Evidence for recombination in the microcystin synthetase (mcy) genes of toxic cyanobacteria Microcystiis spp.

Recombination has been suggested to be an important factor for the genetic variation of bacterial genes, but few Studies have dealt with intragenic recombination between the same or closely related species of cyanobacteria. Here we provide strong evidence for recombination in the nucrocystin synthetase (mcy) gene Cluster of the toxic cyanobacteria pp. This gene cluster contains 10 genes Microcystis spp. (mcyA to J) that encode a mixed polyketide synthase (PKS)/nonribosomal peptide synthetase (NRPS) complex. mcy gene sequences were determined for four selected regions (within mcyA, D, G, and J) within the mcy gene cluster from 1 Canadian and 10 Asian toxic Microcystis and compared with previously published mcy sequences. Split decomposition analysis indicated a reticulate phylogeny of mcyA, and several potential recombination tracts or mcyA were identified by the RDP analysis and a runs test implemented in GENECONV. In contrast, no recombination was detected in the mcyD, G, and J sequences. However, discrepancies among the four mcy gene genealogies were evident from the results Of independent split decomposition analyses,. which were Further supported by incongruence length difference (ILD) tests. Taken together, these findings suggest that both intragenic and intergenic recombination within the mcy gene cluster contributes to the genetic diversity of the mcy genes of Microcystis spp.