UNRAVELING MOLECULAR DIVERSITY AND PHYLOGENY OF APHANIZOMENON (NOSTOCALES, CYANOBACTERIA) STRAINS ISOLATED FROM CHINA1

Fifty-three strains of the genus Aphanizomenon isolated from Chinese waters were employed to conduct morphological examination and sequencing of the 16S rRNA gene, rbcLX (RUBISCO), and cpcBA-IGS gene regions. Based on morphological characteristics, the examined strains were divided into three morphotypes [Aph. flos-aquae Breb. ex Bornet et Flahault, Aph. gracile Lemmerm., and Aph. issatchenkoi (Usacer) Proshk.-Lavr.]. Phylogenetic analysis based on 16S rRNA and rbcLX showed that Aphanizomenon strains could be divided into three main clades (Clade A of Aph. flos-aquae, Clade B of Aph. gracile, and Clade C of Aph. issatchenkoi), but two additional clades formed by Aph. ovalisporum and Aph. aphanizomenoides were detected in the 16S rDNA-based topology. All Aph. issatchenkoi strains contained an additional 175 nucleotides from the 779 to 954 nucleotide location in rbcLX region, compared with strains of Aph. flos-aquae and Aph. gracile. The cpcBA-IGS-based phylogenetic tree revealed that Aph. issatchenkoi strains were not discriminated from Aph. flos-aquae strains; however, a concatenated alignment of 16S rDNA, rbcLX, and cpcBA-IGS led to the three distinct clades (Aph. flos-aquae, Aph. gracile, and Aph. issatchenkoi, respectively). It is suggested that the taxonomic revision of Aphanizomenon and Anabaena genera is required to be performed by employing multilocus sequence analysis and polyphasic studies.