胞外聚合物对细菌还原去除水中Cr(Ⅵ)的作用

Effect of extracellular polymeric substances on the removal of Cr(Ⅵ)from water by bacteria

为了阐明胞外聚合物(EPS)在Cu^(2+)强化Cupriavidus basilensis B-8(简称“B-8”)还原去除水中Cr(Ⅵ)发挥的作用,通过考察不同Cu^(2+)质量浓度作用下EPS的产量,并借助傅里叶变换红外光谱和三维荧光光谱分析EPS的化学组成和结构。结果表明,当有Cu^(2+)存在时,B-8可分泌更多的EPS,其中溶解态EPS中的多糖和蛋白质量比最高分别可达124.66 mg/g干细胞和2790.87 mg/g干细胞,结合态EPS中的多糖和蛋白质量比最高分别可达41.66 mg/g干细胞和228.21 mg/g干细胞。EPS的增加有利于B-8对水中Cr(Ⅵ)的还原去除。对B-8分泌的溶解态EPS化学组成结构表征发现Cu^(2+)的添加虽提高了B-8分泌的EPS总量,但并未改变EPS的化学组成。另外,还发现Cu^(2+)会与EPS中的芳香类蛋白结合,从而使EPS蛋白质量比降低。这也会促进B-8分泌更多的EPS包裹在细菌的外部,对细菌起到保护,减弱Cr(Ⅵ)等有毒物质对细胞的毒害作用,不但保证了细菌的良好生长,而且保证了细菌对Cr(Ⅵ)还原作用的充分发挥,最终可促进B-8达到较好的Cr(Ⅵ)还原去除效果。

This present paper aims to further explore the influence of extracellular polymeric substances(EPS)on the process of Cu^(2+)-enhanced Cr(Ⅵ)reduction by Cupriavidus basileusis B-8(abbreviated as“B-8”).We conducted batch chemical experiments to determine the content of EPS at different mass concentrations(0,10 mg/L,50 mg/L,100 mg/L,and 150 mg/L).Besides,Fourier transforms infrared spectroscopy(FTIR)and the three-dimensional fluorescence spectrum(3 D-EEM)were performed to determine the chemical composition and structure of EPS.The results showed that in the presence of Cu^(2+),B-8 could secrete more EPS.When the Cu^(2+)mass concentration increased from 0 to 50 mg/L,the content of total soluble EPS and total bound EPS reached the maximum of 2915.52 mg/g stem cells and 269.87 mg/g stem cells,respectively.The mass ratio of polysaccharide and protein could reach up to 124.66 mg/g stem cells and 2790.87 mg/g stem cells in soluble EPS,and up to 41.66 and 228.21 mg/g stem cells in bound EPS.However,as the Cu^(2+)mass concentration continued to increase,the mass ratio of polysaccharide and protein showed a downward trend.Based on the experimental results,the chemical composition and structure of soluble EPS secreted by B-8 were characterized.FTIR and 3 D-EEM results demonstrated that the addition of Cu^(2+)increased the content of EPS secreted by B-8,but did not change its chemical composition.Furthermore,Cu^(2+)would also bind to the aromatic proteins in EPS,thereby reducing the mass ratio of EPS protein.As a result,more EPS could be secreted by B-8 and wrap the bacteria outside to protect them.This process could weaken the toxic effect of Cr(VI)and other toxic substances on the cells.This phenomenon not only ensured the stable growth of bacteria,but also ensured that the bacteria could fully exert the reduction effect of Cr(Ⅵ),and finally could promote B-8 to achieve the desired removal efficiency of Cr(Ⅵ).