Publications (11)40.1 Total impact
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Article: Erratum: Optimizing the setup of a flow cytometric cell sorter for efficient quantitative sorting of long filaments.
Cytometry Part A 01/2011; · 3.73 Impact Factor -
Article: Optimizing the setup of a flow cytometric cell sorter for efficient quantitative sorting of long filamentous cyanobacteria.
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ABSTRACT: Heterogeneity within natural phytoplankton communities makes it very difficult to analyze parameters at the single-cell level. Flow cytometric sorting is therefore a useful tool in aquatic sciences, as it provides material for post-sort analysis and culturing. Sorting subpopulations from natural communities, however, often requires handling morphologically diverse and complex particles with various abundances. Long particles, such as filament-forming cyanobacteria (>100-μm long), prove very difficult to handle. These potentially toxic organisms are widespread in eutrophic systems and have important ecological consequences. Being able to sort filamentous cyanobacteria efficiently and as viable cells is therefore highly desirable when studying factors associated with their toxicity and occurrence. This unconventional sorting requires extensive user experience and special instrument setup. We have investigated the effect of hydrodynamic and electromechanical components of a flow cytometer, and sorting protocol on the quantitative sorting efficiency of these long particles using two filamentous cyanobacterial strains with average lengths of ∼100 and ∼300 μm. Sorting efficiency ranged from 9.4 to 96.0% and was significantly affected by filament length, sorting envelope, drop delay (dd), and for the long species also by tip size, but not by cycle time. Filaments survived sorting and were not damaged. The optimal settings found for the modular MoFlo® cell-sorter to sort the filaments were a 100-μm flow tip at 30 psi (207 kPa) with a three-droplet envelope in Enrich mode while using an extended analysis time of 17.6 μs and an intermediate plate charge and deflection percentage combination of 3,000 V/60%, combined with a dd 0 for the cultures with 100-μm filaments and dd +1 for the culture with 300-μm filaments. To the best of our knowledge, the filaments up to 1063.5 μm sorted in this study are the longest ever sorted.Cytometry Part A 10/2010; 77(10):911-24. · 3.73 Impact Factor -
Article: AIDS patient death caused by novel Cryptococcus neoformans x C. gattii hybrid.
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ABSTRACT: Interspecies hybrids of Cryptococcus neoformans and C. gattii have only recently been reported. We describe a novel C. neoformans x C. gattii hybrid strain (serotype AB) that was previously described as C. gattii and that caused a lethal infection in an AIDS patient from Canada.Emerging Infectious Diseases 08/2008; 14(7):1105-8. · 6.79 Impact Factor -
Article: Population dynamics and diversity of viruses, bacteria and phytoplankton in a shallow eutrophic lake.
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ABSTRACT: We have studied the temporal variation in viral abundances and community assemblage in the eutrophic Lake Loosdrecht through epifluorescence microscopy and pulsed field gel electrophoresis (PFGE). The virioplankton community was a dynamic component of the aquatic community, with abundances ranging between 5.5 x 10(7) and 1.3 x 10(8) virus-like particles ml(-1) and viral genome sizes ranging between 30 and 200 kb. Both viral abundances and community composition followed a distinct seasonal cycle, with high viral abundances observed during spring and summer. Due to the selective and parasitic nature of viral infection, it was expected that viral and host community dynamics would covary both in abundances and community composition. The temporal dynamics of the bacterial and cyanobacterial communities, as potential viral hosts, were studied in addition to a range of environmental parameters to relate these to viral community dynamics. Cyanobacterial and bacterial communities were studied applying epifluorescence microscopy, flow cytometry, and denaturing gradient gel electrophoresis (DGGE). Both bacterial and cyanobacterial communities followed a clear seasonal cycle. Contrary to expectations, viral abundances were neither correlated to abundances of the most dominant plankton groups in Lake Loosdrecht, the bacteria and the filamentous cyanobacteria, nor could we detect a correlation between the assemblage of viral and bacterial or cyanobacterial communities during the overall period. Only during short periods of strong fluctuations in microbial communities could we detect viral community assemblages to covary with cyanobacterial and bacterial communities. Methods with a higher specificity and resolution are probably needed to detect the more subtle virus-host interactions. Viral abundances did however relate to cyanobacterial community assemblage and showed a significant positive correlation to Chl-a as well as prochlorophytes, suggesting that a significant proportion of the viruses in Lake Loosdrecht may be phytoplankton and more specific cyanobacterial viruses. Temporal changes in bacterial abundances were significantly related to viral community assemblage, and vice versa, suggesting an interaction between viral and bacterial communities in Lake Loosdrecht.Microbial Ecology 08/2008; 56(1):29-42. · 2.91 Impact Factor -
Article: Estimates of bacterial and phytoplankton mortality caused by viral lysis and microzooplankton grazing in a shallow eutrophic lake
