Simultaneous oxidation of As(III) and reduction of Cr(VI) by Alcaligenes sp.

Arsenic (III) and chromium (VI) are most common environmental contaminants due to its tremendous applications in dye, tannery and pulp industries. They are non-biodegradable as they are heavy metals, and therefore, of major concern. Alcaligenes sp. had the ability to efficiently oxidize As(III) to As(V) and reduce Cr(VI) to Cr(III) separately. It could also simultaneously oxidize As(III) in presence of Cr(VI) under shaking conditions. Simultaneous reduction of 5 mg L⁻¹ Cr(VI) and oxidation of 5mM As(III) was carried out where Cr(VI) was reduced up to 90% and oxidized 36% arsenic in 24 h. With respect to As(III) oxidation, there was no significant decrease in the rate of oxidation of As(III) due to presence of Cr(VI). Whereas, in case of only Cr(VI) exposure, only 40% of Cr(VI) reduction was observed in 24 h. In presence of arsenic the isolate did not show any effect on growth rate, while rate of chromium reduction was enhanced in arsenic presence. So, further scale up experiments can lead to potential use of Alcaligenes sp. to simultaneously biotransform toxic forms of both arsenic and chromium to less toxic forms.