need of improvement to reduce membrane fouling by adsorption of e.g. protein and live cells, which cause sever flux decline during filtration. Therefore, it is not strange that a wide range of modification methods has been published to reduce surface hydrophobicity of PES membranes. However, the methods that are currently suggested are all rather offer random control over the resulting surface structure and may be environmentally adverse

    This study presents enzyme-initiated grafting of PES membranes as the first successful example of an environmentally friendly modification of PES membranes. Various phenolic acids, such as 4-hydroxybenzoic acid and gallic acid (3,4,5-trihydroxybenzoic acid), were coupled to the membrane in aqueous medium at room temperature using laccase from Trametes versicolor as catalyst. This enzyme is able to oxidize phenolic compounds to their corresponding free radicals that are subsequently grafted onto PES membranes, introducing polar groups (OH, COOH) on the membrane surface by formation of a covalent C-O linkage as was proven by spin density calculations and IRRAS.

    We succeed in altering the surface properties of PES membranes using laccase-catalyzed modification method. It was found that the surface structure or shape that can be tuned through both the modification conditions and the modifier structure, has a significant role in prevention of adsorption rather than surface hydrophilicity as is often assumed. Membrane flux is hardly influenced (10% reduction), and foulant (e.g., bovine serum albumin, dextrin, tannin, and pathogenic bacterium Listeriamonocytogenes) repellence is greatly increased.

    In conclusion, the enzyme-catalyzed modification method shows a remarkable flexibility, and allows careful tuning of the membrane properties in such a way that membrane fouling can be suppressed. Besides, the modification method does not influence the bulk properties of the membrane adversely, the modification layer is resistant to a wide range of pH, and the costs of this modification on industrial scale are reasonable, which makes this modification method an interesting eco-friendly alternative to currently used methods.

    Low concentration of powdered activated carbon decreases fouling in membrane bioreactors
    Remy, M.J.J. - \ 2012
    Wageningen University. Promotor(en): Wim Rulkens, co-promotor(en): Hardy Temmink. - S.l. : s.n. - ISBN 9789461732309 - 163
    afvalwaterbehandeling - geactiveerd slib - membranen - bioreactoren - filtratie - waste water treatment - activated sludge - membranes - bioreactors - filtration
    Het doel van deze studie was te onderzoeken welke slibeigenschappen verantwoordelijk zijn voor de membraanvervuiling in MBR systemen, en om een methode te vinden om deze eigenschappen dusdanig te manipuleren dat de membraanvervuiling drastisch kan worden gereduceerd.
    A Multi-Platform Flow Device for Microbial (Co-) Cultivation and Microscopic Analysis
    Hesselman, M.C. ; Odoni, D.I. ; Ryback, B.M. ; Groot, S. de; Heck, R.G.A. van; Keijsers, J. ; Kolkman, P. ; Nieuwenhuijse, D. ; Nuland, Y.M. ; Sebus, E. ; Spee, R. ; Vries, H. de; Wapenaar, M.T. ; Ingham, C.J. ; Schroen, K. ; Martins Dos Santos, V.A.P. ; Spaans, S.K. ; Hugenholtz, F. ; Passel, M.W.J. van - \ 2012
    PLoS ONE 7 (2012)5. - ISSN 1932-6203
    culture - microorganisms - population - resistance - membranes - bacteria - chamber - support - arrays
    Novel microbial cultivation platforms are of increasing interest to researchers in academia and industry. The development of materials with specialized chemical and geometric properties has opened up new possibilities in the study of previously unculturable microorganisms and has facilitated the design of elegant, high-throughput experimental set-ups. Within the context of the international Genetically Engineered Machine (iGEM) competition, we set out to design, manufacture, and implement a flow device that can accommodate multiple growth platforms, that is, a silicon nitride based microsieve and a porous aluminium oxide based microdish. It provides control over (co-)culturing conditions similar to a chemostat, while allowing organisms to be observed microscopically. The device was designed to be affordable, reusable, and above all, versatile. To test its functionality and general utility, we performed multiple experiments with Escherichia coli cells harboring synthetic gene circuits and were able to quantitatively study emerging expression dynamics in real-time via fluorescence microscopy. Furthermore, we demonstrated that the device provides a unique environment for the cultivation of nematodes, suggesting that the device could also prove useful in microscopy studies of multicellular microorganisms
    Dormancy cycling in seeds: mechanisms and regulation
    Claessens, S.M.C. - \ 2012
    Wageningen University. Promotor(en): Linus van der Plas, co-promotor(en): Henk Hilhorst; P.E. Toorop. - S.l. : s.n. - ISBN 9789461731906 - 161
    sisymbrium officinale - arabidopsis thaliana - kiemrust - zaden - genen - levenscyclus - slaaptoestand - membranen - metabolisme - sisymbrium officinale - arabidopsis thaliana - seed dormancy - seeds - genes - life cycle - dormancy - membranes - metabolism

    The life cycle of most plants starts, and ends, at the seed stage. In most species mature seeds are shed and dispersed on the ground. At this stage of its life cycle the seed may be dormant and will, by definition, not germinate under favourable conditions (Bewley, 1997).

    Seasonal dormancy cycling is a characteristic found in plant seeds. Being able to cycle in and out of dormancy allows the seed to survive decades or even centuries, allowing germination to be spread over time, but only when optimal conditions are available, not only for germination but especially for seedling establishment. In this thesis we have attempted to further elucidate the mechanisms behind dormancy, germination and dormancy cycling.

    Sisymbrium officinale seeds need nitrate and light to start germination (Chapter 2, 3, 4, 6). Nitrate acts in part by reducing the abscisic acid (ABA) levels (a plant hormone that elevates dormancy levels). The action of light and nitrate can also be reached by applying gibberellins (GAs) to the seeds (Chapter 2, 3, 4, 6). GAs are capable of inducing enzymes that hydrolyze the ensdosperm walls (Debeaujon and Koornneef, 2000; Chen and Bradford, 2000; Nonogaki et al., 2000; Manz et al., 2005) In this way GAs could be involved in lowering the physical restrictions imposed by the resistance of the seed coat and the endosperm. On the other hand, GAs may also increase the embryo growth potential.

    For successful survival of the dormant seed, metabolic activity is reduced to avoid rapid depletion of reserves. The metabolic activity of the seed was measured using electron paramagnetic resonance (EPR), with TEMPONE as a spin probe, and the respiratory activity was measured with the Q2-test (Chapter 2).We showed that primary dormancy was accompanied by hardly any metabolic or respiratory activity, and this increased considerably when dormancy was broken by nitrate. However, when the light pulse was not given and the seeds had become secondary dormant the metabolic activity slowed down.

    Regulation of dormancy is tightly linked with abiotic stress factors from the environment. The regulation and survival of the seed under stress conditions is largely dependent on the composition of the cytoplasm. We tested this by EPR, using carboxyl-proxyl (CP) spin probe (Chapter 4). The primary dormant and sub-dormant seeds possessed a higher viscosity than the germinating seeds. The viscosity of secondary dormant seeds appeared intermediate; however, the ease at which the vitrified water melted was similar to that of primary dormant seeds. As a result of the differences in viscosity, the temperature of vitrified water melting differed between the different dormancy states. The changes in cytoplasmic viscosity and vitrified water melting may be linked to changes in metabolism and the content of high molecular weight compounds.

    As membranes are the primary target for temperature perception, they are often implicated in regulating dormancy. Therefore, Hilhorst (1998) put forward a hypothesis in which changes in responsiveness to dormancy breaking factors like nitrate and light was a function of cellular membrane fluidity. In Chapter 3 we indeed showed that dormancy is a function of membrane fluidity. Primary dormant seeds of Sisymbrium officinale appeared to have very rigid membranes, whereas breaking dormancy increased membrane fluidity considerably. However, when sub-dormant seeds became secondary dormant membrane fluidity decreased again, but not to the rigidity seen in primary dormant seeds. One of the most common ways in which cells control membrane fluidity is by homeoviscous adaptation with the help of desaturases. Desaturase involvement in changes in membrane fluidity due to changes in dormancy was tested in Chapter 3 (using Sisymbrium officinale) and Chapter 5 (using Arabidopsis thaliana). Here we found that although desaturase activity may change the membrane fluidity or influence the germination/dormancy phenotype, the two are not linked, unless the effects of these enzymes are very local within the seed. Finally, in Chapter 7, we presented a new model in which a membrane anchored dormancy related protein/transcription factor is activated by changes in membrane fluidity. The activated form is transported to the nucleus, where it starts the germination process, which includes changes in metabolism and mobilization of storage reserves.

    Effect of temperature shocks on membrane fouling in membrane bioreactors
    Brink, P. van den; Satpradit, O.A. ; Bentem, A. van; Zwijnenburg, A. ; Temmink, B.G. ; Loosdrecht, M.C.M. - \ 2011
    Water Research 45 (2011)15. - ISSN 0043-1354 - p. 4491 - 4500.
    afvalwaterbehandeling - bioreactoren - membranen - geactiveerd slib - temperatuur - vervuiling door afzetting - viscositeit - waste water treatment - bioreactors - membranes - activated sludge - temperature - fouling - viscosity - waste-water treatment - cross-flow microfiltration - flux-step method - activated-sludge - particle deposition - size distribution - light-scattering - bubble-size - performance - ultrafiltration
    Temperature is known to influence the biological performance of conventional activated sludge systems. In membrane bioreactors (MBRs), temperature not only affects the bioconversion process but is also shown to have an effect on the membrane performance. Four phenomena are generally reported to explain the higher resistance for membrane filtration found at lower temperatures: (1) increased mixed liquor viscosity, reducing the shear stress generated by coarse bubbles, (2) intensified deflocculation, reducing biomass floc size and releasing EPS into the mixed liquor, (3) lower backtransport velocity and (4) reduced biodegradation of COD. Although the higher resistance at low temperatures has been reported in several papers, the relation with supernatant composition has not been investigated before. In this paper, the composition of the soluble fraction of the mixed liquor is related to membrane performance after exposing the sludge to temperature shocks. Flux step experiments were performed in an experimental system at 7, 15, and 25° Celsius with sludge that was continuously recirculated from a pilot-scale MBR. After correcting the permeate viscosity for temperature, higher membrane fouling rates were obtained for the lower temperature in combination with low fouling reversibility. The soluble fraction of the MBR mixed liquor was analysed for polysaccharides, proteins and submicron particle size distribution. At low temperature, a high polysaccharide concentration was found in the experimental system as compared to the MBR pilot. Upon decreasing the temperature of the mixed liquor, a shift was found in particle size towards smaller particles. These results show that the release of polysaccharides and/or submicron particles from sludge flocs could explain the increased membrane fouling at low temperatures
    Electrospun Polyurethane Fibers for Absorption of Volatile Organic Compounds from Air
    Scholten, E. ; Bromberg, L. ; Rutledge, G.C. ; Hatton, T.A. - \ 2011
    ACS Applied Materials and Interfaces 3 (2011). - ISSN 1944-8244 - p. 3902 - 3909.
    shape-memory polyurethane - activated carbon - block-copolymers - polymer nanofibers - hard segment - adsorption - membranes - vapors - desorption - sorption
    Electrospun polyurethane fibers for removal of volatile organic compounds (VOC) from air with rapid VOC absorption and desorption have been developed. Polyurethanes based on 4,4-methylenebis(phenylisocyanate) (MDI) and aliphatic isophorone diisocyanate as the hard segments and butanediol and tetramethylene glycol as the soft segments were electrospun from their solutions in N,N-dimethylformamide to form micrometer-sized fibers. Although activated carbon possessed a many-fold higher surface area than the polyurethane fiber meshes, the sorption capacity of the polyurethane fibers was found to be similar to that of activated carbon specifically designed for vapor adsorption. Furthermore, in contrast to VOC sorption on activated carbon, where complete regeneration of the adsorbent was not possible, the polyurethane fibers demonstrated a completely reversible absorption and desorption, with desorption obtained by a simple purging with nitrogen at room temperature. The fibers possessed a high affinity toward toluene and chloroform, but aliphatic hexane lacked the necessary strong attractive interactions with the polyurethane chains and therefore was less strongly absorbed. The selectivity of the polyurethane fibers toward different vapors, along with the ease of regeneration, makes them attractive materials for VOC filtration.
    Structuring microspheres
    Wagdare, N.A. - \ 2011
    Wageningen University. Promotor(en): Cees van Rijn; Remko Boom, co-promotor(en): Ton Marcelis. - [S.l.] : S.n. - ISBN 9789085859239 - 111
    emulgering - membranen - inkapseling in microcapsules - structuur - emulsification - membranes - microencapsulation - structure

    Encapsulation and use of capsules for controlled release has several applications in pharmaceuticals, foods, cosmetics, detergents and many other products for consumers. It can contribute to sustainability, since it allows an efficient use of active materials, delivery at the required site and possibly a longer shelf life of the products. Many encapsulation systems are basically very thin shells (10 nm – 10 µm) around microscopic reservoirs (100 nm – 100 µm), in which active ingredients are trapped. The release properties are strongly dependent on the material properties of the shell, but also on their size and uniformity.

    The overall objective of this research is to understand the formation process of microcapsules and microspheres by using phase separation in well-defined droplets of a polymeric solution. The primary droplets were produced with microsieve emulsification. The polymer used was Eudragit FS 30D (a commercial copolymer of poly(methyl acrylate-co-methyl methacrylate-co-methacrylic acid) 7:3:1), which contains charged carboxylate groups that make the polymer water-soluble at higher pH (>7), allowing for release by a change in pH.

    Chapter 2 presents results that give more insight into microsieve emulsification with high porosity micro-engineered membranes. The droplet formation was strongly influenced by the dynamics of surfactant adsorption. The presence of suitable surfactants in both phases prevents the coalescence of droplets and wetting of the microsieve membranes by the dispersed phase during oil droplet formation. This resulted in the formation of stable emulsions of droplets with a narrow size distribution. The flux of the dispersed phase could be increased an order of magnitude compared to previous methods, without loss of size-distribution of the droplets. Thus, use of a high-porosity membrane, in combination with suitable surfactants in both the dispersed and continuous phases resulted in a much more effective and efficient emulsification process.

    In Chapter 3 crossflow microsieve emulsification was used to prepare porous microcapsules with an average size of about 30 µm. A mixture of Eudragit and hexadecane in dichloromethane (DCM) was emulsified in water.Being a poor solvent for this polymer, demixing of the droplet into a polymeric shell and a hexadecane-rich core occurred upon extraction of the DCM into the water phase. At a low ratio of polymer to hexadecane, the resulting shells were found to be porous. Increasing this ratio resulted in a reduction of the porosity and pore size of the shell. The Eudragit has a pH-dependent solubility. It is insoluble at acidic conditions and rapidly dissolves at alkaline conditions. The capsules were found to be stable at a pH lower than 7.0, whereas the oil core was released within half an hour at pH 7.1 and within a minute at pH 8.0. The morphology of the microcapsules can be adapted with a careful choice of the concentrations of polymer, hexadecane and solvent. At higher concentrations of polymer, the tiny oil droplets that were captured in the forming Eudragit shell were unable to coalesce completely and small, isolated pores were formed within the shell matrix.

    The potential for new microcapsule morphologies was further explored in Chapter 4 where the formation of Eudragit capsules with other oils instead of hexadecane was studied, and in Chapter 5 where a blend of poly(methyl methacrylate) (PMMA) and Eudragit was used.

    In Chapter 4 the effects of chain lengths of vegetable oils on the formation of porous microcapsules with hollow and multi-compartment structures is discussed. The encapsulation of oil and the morphology of the resulting microcapsules depends on the interaction between the Eudragit polymer and the type of oil that was used. Microcapsule formation using long chain length oils such as sunflower oil, olive oil and coconut oil resulted in well-defined microcapsules with a single encapsulated oil droplet, covered with a Eudragit-rich shell. On the other hand, capsules prepared with relatively short chain length oils, such as medium chain triglyceride oil, resulted in capsules with many individual small oil droplets encapsulated in an Eudragit matrix. Extraction of the oil from the microcapsules with hexane results in the formation of hollow porous shells as was investigated with optical microscopy and SEM. These structures are formed during microcapsule formation due to the complex phase separation processes in the Eudragit-water-oil-DCM quaternary system.

    In Chapter 5 the formation of microcapsules is further explored by using a blend of PMMA and Eudragit. Microspheres formed with this blend were found to consist of a PMMA core inside an Eudragit-rich shell, which tends to be porous. As the amount of Eudragit is increased, a thicker and more porous outer shell is formed due to the enhanced interaction of water with Eudragit. After dissolution of the Eudragit at high pH, different core surface structures resulted, from irregular surfaces to microspheres with a fiber-like, swollen corona around it, and to a surface covered with small nodular structures, dependent on the concentrations of PMMA and Eudragit in the initial mixture. As already indicated above, these structures are formed as a result of complex phase separation processes between polymers and (non)solvents, and between the two polymers.

    In Chapter 6 the results described in this thesis were compared with existing literature, yielding an outlook on the field of microencapsulation through phase separation. A general concept is discussed on how to obtain various interesting complex structures with phase separation combined with microsieve emulsification. Finally, a conceptual process design is discussed for industrial scale production of microcapsules and microspheres with use of microsieve emulsification.

    This thesis has yielded insight in the formation of a range of microcapsule morphologies by investigating a range of new production methods (microsieves and demixing conditions) and formulations (different concentrations, oils and using one polymer or a blend), and through this provides better insight into the mechanisms of microcapsule formation. While some of the structures may be directly used for microcapsule formation, some other structures may well have potential for other applications.

    Figure. Examples of structured microcapsules and microspheres developed in this thesis.