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ABSTRACT: Summary1. Since viral lysis and zooplankton grazing differ in their impact on the aquatic food web, it is important to assess the relative importance of both mortality factors. In this study, an adapted version of the dilution technique was applied to simultaneously estimate the impact of both viral lysis and zooplankton grazing on the mortality of heterotrophic bacteria, eukaryotic algae, unicellular cyanobacteria, prochlorophytes and especially filamentous cyanobacteria in a shallow eutrophic lake.2. Four dilution experiments were performed in December 2004, January 2005, and March and April 2006. Viral and heterotrophic bacterial abundances were obtained by epifluorescence microscopy and abundances of different phytoplankton groups by flow cytometry and light microscopy.3. Viral lysis was identified as the main mortality cause during the December 2004 and January 2005 experiments, apparently removing between 84% and 97% of the potential filamentous cyanobacterial production and up to 101% of the potential heterotrophic bacterial production. Microzooplankton grazing was estimated to remove between 90% and 99% of the potential unicellular cyanobacterial production and up to 46% of the potential heterotrophic bacterial production during the spring 2006 experiments.4. In some cases, no significant impact of viral lysis or zooplankton grazing was detected. Contrary to expectations, the apparent growth rate of filamentous cyanobacteria was even sometimes observed to decrease significantly upon dilution of microzooplankton.5. The dilution technique can give valuable insight into the impact of zooplankton grazing and viral lysis on the mortality of different plankton groups but require some caveats require special care to be taken when comparing and interpreting results.Freshwater Biology 06/2008; 53(6):1126 - 1141. · 3.29 Impact Factor -
Article: Unique hybrids between the fungal pathogens Cryptococcus neoformans and Cryptococcus gattii.
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ABSTRACT: Cryptococcus neoformans and Cryptococcus gattii are yeasts that cause meningoencephalitis, but that differ in host range and geographical distribution. Cryptococcus neoformans occurs world-wide and mostly infects immunocompromised patients, whereas C. gattii occurs mainly in (sub)tropical regions and infects healthy individuals. Anomalous C. neoformans strains were isolated from patients. These strains were found to be monokaryotic, and diploid or aneuploid. Amplified Fragment Length Polymorphism (AFLP) and sequence analyses indicated that AFLP genotypes 2 (C. neoformans) and 4 (C. gattii) were present. The strains were serologically BD. Mating- and serotype-specific PCR reactions showed that the strains were MATa-serotype D/MATalpha-serotype B. This study is the first to describe naturally occurring hybrids between C. neoformans and C. gattii.FEMS Yeast Research 07/2006; 6(4):599-607. · 2.40 Impact Factor -
Article: Molecular characterization of cyanobacterial diversity in a shallow eutrophic lake.
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ABSTRACT: We have studied the diversity of pelagic cyanobacteria in Lake Loosdrecht, The Netherlands, through recovery and analysis of small subunit ribosomal RNA gene sequences from lake samples and cyanobacterial isolates. We used an adapted protocol for specific amplification of cyanobacterial rDNA for denaturing gradient gel electrophoresis (DGGE) analysis. This protocol enabled direct comparison of cyanobacterial community profiles with overall bacterial profiles. The theoretical amplification specificity of the primers was supported by sequence analysis of DNA from excised DGGE bands. Sequences recovered from these bands, in addition to sequences obtained by polymerase chain reaction (PCR) and cloning from lake DNA as well as from cyanobacterial isolates from the lake, revealed a diverse consortium of cyanobacteria, among which are representatives of the genera Aphanizomenon, Planktothrix, Microcystis and Synechococcus. One numerically important and persistent cyanobacterium in the lake, Prochlorothrix hollandica, appeared to co-occur with an unknown but related species. However, the lake is dominated by filamentous species that originally have been termed 'Oscillatoria limnetica-like'. We show that this is a group of several related cyanobacteria, co-occurring in the lake, which belong to the Limnothrix/Pseudanabaena group. The available variation among the coexisting strains of this group can explain the persistent dominance of the group under severe viral pressure.Environmental Microbiology 04/2005; 7(3):365-77. · 5.84 Impact Factor -
Article: LINKING FLOW CYTOMETRIC CELL SORTING AND COMPOUND‐SPECIFIC 13C‐ANALYSIS TO DETERMINE POPULATION‐SPECIFIC ISOTOPIC SIGNATURES AND GROWTH RATES IN CYANOBACTERIA‐DOMINATED LAKE PLANKTON1
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ABSTRACT: A novel methodology was applied to determine the δ13C signatures of natural cyanobacterial and algal populations by combined compound-specific isotope ratio mass spectrometry and pyrolytic methylation-gas chromatography (Py-GC-IRMS) of the fatty acids released from phytoplankton fractions collected using fluorescence-activated cell sorting. Py-GC-IRMS provided direct analysis of the very small samples (<200 ng total C) derived from the cell sorting of individual phototrophic populations, while minimizing the chances on contamination and loss in sample handling. Despite trichome lengths exceeding the diameter of the sort droplets, filamentous cyanobacteria were amenable to population-specific cell sorting. In concert with 13C-CO2 labeling, the combined use of flow cytometric cell sorting and Py-GC-IRMS enabled both the assessment of standing stocks and of population-specific growth rates of the predominant cyanobacterial and algal taxa in Lake Loosdrecht (The Netherlands). Filamentous prochlorophytes, formerly the dominant cyanobacterial taxon in the lake, appeared less abundant in recent years and exhibited growth rates 30%–40% lower than the rates recorded for oscillatorioid populations. Diatom and green algal populations grew at rates 4- to 10-fold higher than filamentous cyanobacteria and are thus important for the lake's carbon budget. This approach offers new possibilities in studying plankton dynamics at a resolution not feasible in the past.Journal of Phycology 09/2004; 40(5):857 - 866. · 2.07 Impact Factor -
Article: Detecting the phosphate status of phytoplankton by enzyme-labelled fluorescence and flow cytometry.
