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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    SNARE Complexity in Arbuscular Mycorrhizal Symbiosis
    Huisman, Rik ; Hontelez, Jan ; Bisseling, Ton ; Limpens, Erik - \ 2020
    Frontiers in Plant Science 11 (2020). - ISSN 1664-462X
    arbuscular mycorrhiza - exocytosis - Medicago - membrane - SNARE - symbiosis - syntaxin - VAMP

    How cells control the proper delivery of vesicles and their associated cargo to specific plasma membrane (PM) domains upon internal or external cues is a major question in plant cell biology. A widely held hypothesis is that expansion of plant exocytotic machinery components, such as SNARE proteins, has led to a diversification of exocytotic membrane trafficking pathways to function in specific biological processes. A key biological process that involves the creation of a specialized PM domain is the formation of a host–microbe interface (the peri-arbuscular membrane) in the symbiosis with arbuscular mycorrhizal fungi. We have previously shown that the ability to intracellularly host AM fungi correlates with the evolutionary expansion of both v- (VAMP721d/e) and t-SNARE (SYP132α) proteins, that are essential for arbuscule formation in Medicago truncatula. Here we studied to what extent the symbiotic SNAREs are different from their non-symbiotic family members and whether symbiotic SNAREs define a distinct symbiotic membrane trafficking pathway. We show that all tested SYP1 family proteins, and most of the non-symbiotic VAMP72 members, are able to complement the defect in arbuscule formation upon knock-down/-out of their symbiotic counterparts when expressed at sufficient levels. This functional redundancy is in line with the ability of all tested v- and t-SNARE combinations to form SNARE complexes. Interestingly, the symbiotic t-SNARE SYP132α appeared to occur less in complex with v-SNAREs compared to the non-symbiotic syntaxins in arbuscule-containing cells. This correlated with a preferential localization of SYP132α to functional branches of partially collapsing arbuscules, while non-symbiotic syntaxins accumulate at the degrading parts. Overexpression of VAMP721e caused a shift in SYP132α localization toward the degrading parts, suggesting an influence on its endocytic turn-over. These data indicate that the symbiotic SNAREs do not selectively interact to define a symbiotic vesicle trafficking pathway, but that symbiotic SNARE complexes are more rapidly disassembled resulting in a preferential localization of SYP132α at functional arbuscule branches.

    Effect of the DGAT1 K232A genotype of dairy cows on the milk metabolome and proteome
    Lu, J. ; Boeren, S. ; Hooijdonk, A.C.M. van; Vervoort, J.J.M. ; Hettinga, K.A. - \ 2015
    Journal of Dairy Science 98 (2015)5. - ISSN 0022-0302 - p. 3460 - 3469.
    h-1-nmr spectroscopy - sample preparation - identification - stomatin - membrane - proteins - gene - cattle - yield
    Diglyceride O-acyltransferase 1 (DGAT1) is the enzyme that catalyzes the synthesis of triglycerides from diglycerides and acyl-coenzyme A. The DGAT1 K232A polymorphism was previously shown to have a significant influence on bovine milk production characteristics (milk yield, protein content, fat content, and fatty acid composition). The mechanism of this influence has, however, not been elucidated. In this study, metabolomics (1H-nuclear magnetic resonance) and proteomics (laser chromatography-tandem mass spectrometry) were applied to determine the serum and lipid metabolite composition and milk fat globule membrane proteome of milk samples from cows with the DGAT1 KK and AA genotypes. The milk samples from cows with the DGAT1 KK genotype contained more stomatin, sphingomyelin, choline, and carnitine, and less citrate, creatine or phosphocreatine, glycerol-phosphocholine, mannose-like sugar, acetyl sugar phosphate, uridine diphosphate (UDP)-related sugar, and orotic acid compared with milk samples from cows with the DGAT1 AA genotype. Based on these results, we propose that the differences between the DGAT1 genotypes may be related to stomatin-sphingomyelin lipid rafts as well as structural (cell membrane) differences in epithelial cells of the mammary gland. In conclusion, our study shows that, in addition to previously described changes in triglyceride composition, cows differing in DGAT1 polymorphism differ in their milk proteome and metabolome, which may help in further understanding the effect of the DGAT1 K232A polymorphism on milk production characteristics.
