The Respond Of Bacteria To Abundant Cyanobacterial Blooms In Taihu

Eutrophication and the subsequent cyanobacterial blooms are worldwide environmental issues in lakes, especially in Chinese lakes. In order to understand the dynamics of bacterial abundance, diversity and community composition during the degradation of abundant cyanobacterial blooms, samples from five lake areas, i.e., Meiliang Bay, Central Lake, Dapu Lake, Gonghu Bay, Zhushan Bay, in the typical shallow, eutrophic and freshwater Lake Taihu, were sampled seanonly. At the same time, cyanobacterial degradation was simulated in laboratory.Using DAPI-combined epiluorescence direct counting method, DNA extraction, PCR amplification, T-RFLP, high-throughput sequencing and other molecular biology techniques, as well as multivariate statistical analysis method, the response of bacteria to environment changes and to degradation of high stock of cyanobacterial blooms were studied. The main results are as follows:1. The bacterial abundance and community composition showed a distinct spatial and temporal heterogeneity in Lake Taihu. The abundance of attached bacteria in summer and autumn was higher than that in spring and winter. Change of attached bacterial abundance was more obvious than change of free-living bacteria. Seasonal variation of bacterial community composition was higher than the variation among lake sites. Furthmore, community composition of attacted and free-living bacteria differed significantly. Temperature, NH+-4N, turbidity and Chl a wree the main factors structured the variation of attached bacterial community composition, while temperature, NH+4-N and PO3-4-P were the main factors structured the variation of free-living bacteria.2. High-throughput sequencing results showed that attached bacterial diversity was much higher than that of free-living bacteria in Meiliang Bay. Overall, the main dominant bacterial phyla in Meiliang Bay were consist of Bacteroidetes、Alphaproteobacteria、 Betaproteobacteria and Actinobacteria. During summer when the concentration of algae increased, bacterial diversity increased, the differences of community composition between attacted and free-living bacteria were not significant.3. Laboratory experiment showed that cyanobacterial degradation changed bacterial community structure and the succession process a lot. Cyanobacterial degradation increased the similarity between attached and free-living bacterial community. A few numbers of bacterial species were dominant in the early stage of degradation. The ritio of a few bacterial species, such as Rhodobacter and Rubrivivax, increased dramaticlly during the first ten days of degradation.4. Dead cyanobacteria can release a great deal of dissolved N, P rapidly, which made bacterial abundance increased explosively in a short time. Meanwhile, the ratio of active bacteria increased rapidly (up to80%). The degradation of cyanobacterial particles by bacteria provided adequate nutrients for the next round of algae blooms. Non-cyanobacteria can release dissolved N, P, slowly, which made the abundance of total bacteria and the ratio of active bacteria maintains at a high level (about30%). Because of the high level of APA activity, nutrients mineralized from cyanobacterial decomposition were exploited quickly by the newborned cyanobacteria. In this system, decomposition of cyanobacteria was interwoven with the growth of newborned cyanobacteria, which maintained the cyanobacteria-dominated microsystem.