Fe(II)-oxidizing bacteria (FeOB) are important catalysts for iron cycling in iron-rich marine, groundwater, and freshwater environments. However, few studies have reported the distribution and diversity of these bacteria in flooded paddy soils. This study investigates the microbial structure and diversity of microaerophilic Fe(II)-oxidizing bacteria (mFeOB) and their possible role in Fe(II) oxidation in iron-rich paddy soils. Using enrichment experiments that employed serial transfers, the changes in microaerophilic microbial community were examined via 16S rRNA gene high-throughput sequencing. During enrichments, the Fe(II) oxidation rate decreased as transfers increased, and the maximum rate of Fe(II) oxidation was observed in the first transfer (0.197 mM day⁻¹). Results from X-ray diffraction of minerals and scanning electron microscopy of the cell-mineral aggregates revealed that cell surfaces in all transfers were partly covered with amorphous iron oxide formed by FeOB. After four transfers, the phyla of Proteobacteria had a dominant presence that reached up to 95%. Compared with the original soil, the relative abundances of Cupriavidus, Massilia, Pseudomonas, Ralstonia, Sphingomonas, and Variovorax increased in FeS gradient tubes and became dominant genera after transfers. Cupriavidus, Pseudomonas, and Ralstonia have been identified as FeOB previously. Furthermore, the structure of the microbial community tended to be stable as transfers increased, indicating that other bacterial species might perform important roles in Fe(II) oxidation. These results suggest the potential involvement of mFeOB and these other microorganisms in the Fe(II)-oxidizing process of soils. It will be helpful for future studies to consider their role in related biogeochemical processes, such as transformation of organic matters and heavy metals.

Fe（II）氧化细菌（FeOB）是富铁海洋，地下水和淡水环境中铁循环的重要催化剂。但是，很少有研究报道这些细菌在水淹稻田中的分布和多样性。这项研究调查了富氧稻田土壤中需氧性Fe（II）氧化细菌（mFeOB）的微生物结构和多样性，及其在Fe（II）氧化中的可能作用。使用采用连续转移的富集实验，通过16S rRNA基因高通量测序检查了需氧微生物群落的变化。在富集过程中，Fe（II）的氧化速率随着转移的增加而降低，并且在第一次转移中观察到最大的Fe（II）氧化速率（0.197 mM第一天^-1）。矿物的X射线衍射结果和细胞矿物聚集体的扫描电子显微镜结果表明，所有转移过程中的细胞表面均部分被FeOB形成的无定形氧化铁覆盖。经过四次转移后，变形杆菌门占主导地位，达到了95％。与原土相比，相对丰度贪铜，马西利亚，假单胞菌，青枯病，鞘氨醇，和贪噬菌菲斯梯度管增加，并成为转移后优势属。铜杯，假单胞菌和罗尔斯通氏菌之前已被确定为FeOB。此外，随着转移的增加，微生物群落的结构趋于稳定，这表明其他细菌可能在Fe（II）氧化中起重要作用。这些结果表明，mFeOB和其他微生物可能参与了土壤的Fe（II）氧化过程。考虑它们在相关生物地球化学过程（例如有机物和重金属的转化）中的作用将对将来的研究有所帮助。