Characterization of two chromate reducing bacteria isolated from heavy metal contaminated soil

Two Bacteria were isolated from heavy metal contaminated soil with high concentration of total chromium (ca. 2300 mg/L) showed their significant ability of chromate reduction. The bacteria were identified as Ochrobactrum sp. and Microbacterium sp., and were designed as Ochrobactrum sp. strain 71 and Microbacterium sp. strain 73, respectively according to their 16S rRNA gene sequence analysis. The ability of the two isolates to reduce hexavalent chromium in actively growing cells as well as in resting cells was examined. The results showed both strains were able to reduce Cr(VI) to trivalent chromium Cr(III) very rapidly when grown in LB medium containing chromate (in the form of K₂Cr₂O₇, 5 mg/L and 50 mg/L). Reduction of Cr(VI) to Cr(III) in the phosphate buffer containing chromate was insignificant when using resting cells collected from exponential growth phase. However, when supplemented with electron donor (ex. acetate, citrate or NADH), resting cells also showed significant ability to reduce Cr(VI) to Cr(III). Reduction of the toxic Cr(VI) to the less toxic Cr(III) is a promising bioremedial process in detoxification of Cr(VI)-contaminated environment. Therefore, traits of chromate reduction by these two indigenous isolates showed significant potential in helping in situ Cr(VI) bioremediation efforts.