Isolation of Cr(VI) reducing bacteria from industrial e uents and their potential use in bioremediation of chromium containing wastewater

The present study was aimed to assess the ability of Bacillus sp. JDM-2-1 and Staphylococcus capitis to reduce hexavalent chromium into its trivalent form. Bacillus sp. JDM-2-1 could tolerate Cr(VI) (4800 g/mL) and S. capitis could tolerate Cr(VI) (2800 g/mL). Both organisms were able to resist Cd2+ (50 g/mL), Cu2+ (200 g/mL), Pb2+ (800 g/mL), Hg2+ (50 g/mL) and Ni2+ (4000 g/mL). S. capitis resisted Zn2+ at 700 g/mL while Bacillus sp. JDM-2-1 only showed resistance up to 50 g/mL. Bacillus sp. JDM-2-1 and S. capitis showed optimum growth at pH 6 and 7, respectively, while both bacteria showed optimum growth at 37°C. Bacillus sp. JDM- 2-1 and S. capitis could reduce 85% and 81% of hexavalent chromium from the medium after 96 h and were also capable of reducing hexavalent chromium 86% and 89%, respectively, from the industrial e uents after 144 h. Cell free extracts of Bacillus sp. JDM-2-1 and S. capitis showed reduction of 83% and 70% at concentration of 10 g Cr(VI)/mL, respectively. The presence of an induced protein having molecular weight around 25 kDa in the presence of chromium points out a possible role of this protein in chromium reduction. The bacterial isolates can be exploited for the bioremediation of hexavalent chromium containing wastes, since they seem to have a potential to reduce the toxic hexavalent form to its nontoxic trivalent form.