Anaerobic Antimonite Oxidation And The Microorganisms Involved In A Typical Antimony-contaminated Soil

Antimony(Sb)is a metalloid element located in the 5th main group in the periodic table of the elements and is listed as a priority pollutant by the US Environmental Protection Agency(EPA).Sb can enter the environment through the natural and anthropogenic approaches.Most of the Sb pollutants mainly come from mining and smelting.Sb has been used in many products,which greatly improves the chance of Sb enter the environment.Sb and its compounds are considered to be harmful to human health and even carcinogenic to humans.Long-term exposure to Sb will pose a great threat to human health.Sb mainly exists as inorganic Sb(i Sb),with very few organic Sb in the environment.Their toxicities are decreased in the order,trivalent antimony(Sb(III))>pentavalent antimony(Sb(V))>methyl antimony.Sb(III)oxidation can lower the toxic of Sb in the environment.Microorganisms in the environment are widely involved in the geochemical cycle of Sb.Moreover,the rate of Sb oxidation driven by microbes is significantly higher than that of chemical oxidation.Hence,study on Sb oxidation microorganisms has vital implications for remediation of Sb contaminations.Despite the importance of microorganisms in the Sb biogeochemical cycle,there are few studies on anaerobic Sb(III)oxidation driven by microbes.In this study,the anaerobic microcosms were established with the Sb-contaminated paddy soil sampled near Xikuangshan mining area.The microcosms were amended with Na HCO₃ as carbon source coupled with Na NO₃ and Sb(III)as electron acceptor and electron donor,respectively.The species of Sb were determined by LC-AFS equipped with an anion exchange column,and the concentration of NO₃^-and NO₂^-was detected by a flow analyzer.The arsenite-oxidizing genes(aio A)have been reported responsible for anaerobic Sb(III)oxidation and thus were quantified by quantitative PCR in this study.DNA-stable isotope probing(DNA-SIP)combined with 16S r RNA high-through sequencing and metagenomic sequencing were performed to investigate the microorganisms responsible for anaerobic Sb(III)oxidation in the typical Sb-contaminated soil.The results showed that the Sb(III)oxidation occurred in the treatment amended with NO₃^-and Sb(III),whereas no obvious Sb(III)oxidation were observed in the treatment without NO₃^-,suggesting that Sb(III)oxidation was coupled with denitrification.Sb(III)oxidation was not observed in the microcosm inoculated with sterilized soil,indicating that the Sb(III)oxidation was mainly driven by microorganisms in the soil.The abundance of the aio A gene was significantly increased in the treatment amended with NO₃^-and Sb(III),indicating that the Sb(III)oxidation might be mediated by microorganisms containing the aio A gene.DNA-SIP experiments identified microorganisms associated with Azoarcus may be involved in the anaerobic Sb(III)oxidation in the Sb-contaminated soil.Metagenomic analysis further indicated that Azoarcus-associated bacteria contained genes catalyzing both As(III)/Sb(III)oxidation and denitrification.