    Excitation energy transfer and trapping in higher plant photosystem II complexes with different antenna sizes
    Caffarri, S. ; Broess, K. ; Croce, R. ; Amerongen, H. van - \ 2011
    Biophysical Journal 100 (2011)9. - ISSN 0006-3495 - p. 2094 - 2103.
    light-harvesting complex - green plants - chlorophyll fluorescence - charge separation - arabidopsis-thaliana - core complex - kinetics - organization - membranes - lhcii
    We performed picosecond fluorescence measurements on well-defined Photosystem II (PSII) supercomplexes from Arabidopsis with largely varying antenna sizes. The average excited-state lifetime ranged from 109 ps for PSII core to 158 ps for the largest C2S2M2 complex in 0.01% a-DM. Excitation energy transfer and trapping were investigated by coarse-grained modeling of the fluorescence kinetics. The results reveal a large drop in free energy upon charge separation (>700 cm-1) and a slow relaxation of the radical pair to an irreversible state (150 ps). Somewhat unexpectedly, we had to reduce the energy-transfer and charge-separation rates in complexes with decreasing size to obtain optimal fits. This strongly suggests that the antenna system is important for plant PSII integrity and functionality, which is supported by biochemical results. Furthermore, we used the coarse-grained model to investigate several aspects of PSII functioning. The excitation trapping time appears to be independent of the presence/absence of most of the individual contacts between light-harvesting complexes in PSII supercomplexes, demonstrating the robustness of the light-harvesting process. We conclude that the efficiency of the nonphotochemical quenching process is hardly dependent on the exact location of a quencher within the supercomplexes
    Biofilm development on new and cleaned membrane surfaces
    Bereschenko, L.A. - \ 2010
    Wageningen University. Promotor(en): Fons Stams; M.C.M. Loosdrecht, co-promotor(en): G.J.W. Euverink. - [S.l. : S.n. - ISBN 9789085858065 - 161
    biofilms - membranen - ongewenste aangroei van levende (micro)organismen - kunstmatige membranen - zuiveringsinstallaties - biofilms - membranes - biofouling - artificial membranes - purification plants
    This thesis presents a comprehensive research report on microbiological aspects of biofouling occurrence in full-scale reverse osmosis (RO) systems. Biofouling is a process in which microorganisms attach to membranes and develop into a thick film that can choke the entire RO system. Management of this problem requires basic understanding of the mechanism of this phenomenon. The basic questions of this PhD research project therefore addressed the origin, succession and spatiotemporal development of biofilms in full-scale RO systems, in particular in relation to operational aspects of RO systems. The multifaceted research strategy involving acquisitions of representative samples and use of many molecular and microscopic analysis techniques in parallel was employed. The investigation showed that biofilms are able to grow on any surface in a full-scale RO plant. This gives local niches for detachment of biomass, either as single cells or cell clumps, and results in a spreading of bacteria to the further stages of the plant. In the RO membrane modules, the enriched bacteria might more easily colonise the surfaces since they will be better adapted to growth in the system than bacteria present in the feed water. Initially, the single cell colonizers (sphingomonads) form a number of flat and abundantly EPS-embedded cell monolayers over the entire membrane surface. The clumps-associated pioneers (mainly Beta- and Gammaproteobacteria) appear to be trapped mainly in the first part of the module, most likely due to a filtering action of the spacer. In time, these bacteria develop in pillar-like structures and slowly spread throughout the whole membrane module on top of the established sphingomonads biofilm. The secondary colonisers (bacteria and eukaryotes) occur in the resulting biofilm formations. Although composition of the biofilm microbial community undergoes a succession in time, the architecture of an established biofilm appears to be rather stable. Conventional treatment of RO membrane modules with chemicals did not lead to cleaning: the sphingomonads cells can be detected under the collapsed but obviously not removed biofilm EPS matrix. After cleaning, the biofouling layer seemed to grow faster (within 6 days) than a fresh biofilm (16 days). To conclude, biofouling is a complex phenomenon with two appearances: a fouling layer on the membrane limiting the water flux and a fouling layer on the spacer limiting the water flow through the spacer channel and resulting in an increased pressure drop. It became clear that cleaning strategies should focus more on the removal of accumulated biomass and not only on the killing of cells. Moreover, the basal Sphingomonas layer requires further research to appropriately control biofouling in RO systems. It might also be possible to design the RO - membrane module in a different manner, leading to a different biofilm morphology which gives less rise to operational problems.
    Why low powdered activated carbon addition reduces membrane fouling in MBRs
    Remy, M.J.J. ; Potier, V. ; Temmink, B.G. ; Rulkens, W.H. - \ 2010
    Water Research 44 (2010)3. - ISSN 0043-1354 - p. 861 - 867.
    afvalwaterbehandeling - waterzuivering - actieve kool - adsorptie - membranen - biologische filtratie - filtreerbaarheid - uitvlokking - biodegradatie - zuiveringsinstallaties - waste water treatment - water treatment - activated carbon - adsorption - membranes - biological filtration - filterability - flocculation - biodegradation - purification plants - waste-water treatment - bioreactor mbr - sludge - flux - performance - filtration - bioflocculation - operation
    Previous research had demonstrated that powdered activated carbon (PAC), when applied at very low dosages and long SRTs, reduces membrane fouling in membrane bioreactor (MBRs). In this contribution several mechanisms to explain this beneficial effect of PAC were investigated, including enhanced scouring of the membrane surface by PAC particles, adsorption of membrane foulants by PAC and subsequent biodegradation and a positive effect of PAC on the strength of the sludge flocs. It was concluded that the latter mechanism best explains why low dosages of PAC significantly reduce membrane fouling. Cheaper alternatives for PAC may have a similar effect
    Water Replacement Hypothesis in Atomic Detail - Factors Determining the Structure of Dehydrated Bilayer Stacks
    Golovina, E.A. ; Golovin, A. ; Hoekstra, F.A. ; Faller, R. - \ 2009
    Biophysical Journal 97 (2009)2. - ISSN 0006-3495 - p. 490 - 499.
    molecular-dynamics simulation - x-ray-diffraction - solid-state nmr - lipid-bilayers - phospholipid-bilayers - na+ counterions - full hydration - phase-behavior - membranes - phosphatidylcholine
    According to the water replacement hypothesis, trehalose stabilizes dry membranes by preventing the decrease of spacing between membrane lipids under dehydration. In this study, we use molecular-dynamics simulations to investigate the influence of trehalose on the area per lipid (APL) and related structural properties of dehydrated bilayers in atomic detail. The starting conformation of a palmitoyloleolylphosphatidylcholine lipid bilayer in excess water was been obtained by self-assembly. A series of molecular-dynamics simulations of palmitoyloleolylphosphatidylcholine with different degrees of dehydration (28.5, 11.7, and 5.4 waters per lipid) and different molar trehalose/lipid ratios (1:1) were carried out in the NPT ensemble. Water removal causes the formation of multilamellar stacks through periodic boundary conditions. The headgroups reorient from pointing outward to inward with dehydration. This causes changes in the electrostatic interactions between interfaces, resulting in interface interpenetration. Interpenetration creates self-spacing of the bilayers and prevents gel-phase formation. At lower concentrations, trehalose does not separate the interfaces, and acting together with self-spacing, it causes a considerable increase of APL. APL decreases at higher trehalose concentrations when the layer of sugar physically separates the interfaces. When interfaces are separated, the model confirms the water replacement hypothesis
    Low dose powdered activated carbon addition at high sludge retention times to reduce fouling in membrane bioreactors
    Remy, M.J.J. ; Marel, P. van der; Zwijnenburg, A. ; Rulkens, W.H. ; Temmink, B.G. - \ 2009
    Water Research 43 (2009)2. - ISSN 0043-1354 - p. 345 - 350.
    afvalwaterbehandeling - waterzuivering - geactiveerd slib - bioreactoren - membranen - biologische filtratie - actieve kool - doseringseffecten - zuiveringsinstallaties - waste water treatment - water treatment - activated sludge - bioreactors - membranes - biological filtration - activated carbon - dosage effects - purification plants - waste-water treatment - performance - filtration - mbr
    The addition of a low concentration of PAC (0.5 g L-1 of sludge, i.e. a dose of 4 mg L-1 of wastewater), in combination with a relatively long SRT (50 days), to improve membrane filtration performance was investigated in two pilot-scale MBRs treating real municipal wastewater. Continuous filterability tests at high flux showed the possibility to run for 18 h at 72 L m-2 h-1 and 180 h at 50 L m-2 h-1, while significant fouling occurred without PAC. In addition, measurements of the critical flux showed an increase of 10% for this strategy. Low dosage and high retention time makes it feasible and cost effective. Further advantages with regard to permeate quality and possible micropollutants removal are currently under investigation.
    Hollow Polylactide Microcapsules with Controlled Morphology and Thermal and Mechanical Properties
    Sawalha, H.I.M. ; Schroën, C.G.P.H. ; Boom, R.M. - \ 2009
    AIChE Journal 55 (2009)11. - ISSN 0001-1541 - p. 2827 - 2834.
    poly(l-lactic acid) - contrast agent - poly(lactic acid) - drug-release - microspheres - nonsolvent - particles - membranes - films
    Hollow polylactide microcapsules were prepared by multistage premix membrane emulsification of polylactide/dichloromethane/oil solutions in water (nonsolvent). The effects of the different oils on the morphology, thermal, and mechanical properties of the hollow microcapsules were investigated. All oils resulted in hollow microcapsules with controlled shell thickness of 60 nm except for eugenol, in which irregular, massive capsules were obtained. The properties of the microcapsules were strongly dependent on the oil used, for example the thermal transition temperatures found for hollow capsules were lower than for solid particles prepared without any oil. The crystallinity and transition temperatures of the capsules prepared with linear alkanes were higher than for cyclic alkanes; terpenes gave the lowest transition temperatures. The shell stiffness, measured with atomic force microscopy, was highly dependent on the oil used. Capsules prepared with dodecane showed higher stiffness (3.3 N m-1) than with limonene (2 N m-1) or cyclohexane (1.4 N m-1)
    A 28-day repeat dose toxicity study of steroidal glycoalkaloids a-solanine and a-chaconine in the Syrian Golden Hamster
    Langkilde, S. ; Mandimika, T. ; Schroder, M. ; Meyer, O. ; Slob, W. ; Peijnenburg, A.A.C.M. ; Poulsen, M. - \ 2009
    Food and Chemical Toxicology 47 (2009)6. - ISSN 0278-6915 - p. 1099 - 1108.
    continuous end-points - potato glycoalkaloids - synergistic interaction - cholesterol - metabolism - rat - biosynthesis - consumption - transport - membranes
    Glycoalkaloids ¿-solanine and ¿-chaconine are naturally present toxicants in the potato plant (Solanum tuberosum). Human intake of high doses of glycoalkaloids has led to acute intoxication, in severe cases coma and death. Previous studies have indicated that the ratio of ¿-solanine to ¿-chaconine may determine the degree and nature of the glycoalkaloid toxicity in potatoes, as the toxicity of the two alkaloids act synergistically. The aim of the present study was to investigate whether an altered ratio of ¿-solanine and ¿-chaconine would reduce the toxicity of the glycoalkaloids. The Syrian Golden hamster was given daily doses of ¿-solanine and ¿-chaconine by gavage for 28 days. Doses of up to 33.3 mg total glycoalkaloids/kg body weight were applied in ratios of 1:3.7 and 1:70 (¿-solanine:¿-chaconine). Administration of the highest doses of both ratios resulted in distended and fluid filled small intestines and stomach. Animals receiving the ratio with the reduced content of ¿-solanine were less affected compared to those receiving the other ratio. Gene expression profiling experiments were conducted using RNA from epithelial scrapings from the small intestines of the hamsters administered the highest doses of the glycoalkaloid treatments. In general, more differential gene expression was observed in the epithelial scrapings of the hamsters fed the ratio of 1:3.7. Mostly, pathways involved in lipid and energy metabolism were affected by the ratio of 1:3.7.
    Dynamics of encapsulation and controlled release systems bases on water-in-water emulsions: Liposomes and polymersomes
    Sagis, L.M.C. - \ 2009
    Physica A 388 (2009)13. - ISSN 0378-4371 - p. 2579 - 2587.
    interfacial permeability - shear-flow - vesicles - deformation - relaxation - membranes - behavior - bilayers
    The deformation relaxation behavior of two types of vesicles, liposomes and polymersomes, was investigated using a general nonequilibrium thermodynamics theory based on the interfacial transport phenomena (ITP) formalism. Liposomes and polymersomes are limiting cases of this theory with respect to rheological behavior of the interfaces. They represent respectively viscous, and viscoelastic surface behavior. We have determined the longest relaxation time for a small perturbation of the interfaces for both these limiting cases. Parameter maps were calculated which can be used to determine when surface tension, bending rigidity, spontaneous curvature, interfacial permeability, or surface rheology dominate the response of the vesicles. In these systems up to nine different scaling regimes were identified for the relaxation time of a deformation with droplet size, with scaling exponent n ranging from 0 to 4
    Polylactide microcapsules and films: preparation and properties
    Sawalha, H.I.M. - \ 2009
    Wageningen University. Promotor(en): Remko Boom, co-promotor(en): Karin Schroen. - [S.l. : S.n. - ISBN 9789085853152 - 219
    inkapselen - films - polyesters - vervangbare hulpbronnen - biodegradatie - membranen - emulgering - hardwording - mechanische eigenschappen - thermische eigenschappen - ultrageluid - kunstmatige membranen - encapsulation - films - polyesters - renewable resources - biodegradation - membranes - emulsification - solidification - mechanical properties - thermal properties - ultrasound - artificial membranes
    This thesis aims at preparation of hollow polylactide (PLA) microcapsules for use as ultrasound contrast agents with controlled size, structure and mechanical and thermal properties. The microcapsules were prepared with multistage premix membrane emulsification. The mechanical and thermal properties of the microcapsules, and of films that were prepared under similar conditions, were highly dependent on the non-solvent and the liquid used as a template for the hollow core of the microcapsule. The size and size distribution of the microcapsules could, amongst others, be controlled through the process conditions that were applied during preparation. The main conclusion of this thesis was that the nonsolvent properties and the template liquid, highly affect the solidification process of the polymer; and through these parameters, the properties of PLA microcapsules and films can be effectively fine-tuned for various applications.
    The role of lipids in the global organization of thylakoid membranes of higher plants
    Krumova, S.K.B. - \ 2009
    Wageningen University. Promotor(en): Herbert van Amerongen, co-promotor(en): G. Garab. - [S.l.] : S.n. - ISBN 9789085852926 - 132
    planten - thylakoïden - membranen - lipiden - chloroplasten - fotosynthese - plants - thylakoids - membranes - lipids - chloroplasts - photosynthesis
    The first steps of photosynthesis (capturing of light and conversion of light energy into chemical energy) occur in the thylakoid membrane of the chloroplasts. It consists for 75% of membrane proteins and 25% of lipid molecules. In this thesis the global properties of the lipids in the thylakoid membrane are studied with a variety of spectroscopic techniques. Special attention is paid to the lipid packing, phase behavior and membrane permeability, as well as the role of the lipids in structural rearrangements and the overall organization of the membrane. The presented results reveal heterogeneity in the packing of the bulk lipid molecules and the participation of the lipids in both bilayer and non-bilayer structures. It is demonstrated that the lipid mixture has an active role in the lateral arrangement of the protein complexes, the formation of macrodomains and their thermal stability and indirectly in the excitation energy trapping by the photosynthetic complexes. This work provides a basis for further future investigations of the properties of the thylakoid lipid matrix and of the lipid-protein interactions in thylakoid membranes and their relevance for different functions of the membrane.
    Primary photosynthetic processes: from supercomplex to leaf
    Broess, K. - \ 2009
    Wageningen University. Promotor(en): Herbert van Amerongen. - [S.l.] : S.n. - ISBN 9789085852988 - 124
    fotosynthese - fluorescentie - fluorescentiemicroscopie - spectroscopie - membranen - chloroplasten - fotosysteem ii - planten - photosynthesis - fluorescence - fluorescence microscopy - spectroscopy - membranes - chloroplasts - photosystem ii - plants
    This thesis describes fluorescence spectroscopy experiments on photosynthetic complexes that cover the primary photosynthetic processes, from the absorption of light by photosynthetic pigments to a charge separation (CS) in the reaction center (RC). Fluorescence spectroscopy is a useful tool in photosynthetic particles, because the latter are densely packed with fluorescence pigments like chlorophylls (Chl). The fluorescence of each pigment is affected by its environment and provide information about structure and dynamics of the photosynthetic complexes. In this thesis time-resolved fluorescence of Chl molecules is used for studying the ultrafast kinetics in membrane particles of photosystem II (PSII) (chapter 2, 3 and 4). In chapter 5 fluorescence lifetime imaging microscopy (FLIM) of is applied to study entire chloroplasts, either in the leaf or in isolated chloroplast form. The advantage of FLIM is that the interactions of the fluorescence pigments in both photosystems can be spatially resolved up to a resolution of 0.5 x 0.5 x 2 µm to indentify and quantify photosynthetic processes in their natural environment.

    Excitation energy transfer and charge separation in PSII membranes (chapter 2,3 and 4)

    In this thesis time-resolved fluorescence measurements of PSII containing membranes, the so called BBY particles, are performed in low-light conditions with open reaction centers. The BBY particles do not contain photosystem I (PSI) or stroma lamellae, but do support electron transfer and carry out oxygen evolution with high activity and are comparable with the grana in vivo. The fluorescence decay kinetics of the BBY particles are faster than observed in previous studies and also faster than observed for PSII in chloroplasts and thylakoid preparations. The average lifetime is 150 ps, which, together with previous annihilation experiments on light-harvesting complex II (LHCII) suggests that excitation migration from the antenna complexes contributes significantly to the overall charge separation time. This is in disagreement with the commonly applied exciton / radical-pair-equilibrium (ERPE) model that assumes that excitation energy diffusion through the antenna to the RC is much faster than the overall charge-separation time.
    A simple coarse-grained method is proposed, based on the supramolecular organization of PSII and LHCII in grana membranes (C2S2M2). The proposed modelling procedure for BBY particles is only approximate and many different combinations of excitation migration time and the charge separation time can explain the observed fluorescence kinetics. However it is clear that charge transfer should be rather fast and is accompanied with a large drop in free energy.
    In chapter 3, the fluorescence kinetics of BBY particles with open RCs are compared after preferential excitation at 420 and 484 nm, which causes a difference in the initial excited-state populations of the inner and outer antenna system. The fluorescence decay is somewhat slower upon preferential excitation of chlorophyll (Chl) b, which is exclusively present in the outer antenna. Using the coarse-grained model it was possible to fit the 420 and 484 nm results simultaneously with a two-step electron transfer model and four parameters: the hopping rate between the protein-pigment complexes, the CS rate, the drop in free energy upon primary charge separation and a secondary charge separation rate. The conclusion is that the average migration time contributes ~25% to the overall trapping time. The hopping time obtained in chapter 3 is significantly faster than might be expected based on studies on trimeric and aggregated LHCII and it is concluded that excitation energy transfer in PSII follows specific pathways that require an optimized organization of the antenna complexes with respect to each other. Analysis of the composition of the BBY particles indicates that the size of the light-harvesting system in PSII is smaller than commonly found for PSII in chloroplasts and explains why the fluorescence lifetimes are smaller for the BBY’s.
    In chapter 4, four different PSII supercomplex preparations were studied. The main difference between these supercomplexes concerns the size of the outer antenna. The average lifetime of the supercomplexes becomes longer upon increasing the antenna size. The results indicate that the rate constants obtained from the coarse-grained method for BBY preparations, which is based on the supercomplex composition C2S2M2, should be slightly faster (~10%) as predicted in chapter 3. The observation that the average lifetime of the supercomplexes is relatively slow compared to what one might expect based on the measurements on BBY particles, and this will require further future studies.

