Potential genetic diversity of Synechococcus-related strains maintained in the Microbial Culture Collection of the National Institute for Environmental Studies, Japan

Abstract

Picocyanobacteria are some of the important primary producers in aquatic environments. Among these, Synechococcus and its relatives possess great physiological and phylogenetic diversity, allowing adaptation to various environmental conditions. Major marine Synechococccus are divided into subclusters 5.1 to 5.3, and their genetic diversity has been the focus of previous studies. In contrast, the diversity of other Synechococcus-related organisms, mainly composed of freshwater species, is less known. The Microbial Culture Collection of the National Institute for Environmental Studies (MCC-NIES) has identified more than 50 strains as Synechococcus sp.; however, their phylogenetic relationships remain unknown. Therefore, in this study, we sequenced two phylogenetic marker genes, 16S rRNA gene and petB, from most Synechococcus strains maintained by the MCC-NIES, and performed phylogenetic analyses. Although only seven strains in MCC-NIES were assigned to the subcluster 5.1, most of the strains were clustered in the other Synechococcus groups. Based on these analyses, we proposed two new clades, groups J and K, which are mainly composed of NIES strains. We also showed that the molecular marker petB can be used to identify a broad range of Synechococcus-related strains. Overall, our results provide new genetic tools for future metagenomic analyses of picocyanobacteria.