Relationship Between Microbial Community Structure And Nutrient Cycles And Algal Bloom In Taihu Lake

Eutrophication is one of the main global problems. Sediment performs as an important internal nutrient sources, which plays the key roles for eutrophication. And microorganisms of sediment, as the main drivers of nutrient cyclings, play important roles in nutrient cycling between water and sediment and also the out break of algal bloom.In this study, temporal (February, May, August and November, different periods of the algal bloom) changes of microbial community structure changes in sediment of different trophic level of eutrophic shallow Taihu Lake were investigated by Terminal restriction fragment length polymorphism (T-RFLP) and pyrosequencing to analyze the relationship between microbial community structure and nutrient cycles and algal bloom in Taihu Lake. The relationship between phosphorus accumulating organisms (PAOs) community and europhication was studied through ppkl clone library and real-time quantitative PCR. And the species of the bacteria in sediment were also isolated.The nutrient, especilly for phosphorus, released from sediment to water2-3months before algal bloom, providing nutrients to algal recruitment and growth. Phosphorus was a vital limiting nutrient for eutrophication in Taihu Lake, but phosphorus and nitrogen were all limiting nutrient in high trophic areas. The bacterial community structures in sediment were obvious different during sampling times based on T-RFLP, and the maximum variance was occurred in August. The diversity of bacterial communities decreased during algal bloom. However, the alchaeal community structures might be related to both the trophic levels and the algal bloom. Three sites, represented high, light trophic areas and lake center respectively, were selected to futher investigate the bacterial community structures by454pyrosequencing. The most dominant group of bacteria was Proteobacteria, followed by Bacteroidetes, Chloroflexi, Verrucomicrobia, Acidobacteria, Firmicutes, Actinobacteria, Planctomycetes and Cyanobacteria, and their relative abundances changed obviously, ε-proteobacteria was only detected in site16and24(1.82-13.76%), which might be large affected by human activitied. Before algal bloom, relative abundances of β-andε-proteobacteria (high trophic level) and Chloroflexi (middle trophic level) increased obviously, and they might play important role in nutrients release from sediment. When algal bloom occurrence and last nearly3months, relative abundances of α-and γ-proteobacteria increased obviously, which were the dominant groups degrading the organic nutrients. And the relative abundance increasing of a-proteobacteria was also a specific characterization of occurrence time of algal blooms. In genus level, Thiobacillus (β-proteobacteria) and Sulfuricurvum (ε-proteobacteria) were the dominant genera in sediment. These two genera of bacteria played an important role in phosphorus releasing, and could be good to predict algal bloom. And NO3--N contents of sediment was first suggested to the most important impact factor for bacterial community. In addition, clone library showed that polyphosphate kinase I (PPK1) gene of Candidatus Accumulibacter in Taihu Lake were classified into clade IID, and quantity and diversity of Candidatus Accumulibacter could reflect trophic level. With the increasing of trophic level, PAOs diversity decreased, but their quantity increased obviously. These results indicated that PAOs were important drivers of phosphorus cycle, and also closely related to the outbreak of algal bloom. This study revealed that microbial community structure, changes and their important roles during algal bloom in a eutrophic shallow lake, and will provid a clue for the rescue of eutrophic lakes and prediction of the algal bloom.20strains of PAOs were isolated through the approaches of low-nutrition and long-term incubation and identified by16S rRNA gene from Taihu Lake sediment. Strains16-28-2was identified as a novel species in a new genus within the genus Novosphingobium, and named as Novosphingobium tardum sp. nov.