Arsenic (As) biotransformation in soil affects As biogeochemical cycling and is associated with As accumulation in rice. After inoculation with 1% iron-oxidizing bacteria (FeOB) in paddy soil, As speciation, As biotransformation genes in soil, As/Fe in Fe plaques, and As accumulation in rice were characterized. Compared with the control, the available As concentrations in soils decreased while amorphous and poorly crystalline Fe–Al oxidized As and crystalline Fe–Al oxidized As fractions increased of F (FeOB) and RF (rice and FeOB) treatments. Fe concentrations increased and positively correlated with As concentrations in Fe plaques on the rice root surface (***P < 0.001). Compared with R (rice), Monomethyl As (MMA), dimethyl As (DMA), arsenate (As(V)), and arsenite (As(III)) concentrations in rice plants showed a downwards trend of RF treatment. The As concentration in grains was below the National Standard for Food Safety (GB 2762-2017). A total of 16 As biotransformation genes in rhizosphere soils of different treatments (CK, F, R and RF were quantified by high-throughput qPCR (HT-qPCR). Compared with the control, the As(V) reduction and As transport genes abundance in other treatments increased respectively by 54.54%–69.17% and 54.63%–73.71%; the As(III) oxidation and As (de) methylation genes did not change significantly; however, several As(III) oxidation genes (aoxA, aoxB, aoxS, and arsH) increased. These results revealed that FeOB could reduce, transport As, and maybe also oxidize As. In addition, As(III) oxidation gene (aoxC) in rhizosphere soil was more abundant than in non-rhizosphere soil. It indicated that radial oxygen loss (ROL) promoted As(III) oxidation in rhizosphere soils. The results provide evidence for As biotransformation by ROL and FeOB in soil-rice system. ROL affects As oxidation and immobilization, and FeOB affects As reduction, transportation and may also affect As oxidation.

土壤中的砷 (As) 生物转化影响砷的生物地球化学循环，并与水稻中的砷积累有关。在稻田土壤中接种 1% 铁氧化菌 (FeOB) 后，对 As 形态、土壤中 As 生物转化基因、Fe 斑块中 As/Fe 和水稻中 As 积累进行了表征。与对照相比，F (FeOB) 和 RF (水稻和 FeOB) 处理的土壤中有效 As 浓度降低，而无定形和低结晶 Fe-Al 氧化 As 和结晶 Fe-Al 氧化 As 分数增加。Fe 浓度增加并与水稻根表面 Fe 斑块中的 As 浓度呈正相关（***P < 0.001）。与 R（水稻）相比，RF 处理后水稻植株中的单甲基砷（MMA）、二甲基砷（DMA）、砷酸盐（As（V））和亚砷酸盐（As（III））的浓度呈下降趋势。粮食中砷含量低于食品安全国家标准（GB 2762-2017）。通过高通量qPCR（HT-qPCR）对不同处理的根际土壤（CK、F、R和RF）共16个As生物转化基因进行定量。与对照相比，As(V)还原和As转运基因丰度其他处理分别增加了 54.54%~69.17% 和 54.63%~73.71%；As(III) 氧化和 As(de) 甲基化基因没有显着变化；然而，一些 As(III) 氧化基因（aoxA、aoxB、 aoxS 和 arsH) 增加。这些结果表明，FeOB 可以还原、转运 As，并可能氧化 As。此外，根际土壤中的 As(III) 氧化基因 (aoxC) 比非根际土壤更丰富。这表明径向氧损失（ROL）促进了根际土壤中的As（III）氧化。该结果为土壤-水稻系统中ROL和FeOB的As生物转化提供了证据。ROL 影响 As 的氧化和固定，FeOB 影响 As 的还原、运输，也可能影响 As 的氧化。