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.

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    Partitioning of humic acids between aqueous solution and hydrogel. 3. Microelectrodic dynamic speciation analysis of free and bound humic metal complexes in the gel phase
    Yasadi, K. ; Pinheiro, J.P. ; Zielinska, K. ; Town, R.M. ; Leeuwen, H.P. van - \ 2015
    Langmuir 31 (2015)5. - ISSN 0743-7463 - p. 1737 - 1745.
    dissolved organic-matter - stability-constants - alginate gel - thin-films - adsorption - ions - fluorescence - substances - cells - soil
    The hydrogel/water partitioning of the various species in the cadmium(II)/soil humic acid (HA) system is studied for two types of gel, using in situ microelectrodic voltammetry. Under the conditions of this work, with HA particles of ca. 25 and 125 nm radius, the CdHA complex is shown to be close to nonlabile toward a 12.5 µm radius microelectrode. This implies that its kinetic contribution to Cd2+ reduction at the medium/microelectrode interface is practically negligible. The polyacrylamide (PAAm) gels equilibrate with the aqueous medium under significant sorption of HA at the gel backbone/gel medium interface, which in turn leads to induced sorption of Cd(II) in the form of immobilized gel-bound CdHA. The rather high total Cd content of the PAAm gel suggests that the binding of Cd2+ by the hydrophobically gel-bound HA is stronger than that for dispersed HA particles. Still, the intraparticulate speciation of Cd(II) over Cd2+ and CdHA corresponds to an intrinsic stability constant similar to that for simple monocarboxylate ligands such as acetate. Alginate gels are negatively charged, and their free [Cdaq2+] is higher than that in the medium by the corresponding Donnan coefficient. On top of that, Cd2+ is specifically sorbed by the gel backbone/gel medium interface to reach accumulation factors as high as a few tens. HA and CdHA accumulate in the outer 20 µm film of gel at the gel/water interface of both gels, but they do not penetrate into the bulk of the alginate gel. Overall, the gel/water interface dictates drastic changes in the speciation of Cd/HA as compared to the aqueous medium, with distinct features for each individual type of gel. The results have broad significance, for example, for predictions of reactivity and bioavailability of metal species which inherently involve partitioning and diffusion into diverse gel layers such as biointerfacial cell walls, biofilm matrices, and mucous membranes.
    Partitioning of humic acids between aqueous solution and hydrogel. 2. Impact of physicochemical conditions
    Zielinska, K. ; Town, R.M. ; Yasadi, K. ; Leeuwen, H.P. van - \ 2015
    Langmuir 31 (2015)1. - ISSN 0743-7463 - p. 283 - 291.
    ionic-strength - alginate gel - heavy-metals - fluorescence - substances - ph - aggregation - media - soil - spectroscopy
    The effects of the physicochemical features of aqueous medium on the mode of partitioning of humic acids (HAs) into a model biomimetic gel (alginate) and a synthetic polyacrylamide gel (PAAm) were explored. Experiments were performed under conditions of different pH and ionic strength as well as in the presence or absence of complexing divalent metal ions. The amount of HA penetrating the gel phase was determined by measuring its natural fluorescence by confocal laser scanning microscopy. In both gel types, the accumulation of HA was spatially heterogeneous, with a much higher concentration located within a thin film at the gel surface. The thickness of the surface film (ca. 15 µm) was similar for both types of gel and practically independent of pH, ionic strength, and the presence of complexing divalent metal ions. The extent of HA accumulation was found to be dependent on the composition of the medium and on the type of gel. Significantly more HA was accumulated in PAAm gel as compared to that in alginate gel. In general, more HA was accumulated at lower background salt concentration levels. The distribution of different types of HA species in the gel body was linked to their behavior in the medium and the differences in physicochemical conditions inside the two phases.
