Phylogenetic analysis of two cyanobacterial genera Cylindrospermopsis and Raphidiopsis based on multi-gene sequences

A multi-gene analysis was performed to investigate the phylogenetic relationship between the cyanobacterial genera Cylindrospermopsis and Raphidiopsis. The phylogeny based on the concatenated sequences of seven gene loci including psbA, 16S rDNA, rbcL, rbcS, rpoC1, cpcB, and ITS1 between 16S and 23S rDNA, indicated that 12 strains of C. raciborskii, 6 strains of R. mediterranea, and 3 strains of R. curvata were clustered into two distinct groups, named as Clade A and Clade B, respectively. Clade A was composed of only strains of C. raciborskii; however, in Clade B, 3 sub-groups were found: 2 well supported sub-groups as termed B1 for R. mediterranea and B2 for R. curvata and R. brookii, and B3 for the remaining strains of C. raciborskii, thus suggesting that Cylindrospermopsis and Raphidiopsis might be congeneric. Additionally, these results also suggested that the traditionally defined C. raciborskii is paraphyletic, and Clade A and Clade B deserved some taxonomic reconsideration, either as separate genera or as separate species within the same genus.