中文摘要：

六价铬[Cr（Ⅵ）]是毒性强、易迁移的主要重金属污染物,通过微生物将Cr（Ⅵ）还原为低毒性的Cr（Ⅲ）是一种经济、高效的处理铬污染的方法.对从浮萍根际分离得到的微小杆菌Exiguobacterium sp.MH3的Cr（VI）去除能力、方式及影响因素进行了研究.结果显示,实验条件下,菌株MH3在12 h或36 h内可完全去除5 mg L-1或15 mg L-1 Cr（Ⅵ）.其去除机理主要为还原作用,且主要发生在细胞外侧,表明菌株MH3还原Cr（Ⅵ）的酶可能为分泌型.此还原反应的最适pH为7.0.外加碳源如甘露醇、葡萄糖、蔗糖等可显著促进菌株MH3还原Cr（Ⅵ）.共存金属离子Cu2＋也可增强此还原作用,但是Zn^2＋、Mn^2＋、Cd^2＋对菌株MH3生长及Cr（Ⅵ）还原有抑制作用.共存阴离子PO4^3-则可促进菌株MH3的生长及Cr（VI）还原.研究表明,Exiguobacterium sp.MH3是一株高效的Cr（Ⅵ）还原菌,在含铬废水处理上具有一定的应用价值.

英文摘要：

The hexavalent chromium [Cr（VI）] is the most toxic and soluble form of chromium, thus the main contaminant. The reduction of Cr（VI） to the much less toxic Cr（III） by microorganisms is an economical and effective method to treat Cr（VI）. In this work, we studied the ability and characteristics of Exiguobacterium sp. MH3 isolated from the rhizosphere of a duckweed Lemna minor in Cr（VI） reduction. We measured the tolerance of MH3 to Cr（VI） in LB or M9 medium; the removal rate of Cr（VI） was analyzed in LB medium under different Cr（VI） concentrations. The concentrations of total Cr and Cr（VI） were measured to determine the mechanism of Cr（VI） removal. In addition, we studied the effects of pH, additional carbon sources, and coexisting ions on the reduction of Cr（VI）. Exiguobacterium sp. MH3 was able to completely remove 5 mg L-1 Cr（VI） in LB medium in 12 h, and 15 mg L-1 in 36 h. The reaction was mostly due to reduction of Cr（VI） since the total concentration of Cr was stable with Cr（VI） decreasing. Both the supernatant of the culture and the extraction of MH3 showed reduction of Cr（VI）. The optimal pH of the reduction was determined as 7.0. Extra carbon sources including mannitol, glucose, and sucrose could promote Cr（VI） reduction, so could Cu^2＋. In contrast, Zn^2＋, Mn^2＋, and Cd^2＋ inhibited the growth of MH3 and reduction of Cr（VI）. PO43- was also able to promote the growth of MH3 and the removal of Cr（VI）. These results indicated that Exiguobacterium sp. MH3 remove s Cr（VI） with very little biosorption of Cr by reduction, most probably through secreted enzymes. It is an effective Cr（VI） reducing bacterium, and should have great potential in treating Cr（VI）-containing wastewaters, particularly in settings with additional carbon source and/or coexisting Cu^2＋.