    Influence of Pluronic F127 on the distribution and functionality of inkjet-printed biomolecules in porous nitrocellulose substrates
    Mujawar, L.H. ; Amerongen, A. van; Norde, W. - \ 2015
    Talanta 131 (2015). - ISSN 0039-9140 - p. 541 - 547.
    protein microarrays - spot morphology - block-copolymer - antibody - surfaces - additives - membrane - flow - hydrophobicities - orientation
    The distribution of inkjet-printed biomolecules in porous nitrocellulose substrates often results in a non-homogeneous spot morphology commonly referred to as 'doughnut-shaped' spots. We have studied the influence of Pluronic F127 (an amphiphilic surfactant) on the functionality of inkjet-printed primary antibody molecules and on the final assay result by performing a one-step antibody binding assay in the nitrocellulose substrate. The primary antibody was printed with and without Pluronic, followed by the addition of double-labelled amplicons as antigen molecules and a fluorophore-labelled streptavidin as detection conjugate. The distribution of the fluorescence intensity down into the nitrocellulose substrate was investigated by confocal laser scanning microscopy in 'Z' stacking mode. Each horizontal slice was further analysed by applying a concentric ring format and the fluorescence intensity in each slice was represented in a colour-coded way. The mean and total fluorescence intensity of the antibody binding assay (fluorescent streptavidin) showed a peak at 0.2% (w/v) Pluronic F127. In addition, an improved spot morphology was observed also peaking at the same Pluronic concentration. Subsequently, we investigated the direct influence of Pluronic F127 on the location of the primary antibody molecules by labelling these molecules with the fluorophore Alexa-488. Our results show that upon increasing the concentration of Pluronic F127 in the printing buffer, the spot diameter increased and the number of primary antibody molecules bound in the spot area gradually decreased. This was confirmed by analysing the distribution of fluorescently labelled primary antibody molecules down into the membrane layers. We conclude that a particular ratio between primary antibody and Pluronic F127 molecules in combination with available substrate binding capacity results in an optimal orientation, that is Fab-UP, of the primary antibody molecules. Consequently, an increased number of antigen molecules (in our case the labelled amplicons) and of the fluorescent detection conjugate (streptavidin) will give an optimal signal. Moreover, distribution of the primary antibody molecules was more homogeneous at the optimal Pluronic F127 concentration, contributing to the better spot morphology observed.
    Temporal proteomic analysis and label-free quantitation of viral proteins of an invertebrate iridovirus
    Ince, I.A. ; Boeren, S. ; Oers, M.M. van; Vlak, J.M. - \ 2015
    Journal of General Virology 96 (2015)1. - ISSN 0022-1317 - p. 196 - 205.
    chilo-iridescent-virus - polypeptides - identification - type-6 - cells - membrane - genome - civ
    Invertebrate iridescent virus 6 (IIV-6) is a nucleocytoplasmic virus with a 212 kb-long linear double-stranded DNA genome that encodes 215 putative open reading frames. The IIV-6 virion-associated proteins consist of at least 54 virally-encoded proteins. One of our previous findings showed that most of these proteins are encoded by genes from the early transcriptional class. This indicates that these structural proteins may not only function in the formation of the virion, but also in the initial stage of viral infection. In the current study, we followed the protein expression profile of IIV-6 over time in Drosophila S2 cells by label-free quantitation using a proteomic approach. A total of 95 viral encoded proteins were detected in infected cells, of which 37 are virion proteins. The expressed IIV-6 virion proteins could be categorized into three main clusters based on their expression profiles. These clusters were: 1) proteins with stably low or 2) exponentially increasing expression levels during infection, and 3) proteins that were initially highly abundant, but showed slightly reduced levels after 48 hours (h) post infection (p.i.). Here, we provide novel information on the kinetics of virion and infected cell-specific protein levels that assists in understanding gene regulation in this lesser known DNA virus model.
    Hydrogen production and ammonium recovery from urine by a Microbial Electrolysis Cell
    Kuntke, P. ; Sleutels, T.H.J.A. ; Saakes, M. ; Buisman, C.J.N. - \ 2014
    International Journal of Hydrogen Energy 39 (2014)10. - ISSN 0360-3199 - p. 4771 - 4778.
