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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    Bowel Biofilms: Tipping Points between a Healthy and Compromised Gut?
    Tytgat, Hanne L.P. ; Nobrega, Franklin L. ; Oost, John van der; Vos, Willem M. de - \ 2019
    Trends in Microbiology 27 (2019)1. - ISSN 0966-842X - p. 17 - 25.
    biofilm - colorectal cancer - microbiota - tipping points

    Bacterial communities are known to impact human health and disease. Mixed species biofilms, mostly pathogenic in nature, have been observed in dental and gastric infections as well as in intestinal diseases, chronic gut wounds and colon cancer. Apart from the appendix, the presence of thick polymicrobial biofilms in the healthy gut mucosa is still debated. Polymicrobial biofilms containing potential pathogens appear to be an early-warning signal of developing disease and can be regarded as a tipping point between a healthy and a diseased state of the gut mucosa. Key biofilm-forming pathogens and associated molecules hold promise as biomarkers. Criteria to distinguish microcolonies from biofilms are crucial to provide clarity when reporting biofilm-related phenomena in health and disease in the gut.

    Emergent strategies for detection and control of biofilms in food processing environments
    Besten, H.M.W. den; Ding, Y. ; Abee, T. ; Liang, Yang - \ 2016
    In: Advances in Food Biotechnology / Rai V, Ravishankar, Chichester, UK : John Wiley and Sons - ISBN 9781118864555
    biofilm - resistance - detection - control - dispersal
    Biofilms are dense surface-attached microbial communities consisting of bacterial colonies embedded in their self-generated matrix materials. Different bacteria species that exist within a biofilm are positioned within many different microenvironments defined by nutrient availability, pH and oxygen levels. To adapt to these myriad niches, bacteria therefore show numerous phenotypes and enormous metabolic and replicative heterogeneity. This heterogeneity provides the biofilm community with great capacity to withstand challenges. Biofilms formed in the food-processing environments cause recalcitrant contaminations and food spoilage, which pose a huge threat to public health. The distinct physiology and slow growth rate of biofilm cells hinder the detection of biofilms hidden in the food-processing environments. Conventional cleaning and disinfecting strategies could be ineffective to eradicate biofilms. The present chapter will focus on describing the latest strategies for detection and control of biofilms in food-processing environments.
    Microbial stratification in low pH oxic and suboxic macroscopic growths along an acid mine drainage
    Méndez-Garcia, C. ; Mesa, V. ; Sprenger, R.R. ; Richter, M. ; Suarez Diez, M. ; Solano, J. ; Bargiela, R. ; Golyshina, O.V. ; Manteca, A. ; Ramos, J.L. ; Gallego, J.R. ; Llorente, I. ; Martins Dos Santos, V.A.P. ; Jensen, O.N. ; Paláez, A.I. ; Sánchez, J. ; Ferrer, M. - \ 2014
    ISME Journal 8 (2014). - ISSN 1751-7362 - p. 1259 - 1274.
    acidophile acidithiobacillus-ferrivorans - community genomic analysis - 16s ribosomal-rna - rio-tinto - metal-rich - anaerobic sediments - oxidizing bacteria - fam. nov - diversity - biofilm
    Macroscopic growths at geographically separated acid mine drainages (AMDs) exhibit distinct populations. Yet, local heterogeneities are poorly understood. To gain novel mechanistic insights into this, we used OMICs tools to profile microbial populations coexisting in a single pyrite gallery AMD (pH ~2) in three distinct compartments: two from a stratified streamer (uppermost oxic and lowermost anoxic sediment-attached strata) and one from a submerged anoxic non-stratified mat biofilm. The communities colonising pyrite and those in the mature formations appear to be populated by the greatest diversity of bacteria and archaea (including 'ARMAN' (archaeal Richmond Mine acidophilic nano-organisms)-related), as compared with the known AMD, with ~44.9% unclassified sequences. We propose that the thick polymeric matrix may provide a safety shield against the prevailing extreme condition and also a massive carbon source, enabling non-typical acidophiles to develop more easily. Only 1 of 39 species were shared, suggesting a high metabolic heterogeneity in local microenvironments, defined by the O2 concentration, spatial location and biofilm architecture. The suboxic mats, compositionally most similar to each other, are more diverse and active for S, CO2, CH4, fatty acid and lipopolysaccharide metabolism. The oxic stratum of the streamer, displaying a higher diversity of the so-called 'ARMAN'-related Euryarchaeota, shows a higher expression level of proteins involved in signal transduction, cell growth and N, H2, Fe, aromatic amino acids, sphingolipid and peptidoglycan metabolism. Our study is the first to highlight profound taxonomic and functional shifts in single AMD formations, as well as new microbial species and the importance of H2 in acidic suboxic macroscopic growths
    pH and Temperature Determine Performance of Oxygen Reducing Biocathodes
    Strik, D.P.B.T.B. ; picot, M. ; Buisman, C.J.N. ; Barrière, F. - \ 2013
    Electroanalysis 25 (2013)3. - ISSN 1040-0397 - p. 652 - 655.
