Multilocus and SSU rRNA gene phylogenetic analyses of available cyanobacterial genomes, and their relation to the current taxonomic system

Abstract

Despite the global significance of cyanobacteria, their taxonomy is still heavily lagging behind the progress in genome sequencing. Besides nomenclatural issues and difficulties in species identification, this problem is largely a consequence of missing reference strains and sequences for many cyanobacterial taxa. In this study, a robust multilocus phylogenetic tree based on 23 conserved proteins from the current set of available genomes is presented and compared to a respective 16S rRNA gene tree. To facilitate further progress in achieving a stable system of monophyletic taxa, the phylogenetic status of eight cyanobacterial orders recently proposed in the botanical system was evaluated. While several orders addressed by previous studies (Gloeobacterales, Spirulinales, Chroococcidiopsidales, Nostocales) retain their monophyly, the remaining big groups (Synechococcales, Pleurocapsales, Chroococcales, Oscillatoriales) are polyphyletic and require thorough revision. Comparison of the 16S rRNA tree to the multilocus tree supports the careful use of this gene in distinguishing cyanobacterial genera, whereas its application at other taxonomic levels is limited.