    waste-water treatment - bioelectrochemical systems - ion-transport - fuel-cells - performance - ph - catalysts - membrane - acetate - energy
    We investigated the use of a Microbial Electrolysis Cell (MEC) for the ammonium removal, COD removal and hydrogen production from five times diluted urine. During operation with a batch cathode, a current density of 23.07 +/- 1.15 A m(-2) was achieved corresponding to a hydrogen production rate of 48.6 +- 7.47 m(3) H-2 m(-3) MEC d(-1), an ammonium removal rate of 173.4 +/- 18.1 g N m(-2) d(-1) and a COD removal rate of 171.0 +/- 16.9 g COD m(-2) d(-1). Ammonia stripping was not possible in the applied MEC and ammonia diffusion from cathode to anode compartment led to a relatively short stable operation period. The stable operation period was prolonged by addition of new cathode media (HRT 6 h), but this resulted in a lower current density (14.64 +/- 1.65 A m(-2)), hydrogen production rate (32.0 +/- 0.89 m(3) H-2 m(-3) MEC d(-1)), ammonium removal rate (162.18 +/- 10.37 g N m(-2) d(-1)) and COD removal rate (130.56 +/- 4.45 g COD m(-2) d(-1)). Copyright (C) 2014, Hydrogen Energy Publications, LLC. Published by Elsevier Ltd. All rights reserved.
    Fractioning electrodialysis: a current induced ion exchange process
    Galama, A.H. ; Daubaras, G. ; Burheim, O.S. ; Rijnaarts, H. ; Post, J.W. - \ 2014
    Electrochimica Acta 136 (2014). - ISSN 0013-4686 - p. 257 - 265.
    divalent ions - seawater desalination - membrane - monovalent - diffusion - transport - charge - nanofiltration - permeability - polarization
    In desalination often multi ionic compositions are encountered. A preferential removal of multivalent ions over monovalent ions can be of interest to prevent scaling in the desalination process. Recently, a novel fractionating electrodialysis stack is described by Zhang et al., 2012 (in Sep. purify. Technol. 88). In the present work a small modification to such a stack was made, to create a current induced ion exchange process, in which no longer desalination occurs. This was done by building a membrane stack in which monovalent-selective ion-exchange membranes and standard grade ion-exchange membranes, with similar charge sign (so either anion or cation exchange groups), were placed alternatingly between an anode and a cathode to form a membrane stack. A proof of principle of the fractioning electrodialysis technology is given. Ternary mixtures, with a divalent-monovalent ion ratio similar to seawater, were used as feed water. For a cation and an anion fractioning stack, maximum fractionations of divalent ions were obtained of approximately 90 and 60%. At higher applied current density, ions can be fractionated to a larger extent than at lower applied current density. For both stacks the water recovery was 50%. Coulombic efficiency of both processes decrease rapidly after the start of the experiment. This leads to relatively large volumetric energy consumptions. (C) 2014 Elsevier Ltd. All rights reserved.
    Soybean SAT1 (Symbiotic Ammonium Transporter 1) encodes a bHLH transcription factor involved in nodule growth and NH4+ transport
    Chiasson, D.M. ; Loughlin, P.C. ; Mazurkiewicz, D. ; Mohammadidehcheshmeh, M. ; Fedorova, E.E. ; Okamoto, M. ; McLean, E. ; Glass, A.D.M. ; Smith, S.E. ; Bisseling, T. ; Tyerman, S.D. ; Day, D.A. ; Kaiser, B.N. - \ 2014
    Proceedings of the National Academy of Sciences of the United States of America 111 (2014)13. - ISSN 0027-8424 - p. 4814 - 4819.
    arabidopsis-thaliana - circadian clock - lotus-japonicus - stress-response - er stress - membrane - protein - expression - domain - gene
    Glycine max symbiotic ammonium transporter 1 was first documented as a putative ammonium (NH4+) channel localized to the symbiosome membrane of soybean root nodules. We show that Glycine max symbiotic ammonium transporter 1 is actually a membrane-localized basic helix–loop–helix (bHLH) DNA-binding transcription factor now renamed Glycine max bHLH membrane 1 (GmbHLHm1). In yeast, GmbHLHm1 enters the nucleus and transcriptionally activates a unique plasma membrane NH4+ channel Saccharomyces cerevisiae ammonium facilitator 1. Ammonium facilitator 1 homologs are present in soybean and other plant species, where they often share chromosomal microsynteny with bHLHm1 loci. GmbHLHm1 is important to the soybean rhizobium symbiosis because loss of activity results in a reduction of nodule fitness and growth. Transcriptional changes in nodules highlight downstream signaling pathways involving circadian clock regulation, nutrient transport, hormone signaling, and cell wall modification. Collectively, these results show that GmbHLHm1 influences nodule development and activity and is linked to a novel mechanism for NH4+ transport common to both yeast and plants.
