Abstract
Picocyanobacteria are essential primary producers in freshwaters yet little is known about their genomic diversity and ecological niches. We report here five draft genomes of freshwater picocyanobacteria: Synechococcus sp. CCAP1479/9, Synechococcus sp. CCAP1479/10, and Synechococcus sp. CCAP1479/13 isolated from Lake Windermere in the Lake District, UK; and Synechococcus sp. CCY0621 and Synechococcus sp. CCY9618 isolated from lakes in The Netherlands. Phylogenetic analysis reveals all five strains belonging to sub-cluster 5.2 of the Synechococcus and Prochlorococcus clade of Cyanobacteria. These five strains are divergent from Synechococcus elongatus, an often-used model for freshwater Synechococcus. Functional annotation revealed significant differences in the number of genes involved in the transport and metabolism of several macro-molecules between freshwater picocyanobacteria from sub-cluster 5.2 and Synechococcus elongatus, including amino acids, lipids, and carbohydrates. Comparative genomic analysis identified further differences in the presence of photosynthesis-associated proteins while gene neighbourhood comparisons revealed alternative structures of the nitrate assimilation operon nirA.