    Photosynthesis in plant leaves (Chapter 5)

    With the use of femtosecond two-photon excitation TPE at 860 nm it appears to be possible to measure fluorescence lifetimes throughout the entire leaves of Arabidopsis thaliana and Alocasia wentii. It turns out that the excitation intensity can be kept sufficiently low to avoid artifacts due to singlet-singlet and singlet-triplet annihilation, while the reaction centers can be kept in the open state during the measurements. The average fluorescence lifetimes obtained for individual chloroplasts of Arabidopsis thaliana and Alocasia wentii in the open and closed state, are approximately ~250 ps and ~1.5 ns, respectively. The maximum fluorescence state correspond to a state in which all reaction centers are closed. The kinetics are very similar to those obtained for chloroplasts in vitro with the FLIM setup and to in vivo results reported in literature. No variations between chloroplasts are observed when scanning throughout the leaves of Arabidopsis thaliana and Alocasia wentii. Within individual chloroplasts some variation is detected for the relative contributions of PSI and PSII to the fluorescence. The results open up the possibility to use FLIM for the in vivo study of the primary processes of photosynthesis at the level of single chloroplasts under all kinds of (stress) conditions.

    General conclusions

    This thesis gives new insight of the kinetic processes in PSII membranes. With the use of a coarse-grained method that provides an easy way to incorporate existing knowledge and models for individual complexes, valuable conclusions can be drawn about the excitation energy transfer and the CS which hopefully contributes to an improvement of the knowledge about PSII functioning. In general it was shown that a large drop in free energy is needed in PSII membranes for all simulations with the coarse-grained method.
    The presented results on the kinetics of chloroplasts obtained in vitro and in vitro are very similar and verify that conclusions drawn from isolated chloroplasts can be extrapolated to photosynthetic processes in their natural environment.