    Stability of (Bio)Functionalized Porous Aluminum Oxide
    Debrassi, A. ; Ribbera, A. ; Vos, W.M. de; Wennekes, T. ; Zuilhof, H. - \ 2014
    Langmuir 30 (2014). - ISSN 0743-7463 - p. 1311 - 1320.
    self-assembled monolayers - lactic-acid bacteria - lactobacillus-plantarum - nanoporous alumina - click chemistry - anodic alumina - surfaces - adsorption - membrane - carbohydrate
    Porous aluminum oxide (PAO), a nanostructured support for, among others, culturing microorganisms, was chemically modified in order to attach biomolecules that can selectively interact with target bacteria. We present the first comprehensive study of monolayer-modified PAO using conditions that are relevant to microbial growth with a range of functional groups (carboxylic acid, a-hydroxycarboxylic acid, alkyne, alkene, phosphonic acid, and silane). Their stability was initially assessed in phosphate-buffered saline (pH 7.0) at room temperature. The most stable combination (PAO with phosphonic acids) was further studied over a range of physiological pHs (4–8) and temperatures (up to 80 °C). Varying the pH had no significant effect on the stability, but it gradually decreased with increasing temperature. The stability of phosphonic acid-modified PAO surfaces was shown to depend strongly on the other terminal group of the monolayer structure: in general, hydrophilic monolayers were less stable than hydrophobic monolayers. Finally, an alkyne-terminated PAO surface was reacted with an azide-linked mannose derivative. The resulting mannose-presenting PAO surface showed the clearly increased adherence of a mannose-binding bacterium, Lactobacillus plantarum, and also allowed for bacterial outgrowth.
    In Situ Spatially and Temporally Resolved Measurements of Salt Concentration between Charging Porous Electrodes for Desalination by Capacitive Deionization
    Suss, M.E. ; Biesheuvel, P.M. ; Baumann, T.E. ; Stadermann, M. ; Santiago, J.G. - \ 2014
    Environmental Science and Technology 48 (2014)3. - ISSN 0013-936X - p. 2008 - 2015.
    mesoporous carbon - constant-current - ion-transport - waste-water - membrane - efficiency - performance - electrolytes - optimization - porosity
    Capacitive deionization (CDI) is an emerging water desalination technique. In CDI, pairs of porous electrode capacitors are electrically charged to remove salt from brackish water present between the electrodes. We here present a novel experimental technique allowing measurement of spatially and temporally resolved salt concentration between the CDI electrodes. Our technique measures the local fluorescence intensity of a neutrally charged fluorescent probe which is collisionally quenched by chloride ions. To our knowledge, our system is the first to measure in situ and spatially resolved chloride concentration in a laboratory CDI cell. We here demonstrate good agreement between our dynamic measurements of salt concentration in a charging, millimeter-scale CDI system to the results of a modified Donnan porous electrode transport model. Further, we utilize our dynamic measurements to demonstrate that salt removal between our charging CDI electrodes occurs on a longer time scale than the capacitive charging time scales of our CDI cell. Compared to typical measurements of CDI system performance (namely, measurements of outflow ionic conductivity), our technique can enable more advanced and better-controlled studies of ion transport in CDI systems, which can potentially catalyze future performance improvements.
    Nonlinear Amplification of a Supramolecular Complex at a Multivalent Interface
    Hsu, S.H. ; Yilmaz, M.D. ; Reinhoudt, D.N. ; Velders, A.H. ; Huskens, J. - \ 2013
    Angewandte Chemie-International Edition 52 (2013)2. - ISSN 1433-7851 - p. 714 - 719.
    self-assembled monolayers - molecular printboards - chemistry - binding - membrane - nanostructures - organization - selection - discrete - peptides
    Competition with a monovalent cyclodextrin host (blue cones) in solution drives the multivalent binding of a Eu3+ complex and a sensitizer molecule to cyclodextrin monolayers through a nonlinear self-assembly process. Adamantyl groups (light-blue spheres) are attached to the EDTA ligand (black) and the antenna molecule (orange), which has a carboxylate group for coordination to the Eu3+ ion (yellow or red in free or complexed form, respectively).
