Hexavalent chromium (Cr(VI)) could be sequestrated by soils via microbial reduction to Cr(III) and association with minerals, however, quantitative understanding of metal reducing bacteria on the coupled kinetics of Cr and Fe minerals is still lacking. Here, microbial-mediated ferrihydrite transformation and reductive sequestration of Cr(VI) were investigated with MR-1 under varying Cr/Fe ratios. Quantitative results depicted that the contents of magnetite from ferrihydrite transformation decreased from 70 % to 22 % after 288 h as Cr/Fe ratios increased from 0 to 8 × 10, and reductive transformation rates increased with decreasing Cr/Fe ratio. Elemental mapping and line scan analyses at nano-scale revealed that Cr(VI) was evenly combined within fresh ferrihydrite, and a part of produced Cr(III) was doped into the crystal lattice of magnetite and goethite. Cr may be sequestrated by secondary Fe minerals via structural substitution, surface complexation, and physical encapsulation. Microscopy-based results exhibited that more Fe minerals adsorbed on the surface of cell and less cells were lysed at low Cr/Fe ratios. Confocal laser scanning microscopy depicted that less cells were alive at high Cr/Fe ratios. The amplification of extracellular electron transfer-associated genes was downregulated as Cr/Fe ratios increased. The Cr/Fe ratios could affect cell activity, the combination with Fe minerals, and gene expression, thus controlling the reductive sequestration of Cr(VI) and phase transformation of ferrihydrite. A kinetic model has been established by combining elementary reductions, and it could well describe Cr(VI) reduction and Cr(III) incorporation under various Cr/Fe ratios during dissimilatory Fe reduction process. These findings could broaden our knowledge of quantifying the migration and transport of Cr in anoxic Cr-contaminated soil environments, and could be useful for simulating Cr dynamic behaviors in the natural soil, aquatic, and sediment environments.

中文翻译：

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Shewanella oneidensis MR-1 对 Cr(VI) 相关水铁矿的还原和转化：动力学和次生矿物


六价铬 (Cr(VI)) 可以通过微生物还原为 Cr(III) 并与矿物质结合而被土壤封存，然而，仍然缺乏对金属还原细菌对 Cr 和 Fe 矿物质耦合动力学的定量了解。在这里，使用 MR-1 在不同的 Cr/Fe 比率下研究了微生物介导的水铁矿转化和 Cr(VI) 的还原封存。定量结果表明，随着 Cr/Fe 比从 0 增加到 8 × 10，288 h 后，水铁矿转化产生的磁铁矿含量从 70% 下降到 22%，还原转化率随着 Cr/Fe 比的降低而增加。纳米尺度的元素分布和线扫描分析表明，Cr(VI)均匀地结合在新鲜水铁矿中，并且部分生成的Cr(III)掺杂到磁铁矿和针铁矿的晶格中。 Cr 可以通过结构取代、表面络合和物理封装被次生铁矿物螯合。基于显微镜的结果表明，在低 Cr/Fe 比率下，细胞表面吸附了更多的 Fe 矿物质，并且裂解的细胞更少。共焦激光扫描显微镜显示，在高 Cr/Fe 比率下，存活的细胞较少。随着 Cr/Fe 比率的增加，细胞外电子转移相关基因的扩增被下调。 Cr/Fe比率可以影响细胞活性、与Fe矿物质的结合以及基因表达，从而控制Cr(VI)的还原螯合和水铁矿的相变。结合元素还原建立了动力学模型，能够很好地描述异化Fe还原过程中不同Cr/Fe比下Cr(VI)的还原和Cr(III)的掺入。 这些发现可以拓宽我们对缺氧铬污染土壤环境中铬迁移和运输的量化认识，并可用于模拟天然土壤、水生和沉积物环境中铬的动态行为。