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Three arsenic hyper tolerant bacteria were isolated and identified as Acinetobacter calcoaceticus J1, Agrobacterium tumefaciens J2 and Bacillus cereus DAS3, with MICs (minimal inhibitory concentrations) were found 310, 300, 280 mM As(V) and 25, 3, 35 mM As(III), respectively. All the three isolates were found efficient in removing arsenic both As(V) as well as As(III) from the growth medium. Maximum removal of As(V) observed was 56.7% by DAS3 and of As(III) was 68% by J2. pH and nutrients strength of medium were found as factors to modulate the potential of As removal by bacteria. Maximum values of removal for As(V) was 64% by DAS3 on 20% dilution of medium and for As(III) was 76% by J2 at pH 8. Study of bacterial growth and chemical toxicity (DHA) had drawn picture of better arsenic [As(V) and As(III)] tolerance than other osmotic stress [NaCl or PEG 6000], indicating the existence of cross-protection between arsenic toxicity and arsenic generated osmotic stress.

The metalloid arsenic (Z = 33) is considered to be a significant potential threat to human health due to its ubiquity and toxicity, even in rural regions. In this study a rural region contaminated with arsenic, located at longitude 85o 32``E and latitude 25o 11``N, was initially examined. Arsenic tolerant bacteria from the rhizosphere of Amaranthas viridis were found and identified as Bacillus licheniformis through 16S rRNA gene sequencing. The potential for the uptake and removal of arsenic at 3, 6 and 9 mM [As(V)], and 2, 4 and 6 mM [As(III)], and for the reduction of the above concentrations of As(V) to As(III) by the Bacillus licheniformis were then assessed. The minimal inhibitory concentrations (MIC) for As(V) and As(III) was determined to be 10 and 7 mM, respectively. At 3 mM 100% As(V) was uptaken by the bacteria with the liberation of 42% As(III) into the medium, whereas at 6 mM As(V), 76% AS(V) was removed from the media and 56% was reduced to As(III). At 2 mM As(III), the bacteria consumed 100%, whereas at 6 mM, the As(III) consumption was only 40%. The role of pH was significant for the speciation, availability and toxicity of the arsenic, which was measured as the variation in growth, uptake and content of cell protein. Both As(V) and As(III) were most toxic at around a neutral pH, whereas both acidic and basic pH favored growth, but at variable levels. Contrary to many reports, the total cell protein content in the bacteria was enhanced by both As(V) and As(III) stress.