RESEARCH ARTICLE Structural Diversity of Bacterial Communities Associated with Bloom-Forming Freshwater Cyanobacteria Differs According to the Cyanobacterial Genus

The factors and processes driving cyanobacterial blooms in eutrophic freshwater ecosys-tems have been extensively studied in the past decade. A growing number of these studies concern the direct or indirect interactions between cyanobacteria and heterotrophic bacte-ria. The presence of bacteria that are directly attached or immediately adjacent to cyano-bacterial cells suggests that intense nutrient exchanges occur between these microorganisms. In order to determine if there is a specific association between cyanobac-teria and bacteria, we compared the bacterial community composition during two cyanobac-teria blooms of Anabaena (filamentous and N2-fixing) andMicrocystis (colonial and non-N2 fixing) that occurred successively within the same lake. Using high-throughput sequencing, we revealed a clear distinction between associated and free-living communities and between cyanobacterial genera. The interactions between cyanobacteria and bacteria appeared to be based on dissolved organic matter degradation and on N recycling, both for N2-fixing and non N2-fixing cyanobacteria. Thus, the genus and potentially the species of cyanobacteria and its metabolic capacities appeared to select for the bacterial community in the phycosphere