Close Links Of Microcystins Production And Bacterioplankton Community In Poyang Lake

In recent years,the pollution of microcystins in freshwater lakes have become increasing severe due to human activities.As an integral part in the freshwater lake,bacterioplankton community can degrade the microcystins and play an irreplaceable role for the stability of the lake ecosystem.Studying the relation between bacterioplankton community and the production of microcystins is of significance for predicting and managing the future environmental changes of freshwater lake ecosystem.Poyang Lake is the largest freshwater lake.With the rapid development of economy,the pollution of microcystins has been increasingly severe and exerted a significant influence on the ecological safety to some extent.The hydrological condition in Poyang Lake is greatly affected by the seasons,therefore,the relation between the production of microcystins and bacteria community is required to master.Poyang Lake was selected as the research subject and four sampling sites were selected on the basis of concluding the previous related researches with representing the main lake area(Xingzi Lake,Duchang Lake and Kangshan Lake)and sub-lake(Zhanbei Lake).Surface water samples were collected in July,September,October and November in 2016 and 2017 respectively.Microcystins,Cyanobacteria community,the microcystins production gene(mcyA gene)and their relationship were analyzed first and then the composition and abundance of aquatic bacterial community were studied by high-throughput sequencing and fluorescence quantitative analysis of 16 S rRNA gene and the effects of microcystins production on the structure and function of bacterial community were further discussed in combination with predicted metabolic function.The major conclusions were as follows:1.The microcystins did not vary among space but time,it was significantly in November higher than other months.The concentration of microcystins in water was mainly affected by pH value,water temperature,water depth,ammonia nitrogen,total nitrogen,orthophosphate,dissolved organic carbon and chlorophyll-?.2.According to the results of microscopy,among Cyanobacteria community,Microcystis sp.and Anabeana sp.dominated over the sampling period.The abundance of Cyanobacteria community in site Zhanbei was significantly higher than that in other sites,and was the highest in September but the lowest in November.Microcystis sp.was negatively related with microcystins.Therefore,Microcystis sp.was the major genera producing microcystins in Poyang Lake,but higher concentration of microcystins in November may be related to the Cyanobacteria die with lower temperature,causing a large number of microcystins releasing.3.The abundance of mcyA gene in October was significantly higher than other other months.mcyA gene did not relate with microcystins,but positively correlated with Microcystis sp.,and this may be due to toxic Microcystis sp.containing mcy gene cluster being the most significant in producing microcystins,but microcystins production related with more complicated genes.4.The diversity in November of Year 2017 was significantly lower than other months,however,the trend of 16 S rRNA gene was converse.Among the bacterial community,Actinobacteria,Proteobacteria and Cyanobacteria were the most advantageous.The bacterioplankton community did not show significant spatial but temporal variations,and the relative abundance of Proteobacteria and Bacteroidetes in November was significantly higher than other months.And among all predicted functions,chemoheterotrophy and phototrophy were most abundant in all predicted functions,the abundance of chemoheterotrophy in November was significantly higher,but the abundance of phototrophy was significantly lower.5.With the increase of the concentration of microcystins,the abundance of bacterial community increased,and the function of chemoheterotrophy increased.Microcystins were positively correlated with Burkholderiaceae and OPB56,but negatively related with Acidimicrobiaceae,Neisseriaceae,Microbacteriaceae and Chitinophagaceae,suggesting that microcystins would provide important carbon source or energy for these bacteria.In summary,Microcystis sp.dominated in the Cyanobacteria community,and was the major genera producing the microcystins.It was also found that Acidimicrobiaceae,Neisseriaceae,Microbacteriaceae and Chitinophagaceae may be take part in microcystins production.The results of this study provide scientific basis for predicting the future production of microcystins in freshwater lake ecosystems and its ecological effects as well as the treatment of the microcystins pollution from the perspective of microorganisms in freshwater lakes.