[Mechanisms and enzymatic characters of hexavalent chromium reduction by Bacillus cereus S5.4]

A strain of bacteria identified as Bacillus cereus S5.4, which was isolated from the electroplating sludge of Baosteel Corporation, Shanghai, was able to completely reduce 2 mmol/L Cr6+ in LB liquid after 72 hours. Experiments on concentrations of hexavalent and total chromium inside and outside bacterial cells after hexavalent chromium reduction, and hexavalent chromium reduction abilities of different cellular components, and SEM analysis of cellular morphology before and after hexavalent chromium reduction, showed that cellular walls and membranes, which were able to prevent hexavalent chromium out from living cells, were the main sites where hexavalent chromium reduction took place, and changes of their permeability would take effect on the function of hexavalent chromium reductase. The reductase was nonsecretive and took effect on the inner side of living cells. Determination of the activity and stability of hexavalent chromium reductase showed that the optimal temperature range and pH of the reductase was 25 - 37 degrees C and pH 7, respectively. Cu2+ had some effect on the promotion of reductase activity. At the temperature of 37 degrees C, Km and Vmax of the reductase was 125.61 micromol/L and 7.68 nmol/(min mg), respectively.