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 μg ml -1, >95% of the total Cr(VI) was reduced in 24 and 72 h of growth, respectively, whereas at 80 μg 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°C. The enzyme was stable up to 30°C and from pH 5.5 to 8, but from pH 4 to 5 the enzyme was severely destabilized. Its Km and Vmax were 14 μM and 3.8 nmol min-1 mg-1 respectively. The enzyme activity was enhanced by Cu2+ and Ni2+ and inhibited by Hg2+. © Springer 2006.