Abstract
The principle organization of microcystin biosynthesis (mcy) gene clusters is characterized in three genera among the microcystin-producing cyanobacteria. To examine the conservation of the mcy gene clusters among the genus Microcystis, internal non-coding regions of the cluster in 21 strains including M. aeruginosa, M. viridis, and M. wesenbergii, were amplified by PCR using specific primer sets and sequenced. PCR-based analysis revealed a completely conserved organization of the bidirectional cluster structure, mcyABC and mcyDEFGHIJ, among all toxic and some microcystin-negative strains. Furthermore, all mcy gene clusters were flanked by a gene with homology to dnaN adjacent to mcyJ and by uma1 with no-homology to any known genes at the 3'-end of mcyC. Transposase homolog genes were observed in a non-coding region between dnaN and mcyJ in three microcystin-producing Microcystis strains. Sequence analysis of a region adjacent to uma1 in mcy-negative strains revealed two types of gene constitution, dnaN-uma1 and the hypothetical protein gene-uma1. PCR-based analyses can be used to assess the identification of microcystin-producer strains in Microcystis spp.
