Insights into the cyanosphere: capturing the respective metabolisms of cyanobacteria and chemotrophic bacteria in natural conditions?

International audienceSpecific interactions have been highlighted betweencyanobacteria and chemotrophic bacteria within thecyanosphere, suggesting that nutrients recycling couldbe optimized by cyanobacteria/bacteria exchanges. Inorder to determine the respective metabolic roles ofthe cyanobacterial and bacterial consortia (micro-biome), a day–night metatranscriptomic analysis wasperformed onDolichospermumsp. (N2-fixer) andMicro-cystissp. (non N2-fixer) natural blooms occurringsuccessively within a Frenchperi-urban lake. The taxo-nomical and functional analysis of the metatran-scriptoms have highlighted specific association ofbacteria within the cyanosphere, driven by the cyano-bacteria identity, without strongly modifying the func-tional composition of the microbiomes, suggestingfunctional redundancy within the cyanosphere. More-over, the functional composition of these active com-munities was driven by the living mode. During the twosuccessive bloom events, it appeared that NH4+(newlyfixed and/or allochthonous) was preferentially trans-formed into amino acids for the both the microbiomeand the cyanobacteria, while phosphate metabolismwas enhanced, suggesting that due to a high cellulargrowth, P limitation might take place within the cyano-sphere consortium