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.