Dynamics of organic-aggregate-associated bacterial communities and related environmental factors in Lake Taihu, a large eutrophic shallow lake in China

To investigate the spatial and temporal variations of organic-aggregate-associated bacterial communities (OABC), a 25-month observation was conducted at two contrasting sites (Meiliang Bay and the lake center) in Lake Taihu, China. The structures and dynamics of the OABC were determined by partially sequencing cloned 16S rRNA genes, and by terminal restriction fragment length polymorphism (T-RFLP) analysis. One hundred ninety-two T-RFs were detected from the two sites, but only 17 T-RFs were dominant, suggesting that specific microbial populations were adapted to the unique niche provided by the organic aggregates (OA). Phylogenetically, Beta-and Alphaproteobacteria constituted the numerically most important heterotrophic bacterial group. Analysis of similarity revealed significant intra-lake heterogeneity, and significant temporal shifts in OABC. Canonical correspondence analysis demonstrated that site-specific differences in sediment resuspension and nutrient enrichment (namely nitrate and total phosphorus) were the forces driving the intra-lake differences in OABC. Water temperature and dissolved oxygen were related to the seasonal dynamics of OABC. The annual succession in OABC was significant in Meiliang Bay, but not in the lake center. In addition, nearly 35% of the bacterial sequences from OA related to bacteria from soils, activated sludge, sediments, and other habitats, indicating the potential importance of allochthonous bacteria in OABC.