    Biological black water treatment combined with membrane separation
    Voorthuizen, E.M. van; Zwijnenburg, A. ; Meer, W. van der; Temmink, H. - \ 2008
    Water Research 42 (2008)16. - ISSN 0043-1354 - p. 4334 - 4340.
    afvalwaterbehandeling - biologische behandeling - filtratie - membranen - voedingsstoffen - terugwinning - scheiding - verzamelen - rioolwater - prestatieniveau - waste water treatment - biological treatment - filtration - membranes - nutrients - recovery - separation - collection - sewage - performance - bioreactors - phosphorus
    Separate treatment of black (toilet) water offers the possibility to recover energy and nutrients. In this study three combinations of biological treatment and membrane filtration were compared for their biological and membrane performance and nutrient conservation: a UASB followed by effluent membrane filtration, an anaerobic MBR and an aerobic MBR. Methane production in the anaerobic systems was lower than expected. Sludge production was highest in the aerobic MBR, followed by the anaerobic MBR and the UASB-membrane system. The level of nutrient conservation in the effluent was high in all three treatment systems, which is beneficial for their recovery from the effluent. Membrane treatment guaranteed an effluent which is free of suspended and colloidal matter. However, the concentration of soluble COD in the effluent still was relatively high and this may seriously hamper subsequent nutrient recovery by physical¿chemical processes. The membrane filtration behaviour of the three systems was very different, and seemed to be dominated by the concentration of colloidals in the membrane feed. In general, membrane fouling was the lowest in the aerobic MBR, followed by the membranes used for UASB effluent filtration and the anaerobic MBR.
    Effect of the type of ion exchange membrane on performance, ion transport, and pH in biocatalyzed electrolysis of wastewater
    Rozendal, R.A. ; Sleutels, T.H.J.A. ; Hamelers, H.V.M. ; Buisman, C.J.N. - \ 2008
    Water Science and Technology 57 (2008)11. - ISSN 0273-1223 - p. 1757 - 1762.
    afvalwaterbehandeling - waterzuivering - membranen - filtratie - elektrolyse - waterstof - ionenuitwisselingsbehandeling - ionentransport - anionenwisseling - waste water treatment - water treatment - membranes - filtration - electrolysis - hydrogen - ion exchange treatment - ion transport - anion exchange - microbial fuel-cells - bacterium - acetate - cation
    Previous studies have shown that the application of cation exchange membranes (CEMs) in bioelectrochemical systems running on wastewater can cause operational problems. In this paper the effect of alternative types of ion exchange membrane is studied in biocatalyzed electrolysis cells. Four types of ion exchange membranes are used: (i) a CEM, (ii) an anion exchange membrane (AEM), (iii) a bipolar membrane (BPM), and (iv) a charge mosaic membrane (CMM). With respect to the electrochemical performance of the four biocatalyzed electrolysis configurations, the ion exchange membranes are rated in the order AEM > CEM > CMM > BPM. However, with respect to the transport numbers for protons and/or hydroxyl ions (t(H/OH)) and the ability to prevent pH increase in the cathode chamber, the ion exchange membranes are rated in the order BPM > AEM > CMM > CEM.
    Energy recovery from controlled mixing salt and fresh water with a reverse electrodialysis system
    Post, J.W. ; Hamelers, H.V.M. ; Buisman, C.J.N. - \ 2008
    Environmental Science and Technology 42 (2008)15. - ISSN 0013-936X - p. 5785 - 5790.
    energiebronnen - zout water - zoet water - dijken - zeewater - elektrodialyse - energieterugwinning - membranen - duurzame energie - energy sources - saline water - fresh water - dykes - sea water - electrodialysis - energy recovery - membranes - sustainable energy - electric-power - salinity - model
    The global potential to obtain clean energy from mixing river water with seawater is considerable. Reverse electrodialysis is a membrane-based technique for direct production of sustainable electricity from controlled mixing of river water and seawater. It has been investigated generally with a focus on obtained power, without taking care of the energy recovery. Optimizing the technology to power output only, would generally give a low energetic efficiency. In the present work, therefore, we emphasized the aspect of energy recovery. No fundamental obstacle exists to achieve an energy recovery of > 80%. This number was obtained with taking into account no more than the energetic losses for ionic transport. Regarding the feasibility, it was assumed to be a necessary but not sufficient condition that these internal losses are limited. The internal losses could be minimized by reducing the intermembrane distance, especially from the compartments filled with the low-conducting river water. It was found that a reduction from 0.5 to 0.2 mm indeed could be beneficial, although not to the expected extent. From an evaluation of the internal losses, it was supposed that besides the compartment thickness, also the geometry of the spacer affects the internal resistance.
    High rate sulfate reduction at pH 6 in a Ph-auxostat submerged membrane bioreactor fed with formate
    Bijmans, M.F.M. ; Peeters, T.W.T. ; Lens, P.N.L. ; Buisman, C.J.N. - \ 2008
    Water Research 42 (2008)10-11. - ISSN 0043-1354 - p. 2439 - 2448.
    afvalwaterbehandeling - industrieel afval - bioreactoren - membranen - filtratie - sulfaat reducerende bacteriën - sulfaatreductie - waste water treatment - industrial wastes - bioreactors - membranes - filtration - sulfate reducing bacteria - sulfate reduction - gas-lift reactor - reducing bacteria - hydrogen-sulfide - carbon-dioxide - growth - methanogenesis - conversion - removal - sludge - water
    Many industrial waste and process waters contain high concentrations of sulfate, which can be removed by sulfate-reducing bacteria (SRB). This paper reports on mesophilic (30 °C) sulfate reduction at pH 6 with formate as electron donor in a membrane bioreactor with a pH-auxostat dosing system. A mixed microbial community from full-scale industrial wastewater treatment bioreactors operated at pH 7 was used as inoculum. The pH-auxostat enabled the bacteria to convert sulfate at a volumetric activity of 302 mmol sulfate reduced per liter per day and a specific activity of 110 mmol sulfate reduced per gram volatile suspended solids per day. Biomass grew in 15 days from 0.2 to 4 g volatile suspended solids per liter. This study shows that it is possible to reduce sulfate at pH 6 with formate as electron donor at a high volumetric and specific activity with inocula from full-scale industrial wastewater treatment bioreactors operated at neutral pH. The combination of a membrane bioreactor and a pH-auxostat is a useful research tool to study processes with unknown growth rates at maximum activities.
    Anaerobic wastewater treatment and membrane filtration: a one night stand or a sustainable relationship?
    Jeison, D.A. ; Lier, J.B. van - \ 2008
    Water Science and Technology 57 (2008)4. - ISSN 0273-1223 - p. 527 - 532.
    afvalwaterbehandeling - vervuiling door afzetting - membranen - anaërobe afbraak - filtratie - anaërobe behandeling - deeltjesgrootte - slib - bioreactoren - waste water treatment - fouling - membranes - anaerobic digestion - filtration - anaerobic treatment - particle size - sludges - bioreactors - reactors
    Several anaerobic membrane bioreactors (AnMBR) were operated, under various conditions, applying different reactor configurations. Applicable fluxes were strongly determined by the physical properties of the sludge present in the reactors. Results show that particle size is a key determining factor for the attainable fluxes. Under thermophilic conditions, small sludge particle size was observed, resulting in low critical fluxes reaching 6¿7 L/m2 h for the submerged configuration and acidified substrate. In contrast, under mesophilic conditions critical fluxes of 20 L/m2 h were obtained. The acidification level also showed a strong effect. Under thermophilic conditions, the presence of a significant fraction of non-acidified organic matter induced the growth of suspended acidogenic biomass that seriously affected the applicable fluxes, both in submerged and side-stream configurations. Under all conditions tested cake formation showed to be the limiting factor determining the applicable fluxes. Only low levels of irreversible fouling were observed. Due to technical and economical considerations, most interesting perspectives for the application of AnMBR are expected with the treatment of high-strength particulate wastewaters, and with extreme wastewaters characterised by high temperature, salinity, etc.
    Emulsification with microstructured systems : process principles
    Zwan, E.A. van der - \ 2008
    Wageningen University. Promotor(en): Remko Boom, co-promotor(en): Karin Schroen. - [S.l.] : S.n. - ISBN 9789085049234 - 119
    emulgering - emulgeren - emulsies - membranen - microporiën - filterbedden - druppelgrootte - kunstmatige membranen - emulsification - emulsifying - emulsions - membranes - micropores - filter beds - droplet size - artificial membranes
    The aim of this thesis is to elucidate the underlying processes and mechanisms that determine the droplet size of emulsions produced with microstructured systems, such as premix microstructure homogenization and microchannel emulsification. The ultimate goal is to describe these methods based on detailed knowledge on droplet break-up and droplet formation mechanisms. This includes, amongst others, the influence of viscosity of the (to-be) dispersed and continuous phase, interfacial tension, velocity, and the geometry of the system on droplet break-up and formation. This was done both computationally and experimentally. The insight that was generated was translated into several design rules that can be used for optimization.
    Structure of mixed Beta-lactoglobulin/pectin adsorbed layers at air/water interfaces; a spectroscopy study
    Ganzevles, R.A. ; Fokkink, R.G. ; Vliet, T. van; Cohen Stuart, M.A. ; Jongh, H.H.J. de - \ 2008
    Journal of Colloid and Interface Science 317 (2008)1. - ISSN 0021-9797 - p. 137 - 147.
    air-water-interface - o/w emulsions - neutron reflection - protein adsorption - pectin - casein - films - polysaccharides - complexes - membranes
    Based on earlier reported surface rheological behaviour two factors appeared to be important for the functional behaviour of mixed protein/polysaccharide adsorbed layers at air/water interfaces: (1) protein/polysaccharide mixing ratio and (2) formation history of the layers. In this study complexes of ß-lactoglobulin (positively charged at pH 4.5) and low methoxyl pectin (negatively charged) were formed at two mixing ratios, resulting in negatively charged and nearly neutral complexes. Neutron reflection showed that adsorption of negative complexes leads to more diffuse layers at the air/water interface than adsorption of neutral complexes. Besides (simultaneous) adsorption of protein/polysaccharide complexes, a mixed layer can also be formed by adsorption of (protein/)polysaccharide (complexes) to a pre-formed protein layer (sequential adsorption). Despite similar bulk concentrations, adsorbed layer density profiles of simultaneously and sequentially formed layers were persistently different, as illustrated by neutron reflection analysis. Time resolved fluorescence anisotropy showed that the mobility of protein molecules at an air/water interface is hampered by the presence of pectin. This hampered mobility of protein through a complex layer could account for differences observed in density profiles of simultaneously and sequentially formed layers. These insights substantiated the previously proposed organisations of the different adsorbed layers based on surface rheological data.
    Mechanical properties and porosity of polylactide for biomedical applications
    Sawalha, H.I.M. ; Schroën, C.G.P.H. ; Boom, R.M. - \ 2008
    Journal of Applied Polymer Science 107 (2008)1. - ISSN 0021-8995 - p. 82 - 93.
    guided tissue regeneration - poly(lactic acid) - barrier properties - inorganic fillers - glass composites - in-vitro - films - membranes - poly(l-lactide) - degradation
    In this study, the strength, ductility, and porosity of polylactide films prepared by immersion precipitation and film casting in air were investigated. To induce extra porosity in the films, dodecane was added to the polymer casting solution. The structure, porosity, and mechanical properties of the films were evaluated. The ultimate strength and elastic modulus of neat poly(L-lactide) prepared by film casting were at least twice those of the same film prepared in methanol, whereas the ductility of these films was considerably higher than that for air. The porosity, size of pores, and interconnectivity of pores increased gradually with increasing dodecane concentration. This dodecane-induced porosity (as high as 80%), progressively reduced the ultimate strength and modulus of practically all films but remarkably improved the ductility of films prepared in air, and this can be related to a decrease in the crystallization temperature. For films prepared in water or poly(D,L-lactide) films in general, the ultimate strength, modulus, and ductility of films prepared in water were significantly lower than those of air-cast poly(L-lactide) films. In summary, the results obtained in this research show that it is possible to tailor the properties of films for various biomedical applications through the use of the polymer type, preparation method, and dodecane-induced porosity as tools
    Ostreolysin enhances fruiting initiation in the oyster mushroom (Pleurotus ostreatus)
    Berne, S. ; Pohleven, J. ; Vidic, I. ; Rebolj, K. ; Pohleven, F. ; Turk, T. ; Macek, P. ; Sonnenberg, A.S.M. ; Sepcic, K. - \ 2007
    Mycological Research 111 (2007)12. - ISSN 0953-7562 - p. 1431 - 1436.
    aspergillus-fumigatus - pseudomonas-tolaasii - cytolytic protein - membranes - toxin - pathogen - sequence - binding - cloning - growth
    Fruiting initiation in mushrooms can be triggered by a variety of environmental and biochemical stimuli, including substances of natural or synthetic origin. In this work ostreolysin, a cytolytic protein specifically expressed during the formation of primordia and fruit bodies of Pleurotus ostreatus, was applied to nutrient media inoculated with mycelium of P. ostreatus, and its effects on mycelial growth and fructification of the mushroom studied. The addition of ostreolysin slightly inhibited the growth of mycelium, but strongly induced the formation of primordia, which appeared 10 d earlier than in control plates supplemented with bovine serum albumin or with the dissolving buffer alone. Moreover, ostreolysin stimulated the subsequent development of primordia into fruit bodies. However, direct involvement of this protein in the sporulation of the mushroom is unlikely, as it was also detected in large amounts in the non-sporulating strain of P. ostreatus.
    Salinity-gradient power: Evaluation of pressure-retarded osmosis and reverse electrodialysis
    Post, J.W. ; Veerman, J. ; Hamelers, H.V.M. ; Euverink, G.J.W. ; Metz, S.J. ; Nymeijer, K. ; Buisman, C.J.N. - \ 2007
    Journal of Membrane Science 288 (2007)1-2. - ISSN 0376-7388 - p. 218 - 230.
    electric-power - concentrated brines - osmotic flow - energy - membranes - water - sea - desalination
    A huge potential to obtain clean energy exists from mixing water streams with different salt concentrations. Two membrane-based energy conversion techniques are evaluated: pressure-retarded osmosis and reverse electrodialysis. From the literature, a comparison is not possible since the reported performances are not comparable. A method was developed which allows for a comparison of both techniques at equal conditions, with respect to power density and energy recovery. Based on the results from the model calculations, each technique has its own field of application. Pressure-retarded osmosis seems to be more attractive for power generation using concentrated saline brines because of the higher power density combined with higher energy recovery. Reverse electrodialysis seems to be more attractive for power generation using seawater and river water. These conclusions are valid for present and latent performances of both techniques. According to the model, the potential performances of both techniques are much better than the current performances. In order to achieve these potential performances, the development of pressure-retarded osmosis must focus on membrane characteristics, i.e. increasing the water permeability of the membrane skin and optimization of the porous support. The development of reverse electrodialysis, however, must focus on system characteristics, i.e. optimization of the internal resistance, which is mainly determined by the width of the spacers.
    Opposing effects of cation binding and hydration on the bending rigidity of anionic lipid bilayers
    Claessens, M.M.A.E. ; Leermakers, F.A.M. ; Hoekstra, F.A. ; Cohen Stuart, M.A. - \ 2007
    The Journal of Physical Chemistry Part B: Condensed Matter, Materials, Surfaces, Interfaces & Biophysical 111 (2007)25. - ISSN 1520-6106 - p. 7127 - 7132.
    vesicles - adsorption - membranes - phases - thermodynamics - curvature - liposomes - dilute - salt
    We correlate the molecularly realistic self-consistent field predictions for the mean bending modulus kc of charged lipid vesicles with experimental observations of the size R of corresponding vesicles that are produced by the freeze-thaw method. We elaborate on the Ansatz that the bending modulus is related to the membrane persistence length and that this length scale sets the radius of the vesicles. Alkali cations have a remarkable effect on the mean bending modulus and thus on the equilibrium radius of negatively charged entropically stabilized dioleoylphosphatidylglycerol (DOPG) vesicles. Where cation hydration typically results in thicker and thus stiffer membranes, specific adsorption to the bilayer surface results in a decrease of the surface charge density and the thickness of the membrane-associated electric double layer. As a result of these opposing effects on kc and R, the largest DOPG vesicles are found in the presence of K+, which combines an intermediate hydration enthalpy and PG-binding affinity.
    Bending rigidity of mixed phospholipid bilayers and the equilibrium radius of corresponding vesicles
    Claessens, M.M.A.E. ; Oort, B.F. van; Leermakers, F.A.M. ; Hoekstra, F.A. ; Cohen Stuart, M.A. - \ 2007
    Physical Review. E, Statistical nonlinear, and soft matter physics 76 (2007). - ISSN 1539-3755 - p. 011903/1 - 011903/6.
    curvature elasticity - lipid-bilayers - surfactant - stability - membranes - mixtures - dilute - phases
    In spite of the large mean bending moduli observed for phospholipid bilayers, stable vesicle phases were recently observed for dilute solutions of charged phospholipids. A correspondingly large negative Gaussian bending modulus associated with charged membranes results in an overall curvature energy that is so low that entropic stabilization is possible. The mean bending modulus determines the membrane persistence length and therefore it is reasonable that there is a correlation between the membrane rigidity and the size of the lipid vesicles. Here we show that in mixtures of the anionic phospholipid dioleoylphosphatidylglycerol and the zwitterionic phospholipid dioleoylphosphatidylcholine the radius of vesicles produced by repetitive freeze-thaw cycles is considerably smaller than expected from the rigidities of the corresponding pure lipid bilayers. Self-consistent field calculations indicate that the changes in the equilibrium radius of mixed bilayers can be attributed to the dependences of the mean bending modulus k(c) on lipid mixing and the average surface charge density.
    Anaerobic membrane bioreactors for wastewater treatment: feasibility and potential applications
    Jeison, D.A. - \ 2007
    Wageningen University. Promotor(en): Jules van Lier. - [S.l.] : S.n. - ISBN 9789085046998 - 199
    bioreactoren - anaërobe behandeling - afvalwaterbehandeling - membranen - biologische filtratie - biomassa - vervuiling door afzetting - bioreactors - anaerobic treatment - waste water treatment - membranes - biological filtration - biomass - fouling
    Biomass retention is a necessary feature for the successful application of anaerobic digestion for wastewater treatment. Biofilms and granule formation are the traditional way to achieve such retention, enabling reactor operation at high biomass concentrations, and therefore at high organic loading rates. Membrane filtration represents an alternative way to achieve biomass retention. In membrane bioreactors, complete biomass retention can be achieved, irrespective of cells capacity to form biofilms or granules. Membrane bioreactor systems represent then a promising technology for those conditions where biomass aggregation cannot be ensured, or when an effluent completely free of suspended solids is of interest. In the present thesis the feasibility of anaerobic membrane bioreactors (AnMBR) is described, under a wide range of conditions and reactor configurations
    Prediction of permeation fluxes of small volatile components through starch-based films
    Habeych Narvaez, E.A. ; Goot, A.J. van der; Boom, R.M. - \ 2007
    Carbohydrate Polymers 68 (2007)3. - ISSN 0144-8617 - p. 528 - 536.
    diffusion - model - pervaporation - membranes
    Simple formulas for estimating the Maxwell¿Stefan diffusion of trace volatile compounds through polymeric films in multicomponent mixtures are developed based on free-volume theory and Flory¿Huggins¿Maxwell¿Stefan (FHMS) equation. The model includes the solution-diffusion theory, and predicts the order of magnitude of the permeation fluxes of diacetyl and carvone through starch films. The permeability of volatile components within starch films was dominated by the swelling of the matrix. The methodology required only some physical properties of the components sorption equilibrium.
    Stabilization of Polymersome Vesicles by an Interpenetrating Polymer Network
    Li, F. ; Ketelaar, M.J. ; Marcelis, A.T.M. ; Leermakers, F.A.M. ; Cohen Stuart, M.A. ; Sudhölter, E.J.R. - \ 2007
    Macromolecules 40 (2007)2. - ISSN 0024-9297 - p. 329 - 333.
    dilute aqueous-solution - diblock copolymers - triblock copolymer - block-copolymers - force microscopy - drug-delivery - nile red - micelles - microspheres - membranes
    Vesicles from Pluronic L121 (PEO5-PPO68-PEO5) triblock copolymers were stabilized by an interpenetrating polymer network from pentaerythritol tetraacrylate by UV or thermal initiator induced radical polymerization. Fluorescence labeling, atomic force microscopy, and electron microscopy studies were used to study the morphology of the particles and showed that stable vesicles are formed. The block copolymers are noncovalently trapped in the interpenetrating polyacrylate network. The stabilized vesicles retain their size for more than 1 month at room temperature. Upon cooling, the vesicles reversibly lose block copolymer
    Oestrogen removal from biological pre-treated wastewater within decentralised sanitation and re-use concepts
    Mes, T.Z.D. de; Urmenyi, A.M. ; Poot, A.A. ; Wessling, M. ; Mulder, M.H.V. ; Zeeman, G. - \ 2006
    Water Science and Technology 53 (2006)9. - ISSN 0273-1223 - p. 141 - 150.
    sewage-treatment plants - activated-sludge - stw effluent - chemicals - identification - vitellogenin - substances - membranes - biomarker - behavior
    Two parallel researches were performed; one focused on the fate of oestrogens in the biological treatment systems within decentralised sanitation and re-use concepts (DESAR), the second related to the development of a suitable specific removal method. A new affinity membrane was developed using antibodies as specific binding sites for hormone removal. It was found that, especially in anaerobic treatment, the core technology in DESAR, the removal is insufficient and therefore an additional separation method is required. The affinity membrane with antibodies was found to be a suitable additional method, though in the current system it only removes one selected compound. Future research will focus on making this method more feasible in practise
    Design of membrane systems for fractionation of particle suspensions
    Brans, G.B.P.W. - \ 2006
    Wageningen University. Promotor(en): Remko Boom, co-promotor(en): Karin Schroen; Ruud van der Sman. - Wageningen : s.n. - ISBN 9789085043799 - 60
    deeltjes - fractionering - membranen - computersimulatie - deeltjesgrootteverdeling - particles - fractionation - membranes - computer simulation - particle size distribution
    The aim of this research was to obtain more insight in membrane processes for the fractionation of micro sized particles (0.1 - 10 μm) with small size differences, and with special attention for microsieve technology as an alternative for conventional membranes.
    Membrane emulsification: droplet formation and effects of interfacial tension
    Graaf, S. van der - \ 2006
    Wageningen University. Promotor(en): Remko Boom, co-promotor(en): Karin Schroen; Ruud van der Sman. - Wageningen : s.n. - ISBN 9789085043485 - 159
    emulgering - emulsies - membranen - druppels - druppelstudies - oppervlaktespanning - simulatiemodellen - computersimulatie - kunstmatige membranen - emulsification - emulsions - membranes - droplets - droplet studies - surface tension - simulation models - computer simulation - artificial membranes
    Membrane emulsification is a relatively new technique to produce emulsions. In this method the oil phase is pushed through a membrane, a sieve with very small holes, and forms droplets in the water phase at the other side of the membrane. The most important advantage of this technique is that all the formed droplets have the same size and the emulsion has therefore a better quality. In this research, the influence of surfactants on the droplet formation and detachment process has been studied with the help of experiments and computer simulations.The results showed that both the concentration surfactant and the velocity of the oil phase flowing through the membrane influence the droplet size.
    Bending moduli and spontaneous curvature of the monolayer in a surfactant bilayer
    Kik, R.A. ; Kleijn, J.M. ; Leermakers, F.A.M. - \ 2005
    The Journal of Physical Chemistry Part B: Condensed Matter, Materials, Surfaces, Interfaces & Biophysical 109 (2005)30. - ISSN 1520-6106 - p. 14251 - 14256.
    lipid-bilayers - membranes - thermodynamics - elasticity - micelles - systems - length
    We developed a method to evaluate the mechanical properties of the monolayers in symmetric surfactant bilayers using self-consistent field theory. A specific boundary condition is used to impose the same curvature onto the two opposing monolayers at the surfactant chemical potential equal to that of the corresponding homogeneously curved bilayer. Typically, the spontaneous monolayer curvature J0m ¿ 0 and its value depend on the surfactant architecture. This is of importance for the thermodynamics and topology of lamellar surfactant phases. Furthermore, it may be relevant in processes involving biological membranes, for example, the fusion and budding of vesicles and the incorporation of proteins in lipid bilayers.
    MBR Technology: future research directions
    Brouwer, H. ; Temmink, B.G. ; Remy, M.J.J. ; Geilvoet, S. - \ 2005
    H2O : tijdschrift voor watervoorziening en afvalwaterbehandeling 2005 (2005)spec. III. - ISSN 0166-8439 - p. 19 - 22.
    afvalwaterbehandeling - membranen - filtratie - biologische behandeling - technologie - innovaties - toekomst - waste water treatment - membranes - filtration - biological treatment - technology - innovations - future
    Cutting down the operational costs of MBR technology will be the key driver for research. This article outlines some research areas and specific topics that potentially will contribute to lower costs. Special attention to these topics should be given the coming years. Long term research should focus on sustainable MBR concepts. A few innovative developments will be presented
    Spin label EPR-based characterization of biosystem complexity
    Strancar, J. ; Koklic, T. ; Arsov, Z. ; Filipic, B. ; Stopar, D. ; Hemminga, M.A. - \ 2005
    Journal of Chemical Information and Modeling 45 (2005)2. - ISSN 1549-9596 - p. 394 - 406.
    major coat protein - paramagnetic-resonance-spectra - lipid interactions - membranes - dynamics - simulations - parameters - motion - domain - model
    Following the widely spread EPR spin-label applications for biosystem characterization, a novel approach is proposed for EPR-based characterization of biosystem complexity. Hereto a computational method based on a hybrid evolutionary optimization (HEO) is introduced. The enormous volume of information obtained from multiple HEO runs is reduced with a novel so-called GHOST condensation method for automatic detection of the degree of system complexity through the construction of two-dimensional solution distributions. The GHOST method shows the ability of automatic quantitative characterization of groups of solutions, e.g. the determination of average spectral parameters and group contributions. The application of the GHOST condensation algorithm is demonstrated on four synthetic examples of different complexity and applied to two physiologically relevant examples - the determination of domains in biomembranes (lateral heterogeneity) and the study of the low-resolution structure of membrane proteins
    Particle separation and fractionation by microfiltration
    Kromkamp, J. - \ 2005
    Wageningen University. Promotor(en): Remko Boom, co-promotor(en): Karin Schroen; Ruud van der Sman. - [S.l.] : s.n. - ISBN 9789085042396 - 184
    microfiltratie - membranen - deeltjes - deeltjesgrootte - simulatiemodellen - computersimulatie - microfiltration - membranes - particles - particle size - simulation models - computer simulation - cum laude
    cum laude graduation (with distinction) For the production of present-day dairy products, raw milk is often considered an entity. However, a large quality improvement could be reached if selected constituents were available. In order to achieve this, milk will have to be fractionated prior to use in dairy products. Microfiltration is an important technique for the fractionation of milk; the pore size typically being in the order of micrometers. However, due to insufficient separation caused by blockage of the filter, the potential of microfiltration is still hardly used. This instigated the Ph.D. research project of Janneke Kromkamp which aims at using microfiltration for fractionation to its fullest potential. The interaction between the different microparticles in milk and the surrounding liquid were studied at a fundamental level by means of computer simulation techniques. By coupling this information to observations on the microfiltration of milk, important new insights were obtained which can substantially improve the fractionation process. Paradoxically enough, the liquid flow was better able to fractionate particles than the membrane alone. Because the particles organise in the liquid flow, the large ones moving to the centre of the channel, the smaller ones can be separated easily. Herewith, membrane blockage, which was the biggest challenge in this thesis, is prevented. An additional advantage is that the fractionation process can be completely controlled by easily controllable process parameters. The high-quality dairy products mentioned earlier have now come within reach.
    Molecular basis of photoprotection and control of photosynthetic light-harvesting
    Pascal, A.A. ; Liu, Z. ; Broess, K. ; Oort, B.F. van; Amerongen, H. van; Wang, C. ; Horton, P. ; Robert, B. ; Chang, W. ; Ruban, A.V. - \ 2005
    Nature 436 (2005)7047. - ISSN 0028-0836 - p. 134 - 137.
    chlorophyll-protein complex - time-resolved fluorescence - green plants - excitation-energy - binding - lhcii - mechanism - xanthophylls - zeaxanthin - membranes
    In order to maximize their use of light energy in photosynthesis, plants have molecules that act as light-harvesting antennae, which collect light quanta and deliver them to the reaction centres, where energy conversion into a chemical form takes place. The functioning of the antenna responds to the extreme changes in the intensity of sunlight encountered in nature1, 2, 3. In shade, light is efficiently harvested in photosynthesis. However, in full sunlight, much of the energy absorbed is not needed and there are vitally important switches to specific antenna states, which safely dissipate the excess energy as heat2, 3. This is essential for plant survival4, because it provides protection against the potential photo-damage of the photosynthetic membrane5. But whereas the features that establish high photosynthetic efficiency have been highlighted6, almost nothing is known about the molecular nature of the dissipative states. Recently, the atomic structure of the major plant light-harvesting antenna protein, LHCII, has been determined by X-ray crystallography7. Here we demonstrate that this is the structure of a dissipative state of LHCII. We present a spectroscopic analysis of this crystal form, and identify the specific changes in configuration of its pigment population that give LHCII the intrinsic capability to regulate energy flow. This provides a molecular basis for understanding the control of photosynthetic light-harvesting
    Nanofiltration of multi-component feeds. Interactions between neutral and charged components and their effect on retention
    Bargeman, G. ; Vollenbroek, J.M. ; Straatsma, J. ; Schroën, C.G.P.H. ; Boom, R.M. - \ 2005
    Journal of Membrane Science 247 (2005)1-2. - ISSN 0376-7388 - p. 11 - 20.
    membranes - transport - model - salt - rejection
    Membrane characterization and modeling of membrane processes are essential steps in the development and implementation of new membrane filtration processes. The generalized Maxwell-Stefan equation is frequently used to describe, these processes. However, predictive modeling on the basis of characterization experiments using single solutes is still troublesome in a lot of cases. Consequently, a better understanding of the effect of the interaction between different components on the membrane separation characteristics is required. In this work, four well-known commercially available membranes, Desal 5DK, Desal 5DL Desal G5, NTR-7450. and a newly introduced membrane NF have been characterized. The pore radii of these membranes determined from glucose retention experiments increase in the following sequence: Desal 5DK approximate to NF
    Particle related fractionation and characterisation of municipal wastewater
    Nieuwenhuijzen, A.F. van; Graaf, J.H.J.M. van der; Kampschreur, M.J. ; Mels, A.R. - \ 2004
    Water Science and Technology 50 (2004)12. - ISSN 0273-1223 - p. 125 - 132.
    afvalwaterbehandeling - deeltjesgrootte - besmetters - deeltjesgrootteverdeling - filtratie - membranen - fractionering - waste water treatment - particle size - contaminants - particle size distribution - filtration - membranes - fractionation
    Several studies show that a more detailed characterisation of the particulate matter in municipal wastewater gives a better understanding and prediction of removal efficiencies of physical-chemical treatment techniques and the application of optimal chemical dosages. Such a characterisation should include the distribution of contaminants over various particle sizes. This article describes a method and results of experimental and full-scale investigations, conducted to determine how contaminants in wastewater are distributed over different particle sizes. For this purpose, particle size fractionations of wastewater influents originating from more than thirteen WWTP were carried out. One of these fractionations (WWTP Venray) is shown and interpreted in this article. First, the wastewaters were fractionated into 5 to 6 particle fractions (45, 5.0, 1.0/1.2, 0.45 and 0.1 m) after which the fractions were analyzed for various water quality parameters like organic components, nutrients, salts, solids and turbidity. Based on the results the effects of removal of the different size fractions on design of the biological treatment and energy balance of a wastewater treatment plant can be assessed. The method also indicates whether a certain wastewater is efficiently treatable with physical-chemical pre-treatment methods. It is concluded wastewater fractionation on particle size is very useful, but that wastewater characteristics and particle size distributions should not be generalised, but have to be interpreted as indications for a certain average wastewater composition. To give more insight into the distribution of contaminants over particle size and the particle removal potential, a specific wastewater fractionation has to be carried out per WWTP
    Membrane-aerated biofilm reactor for the removal of 1,2-dichloroethane by Pseudomonas sp strain DCA1
    Hage, J.C. ; Houten, R.T. ; Tramper, J. ; Hartmans, S. - \ 2004
    Applied Microbiology and Biotechnology 64 (2004)5. - ISSN 0175-7598 - p. 718 - 725.
    biologische behandeling - membranen - ethyleendichloride - biofilms - biodegradatie - verwijdering - afvalwaterbehandeling - pseudomonas - insecticiden - beluchting - biological treatment - membranes - ethylene dichloride - biofilms - biodegradation - removal - waste water treatment - pseudomonas - insecticides - aeration - waste-gas treatment - aliphatic-compounds - aerobic biofilms - degradation - groundwater - bioreactor - kinetics - trichloroethylene - model - water
    A membrane-aerated biofilm reactor (MBR) with a biofilm of Pseudomonas sp. strain DCA1 was studied for the removal of 1,2-dichloroethane (DCA) from water. A hydrophobic membrane was used to create a barrier between the liquid and the gas phase. Inoculation of the MBR with cells of strain DCA1 grown in a continuous culture resulted in the formation of a stable and active DCA-degrading biofilm on the membrane. The maximum removal rate of the MBR was reached at a DCA concentration of approximately 80 µM. Simulation of the DCA fluxes into the biofilm showed that the MBR performance at lower concentrations was limited by the DCA diffusion rate rather than by kinetic constraints of strain DCA1. Aerobic biodegradation of DCA present in anoxic water could be achieved by supplying oxygen solely from the gas phase to the biofilm grown on the liquid side of the membrane. As a result, direct aeration of the water, which leads to undesired coagulation of iron oxides, could be avoided
    A membrane-aerated biofilm reactor (MBR) with a biofilm of Pseudomonas sp. strain DCA1 was studied for the removal of 1,2-dichloroethane (DCA) from water. A hydrophobic membrane was used to create a barrier between the liquid and the gas phase. Inoculation of the MBR with cells of strain DCA1 grown in a continuous culture resulted in the formation of a stable and active DCA-degrading biofilm on the membrane. The maximum removal rate of the MBR was reached at a DCA concentration of approximately 80 muM. Simulation of the DCA fluxes into the biofilm showed that the MBR performance at lower concentrations was limited by the DCA diffusion rate rather than by kinetic constraints of strain DCA1. Aerobic biodegradation of DCA present in anoxic water could be achieved by supplying oxygen solely from the gas phase to the biofilm grown on the liquid side of the membrane. As a result, direct aeration of the water, which leads to undesired coagulation of iron oxides, could be avoided.
    Vier grove zeven vangen meer aaltjes dan één fijne
    Amsing, J.J. ; Zijlstra, C. - \ 2004
    Vakblad voor de Bloemisterij 59 (2004)3. - ISSN 0042-2223 - p. 34 - 35.
    nematoda - snijbloemen - rozen - diagnostische technieken - gewasbescherming - filtratie - membranen - glastuinbouw - nematoda - cut flowers - roses - diagnostic techniques - plant protection - filtration - membranes - greenhouse horticulture
    Opsporen van heel lage aaltjesbesmetting in water bij de teelt van kasrozen: presentatie van door PPO en PRI ontwikkelde detectiemethode
    Effect of protein adsorption and ionic strength on the equilibrium partition coefficient of ionizable macromolecules in charged nanopores
    Biesheuvel, P.M. ; Stroeve, P. ; Barneveld, P.A. - \ 2004
    The Journal of Physical Chemistry Part B: Condensed Matter, Materials, Surfaces, Interfaces & Biophysical 108 (2004)45. - ISSN 1520-6106 - p. 17660 - 17665.
    electrostatic interactions - spherical colloids - cylindrical pores - transport - membranes - ultrafiltration - stability - size
    Recent experimental data on the diffusive transport of globular protein molecules through nanopores (D ~ 20 nm), covered with chemisorbed self-assembled monolayers (SAMs) of carboxylic acid functional groups (Ku, J.-R.; Stroeve, P. Langmuir 2004, 20, 2030), show a strong increase in flux around the isoelectric point of the protein molecule at 10 mM ionic strength (on-off behavior), but not at 100 mM. To understand these observations we calculated the equilibrium partition coefficient (distribution coefficient) of a spherical protein molecule in a nanopore consisting of ionizable carboxylic acid groups as a function of ionic strength, pH, charge and size of the protein and the pore wall. When transport is diffusion-controlled, the flux of macromolecules through porous media is directly proportional to the equilibrium partition coefficient. To calculate the charge on the pore wall, the ionizable character of the carboxylic acid groups is incorporated as well as protein adsorption. At values sufficiently above the isoelectric point of the protein, pi, protein adsorption is zero. However, with decreasing pH, adsorption strongly increases. Therefore, the pore is negatively charged at sufficiently high pH (just as the protein molecule) and positively charged at sufficiently low pH (just as the protein molecule). Consequently, the equilibrium partition coefficient of additional, thus nonadsorbing, protein molecules is strongly pH-dependent with a maximum at pH around pl. The predicted influence of ionic strength on the peak width of the equilibrium partition coefficient is in qualitative agreement with the experiments, suggesting that electrostatic interactions and especially protein adsorption are important determinants of protein transport through charged nanopores.
    Mean-field stationary diffusion: polymers in steady-state systems
    Scheinhardt-Engels, S.M. - \ 2004
    Wageningen University. Promotor(en): Gerard Fleer, co-promotor(en): Frans Leermakers. - [s.I.] : S.n. - ISBN 9789085040613 - 165
    polymeren - moleculaire structuur - membranen - diffusiecoëfficiënt - diffusieweerstand - polymers - molecular conformation - membranes - diffusivity - diffusion resistance
    Application of Pseudomonas sp. strain DCA1 for the removal of chlorinated hydrocarbons
    Hage, J.C. - \ 2004
    Wageningen University. Promotor(en): Hans Tramper, co-promotor(en): S. Hartmans. - [S.l.] : S.n. - ISBN 9789085040798 - 126
    oplosmiddelverwijdering - gechloreerde koolwaterstoffen - biofilms - bioreactoren - microbiële afbraak - pseudomonas - membranen - solvent removal - chlorinated hydrocarbons - biofilms - bioreactors - microbial degradation - pseudomonas - membranes
    The large-scale application of chlorinated aliphatic hydrocarbons (CAHs) has resulted in many cases of groundwater contamination. Contaminated groundwater can be remediated by pump-and-treat: the groundwater is pumped to the surface and treated. The groundwater can be treated in bioreactors, in which the contaminants are biodegraded. Since extracted groundwater is often anaerobic, it has to be oxygenated in order to allow aerobic biodegradation of the contaminants. However, direct oxygenation of (anaerobic) groundwater may result in two undesired effects: stripping of volatile contaminants and coagulation of iron oxides. The use of a membrane-aerated biofilm reactor (MABR) can solve these problems. At one side of the membrane a gas phase is present for the supply of oxygen. A biofilm is located at the other side of the membrane, where the contaminant is present in the liquid phase. The contaminant diffuses into the biofilm, where biodegradation takes place. The combination of a membrane with a biofilm allows oxygenation and biodegradation without stripping the contaminant and coagulation of iron oxides.