    Colocalization and interaction between elongasome and divisome during a preparative cell division phase in Escherichia coli
    Ploeg, R. van der; Verheul, J. ; Vischer, N.O.E. ; Alexeeva, S.V. ; Hoogendoorn, E. ; Postma, M. ; Banzhaf, M. ; Vollmer, W. ; Blaauwen, T. den - \ 2013
    Molecular Microbiology 87 (2013)5. - ISSN 0950-382X - p. 1074 - 1087.
    penicillin-binding-proteins - resonance energy-transfer - bacterial actin mreb - peptidoglycan synthesis - septal ring - caulobacter-crescentus - fluorescent proteins - lateral wall - ftsi pbp3 - membrane
    The rod-shaped bacterium Escherichia coli grows by insertion of peptidoglycan into the lateral wall during cell elongation and synthesis of new poles during cell division. The monofunctional transpeptidases PBP2 and PBP3 are part of specialized protein complexes called elongasome and divisome, respectively, which catalyse peptidoglycan extension and maturation. Endogenous immunolabelled PBP2 localized in the cylindrical part of the cell as well as transiently at midcell. Using the novel image analysis tool Coli-Inspector to analyse protein localization as function of the bacterial cell age, we compared PBP2 localization with that of other E.¿coli cell elongation and division proteins including PBP3. Interestingly, the midcell localization of the two transpeptidases overlaps in time during the early period of divisome maturation. Försters Resonance Energy Transfer (FRET) experiments revealed an interaction between PBP2 and PBP3 when both are present at midcell. A decrease in the midcell diameter is visible after 40% of the division cycle indicating that the onset of new cell pole synthesis starts much earlier than previously identified by visual inspection. The data support a new model of the division cycle in which the elongasome and divisome interact to prepare for cell division
    Hyphenation of optimized microfluidic sample preparation with nano liquid chromatography for faster and greener alkaloid analysis
    Shen, Y. ; Beek, T.A. van; Zuilhof, H. ; Chen, B. - \ 2013
    Analytica Chimica Acta 797 (2013). - ISSN 0003-2670 - p. 50 - 56.
    aqueous 2-phase extraction - microchannel system - gas-chromatography - chip - membrane - droplet - cells
    A glass liquid–liquid extraction (LLE) microchip with three parallel 3.5 cm long and 100 µm wide interconnecting channels was optimized in terms of more environmentally friendly (greener) solvents and extraction efficiency. In addition, the optimized chip was successfully hyphenated with nano-liquid chromatography with ultraviolet and mass spectrometric detection (nanoLC–UV–MS) for on-line analysis. In this system, sample pretreatment, separation and detection are integrated, which significantly shortens the analysis time, saves labor and drastically reduces solvent consumption. Strychnine was used as model analyte to determine the extraction efficiency of the optimized 3-phase chip. Influence of organic solvent, pH of feed phase, type of alkaloid, and flow rates were investigated. The results demonstrated that the 3-phase chip nanoLC–UV/MS hyphenation combines rapid (~25 s) and efficient (extraction efficiency >90%) sample prep, with automated alkaloid analyses. The method was applied to real samples including Strychnos nux-vomica seeds, Cephaelis ipecacuanha roots, Atropa belladonna leaves, and Vinca minor leaves.
    Managing hytrosavirus infections in Glossina pallidipes colonies: Feeding regime affects the prevalence of the salivary gland hypertrophy syndrome
    Kariithi, H.M. ; Abd-Alla, A.M.M. ; Mohamed, H.A. ; Lapiz, E. ; Parker, A.G. ; Vreysen, M.J.B. - \ 2013
    PLoS ONE 8 (2013)5. - ISSN 1932-6203
    tsetse flies glossina - lop-eared rabbits - dna virus - austeni newst - morsitans centralis - living host - diptera - membrane - absence
    Many species of tsetse flies are infected by a virus that causes salivary gland hypertrophy (SGH) syndrome and the virus isolated from Glossina pallidipes (GpSGHV) has recently been sequenced. Flies with SGH have a reduced fecundity and fertility. Due to the deleterious impact of SGHV on G. pallidipes colonies, several approaches were investigated to develop a virus management strategy. Horizontal virus transmission is the major cause of the high prevalence of the GpSGHV in tsetse colonies. Implementation of a “clean feeding” regime (fresh blood offered to each set of flies so that there is only one feed per membrane), instead of the regular feeding regime (several successive feeds per membrane), was among the proposed approaches to reduce GpSGHV infections. However, due to the absence of disposable feeding equipment (feeding trays and silicone membranes), the implementation of a clean feeding approach remains economically difficult. We developed a new clean feeding approach applicable to large-scale tsetse production facilities using existing resources. The results indicate that implementing this approach is feasible and leads to a significant reduction in virus load from 109 virus copies in regular colonies to an average of 102.5 and eliminates the SGH syndrome from clean feeding colonies by28 months post implementation of this approach. The clean feeding approach also reduced the virus load from an average of 108 virus copy numbers to an average of 103 virus copies and SGH prevalence of 10% to 4% in flies fed after the clean fed colony. Taken together, these data indicate that the clean feeding approach is applicable in large-scale G. pallidipes production facilities and eliminates the deleterious effects of the virus and the SGH syndrome in these colonies.
