Phylogenetic diversity of freshwater picocyanobacteria

HUBER, M. P.; UNREIN, F.

Workshop; 18th Workshop of the International Association of Phytoplankton Taxonomy and Ecology (IAP); 2017

The phylogenetic relationships of freshwater picocianobacteria remain poorly known. Studies carried out in freshwater systems are still scarce and restricted to a limited number of environments. Here, we aimed at expand the knowledge about the diversity of freshwater picocyanobacteria linking phylogenetic and morphology information with ecological traits. To investigate this, we constructed phylogenetic trees based on 16S rRNA and 16S rRNA+ITS sequences from literature and 206 new sequences from strains and environmental clones retrieved from eutrophic pampean shallow lakes. The topology of the two phylogenetic trees were similar, and consistent with published trees. We identified 17 clades previously described by other authors and 8 new lineages, 5 of which were exclusive to pampean shallow lakes. Some clades were cosmopolitan while others were restricted to certain environment. In the 16S rRNA+ITS tree the most cosmopolitan clades were divided into subclades, that seems to be related with particular limnological features of the systems. At least 6 clades were conformed by single-cells (Pcy) and colonial (CPcy) picocyanobacteria, while other clades were exclusive of each morphotype. Our findings revealed the existence of a great phylogenetic diversity of freshwater picocyanobacteria, and highlighting the importance of enlarge the data set with sequences from diferent environments. Besides, our results support the importance of the ITS region in phylogenies of picocyanobacteria as a valuable molecular marker that allows the analysis of microdiversity within lineages of closely related taxa. Finally, we can conclude that the colonial and unicellular morphotypes of picocianobacterias are closely related, and the phenotypic plasticity of Synechococcales (i.e. the ability of single-cell to aggregae into colonies) would be associated to certain phylogenetic groups.