Actinobacteria mediate anaerobic methane oxidation in iron-rich environment

Recent research has identified the Actinobacterium Candidatus Mycobacterium methanotrophicum, which oxidizes methane aerobically in extremely acidic environments. In a previous study, we observed significant enrichment of Actinobacteria in an anaerobic iron-rich methane-oxidation reactor. Therefore, in this study, we assessed the anaerobic methane utilization potential of Actinobacteria using microcosm experiments, isotope labeling, and DNA stable isotope probing. Metabolic pathway analysis indicated that Actinobacteria harbor genetic potential for multiple pathways in iron-rich anaerobic environments. Additionally, we propose that Propionibacteriales may activate methane using oxygen produced by Rhodospirillales through iron-containing methanobactin analog-dependent H₂O reduction. The resulting intermediates of methane oxidation could serve as carbon and energy sources for these microorganisms. Actinobacteria were also involved in the conversion of nitrite to ammonia. Iron may be an important trigger in Actinobacteria mediating anaerobic methane oxidation. Our findings reveal the potential role of Actinobacteria in contributing to anaerobic methane oxidation in iron-rich environments through interbacterial cooperation.