    microbial fuel-cells - bioelectrochemical systems - electricity production - reduction - biofilm - catalysis - cathodes - bacteria - water
    In this paper we investigate the performance of oxygen reducing biocathodes for microbial fuel cells in relation to temperature and pH. Lower pH does likely improve biocatalytic activity and/or proton availability, and results in higher current. Lower temperature does reduce biocatalytic activity and does not reduce possible oxygen mass transfer limitations. The cathode resistance was in the same order of magnitude at pH 5 to 7 which shows that MFC energy recovery can be higher at lower pH. Overall, these results show that oxygen reducing biocathodes are robust at 660 mA per m2 at +0.15 V vs. Ag/AgCl, pH 5 and 31¿°C.
    Resilience of roof-top Plant-Microbial Fuel Cells during Dutch winter
    Helder, M. ; Strik, D.P.B.T.B. ; Timmers, R.A. ; Reas, S.M.T. ; Hamelers, H.V.M. ; Buisman, C.J.N. - \ 2013
    Biomass and Bioenergy 51 (2013). - ISSN 0961-9534 - p. 1 - 7.
    time-domain reflectometry - electricity production - temperature - performance - biofilm
    The Plant-Microbial Fuel Cell (P-MFC) is in theory a technology that could produce sustainable electricity continuously. We operated two designs of the P-MFC under natural roof-top conditions in the Netherlands for 221 days, including winter, to test its resilience. Current and power densities are not stable under outdoor conditions. Highest obtained power density was 88 mW m-2, which is lower than was achieved under lab-conditions (440 mW m-2). Cathode potential was in our case dependent on solar radiation, due to algae growth, making the power output dependent on a diurnal cycle. The anode potential of the P-MFC is influenced by temperature, leading to a decrease in electricity production during low temperature periods and no electricity production during frost periods. Due to freezing of the roots, plants did not survive winter and therefore did not regrow in spring. In order to make a sustainable, stable and weather independent electricity production system of the P-MFC attention should be paid to improving cathode stability and cold insulation of anode and cathode. Only when power output of the Plant-Microbial Fuel Cell can be increased under outdoor conditions and plant-vitality can be sustained over winter, it can be a promising sustainable electricity technology for the future
    The impact of metal transport processes on bioavailability of free and complex metal ions in methanogenic granular sludge
    Bartacek, J. ; Fermoso, F.G. ; Vergeldt, F. ; Gerkema, E. ; Maca, J. ; As, H. van; Lens, P.N.L. - \ 2012
    Water Science and Technology 65 (2012)10. - ISSN 0273-1223 - p. 1875 - 1881.