    Effect of Selected Plant Extracts and D- and L-Lysine on the Cyanobacterium Microcystis aeruginosa
    Lurling, M.F.L.L.W. ; Oosterhout, J.F.X. - \ 2014
    Water 6 (2014)6. - ISSN 2073-4441 - p. 1807 - 1825.
    moringa-oleifera seeds - controlling eutrophication - fresh-water - amino-acid - blooms - coagulation - inhibition - mechanism - substances - phosphorus
    We tested extracts from Fructus mume, Salvia miltiorrhiza and Moringa oleifera as well as L-lysine and D-Lysine as curative measures to rapidly suppress the cyanobacterium Microcystis aeruginosa NIVA-CYA 43. We tested these compounds under similar conditions to facilitate comparisons. We hypothesized that for each compound, relatively low concentrations—i.e., 5–50 mg L-1, would reduce M. aeruginosa biomass. At these low concentrations, only L-lysine caused a decline in M. aeruginosa biomass at =4.3 mg L-1. F. mume extract was effective to do so at high concentrations, i.e., at =240 mg L-1, but the others were virtually non-effective. Low pH caused by organic acids is a probable explanation for the effect of F. mume extract. No complete wipe-outs of the experimental population were achieved as Photosystem II efficiency showed a recovery after six days. L-lysine may be effective at low concentrations—meaning low material costs. However, the effect of L-lysine seems relatively short-lived. Overall, the results of our study did not support the use of the tested plant extracts and amino-acid as promising candidates for curative application in M. aeruginosa bloom control.
    Partitioning of humic acids between aqueous solution and hydrogel: Concentration profiling of humic acids in hydrogel phases.
    Zielinska, K. ; Town, R.M. ; Yasadi, K. ; Leeuwen, H.P. van - \ 2014
    Langmuir 30 (2014)8. - ISSN 0743-7463 - p. 2084 - 2092.
    natural organic-matter - fluorescence correlation spectroscopy - diffusion-coefficients - mineral particles - ionic-strength - alginate gel - fulvic-acid - substances - adsorption - soil
    The partitioning of the natural polyelectrolyte humic acid (HA) from an aqueous dispersion into a model biomimetic gel (alginate) and a synthetic polyacrylamide gel (PAAm) is explored. In both gels, the spatial distribution of HA in the gel body, as measured by confocal laser scanning microscopy, is markedly nonhomogeneous. A striking feature is the enhanced accumulation of HA in a thin film of thickness ca. 15 µm at the surface of the gel body, resulting in average local concentrations that are, for PAAm and alginate respectively, a factor of 10 and 4 greater than that in the bulk solution. The time dependence of accumulation in the surface film is predominantly controlled by the diffusive supply of HA from the aqueous medium, with a time constant on the order of 103 s for both gels. The concentration of HA within the bulk gel body differs significantly from that in the bulk aqueous medium: substantially higher for PAAm but much lower for alginate. The results are significant for understanding the nature and rate of sink/source functioning at permeable phases in contact with aqueous media, e.g., biofilms and gel-like layers at biological interfaces or employed in chemical speciation sensors.
    Lead binding to soil fulvic and humic acids: NICA-Donnan modeling and XAFS spectroscopy
    Xiong, J. ; Koopal, L.K. ; Tan, W. ; Fang, L. ; Wang, W. ; Zhao, W. ; Liu, T. ; Zhang, J. ; Weng, L. - \ 2013
    Environmental Science and Technology 47 (2013)20. - ISSN 0013-936X - p. 11634 - 11642.
    natural organic-matter - metal-ion binding - conditional affinity spectra - ombrotrophic peat bog - proton binding - chemical-composition - contaminated soils - cation-binding - molecular-size - substances
    Binding of lead (Pb) to soil fulvic acid (JGFA), soil humic acids (JGHA, JLHA), and lignite-based humic acid (PAHA) was investigated through binding isotherms and XAFS. Pb binding to humic substances (HS) increased with increasing pH and decreasing ionic strength. The NICA-Donnan model described Pb binding to the HS satisfactorily. The comparison of the model parameters showed substantial differences in median Pb affinity constants among JGFA, PAHA, and the soil HAs. Milne’s “generic” parameters did not provide an adequate prediction for the soil samples. The Pb binding prediction with generic parameters for the soil HAs was improved significantly by using the value nPb1 = 0.92 instead of the generic value nPb1 = 0.60. The nPb1/nH1 ratios obtained were relatively high, indicating monodentate Pb binding to the carboxylic-type groups. The nPb2/nH2 ratios depended somewhat on the method of optimization, but the values were distinctly lower than the nPb1/nH1 ratios, especially when the optimization was based on Pb bound vs log [Pb2+]. These low values indicate bidentate binding to the phenolic-type groups at high Pb concentration. The NICA-Donnan model does not consider bidentate binding of Pb to a carboxylic- and a phenolic-type group. The EXAFS results at high Pb loading testified that Pb was bound in bidentate complexes of one carboxylic and one phenolic group (salicylate-type) or two phenolic groups (catechol-type) in ortho position.
