Simultaneous reduction of Cr(VI) and oxidation of As(III) by Bacillus firmus TE7 isolated from tannery effluent.

Hexavalent chromium [Cr(VI)] and arsenite [As(III)] are the most toxic forms of chromium and arsenic respectively, and reduction of Cr(VI) to Cr(III) and oxidation of As(III) to As(V) has great environmental implications as they affect toxicity and mobility of these toxic species. Bacillus firmus strain TE7, resistant to chromium and arsenic was isolated from tannery effluent. The strain exhibited ability to reduce Cr(VI) and oxidize As(III). It reduced 100 mg L(-1) Cr(VI) within 60 h in nutrient broth and oxidized 150 mg L(-1) As(III) within 10 h in minimal medium. It also completely reduced 15 mg L(-1) Cr(VI) and oxidized 50 mg L(-1) of As(III) simultaneously in minimal medium. To the best of our knowledge, this is the first bacterial strain showing simultaneous reduction of Cr(VI) and oxidation of As(III) and is a potential candidate for bioremediation of environments contaminated with these toxic metal species.