Seasonal shifts in chemotype composition of Microcystis sp. communities in the pelagial and the sediment of a shallow reservoir

Welker, Martin; Šejnohová, Lenka; Némethová, Danka; Döhren, Hans von; Jarkovský, Jiří; Maršálek, Blahoslav

doi:10.4319/lo.2007.52.2.0609

Cited by 68 publications

(61 citation statements)

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“…Field studies have indicated that different Microcystis morphotypes may show different ecostrategies in the field (36). MrpC, as a potential colony type-specific factor, may be highly important for the competitive advantage of specific Microcystis ecotypes in the field.…”

Section: Discussionmentioning

confidence: 99%

An Extracellular Glycoprotein Is Implicated in Cell-Cell Contacts in the Toxic CyanobacteriumMicrocystis aeruginosaPCC 7806

et al. 2008

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Microcystins are the most common cyanobacterial toxins found in freshwater lakes and reservoirs throughout the world. They are frequently produced by the unicellular, colonial cyanobacterium Microcystis aeruginosa; however, the role of the peptide for the producing organism is poorly understood. Differences in the cellular aggregation of M. aeruginosa PCC 7806 and a microcystin-deficient ⌬mcyB mutant guided the discovery of a surface-exposed protein that shows increased abundance in PCC 7806 mutants deficient in microcystin production compared to the abundance of this protein in the wild type. Microcystis aeruginosa is a unicellular colonial cyanobacterium frequently producing mass developments and surface scums in freshwater habitats. Microcystis cyanobacteria are widely known for their production of the potent hepatotoxin microcystin. Microcystins are a family of cyclic heptapeptides that potently inhibit protein phosphatases of the eukaryotic protein phosphatase P family. Several cases of human and animal poisonings have been attributed to the presence of these toxins in water supplies and recreational lakes (6, 15). Microcystins are synthesized by a large enzyme complex comprising nonribosomal peptide synthetases, polyketide synthases, and tailoring enzymes (32).In the environment, Microcystis occurs as a mixture of morphotypes that differ in their cell and sheath characteristics (17). The formation of large colonies embedded in mucilage and the presence of gas vesicles enable Microcystis colonies to regulate their buoyancy (35). The ability to migrate vertically in lakes provides a significant advantage over many other phytoplankton species (1). Several studies have shown a correlation of Microcystis morphotypes with the presence of specific peptides. Microcystins are most frequently associated with M. aeruginosa and M. viridis, whereas other Microcystis morphotypes, such as M. wesenbergii and M. ichthyoblabe, usually lack these peptides (8, 34). A possible correlation of colony form and the nonribosomal peptide microcystin was further supported by the finding that microcystin influences the expression and oligomerization of a surface-exposed lectin that may facilitate the recognition and attachment of Microcystis cells (16). In addition, there is increasing evidence that microcystin released from dead cells may serve as an infochemical in the Microcystis community, thereby enhancing the fitness of surviving cells (26). The microcystin-dependent expression of the two microcystin-related proteins MrpA and MrpB that show similarity to the quorum sensing-controlled RhiA and RhiB proteins in Rhizobium leguminosarum (11) further supports the idea that microcystin may be perceived as an intercellular signal (4).In the present study, the correlation of microcystin with a novel surface-exposed component, a glycoprotein, is reported. In the past few decades, an increasing number of bacterial proteins have been shown to be glycosylated, including a wide range of different cell envelope components such as membrane-ass...

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Section: Discussionmentioning

confidence: 99%

An Extracellular Glycoprotein Is Implicated in Cell-Cell Contacts in the Toxic CyanobacteriumMicrocystis aeruginosaPCC 7806

et al. 2008

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“…Microcystis populations often consist of mixtures of microcystin-producing and non-microcystin-producing strains (10,23,48,52). Interestingly, several studies show that the average microcystin content expressed per cell is typically high at the onset of Microcystis blooms but much lower at the height of these blooms (22,51,53). In other words, with increasing Microcystis biomass, the Microcystis cells become, on average, less toxic.…”

