Publications (8)23.89 Total impact
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Article: Reversal in competitive dominance of a toxic versus non-toxic cyanobacterium in response to rising CO2.
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ABSTRACT: Climate change scenarios predict a doubling of the atmospheric CO(2) concentration by the end of this century. Yet, how rising CO(2) will affect the species composition of aquatic microbial communities is still largely an open question. In this study, we develop a resource competition model to investigate competition for dissolved inorganic carbon in dense algal blooms. The model predicts how dynamic changes in carbon chemistry, pH and light conditions during bloom development feed back on competing phytoplankton species. We test the model predictions in chemostat experiments with monocultures and mixtures of a toxic and non-toxic strain of the freshwater cyanobacterium Microcystis aeruginosa. The toxic strain was able to reduce dissolved CO(2) to lower concentrations than the non-toxic strain, and became dominant in competition at low CO(2) levels. Conversely, the non-toxic strain could grow at lower light levels, and became dominant in competition at high CO(2) levels but low light availability. The model captured the observed reversal in competitive dominance, and was quantitatively in good agreement with the results of the competition experiments. To assess whether microcystins might have a role in this reversal of competitive dominance, we performed further competition experiments with the wild-type strain M. aeruginosa PCC 7806 and its mcyB mutant impaired in microcystin production. The microcystin-producing wild type had a strong selective advantage at low CO(2) levels but not at high CO(2) levels. Our results thus demonstrate both in theory and experiment that rising CO(2) levels can alter the community composition and toxicity of harmful algal blooms.The ISME Journal 03/2011; 5(9):1438-50. · 7.38 Impact Factor -
Article: Spatial divergence in the proportions of genes encoding toxic peptide synthesis among populations of the cyanobacterium Planktothrix in European lakes.
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ABSTRACT: It has been frequently reported that seasonal changes in toxin production by cyanobacteria are due to changes in the proportion of toxic/nontoxic genotypes in parallel to increases or decreases in population density during the seasonal cycle of bloom formation. In order to find out whether there is a relationship between the proportion of genes encoding toxic peptide synthesis and population density of Planktothrix spp. we compared the proportion of three gene regions that are indicative of the synthesis of the toxic heptapeptide microcystin (mcyB), and the bioactive peptides aeruginoside (aerB) and anabaenopeptin (apnC) in samples from 23 lakes of five European countries (n=153). The mcyB, aerB, and apnC genes occurred in 99%, 99%, and 97% of the samples, respectively, and on average comprised 60 ± 3%, 22 ± 2%, and 54 ± 4% of the total population, respectively. Although the populations differed widely in abundance (10(-3)-10(3) mm(3) L(-1)) no dependence of the proportion of the mcyB, aerB, and apnC genes on the density of the total population was found. In contrast populations differed significantly in their average mcyB, aerB, and apnC gene proportions, with no change between prebloom and bloom conditions. These results emphasize stable population-specific differences in mcyB, aerB, and apnC proportions that are independent from seasonal influences.FEMS Microbiology Letters 01/2011; 317(2):127-37. · 2.04 Impact Factor -
Article: Pulsed nitrogen supply induces dynamic changes in the amino acid composition and microcystin production of the harmful cyanobacterium Planktothrix agardhii.
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ABSTRACT: Planktothrix agardhii is a widespread harmful cyanobacterium of eutrophic waters, and can produce the hepatotoxins [Asp(3)]microcystin-LR and [Asp(3)]microcystin-RR. These two microcystin variants differ in their first variable amino acid position, which is occupied by either leucine (L) or arginine (R). Although microcystins are extensively investigated, little is known about the mechanisms that determine the production of different microcystin variants. We hypothesize that enhanced nitrogen availability will increase the intracellular content of the nitrogen-rich amino acid arginine, and thereby promote the production of the variant [Asp(3)]microcystin-RR. To test this hypothesis, we transferred P. agardhii strain 126/3 from nitrogen-replete to nitrogen-deficient conditions, and after 2 weeks of growth under nitrogen deficiency, we added a nitrogen pulse. We found a rapid increase in the cellular nitrogen to carbon ratio and the amino acids aspartic acid and arginine, indicative of cyanophycin synthesis. This was followed by a more gradual increase of the total amino acid content connected to balanced growth. As expected, the [Asp(3)]microcystin-RR variant increased strongly after the nitrogen pulse, while the [Asp(3)]microcystin-LR increased to a much lesser extent. We conclude that sudden nitrogen enrichment affects the amino acid composition of harmful cyanobacteria, which, in turn, affects the production and composition of their microcystins.FEMS Microbiology Ecology 11/2010; 74(2):430-8. · 3.41 Impact Factor -
Article: Amino acid availability determines the ratio of microcystin variants in the cyanobacterium Planktothrix agardhii.