    afvalwaterbehandeling - bioreactoren - anaërobe omstandigheden - korrelslib - biologische beschikbaarheid - metalen - toxiciteit - kernspintomografie - waste water treatment - bioreactors - anaerobic conditions - granular sludge - bioavailability - metals - toxicity - magnetic resonance imaging - magnetic-resonance - dynamics - immobilization - biofilm - nickel
    Bioavailability of metals in anaerobic granular sludge has been extensively studied, because it can have a major effect on metal limitation and metal toxicity to microorganisms present in the sludge. Bioavailability of metals can be manipulated by bonding to complexing molecules such as ethylenediaminetetraacetate (EDTA) or diethylenetriaminepentaacetate (DTPA). It has been shown that although the stimulating effect of the complexed metal species (e.g. [CoEDTA]2-) is very fast, it is not sustainable when applied to metal-limited continuously operated reactors. The present paper describes transport phenomena taking place inside single methanogenic granules when the granules are exposed to various metal species. This was done using magnetic resonance imaging (MRI). The MRI results were subsequently related to technological observations such as changes in methanogenic activity upon cobalt injection into cobalt-limited up-flow anaerobic sludge blanket (UASB) reactors. It was shown that transport of complexed metal species is fast (minutes to tens of minutes) and complexed metal can therefore quickly reach the entire volume of the granule. Free metal species tend to interact with the granular matrix resulting in slower transport (tens of minutes to hours) but higher final metal concentrations.
    Identifying charge and mass transfer resistances of an oxygen reducing biocathode
    Heijne, A. ter; Schaetzle, O. ; Gimenez, S. ; Fabregat-Santiago, F. ; Bisquert, J. ; Strik, D.P.B.T.B. ; Barrière, F. ; Buisman, C.J.N. ; Hamelers, H.V.M. - \ 2011
    Energy & Environmental Science 4 (2011)12. - ISSN 1754-5692 - p. 5035 - 5043.
    microbial fuel-cells - anode-respiring bacteria - performance - electrodes - biofilm - mechanism - graphite - model
    this study, we identified mass and charge transfer resistances for an oxygen reducing biocathode in a microbial fuel cell (MFC) by electrochemical impedance spectroscopy (EIS). The oxygen reducing biocathode was grown using nitrifying sludge as the inoculum. A standard model for charge transfer at the electrode surface combined with diffusion across a boundary layer was used. EIS measurements were performed under variation of both linear flow velocities and cathode potentials. Fitting the impedance data to the standard model at constant potential and different flow rates confirmed that increasing flow rate had no effect on charge transfer resistance, but led to a decrease in mass transfer resistance. From the variation in cathode potential at constant flow rate, a minimum in charge transfer resistance was found at 0.28 V vs. Ag/AgCl. The minimum in charge transfer resistance could be explained by the combined biochemical and electrochemical kinetics typical for bioelectrochemical systems.
    Electricity-Assisted Biological Hydrogen Production from Acetate by Geobacter sulfurreducens
    Geelhoed, J.S. ; Stams, A.J.M. - \ 2011
    Environmental Science and Technology 45 (2011)2. - ISSN 0013-936X - p. 815 - 820.
    microbial electrolysis cells - fuel-cells - fe(iii) oxide - electrodes - reduction - perspective - cathodes - biofilm
    Geobacter sulfurreducens is a well-known current-producing microorganism in microbial fuel cells, and is able to use acetate and hydrogen as electron donor. We studied the functionality of G. sulfurreducens as biocatalyst for hydrogen formation at the cathode of a microbial electrolysis cell (MEC). Geobacter sulfurreducens was grown in the bioelectrode compartment of a MFC with acetate as the substrate and reduction of complexed Fe(III) at the counter electrode. After depletion of the acetate the electrode potential of the bioelectrode was decreased stepwise to -1.0 V vs Ag/AgCl reference. Production of negative current was observed, which increased in time, indicating that the bioelectrode was now acting as biocathode. Headspace analyses carried out at electrode potentials ranging from -0.8 to -1.0 V showed that hydrogen was produced, with higher rates at more negative cathode potentials. Subsequently, the metabolic properties of G. sulfurreducens for acetate oxidation at the anode and hydrogen production at the cathode were combined in one-compartment membraneless MECs operated at applied voltages of 0.8 and 0.65 V. After two days, current densities were 0.44 A m(-2) at 0.8 V applied voltage and 0.22 A m(-2) at 0.65 V, using flat-surface carbon electrodes for both anode and cathode. The cathodic hydrogen recovery ranged from 23% at 0.5 V applied voltage to 43% at 0.9 V
    Polyurethane rotating disc system for post-treatment of anaerobically pre-treated sewage
    Tawfik, A. ; Klapwijk, A. - \ 2010
    Journal of Environmental Management 91 (2010)5. - ISSN 0301-4797 - p. 1183 - 1192.
