Enhanced Aerobic Methane Oxidation: Influence of Ammonium Introduction and Complete Nitrification Coupling on Metabolic Activity

Abstract The biological process of methane (CH₄) oxidation is crucial for reducing fugitive CH₄ emissions into the atmosphere. Within the nitrogen cycle, ammonium (NH₄⁺) and nitrate (NO₃⁻) significantly influence the growth and activity of methane-oxidizing bacteria (MOB). However, the stimulatory effects of NH₄⁺ and NO₃⁻ on aerobic CH₄ oxidation and the associated metabolic remain to be comprehensively elucidated. In this study, NH₄⁺ and NO₃⁻ were loaded onto zeolites and mixed with MOB-rich soil to conduct CH₄ incubation experiments. The CH₄ oxidation rate and metabolomic changes during the second cycle, characterized by distinct MOB activities, were determined. The NH₄⁺-added group showed a significant increase in the CH₄ oxidation rate (up to 1.25 mg CH₄·g⁻¹·d⁻¹) compared with the NO₃⁻-added group. Analysis of the microbial community and metabolomics revealed that NH₄⁺ stimulated the population of two electroactive bacterial Clostridia and Thermincolales within the Firmicutes phylum. On the metabolic level, NH₄⁺ was noted to promote nucleotide and active amino acid metabolic pathways. Nitrospirota drove the synthesis of glucogenic and ketogenic amino acids, which could be used by the MOB in the tricarboxylic acid cycle. Additionally, this study clarified the plausible interplay between nitrification and the CH₄ oxidation process. These insights could help enhance our understanding of the interaction between the global nitrogen cycle and aerobic CH₄ oxidation.