    Influence of soil humic and fulvic acid on the activity and stability of lysozyme and urease
    Li, Y. ; Tan, W. ; Koopal, L.K. ; Wang, M. ; Liu, Fan ; Norde, W. - \ 2013
    Environmental Science and Technology 47 (2013). - ISSN 0013-936X - p. 5050 - 5056.
    isothermal titration calorimetry - insecticidal cry1ab protein - ionic-strength - prion protein - ph - adsorption - complexes - binding - substances - fractions
    Humic substances (HS), including humic acids (HA) and fulvic acids (FA), are important components of soil systems. HS form strong complexes with oppositely charged proteins, which will lead to changes in the enzyme activity. The effect of soil HS on the activity and stability of two enzymes was investigated as a function of pH, ionic strength, and mass ratio HS/enzyme. Humic acid (JGHA) and fulvic acid (JGFA) are negatively charged, lysozyme is net positive at pH values below 10.4, and urease is net positive below pH 5.2 or net negative above pH 5.2. The enzyme activities in the HS-enzyme complexes were suppressed when the enzymes were oppositely charged to the HS. The largest activity suppression was observed around the mass ratio HS/enzyme where the HS-protein complex was at its isoelectric point (IEP). At the IEP strong aggregation of the complexes led to encapsulation of the enzyme. The ionic strength was important; an increase decreased complex formation, but increased aggregation. Due to the larger hydrophobicity of JGHA than JGFA, the reduction in enzyme activity was stronger for JGHA. The enzyme stability also decreased maximally at mass ratio around the IEP of the complex when HS and protein were oppositely charged. When urease and HS were both negatively charged no complexes were formed, but the presence of JGHA or JGFA improved the activity and stability of the enzyme.
    Proton binding to soil humic and fulvic acids: Experiments and NICA-Donnan modelling
    Tan, W. ; Xiong, J. ; Li, Y. ; Wang, M. ; Weng, L. ; Koopal, L.K. - \ 2013
    Colloids and Surfaces. A: Physicochemical and Engineering Aspects 436 (2013). - ISSN 0927-7757 - p. 1152 - 1158.
    natural organic-matter - metal-ion binding - potentiometric titrations - affinity distributions - base properties - substances - heterogeneity - parameters - adsorption
    Proton binding to one soil fulvic acid (JGFA), two soil humic acids (JGHA, JLHA) and a lignite-based humic acid (PAHA) was investigated. The results were fitted to NICA-Donnan model and compared directly with the predictions using the generic parameters. NICA-Donnan model can describe proton binding satisfactorily when parameter fitting is allowed for humic substance (HS). However, predictions based on the generic parameter sets deviate for soil samples in a non-systematic way from the measured results. Replacing Qmax,H1 in generic parameter sets with material-specific values improves the predictions for soil HA significantly. For JGFA, the agreement between the model prediction and data is still not satisfactory after substitution. This is due to a very different pattern of site distribution of JGFA from that of generic FA. For two other soil FAs (FH-14, FH-22 of Milne's database) the generic predictions can be improved significantly with material-specific Qmax,H1. Adjusting also Qmax,H2 to HS material-specific value improves the prediction only slightly further. In practice, Qmax,H1 and Qmax,H2 of HS can be obtained in a relatively simple way by performing one acid–base titration at a given ionic strength and applying the procedure of Lenoir et al. to fit data to NICA equation. Introduction of thus obtained Qmax,H1 and Qmax,H2 into generic parameter sets improves the generic predictions significantly. The functional group contents as obtained by SG-method are not adequate for this purpose.
    POPs analysis reveals issues in bringing laboratories in developing countries to a higher quality level
    Leeuwen, S.P.J. van; Bavel, B. van; Abad, E. ; Leslie, H.A. ; Fiedler, H. ; Boer, J. de - \ 2013
    TrAC : Trends in Analytical Chemistry 46 (2013). - ISSN 0165-9936 - p. 198 - 206.
    polybrominated diphenyl ethers - brominated flame retardants - mass-spectrometry - human samples - perfluoroalkyl - substances - pbdes - polyfluoroalkyl - environment - sulfonate
    We assessed the performance of laboratories in 18 developing countries in analyzing persistent organic pollutants (POPs) in environmental and human samples, as part of a capacity-building program with the goal of helping laboratories increase proficiency in the types of analyses required for the POPs Global Monitoring Program (GMP) under the Stockholm Convention. We identified several issues that need improvement before the laboratories can contribute to the GMP, including technical aspects of POPs analysis, QA/QC issues and laboratory-management problems. (C) 2013 Elsevier Ltd. All rights reserved.
