Molecular separation of two long taxonomically debated cyanobacterial genera Cylindrospermopsis and Raphidiopsis (Nostocales) based on the ITS-L phylogeny

The cyanobacterial genera Raphidiopsis and Cylindrospermopsis morphologically resembled each other and are difficult to distinguish, especially when heterocytes do not form in Cylindrospermopsis species. The phylogeny based on multiple gene loci sequences in previous studies cannot divide the strains of these two genera into separate clusters. In the present study, four gene loci 16S rRNA, ITS-L, cpcBA-IGS and rpoC1, sequenced from many Chinese strains (44 Cylindrospermopsis strains and 16 Raphidiopsis strains), were analyzed to infer the phylogenetic relationship between the two genera. According to the 16S rRNA, cpcBA-IGS and rpoC1 gene phylogeny, Cylindrospermopsis and Raphidiopsis strains are intermixed and divide into two or three groups. By contrast, the ITS-L analysis implied that they respectively form two separate and unique clusters. A fragment of 7 bp (RAGAAACT) in ITS-L was conserved for Raphidiopsis strains, which could be distinguished from Cylindrospermopsis strains. A pair of primers targeting the ITS-L fragment specific to Raphidiopsis strains were designed and further verified.