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“…Thus, it seems that the changes in microcystin contents during the development of Microcystis blooms are due to a seasonal succession of toxic and nontoxic strains, in which nontoxic strains prevail at the height of the Microcystis bloom. A seasonal succession of toxic and nontoxic Microcystis geno-or chemotypes has indeed been observed in several lakes (11,53).Competition for light is an important selective factor in phytoplankton communities of eutrophic waters (16,18,28). Competition models predict that the species (or genotype) with the lowest "critical light intensity" is the best competitor for light, as it can withstand the shading cast by its competitors (15,50).…”

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Competition for Light between Toxic and Nontoxic Strains of the Harmful Cyanobacterium Microcystis

Kardinaal

Tonk

Janse

et al. 2007

Appl Environ Microbiol

185

160

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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.Blooms of the cyanobacterium Microcystis can be a major hazard in recreational lakes, drinking water reservoirs, and protected wetland areas (6,47,49). Microcystis often forms dense blooms that may cause anoxia when cells die off massively. Moreover, Microcystis can produce the toxin microcystin. This hepatotoxin poses serious health risks for animals and humans (3, 7). Especially in dense scums, the concentration of microcystins may increase dramatically. Microcystin concentrations up to 25,000 g liter Ϫ1 have been reported (10), exceeding the guideline values for recreational waters of 20 g liter Ϫ1 by more than 3 orders of magnitude (5). Microcystis populations often consist of mixtures of microcystin-producing and non-microcystin-producing strains (10, 23, 48, 52). Interestingly, several studies show that the average microcystin content expressed per cell is typically high at the onset of Microcystis blooms but much lower at the height of these blooms (22,51,53). In other words, with increasing Microcystis biomass, the Microcystis cells become, on average, less toxic. Examples from three Microcystis-dominated Dutch lakes are shown in Fig. 1. This striking seasonal variability in microcystin content of Microcystis blooms exceeds the physiological variability in cellular microcystin content reported for isolated Microcystis strains in laboratory experiments (13,29,54). Thus, it seems that the changes in...

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“…Although some studies have explained the decrease of cyanobacterial biomass by cyanophage (lysis viruses) (Yoshida et al, 2006), predatory bacteria (Mayali and Azam, 2004) in the water column and/or sedimentation of the population (Visser et al, 1995;Welker et al, 2007), the degenerative process in water blooms is still not thoroughly understood. The stage of decline 38 Vol.30 CHIN.…”

Section: Introductionmentioning

confidence: 99%

The decline process and major pathways of Microcystis bloom in Taihu Lake, China

Wang

et al. 2012

Chin. J. Ocean. Limnol.

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Eutrophication has become a serious concern in many lakes, resulting in cyanobacterial blooms. However, the mechanism and pathways of cyanobacteria decline are less understood. To identify and define the growth and decline of Microcystis blooms in Taihu Lake of China, and to illuminate the destination of surface floating blooms, we investigated the biomass distribution and variations in colony size, morphology, and floating velocity from October 2008 to September 2009. The results showed that the Microcystis bloom declined in response to biomass decrease, colony disaggregation, buoyancy reduction, and increased phytoplankton biodiversity, and these indicative parameters could be applied for recognition of the development phases of the bloom. Three major decline pathways were proposed to describe the bloom decline process, colony disaggregation (Pathway I), colony settlement (Pathway II), and cell lysis in colonies (Pathway III). We proposed a strategy to define the occurrence and decline of Microcystis blooms, to evaluate the survival state under different stress conditions, and to indicate the efficiency of controlling countermeasures against algal blooms.

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Seasonal shifts in chemotype composition of Microcystis sp. communities in the pelagial and the sediment of a shallow reservoir

Cited by 68 publications

References 40 publications

An Extracellular Glycoprotein Is Implicated in Cell-Cell Contacts in the Toxic CyanobacteriumMicrocystis aeruginosaPCC 7806

An Extracellular Glycoprotein Is Implicated in Cell-Cell Contacts in the Toxic CyanobacteriumMicrocystis aeruginosaPCC 7806

Competition for Light between Toxic and Nontoxic Strains of the Harmful Cyanobacterium Microcystis

The decline process and major pathways of Microcystis bloom in Taihu Lake, China

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