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ABSTRACT: Cyanobacteria are capable of producing multiple microcystin variants simultaneously. The mechanisms that determine the composition of microcystin variants in cyanobacteria are still debated. [Asp(3)]microcystin-RR contains arginine at the position where the more toxic [Asp(3)]microcystin-LR incorporates leucine. We cultured the filamentous cyanobacterium Planktothrix agardhii strain 126/3 with and without external addition of leucine and arginine. Addition of leucine to the growth medium resulted in a strong increase of the [Asp(3)]microcystin LR/RR ratio, while addition of arginine resulted in a decrease. This demonstrates that amino acid availability plays a role in the synthesis of different microcystin variants. Environmental changes affecting cell metabolism may cause differences in the intracellular availability of leucine and arginine, which can thus affect the production of microcystin variants. Because leucine contains one nitrogen atom while arginine contains four nitrogen atoms, we hypothesized that low nitrogen availability might shift the amino acid composition in favor of leucine, which might explain seasonal increases in the [Asp(3)]microcystin LR/RR ratio in natural populations. However, when a continuous culture of P. agardhii was shifted from nitrogen-saturated to a nitrogen-limited mineral medium, leucine and arginine concentrations decreased, but the leucine/arginine ratio did not change. Accordingly, while the total microcystin concentration of the cells decreased, we did not observe changes in the [Asp(3)]microcystin LR/RR ratio in response to nitrogen limitation.FEMS Microbiology Ecology 07/2008; 65(3):383-90. · 3.41 Impact Factor -
Article: Competition for light between toxic and nontoxic strains of the harmful cyanobacterium Microcystis.
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ABSTRACT: The cyanobacterium Microcystis can produce microcystins, a family of toxins that are of major concern in water management. In several lakes, the average microcystin content per cell gradually declines from high levels at the onset of Microcystis blooms to low levels at the height of the bloom. Such seasonal dynamics might result from a succession of toxic to nontoxic strains. To investigate this hypothesis, we ran competition experiments with two toxic and two nontoxic Microcystis strains using light-limited chemostats. The population dynamics of these closely related strains were monitored by means of characteristic changes in light absorbance spectra and by PCR amplification of the rRNA internal transcribed spacer region in combination with denaturing gradient gel electrophoresis, which allowed identification and semiquantification of the competing strains. In all experiments, the toxic strains lost competition for light from nontoxic strains. As a consequence, the total microcystin concentrations in the competition experiments gradually declined. We did not find evidence for allelopathic interactions, as nontoxic strains became dominant even when toxic strains were given a major initial advantage. These findings show that, in our experiments, nontoxic strains of Microcystis were better competitors for light than toxic strains. The generality of this finding deserves further investigation with other Microcystis strains. The competitive replacement of toxic by nontoxic strains offers a plausible explanation for the gradual decrease in average toxicity per cell during the development of dense Microcystis blooms.Applied and Environmental Microbiology 06/2007; 73(9):2939-46. · 3.83 Impact Factor -
Article: The microcystin composition of the cyanobacterium Planktothrix agardhii changes toward a more toxic variant with increasing light intensity.
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ABSTRACT: The cyanobacterium Planktothrix agardhii, which is dominant in many shallow eutrophic lakes, can produce hepatotoxic microcystins. Currently, more than 70 different microcystin variants have been described, which differ in toxicity. In this study, the effect of photon irradiance on the production of different microcystin variants by P. agardhii was investigated using light-limited turbidostats. Both the amount of the mRNA transcript of the mcyA gene and the total microcystin production rate increased with photon irradiance up to 60 micromol m(-2) s(-1), but they started to decrease with irradiance greater than 100 micromol m(-2) s(-1). The cellular content of total microcystin remained constant, independent of the irradiance. However, of the two main microcystin variants detected in P. agardhii, the microcystin-DeRR content decreased twofold with increased photon irradiance, whereas the microcystin-DeLR content increased threefold. Since microcystin-DeLR is considerably more toxic than microcystin-DeRR, this implies that P. agardhii becomes more toxic at high light intensities.Applied and Environmental Microbiology 10/2005; 71(9):5177-81. · 3.83 Impact Factor -
Article: The microcystin composition of the cyanobacterium Planktothrix agardhii changes towards a more toxic variant with increasing light intensity
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ABSTRACT: The cyanobacterium Planktothrix agardhii, which is dominant in many shallow eutrophic lakes, can produce hepatotoxic microcystins. Currently, more than 70 different microcystin variants have been described, which differ in toxicity. In this study, the effect of photon irradiance on the production of different microcystin variants by P. agardhii was investigated using light-limited turbidostats. Both the amount of the mRNA transcript of the mcyA gene and the total microcystin production rate increased with photon irradiance up to 60 µmol m–2 s–1, but they started to decrease with irradiance greater than 100 µmol m–2 s–1. The cellular content of total microcystin remained constant, independent of the irradiance. However, of the two main microcystin variants detected in P. agardhii, the microcystin-DeRR content decreased twofold with increased photon irradiance, whereas the microcystin-DeLR content increased threefold. Since microcystin-DeLR is considerably more toxic than microcystin-DeRR, this implies that P. agardhii becomes more toxic at high light intensities. Copyright © 2005, American Society for Microbiology. All Rights Reserved. -
Article: Production of cyanopeptolins, anabaenopeptins, and microcystins by the harmful cyanobacteria Anabaena 90 and Microcystis PCC 7806
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Institutions
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2005–2011
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Universiteit van Amsterdam
- Institute for Biodiversity and Ecosystem Dynamics
Amsterdam, North Holland, Netherlands
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