Isolation of Cr(VI) reducing bacteria from industrial effluents 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 μg/mL) and S. capitis could tolerate Cr(VI) (2800 μg/mL). Both organisms were able to resist Cd2+ (50 μg/mL), Cu2+ (200 μg/mL), Pb2+ (800 μg/mL), Hg2+ (50 μg/mL) and Ni2+ (4000 μg/mL). S. capitis resisted Zn2+ at 700 μg/mL while Bacillus sp. JDM-2-1 only showed resistance up to 50 μg/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 effluents 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 μg 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.