Characterization And Biogeochemical Functions Of Indigeneous Microbes In The Hetao Aquifer Systems, Inner Mongolia

In this study, microbially mediated arsenic release and mobiliaztion in high arsenic aquifers of Hetao Basin were studied using microscom experiments and microbial molecular methods, to analyse the geochemistry of groundwater and sediments, to investigate microbial community structure and diversity in groundwater and sediments with different geochemical characteristics, and to explore functional microbial communities in aquifer sediments enrichment culture. The following are the main points.First, the microbial community structures of groundwater changed substantially with depth at the same location. It indicated that a relatively higher bacterial diversity was present in the groundwater sample with lower arsenic concentration. Second, the CCA（Canonical Correlation Analysis） and the evolutionary tree drawed by beta diversity display the bacterial communites of the sediment samples were influenced by sample depth, As, S, TOC content significantly, which is in accordance with the comparison of clone libraries.Third, sequence analysis of 16S rDNA demonstrated that the sediment indigenous bacteria including NO₃^--reducing bacteria such as Pseudomonas sp., Fe（III）-reducing bacteria such as Aquabacterium sp.,Thauera sp.,Georgfuchsia sp.,Methyloversatilis sp., Clostridium sp., SO₄^2--reducing such as Spirochaetales sp.,Desulfuromonadales sp.,Geobacter sp.,Desulfobacca sp., Desulfosporosinus sp. and As（V）-reducing bacteria used the specific oxyanions as electron acceptor and played a significant role in reductive dissolution of Fe oxide minerals, reduction of As（V）, and release of arsenic from sediments into groundwater.Fourth, the natural organic matter in sediments was the potential electron donor for microbially mediated arsenic release from these aquifer sediments by the above bacteria. Microcosm experiments, using intact aquifer sediments, confirmed that high arsenic concentration especially As（III） was released in the batch without amendment of organic carbon.Fifth, indigenous bacteria also influenced the potential sequestration of As. Dehalococcoides sp. and sulfte reducing bacteria abundant in sediment sample with arsenic bound to organic matter and sulfides according to the sequential extraction results and XANES spectroscopy. Higher concentrations of organic matter may stimulate reduction of As（V）, SO₄^2- and Fe（III） by Dehalococcoides sp.and the Dletaproteobacteria. Arsenic can also remain in associated with the solid phase through precipitation of authigenic solids including Fe（II）-As（V） or As-S and the transformation of Fe minerals with subsequent As sequestration in the authigenic mineral.Finally, the 16S rRNA sequence anslysis and the results of functional gene ars C and arr A PCR amplification shows arsenic resistant bacteira and dissimilatory arsenate reducing prokaryotes（DARPs） are common in sediment samples which are related to As（V） reduction. As（V） was reduced remarkably in two deeper sediment encrichment cultures because of the existence of DARPs. Phylogenetic tree exhibited DARPs in the selected samples are close to DARPs Desulfosporosinus Y5,Sulfurospirillum barnesii SES-3 and Bacillus selenitireducens MLS10.