Zhou Dan, Liang Mengmeng, Xia Yonglian, Li Chao, Huang Mingzheng, Peng Shuming, Huang Yi
State Key Laboratory of Geohazard Prevention and Geoenvironment Protection, College of Ecology and Environment, Chengdu University of Technology, Sichuan 610059, China; State Environmental Protection Key Laboratory of Synergetic Control and Joint Remediation for Soil & Water Pollution, College of Ecology and Environment, Chengdu University of Technology, Chengdu 610059, China.
State Key Laboratory of Geohazard Prevention and Geoenvironment Protection, College of Ecology and Environment, Chengdu University of Technology, Sichuan 610059, China.
Sci Total Environ. 2022 Dec 15;852:158394. doi: 10.1016/j.scitotenv.2022.158394. Epub 2022 Sep 2.
Extracellular polymeric substances (EPS) are high-molecular polymers secreted by microbes and play essential roles in metallic biogeochemical cycling. Previous studies demonstrated the reducing capacity of the functional groups on EPS for metal reduction. However, the roles of different EPS components in vanadium speciation and their responsible reducing substances for vanadium reduction are still unknown. In this study, the EPS of Bacillus sp. PFYN01 was fractionated via ultrafiltration into six components with different kDa (EPS, EPS, EPS, EPS, EPS, and EPS). Batch reduction experiments of the intact cells, EPS-free cells, the pristine and fractionated EPS with V were conducted and characterized. The results demonstrated that the extracellular reduction of V into V by EPS was the major reduction process. Among the functional groups in EPS, C=O/C-N of amide in protein/polypeptide and CO of carboxyl in fulvic acid-like substances might act as the reductants for V, while CO in polysaccharide molecules and PO in phosphodiester played a key role in the adsorption process. The intracellular reduction was via translocating V into the cells and releasing V by the intracellular reductases. The reducing capacity of the fractionated EPS followed a sequence of EPS > EPS > EPS > EPS > EPS > EPS. The small molecules of fulvic acid-like substances and amino acids were responsible for the high reducing capacity of EPS. EPS had the lowest reducing capacity due to its macromolecular structure decreasing the exposure of the reactive sites. In addition to reduction, those intermediate EPS components may also have supporting functions, such as connecting protein skeletons and increasing the specific surface area of EPS. Therefore, the diverse effects of the EPS components cannot be neglected in vanadium biogeochemical cycling.
胞外聚合物（EPS）是微生物分泌的高分子聚合物，在金属生物地球化学循环中发挥着重要作用。先前的研究表明EPS上的官能团具有金属还原能力。然而，不同EPS组分在钒形态变化中的作用及其负责钒还原的物质仍然未知。在本研究中，通过超滤将芽孢杆菌属PFYN01的EPS分离为六个不同千道尔顿的组分（EPS1、EPS2、EPS3、EPS4、EPS5和EPS6）。进行了完整细胞、无EPS细胞、原始EPS和分级EPS与钒的批量还原实验并进行了表征。结果表明，EPS将V（V）还原为V（IV）的胞外还原是主要还原过程。在EPS的官能团中，蛋白质/多肽中酰胺的C=O/C-N和类富里酸物质中羧基的CO可能作为V的还原剂，而多糖分子中的CO和磷酸二酯中的PO在吸附过程中起关键作用。细胞内还原是通过将V转运到细胞内并由细胞内还原酶释放V。分级EPS的还原能力顺序为EPS1 > EPS2 > EPS3 > EPS4 > EPS5 > EPS6。类富里酸物质和氨基酸的小分子导致EPS具有高还原能力。EPS6由于其大分子结构减少了反应位点的暴露，还原能力最低。除了还原作用外，那些中间EPS组分可能还具有支持功能，如连接蛋白质骨架和增加EPS的比表面积。因此，在钒生物地球化学循环中，EPS组分的多种作用不可忽视。
