State Key Laboratory of Agricultural Microbiology, Huazhong Agricultural University, Wuhan, 430070, China.
State Key Laboratory of Agricultural Microbiology, Huazhong Agricultural University, Wuhan, 430070, China; State Environmental Protection Key Laboratory of Soil Health and Green Remediation, Huazhong Agricultural University, Wuhan, 430070, China.
Environ Pollut. 2022 Feb 15;295:118651. doi: 10.1016/j.envpol.2021.118651. Epub 2021 Dec 6.
Bacteria and their secreted extracellular polymeric substances (EPS) are widely distributed in ecosystems and have high capacity for heavy metal immobilization. The knowledge about the molecular-level interactions with heavy metal ions is essential for predicting the behavior of heavy metals in natural and engineering systems. This comprehensive study using potentiometric titration, Fourier-transform infrared (FTIR) spectroscopy, isothermal titration calorimetry (ITC) and X-ray absorption fine structure (XAFS) was able to reveal the functional diversity and adsorption mechanisms for Pb onto bacteira and the EPS in greater detail than ever before. We identified mono-carboxylic, multi-carboxylic, phosphodiester, phosphonic and sulfhydryl sites and found the partitioning of Pb to these functional groups varied between gram-negative and gram-positive bacterial strains, the soluble and cell-bound EPS and Pb concentrations. The sulfhydryl and phosphodiester groups preferentially complexed with Pb in P. putida cells, while multifunctional carboxylic groups promoted Pb adsorption in B. subtilis cells and the protein fractions in EPS. Though the functional site diversity, the adsorption of Pb to organic ligands occurred spontaneously through a universal entropy increase and inner-sphere complexation mechanism. The functional group scale knowledge have implications for the modeling of heavy metal behavior in the environment and application of these biological resources.
细菌及其分泌的胞外聚合物（EPS）广泛分布于生态系统中，具有很强的重金属固定能力。了解其与重金属离子的分子水平相互作用，对于预测重金属在自然和工程系统中的行为至关重要。本研究采用电位滴定、傅里叶变换红外（FTIR）光谱、等温热滴定（ITC）和 X 射线吸收精细结构（XAFS）等多种方法，深入揭示了细菌和 EPS 对 Pb 的功能多样性和吸附机制，比以往任何时候都更加详细。我们鉴定了单羧基、多羧基、磷酸二酯、膦酸和巯基等功能基团，并发现 Pb 在革兰氏阴性和革兰氏阳性菌、可溶性和细胞结合型 EPS 以及 Pb 浓度之间的分配存在差异。在 P. putida 细胞中，巯基和磷酸二酯基团优先与 Pb 络合，而多功能羧酸基团则促进了 B. subtilis 细胞和 EPS 中蛋白质部分对 Pb 的吸附。尽管功能基团多样性很大，但 Pb 与有机配体的吸附是通过普遍的熵增加和内球络合机制自发发生的。该研究结果为重金属在环境中的行为建模以及这些生物资源的应用提供了重要的功能组尺度知识。
