Microbial Community Structures In A Typical Sb-contaminated Area And Screening Of Anaerobic Sb(Ⅲ) Oxidizing Bacteria

Antimony（Sb）has chronic toxicity and potential carcinogenicity.The prevention and control of the source of pollution and environment remediation are urgent.The valence of antimony changes slowly under abiotic conditions,but this process will be significantly accelerated under the influence of microorganisms.Sb（Ⅲ）oxidizing bacteria can oxidize more toxic Sb（Ⅲ）to less toxic Sb（V）.However,most of the studies on Sb（Ⅲ）microbial oxidation were carried out under aerobic conditions.The screening and genomic information of Sb（Ⅲ）anaerobic oxidizing bacteria were relatively few,and the understanding of antimony resistance mechanism of antimony oxidizing bacteria was also very limited.The microbial community structure of different depths of typical antimony contaminated sites also needed to be explored.In this paper,the soil microbial community of Dafu Antimony Mine in Yiyang,Hunan Province was investigated.The physical and chemical properties of different soils（mining waste heap,flotation tailings and smelting slag）and depths（0-20cm,40-60cm and 80-100cm）were compared.The results showed that antimony（Sb）and arsenic（As）were the main pollutants in that area,and their concentrations could reach 5524.7mg/kg and 3433.7 mg/kg,respectively.Xanthates were also found in the flotation tailings and smelting slag,and the highest concentration was585.1 mg/kg.The microbial communities were analyzed by high-throughput sequencing,and it was shown that Proteobacteria,Acidobacteria,Chlorobacterium,Bacteroides,and Actinomycetes were the dominant taxa at the phylum level.There were significant differences in microbial community structure in different locations.Among different soil physical and chemical parameters,MC had the strongest effect on microbial community structure.As,Sb,and xanthates were the main factors affecting the diversity and composition of bacteria in the flotation tailings and smelting slag areas.The strain X4 screened from flotation tailings has the best oxidation rate.The effects of Sb（Ⅲ）stress and electron acceptor NO₃^-on the growth status and anaerobic oxidation rate of X4 were studied.The results show that under the condition of 10 m M Sb（Ⅲ）,X4 can anaerobically oxidize61.7%Sb（Ⅲ）within 110 h,the oxidation rate was 56.09μM/h,and the optimum NO₃^-concentration was 5 m M.16s r RNA analysis showed that the strain with closest evolutionary relationship was Phytobacter diazotrophicus strain LS8.Finally,the whole genome of Phytobacter sp.X4 was sequenced.After assembly,it was found that the genome of Phytobacter sp.X4 was composed of one chromosome and two plasmids.Genome-wide species identification and average nucleotide identity（ANI）analysis showed that Phytobacter sp.X4 was at the phylum of Phytobacter,which was found for the first time with antimony resistance and antimony anaerobic oxidation ability.Functional gene annotation showed that Phytobacter sp.The genome X4 contained many genes related to nitrogen cycle,such as nitrate reduction,nitrite reduction,ammoniation and so on,which helped it to use nitrate as electron acceptor.We also found that Phytobacter sp.X4 had many genes related to heavy metal resistance,including ars H,isc R genes mediating As/Sb oxidation and other As/Sb resistance genes:ars B,ars C,ars H.Phytobacter sp.X4 may use specific enzymatic reaction and non-enzymatic reaction of H₂O₂ for anaerobic oxidation.