Reduction of Cr(VI) by a Bacillus sp.

A Bacillus sp. RE was resistant to chromium and reduced Cr(VI) without accumulating chromium inside the cell. When Cr(VI) was 10 and 40 mu g ml(-1)p, > 95% of the total Cr(VI) was reduced in 24 and 72 h of growth, respectively, whereas at 80 mu g Cr(VI) ml(-1) only 50% of Cr(VI) was reduced. However growth was not affected; the cell mass was 0.7-0.8 mg ml(-1) in all cases. The cell-free extract showed Cr(VI) reducing enzyme activity which was enhanced (> 5 fold) by NADH and NADPH. Like whole cells the enzyme also reduced Cr(VI) with decreasing efficiency on increasing Cr(VI) concentration. The enzyme activity was optimal at pH 6.0 and 30 degrees C. The enzyme was stable up to 30 degrees C and from pH 5.5 to 8, but from pH 4 to 5 the enzyme was severely destabilized. Its K-m and V-max were 14 mu M and 3.8 nmol min(-1) mg(-1) respectively. The enzyme activity was enhanced by Cu(2+)and Ni2+ and inhibited by Hg2+.