Context-dependent anaerobic oxidation of methane: Insight for methane emission mitigation

Anaerobic oxidation of methane (AOM) exhibits context-dependent metabolic versatility, governed by electron acceptor heterogeneity and anthropogenic perturbations. This study investigates the AOM potential by simulating three environments, high-dissolved organic carbon (DOC), high-nitrate with moderate sulfate, and sulfate-enhanced conditions, to investigate AOM potential under controlled perturbations. Substrate conversion dynamics were observed by monitoring the variation of methane, sulfate, nitrate, iron, etc., and microbial community shifts were analyzed by 16S rDNA high-throughput sequencing. In the high-carbon condition, characterized by high DOC (5.65–21.83 mmolC·L⁻¹) but low nitrate and sulfate (both <1 mmol L⁻¹) levels, methanogens such as Methanobacterium sp. IM1 and Thermoplasmata dominated the stage, overpowering anaerobic methanotrophic archaea (ANME), while no methane oxidation but obvious methane production occurred. Shifting to the scenario with high nitrate (3.51 mmolN·L⁻¹) and moderate sulfate (1.36 mmolS·L⁻¹), ammonium accumulation played the role of a spoiler. It weakened AOM process (K_mo = 0.58 d⁻¹) and stirred up a competitive relationship between sulfur-driven ammonium-oxidizing archaea (e.g., Nitrososphaeraceae, Nitrosotaleaceae) and methanotrophs (e.g., Marine group II, Wosearchaeales, Roseiarcus). However, once nitrate was consumed to a low level, sulfate reduction relieved the ammonium pressure and re-activated iron, the suppression of AOM eased (K_mo = 1.44 d⁻¹). Under the sulfate-enhanced circumstances, where the sulfate level increased to 1.47–2.55 mmolS·L⁻¹, the AOM process accelerated (K_mo = 4.02 d⁻¹) even under high-nitrate conditions (1.66 ± 0.12 mmolN·L⁻¹). Methanotrophs and sulfur-metabolizing bacteria then co-thrived, showing a close display of cooperation. Our findings offer a pivotal framework to clarify AOM's contribution to natural methane emissions and give a new perspective for the development of methane mitigation technologies.