    Betabaculovirus F proteins showed different efficiencies when rescuing the infectivity of gp64-null Autographa californica nucleopolyhedrovirus
    Yin, F. ; Wang, M. ; Ying, T. ; Deng, F. ; Vlak, J.M. ; Hu, Z. ; Wang, H. - \ 2013
    Virology 436 (2013)1. - ISSN 0042-6822 - p. 59 - 66.
    envelope fusion protein - armigera single nucleopolyhedrovirus - granulovirus genome - multicapsid nucleopolyhedrovirus - multiple nucleopolyhedrovirus - sequence-analysis - baculovirus gp64 - identification - membrane
    The Agrotis segetum granulovirus (AgseGV) F protein was previously identified as the first betabaculovirus F protein with functional homology to Autographa californica nucleopolyhedrovirus (AcMNPV) GP64. In the current study, F proteins from Xestia c-nigrum granulovirus (XecnGV), Cydia pomonella granulovirus (CpGV), Phthorimaea operculella granulovirus (PhopGV), Choristoneura occidentalis granulovirus (ChocGV) and Plutella xylostella GV (PlxyGV) were studied for their ability to rescue the infectivity of gp64-null AcMNPV. Our results showed that most studied betabaculovirus F proteins could replace the function of AcMNPV GP64, however, their efficiencies to rescue the infectivity of gp64-null AcMNPV were substantially different. PlxyF, although fusogenic, was the only protein that failed to substitute the function of AcMNPV GP64. Further studies using Sf9(0p1D) cell line showed that PlxyF appeared to be properly incorporated into AcMNPV virions and underwent correct post-translational cleavage and N-linked glycosylation. However, the gp64-null AcMNPV containing PlxyF could not be propagated in either Sf9 or P. xylostella cells.
    Rhizobium-legume symbiosis shares an exocytotic pathway required for arbuscle formation
    Ivanov, S. ; Fedorova, E.E. ; Limpens, E.H.M. ; Mita, S. De; Genre, A. ; Bonfante, P. ; Bisseling, T. - \ 2012
    Proceedings of the National Academy of Sciences of the United States of America 109 (2012)21. - ISSN 0027-8424 - p. 8316 - 8321.
    medicago-truncatula - root-nodules - intracellular accommodation - n-2-fixing symbiosomes - mycorrhizal symbiosis - infection threads - cell wall - membrane - genes - nodulation
    Endosymbiotic interactions are characterized by the formation of specialized membrane compartments, by the host in which the microbes are hosted, in an intracellular manner. Two well-studied examples, which are of major agricultural and ecological importance, are the widespread arbuscular mycorrhizal symbiosis and the Rhizobium–legume symbiosis. In both symbioses, the specialized host membrane that surrounds the microbes forms a symbiotic interface, which facilitates the exchange of, for example, nutrients in a controlled manner and, therefore, forms the heart of endosymbiosis. Despite their key importance, the molecular and cellular mechanisms underlying the formation of these membrane interfaces are largely unknown. Recent studies strongly suggest that the Rhizobium–legume symbiosis coopted a signaling pathway, including receptor, from the more ancient arbuscular mycorrhizal symbiosis to form a symbiotic interface. Here, we show that two highly homologous exocytotic vesicle-associated membrane proteins (VAMPs) are required for formation of the symbiotic membrane interface in both interactions. Silencing of these Medicago VAMP72 genes has a minor effect on nonsymbiotic plant development and nodule formation. However, it blocks symbiosome as well as arbuscule formation, whereas root colonization by the microbes is not affected. Identification of these VAMP72s as common symbiotic regulators in exocytotic vesicle trafficking suggests that the ancient exocytotic pathway forming the periarbuscular membrane compartment has also been coopted in the Rhizobium–legume symbiosis.
