Microbial diversity and toxin risk in tropical freshwater reservoirs of Cape Verde

The Cape Verde islands are part of the African Sahelian arid belt that possesses an irregular rainy season between August and October. This erratic rain pattern has prompted the need for water reservoirs, now critical for the countrys sustainability. Worldwide, freshwater cyanobacterial blooms are increasing in frequency due to global climate change and eutrophication of water bodies, particularly in reservoirs. To date there have been no risk assessments of cyanobacterial toxin production in these man-made structures. We evaluated this potential risk using 16S rRNA gene amplicon sequencing and full metagenome sequencing in freshwater reservoirs of Cape Verde.\n\nOur analysis revealed the presence of several potentially toxic cyanobacterial genera in all sampled reservoirs (Poilao, Saquinho and Faveta). In Faveta Microcystis sp., a genus well known for toxin production and bloom-formation, dominated our samples, while a green algae of the genus Cryptomonas and Gammaproteobacteria dominated Saquinho and Poilao.\n\nTaking advantage of the dominance of Microcystis in the Faveta reservoir, we were able to reconstruct and assemble its genome, extracted from a metagenome of bulk DNA from Faveta water. We named it Microcystis cf. aeruginosa CV01, for which a phylogenetic analysis revealed to have a close relationship with other genomes from those taxa, as well as other continental African strains, suggesting geographical coherency. In addition, it revealed several clusters of known toxin-producing genes. This assessment of Cape Verdean freshwater microbial diversity and potential for toxin production reinforces the need to better understand the microbial ecology as a whole of water reservoirs on the rise.