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ABSTRACT: The novel phosphatase substrate, ELF-97 phosphate, yields intensely green fluorescent precipitates of ELF-97 alcohol (ELFA) upon enzymatic dephosphorylation, and thereby traces phosphatase activity back to its producer. In this study, we show that ELFA fluorescence is a useful tool in flow cytometric analysis of natural phytoplankton populations. Presence of endogenous fluorescent pigments allowed flow cytometric distinction of clusters in the phytoplankton community in Lake Loosdrecht (The Netherlands): Eukaryotes (diatoms and green algae), chlorophyll a and b containing but phycobilin-less cyanobacteria (Prochlorothrix hollandica), and phycocyanin-containing cyanobacteria (predominantly Limnothrix sp.). Several, but not all tested cyanobacteria showed ELFA fluorescence. The dominant Limnothrix sp. possesses a derepressible phosphatase, whereas the second most abundant strain, P. hollandica, did not have phosphatase activity. Within both natural and cultured populations of Limnothrix sp. we found discernible levels of ELFA fluorescence, indicating the presence of subpopulations with different physiological characteristics.FEMS Microbiology Ecology 05/2004; 48(1):29-38. · 3.41 Impact Factor -
Article: Observations on cyanobacterial population collapse in eutrophic lake water.
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ABSTRACT: In two laboratory-scale enclosures of water from the shallow, eutrophic Lake Loosdrecht (the Netherlands), the predominating filamentous cyanobacteria grew vigorously for 2 weeks, but then their populations simultaneously collapsed, whereas coccoid cyanobacteria and algae persisted. The collapse coincided with a short peak in the counts of virus-like particles. Transmission electron microscopy showed the morphotype Myoviridae phages, with isometric heads of about 90 nm outer diameter and > 100-nm long tails, that occurred free, attached to and emerging from cyanobacterial cells. Also observed were other virus-like particles of various morphology. Similar mass mortality of the filamentous cyanobacteria occurred in later experiments, but not in Lake Loosdrecht. As applies to lakes in general, this lake exhibits high abundance of virus-like particles. The share and dynamics of infectious cyanophages remain to be established, and it is as yet unknown which factors primarily stabilize the host-cyanophage relationship. Observations on shallow, eutrophic lakes elsewhere indicate that the cyanophage control may also fail in natural water bodies exhibiting predominance of filamentous cyanobacteria. Rapid supply of nutrients appeared to be a common history of mass mortality of cyanobacteria and algae in laboratory and outdoor enclosures as well as in highly eutrophic lakes.Antonie van Leeuwenhoek 08/2002; 81(1-4):319-26. · 2.09 Impact Factor -
Article: Nitrite as a stimulus for ammonia-starved Nitrosomonas europaea.
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ABSTRACT: Ammonia-starved cells of Nitrosomonas europaea are able to preserve a high level of ammonia-oxidizing activity in the absence of ammonium. However, when the nitrite-oxidizing cells that form part of the natural nitrifying community do not keep pace with the ammonia-oxidizing cells, nitrite accumulates and may subsequently inhibit ammonia oxidation. The maintenance of a high ammonia-oxidizing capacity during starvation is then nullified. In this study we demonstrated that cells of N. europaea starved for ammonia were not sensitive to nitrite, either when they were starved in the presence of nitrite or when nitrite was supplied simultaneously with fresh ammonium. In the latter case, the initial ammonia-oxidizing activity of starved cells was stimulated at least fivefold.Applied and Environmental Microbiology 04/2002; 68(3):1454-7. · 3.83 Impact Factor
Top co-authors
Top Journals
Institutions
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2005–2010
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Netherlands Institute of Ecology (NIOO-KNAW)
Wageningen, Provincie Gelderland, Netherlands
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2008
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Universiteit van Amsterdam
Amsterdam, North Holland, Netherlands
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