    Structural and water-holding characteristics of untreated and ensiled chicory root pulp
    Ramasamy, U. ; Gruppen, H. ; Schols, H.A. - \ 2013
    Journal of Agricultural and Food Chemistry 61 (2013)25. - ISSN 0021-8561 - p. 6077 - 6085.
    cell-walls - nonstarch polysaccharides - liquid-chromatography - by-products - xyloglucan - cellulose - pectins - fiber - purification - substances
    Cell wall polysaccharides (CWPs) from chicory root pulp (CRP) and the effect of ensiling on CWP structure to reduce the water-holding capacity (WHC) were studied. Sequential extractions of CRP showed that hot water extraction solubilized arabinan-rich pectin and inulin, each representing 6% of all CRP sugars. A significant amount of pectic sugars (46%) rich in uronic acid from CRP was solubilized by chelating agents. Both dilute alkali extraction, which solubilized branched pectin (14% from CRP), and concentrated alkali extraction, which solubilized hemicellulose dominant in yloglucans (2.5%) mostly of the XXXG type and mannan (0.9%), from CRP CWPs seemed to influence the WHC of CRP. Alkali-insoluble residue (39% of CRP sugars) mainly comprised cellulose and some branched pectin (17% from CRP). Ensiling reduced the methyl esterification of pectin, caused degradation of homogalacturonan and rhamnogalacturonan, and possibly modified the xyloglucan, mannan, and glucan network, reducing the WHC from 6 mL/g to 3.4 mL/g.
    Chemical and spectroscopic characteristics of humic acids
    Ferreira, F. ; Vidal-Torrado, P. ; Otero, X.L. ; Buurman, P. - \ 2013
    Journal of Soils and Sediments 13 (2013)2. - ISSN 1439-0108 - p. 253 - 264.
    soil organic-matter - estuarine soils - nmr-spectroscopy - salt marshes - substances - spain - resonance - sediments - c-13 - environments
    To characterise soil humic acids (HAs) extracted from Spanish marshes formed under different vegetation types (Spartina maritima (GSp), Juncus maritimus (GJc), Phragmites australis (GPh), and Scirpus maritimus (VSc)), soil depths (0-20, 20-40 and 40-60 cm), physiographic position (low and high marshes), wetland types (salt marshes and lagoons) and environmental conditions (Atlantic and Mediterranean coast). Soil samples were collected in five Spanish marshes, three on the Galicia province and two on the Valencia province. Humic acids were extracted and their elemental composition, semiquinone-type free radical (SFR) content, FTIR and CPMAS C-13 NMR spectra determined. Total carbon (TC), total nitrogen (TN), total sulphur (TS), CaCO3 content, and field pH and Eh (mV) in the marsh soils sampled were also measured. The field pH and Eh values were typical of coastal areas submitted to periodic inundations and the highest TC, TN and TS contents were found in the soil of lagoon marshes as an effect of physiographic position and wetland type. The HAs, in general, were highly aliphatic and exhibited a low SFR content, which suggests a low humification degree of the SOM formed in the studied areas. This is a result of the anaerobic decomposition to which SOM is submitted and the high input of plant-derived organic matter (OM) by vegetation. However, among the studied sites low salt marsh and subsurface layer of the high salt marsh showed higher SFR content, simpler FTIR spectra, higher lignin degradation and lower O-alkyl C/alkyl C ratio than the lagoon marshes, thus suggesting the presence of a more humificated SOM in these sites. From the different factors analysed, only physiographic position (low versus high salt marshes) and wetland type (marshes versus lagoons) caused variations in the HAs characteristics, because as the studied soils are under anaerobic conditions, they control the exportation of plant-derived OM and the allochthonous OM contribution in the studied areas.
