Vertical Heterogeneity of Genotypic Structure and Toxic Potential within Populations of the Harmful Cyanobacterium Microcystis aeruginosa

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Vie planctonique et vie benthique de la Cyanobactérie Microcystis aeruginosa sur la retenue de Grangent (Loire)

ST ETIENNE-BU Sciences (422182103) / SudocSudocFranceF

Potential of cyanobacterial akinetes reviviscence through a 6700 years core in a eutrophic lake

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A dynamical model of toxic cyanobacteria growth in the case of lake eutrophication

International audienc

Effect of sedimentation ponds on the mitigation of eutrophication lake: evidence from lake Aydat (France)

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Higher sensitivity to hydrogen peroxide and light stress conditions of the microcystin producer Microcystis aeruginosa sp PCC7806 compared to non-producer strains.

The increasing incidence of cyanobacterial blooms with their associated production of cyanotoxins lead managers of aquatics systems to control their biomass to limit the health risk. Among the variety of existing treatment approaches, hydrogen peroxide (H2O2) shows increasing use but the effects of environmental parameters on its effectiveness are still not completely known. With the aim to assess the efficiency of H2O2 treatments in the control of cyanobacterial blooms and decrease toxic risk, we tested three Microcystis strains according to their ability to produce cyanotoxins (a microcystin-producing, non-microcystin-producing and mcyB-knockout mutant). Photochemical efficiency, percentage of living cells and microcystin cell content were compared under various hydrogen peroxide concentrations coupled with stress conditions encountered during the life cycle of cyanobacteria as darkness and high light. The microcystin-producing strain appeared the more sensitive to hydrogen peroxide treatment and to light condition, probably due to a lower rate of repair of Photo System II (PSII). We also highlighted various responses of PSII activity according to Microcystis strains which could partly explain the shift of dominant genotypes often occurring during a bloom event. Our results confirm the link between light and microcystin content and variations of microcystin contents appear as a consequence of photosynthetic activity. These findings could be of particular interest regarding water quality management, especially the use of H2O2 as a potential algaecide which seems to be more effective to use during periods of high light

Benthic survival of Microcystis: Long-term viability and ability to transcribe microcystin genes

International audienceMicrocystis is a microcystin-producing cyanobacterium known to proliferate in the water column of freshwater ecosystems, and to overwinter in the sediment. In this study, we demonstrate that microcystins can remain present in benthic cells buried in the sediment for long periods, and suggest that Microcystis is able to produce microcystins throughout its benthic survival. We investigated the viability and ability to transcribe one microcystin gene (mcyB) in three benthic populations of Microcystis containing microcystins. We chose deeply buried benthic populations that had been trapped in the sediment for periods ranging from several months to more than 6 years. Merely by revealing the presence of mcyB mRNA in every benthic population we investigated, we showed that benthic Microcystis could remain viable and able to initiate microcystin production after more than 6 years of benthic life. This finding also suggests that microcystins could be involved in the benthic survival mechanisms of Microcystis. The quantification of mcyB transcripts by RT-qPCR did not detect any visible influence of the duration of the benthic life stage, although the three populations did display different mcyB transcription levels