Genetic Variation of Microcystis Strains from Reservoirs in Guangdong Province Based on DNA-Sequences of the cpcBA–IGS Region

Abstract

With the global increase of eutrophication and water quality deterioration, cyanobacterial blooms become more and more frequent around the world. Microcystis is the most frequent bloom-causing Cyanobacterium in freshwater bodies. Not only do its blooms emit foul odors and increase the cost of water treatment but also produce carcinogenic hepatotoxic microcystins. The taxonomy of Microcystis is the basis of water quality evaluation and management of harmful algae. However, the current taxonomy is mainly based on morphological criteria, and morphospecies do not necessarily reflect the genetic background of these notorious Microcystis strains. As the rapid economic development in the Pearl River Delta has caused river environment degradation, reservoirs have become the main source of drinking water in Guangdong Province; however, Microcystis blooms also plagued these reservoirs. In the present study, cpcBA–IGS of 30 Microcystis strains isolated from 12 reservoirs in Guangdong Province were sequenced, combined with selected 24 Microcystis strains of various geographic origin downloaded from GenBank, to determine their taxonomic status, phylogenetic affinities and geographic distributions. Sixty-seven variable sites and 50 parsimony-informative sites were found in 568 bp cpcBA–IGS region, 54 Microcystis strains were clustered into two major clades, of which clade two involved three strains of M. wesenbergii and one strain of M. marginata and clade 1 included the remaining species and strains. Strains of the same geographic origin did not necessarily cluster together, the same morphospecies may exhibit different genotypes, and the same genotype may represent various morphological characters, indicating that morphological criteria alone are not sufficient to determine species status of Microcystis and molecular markers-based taxonomy of Microcystis is feasible. Although genetic variation of cpcBA–IGS were not large yet in intrageneric level, more sensitive molecular methods such as AFLP and microsatellites are potentially suitable to resolve species status and evaluate the growth and decline of specific Microcystis blooms. Molecular markers will play an evermore important role in studies of Microcystis bloom.