    Influence of lysozyme complexation with purified Aldrich humic acid on lysozyme activity
    Li, Y. ; Tan, W.F. ; Wang, M.X. ; Liu, F. ; Weng, L.P. ; Norde, W. ; Koopal, L.K. - \ 2012
    European Journal of Soil Science 63 (2012)5. - ISSN 1351-0754 - p. 550 - 557.
    streaming current detector - nica-donnan model - cationic polyelectrolytes - charge determination - substances - soil - stability - adsorption - titration - binding
    Humic acid is an important component of dissolved organic matter and in two previous papers it has been shown that purified Aldrich humic acid (PAHA) forms strong complexes with the oppositely charged protein lysozyme (LSZ). The complexation and aggregation of enzymes with humic acids may lead to changes in their activity. Therefore, the enzyme activity of LSZ in the PAHA – LSZ complex as a function of mass ratio PAHA:LSZ was investigated at two pH values (pH 5 and pH 8 where PAHA and LSZ are oppositely charged) and two ionic strengths (5 mmol l-1; 50 mmol l-1). The newly prepared complex was characterized and the mass ratios PAHA:LSZ at the isoelectric point (IEP) of the complex at the assayed conditions were obtained with the Mütek particle charge detector. The LSZ activity was measured with an assay specific for LSZ. The activity of LSZ decreased upon complex formation with PAHA and the PAHA effect on the enzyme activity was increased by the subsequent aggregation. A critical PAHA:LSZ mass ratio for the behaviour of the enzyme activity was that at the IEP of the complex. Before this mass ratio was reached the LSZ activity strongly decreased under all conditions. Beyond this mass ratio both pH and ionic strength affected the activity of LSZ in the complex. The results can be explained by the effects that pH and ionic strength have on (i) the electrostatic attraction between LSZ and PAHA in the complex and (ii) the electrostatic repulsion between the complexes. These two factors plus the hydrophobic attraction determine the structure of the complexes and the size of the aggregates and hence the screening of the active site of the protein.
    Simultaneous analysis of small organic acids and humic acids using high performance size exclusion chromatography
    Qin, X.P. ; Liu, F. ; Wang, G.C. ; Weng, L.P. - \ 2012
    Journal of Separation Science 35 (2012)24. - ISSN 1615-9306 - p. 3455 - 3460.
    spectroscopic properties - molecular-weight - iron-oxide - adsorption - substances - goethite - matter - water - polydispersity - complexation
    An accurate and fast method for simultaneous determination of small organic acids and much larger humic acids was developed using high performance size exclusion chromatography. Two small organic acids, i.e. salicylic acid and 2,3-dihydroxybenzoic acid, and one purified humic acid material were used in this study. Under the experimental conditions, the UV peaks of salicylic acid and 2,3-dihydroxybenzoic acid were well separated from the peaks of humic acid in the chromatogram. Concentrations of the two small organic acids could be accurately determined from their peak areas. The concentration of humic acid in the mixture could then be derived from mass balance calculations. The measured results agreed well with the nominal concentrations. The detection limits are 0.05 mg/L and 0.01 mg/L for salicylic acid and 2,3-dihydroxybenzoic acid, respectively. Applicability of the method to natural samples was tested using groundwater, glacier, and river water samples (both original and spiked with salicylic acid and 2,3-dihydroxybenzoic acid) with a total organic carbon concentration ranging from 2.1 to 179.5 mg C/L. The results obtained are promising, especially for groundwater samples and river water samples with a total organic carbon concentration below 9 mg C/L.
    Chemodynamics of metal complexation by natural soft colloids: Cu(II) binding by humic acid
    Town, R.M. ; Duval, J.F.L. ; Buffle, J. ; Leeuwen, H.P. van - \ 2012
    The Journal of Physical Chemistry Part A: Molecules, Spectroscopy, Kinetics, Environment, & General Theory 116 (2012)25. - ISSN 1089-5639 - p. 6489 - 6496.