    The main contaminant studied in this thesis is 1,2 dichloroethane (DCA), a synthetic chemical that is mainly used as a feedstock for the production of vinyl chloride. Known bacterial strains that are able to aerobically degrade DCA, Xanthobacter autotrophicus GJ10 and Ancylobacter autotrophicus AD25, do not have the desired characteristics for treatment of DCA-contaminated groundwater. Both strains require additional organic nutrients, such as vitamins, for optimal growth. Moreover, strain GJ10 has a very low affinity for DCA ( K m value of 570 µM).

    Two major objectives were proposed at the start of this research. The first objective was to isolate DCA-degrading microorganisms with a high affinity for DCA and without requirements for additional organic nutrients for optimal growth. The second objective was to apply the isolated microorganisms in a MABR that allows aerobic biodegradation of DCA, without direct oxygenation of the contaminated groundwater.

    In Chapter 2, the isolation and characterization of a bacterial strain, designated Pseudomonas sp. strain DCA1, is described. Strain DCA1 utilizes DCA as the sole carbon and energy source and does not require additional organic nutrients for optimal growth. The maximum specific growth rate of strain DCA1 on DCA is 0.14 h -1 . The affinity of strain DCA1 for DCA is very high, with a K m value below the detection limit of 0.5 µM. Instead of a hydrolytic dehalogenation, as was shown in other DCA utilizers, the first step in DCA degradation in strain DCA1 is an oxidation reaction. Oxygen and NAD(P)H are required for this initial step. Propene was converted to 1,2-epoxypropane by DCA-grown cells, and competitively inhibited DCA degradation. We concluded that a monooxygenase is responsible for the first step in DCA degradation in strain DCA1. Oxidation of DCA probably results in the formation of the unstable intermediate 1,2-dichloroethanol, which spontaneously releases chloride, yielding chloroacetaldehyde. The DCA degradation pathway in strain DCA1 proceeds from chloroacetaldehyde via chloroacetic acid and glycolic acid, which is similar to degradation routes observed in other DCA-utilizing bacteria.

    Strain DCA1 was applied in a MABR for the removal of DCA from (ground)water (Chapter 3). A hydrophobic membrane was used to create a barrier between the liquid and the gas phase. Inoculation of the MBR with cells of strain DCA1 grown in a continuous culture resulted in the formation of a stable and active DCA-degrading biofilm on the membrane. The maximum DCA removal rate in the MABR was 410 g m -3 h -1 . This maximum removal rate was reached at a DCA concentration of approximately 80 µM. Simulation of the DCA fluxes into the biofilm showed that the MABR performance at lower concentrations was limited by the DCA diffusion rate rather than by kinetic constraints of strain DCA1. To determine the effect of bacterial kinetics on reactor performance, we also simulated the performance of strain GJ10 in our MABR. At 80 µM the simulated DCA flux into a strain GJ10 biofilm is more than 8 times lower. At a concentration of 4 µM (the intervention value for DCA in The Netherlands), the simulated flux into a biofilm of strain GJ10 is less than 5% of the flux generated into a biofilm of strain DCA1. Aerobic biodegradation of DCA present in anoxic water could be achieved by supplying oxygen solely from the gas phase to the biofilm grown on the liquid side of the membrane.

    Since the degradation of DCA by strain DCA1 is mediated by a monooxygenase, and these enzymes generally have a broad substrate spectrum, strain DCA1 was used to co-metabolically oxidize chlorinated methanes, ethanes, propanes and ethenes (Chapter 4).Chloroaceticacid, an intermediate in the DCA degradation pathway of strain DCA1, was used as a co-substrate since it was readily oxidized by DCA-grown cells of strain DCA1 and did not compete for the monooxygenase. All of the tested compounds except tetrachloroethene were oxidized by cells expressing DCA monooxygenase. Strain DCA1 could not utilize any of these compounds as a growth substrate. Co-metabolic oxidation during growth on DCA was tested with 1,2-dichloropropane, since this compound shows structure analogy to DCA but is recalcitrant to aerobic biodegradation. Although growth on this mixture occurred, 1,2-dichloropropane strongly inhibited growth of strain DCA1. This inhibition was not caused by competition for the monooxygenase. It was shown that the oxidation of 1,2-dichloropropane resulted in the accumulation of 2,3-dichloro-1-propanol and 2-chloroethanol.

    An alternative to pump-and-treat is in situ bioremediation. This technology is based on microorganisms biodegrading the contaminants in the subsurface. Besides addition of electron donors, electron acceptors and/or nutrients to stimulate the biodegradation ('biostimulation'), also non-indigenous microorganisms can be injected into the subsurface, a process called 'bioaugmentation' (Chapter 5). Bioaugmentation can be applied in case the indigenous microorganisms are:

    - degrading the contaminant at rates that are too low;

    - inhibited by the presence of multiple contaminants;

    - killed as a result of drastic (abiotic) remediation techniques;

    - not capable to carry out the desired reactions.

    The latter case seems to be the most promising field for application of bioaugmentation. A good example is the incomplete reduction of tetrachloroethene, which often stalls at cis- 1,2-dichloroethene. Bioaugmentation with members of the Dehalococcoides group has proven its success, resulting in complete reduction of tetrachloroethene to the harmless end product ethene. To efficiently bioaugmentate a contaminated site, the introduced microorganisms have to be distributed in the subsurface and come into close contact with the contaminant(s). Transport of cells in the subsurface is often limited because injected cells are filtered by soil particles, but can be enhanced by using solutions of low ionic strength, surfactants and bacteria with limited adhesive properties. The survival of injected bacteria depends on factors such as competition for electron donors and acceptors, contaminant toxicity and the availability of inorganic nutrients. The use of genetically engineered microorganisms (GMOs) for bioaugmentation has not made much progress over the past decades due to regulatory constraints and public adversity. To justify the cost of bioaugmentation it is important to accurately assess the effect of bioaugmentation on the biodegradation. Molecular techniques have evolved rapidly, allowing the determination of both numbers and types of bacteria present. Future research on bioaugmentation should focus on large-scale field studies and more attention has to be paid to proper control plots and assessment of bioaugmentation efficacy.
    Influence of hydrophobic Teflon particles on the structure of amyloid beta-peptide
    Giacomelli, C.E. ; Norde, W. - \ 2003
    Biomacromolecules 4 (2003)6. - ISSN 1525-7797 - p. 1719 - 1726.
    circular-dichroism - sheet formation - homomolecular exchange - alzheimers-disease - aggregation - proteins - transitions - mechanism - membranes - water
    The amyloid beta-protein (Abeta) constitutes the major peptide component of the amyloid plaque deposits of Alzheimer's disease in humans. The Abeta changes from a nonpathogenic to a pathogenic conformation resulting in self-aggregation and deposition of the peptide. It has been established that denaturing factors (such as the interaction with membranes) are involved in the structural transition. This work is aimed at determining the effect of hydrophobic Teflon on the conformation of the Abeta (1-40). Prior to adsorption, the secondary structure and self-aggregation state of the Abeta in solution were established as a function of pH. Three different species coexist: unordered monomers/dimers, small oligomers in mainly a regular beta-sheet structure, and bigger aggregates having a twisted beta-sheet conformation. Transferring the Abeta from the solution to the Teflon surface strongly promotes alpha-helix formation. Furthermore, increasing the degree of coverage of the Teflon by the Alphabeta protein leads to a conformational change toward a more enriched beta-sheet structure.
    Sulfate reducing processes at extreme salinity and temperature. extending its application window
    Vallero, M.V.G. - \ 2003
    Wageningen University. Promotor(en): Gatze Lettinga, co-promotor(en): Piet Lens. - [S.l.] : S.n. - ISBN 9789058089090 - 214
    sulfaat reducerende bacteriën - zoutgehalte - anaërobe behandeling - bioreactoren - membranen - sulfate reducing bacteria - salinity - anaerobic treatment - bioreactors - membranes
    The characteristics of various sulfate-rich wastewaters, such as temperature, pH and salinity, are determined by the (industrial) process from which they originate, and can be far from the physiological optima of the sulfur cycle microorganisms. The main goal of the research described in this thesis was to investigate and develop high rate sulfate reducing wastewater treatment processes for the treatment of inorganic sulfate-rich wastewaters under extreme conditions, i.e. high temperature and high salinity. In this thesis, several simple organic bulk chemicals were tested as electron donor, viz. lower alcohols (methanol and ethanol) and volatile fatty acids (formate, acetate and propionate).

    With respect to the start-up of anaerobic sludge bed (UASB) reactors at high salinity or high temperature, the results obtained in this investigation indicate that the appearance of a targeted metabolic property (sulfate reduction at high salinity or at high temperature) is independent of the strategy for biomass acclimation (direct exposure vs. stepwise exposure).The stepwise adaptation of thermophilicsulfidogenic methanol degrading biomass to a highosmolarity environment, both at 55C or at 70C, likely does not occur in UASB reactors, as probably no methanol halotolerant thermophilic sulfate reducing bacteria (SRB) were present in the thermophilicinoculumsludge used in the investigations described in this thesis. Exposing the sludge directly to a very high salinity (50 g NaCl.L -1 ) stimulated the growth of amesophilic(30C) propionate- and ethanol-utilizinghalotolerantSRB population, which supported high rate sulfate reduction (up to 3.6 g SO 42- .L -1 .day -1 ) in a UASB reactor. The start-up ofthermophilic(55 to 65C) and extremethermophilicC or higher) anaerobic bioreactors inoculated withmesophilicsludgesat the targeted temperature proceeded fast and stable, as it provoked the rapid selection of (extreme)thermophiles. Therefore, the key for the successful treatment of high salinity or hot wastewaters is to invest enough time for the growth of the targeted microorganism in the biomass.

    The results of this investigation show that the competition between SRB, methane producingarchaeaandacetogenicbacteria for substrate is highly dependent of the type of substrate and operational conditions imposed to the bioreactor. This thesis describes a situation where the production of acetate and methane was completely suppressed in methanol-fed sulfate reducing UASB reactors operated at 70C. As a result, for the first time a fully sulfate reducing granular sludge has been cultivated in a methanol-fedthermophilicsulfate reducing reactor (with sulfate reduction rates as high as 14.4 g SO 42- .L -1 .day -1 ), provided that an operational temperature of 70C is kept. The production of methane can be easily suppressed inthermophilicmethanol fed reactors, either by running the reactor at temperatures equal or higher than 65C or by exposing 55C operated reactors to a short (2 days) temperature (65 - 70C) shock.Methanogenesiscan also be easily suppressed inmesophilicpropionate- and ethanol-fed reactors, provided high salinity conditions prevail (e.g. above 50 -1 ). It seems, however, that the production of acetate, with the exception of methanol-fed reactors operated at 70C, is unavoidable both inthermophilicandmesophilicreactors.

