Methanotroph-Derived Reactive Oxygen Species Facilitate Arsenic Oxidation in Paddy Soils

Reactive oxygen species (ROS) are increasingly recognized as important oxidants in soil redox processes, with microbially produced ROS contributing broadly to elemental transformations. Given the active methane oxidation in paddy soils, methanotrophs have considerable potential to generate ROS yet their role in As(III) oxidation remains unclear. Here, we identify methanotroph-derived ROS as an important yet previously overlooked pathway for As(III) oxidation in paddy soils. Soil microcosm experiments and pure culture experiments revealed that methane oxidation enhanced ROS-mediated As(III) oxidation, with H2O2 identified as the dominant ROS. Inhibitor assays and functional gene analyses indicated that oxygen activation and respiratory electron transfer were closely associated with ROS generation during methane oxidation. These findings reveal methanotroph-derived ROS as a distinct route contributing to As(III) oxidation beyond dedicated arsenite oxidases. By revealing an overlooked connection between methane metabolism and arsenic transformation, this work expands our understanding of arsenic biogeochemistry and provides a conceptual basis for the coordinated mitigation of methane emissions and arsenic toxicity in agroecosystems.