    physicochemical heterogeneity - solvent exchange - copper-binding - simple ligands - fulvic-acids - ion-binding - relaxation - substances - kinetics - model
    The chemodynamics of Cu(II) complexation by humic acid is interpreted in terms of recently developed theory for permeable charged nanoparticles. Two opposing electric effects are operational with respect to the overall rate of association, namely, (i) the conductive enhancement of the diffusion of Cu2+, expressed by a coefficient f(e nu), which accounts for the accelerating effect of the negative electrostatic field of the humic particle on the diffusive transport of metal ions toward it, and (ii) the ionic Boltzmann equilibration with the bulk solution, expressed by a factor f(B), which quantifies the extent to which Cu2+ ions accumulate in the negatively charged particle body. These effects are combined in the probability of outer-sphere metal site complex formation and the covalent binding of the metal ion by the complexing site (inner-sphere complex formation) as in the classical Eigen mechanism. Overall "experimental" rate constants for CuHA complex formation, k(a), are derived from measurements of the thermodynamic stability constant, K*, and the dissociation rate constant, k(d)(*), as a function of the degree of metal ion complexation, theta. The resulting k(a) values are found to be practically independent of theta. They are also compared to theoretical values; at an ionic strength of 0.1 mol dm(-3), the rate of diffusive supply of metal ions toward the particles is comparable to the rate of inner-sphere complex formation, indicating that both processes are significant for the observed overall rate. As the ionic strength decreases, the rate of diffusive supply becomes the predominant rate-limiting process, in contrast with the general assumption made for complexes with small ligands that inner-sphere dehydration is the rate-limiting step. The results presented herein also resolve the discrepancy between experimentally observed and predicted dissociation rate constants based on the above assumption.
    Genome sequence of the button mushroom Agaricus bisporus reveals mechanisms governing adaptation to a humic-rich ecological niche
    Morin, E. ; Kohler, A. ; Baker, A.R. ; Foulongne-Oriol, M. ; Lombard, V. ; Nagy, L.G. ; Ohm, R.A. ; Patyshakuliyeva, A. ; Brun, A. ; Aerts, A.L. ; Bailey, A.M. ; Billette, C. ; Coutinho, P.M. ; Deakin, G. ; Doddapaneni, H. ; Floudas, D. ; Grimwood, J. ; Hildén, K. ; Kües, U. ; LaButti, K.M. ; Lapidus, A. ; Lindquist, E.A. ; Lucas, S.M. ; Murat, C. ; Riley, R.W. ; Salamov, A.A. ; Schmutz, J. ; Subramanian, V. ; Wösten, H.A.B. ; Xu, J. ; Eastwood, D.C. ; Foster, G.D. ; Sonnenberg, A.S.M. ; Cullen, D. ; Vries, R.P. de; Lundell, T. ; Hibbett, D.S. ; Henrissat, B. ; Burton, K.S. ; Kerrigan, R.W. ; Challen, M.P. ; Grigorievf, I.V. ; Martin, M. - \ 2012
    Proceedings of the National Academy of Sciences of the United States of America 109 (2012)43. - ISSN 0027-8424 - p. 17501 - 17506.
    cultivated mushroom - coprinus-cinereus - schizophyllum-commune - coprinopsis-cinerea - fungi - gene - decomposition - chromosomes - degradation - substances
    Agaricus bisporus is the model fungus for the adaptation, persistence, and growth in the humic-rich leaf-litter environment. Aside from its ecological role, A. bisporus has been an important component of the human diet for over 200 y and worldwide cultivation of the “button mushroom” forms a multibillion dollar industry. We present two A. bisporus genomes, their gene repertoires and transcript profiles on compost and during mushroom formation. The genomes encode a full repertoire of polysaccharide-degrading enzymes similar to that of wood-decayers. Comparative transcriptomics of mycelium grown on defined medium, casing-soil, and compost revealed genes encoding enzymes involved in xylan, cellulose, pectin, and protein degradation are more highly expressed in compost. The striking expansion of heme-thiolate peroxidases and ß-etherases is distinctive from Agaricomycotina wood-decayers and suggests a broad attack on decaying lignin and related metabolites found in humic acid-rich environment. Similarly, up-regulation of these genes together with a lignolytic manganese peroxidase, multiple copper radical oxidases, and cytochrome P450s is consistent with challenges posed by complex humic-rich substrates. The gene repertoire and expression of hydrolytic enzymes in A. bisporus is substantially different from the taxonomically related ectomycorrhizal symbiont Laccaria bicolor. A common promoter motif was also identified in genes very highly expressed in humic-rich substrates. These observations reveal genetic and enzymatic mechanisms governing adaptation to the humic-rich ecological niche formed during plant degradation, further defining the critical role such fungi contribute to soil structure and carbon sequestration in terrestrial ecosystems. Genome sequence will expedite mushroom breeding for improved agronomic characteristics.
