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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Physiological parameters of Bacillus cereus marking the end of acid-induced lag phases
Biesta-Peters, E.G. ; Mols, J.M. ; Reij, M.W. ; Abee, T. - \ 2011
International Journal of Food Microbiology 148 (2011)1. - ISSN 0168-1605 - p. 42 - 47.
flow-cytometry - bacterial-growth - intracellular ph - temperature - state
During lag phases microbial cells adapt to their environment and prepare to proliferate. Physiological parameters of B. cereus cells upon exposure to near-growth-boundary acid stress were investigated and markers for the transition between lag phase and growth were identified using fluorescent probes combined with flow cytometry. Determination of cell counts and optical density revealed lag phases of 1 h, 2 h and 5 h, in cultures shifted to pH 7, pH 5.3 (set with lactic acid) and pH 4.9 (set with sulfuric acid), respectively. The obtained lag phases fitted the trends in ATP levels, which were constant during the lag phase and increased after the onset of growth. Both the percentage of PI-stained cells and cells with a significant membrane potential decreased during the lag phase. This points to repair of membrane damage and the loss of membrane potential. However, both trends extended in the growth phase, thus not suitable to mark the onset of growth. The activity of the electron transfer chain and esterases did allow for assessment of transition between lag and growth phase. These activities were generally low during the lag phase and increased after the onset of growth. Our results show that, independent of the duration of the lag phase, for different conditions the same physiological trends could be observed. The change in signal of selected probes can be used as a marker for transition from lag phase to the growth phase and may aid in identification of novel targets interfering with bacterial exit from lag phase.
Ecosystem responses to reduced and oxidised nitrogen inputs in European terrestrial habitats
Stevens, C.J. ; Manning, P. ; Berg, L.J.L. van den; Graaf, M.C.C. de; Wamelink, G.W.W. ; Boxman, A.W. ; Bleeker, A. ; Vergeer, P. ; Arroniz-Crespo, M. ; Limpens, J. ; Lamers, L.P.M. ; Bobbink, R. ; Dorland, E. - \ 2011
Environmental Pollution 159 (2011)3. - ISSN 0269-7491 - p. 665 - 676.
spruce picea-abies - soil solution chemistry - pinus-sylvestris l - atmospheric ammonia - throughfall deposition - nitrate reduction - acidic grasslands - intracellular ph - species richness - vascular plants
While it is well established that ecosystems display strong responses to elevated nitrogen deposition, the importance of the ratio between the dominant forms of deposited nitrogen (NHx and NOy) in determining ecosystem response is poorly understood. As large changes in the ratio of oxidised and reduced nitrogen inputs are occurring, this oversight requires attention. One reason for this knowledge gap is that plants experience a different NHx:NOy ratio in soil to that seen in atmospheric deposits because atmospheric inputs are modified by soil transformations, mediated by soil pH. Consequently species of neutral and alkaline habitats are less likely to encounter high NH4+ concentrations than species from acid soils. We suggest that the response of vascular plant species to changing ratios of NHx:NOy deposits will be driven primarily by a combination of soil pH and nitrification rates. Testing this hypothesis requires a combination of experimental and survey work in a range of systems.