    This thesis also describes the use of specialized microorganisms, the halophilicDesulfobacterhalotolerans , in bioreactors for the treatment of saline sulfate-rich wastewaters. Very high specific sulfate reduction rates (up to 6.6 g SO 42- .gVSS -1 .day -1 ) can be obtained in completely mixed tank reactors where the biomass grows in suspension and can be efficiently retained by membranes which are submerged in the reactor system. This investigation showed that anaerobic membrane bioreactors can be operated over extended periods of time at a fixed flux, if this flux is substantially below the nominal critical flux determined experimentally (18-21 L.m -2 .h -1 ). Chemical cleaning of the membranes will be required only at about 106 days, as long a low constant flux is imposed (4.7 L.m -2 .h .1 ) and intermittentbackflush(e.g. 1 minute each 10 minutes) is adopted as operational strategy.
    Structural changes in membranes of developing wheat embryos during the acquisition of desiccation tolerance
    Golovina, E.A. ; Hoekstra, F.A. - \ 2003
    In: The Biology of Seeds: recent research advances / Nicolás, G., Bradford, K.J., Come, D., Pritchard, H.W., Wallingford : CABI Publishing - ISBN 9780851996530 - p. 337 - 344.
    triticum aestivum - plantenembryo's - membranen - verdroging - tolerantie - triticum aestivum - plant embryos - membranes - desiccation - tolerance
    Fluorescence correlation spectroscopy of GFP fusion proteins in living plant cells
    Hink, M.A. ; Borst, J.W. ; Visser, A.J.W.G. - \ 2003
    Methods in Enzymology 361 (2003). - ISSN 0076-6879 - p. 93 - 112.
    cross-correlation spectroscopy - correlation microscopy - subcellular-localization - single molecules - nod factors - membranes - binding - fluctuations - diffusion - kinetics
    This chapter presents an overview of the fluorescence correlation spectroscopy (FCS) of green fluorescent protein (GFP) fusion proteins in living plant cells. FCS is mainly applied to well-defined in vitro systems. However, the possibility of monitoring molecular dynamics under equilibrium conditions at a single-molecule level makes FCS an attractive technique for intracellular studies. The fluorescence photons pass through a pinhole and are detected by a highly sensitive detector. The signal-to-noise ratio achieved by this method is very high, as signal interference from scattered laser light, background fluorescence, and Raman emission can be largely eliminated. The chapter also mentions the applications of fluorescence cross-correlation spectroscopy (FCCS), including enzyme kinetics, nucleotide hybridization, conformational dynamics in DNA, and protein-DNA interactions. From these studies it is clear that FCCS is an attractive technique to observe very specific molecular interactions. At present, it is a challenge to apply this technique to cellular systems to monitor molecular interactions.
    Self-consistent field modeling of hydrated unsaturated lipid bilayers in the liquid-crystal phase and comparison to molecular dynamics simulations
    Leermakers, F.A.M. ; Rabinovich, A.L. ; Balabaev, N.K. - \ 2003
    Physical Review. E, Statistical nonlinear, and soft matter physics 67 (2003). - ISSN 1539-3755 - p. 011910/1 - 011910/17.
    statistical thermodynamics - association colloids - neutron-diffraction - membranes - transition - vesicles - micelles - systems
    A molecular-level self-consistent-field (SCF) theory is applied to model the lipid bilayer structures composed of 1-stearoyl-2-oleoyl-sn-glycero-3-phosphatidylcholine (18:0/18:1omega9cis PC) and 1-stearoyl-2-docosahexaenoyl-sn-glycero-3-phosphatidylcholine (18:0/22:6omega3cis PC). As compared to earlier attempts to model (saturated) PC membranes several additional features are implemented: (i) A water model is used which correctly leads to low water concentration in the bilayers. (ii) Free volume is allowed for, which is important to obtain bilayers in the fluid state. (iii) A polarization term is included in the segment potentials; this new feature corrects for a minor thermodynamic inconsistency present in (all) earlier results for charged bilayers. (iv) The CH3 groups in the lipid molecules are assumed to have twice the volume of a CH2 group; this leads to stable noninterdigitated bilayers. (v) A cis double bond is simulated by forcing gauche conformations along the sn-2 acyl chain. Results of an all-atom molecular dynamics (MD) simulation, using the collision dynamics method, on the same system are presented. Both SCF and MD prove, in accordance with experimental facts, that acyl unsaturation effectively reduces the length of the chain which counteracts interdigitation. It is also found that the phosphatidylcholine head group is lying almost flat on the membrane surface and the water penetrates into the bilayer upto the glycerol backbone units. From the SCF results it further followed that the free volume is not exactly evenly distributed over the bilayer. There is a small increase in free volume in the center of the bilayer as well as in the glycerol backbone region.
    Emulsies uit membranen
    Boom, R.M. ; Gijsbertsen-Abrahamse, A.J. ; Schroën, C.G.P.H. - \ 2003
    Voedingsmiddelentechnologie 36 (2003)14/15. - ISSN 0042-7934 - p. 14 - 16.
    emulgeren - emulsies - membranen - energie - besparingen - conferenties - voedselindustrie - voedseltechnologie - emulgering - emulsifying - emulsions - membranes - energy - savings - conferences - food industry - food technology - emulsification
    Membraanemulgeren is een veelbelovende jonge techniek waarbij met weinig energie een betere productkwaliteit wordt verkregen. Op 4 juni werd door onderzoeksschool VLAG in Wageningen een themadag georganiseerd over het betreffende onderwerp. De aanleiding to deze dag was de promotie van ir. A. Gijsbertsen - Abrahamse. Zij promoveerde als eerste in Nederland op deze nieuwe techniek
    Investigation of the functional lifetime of TRISOPLASTr in relation to chemical compositions of pore water solutions in barriers
    Boels, D. ; Beest, H. te; Zweers, H. ; Groeneveld, P. - \ 2003
    Wageningen : Alterra (Alterra-rapport 528) - 49
    barrières - chemische samenstelling - permeabiliteit - bodemwaterbeweging - poriën - kationenwisseling - stortterreinen - bodembescherming - membraanpermeabiliteit - membranen - barriers - chemical composition - permeability - soil water movement - pores - cation exchange - landfills - soil conservation - membrane permeability - membranes
    Trisoplastr is a mixture of sand, bentonite and a polymer, used amongst others as landfill cover as well as barriers. Its permeability is generally lower than 1-2 x 10-11 m/s. Trisoplast keeps its functionality even in contact with different kinds of liquids, is not susceptible to cyclic drying and rewetting, and the permeability hardly depends on its dry bulk density. Tests with 10¿iaxial strain show only a slight increase in permeability. The functional lifetime of Trisoplast is governed by exchange of adsorbed sodium ions against dissolved calcium ions. This process depends on the composition of the pore water solution in the soil layers directly in contact with Trisoplast and the displacement rate of dissolved calcium ions either by convectiveor diffusive transport phenomena. The functional lifetime of Trisoplast even under relatively extreme conditions is at least 100 years and scores clearly better than the reference sand-bentonite barrier.
    Membrane emulsification: process principles
    Gijsbertsen-Abrahamse, A.J. - \ 2003
    Wageningen University. Promotor(en): Remko Boom, co-promotor(en): A. van der Padt. - [S.I.] : S.n. - ISBN 9789058088451 - 104
    emulsies - emulgeren - membranen - druppelstudies - computationele vloeistofdynamica - emulsions - emulsifying - membranes - droplet studies - computational fluid dynamics
    With membrane emulsification in principle monodisperse emulsions can be produced, requiring a relatively low energy density which implies that the shear stress exerted on the ingredients is low. In membrane emulsification the to-be-dispersed phase is pressed through the membrane pores; under certain conditions droplets are formed at the membrane surface. In cross-flow membrane emulsification the droplets are detached by the continuous phase flowing across the membrane surface. A limiting factor for emulsion production on a commercial scale will be a low disperse phase flux. Better knowledge of how membrane parameters affect the disperse phase flux would enable the targeted development of membranes, optimal for the process of cross-flow membrane emulsification for a given application. Therefore, the objective of this research is to gain a fundamental understanding of the mechanism of droplet formation at the membrane surface and of the flow of the disperse phase through the membrane as a function of the membrane characteristics.
    Droplet formation was studied at a microscopic level with computational fluid dynamics (CFD) simulations and by microscopic experiments of droplet formation at a very thin microsieve with uniform pores. Since these membranes are extremely well defined, they are a good model system for detailed study. Results from both simulations and experiments indicate that to prevent coalescence and steric hindrance of droplets, the membrane porosity should be very low. Steric hindrance resulted in polydisperse emulsions and led to coupling of droplet detachment from neighboring pores. Furthermore, although the pores all had the same diameter, the number of pores at which droplets were formed only increased gradually with increasing transmembrane pressure. This effect was further studied with a scaled-up analogon and could be modeled by taking the resistance of the pores and the resistance of a membrane substructure into account. This model is compared with a model for flow through an isotropic membrane with interconnected uniform pores and extended to describe flow through a membrane with a pore size distribution. This model is used to show that in most cases the estimation of a membrane pore size distribution by using the liquid displacement method is not correct. Just as in membrane emulsification, pores become active at higher transmembrane pressures than expected. Finally, the effects of several membrane parameters on membrane emulsification performance are summarized. As an example, the membrane area required for a typical industrial application is estimated using the models mentioned above, for different types of membranes.
    Mestverwerking varkenshouderij Mobiele mestontwatering Mestec te Papendrecht
    Verdoes, N. ; Starmans, D.A.J. - \ 2002
    Lelystad : Praktijkonderzoek Veehouderij (Praktijkboek / Praktijkonderzoek Veehouderij 11) - 44
    varkensmest - mest - varkenshouderij - dierhouderij - membranen - ontwateren - mestverwerking - pig manure - manures - pig farming - animal husbandry - membranes - dewatering - manure treatment
    Er is onderzoek uitgevoerd aan het Mestec mestontwateringsproces. Het proces bestond uit een voorfiltratie via twee zeven, een vetflotatie, een ultrafiltratie- en omgekeerde osmoseproces. Getracht is via een meetprogramma inzicht te krijgen in de capaciteit van het proces, de samenstelling van de eindproducten, de emissies die bij het proces optreden, de operationele kosten en het perspectief van de techniek. Het onderzoek heeft plaatsgevonden van januari 2000 tot maart 2002.
    Mestverwerking varkenshouderij 'Mest op maat' - Mestac te Nuenen
    Verdoes, N. ; Starmans, D.A.J. - \ 2002
    Lelystad : Praktijkonderzoek Veehouderij (Praktijkboek / Praktijkonderzoek Veehouderij 10) - 32
    mest - varkensmest - varkenshouderij - dierhouderij - membranen - ontwateren - mestverwerking - manures - pig manure - pig farming - animal husbandry - membranes - dewatering - manure treatment
    Er is onderzoek uitgevoerd naar de toepassing van een 'Mest-op-maat' concept, waarbij op basis van ruwe drijfmestsoorten, door een gecontroleerd procédé mestproducten op maat voor de afnemer kunnen worden geproduceerd. Aan de ruwe drijfmestsoorten, worden stikstof (N), fosfaat (P) en kalium (K) houdende toeslagstoffen bijgevoegd om tot de gewenste receptuur te komen.
    Aluminium speciation in natural waters: measurement using Donnan membrane technique and modeling using NICA-Donnan
    Weng, L.P. ; Temminghoff, E.J.M. ; Riemsdijk, W.H. van - \ 2002
    Water Research 36 (2002)17. - ISSN 0043-1354 - p. 4215 - 4226.
    metaalionen - aluminium - modellen - bodemoplossing - membranen - chemische speciatie - adsorptie - grondanalyse - bodemwater - metal ions - aluminium - models - soil solution - membranes - chemical speciation - adsorption - soil analysis - soil water - dissolved organic-matter - contaminated sandy soil - metal-ion binding - humic substances - ph - complexation - copper - solubility - protons - field
    The study of Al speciation is of interest for the assessment of soil and water quality. For the measurement of "free" aluminum (Al3+), a recently developed Donnan membrane technique was tested by measuring Al3+ in aluminum-fluoride solutions and gibbsite suspensions. It shows that the Donnan membrane technique can measure free Al3+ reliably up to 10¿9 M and the equilibration takes 3¿4 days. Next, Al binding to humic acid (HA) purified from a forest soil was measured using either the Donnan membrane technique or gibbsite suspension. Results were compared with those predicted with the non-ideal consistent competitive adsorption (NICA)-Donnan model. The predictions using the generic parameters without fitting were in reasonable agreement with the measured data. Finally, the Donnan membrane technique was used to determine Al binding to dissolved organic matter (DOM) in the solutions of 24 soil samples at pH interval of 3¿7. Measurements agree well with the predictions using the NICA-Donnan model assuming 30% of DOM is HA and 30% is fulvic acid. With this model, the effects of pH and DOM changes on the concentration of Al in 81 soil solutions were predicted reasonably without adjustment of model parameters. The comparison between the results of analysis and the modeling provides a mutual validation for the two methods
    Enantiomer separation using membrane systems
    Ent, E. van der - \ 2002
    Wageningen University. Promotor(en): K. van 't Riet; J.T.F. Keurentjes; M.A. Cohen Stuart. - S.l. : S.n. - ISBN 9789058086006 - 115
    enantiomeren - scheidingsapparaten - membraanpermeabiliteit - elektrodialyse - membranen - enantiomers - separators - membrane permeability - electrodialysis - membranes

    Many compounds applied in the agrochemical, food and pharmaceutical industry contain one or more chiral centers. The enantiomers of these compounds often have different effects on their targets. To prevent unwanted side effects or environmental burden, these compounds should rather be applied in their optically pure form. In this thesis two processes for large-scale enantiomer separations have been studied based on membrane technology: direct separation using an "intrinsic" enantioselective membrane and indirect separation in which a non-selective membrane assists an enantioselective process.

    For intrinsic enantioselective membranes the design criteria have been evaluated, using literature data, model calculations and experimental data. This has resulted in a categorization of these membranes into two different classes: diffusion selective membranes and sorption selective membranes.

    Besides intrinsic enantioselective membranes, a new stacked membrane system is developed using chiral selectors that are retained by size-selective membranes. Applying an electrical potential, selective transport of the free enantiomer will occur, thus providing separation. This separation concept is evaluated for different process conditions, showing a distinct influence of the pH. Isothermal titration calorimetry is used to compare this pH dependency of the operational selectivity and the intrinsic selector selectivity, showing no influence of the process.

    In the last part of this thesis a model is developed for the continuous multi-stage electrodialysis system. This model is evaluated using a 20-compartment counter-current electrodialysis stack. Model calculations have shown that using an electrodialysis stack of 250 membrane compartments allows for complete separation (99%+) for our low selective (α=1.12) model system. In conclusion, the proposed multi-stage electrodialysis separation principle, which has the advantage of making use of chiral selectors developed for existing analytical separation methods, is suitable for low selectivity (1.1-2) separations. Therefore, it provides a viable addition for the current range of large-scale enantiomer separation processes

    Origin of the membrane compartment for cowpea mosaic virus RNA replication
    Carette, J.E. - \ 2002
    Wageningen University. Promotor(en): A. van Kammen; J. Wellink. - S.l. : S.n. - ISBN 9789058085573 - 120
    koebonenmozaïekvirus - dna-replicatie - membranen - vigna unguiculata - vignabonen - blaasjes - virusreplicatie - plantenziekten - cowpea mosaic virus - dna replication - membranes - vigna unguiculata - cowpeas - vesicles - viral replication - plant diseases

    Replication of many positive-stranded RNA viruses takes place in association with intracellular membranes. Often these membranes are induced upon infection by vesiculation or rearrangement of membranes from different organelles including the early and late endomembrane system. Upon infection of cowpea cells with cowpea mosaic virus (CPMV) typical cytopathological structures are formed, which consist of an amorphous matrix of electron-dense material traversed by rays of small membranous vesicles. This thesis describes the studies that were undertaken to define the cellular components involved in the establishment of the site of viral RNA replication consisting of vesiculated membranes and electron-dense material. Furthermore, the role of individual viral proteins as well as host proteins in this process was investigated.

    Electrodialysis system for large-scale enantiomer separation
    Ent, E.M. van der; Thielen, T.P.H. ; Cohen Stuart, M.A. ; Padt, A. van der; Keurentjes, J.T.F. - \ 2001
    Industrial & Engineering Chemistry Research 40 (2001). - ISSN 0888-5885 - p. 6021 - 6027.
    beta-cyclodextrin - chiral recognition - racemic mixtures - amino-acids - electrophoresis - thermodynamics - membranes - ultrafiltration - complexation - resolution
    In contrast to analytical methods, the range of technologies currently applied for large-scale enantiomer separations is not very extensive. Therefore, a new system has been developed for large-scale enantiomer separations that can be regarded as the scale-up of a capillary electrophoresis system. In this stacked membrane system, chiral selectors that are retained by size-selective membranes are used. Upon application of an electrical potential, selective transport of the free enantiomer will occur, thus providing separation. In principle, this system can handle the same extensive range of enantiomers that can be separated in capillary electrophoresis systems on an analytical scale. In a system containing four separation compartments, alpha -cyclodextrin has been used as a chiral selector to separate D,L-Trp. Based on a transport model, a factorial design is used to investigate the effects of various process parameters. The results show that the addition of methanol is of minor influence, whereas the pH has a major effect, both on the operational selectivity and on the transport number. Experiments with AgNO3 as the background electrolyte showed that the operational selectivity has a plateau value of 1.08 at a pH ranging from 3 to 6. Because of the ease of scale-up of electrodialysis processes, this operational selectivity will allow for the separation of enantiomers on a large scale.
    Probing nod factor perception in legumes by fluorescence microspectroscopy
    Goedhart, J. - \ 2001
    Wageningen University. Promotor(en): A.H.J. Bisseling; T.W.J. Gadella Jr.. - S.l. : S.n. - ISBN 9789058084811 - 142
    peulgewassen - rhizobium - stikstof - groei - symbiose - wortels - wortelharen - wortelknolletjes - membranen - n-acetylglucosamine - cytologie - fluorescentiemicroscopie - moleculaire biologie - legumes - rhizobium - nitrogen - growth - symbiosis - roots - root hairs - root nodules - membranes - n-acetylglucosamine - cytology - fluorescence microscopy - molecular biology

    Plants of the family of legumes are capable of forming a symbiosis with Rhizobium bacteria. These Gram-negative bacteria invade the root system of a host legume and fix nitrogen in a specialized organ, the so-called root nodule. In exchange for sugars, the bacteria convert atmospheric nitrogen to ammonia which can be used by the plant. This remarkable alliance allows the plant to grow independently from nitrogen sources provided by the soil. Examples of leguminous plants are clover, pea, and soybean.

    The symbiosis is initiated by a molecular dialogue. The plant produces flavonoid compounds which are recognized by the bacterial NodD protein. The signaling pathway which is activated leads to the synthesis and secretion of lipo-chitooligosaccharides which are also called Nod factors. The production of Nod factors by the Rhizobium bacteria is an essential step for accomplishing symbiosis and also determines host specificity. The general structure of Nod factors comprises a chitin backbone of three to five b-1,4-linked N-acetylglucosamine units. A fatty acid of 16-20 carbon atoms is N-linked to the terminal non-reducing sugar residue. The exact molecular structure can comprise different acyl chains and a variety of decorations on the chitin backbone depending on the Rhizobium species.

    After successful recognition of the bacteria by the legume, a remarkable morphogenic process takes place, which is known as root hair curling. The root hair curls around the Rhizobium colony by which the bacteria are entrapped within the so-called shepherd's crook. Subsequently, the rhizobia enter the root hair through an infection thread, starting from the center of the curl. Via the infection thread several cell layers are crossed after which the bacteria are released in nodule primordium cells, where they differentiate into bacteroids that fix nitrogen.