    municipal waste-water - biological contactor rbc - domestic sewage - nitrogen removal - escherichia-coli - bacteria - effluent - biofilm - feasibility - performance
    The performance of polyurethane rotating discs (RBC-1) versus polystyrene rotating discs (RBC-2) for the treatment of an up-flow anaerobic sludge blanket (UASB) reactor effluent fed with domestic wastewater was investigated. Both RBC units were operated at the same organic loading rate (OLR) of 10.5 gCOD/m(2) d. and a hydraulic retention time (HRT) of 2.5 h. The residual values of COD fractions (CODsuspended, CODcolloidal and CODsoluble) in the treated effluent of RBC-1 and RBC-2 were similar. However, the removal efficiency of ammonia in the RBC-1 (87 +/- 4%) was significantly higher than that found for RBC-2 i.e. 24 +/- 6%. Moreover, RBC-1 achieved a substantial removal efficiency of 99.0 +/- 1% for Escherichia colt (E. coli), while RBC-2 removed 91.2 +/- 0.3%. Based on these results, optimization of RBC-1 treating UASB reactor effluent was extensively performed. The RBC-1 was operated at an OLR's of 4.0, 11 and 23 gCOD/m(2) d. The results obtained showed that increasing the OLR from 11.0 to 23.0 gCOD/m(2) d and decreasing the HRT from 2.5 to 1.25 h significantly declined the effluent quality of CODtotal and ammonia. However, the residual values of CODtotal and ammonia remained unaffected when increasing the OLR from 4.0 to 11.0 gCOD/m(2) d and by decreasing the HRT from 5 to 2.5 h. Bacteriological examination showed that the mean residual count of E. coli remained at a level of 10(4)/100 ml, in the effluent of RBC-1 independent on the imposed HRT. Accordingly, it is recommended to operate RBC-1 for treatment of anaerobically pre-treated sewage at an OLR of 11 gCOD/m(2) d and an HRT of 2.5 h. A feed-less (ammonia limitation) period of 9.0 days followed by 9.0 days feeding with high OLR of 26 gCOD/m(2) d. (raw sewage) was investigated to elaborate, if the nitrifiers of the RBC-1 are capable to convert ammonia to nitrate after totally 18 days when retuning back to the normal operating conditions. The results of the experiment clearly show a strong and immediate detrimental effect of imposing high OLR of 26 gCOD/m(2) d on the nitrification process in the nitrifying RBC unit. However, after returning back to the original OLR of 10.6 gCOD/m(2) d, the nitrification efficiency in the RBC unit was recovered within 2-3 days.
    Stabilizing the baseline current of a microbial fuel cell-based biosensor through overpotential control under non-toxic conditions
    Stein, N.E. ; Hamelers, H.V.M. ; Buisman, C.J.N. - \ 2010
    Bioelectrochemistry 78 (2010)1. - ISSN 1567-5394 - p. 87 - 91.
