Global metabolomic characterizations of Microcystis spp. highlights clonal diversity in natural bloom-forming populations and expands metabolite structural diversity

Cyanobacteria are photosynthetic prokaryotes that are able to synthetize a wild rang of secondary metabolites exhibiting noticeable bioactivity, comprising toxicity. Microcystis represents one of the most common cyanobacteria taxa constituting the intensive blooms that arise nowadays in freshwater ecosystems worldwide. They produce numerous cyanotoxins (toxic metabolites), which are potentially harmful to Human health and aquatic organisms. In order to better understand the variations in cyanotoxins production between clones of the Microcystis , we investigate the diversity of several strains isolated from the same blooms, from different populations in various geographical area. Twenty-four clonal strains were compared by genotyping with 16S-ITS fragment sequencing and metabolites chemotyping using LC ESI-qTOF mass spectrometry. While, genotyping can only discriminate between the different species, the global metabolomes reveal clear discriminant molecular profiles between strains. These profiles can be clustered primarily according to their global metabolite content, then to their genotype, and finally to their sampling localities. A global molecular network of all metabolites highlights the production of a wide set of chemically diverse metabolites, comprising only few microcystins, but many aeruginosins, cyanopeptolins and microginins, along with a large set of unknown molecules. They represent the molecular biodiversity that still remain to be investigated and characterized at their structure as well as at their potential bioactivity or toxicity levels.