Impaired barrier function by dietary fructo-oligosaccharides (FOS) in rats is accompanied by increased colonic mitochondrial gene expression
Rodenburg, G.C.H. ; Keijer, J. ; Kramer, E.H.M. ; Vink, C. ; Meer, R. van der; Bovee-Oudenhoven, I.M.J. - \ 2008
BMC Genomics 9 (2008). - ISSN 1471-2164
glucagon-like peptide-2 - chain fatty-acids - ubiquitin-proteasome system - permeability changes - tight junctions - intestinal permeability - enrichment analysis - intracellular ph - mucosal injury - protein-kinase
Background Dietary non-digestible carbohydrates stimulate the gut microflora and are therefore presumed to improve host resistance to intestinal infections. However, several strictly controlled rat infection studies showed that non-digestible fructo-oligosaccharides (FOS) increase, rather than decrease, translocation of Salmonella towards extra-intestinal sites. In addition, it was shown that FOS increases intestinal permeability already before infection. The mechanism responsible for this adverse effect of FOS is unclear. Possible explanations are altered mucosal integrity due to changes in tight junctions or changes in expression of defense molecules such as antimicrobials and mucins. To examine the mechanisms underlying weakening of the intestinal barrier by FOS, a controlled dietary intervention study was performed. Two groups of 12 rats were adapted to a diet with or without FOS. mRNA was collected from colonic mucosa and changes in gene expression were assessed for each individual rat using Agilent rat whole genome microarrays. Results Among the 997 FOS induced genes we observed less mucosal integrity related genes than expected with the clear permeability changes. FOS did not induce changes in tight junction genes and only 8 genes related to mucosal defense were induced by FOS. These small effects are unlikely the cause for the clear increase in intestinal permeability that is observed. FOS significantly increased expression of 177 mitochondria-related genes. More specifically, induced expression of genes involved in all five OXPHOS complexes and the TCA cycle was observed. These results indicate that dietary FOS influences intestinal mucosal energy metabolism. Furthermore, increased expression of 113 genes related to protein turnover, including proteasome genes, ribosomal genes and protein maturation related genes, was seen. FOS upregulated expression of the peptide hormone proglucagon gene, in agreement with previous studies, as well as three other peptide hormone genes; peptide YY, pancreatic polypeptide and cholecystokinin. Conclusion We conclude that altered energy metabolism may underly colonic barrier function disruption due to FOS feeding in rats.
Differentiation inside multicelled macroconidia of Fusarium culmorum during early germination
Chitarra, G.S. ; Breeuwer, P. ; Rombouts, F.M. ; Abee, T. ; Dijksterhuis, J. - \ 2005
Fungal Genetics and Biology 42 (2005)8. - ISSN 1087-1845 - p. 694 - 703.
rice blast fungus - magnaporthe-grisea - spore germination - intracellular ph - cytoplasmic ph - chlamydospores - growth - cells - oxysporum - surface
Multicelled conidia are formed by many fungal species, but germination of these spores is scarcely studied. Here, the germination and the effects of antimicrobials on multicompartment macroconidia of Fusarium culmorum were investigated. Germ-tube formation was mostly from apical compartments. The intracellular pH (pHin) of the different individual cells of the macroconidia was monitored during germination. The pHin varied among different compartments and during different stages of germination. The internal pH was lowest in ungerminated cells and rose during germ-tube formation and was highest in new germ tubes. Antifungal compounds affect the pHin and differentiation of the conidia. The pHin inside the macroconidial compartments was lowered very fast in the presence of nystatin (1 and 4 ¿g/ml). At sublethal doses (0.3 ¿g/ml), the apical compartments were preferentially targeted showing lower pHin values. The reduced germination capacity of apical compartments under these conditions was compensated by an increased germination capacity of middle compartments.
Different control mechanisms regulate glucoamylase and protease gene transcription in Aspergillus oryzae in solid-state and submerged fermentation
Biesebeke, R. te; Biezen, N. de; Vos, W.M. de; Hondel, C.A.M.J.J. van den; Punt, P.J. - \ 2005
Applied Microbiology and Biotechnology 67 (2005)1. - ISSN 0175-7598 - p. 75 - 82.
