Microbial Community And Heavy Metals Transformational Genes In Dianchi Lake

There are different levels of heavy metal pollution in freshwater around the word and the ecological risk associated with their forms.An important factor which would transfer the forms of heavy metals and affect the ecological risk is microorganism in water and sediment.The past research in our lab found that Dianchi is polluted by heavy metals,such as arsenic,mercury and cadmium.But there are few researches focusing on microbial community,the functional genes about arsenic,mercury and cadmium and the screening of resistant microorganisms in Dianchi lake at the same time.In this study,we use bacterial 16 s rDNA high-throughput sequencing method to analyze the microbial community structure and diversity in Dianchi lake.At the same time,we use the qPCR technique to analyze the abundance of merA,arsM,aoxB,czcA,czcC and Delta-hgcA genes.And some strains of As/Hg/Cd-resistance bacteria have been selected.Combining with the heavy metals data,the correlation between microbial community information,functional genes and environmental factors was explored,and the results are followed.(1)Microbial communities in the sediment samples of Dianchi lake are dominanted by some genus,such as LCP-6,Dechloromonas,Thiobacillus,Candidatus methanol,and Bacillus.Microbial communities in the water samples of Dianchi lake are dominanted by some genus,such as Planktothrix,Bacillus,Microcystis,Synechococcus,Comamonas,Candidatus Xiphinematobacter,Paulinella,Polynucleobacter,Gemmatimonas and Dolichospermum.The correlation between Dechloromonas and concentrations of mercury and cadmium were significantly positive.The correlation between Bacillus,Comamonas,Polynucleobacter,Dolichospermum and concentrations of As,Hg were very significantly positive.Some dominant bacteria transfer the heavy metals through the pathway of arsenic oxidation/ methylation,mercury reduction/methylation.(2)The index of microbial diversity in Caohai lake(water)was lower than that in outer lake,and the trend was gradually increasing from north to south.The ?-diversity index was significantly negatively correlated with the contents of As,Hg and Cd in the sample.The higher levels of heavy metals,the higher index of microbial diversity.Due to the screening of environmental factors on the microorganisms,some bacteria can't survive in the environmrnt containning arsenic,mercury and cadmium.The others survived,and there is low index of microbial diversity in sample with high heavy-metal concentration.(3)The copies of arsM gene in the three southern sites were lower than the northern sites.The situation is similar to the concentrations of Hg.So there is high potential of some dominant bacteria resisting the Hg.And some of these bacteria contain the pathway of merA.The copies of Delta-hgcA gene are positively related to the concentrations Hg.Some bacteria could catalyze the synthesis of methyl mercury.So there is a high potential of some dominant bacteria resisting the Hg,and most of them are related to Deltaproteobacteria.And the methylation of Hg would cause high levels of ecological risk.There are a high level copies of aoxB gene were detected in Dianchi lake especialliy in Caohai lake.And the copies are positively related to the concentrations of As.There are some As-transfomation bacteria in Dianchi lake,and they oxdize the As through the aoxB pathway.(4)3 strains of As/Hg/Cd-resistance bacteria have been selected.And the bacteria could survive in the culture medium containing arsenic(80mg/L),mercury(20 mg/L)and cadmium(40mg/L).They were identified as Phoma,Alcaligenes and Curtobacterium.And there were some reports about aoxSRABCD in Alcaligenes faecalis.In summary,the heavy metals pollution and microbes are interrelated and interact on each other in Dianchi lake.The heavy metals affect the microbial community composition,and microbes affect the heavy metals by adsorption and conversion.These microbes maybe beneficial or harmful to the lake ecosystem.