RESUMO
Picocyanobacteria are important primary producers in freshwater; however, there is still a knowledge gap regarding their diversity at the strain level. For this reason, the microbial diversity of four lakes with different trophic states was investigated by sequencing of the 16S rRNA gene using universal primers. The study was performed in selected lakes of the Osterseen Lake District, Germany, from 2012 to 2014 (Lake Schiffhuettensee: eutrophic; Lake Ostersee: meso-oligotrophic; Lake Groebensee: oligotrophic; Lake Lustsee: oligotrophic). It was determined that the bacterial community of each of these lakes was characterized by one or more specific phyla. Within the autotrophic plankton, the picocyanobacterium Synechococcus sp. dominated oligotrophic habitats, whereas eukaryotic algae prevailed in eutrophic lakes. The study focused on the occurrence of cyanobacteria, specifically the genus Synechococcus. Genetic analysis of the 16S rRNA gene revealed an extendend diversity of freshwater Synechococcus. The occurrence of the identified operational taxonomic units of Synechococcus did not correlate with the trophic state of their habitat, suggesting that the current, underestimated diversity of picocyanobacteria deserves increased consideration in assessments of microbial and freshwater biodiversity.