[Composition of Microcystis species of the cyanobacterial bloom in Xuanwu Lake of Nanjing].

The aim of the present study was to clarify the community composition of cyanobacterial bloom in Xuanwu Lake of Nanjing city. The Microcystis colonies in cyanobacterial blooms sampled from Xuanwu Lake during August 2005 and September 2006 were identified by morphological characteristics and internal transcribed spacer sequence (ITS). The results indicated that the bloom was composed mainly by Microcystis aeruginosa, M. novacekii and M. wesenbergii. The biomass percentage of them was 30%-45%, 35%-40% and 10%-15%, respectively. ITS of two dominant Microcystis strains were amplified by PCR and sequenced to identify their species. The analysis of ITS sequences and the ITS phylogenetic tree demonstrated that the two dominant species should be M. aeruginosa and M. novacekii. A microcystin-producing gene mcyB was detected to test toxic strain. A unique product of approximately 780 bp was amplified in two dominant strains. It indicated that both of them were of microcystin-producing genotype. High performance liquid chromatography (HPLC) analysis showed that the toxins in the native bloom biomass were mainly MC-LR and MC-RR.