Manganese-coupled anaerobic oxidation of methane: Mechanisms, influencing factors and environmental implications

Methane (CH₄) is a potent greenhouse gas, and its global budget has attracted wide attention. Manganese-driven anaerobic oxidation of methane (Mn-AOM) acts as a critical biological sink for methane emissions and serves as a key link among multiple biogeochemical cycles. Despite its recognized importance, a systematic synthesis of the mechanisms, influencing factors, and environmental implications of Mn-AOM has been lacking. This review summarizes the core microorganisms involved, including anaerobic methanotrophic archaea (ANME) and metal-reducing bacteria, and examines the electron transfer pathways. Direct pathways include multiheme c-type cytochromes, conductive nanowires, pili, and minerals, while indirect pathways are mediated by electron shuttles. Furthermore, we evaluate key environmental factors that regulate the kinetics of Mn-AOM, such as temperature, pH, salinity, type of Mn oxide, and elevated CO₂ concentrations. The significance of Mn-AOM is discussed from several perspectives, including its role in mitigating greenhouse gas emissions and facilitating the coupled cycles of carbon, nitrogen, phosphorus, and sulfur. The review further explores its dual effects on heavy metal(loid)s such as cadmium (Cd), zinc (Zn), lead (Pb), and arsenic (As), which can lead to both in situ immobilization and secondary mobilization. Finally, we highlight knowledge gaps, future research directions, engineering potentials, and ecological risks. This review seeks to deepen the mechanistic understanding of Mn-AOM while facilitating greenhouse gas mitigation, environmental remediation, and heavy metal(loid) risk management.