Genetic diversity along the life cycle of the cyanobacterium Microcystis: highlight on the complexity of benthic and planktonic interactions.

Microcystis is a toxic freshwater cyanobacterium with an annual life cycle characterized by the alternation of a planktonic proliferation stage in summer and a benthic resting stage in winter. Given the importance of both stages for the development and the survival of the population, we investigated the genotypic composition of the planktonic and benthic Microcystis subpopulations from the Grangent reservoir (France) during two distinct proliferation periods. Our results showed a succession of different dominant genotypes in the sediment as well as in the water all along the study periods with some common genotypes to both compartments.

The importance of small colonies in sustaining Microcystis population exposed to mixing conditions: an exploration through colony size, genotypic composition and toxic potential.

Microcystis is a toxic colony-forming cyanobacterium, which can bloom in a wide range of freshwater ecosystems. Despite the ecological advantage of the colonial form, few studies have paid attention to the size of Microcystis colonies in the field. With the aim of evaluating the impact of a fluctuating physical environment on the colony size, the genotypic composition and the toxic potential of a Microcystis population, we investigated five different colony size classes of a Microcystis bloom in the Grangent reservoir (France).

Evidence of the cost of the production of microcystins by Microcystis aeruginosa under differing light and nitrate environmental conditions.

The cyanobacterium Microcystis aeruginosa is known to proliferate in freshwater ecosystems and to produce microcystins. It is now well established that much of the variability of bloom toxicity is due to differences in the relative proportions of microcystin-producing and non-microcystin-producing cells in cyanobacterial populations. In an attempt to elucidate changes in their relative proportions during cyanobacterial blooms, we compared the fitness of the microcystin-producing M.

Spatiotemporal variations in microcystin concentrations and in the proportions of microcystin-producing cells in several Microcystis aeruginosa populations.

With the aim of explaining the variations in microcystin (MC) concentrations during cyanobacterial blooms, we studied several Microcystis aeruginosa populations blooming in different freshwater ecosystems located in the same geographical area. As assessed by real-time PCR, it appeared that the potentially MC-producing cells (mcyB(+)) were predominant (70 to 100%) in all of these M. aeruginosa populations, with the exception of one population in which non-MC-producing cells always dominated.

Spatiotemporal changes in the genetic diversity in French bloom-forming populations of the toxic cyanobacterium, Microcystis aeruginosa.

Microcystis aeruginosa is a toxic cyanobacterium, which is able to bloom in a wide range of freshwater ecosystems. By sequencing the Internal Transcribed Spacer (ITS) of the ribosomal operon, we compared the genetic composition of several French bloom-forming M. aeruginosa populations from two reservoirs located on the Loire River, at two sampling points located between these reservoirs, and finally in two ponds closely linked to this river.

Genetic diversity in Microcystis populations of a French storage reservoir assessed by sequencing of the 16S-23S rRNA intergenic spacer.

We compared the genetic diversity of the 16S-23S spacer of the rRNA gene (ITS1) in benthic and pelagic colonies of the Microcystis genus isolated from two different sampling stations with different depths and at two different sampling times (winter and summer) in the French storage reservoir of Grangent. In all, 66 ITS1 sequences were found in the different clone libraries. The nucleotide diversity of all the sampled isolates were in the same range (average number = 0.

[Sampling method adapted for colonial cyanobacteria in a lake environment. Case study of Microcystis aeruginosa in the Grangent reservoir (Loire, France)].

New method of sampling adapted to colonial cyanobacteria was developed on the Grangent reservoir (Loire, France). These prokaryotes were sampled using a filtering pump and were counted at laboratory under epifluorescence microscope. This method allowed us to follow the annual cycle of Microcystis aeruginosa, since benthic spring recruitment (cyanobacteria being used as inoculum) until autumnal sedimentation, and even revealed the presence of this cyanobacterian species in winter in the epilimnion.

Simulation of carbon reserve dynamics in Microcystis and its influence on vertical migration with Yoyo model.

Blue-green algae control their buoyancy depending upon the surrounding conditions. This process is essential for Cyanobacteria development and can account for their dominance in eutrophic waters in summer. In order to determine the main regulating factors of those movements, we developed a mechanistic and deterministic model, based on differential equations, that simulates the vertical migration of Microcystis sp.