Complexation by cysteine and iron mineral adsorption limit cadmium mobility during metabolic activity of Geobacter sulfurreducens.
Complexation by cysteine and iron mineral adsorption limit cadmium mobility during metabolic activity of Geobacter sulfurreducens.
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DOI：
10.1039/d0em00244e
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发表时间：
2020-08
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通讯作者：
E. Tomaszewski;E. Tomaszewski;L. Olson;Martin Obst;James Byrne;James Byrne;Andreas Kappler;E. Muehe;E. Muehe
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文献类型：
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作者：
E. Tomaszewski;E. Tomaszewski;L. Olson;Martin Obst;James Byrne;James Byrne;Andreas Kappler;E. Muehe;E. Muehe
镉 (Cd) 通过人类活动进入食物链，对人类健康产生不利影响。为了降低风险，需要更好地了解限制镉在环境中迁移的生物地球化学机制。虽然 Cd 不具有氧化还原活性，但 Cd 形态会发生变化（即水相、络合、吸附），并影响迁移率。在这里，研究了硫还原地杆菌生长过程中与初始形态形成相关的镉循环。富马酸盐或水铁矿 (Fh) 被提供作为电子受体，Cd 以以下形式存在：(1) 水性阳离子，(2) 与半胱氨酸的水性络合物，其通常存在于金属胁迫的土壤环境中，或 (3) 吸附到 Fh 上。在微生物 Fe(iii) 还原过程中，尽管大量产生 Fe(ii)（Fe(ii) 总量 : Fetotal = 0.8），但 Cd 的去除量很大（~80% 去除）。当富马酸盐为电子受体时，与水溶液中的 Cd 去除率 (34-50%) 相比，当 Cd 与半胱氨酸络合时，溶液中的 Cd 去除率更高 (97-100% 去除率)。共焦激光扫描显微镜 (CLSM) 证明了在所有条件下都会形成胞外聚合物 (EPS)，并且在没有铁矿物的情况下，Cd 与 EPS 相关 (r = 0.51-0.56)。最值得注意的是，与 Cd-半胱氨酸复合物 (r = 0.51) 相比，水性 Cd 与地杆菌细胞 (r = 0.72) 的相关性更强。这项工作表明，Cd 与细胞表面和 EPS 的相互作用以及代谢活动过程中 Cd 的溶解度取决于初始形态。这些过程在硫有限、铁和有机碳丰富的土壤环境中可能尤其重要。
Cadmium (Cd) adversely affects human health by entering the food chain via anthropogenic activity. In order to mitigate risk, a better understanding of the biogeochemical mechanisms limiting Cd mobility in the environment is needed. While Cd is not redox-active, Cd speciation varies (i.e., aqueous, complexed, adsorbed), and influences mobility. Here, the cycling of Cd in relation to initial speciation during the growth of Geobacter sulfurreducens was studied. Either fumarate or ferrihydrite (Fh) was provided as an electron acceptor and Cd was present as: (1) an aqueous cation, (2) an aqueous complex with cysteine, which is often present in metal stressed soil environments, or (3) adsorbed to Fh. During microbial Fe(iii) reduction, the removal of Cd was substantial (∼80% removal), despite extensive Fe(ii) production (ratio Fe(ii)total : Fetotal = 0.8). When fumarate was the electron acceptor, there was higher removal from solution when Cd was complexed with cysteine (97-100% removal) compared to aqueous Cd (34-50%) removal. Confocal laser scanning microscopy (CLSM) demonstrated the formation of exopolymeric substances (EPS) in all conditions and that Cd was correlated with EPS in the absence of Fe minerals (r = 0.51-0.56). Most notable is that aqueous Cd was more strongly correlated with Geobacter cells (r = 0.72) compared to Cd-cysteine complexes (r = 0.51). This work demonstrates that Cd interactions with cell surfaces and EPS, and Cd solubility during metabolic activity are dependent upon initial speciation. These processes may be especially important in soil environments where sulfur is limited and Fe and organic carbon are abundant.