    Forces between clustered stereocilia minimize friction in the ear on a subnanometre scale
    Kozlov, A.S. ; Baumgart, J. ; Risler, T. ; Versteegh, C.P.C. ; Hudspeth, A.J. - \ 2011
    Nature 474 (2011). - ISSN 0028-0836 - p. 376 - 379.
    hair cell stereocilia - transduction channels - mechanical amplification - coherent motion - bundle - membrane
    The detection of sound begins when energy derived from an acoustic stimulus deflects the hair bundles on top of hair cells1. As hair bundles move, the viscous friction between stereocilia and the surrounding liquid poses a fundamental physical challenge to the ear’s high sensitivity and sharp frequency selectivity. Part of the solution to this problem lies in the active process that uses energy for frequency-selective sound amplification2, 3. Here we demonstrate that a complementary part of the solution involves the fluid–structure interaction between the liquid within the hair bundle and the stereocilia. Using force measurement on a dynamically scaled model, finite-element analysis, analytical estimation of hydrodynamic forces, stochastic simulation and high-resolution interferometric measurement of hair bundles, we characterize the origin and magnitude of the forces between individual stereocilia during small hair-bundle deflections. We find that the close apposition of stereocilia effectively immobilizes the liquid between them, which reduces the drag and suppresses the relative squeezing but not the sliding mode of stereociliary motion. The obliquely oriented tip links couple the mechanotransduction channels to this least dissipative coherent mode, whereas the elastic horizontal top connectors that stabilize the structure further reduce the drag. As measured from the distortion products associated with channel gating at physiological stimulation amplitudes of tens of nanometres, the balance of viscous and elastic forces in a hair bundle permits a relative mode of motion between adjacent stereocilia that encompasses only a fraction of a nanometre. A combination of high-resolution experiments and detailed numerical modelling of fluid–structure interactions reveals the physical principles behind the basic structural features of hair bundles and shows quantitatively how these organelles are adapted to the needs of sensitive mechanotransduction.
    Do plastids in Dendrobium cv. Lucky Duan petals function similar to autophagosomes and autolysosomes
    Doorn, W.J. van; Kirasak, K. ; Sonong, A. ; Srihiran, Y. ; Lent, J.W.M. van; Ketsa, S. - \ 2011
    Autophagy 7 (2011)6. - ISSN 1554-8627 - p. 584 - 597.
    acid-phosphatase-activity - cell-death - arabidopsis-thaliana - embryo-suspensor - protein - stromules - membrane - vacuoles - plants - visualization
    In animal cells a double-membrane-bound structure, the autophagosome, encloses a portion of the cytoplasm. The encapsulated material becomes digested after fusion of the autophagosome with a vesicle containing lytic enzymes. The autophagosome is then termed autolysosome. In intact plants, structures similar to animal autophagosomes/autolysosomes have been found only in a few types of cells. Additionally, some early papers indicated that plastids can function similar to autophagosomes/autolysosomes. Here, we report that plastids in Dendrobium cv. Lucky Duan petals produced an endocytosis-like invagination of the two outer membranes. The opening between the invagination space and the cytoplasm was almost isodiametric, less than 0.2 µm in diameter. The volume of the space formed by the invagination had a maximum of about half of the total plastid volume. Staining of the invagination lumen for acid phosphatase, a marker of organelles showing autophagic activity, was positive. Membranes and numerous ribosomes were observed inside the lumen of the invagination. The structure of the material inside the lumen varied from that of the cytoplasm to uniform electron-translucent, indicating that the enclosed cytoplasmic material became completely digested. No support was found for the idea that the material engulfed by the plastid or the whole plastid became transferred to a vacuole. Taken together, the data suggested the hypothesis that plastids in Dendrobium petal mesophyll cells can function in a way similar to both autophagosomes and autolysosomes in animal cells
    Characterization of germination and outgrowth of sorbic acid-stressed Bacillus cereus ATCC 14579 spores: Phenotype and transcriptome analysis
    Melis, C.C.J. van; Nierop Groot, M.N. ; Tempelaars, M.H. ; Moezelaar, R. ; Abee, T. - \ 2011
    Food Microbiology 28 (2011)2. - ISSN 0740-0020 - p. 275 - 283.
