Genetic diversity in two species of freshwater cyanobacteria, Planktothrix (Oscillatoria) rubescens and P. agardhii

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Monitoring a toxic cyanobacteria bloom in lake Bourget (France) and its consequences for water quality

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Monitoring a toxic cyanobacteria bloom in lake Bourget (France) and its consequences for water quality

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Comparative 16s RRNA sequencing analysis of the composition of the bacterial communities in contrasting freshwater ecosystems in France and Burkina Faso

International audienceWe compared the composition of the freeliving eubacterioplankton communities in the pelagic zone of three large French sub-Alpine lakes (Annecy, Bourget and Geneva) and of six small reservoirs located in Burkina Faso. More than 1,100 sequences of a 16S rRNA fragment were obtained from 25 clone libraries. In all these freshwater ecosystems, Actinobacteria was the dominant phylum (>40%), followed by Alpha- and Beta-proteobacteria. These three groups contain between 60 and 90% of the sequences retrieved. Picocyanobacteria were found in variable proportions (0-25%), and the remaining sequences were mainly affiliated to Bacteroidetes or Gammaproteobacteria. Despite contrasting trophic levels (oligotrophic to meso-eutrophic), there was no significant difference in the global composition of the bacterioplankton communities of the alpine lakes at the scale of the year. On the other hand, significant differences were found between reservoirs in Burkina Faso, suggesting the presence of local drift in the global composition of the bacterial communities in these small ecosystems. Operational Taxonomic Units (OTUs) were defined on the basis of a taxon resolution of at least 98% sequence similarity. At this taxonomic level, the diversity of the bacterial communities in small African reservoirs, estimated using the Shannon and the Chao1 estimators, was generally greater than the diversities found in Alpine lakes. Finally, a small number of OTUs belonging to the Alphabroteobacteria and to Actinobacteria phyla were found in all the ecosystems studied. It will be very interesting to go on to isolate and characterize these ubiquitous species, which probably play key functional roles in freshwater ecosystems

First evidence of an important organic matter trophic pathway between temperate corals and pelagic microbial communities

International audienceMucus, i.e., particulate and dissolved organic matter (POM, DOM) released by corals, acts as an important energy carrier in tropical ecosystems, but little is known on its ecological role in temperate environments. This study assessed POM and DOM production by the temperate coral Cladocora caespitosa under different environmental conditions. The subsequent enzymatic degradation, growth of prokaryotes and virus-like particles (VLPs) as well as changes in the structure of the prokaryotic communities were also monitored. C. caespitosa produced an important quantity of mucus, which varied according to the environmental conditions (from 37.8 to 67.75 nmol carbon h(-1) cm(-2)), but remained higher or comparable to productions observed in tropical corals. It has an important nutritional value, as highlighted by the high content in dissolved nitrogen (50% to 90% of the organic matter released). Organic matter was rapidly degraded by prokaryotes' enzymatic activities, and due to its nitrogen content, aminopeptidase activity was 500 fold higher than the a-glucosidase activity. Prokaryotes, as well as VLPs, presented a rapid growth in the mucus, with prokaryote production rates as high as 0.31 mu g h(-1) L-1. Changes in bacterial and archaeal communities were observed in the ageing mucus and between mucus and the water column, suggesting a clear impact of mucus on microorganism diversity. Overall, our results show that the organic matter released by temperate corals, such as C. caespitosa, which can form reef structures in the Mediterranean Sea, stimulates microbial activity and thereby functions as a significant carbon and nitrogen supplier to the microbial loop

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

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Genetic Diversity of Cylindrospermopsis Strains (Cyanobacteria) Isolated from Four Continents

The genetic diversity of Cylindrospermopsis strains (cyanobacteria) was examined using mainly the 16S-23S internally transcribed spacer (ITS1) sequences. Strains were grouped in three clusters: (i) America, (ii) Europe, and (iii) Africa and Australia. These results suggested a recent spread of Cylindrospermopsis across the American and European continents from restricted warm refuge areas instead of exchanges between continents. On the other hand, they also suggested a recent colonization of Australia by African strains

Application of submersible spectrofluorometer for rapid monitoring of freshwater cyanobacterial blooms : a case study

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