The microbial nexus: linking arsenic biogeochemistry with greenhouse gas emissions

Microorganisms play a pivotal role in driving both arsenic (As) biogeochemical cycling and the significantly anomalous greenhouse gas (GHG) levels frequently observed in naturally high-As environments; however, the mechanistic coupling between these two processes remains insufficiently characterized. This review presents a comprehensive synthesis of the interplay between microbial transformations of As (oxidation, reduction, and methylation/demethylation) and three major greenhouse gases-CH₄, N₂O, and CO₂. We first summarize the key microbial taxa and molecular mechanisms governing As redox transformation, CH₄ oxidation and methanogenesis, autotrophic CO₂ fixation, and denitrification-driven N₂O production. Building on this mechanistic foundation, we elucidate four experimentally and environmentally validated linkages, including (1) direct methane oxidation coupled with As(V) reduction (AOM-AsR), highlighting the molecular mechanisms that drive arsenic mobilization during anaerobic/aerobic methane oxidation and their environmental implications; (2) direct As(III) oxidation coupled with denitrification, linking the As and nitrogen cycles, wherein incomplete denitrification acts as a significant biological source of N₂O; (3) direct As(III) oxidation driving autotrophic carbon fixation, offering a potential regional net carbon sink across diverse environments; and (4) indirect feedbacks mediated by As methylation/demethylation and geochemical mobilization, where detoxification-driven shifts in As speciation and local toxicity indirectly regulate downstream methanogenic communities and CH₄ fluxes. Finally, we identify critical knowledge gaps regarding specific molecular pathways and multi-element interactions underlying these microbially driven couplings, and propose future research directions centered on deeper mechanistic elucidation. Overall, this review provides a robust scientific foundation for understanding the complex interplay between As biogeochemistry and GHG dynamics in specific environmental niches.