中性厌氧的富铁环境中，微生物驱动硝酸盐还原–亚铁氧化（NRFO）过程和异化铁还原过程，然而异化铁还原菌能否介导NRFO仍未知。选取异化铁还原菌（Klebsiella pneumoniae L17、Shewanella oneidensis MR-1、Shewanella putrefaciens strain CN32）、亚铁和硝酸盐，构建厌氧NRFO体系。结果表明：亚铁氧化、硝酸盐还原同步发生，主要是因为硝酸盐还原产物亚硝酸盐可以直接氧化亚铁；亚铁抑制了硝酸盐还原，且该抑制作用随亚铁浓度升高而增强；亚铁对亚硝酸盐的竞争性还原导致了铵根大量减少；亚铁氧化的次生矿物沉淀在细胞表面，阻碍硝酸盐进入细胞进行还原。在低浓度亚铁条件下，亚铁的毒害和氧化成矿作用抑制L17还原硝酸盐；亚铁氧化成矿作用是抑制CN32还原硝酸盐的主要原因；而亚铁的毒害是抑制MR-1还原硝酸盐的主要原因。在高浓度亚铁条件下，亚铁氧化导致细胞结壳是抑制微生物硝酸盐还原的主要原因。强调了厌氧富铁环境中非模式菌介导的硝酸盐还原–亚铁氧化过程，拓展了硝酸盐还原亚铁氧化过程的微生物范畴，有助于深入理解厌氧环境中硝酸盐还原亚铁氧化过程中微生物的功能和相对贡献。

Microbially-mediated nitrate-reducing Fe(II) oxidation (NRFO) is ubiquitous under neutral anaerobic iron-rich environments. However, it is still unknown whether NRFO can be mediated by dissimilatory iron reducing bacteria. In this study, Klebsiella pneumoniae L17, Shewanella oneidensis MR-1, and Shewanella putrefaciens strain CN32 were used as the model iron reducing strains to study the process of anaerobic NRFO. The results show that nitrate reduction and Fe(II) oxidation occurred simultaneously. The intermediate product nitrite during nitrate reduction is considered the dominant contributor to the overall Fe(II) oxidation. The presence of Fe(Ⅱ) inhibited microbial nitrate reduction, and the inhibitory effect of Fe(Ⅱ) was more significant with the higher Fe(Ⅱ) concentration. The competition between chemical reduction of nitrite by Fe(Ⅱ) and biological nitrite reduction resulted in the decrease of ammonium production. Iron oxides precipitated on the cell surface and subsequently prevented nitrate uptake and microbial nitrate reduction. The cell toxicity of Fe(Ⅱ) and secondary minerals inhibited biological nitrate reduction by L17 with low Fe(Ⅱ) concentration. Nitrate reduction by CN32 was inhibited by the secondary minerals during Fe(II) oxidation while the inhibition of nitrate reduction by MR-1 was attributed to cell toxicity of Fe(Ⅱ). Under high Fe(Ⅱ) concentration, microbial nitrate reduction was inhibited by cell encrustation. This study emphasizes iron-reducing bacteria mediated nitrate-reducing Fe(Ⅱ) oxidation in the anaerobic iron-rich environment, and expands the scope of microbial species with the ability of nitrate-reducing Fe(Ⅱ) oxidation. Therefore, the findings would be helpful for understanding the function and relative contribution of various microorganisms in the process of nitrate-reducing Fe(Ⅱ) oxidation in anaerobic environment.

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国家自然科学基金（41907020、41807026、42077018）