六价铬还原细菌Bacillus cereus S5.4还原机理及酶学性质研究

从宝钢电镀污泥中分离得到1株六价铬还原细菌Bacillus cereus S5.4,在液体LB培养基中培养72　h完全还原2　mmol/L Cr⁶⁺.测定该菌株六价铬还原后细胞内外六价铬和总铬浓度,检测细胞各组分六价铬还原能力,并结合扫描电镜分析六价铬还原前后细胞形态的变化.结果表明,细菌的细胞壁膜能阻止六价铬进入细胞,是六价铬发生还原的主要场所,其通透性的改变将影响六价铬还原酶的作用;该菌株六价铬还原酶为非分泌型,在细菌细胞内侧发生作用.测定六价铬还原酶活性和稳定性：其最适温度范围25～37℃,最适pH 7,Cu2＋有增强六价铬还原酶活性的作用;在37℃,该菌株六价铬还原酶K_m为125.61 μmol/L,V_max为7.68 nmol/(min·mg).

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.