Biodegradation Of Microcystin-LR By Indigenous Microorganism And Their Community Structure In Sediment Of Chaohu Lake

Microcystin (MCs) are a group of cyclic heptapeptide hepatotoxins mainly produced by freshwater cyanobacteria blooms. MCs are responsible for liver failure in wild animals and human. As biodegradation is one of the main approaches to eliminate microcystin in the water body, it is very important to understand the biodegradation process of microcystin in water body. In this thesis, biodegradation of microcystin in sediments collected from different depths under aerobic and anaerobic conditions was investigated through laboratory simulation. The microbial community structure of sediment was analysed by polymerase chain reaction-density gradient gel electrophoresis(PCR-DGGE) of 16 SrDNA. The goal of this study is to obtain the in-depth understanding of biodegradation of microcystin and the effect of microcystin addition on the microbial community structure of sediment. The main conclusions obtained are listed as follows:(1)Biodegradation of microcystin-LR in sediment collected from different depths under aerobic and anaerobic conditions.Microcystin-LR in sedimet collected from different dephts of three sampling points couLd be rapidly degraded under both aerobic and anearobic conditions. Microcystin-LR couLd be degraded to below detection limite in 3 days after a lag phase about 4 to 5 days. The biodegradation rate of microcystin in lake water was much lower than that in sediment, indicating that the biomass of microcystin degrading bacteria in surface lake water was much lower than that in sediment.Under the aerobic condition, the biodegradation rate in sediment decreased with depth. Under the anaerobic condition, the hihgest rates were found in surface layer and deepest layer. A biodegradation product was detected during the anearobic biodegradation process and it disappeared after microcystin completly degraded. The biodegradation potential of microorganism in sediment was enhanced by the addition of microcystin. After the initial biodegradation process, extra added microcystin of 5 mgL-1 could be completely degraded within 1 day without a lag phase.(2) The depth-related microbial community structure in sedimentAccording to cluster analysis, the DGGE bands decreased with depth, indicating that the overall community structure diversity was decreased with depth. (3)Change of microbial community structure before and after the biodegradation of microcystin-LR.After the aerobic biodegradation of MCLR, total bands of DGGE increased and some abundant species generated, suggesting that the microbial community structure has been affected by the addition and biodegradation process of MCLR...