    gram-positive bacteria - subtilis spores - vegetative cells - flow-cytometry - organic-acids - cold-shock - membrane - inhibition - genes - identification
    Sorbic acid (SA) is widely used as a preservative, but the effect of SA on spore germination and outgrowth has gained limited attention up to now. Therefore, the effect of sorbic acid on germination of spores of Bacillus cereus strain ATCC 14579 was analyzed both at phenotype and transcriptome level. Spore germination and outgrowth were assessed at pH 5.5 without and with 0.75, 1.5 and 3.0 mM (final concentrations) undissociated sorbic acid (HSA). This resulted in distinct HSA concentration-dependent phenotypes, varying from reduced germination and outgrowth rates to complete blockage of germination at 3.0 mM HSA. The phenotypes reflecting different stages in the germination process could be confirmed using flow cytometry and could be recognized at transcriptome level by distinct expression profiles. In the absence and presence of 0.75 and 1.5 mM HSA, similar cellular ATP levels were found up to the initial stage of outgrowth, suggesting that HSA-induced inhibition of outgrowth is not caused by depletion of ATP. Transcriptome analysis revealed the presence of a limited number of transcripts in dormant spores, outgrowth related expression, and genes specifically associated with sorbic acid stress, including alterations in cell envelope and multidrug resistance. The potential role of these HSA-stress associated genes in spore outgrowth is discussed.
    Effects of ammonium concentration and charge exchange on ammonium recovery from high strength wastewater using a microbial fuel cell
    Kuntke, P. ; Geleij, M. ; Bruning, H. ; Zeeman, G. ; Hamelers, H.V.M. ; Buisman, C.J.N. - \ 2011
    Bioresource Technology 102 (2011)6. - ISSN 0960-8524 - p. 4376 - 4382.
    ion-transport - performance - ph - electrolysis - membrane - toxicity
    Ammonium recovery using a 2 chamber microbial fuel cell (MFC) was investigated at high ammonium concentration. Increasing the ammonium concentration (from 0.07 g to 4 g ammonium-nitrogen/L) by addition of ammonium chloride did not affect the performance of the MFC. The obtained current densities by DC-voltammetry were higher than 6 A/m2 for both operated MFCs. Also continuous operation at lower external resistance (250O) showed an increased current density (0.9 A/m2). Effective ammonium recovery can be achieved by migrational ion flux through the cation exchange membrane to the cathode chamber, driven by the electron production from degradation of organic substrate. The charge transport was proportional to the concentration of ions. Nonetheless, a concentration gradient will influence the charge transport. Furthermore, a charge exchange process can influence the charge transport and therefore the recovery of specific ions.
    Photoelectrochemical control of the balance between cyclic- and linear electron transport in photosystem. I. Algorithm for P700+ induction kinetics
    Vredenberg, W.J. ; Bulychev, A.A. - \ 2010
    Biochimica et Biophysica Acta. B, Bioenergetics 1797 (2010)8. - ISSN 0005-2728 - p. 1521 - 1532.
    a fluorescence induction - far-red light - p515 response - c3 plants - leaves - flow - chloroplasts - quantification - membrane - energy
    Redox transients of chlorophyll P700, monitored as absorbance changes DeltaA810, were measured during and after exclusive PSI excitation with far-red (FR) light in pea (Pisum sativum, cv. Premium) leaves under various pre-excitation conditions. Prolonged adaptation in the dark terminated by a short PSII+PSI- exciting light pulse guarantees pre-conditions in which the initial photochemical events in PSI RCs are carried out by cyclic electron transfer (CET). Pre-excitation with one or more 10s FR pulses creates conditions for induction of linear electron transport (LET). These converse conditions give rise to totally different, but reproducible responses of P700- oxidation. System analyses of these responses were made based on quantitative solutions of the rate equations dictated by the associated reaction scheme for each of the relevant conditions. These provide the mathematical elements of the P700 induction algorithm (PIA) with which the distinguishable components of the P700+ response can be resolved and interpreted. It enables amongst others the interpretation and understanding of the characteristic kinetic profile of the P700+ response in intact leaves upon 10s illumination with far-red light under the promotive condition for CET. The system analysis provides evidence that this unique kinetic pattern with a non-responsive delay followed by a steep S-shaped signal increase is caused by a photoelectrochemically controlled suppression of the electron transport from Fd to the PQ-reducing Qr site of the cytb6f complex in the cyclic pathway. The photoelectrochemical control is exerted by the PSI-powered proton pump associated with CET. It shows strong similarities with the photoelectrochemical control of LET at the acceptor side of PSII which is reflected by release of photoelectrochemical quenching of chlorophyll a fluorescence
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