Phylogenetic relationships among filamentous helical cyanobacteria investigated on the basis of 16S ribosomal RNA gene sequence analysis

The cyanobacterial genera Spirulina and Arthrospira are both characterized by helical trichomes but their taxonomy is controversial and a phylogenetic study is necessary. The sequence of the 16S rRNA gene and the spacer between the 16S and 23S rRNA genes (ITS) was determined for three filamentous coiled cyanobacteria: Spirulina PCC 6313, Arthrospira PCC 7345 and Arthrospira PCC 8005. A distance tree based on the 16S rRNA sequences was constructed using the neighbor-joining method. This tree shows that the two Arthrospira strains are not closely related to the Spirulina strain but belong to a cluster of strains assigned to the genera Oscillatoria, Lyngbya, and Microcoleus. The strain Spirulina PCC 6313 belongs to a branching containing unicellular cyanobacteria. For the two Arthrospira strains, the sequenced ITS region contains the tRNA(Ile) and tRNA(Ala) genes, whereas the spacer region of strain Spirulina PCC 6313 contains only the tRNA(Ile) gene.3. Good health and well-bein