    Nod factors in the absence of bacteria, either purified from Rhizobium cultures or chemically synthesized can elicit a wide variety of responses on a compatible legume host. When Nod factors are applied to roots, the earliest visible response takes place in root hairs. Root hairs are single tip-growing cells that develop from the epidermis of a root and grow perpendicular from the longitudinal axis of the root. Generally, root hairs that are terminating growth are susceptible to Nod factors and respond by swelling of the tip of the root hairs, followed by the re-initiation of tip growth in a random direction. This typical Nod factor response is referred to as root hair deformation and can be observed with a microscope 2-3 hours after addition of Nod factors.

    The perception of Nod factors by the plant, and the downstream signaling cascades that are activated are major research topics in the Rhizobium-legume interaction. The low concentration (down to 10-12 M) at which Nod factors can still induce root hair deformation and the dependence of the bioactivity on specific decorations of the Nod factor suggest that these molecules are perceived by receptors at the root hair. However, to date no such receptors are characterized. Moreover, it is far from clear where Nod factor recognition by root hairs takes place. Therefore an approach was taken in which fluorescent Nod factor derivatives are synthesized, allowing to probe the ligand binding sites on legume root hairs.

    The research described in this thesis focuses on the quantification, characterization and perception by legumes of Nod factors. In order to detect Nod factors at physiologically relevant concentrations sensitive techniques are required. A number of fluorescence spectroscopy and microscopy based techniques can be used to study fluorescent derivatives of signaling molecules. In chapter 1, the use of fluorescence microspectroscopic techniques available in the laboratory are discussed. Examples how these techniques can be used for the study of root hairs and other living cells are described.

    In chapter 2, two methods to quantify purified Nod factors are described. An enzymatic step which is crucial for the first method was analyzed in detail. The second method was optimized and validated using fluorescent and radiolabeled Nod factor derivatives. The chapter describes in detail how the two optimized methods can be used for quantifying Nod factors as well as potential pitfalls.

    In chapter 3, the spectral properties of three novel fluorescent Nod factor derivatives are described. It is checked whether these fluorescent Nod factors can still elicit root hair deformation on Vicia sativa roots. The properties of the amphiphilic signaling molecules were characterized in vitro in the absence and presence of micelles and model membrane systems using fluorescence spectroscopy. Time-correlated single photon counting fluorescence spectroscopy was used to measure rotational mobility of the fluorophore. These experiments are complemented with fluorescence correlation spectroscopy to examine diffusional mobility of the Nod factors. A lipid transfer assay was used to measure the rate of intermembrane transfer and intramembrane flip-flop of Nod factors.

    In chapter 4, a detailed study is reported describing the sites at which the fluorescent Nod factors accumulate. Fluorescence microscopy is used to examine the location of fluorescent Nod factors on root hairs during the initial perception and during root hair deformation. Subsequently, the diffusional mobility of the fluorescent Nod factors is measured in vivo using fluorescence correlation microscopy (FCM), allowing quantification of molecular mobility and concentration of fluorescent Nod factors in living root hairs at a molecular level. This study is continued in chapter 5 in which also novel sulfated fluorescent Nod factors are used and characterized, enabling a direct comparison between sulfated and non-sulfated Nod factors on a host and non-host legume. Also, the origin of the molecular mobility of the Nod factors is studied in more detail.

    In chapter 6 a novel approach towards manipulating phospholipid second messengers in single cells with spatiotemporal control is presented. The synthesis of a fluorescent and caged derivative, NPE-phosphatidic acid, which releases phosphatidic acid upon exposure to UV is described. The release of phosphatidic acid from the caged compound is studied in vitro and in vivo. The use of photoreleasable phosphatidic acid for studying phospholipid signaling in vivo is evaluated.

    Chapter 7 summarizes the conclusions that can be drawn from the results described in this thesis. The implications for Nod factor secretion by the bacterium and subsequent perception by legume root hairs are discussed. Based on the results presented in this thesis, it is tempting to speculate that spatial restriction of signaling molecules in plants is achieved by immobilization in the cell wall. Subseqent perception of Nod factor takes place either in the plasma membrane or within the cell wall as is illustrated by two proposed modes of perception. The results of this thesis are discussed with respect to these two models.

    The electrophysiology of chloroplast protein import : the involvement of an anion channel in protein translocation across the inner membrane
    Wijngaard, P.W.J. van den - \ 1999
    Agricultural University. Promotor(en): W.J. Vredenberg; J.F.H. Snel. - S.l. : S.n. - ISBN 9789058081186 - 100
    elektrofysiologie - chloroplasten - membranen - eiwittransport - precursors - eiwitten - onderzoek - electrophysiology - chloroplasts - membranes - protein transport - precursors - proteins - research

    The electrophysiological response of the chloroplast envelope during protein import is investigated by using single channel recordings of the chloroplast envelope. An anion channel localised in the inner envelope membrane is identified. The channel has a single channel conductance of 50 pS (chapter 2 and 5). It is found that this channel is inactivated by precursor protein. The precursor induced inactivation of the channel is dependent on the presence of ATP and a functional transit sequence. A deletion mutant of preferredoxin (preFd), that is defective in in vitro import and initial binding, is unable to inactivate the channel (chapter 2). From this it is concluded that the 50 pS anion channel is involved in protein import. The channel is therefore termed P rotein I mport R elated A nion C hannel (PIRAC).

    Inactivation of PIRAC is shown to require the translocation of precursor protein across the outer membrane and association of the precursor with Tic. In the presence of GTP preFd is unable to inactivate PIRAC (chapter 3). A deletion mutant of preFd (Δ15-25-preFd) is shown to inactivate PIRAC (chapter 3). This deletion mutant can compete with the wild-type precursor for import, but is not imported into the stroma. Furthermore evidence has been presented before that Δ15-25-preFd does interact with Tic. It is therefore concluded that translocation of the precursor across the inner envelope membrane is not required for PIRAC inactivation.

    Blocking PIRAC activity with the anion channel blocker DIDS leads to a decrease in import efficiency of isolated pea chloroplasts (chapter 3). This indicates that normal functioning of the channel is required for protein translocation.

    It is shown that the precursor protein induces a long-lived closed state of PIRAC, which is not observed in the absence of precursor (chapter 4). The mean duration of this inactive state is found to be independent of the overall precursor length. In the absence of precursor protein PIRAC is observed to have two distinct open and three distinct closed states (chapter 4). These states can be distinguished on the basis of there mean durations. It is found that the addition of precursor protein decreases the mean duration of one of the open states and two of the closed states (chapter 4). The only states of PIRAC that are unaffected by the addition of precursor are of very short duration (below 1 ms). The precursor induced decrease of the mean duration of PIRAC states is found to be concentration dependent. This leads to the conclusion that there is a direct interaction between the translocating precursor and PIRAC, leading to the switching of the channel to the long-lived inactive state.

    It is observed that addition of antibodies to Tic110 at the stromal side of an excised inside out patch irreversibly inactivated PIRAC activity (chapter 5). Tic110 is a known component of the translocon of the inner membrane of the chloroplast envelope. It is an integral membrane protein with a large hydrophilic loop facing the stroma. It is therefore concluded that PIRAC is associated with the translocon of the inner membrane of the chloroplast envelope.

    Enzyme immobilization on graft copolymers
    Mohy Eldin, M.S. - \ 1999
    Agricultural University. Promotor(en): J. Tramper; D.G. Mita; A.E.M. Janssen. - S.l. : S.n. - 182
    enzymen - immobilisatie - membranen - enzymes - immobilization - membranes

    Immobilised enzymes can be reused, easily separated from the reaction medium, and are more stable in most of the cases. Despite of these advantages, there are still some problems facing the usage of the immobilised enzyme in industry. One of those problems is diffusion-limitation of both the reactants and the products. This problem becomes even more serious when the products are inhibitors of the enzymes. Different strategies for overcoming this problem have been discussed in this thesis.

    A new solution to overcome diffusion limitation is based on processing the enzymatic reaction under non-isothermal conditions. In such a bioreactor the enzymes have to be immobilised on a hydrophobic membrane.

    In this thesis, two enzymes,β-galactosidase and penicillin G acylase have been immobilised onto teflon and nylon membranes. Two grafting techniques have been used to modify the membranes in order to be able to bind the enzyme. These grafting techniques were based on using high-energy radiation as well as chemical modification. Both the grafting technique and enzyme immobilisation method has been optimised. The performance of the membranes has been tested in the non-isothermal bioreactor. A higher activity under non-isothermal conditions was found in comparison to isothermal operation. Furthermore, the application of the non-isothermal conditions is promising for solving the diffusion-limitation problems.

    Copolymer adsorption and the effect on colloidal stability
    Bijsterbosch, H.D. - \ 1998
    Agricultural University. Promotor(en): M.A. Cohen Stuart; G.J. Fleer. - S.l. : S.n. - ISBN 9789054857907 - 139
    adsorptie - membranen - colloïden - oppervlakteverschijnselen - adsorption - membranes - colloids - surface phenomena
    The main aim of the work described in this thesis is to study the effect of different types of copolymers on the stability of aqueous oxide dispersions. Such dispersions are a major component in water-borne paints. In order to obtain a better insight in steric stabilisation we first investigated the relation between the adsorbed amount and layer thickness, and paid attention to the effect of the type of copolymer on the adsorbed amount. We also studied the adsorption kinetics as these are relevant for industrial purposes.

    An introduction on steric stabilisation is given in Chapter 1. For block copolymers the solvent may be non-selective or selective. In a non-selective solvent both blocks are solvated and the polymer molecules are likely to be in a non-aggregated conformation. However, in a selective solvent the molecules form micelles in which the non-soluble blocks are clustered together, surrounded by a layer of solubilised chains. The adsorption kinetics are expected to be affected by the existence of such micelles. Another important feature for the adsorption of block copolymers is the selectivity of the surface. When only one of the blocks has affinity for the surface this will give rise to selective adsorption. On the other hand, the adsorption of a block copolymer in which both blocks have affinity for the surface is non-selective. The resultant polymer layer will differ for both cases. In thesis we studied selective and non-selective adsorption from a selective and a non-selective solvent. As the architecture of the copolymers is also relevant we paid attention to the adsorption of both block copolymers and graft copolymers.

    In Chapter 2 we describe the properties of spread monolayers of polystyrene-poly(ethylene oxide) (PS-PEO) diblock copolymers at the air-water interface. The surface pressure and the thickness of the layer were measured as a function of the adsorbed amount. The thickness was determined with neutron reflectivity measurements.

    Upon compression of the polymer monolayer the surface pressure increases over the entire experimental range of compression. At low coverage the adsorbing PEO block forms a flat "pancake" structure at the surface. When the surface area per molecule is decreased the PEO is pushed out of the surface layer into the solution to form a "cigar" or "brush" structure, which is firmly anchored by the PS block. Some scaling analysis have suggested that this desorption occurs as a first-order surface phase transition. When the polymer layer is compressed further, so that the surface density σincreases, the chains stretch and the thickness H of the layer increases too. Theories predict that H scales as Nσ 1/3, where N is the number of monomers per polymer chain. This is confirmed by our results. However, our experimental data do not show the first-order surface phase transition between pancake and brush. Numerical self-consistent-field calculations also show a gradual transition rather than a first-order phase transition.

    In Chapter 3 we present a study on the non-selective adsorption of two series of diblock copolymers, poly(vinyl methyl ether)-poly(2-ethyl-2-oxazoline) and poly(2-methyl-2oxazoline)- poly(ethylene oxide), from aqueous solution on a macroscopically flat silicium oxide surface. The adsorbed amounts in this study, and in that of Chapters 4 and 5, were measured with an optical reflectometer in an impinging jet flow cell. The hydrodynamic layer thickness was determined by dynamic light scattering.

    The different blocks in the copolymers all have affinity for the silica surface. In all cases there is a small difference between the segmental adsorption energies of the two blocks, giving rise to non-selective adsorption of the block copolymers. For the two types of block copolymers used in this study, the adsorbed amount as a function of block copolymer composition shows a shallow maximum; at this maximum the longest block is also the more strongly adsorbing block. The same trend is found for the hydrodynamid layer thickness. These findings differ from theoretical predictions concerning selective adsorption, where a pronounced maximum is found for a short anchor block. With numerical self-consistent field calculations we demonstrate that the same trends as in our experimental findings can be predicted by theory. In non-selective adsorption of diblock copolymers, with a small difference between the adsorption energies of the blocks, both blocks compete for the same adsorption sites on the surface. When the blocks are incompatible they try to avoid each other, which promotes an anchor-buoy structure. These factors then give rise to a maximum in the adsorbed amount as a function of the block copolymer composition. At this maximum the longest block is also the more strongly adsorbing block. The adsorbed layer has the typical anchor-buoy structure which is necessary for an effective steric stabilisation, but this structure is less pronounced than for selective adsorption.

    The kinetics of adsorption of diblock copolymers can be very slow if the polymers form micelles in solution. In Chapter 4 we compare the experimental adsorption rates on silica and titania with the theoretical flux of copolymer molecules towards the surface for four poly(dimethyl siloxane)-poly(2-ethyl-2-oxazoline) diblock copolymers with the same block length ratio but different molar masses. In aqueous solution these block copolymers form large polydisperse micelles with a very low critica l micellisation concentration (lower than 2 mg 1-1).

    On both surfaces the adsorption behaviour is governed by the anchoring of the hydrophobic siloxane blocks The adsorption kinetics are affected by the exchange rate of free polymer molecules between micelles and solution. For the three smallest molar masses the exchange rate is fast compared to the time a micelle needs to diffuse across the diffusive layer. Before the micelles arrive at the surface they have already broken up into free polymers. Because the cmc is very low, the experimental adsorption rate is determined by the diffusion of micelles towards the surface. For the longest polymer this is not the case: the exchange of polymer molecules between micelles and solution is now relatively slow. As the micelles do not adsorb directly, the adsorption rate is retarded by the slow exchange process. We were able to make an estimate of the micellar relaxation time, i.e., the time a micelle needs to break up. For the largest polymer the relaxation time is of the order of a few tens of seconds. The other polymers have a micellar relaxation time that is shorter than roughly one second.

    The adsorption increases linearly as a function of time, up to very high adsorbed amounts where it reaches a plateau. Such high adsorbed amount is expected for strongly (and selectively) adsorbing diblock copolymers with a relatively short anchor block. The adsorbed amount on silica is considerably higher than on titania. The reason is probably that the hydrophobic block is more strongly anchored to a silica surface than to titania, so that the density of the adsorbed layer can become higher on silica.

    In Chapter 5 we investigate the interfacial behaviour of graft or comb copolymers. We compare the adsorption of graft copolymers with an adsorbing backbone and nonadsorbing side chains to the reverse situation of adsorbing side chains and a nonadsorbing backbone. Two high- molar-mass poly(acryl amide)-graft-poly(ethylene oxide) copolymers with different side chain densities were used in this study.

    On titania only the backbone of these polymers adsorbs and the side chains do not. The adsorbed amount is then about the same as that found for the homopolymer without side chains. On the other hand, on silica the side chains adsorb and the backbone does have no affinity for the surface. For both polymer samples we observe a maximum in the adsorbed amount as a function of time ("overshoot"), after which the adsorbed amount decreases and a plateau is reached. The plateau adsorbed amount on silica is much higher than on titania and also much higher than for both types of homopolymers. Upon adsorption the graft copolymers initially adopt a conformation in which only part of the side chains are adsorbed. Following the overshoot, the graft copolymers show a decrease in the total adsorbed amount. The overshoot depends on the polymer concentration, which suggests that it is not caused by conformational changes in the adsorbed layer but by an exchange process between surface and solution.

    Differences in graft distribution and graft density in the polymer sample are probably responsible for the displacement of adsorbed chains by polymer molecules from solution. The average number of grafts per molecule is rather low in our polymer samples. On statistical grounds there is probably an appreciable polydispersity in graft distribution and in graft density. Molecules in which the grafts are clustered to some extend can displace molecules with more regularly separated grafts, and molecules with a high graft density can displace those with a lower number of side chains. The newly arriving molecules can then adsorb in a flatter conformation with a lower adsorbed amount as the extra loss in conformational entropy is compensated by the gain in adsorption energy.

    The effect of the polymers used in Chapters 3 to 5 on the stability of an aqueous silicium oxide dispersion is described in Chapter 6. The time-dependent increase of the average hydrodynamic radius of silicium oxide aggregates in the presence of electrolyte was measured. The increase of this radius with time is a measure of the aggregation rate of the dispersion. The effect of polymers on the stability of a dispersion was studied by adding polymer to the dispersion and recording the effect in the aggregation rate

    Comparison of the aggregation rate of this "protected" silica with that of uncovered silica particles gives then an indication of the steric stabilisation by the adsorbing polymers.

    Four different series of diblock and graft copolymers were used in these stability measurements. For two series of non-selectively adsorbing diblock copolymers, poly(vinyl methyl ether)-poly(2-ethyl-2-oxazoline) and poly(2-methyl-2-oxazoline)poly(ethyiene oxide), we find a good correlation between the adsorbed amount and the stabilising effect. A higher adsorbed amount provides a better steric stabilisation. Nevertheless, for these polymers the adsorbed amounts are not high enough (up to about 1.2 mg M -2) to protect the dispersion completely against aggregation. A series of amphiphilic diblock copolymers of poly(dimethyl siloxane)-poly(2-ethyl-2-oxazoline) with very high adsorbed amounts (between 3.5 and 8 mg M -2) give excellent steric stabilisation of the dispersion. Adsorbed layers of the two graft copolymers of poly(acryl amide)-poly(ethylene oxide), with a non-adsorbing backbone and adsorbing side chains, are also effective in preventing the silica from aggregating. Even though the adsorbed amount of these graft copolymers is only around 1.3 mg M -2, which is much lower than that of the amphiphilic polymers, aggregation is completely prevented.

    The best steric stabilisation is found for those systems in which either the surface or the solvent is selective. In practical aqueous systems, however, it is difficult to synthesise diblock copolymers in which both blocks are soluble and where only one of the blocks has affinity for the surface. We have shown that copolymers with a different architecture, graft copolymers, also can provide good steric stabilisation and may be a good alternative to diblock copolymers. Very good steric stabilisers are amphiphilic diblock copolymers in a selective solvent. However, it is important that the hydrophobic blocks are flexible enough for fast adsorption kinetics and that they completely wet the surface. Which copolymer should be chosen for the steric stabilisation of a practical colloidal system depends largely on the nature of the particles and the solvent, and on the availability of suitable copolymers.

