Molecular Ecology Research On Microbial Community In The Water And Sediment Of Eutrophic Lake Taihu

Since the 20th century, eutrophication has affected many freshwater lakes worldwide. The characteristic of eutrophication in freshwater ecosystem is the annual cyanobacterial blooms in spring and summer, which could not only break the balance of microbial ecology in the water but also pose a health risk to the public due to the production of toxic compounds. Nowaday, eutrophication has become a serious environmental problem in China. However, few systematic investigations of the microbial community have been conducted on eutrophic lakes. As a prerequisite to the ecosystem level management of cyanobacterial bloom events, it is essential to understand the relationship between the distribution of microbial community (especially for cyanobacteria) and the development of eutrophication in freshwater ecosystem.Therefore, this study was conducted to characterize the composition and abundance of the microbial community in the water and sediment samples collected from Lake Taihu, using the clone library, denaturing gradient gel electrophoresis (DGGE) and real-time PCR technique. Specifically, this study focused on the variation of cyanobacterial populations in Lake Taihu. Therefore, the goals of this study were to reveal the composition, diversity and abundance of the important microorganisms in Lake Taihu, and to uncover the influence of eutrophication on the sediment ecosystem, which would provide the evidence for the management of eutrophication in Lake Taihu in the future.This study was conducted to provide a detailed understanding of the variation in cyanobacterial communities in the water of Lake Taihu around a year. Based on 16S rRNA gene, DGGE and real-time PCR techniques were conducted to describe the structure and shift of cyanobacterial community in the water. The results suggested that the diversity of the cyanobacterial populations in the pelagic water changed with the development of blooms. The cyanobacterial communities in winter and summer formed two distinguished clusters respectively, but the cyanobacterial communities in spring and autumn were very similar. Microcystis and Synechococcus were the two most dominant in the blooms, which would affect the growth of other cyanobacterial populations and cause the decrease of cyanobacterial diversity in the bloom season. Microcystis and Synechococcus showed different growth dynamics around a year. In the early period of blooms, Synechococcus grew faster than Microcystis, while Microcystis grew faster than Synechococcus in the late period of blooms. After the blooms, Microcystis seemed to better survive the winter than Synechococcus. The diversity and abundance of potential MC (Microcystin)- producing cyanobacteria was evaluated based on the mcyA-Cd gene fragment. The results revealed that all MC-producing genotypes detected in Lake Taihu belonged to the genus Microcystis. The MC-producing genotype communities changed with the development of blooms. The MC-producing genotype communities were more diverse during the bloom season than the non-bloom season. And during the bloom season, the diversity in the early bloom period (May-June) was higher than the diversity in the late bloom period (July-October). Furthermore, the quantitative results suggested that the abundance of MC-producing genotypes increased dramatically with the development of blooms and was very high in the bloom season. Although there was no detection of MC during winter (non-bloom season), MC-producing genotypes were still detected in the samples, which indicated that the potential MC threat is present both during the bloom season and the non-bloom season in Lake Taihu. There was no significant correlation observed between the MC concentration and MC-producing genotypes in Lake Taihu. However, the results suggested that the highest mcy gene concentration lagged behind the highest MC concentration.It was investigated that the structure and abundance of cyanobacterial communities in 6 sediment samples of different depth collected from Lake Taihu. The results suggested that Microcystis and Synechococcus showed high diversity in the sediment of Lake Taihu. There was a higher abundance of Microcystis and Synechococcus in the upper layers of the sediment than in the deeper layers. The distribution of Microcystis and Synechococcus in the sediment reflected a trend in which Synechococcus gradually became one of the major bloom-forming components instead of the Microcystis in the pelagic water of Lake Taihu when the water quality deteriorated from mesotrophic to hypertrophic.It was conducted to characterize the structure and abundance of the bacterial and archaeal communities at various depths in the sediment collected from Lake Taihu. To accomplish this, samples were evaluated using the clone library, denaturing gradient gel electrophoresis (DGGE) and real-time PCR technique. The results suggested that the eutrophication seemed to have little effect on the bacterial communities in the sediment of Lake Taihu. The composition of bacterial communities appeared to be relatively homogeneous among the sediment samples. The Deltaproteobacteria- and Nitrospira-related sequences were found to be very diverse in the sediment. The results also suggested that the abundance of bacterial groups increased slightly with depth. The archaeal communities were primarily related to Euryarchaeota and Crenarchaeota. Methanogenic archaeal communities were an important group in the sediment of Lake Taihu, and they were highly diverse and varied greatly in the sediment. The archaeal communities varied greatly among sediment samples whereas the concentration of Archaea was not significantly influenced by the eutrophication. However, the archaeal abundance contributed a larger proportion of the total prokaryotic community in Lake Taihu sediment than other mesotrophic lake sediment. Sequences related to putative ammonia-oxidizing Archaea were also detected in the deep layer of sediment sample in Lake Taihu. Nitrospira showed high diversity in the sediment and the quantity of Nitrospira decreased with depth. Meanwhile, it was easier to detect Nitrospira-like sequences in sediment samples than in water samples.