State Key Laboratory of Soil Erosion and Dryland Farming on the Loess Plateau, College of Life Sciences, Northwest A&F University, Yangling, Shaanxi 712100, China.
J Hazard Mater. 2013 Oct 15;261:614-20. doi: 10.1016/j.jhazmat.2013.06.043. Epub 2013 Jun 26.
The copper tolerance gene of wild-type heavy metal-tolerance Sinorhizobium meliloti CCNWSX0020 was mutated by transposon Tn5-a. The mutant was sensitive up to 1.4mM Cu(2+). Production, components, surface morphology, and functional groups of extracellular polymeric substances (EPS) of the wild-type strains were compared with sensitive mutant in immobilization of Cu(2+). EPS produced by S. meliloti CCNWSX0020 restricts uptake of Cu(2+). The cell wall EPS were categorized based on the compactness and fastness: soluble EPS (S-EPS), loosely bound EPS (LB-EPS), and tightly bound EPS (TB-EPS). LB-EPS played a more important role than S-EPS and TB-EPS in Cu(2+) immobilization. Scanning electron microscopy (SEM) analysis LB-EPS had rough surface and many honeycomb pores, making them conducive to copper entry; therefore, they may play a role as a microbial protective barrier. Fourier transform-infrared (FT-IR) analysis further confirm that proteins and carbohydrates were the main extracellular compounds which had functional groups such as carboxyl (COOH), hydroxyl (OH), and amide (NH), primarily involved in metal ion binding.
野生型耐重金属根瘤菌 Sinorhizobium meliloti CCNWSX0020 的铜耐受基因被转座子 Tn5-a 突变。突变体对 1.4mM Cu(2+)敏感。将野生型菌株与敏感突变体在固定 Cu(2+)方面进行了胞外聚合物（EPS）的产生、组成、表面形态和官能团的比较。根瘤菌 CCNWSX0020 产生的 EPS 限制了 Cu(2+)的吸收。根据致密性和牢固性将细胞壁 EPS 分为可溶性 EPS（S-EPS）、松散结合 EPS（LB-EPS）和紧密结合 EPS（TB-EPS）。LB-EPS 在 Cu(2+)固定化中比 S-EPS 和 TB-EPS 更重要。扫描电子显微镜（SEM）分析 LB-EPS 表面粗糙，有许多蜂窝状孔，有利于铜进入；因此，它们可能起到微生物保护屏障的作用。傅里叶变换红外（FT-IR）分析进一步证实，蛋白质和碳水化合物是主要的胞外化合物，具有羧基（COOH）、羟基（OH）和酰胺（NH）等官能团，主要参与金属离子结合。