    oxygen-demand sensor - bod sensor - performance - generation - biofilm
    A MFC-based biosensor can act as online toxicity sensor Electrical current is a direct linear measure for metabolic activity of electrochemically active microorganisms Microorganisms gain energy from anodic overpotential and current strongly depends on anodic overpotential Therefore control of anodic overpotential is necessary to detect toxic events and prevent false positive alarms Anodic overpotential and thus current is influenced by anode potential. pH. substrate and bicarbonate concentrations In terms of overpotential all factor showed a comparable effect, anode potential 1.2% change in current density per mV, pH 0.43%/mV, bicarbonate 0.75%/mV and acetate 0.8%/mV At acetate saturation the maximum acetate conversion rate is reached and with that a constant bicarbonate concentration Control of acetate and bicarbonate concentration can be less strict than control of anode potential and pH Current density changes due to changing anode potential and pH are in the same order of magnitude as changes due to toxicity Strict control of pH and anode potential in a small range is required The importance of anodic overpotential control for detection of toxic compounds is shown To reach a stable baseline current under nontoxic conditions a MFC-based biosensor should be operated at controlled anode potential, controlled pH and saturated substrate concentrations (C) 2009 Elsevier B.V All rights reserved
    Solar energy powered microbial fuel cell with a reversible bioelectrode
    Strik, D.P.B.T.B. ; Hamelers, H.V.M. ; Buisman, C.J.N. - \ 2010
    Environmental Science and Technology 44 (2010)1. - ISSN 0013-936X - p. 532 - 537.
    cathodic oxygen reduction - electricity-generation - ion-transport - waste-water - performance - membrane - bacteria - biofilm - anode - ph
    The solar energy powered microbial fuel cell is an emerging technology for electricity generation via electrochemically active microorganisms fueled by solar energy via in situ photosynthesized metabolites from algae, cyanobacteria, or living higher plants. A general problem with microbial fuel cells is the pH membrane gradient which reduces cell voltage and power output. This problem is caused by acid production at the anode, alkaline production at the cathode, and the nonspecific proton exchange through the membrane. Here we report a solution for a new kind of solar energy powered microbial fuel cell via development of a reversible bioelectrode responsible for both biocatalyzed anodic and cathodic electron transfer. Anodic produced protons were used for the cathodic reduction reaction which held the formation of a pH membrane gradient. The microbial fuel cell continuously generated electricity and repeatedly reversed polarity dependent on aeration or solar energy exposure. Identified organisms within biocatalyzing biofilm of the reversible bioelectrode were algae, (cyano)bacteria and protozoa. These results encourage application of solar energy powered microbial fuel cells.
    Cathode potential and mass transfer determine performance of oxygen reducing biocathodes in microbial fuel cells
    Heijne, A. ter; Strik, D.P.B.T.B. ; Hamelers, H.V.M. ; Buisman, C.J.N. - \ 2010
    Environmental Science and Technology 44 (2010)18. - ISSN 0013-936X - p. 7151 - 7156.
    biofilm - reduction - graphite - anodes
    The main limiting factor in Microbial Fuel Cell (MFC) power output is the cathode, because of the high overpotential for oxygen reduction. Oxygen reducing biocathodes can decrease this overpotential by the use of microorganisms as a catalyst. In this study, we investigated the factors limiting biocathode performance. Three biocathodes were started up at different cathode potentials, and their performance and catalytic behavior was tested by means of polarization curves and cyclic voltammetry. The biocathodes controlled at +0.05 V and +0.15 V vs Ag/AgCl produced current almost immediately after inoculation, while the biocathode controlled at +0.25 V vs Ag/AgCl produced no current until day 15. The biocathode controlled at +0.15 V vs Ag/AgCl reached the highest current density of 313 mA/m2. Cyclic voltammetry showed clear catalysis for all three biocathodes. The biocathodes were limited by both mass transfer of oxygen and by charge transfer. Mass transfer calculations show that the transfer of oxygen poses a serious limitation for the use of dissolved oxygen as an electron acceptor in MFCs.
    Chemodynamics and bioavailability in natural waters
    Buffle, J. ; Wilkinson, K.J. ; Leeuwen, H.P. van - \ 2009
    Environmental Science and Technology 43 (2009)19. - ISSN 0013-936X - p. 7170 - 7174.
    dynamic speciation - nutrient uptake - metal flux - diffusion - transport - limitation - complexes - bacteria - biofilm - systems
    Magnetic resonance microscopy of iron transport in methanogenic granules
    Bartacek, J. ; Vergeldt, F.J. ; Gerkema, E. ; Jenicek, P. ; Lens, P. ; As, H. van - \ 2009
    Journal of Magnetic Resonance 200 (2009)2. - ISSN 1090-7807 - p. 303 - 312.
