Biotransformation of As (III) to As (V) and their stabilization in soil with <em>Bacillus</em> sp. XS2 isolated from gold mine tailing of Xinjiang, China

Abstract

Xinjiang province is one of the most polluted region in China, this region affected by multi-metal problem, especially arsenic (As) affect very badly. Two major forms of As present in the environment As (III) and As (V) as compared to As (V), As (III) is much more toxic. Our aim is to remediate As (III) contaminated soil by using As (III) resistant microbe, having the high transforming ability for As (III) to As (V). An As (III) oxidizing bacterium Bacillus sp. XS2, isolated and selected from gold mine tailing which have shown high resistance up to 6400 mg L−1 and efficiently transformed up to 4000 mg L−1 in sucrose low phosphate medium (SLP), higher than any of the previous reported Bacillus sp.. In soil, we found that XS2 successfully transformed up to 81% of soluble exchangeable fraction within 10 d in contaminated soil (with 500 mg kg−1), which makes it potential microbe for the removal of contaminated site with arsenic in the environment. Further XS2 was characterized for their molecular basis of resistance and we establish that XS2 having arsenic oxidase enzyme activity which is accountable for the detoxification of arsenic at high concentration and provide resistance to the bacterium. Gene encoding arsenic oxidase (aioA-gene) was also amplified from this bacterium using polymerase chain reaction (PCR) with degenerate primer. The aioA-gene is specific for the arsenite-oxidizing bacteria. The deduced amino acid sequence had shown 42% similarity with pseudomonas sp. arsenic oxidase. Further, the strain was characterized by 16s rRNA gene sequence analysis and shown maximum similarity with Bacillus sp.