    Membrane bioreactor for waste gas treatment
    Reij, M.W. - \ 1997
    Agricultural University. Promotor(en): J.A.M. de Bont; S. Hartmans. - S.l. : Reij - ISBN 9789054856351 - 114
    biotechnologie - afvoergassen - biochemie - membranen - bioreactoren - biotechnology - waste gases - biochemistry - membranes - bioreactors

    This thesis describes the design and testing of a membrane bioreactor (MBR) for removal of organic pollutants from air. In such a bioreactor for biological gas treatment pollutants are degraded by micro-organisms. The membrane bioreactor is an alternative to other types of bioreactors for waste gas treatment, such as compost biofilters and bioscrubbers. Propene was used as a model pollutant to study the membrane bioreactor.

    A membrane bioreactor for waste gas treatment consists of a gas and a liquid compartment, separated by a membrane. Gaseous pollutants diffuse through the membrane and are consumed by microorganisms present in the liquid phase. The organisms are supplied with water and inorganic nutrients via this liquid phase. Various membrane bioreactors described in the literature are reviewed in Chapter 2. In the work presented in this thesis, microporous hydrophobic material was selected because of its low mass transfer resistance and the availability of both sheets and fibres. For the removal of propene from air the mass transfer resistance of this type of membrane was found to be negligible (Chapter 3).

    The propene-degrading bacterium Xanthobacter Py2 was shown to form biofilms in membrane bioreactors. Continuous propene removal by biofilms of Xanthobacter Py2 was demonstrated in both flat sheet reactors and hollow-fibre reactors. In both configurations the biofilms are situated on the membrane in the liquid phase. Propene consumption rates could be described quite accurately with the computer programme BIOSIM, that describes simultaneous diffusion and reaction in a biolayer (Chapter 3).

    During continuous operation of hollow-fibre reactors at inlet concentrations of 0.5 to 6 gram propene per m 3, the propene conversion decreased after several weeks (Chapter 4). Clogging of the fibres by excess biomass formation and acidification due to ammonium oxidation, were identified as possible causes. However, when both clogging and ammonium oxidation were prevented, the propene conversion still decreased in time.

    Apparently other factors than clogging and nitrification affect the long-term performance of biofilms of Xanthobacter Py2, growing In an MBR. These factors might be Identified with new methods for biofilm analysis, which allow the localization of activity within the biofilm.

    According to the Dutch emission standards, hydrocarbons such as propene, in offgas have to be reduced to less than 150 mg m -3. In Chapter 5, two propenedegrading strains were compared for their ability to degrade such low concentrations of propene and the faster growing strain, Xanthobacter Py2, was selected. At a concentration of 300 to 600 mg m -3in the gas phase, a 20 days startup period was required for biofilm formation. Once the biofilm had been established, the amount of active biomass adapted to the amount of propene available Within several days. Propene could be removed continuously from air at a concentration of 15 to 50 mg m -3in the gas phase without supplying other organic nutrients to the microbial population (Chapter 5).

    Besides the removal of poorly water soluble pollutants like propene, the membrane bioreactor is also suitable for the removal of pollutants that result in acidification, such as chlorinated hydrocarbons. Therefore, in Chapter 6 the biodegradation of trichloroethene (TCE) by Xanthobacter Py2 was tested during growth on propene in a stirred vessel. The aerobic biodegradation of TCE is difficult because of toxic intermediates that are formed. With Xanthobacter Py2 continuous cometabolic degradation of TCE was shown to be feasible with concentrations up to 206 μM in the liquid phase. The amount of TCE that could be degraded, depended on the TCE concentration and ranged from 0.03 to 0.34 grams of TCE per gram of biomass.

    Membrane bioreactors for gas-liquid contact have several potential applications. They are suitable for the removal of poorly soluble pollutants from air because of their large gas-liquid interface and small mass transfer resistance. Especially if biodegradation of a poorly soluble pollutant results in acidification, the membrane bioreactor might be a unique tool, since the acidic product can be removed via the liquid phase. Other applications might be the removal of highly chlorinated hydrocarbons from air by an aerobic or a combined anaerobic/aerobic: process, as was recently suggested in literature. Membrane bioreactors may also be useful tools in biofilm research, because of easy handling and processing of biofilm samples, excellent oxygen transfer properties and the possibility to apply counter gradients.

    Membranes as separators of dispersed emulsion phases
    Lefferts, A.G. - \ 1997
    Agricultural University. Promotor(en): K. van 't Riet; M.A. Cohen Stuart; A. van der Padt. - S.l. : Lefferts - ISBN 9789054857099 - 157
    membranen - omgekeerde osmose - ultrafiltratie - waterzuivering - afvalwaterbehandeling - filters - zand - rioolwater - afvalwater - industrie - industrieel afval - membranes - reverse osmosis - ultrafiltration - water treatment - waste water treatment - filters - sand - sewage - waste water - industry - industrial wastes

    The reuse or discharge of industrial waste waters, containing small fractions of dispersed oil, requires a purification treatment for which membranes can be used. If only little oil is present, removal of the dispersed phase might be preferable to the more commonly applied removal of the continuous phase. For this purpose dispersed phase separators can be applied, which combine the features of conventional coalescers and membrane filtration. The membrane surface promotes coalescence (similar to a coalescer) but in the mean time the coalesced phase is separated and transferred in a continuous oil permeate phase.

    In the present thesis the possibility to use sheets of polypropylene membrane (with a pore diameter of 0. 1 μm) as dispersed phase separators for treatment of secondary (bromo-) hexadecane-in-water emulsions stabilized by Tween-40 is investigated. The weight fraction of the dispersed phase is always lower than 0.06 and the volume to surface averaged diameter of the oil droplets is generally smaller than 10 μm. The research focuses on understanding the mechanisms controlling the permeation behavior of the oil droplets. The process can be described in two stages: firstly the droplets have to be transported form the bulk of the emulsion towards the membrane and secondly they have to coalesce and permeate.

    In chapter 2 and 3 the transport mechanisms are determined both experimentally and theoretically. It is shown that the theories developed for collectors of solid particles, based on the convective diffusion equation, can be used to describe the transport behavior of the oil droplets in membrane modules. The main transport mechanisms are diffusion, gravity and interception. The latter occurs if the location of the stream lines and the droplet size results in contact between droplet and membrane. The influence of several parameters, such as droplet size, density of the dispersed phase, flow rate and module design can be explained using the convective diffusion theory, assuming the membrane to be a perfect sink. This means that as soon as a droplet reaches the membrane it coalesces and permeates. Since theory and experimental results agree qualitatively, it can be concluded that the system is transport limited in most cases.

    In chapter 4, the coalescence mechanism is discussed. Only if the contact time between droplet and membrane becomes smaller than the time needed for coalescence, the system will be coalescence limited. The coalescence time, t c [s], is determined by the drainage of the aqueous film between droplet and membrane. Calculations show that t c for the small droplets under investigation against a liquid interface is smaller than I second while in case of the presence of a membrane t c will be even smaller. As the contact times are at least a few seconds, coalescence will occur which is in agreement with the perfect sink assumption. Only in case of a dead end module at high flow velocities the system becomes coalescence limited because of short contact times. Finally, at high surfactant concentrations coalescence is not detected.

    As oil droplets are slightly negatively charged, the transport can be enhanced by electrophoresis. Therefor, in chapter 5 possibilities to apply an electric field over the emulsion are investigated. If the anode is placed at the feed side of the membrane the transport velocity is increased significantly. However, not all droplets permeate and a cream layer is formed in front of the membrane. If the anode is placed at the permeate side of the membrane, problems are encountered because of the large resistance of the continuous oil permeate phase. The electric field is situated mainly over this phase, at the cost of the electric field over the emulsion. The resistance of the permeate phase can be successfully decreased by addition of an apolar electrolyte (TBAI). Also, it is possible to circulate an aqueous phase at the permeate side. In this case, oil droplets with a diameter of several millimeters are detected in the permeate. Here, the membrane acts as a conventional coalescer. All systems show indeed an enhanced extraction in the presence of an electric field. However, we think that only the first and the last are scaleable.

    Finally, in the general discussion the dispersed phase separator is compared to conventional emulsion separation methods. The dispersed phase separator becomes advantageous at low oil concentrations. Feasibility will increase if the remaining oil fraction in the retentate can be decreased further. Ideas for optimization in case of transport limitation are introduced, such as adjusting the flow profile to increase the interception mechanism. Problems are encountered in practice because of the presence of all kinds of impurities in industrial waste waters which will hinder the coalescence. In that case, research should focus on coalescence enhancing parameters of the membrane material such as surface potential and surface roughness. Preliminary experiments using a reflectometer indicate the importance of surface roughness, which is explained theoretically.

    Photosystem II electron flow as a measure for phytoplankton gross primary production = [Fotosysteem II elektronentransport als een maat voor de bruto primaire produktie van fytoplankton]
    Geel, C. - \ 1997
    Agricultural University. Promotor(en): W.J. Vredenberg; J.F.H. Snel. - S.l. : Geel - ISBN 9789054857891 - 110
    fotosynthese - fytoplankton - vegetatie - ecosystemen - membranen - bio-energetica - elektrische eigenschappen - planten - biomassa - primaire productie - photosynthesis - phytoplankton - vegetation - ecosystems - membranes - bioenergetics - electrical properties - plants - biomass - primary production
    Saturating pulse fluorescence measurements, well known from studies of higher plants for determination of photosystem II (PS II) characteristics, were applied to cultures of the green alga Dunaliella teitiolecta (Chapter 2). The actual efficiency of PS II (φ PS II ), the maximal efficiency of PS II (F v /F m ), and both photochemical and non- photochemical fluorescence quenching were determined for cultures of D. tertiolecta growing under varying light intensities. The rate of PS II electron flow (J E ) estimated as the product of φ PS II , and the photon flux density (PFD), appeared to correlate well with growth rates determined for the D. tertiolecta cultures . The results indicated that the saturating pulse fluorescence method may be successfully used to determine photosynthetic characteristics of phytoplankton. However, an increase of sensitivity by a factor 1000 was found to be needed for the application of this technique to in situ measurements. Conditions were outlined which have led to the development of the Xe-PAM fluorometer with a manyfold higher sensitivity.

    The relation between photosynthetic oxygen evolution (J 0 , expressed as oxygen production per chlorophyll a ) and J E was investigated for the marine algae Phaeodactylum tricornutum, D. tertiolecta, Tetraselmis sp., Isochrysis sp. and Rhodomonas sp , by varying the ambient PFD (Chapter 3). At limiting light a linear relation was found in all species. At PFD's approaching light saturation linearity was lost. The observed non-linearity at high M's is most probably not caused by photorespiration but by a Mehler-type of oxygen reduction. The relationship could be modelled by including a redox-state dependent oxygen uptake. The linear range between J E and J 0 extends to a PFD which is 2 to 10 times higher than the PFD at which the species were grown. The ratio of J E and J 0 in the light-limited range is species dependent and related to differences in absorption cross-section of PS II (σ PS II ). The ratio of J E and J 0 in the light-limited range is not dependent on temperature. F v /F m was found to be temperature dependent with an optimum near 10 °C in the diatom P. tricornutum .

    The photosynthetic electron flux in a phytoplankton sample (PEF) was shown to depend on the product of J E (= φ PS II · PFD), σ PS II and the number of PS II (n PS II ) in the sample (Chapter 4). A mathematical expression was derived which relates the minimal fluorescence (F 0 ) to n PS II and σ PS II under the condition that the spectral distribution of the ambient light and the measuring light are identical. This condition can be approximated measuring F 0 with the Xe-PAM fluorometer. The experimental conditions under which the relationship between PEF, φ PS II , and F 0 is valid, were examined. The maximal value of φ PS II (F v /F m ) was shown to be independent on the wavelength under the measuring conditions. The apparent F v /F m depends on the intensity of the measuring light and the duration and intensity of the saturating light pulse. It is shown that, under certain conditions, the minimal fluorescence can be used as a measure of PS II excitation in the light. F 0 , obtained with the broad band excitation light of a filtered Xenon flash lamp, thus was used as a measure for the product of n PS II and σ PS II . The relationship between PEF calculated with this expression and net oxygen evolution (phytoplankton oxygen flux, POF, expressed as oxygen production per sample volume) was found to be similar in the diatom P tricornutum and the green alga D. tertiolecta. Therefore we conclude that the use of PEF as a measure for POF yields better results than the use of J E for J 0 . The Xe-PAM fluorometer was found to be sensitive enough for coastal applications.

    The relation between PEF and carbon fixation (phytoplankton carbon flux, PCF, expressed as the carbon dioxide fixed per sample volume) was examined in cultures of Isochrysis sp. , Phaeocystis sp. macroflagellates and Skeletonema costatum (Chapter 5). The F 0 used to calculate PEF was measured at the start of the experiments. Both the PFD and the duration of the incubation were varied. As found before for the relation between J E and J 0 , the relation between PEF and PCF was also approximately linear at limiting light and deviated from linearity at saturating light. The linear range between PCF and PEF also extends to a PFD which is 2 to 10 times higher than the PFD at which the species were grown. The length of the incubation did not affect PEF and PCF except for the highest PFD (1530 μmol m -2s -1). The decline of F v /F m of the samples irradiated at the highest PFD showed a fast component within 30 minutes incubation and a minor slow component, indicating that photoinhibition was induced in the first 30 minutes.

    PEF, PCF, oxygen production and their relationships were furthermore examined during phytoplankton development in a mesocosm at the field station (Chapter 6). PEF was calculated from F 0 , φ PS II and the PFD which were continuously monitored for three weeks in the upper water layer of the mesocosm. In addition PEF and PCF were estimated from laboratory measurements on samples taken from the mesocosms. Daily primary production in the mesocosm, measured as either PSII electron flow (PPE) or carbon fixation (PPC), was calculated using a photosynthesis model. Daily photosynthetic oxygen evolution (PPO) was calculated from changes in the oxygen concentration over the day. In the period between the 2 blooms the ration of PPO and PPE was higher than during the peak of the blooms. The ratio of PPC and PPE was much more constant. In general PPE gave a reasonable measure of both PPC and PPO.

    The effects of chlororespiration and state transitions on F 0 were determined in the diatom P. tricornutum (Chapter 7). Inhibition of chlororespiration by antimycin A or anaerobiosis did not affect F v /F m . The observed F 0 was insignificantly (8%) increased upon addition of antimycin A and slightly decreased upon illumination with farred light (6 μmol m -2s -1). These effects might be attributed to chlororespiratory activity, but could as well be caused by reduction of Q A by the weak fluorescence measuring light. Addition of the uncouplers CCCP or nigericin did not increase the maximal fluorescence (F M ). The data show that under our conditions reduction of Q A and energy dependent quenching in the dark by chlororespiration do not occur in P. tricornutum . Light-induced increases in F M , therefore, are suggested to be caused by state transitions. Use of the F 0 to estimate photon capture in the light might lead to an underestimation of the PEF The error is estimated to be not more than about 10 % as calculated from the increase in maximal fluorescence in the light.

    The present work illustrates that the fluorescence pulse method is a reliable technique to get insight into the photosynthetic performance and gross primary production of the population of algal cells in a marine ecosystem.

    Structure-function relationship of viral coat proteins : a site-directed spectroscopic study of M13 coat protein
    Stopar, D. - \ 1997
    Agricultural University. Promotor(en): T.J. Schaafsma; M.A. Hemminga. - S.l. : Stopar - ISBN 9789054857730 - 101
    virologie - moleculaire biologie - spectroscopie - resonantie - eiwitten - membranen - viruseiwitten - manteleiwitten - virology - molecular biology - spectroscopy - resonance - proteins - membranes - viral proteins - coat proteins
    This thesis describes the results of a spectroscopic study of the major coat protein of bacteriophage M13. During the infection process this protein is incorporated into the cytoplasmic membrane of Escherichia coli host cells. To specifically monitor the local structural changes and changes in the environment of the protein upon membrane insertion, a set of cysteine site-specific mutants of protein was produced for the purpose of ESR spin labeling and fluorescence spectroscopy. These spectroscopic techniques, in combination with CD spectroscopy, are particularly suitable for comparison of protein structural changes in different membrane model systems. The spectroscopic experiments indicate that the very tight structure of the phage particle was disrupted only with strong ionic detergents, such as SDS and CTAB. However the phage structure was not affected by either lipids or nonionic detergents. On the other hand, after a chloroform-induced transformation of the filamentous phage particle into the S- form, the major coat protein was completely solubilized under these conditions. Upon solubilization of the phage particle in sodium cholate at low pH, a protein "structural dimer" appeared to be the most stable aggregate. This structural dimer, in which the protein subunits that are slightly shifted with respect to each other, is proposed to play a key role in the assembly and disassembly of the phage particle in vivo. However, when completely solubilized in the membrane, the major coat protein is stable in a monomer state, and does not have a tendency to aggregate. Site-directed ESR spin labeling was found to be a useful technique to compare the protein structure and topology in micellar and lipid bilayer model systems. To allow a stable association with different membrane model systems, the local structure of the major coat protein changed significantly, but surprisingly the major structural elements, such as the α-helix content, are largely retained. The detailed topology of the major coat protein in lipid bilayers was determined by using Ni 2+quenchers with the spin-labeled mutants. The results show that the part of the major coat protein around amino acid residue Thr36 is situated in the centre of the membrane. Amino acid residues 25 and 46 are located in the lipid head group region at the two water-membrane interfaces, with only a short part of the C-terminus (three to four amino acid residues) extending into the aqueous phase. This transmembrane topology leaves the α-carbons of Lys40, Lys43, and Lys44 in the membrane interior, while the ε-amino groups of the lysine side chains probably interact with the large excess of phosphates in the lipid head groups. Since the major coat protein has to aggregate to form a protective coat around viral DNA, these results indicate that lipids should be removed first at the assembly site, before the major coat protein can interact with DNA to form a new virus coat.
    Vermindering van het volume van zeugenmest door middel van omgekeerde osmose
    Gastel, J.P.B.F. van; Thelosen, J.G.M. - \ 1995
    Rosmalen : Praktijkonderzoek varkenshouderij (Proefverslag / Praktijkonderzoek Varkenshouderij P1.129) - 48
    dierlijke meststoffen - membranen - omgekeerde osmose - drijfmest - zeugen - ultrafiltratie - animal manures - membranes - reverse osmosis - slurries - sows - ultrafiltration
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