Sporadic Distribution and Distinctive Variations of Cylindrospermopsin Genes in Cyanobacterial Strains and Environmental Samples from Chinese Freshwater Bodies

Abstract

ABSTRACTIncreasing reports of cylindrospermopsins (CYNs) in freshwater ecosystems have promoted the demand for identifying all of the potential CYN-producing cyanobacterial species. The present study explored the phylogenetic distribution and evolution ofcyrgenes in cyanobacterial strains and water samples from China. FourCylindrospermopsisstrains and twoRaphidiopsisstrains were confirmed to produce CYNs. MutantcyrIandcyrKgenes were observed in these strains. Clonedcyrgene sequences from eight water bodies were clustered withcyrgenes fromCylindrospermopsisandRaphidiopsis(C/R group) in the phylogenetic trees with high similarities (99%). FourcyrIsequence types and threecyrJsequence types were observed to have different sequence insertions and repeats. Phylogenetic analysis of therpoC1sequences of the C/R group revealed four conserved clades, namely, clade I, clade II, clade III, and clade V. High sequence similarities (>97%) in each clade and a divergent clade IV were observed. Therefore, CYN producers were sporadically distributed in congeneric and paraphyletic C/R group species in Chinese freshwater ecosystems. In the evolution ofcyrgenes, intragenomic translocations and intergenomic transfer between localCylindrospermopsisandRaphidiopsiswere emphasized and probably mediated by transposases. This research confirms the existence of CYN-producingCylindrospermopsisin China and reveals the distinctive variations ofcyrgenes.