School of Environmental Science and Engineering, Shanghai Jiao Tong University, Shanghai 200240, China.
School of Geographic Sciences, East China Normal University, Shanghai 200241, China.
J Hazard Mater. 2021 Aug 5;415:125616. doi: 10.1016/j.jhazmat.2021.125616. Epub 2021 Mar 12.
Microbial extracellular polymeric substances (EPS) significantly influence metal behavior in the environment, but the electron transfer reaction between EPS and copper that determine the speciation and fate of copper is lacking. Here, we investigated the role of EPS from Shewanella oneidensis MR-1, Bacillus subtilis, and Saccharomyces cerevisiae and its redox state in the Cu(II) reduction under anoxic conditions. Both pristine and reduced EPS mediated copper transformation from Cu(II) to Cu(I) within 10 min. The Cu(II) reduction efficiency by the reduced EPS was ten times higher than that by the pristine EPS, which could be ascribed to the varied electron transfer ability of EPS. Multiple spectroscopic results indicated that c-type cytochromes and O-/N-containing groups were effective redox moieties responsible for copper transformation. The c-type cytochromes contributed for about 80% to the overall electron flux in S. oneidensis MR-1 EPS, which was significantly higher than in B. subtilis (27%) and S. cerevisiae EPS (22%). In contrast, functional groups such as phenolic and amide, dominated Cu(II) reduction for the B. subtilis and S. cerevisiae EPS. This study emphasizes the significant contribution of microbial EPS that serve as reducing agents and electron transfer mediators for cupric reduction and cuprous formation in the natural environments.
微生物胞外聚合物（EPS）显著影响金属在环境中的行为，但决定铜的形态和归宿的 EPS 与铜之间的电子转移反应尚不清楚。在这里，我们研究了希瓦氏菌（Shewanella oneidensis MR-1）、枯草芽孢杆菌（Bacillus subtilis）和酿酒酵母（Saccharomyces cerevisiae）的 EPS 及其在缺氧条件下还原态下对 Cu(II)还原的作用。原始和还原的 EPS 均在 10 分钟内将铜从 Cu(II)转化为 Cu(I)。还原的 EPS 介导的 Cu(II)还原效率比原始 EPS 高十倍，这归因于 EPS 电子转移能力的不同。多种光谱结果表明，c 型细胞色素和含 O/N 的基团是负责铜转化的有效氧化还原基团。c 型细胞色素对 S. oneidensis MR-1 EPS 中的总电子通量的贡献约为 80%，明显高于枯草芽孢杆菌（27%）和酿酒酵母（22%）。相比之下，对于枯草芽孢杆菌和酿酒酵母 EPS，酚类和酰胺等功能基团则主导 Cu(II)还原。本研究强调了微生物 EPS 在自然环境中作为还原剂和电子转移介质对铜的还原和亚铜形成的重要贡献。