    Antioxidative activities and chemical characterization of polysaccharide extracts from the widely used mushrooms Ganoderma applanatum, Ganoderma lucidum, Lentinus edodes and Trametes versicolor
    Kozarski, M. ; Klaus, A. ; Niksic, M. ; Vrvic, M.M. ; Todorovic, N. ; Jakovljevic, D. ; Griensven, L.J.L.D. van - \ 2012
    Journal of Food Composition and Analysis 26 (2012)1-2. - ISSN 0889-1575 - p. 144 - 153.
    medicinal mushrooms - phenolic-compounds - edible mushrooms - free-radicals - metal-ions - perspective - monophenols - substances - tyrosinase - glucans
    Antioxidant activities of polysaccharide extracts of four of the most widely known mushrooms often used in medicinal applications as well as in tea and food, namely Ganoderma applanatum, Ganoderma lucidum, Lentinus edodes and Trametes versicolor, were studied. G. applanatum and L edodes extracts were the strongest DPPH scavengers, i.e. EC50 <0.1 mg/mL. G. applanatum extract had the highest chelating ability of ferrous ion (EC50 = 3.58 mg/mL), inhibition of lipid peroxidation (EC50 = 2.07 mg/mL) and had the highest reducing power, EC50 = 0.18. All four polysaccharide extracts showed a strong correlation between the reducing power and the total amount of phenols and alpha-glucans: no such correlation was found between the reducing power and the amount of total polysaccharides and proteins. The extracts contained a mixture/complex of polysaccharides, proteins and polyphenols, still present after hot water treatment, ethanol precipitation and dialysis. Glucose was the prevalent monosaccharide of all polysaccharides and samples contained both alpha- and beta-glucans. Total glucan contents varied considerably, i.e. from 35% for G. applanatum to 83% for G. lucidum. Uronic acid was found in the G. applanatum polysaccharides. Fourier transform infrared (FT-IR) analysis showed strong aromatic and ester peaks next to the different sugar and polysaccharide signals. (C) 2012 Elsevier Inc. All rights reserved.
    Toxic concentrations in fish early life stages peak at a critical moment
    Foekema, E.M. ; Fischer, A. ; Lopez Parron, M. ; Kwadijk, C. ; Vries, P. de; Murk, A.J. - \ 2012
    Environmental Toxicology and Chemistry 31 (2012)6. - ISSN 0730-7268 - p. 1381 - 1390.
    medaka oryzias-latipes - organochlorine compounds - aquatic organisms - maternal transfer - risk-assessment - pcb congeners - exposure - accumulation - substances - bioaccumulation
    During the development of an embryo into a juvenile, the physiology and behavior of a fish change greatly, affecting exposure to and uptake of environmental pollutants. Based on experimental data with sole (Solea solea), an existing bioaccumulation model was adapted and validated to calculate the development of concentrations of persistent organic pollutants in the tissue of developing fish. Simulation revealed that toxic tissue concentrations of pollutants with log octanol–water partition ratio (KOW)¿>¿5 peak at the moment when the larvae become free-feeding, when the lipid reserves are depleted. This may explain the delayed effects observed in fish early-life-stage experiments with exposed eggs. In the field, eggs can be exposed through maternal transfer to adult pollutant tissue concentrations, which will increase in the larva to peak tissue concentrations, exceeding those of the adult fish. The results demonstrate the risk of underestimating the effects of lipophilic persistent organic pollutants with log KOW¿>¿5 in short-term, early-life-stage fish tests and underscore the importance of maternal transfer as an exposure route in the field situation.
    The effect of recirculating aquaculture systems on the concentrations of heavy metals in culture water and tissues of Nile tilapia Oreochromis niloticus
    Martins, C.I. ; Eding, E.H. ; Verreth, J.A.J. - \ 2011
    Food Chemistry 126 (2011)3. - ISSN 0308-8146 - p. 1001 - 1005.
