Morphological and physiological impacts of salinity on colonial strains of the cyanobacteria <i>Microcystis aeruginosa</i>

Bormans, Myriam; Legrand, Benjamin; Waisbord, Nicolas; Briand, Enora

doi:10.1002/mbo3.1367

Cited by 4 publications

References 33 publications

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Morphological and physiological impacts of salinity on colonial strains of the cyanobacteria Microcystis aeruginosa

et al. 2023

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In the context of global change and enhanced toxic cyanobacterial blooms, cyanobacterial transfer to estuaries is likely to increase in frequency and intensity and impact animal and human health. Therefore, it is important to evaluate the potential of their survival in estuaries. In particular, we tested if the colonial form generally observed in natural blooms enhanced the resistance to salinity shock compared to the unicellular form generally observed in isolated strains. We tested the impact of salinity on two colonial strains of Microcystis aeruginosa, producing different amounts of mucilage by combining classical batch methods with a novel microplate approach. We demonstrate that the collective organization of these pluricellular colonies improves their ability to cope with osmotic shock when compared to unicellular strains. The effect of a sudden high salinity increase (S ≥ 20) over 5 to 6 days had several impacts on the morphology of M. aeruginosa colonies.For both strains, we observed a gradual increase in colony size and a gradual decrease in intercellular spacing. For one strain, we also observed a decrease in cell diameter with an increase in mucilage extent. The pluricellular colonies formed by both strains could withstand higher salinities than unicellular strains studied previously. In particular, the strain producing more mucilage displayed a sustained autofluorescence even at S = 20, a limit that is higher than the most robust unicellular strain. These results imply survival and possible M. aeruginosa proliferation in mesohaline estuaries.

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Morphological and physiological impacts of salinity on colonial strains of the cyanobacteria Microcystis aeruginosa

et al. 2023

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Production and composition of extracellular polymeric substances by a unicellular strain and natural colonies of Microcystis: Impact of salinity and nutrient stress

Reignier,

Bormans,

Marchand

et al. 2023

Environ Microbiol Rep

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The transfer of toxic cyanobacterial Microcystis blooms from freshwater to estuaries constitutes a serious environmental problem worldwide that is expected to expand in scale and intensity with anthropogenic and climate change. The formation and maintenance of Microcystis in colonial form is conditioned to the presence of extracellular polymeric substances (EPS). In this study, we attempted to better understand how the mucilaginous colonial form of Microcystis evolves under environmental stress conditions. In particular, we studied and compared the production and the composition of EPS fractions (attached and free) from natural colonies of a Microcystis bloom and from a unicellular M. aeruginosa strain under salinity and nutrient stress (representing a land‐sea continuum). Our results highlighted a greater production of EPS from the natural colonies of Microcystis than the unicellular one under nutrient and combined stress conditions dominated by the attached form. In comparison to the unicellular Microcystis, EPS produced by the colonial form were characterized by high molecular weight polysaccharides which were enriched in uronic acids and hexosamines, notably for the free fraction in response to increased salinities. This complex extracellular matrix gives the cells the ability to aggregate and allows the colonial cyanobacterial population to cope with osmotic shock.

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Effects of salinity and nutrient stress on a toxic freshwater cyanobacterial community and its associated microbiome: An experimental study

Reignier,

Briand,

Hervé

et al. 2024

Environ Microbiol Rep

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We aimed to evaluate the ability of naturally occurring colonies of Microcystis, embedded in a thick mucilage, to persist in estuarine waters. In two batch experiments, we examined the dynamics of microbial communities, including cyanobacteria and associated heterotrophic bacteria, sampled from the field during both a cyanobacterial bloom (non‐limiting nutrient condition) and the post‐bloom period (limiting nutrient condition), and subjected them to a salinity gradient representative of the freshwater‐marine continuum. We demonstrated that both Microcystis aeruginosa and M. wesenbergii survived high salinities due to osmolyte accumulation. Specifically, prolonged exposure to high salinity led to betaine accumulation in the cyanobacterial biomass. The relative abundance of the mcyB gene remained around 30%, suggesting no selection for toxic genotypes with salinity or nutrient changes. Microcystins were predominantly intracellular, except at high salinity levels (>15), where more than 50% of the total microcystin concentration was extracellular. In both nutrient conditions, over 70% of the heterotrophic bacterial community belonged to the Gammaproteobacteria family, followed by the Bacteroidota. Bacterial community composition differed in both size fractions, as well as along the salinity gradient over time. Finally, genus‐specific core microbiomes were identified and conserved even under highly stressful conditions, suggesting interactions that support community stability and resilience.

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Morphological and physiological impacts of salinity on colonial strains of the cyanobacteria Microcystis aeruginosa

Cited by 4 publications

References 33 publications

Morphological and physiological impacts of salinity on colonial strains of the cyanobacteria Microcystis aeruginosa

Morphological and physiological impacts of salinity on colonial strains of the cyanobacteria Microcystis aeruginosa

Production and composition of extracellular polymeric substances by a unicellular strain and natural colonies of Microcystis: Impact of salinity and nutrient stress

Effects of salinity and nutrient stress on a toxic freshwater cyanobacterial community and its associated microbiome: An experimental study

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