    heavy-metal uptake - porous-media - nmr - biofilm - sludge - diffusion - complexes - alginate - immobilization - biosorbents
    Interactions between anaerobic biofilms and heavy metals such as iron, cobalt or nickel are largely unknown. Magnetic resonance imaging (MRI) is a non-invasive method that allows in situ studies of metal transport within biofilm matrixes. The present study investigates quantitatively the penetration of iron (1.75 mM) bound to ethylenediaminetetraacetate (EDTA) into the methanogenic granules (spherical biofilm). A spatial resolution of 109 × 109 × 218 µm3 and a temporal resolution of 11 min are achieved with 3D Turbo Spin Echo (TSE) measurements. The longitudinal relaxivity, i.e. the slope the dependence of the relaxation rate (1/T1) on the concentration of paramagnetic metal ions, was used to measure temporal changes in iron concentration in the methanogenic granules. It took up to 300 min for the iron–EDTA complex ([FeEDTA]2-) to penetrate into the methanogenic granules (3–4 mm in diameter). The diffusion was equally fast in all directions with irregularities such as diffusion-facilitating channels and diffusion-resistant zones. Despite these irregularities, the overall process could be modeled using Fick’s equations for diffusion in a sphere, because immobilization of [FeEDTA]2- in the granular matrix (or the presence of a reactive barrier) was not observed. The effective diffusion coefficient (Dejf) of [FeEDTA]2- was found to be 2.8 × 10-11 m2 s-1, i.e. approximately 4% of Dejf of [FeEDTA]2- in water. The Fickian model did not correspond to the processes taking place in the core of the granule (3–5% of the total volume of the granule), where up to 25% over-saturation by iron (compare to the concentration in the bulk solution) occurred
    Bacterial factors influencing adhesion of Pseudomonas aeruginosa strains to a poly(ethylene oxide) brush
    Roosjen, A. ; Busscher, H.J. ; Norde, W. ; Mei, H.C. van der - \ 2006
    Microbiology 152 (2006)9. - ISSN 1350-0872 - p. 2673 - 2682.
    streptococcus-mitis strains - staphylococcus-epidermidis - microbial adhesion - glass surfaces - cell-surfaces - polymers - inhibition - attachment - biofilm - steps
    Most bacterial strains adhere poorly to poly(ethylene oxide) (PEO)-brush coatings, with the exception of a Pseudomonas aeruginosa strain. The aim of this study was to find factors determining whether P. aeruginosa strains do or do not adhere to a PEO-brush coating in a parallel plate flow chamber. On the basis of their adhesion, a distinction could be made between three adhesive and three non-adhesive strains of P. aeruginosa, while bacterial motilities and zeta potentials were comparable for all six strains. However, water contact angles indicated that the adhesive strains were much more hydrophobic than the non-adhesive strains. Furthermore, only adhesive strains released surfactive extracellular substances, which may be engaged in attractive interactions with the PEO chains. Atomic force microscopy showed that the adhesion energy, measured from the retract curves of a bacterial-coated cantilever from a brush coating, was significantly more negative for adhesive strains than for non-adhesive strains (P
    A bipolar membrane combined with ferric iron reduction as an efficient cathode system in microbial fuel cells
    Heijne, A. ter; Hamelers, H.V.M. ; Wilde, V. de; Rozendal, R.A. ; Buisman, C.J.N. - \ 2006
    Environmental Science and Technology 40 (2006)17. - ISSN 0013-936X - p. 5200 - 5205.