    fish - accumulation - wild - substances - anguilla - mykiss - lake
    To date, farming fish in recirculating aquaculture systems (RAS) is one of the most environmentally friendly ways of producing fish. However, with the trend towards intensification, and consequently decrease in water exchange rates, these systems may accumulate substances, such as heavy metals, in the water and fish. Inductively-coupled plasma-optical emission spectrometry (ICP-OES) and inductively coupled plasma-mass spectroscope (ICP-MS) were used to determine Al, As, Cd, Cr, Cu, Fe, Mn, Ni, Pb and Zn, in the water and fish (Nile tilapia Oreochromis niloticus). Three RAS were used, differing in daily water exchange rates (30, 70 and 1500 l/kg feed/d). The concentrations of As, Fe, Mn, Ni and Zn in the water increased with decreasing water exchange rates, suggesting an accumulation of heavy metals as more water was re-used. Such accumulation in the water was, however, not translated into accumulation in the liver and muscle. Accumulation of heavy metals was always higher in the liver than in the muscle; however, As reached 1.61 mg/kg wet weight in the muscle of fish farmed in RAS-70 l/kg feed/d. However, these levels are considerably lower than permissible safety levels for human consumption
    Low powdered activated carbon concentrations to improve MBR sludge filterability at high salinity and low temperature
    Remy, M.J.J. ; Temmink, B.G. ; Brink, P. van den; Rulkens, W.H. - \ 2011
    Desalination 276 (2011)1-3. - ISSN 0011-9164 - p. 403 - 407.
    waste-water treatment - membrane bioreactor - critical flux - performance - substances - impact - smp
    Previous research has demonstrated that powdered activated carbon (PAC), when applied at very low dosages and long SRTs, reduces membrane fouling in membrane bioreactor (MBRs). This effect was related to stronger flocs which are less sensitive to shear. Low temperature and high salt concentration are known to drastically decrease the filterability of the sludge. In this paper the effect of PAC addition on the robustness of MBR when submitted to these disrupting conditions was investigated. PAC amended sludge showed a higher resistance to high salinity with a lower fouling development and release of foulants. When submitted to lower temperatures, the sludge without PAC showed a clear decrease of the filterability, while the filterability of PAC amended sludge was much less affected. PAC addition does not only improve the filterability in the MBR under normal conditions but also when the sludge is submitted to stress. A low PAC dosage could be used during startup and difficult conditions (e.g. winter) to minimize detrimental effects of such conditions
    Hormonal control of the outgrowth of axillary buds in Alstroemeria cultured in vitro
    Pumisutapon, P. ; Visser, R.G.F. ; Klerk, G.J.M. de - \ 2011
    Biologia Plantarum 55 (2011)4. - ISSN 0006-3134 - p. 664 - 668.
    apical dominance - growth - auxin - inhibition - substances - rhizome
    We study apical dominance in Alstroemeria, a plant with an architecture very different from the model species used in research on apical dominance. The standard explant was a rhizome with a tip and two vertically growing shoots from which the larger part had been excised leaving ca. 1 cm stem. The axillary buds that resumed growth were located at this 1-cm stem just above the rhizome. They were released by removal of the rhizome tip and the shoot tips. Replacement of excised tips by lanolin with indole-3-butyric acid (IBA) restored apical dominance. The auxin transport inhibitors 2,3,5-triiodobenzoic acid (TIBA) and N-1-napthylphthalamic acid (NPA) reduced apical dominance. 6-Benzylaminopurine (BAP) enhanced axillary bud outgrowth but the highest concentrations (> 9 µM) caused fasciation. Thidiazuron (TDZ) did not show improvement relative to BAP. Even though the architecture of Alstroemeria and the model species are very different, their hormonal mechanisms in apical dominance are for the greater part very similar.
    Determination of pectin content of eucalyptus wood
    Coetzee, B. ; Schols, H.A. ; Wolfaardt, F. - \ 2011
    Holzforschung 65 (2011)3. - ISSN 0018-3830 - p. 327 - 331.
    quince chaenomeles-japonica - cell - polysaccharides - degradation - substances - responses - fruits - plants - hplc - wall
    Very little is known about the occurrence of pectin in wood and it is speculated that between 10 mg g-1 and 40 mg g-1 of wood consists of pectin. The present study aimed to quantify pectin in eucalyptus wood and to determine the influence of tree species, yield potential of the site, tree age class and wood tissue type on its occurrence. Wood was hydrolysed using the Saeman procedure and the neutral and acidic monosaccharides quantified with high-performance liquid chromatography (HPLC). The d-galacturonic acid was the predominant pectic monosaccharide followed by d-galactose, l-arabinose and l-rhamnose. Through the addition of all pectic monosaccharides, it was determined that eucalyptus wood contained between 15.2 mg g-1 and 25.8 mg g-1 pectin. Wood tissue type had a major influence on the total pectin content of the samples. The cambium contained the highest concentration of pectin, reflecting more active growth. These results contribute to the understanding of wood biochemistry and can be useful in the industries producing biofuels or paper.
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