Identification of genes for anatoxin-a biosynthesis in Cuspidothrix issatschenkoi

• The ana gene clusters of Cuspidothrix issatschenkoi strains were sequenced.
• The ana genes of C. issatschenkoi differed from those of Oscillatoria and Anabaena.
• Truncation and deletion of ana genes were observed in C. issatschenkoi strains.
• C. issatschenkoi strains formed an independent clade in the phylogenetic tree of 16S rrn.

Considerable attention has been paid to anatoxin-a due to its severe neurotoxicity, and anatoxin-a biosynthesis gene cluster (ana) has recently been characterized in the Oscillatoria and Anabaena genera. To gain further insight into the genetic basis of anatoxin-a biosynthesis in cyanobacteria, the ana gene clusters of three Cuspidothrix issatschenkoi strains were sequenced. The ana gene arrangement patterns of C. issatschenkoi strains were identical and differed from those of Oscillatoria and Anabaena. A conserved section containing anaB through anaG was observed in these species. The ana genes of C. issatschenkoi strains were highly similar (95% to 100%), and were more similar to those of Anabaena (84% to 96%) than to those of Oscillatoria (82% to 90%) except anaA and orf1. Low similarities were observed for orf1 (67% to 77%) between C. issatschenkoi and Anabaena and Oscillatoria. The Orf1 sequences in anatoxin-a-producing C. issatschenkoi RM-6 and C. issatschenkoi LBRI48 were truncated at the N-terminal. The methyltransferase domain of AnaG in non-anatoxin-a-producing C. issatschenkoi CHABD3 was absent and transcription of anaG can be detected in this strain. All the C. issatschenkoi strains were clustered into an independent clade in the phylogenetic tree based on 16S rrn. In conclusion, the ana genes have experienced different degrees of sequence variations and loss of the ability to produce anatoxin-a in cyanobacterial strains may be due to deletion of ana genes.