    electricity-generation - ferrous iron - thiobacillus-ferrooxidans - oxygen reduction - mediator-less - biofuel cell - oxidation - biofilm - reactor - water
    There is a need for alternative catalysts for oxygen reduction in the cathodic compartment of a microbial fuel cell (MFC). In this study, we show that a bipolar membrane combined with ferric iron reduction on a graphite electrode is an efficient cathode system in MFCs. A flat plate MFC with graphite felt electrodes, a volume of 1.2 L and a projected surface area of 290 cm2 was operated in continuous mode. Ferric iron was reduced to ferrous iron in the cathodic compartment according to Fe3+ + e- Fe2+ (E0 = +0.77 V vs NHE, normal hydrogen electrode). This reversible electron transfer reaction considerably reduced the cathode overpotential. The low catholyte pH required to keep ferric iron soluble was maintained by using a bipolar membrane instead of the commonly used cation exchange membrane. For the MFC with cathodic ferric iron reduction, the maximum power density was 0.86 W/m2 at a current density of 4.5 A/m2. The Coulombic efficiency and energy recovery were 80-95% and 18-29% respectively
    Characterization of the surface of protein-adsorbed dental materials by wetting and streaming potential measurements
    Matsumura, H. ; Kawasaki, K. ; Okumura, N. ; Kambara, M. ; Norde, W. - \ 2003
    Colloids and Surfaces. B: Biointerfaces 32 (2003)2. - ISSN 0927-7765 - p. 97 - 103.
    in-vitro - dynamic method - biofilm - enamel - hydroxyapatite - interfaces - adsorption
    In this study we have elucidated the water-wettability and the electrokinetic surface potential of protein-covered dental materials. The proteins used here as typical proteins were human serum albumin and lysozyme from hen*s egg. The wettability (hydrophobicity/hydrophilicity) and the surface potential may dominate bacterial adhesion on the tooth materials and hence influence their biological activity. The artificial tooth materials we investigated were platinum-gold alloy, porcelain and dental resin. Hydroxyapatite was chosen as a reference reflecting natural tooth surface. The wetting was measured by the dropping time method of a thin liquid film along the surface of a protein-covered solid plate sample. The zeta potential was derived from the streaming potential invoked by flowing an electrolyte solution between two parallel sample plates. A variety of surface properties have been found for different combinations of protein and dental material.
    The effects of periphyton, fish and fertilizer dose on biological processes affecting water quality in earthen fish ponds.
    Milstein, A. ; Azim, M.E. ; Wahab, M.A. ; Verdegem, M.C.J. - \ 2003
    Environmental Biology of Fishes 68 (2003)3. - ISSN 0378-1909 - p. 247 - 260.
    indian major carps - aquaculture - culture - hamilton - polyculture - biofilm
    The potential of periphyton-based aquaculture in South Asia is under investigation in an extensive research program. This paper is a further analysis of data from four experiments carried out in that framework, to explore periphyton, fish and fertilizer dose effects on water quality. Factor analysis and ANOVA models applied to a data matrix of water quality parameters in ponds with and without artificial substrates (bamboo poles and kanchi sticks), with and without fish (filter feeders catla and rohu, with and without bottom feeder kalbaush), and with a standard or 50% increased fertilizer dose, allowed us to identify the underlying ecological processes governing this novel periphyton-based pond system, and construct conceptual graphic models of the periphyton-environment relationships observed. We clearly established that the phosphorus flow is mainly linked to phytoplankton activity in the water column and decomposition on the pond bottom, while nitrogen flow is mainly linked to autotrophic (photosynthesis) and heterotrophic (decomposition and nitrification) processes that take place in the periphyton in addition to the water column and pond bottom. Consequently, disruption of the pond bottom by bottom feeding fish primarily promoted phosphate cycling and phytoplankton, while periphyton development on the supplied substrates and fertilization mainly improved oxygen balance and nitrogen related processes developing in the water column. The use of bamboo poles led to better results than kanchi sticks, related to the greater autotrophic periphyton development on bamboo and to the larger surface of bamboo poles that facilitate fish grazing and periphyton dislodgment that in turn have a renewal effect on periphyton. Stocking bottom feeding fish produces a fertilizing effect through the food web that benefits the filter-feeding fish and that makes it unnecessary to increase the dose of inorganic and organic fertilizers applied to the ponds. Thus, the output of this analysis will help the fish farmers in resource constrained countries to improve their production in periphyton-based ponds just by choosing bamboo substrates, stocking a bottom feeder fish together with the filter feeders, and saving money on fertilizers.
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