| Water samples were collected in the outbreak and decline of Microcystis spp. bloom in three different lake areas of Lake Xuanwu for studying the bacterial community composition during the bloom to provide clew for understanding the dynamics of water bloom. Traditional microbiological methods were used for culturable bacterial analysis, while the amplified products of variable V3 region of bacterial 16S rDNA were used for bacterial community DNA finger print by using denaturing gradient gel electrophoresis (DGGE), and the 16S rDNA sequences of predominant bacteria in the community were used for phylogenetic analysis. Results showed three groups of bacteria were detected during Microcystis spp. bloom, including Proteobacteria, Firmicutes and Bacteroides. In the outbreak of the boom, the propotion of Firmicutes, Bacteroides and α-,β-,γ-Proteobacteria in total bacteria account for 31.25%, 25%, 18.75%, 12.5% and 12.5% respectively, and sixteen genera of bacteria are predominant in the bacterial community. While in the decline of the bloom, the proportion of γ-Proteobacteria increases up to 50%, followed by Firmicutes and α-Proteobacteria, with the proportion of 33.3% and 16.7% respectively. Some species including Hydrogenophaga, Vogesella, Sphingomonas, and Exiguobacterium disappear when the bloom declining, but the abundance of total bacterial goes up. Pseudomonas and Bacillus are always the leading genera but with changing in species. During the same stage of the bloom, bacterial diversity in the lake area with more Microcystis spp. aggregates is lower. The variation in bacterial community composition may be correlated with changes of organic matters and other environmental factors that affected directly by wax and wane of Microcystis spp. aggregates, and the density of the aggregates may have effect on bacterial diversity. |