encoding gene - nucleotide-sequence - filamentous fungus - alkaline protease - intracellular ph - expression - culture - cloning - glab - acid
Solid-state fermentation (SSF) with Aspergillus oryzae results in high levels of secreted protein. However, control mechanisms of gene expression in SSF have been only poorly studied. In this study we show that both glucoamylase (glaB) and protease (alpA, nptB) genes are highly expressed during surface cultivation on wheat-based solid medium, and even higher during cultivation on wheat kernels. In wheat-based liquid medium, low levels of gene expression are observed. Typical SSF cultivation conditions, such as low water activity and the formation of aerial hyphae, did not contribute to the high-level gene expression on wheat-based solid medium. Analysis of wheat-based solid and liquid cultivations showed differences in carbon and nitrogen utilisation and external pH. The results presented show that the difference in regulation of transcription of the alpA and nptB genes in wheat-based liquid and solid medium could be pH dependent, involving a pH-dependent transcription regulator. The results obtained suggest that the difference in regulation of transcription of the glaB gene in wheat-based liquid and solid medium is caused by a difference in carbohydrate degradation and consumption under the different culture conditions
Selection of fluorescent probes for flow cytometric viability assessment of Listeria monocytogenes exposed to membrane-active and oxidizing disinfectants
Luppens, S.B.I. ; Barbaras, B. ; Breeuwer, P. ; Rombouts, F.M. ; Abee, T. - \ 2003
Journal of Food Protection 66 (2003)8. - ISSN 0362-028X - p. 1393 - 1401.
5-cyano-2,3-ditolyl tetrazolium chloride - staphylococcus-aureus - respiratory activity - bacterial viability - intracellular ph - growth-phase - cells - biofilms - heterogeneity - environments
The aim of this study was to select fluorescence methods for use as alternatives to plate counting to assess the viability of Listeria monocytogenes cells exposed to benzalkonium chloride (BAC) and hydrogen peroxide, two disinfectants with different mechanisms of action. A further aim of this study was to determine whether growth phase influences fluorescence labeling and whether it is possible to predict whether a probe will be a good viability indicator for cells exposed to a certain disinfectant on the basis of the mechanism of action of the disinfectant and the target of the fluorescent probe. The fluorescence methods used were labeling with 5-cyano-2,3-ditolyl tetrazolium chloride (CTC; dehydrogenase activity), labeling with TOTO1 iodide (TOTO; membrane-impermeant probe), and assessment of pH gradient maintenance in a low-pH buffer after labeling with the pH-sensitive probe 5-(and 6)-carboxyfluorescein succinimidyl ester (CFSE) (the pHin method). Growth phase influenced fluorescent labeling. However, the cutoff value for distinction between viable and nonviable cells was the same for both growth phases. The viability (determined by plate counts) of BAC-exposed cells correlated well with CTC labeling and TOTO exclusion. For both BAC-exposed and hydrogen peroxide-exposed cells, the pHin method gave a good qualitative indication of viability, sublethal damage, and cell death. CTC labeling and TOTO exclusion did not correlate with the viability of hydrogen peroxide-exposed cells. Our results demonstrate that even if the mechanism of action of a disinfectant is known, in some cases it is still difficult to predict whether a certain fluorescent probe is suitable for viability assessment. Thus, the proper selection of fluorescent probes for the assessment of the efficacy of antimicrobial agents is essential.
The application of flow cytometry and fluorescent probe technology for detection and assessment of viability of plant pathogenic bacteria
Chitarra, L.G. ; Bulk, R.W. van den - \ 2003
European Journal of Plant Pathology 109 (2003). - ISSN 0929-1873 - p. 407 - 417.
campestris pv-campestris - propidium iodide - monoclonal-antibodies - intracellular ph - rapid assessment - rhodamine 123 - dna content - cells - soil - fluorochromes
Conventional methods to detect and assess the viability of plant pathogenic bacteria are usually based on plating assays or serological techniques. Plating assays provide information about the number of viable cells, expressed as colony-forming units, but are time-consuming and laborious. Serological methods, such as the enzyme-linked immunosorbent assay (ELISA) and immunofluorescence microscopy (IF), can be performed in a shorter timespan than most plating assays, but they do not discriminate between live and dead cells. Flow cytometry (FCM) in combination with fluorescent probe technology is a rapid, sensitive, and quantitative technique to detect microorganisms and assess their viability. Quantitative information on the presence and viability of plant pathogenic microorganisms is valuable for risk assessment regarding disease transmission and disease development. FCM has been applied successfully in the fields of food microbiology, veterinary science, and medical research to detect and distinguish between viable and non-viable bacteria. The aim of this review is to show the potential of FCM and fluorescent probe technology for the field of plant pathology.
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