School of Water Resources and Environment, China University of Geosciences, Beijing 100083, China.
Key Laboratory of Mineralogy and Metallogeny, Guangzhou Institute of Geochemistry, Chinese Academy of Science, Guangzhou 510640, China.
Environ Sci Technol. 2021 Dec 7;55(23):16236-16245. doi: 10.1021/acs.est.1c05341. Epub 2021 Nov 26.
Manganese (Mn) oxides are considered as the primary oxidant of trivalent chromium [Cr(III)] in the environment. Microbial activities are responsible for the majority of Mn oxide formation in nature, thus likely influencing Cr(III) oxidation. Previous studies have been limited to Cr(III) oxidation by bacterial Mn oxides. Herein, we report coupled Mn(II) and Cr(III) oxidation in the presence of three Mn(II)-oxidizing Ascomycete fungi. In contrast to the previously reported inhibitory effect of Cr(III) on bacterial Mn(II) oxidation, varying effects of Cr(III) on fungal Mn(II) oxidation were observed, which may be linked to their Mn(II)-oxidation mechanisms. Under the concentrations of Mn(II) and Cr(III) applied in this study, Cr(III) promoted Mn(II) oxidation if it was mediated by hyphae-associated processes, but inhibited Mn(II) oxidation if it was achieved via extracellular enzymes/metabolites. The Cr(III) oxidation rate and extent were affected by Cr(III) speciation, Cr(VI) removal capacity (i.e., adsorption/reduction) of fungi, and organic content. The morphology and spatial relationship of Mn oxides with fungi varied, depending on fungal species and Cr(III) presence. Our findings highlight the importance of Mn(II)-oxidizing fungi in biogeochemical cycles of Mn and Cr and have significant implications for the origin of geogenic Cr(VI) and stability of reduced chromium in contaminated environments.
锰 (Mn) 氧化物被认为是环境中三价铬 [Cr(III)] 的主要氧化剂。微生物活动是自然界中大多数 Mn 氧化物形成的原因，因此可能会影响 Cr(III)的氧化。以前的研究仅限于细菌 Mn 氧化物对 Cr(III)的氧化。在此，我们报告了在三种 Mn(II)氧化的子囊菌真菌存在下，Mn(II)和 Cr(III)的耦合氧化。与先前报道的 Cr(III)对细菌 Mn(II)氧化的抑制作用相反，观察到 Cr(III)对真菌 Mn(II)氧化的影响不同，这可能与其 Mn(II)氧化机制有关。在本研究中应用的 Mn(II)和 Cr(III)浓度下，如果 Cr(III)是通过菌丝体相关过程介导的，则促进 Mn(II)氧化，但如果是通过细胞外酶/代谢物实现的，则抑制 Mn(II)氧化。Cr(III)的氧化速率和程度受 Cr(III)形态、真菌的 Cr(VI)去除能力（即吸附/还原）和有机含量的影响。Mn 氧化物与真菌的形态和空间关系因真菌种类和 Cr(III)的存在而不同。我们的研究结果强调了 Mn(II)氧化真菌在 Mn 和 Cr 生物地球化学循环中的重要性，对地球成因 Cr(VI)的起源和污染环境中还原态铬的稳定性具有重要意义。
