Methane-Dependent Mineral Reduction by Aerobic Methanotrophs under Hypoxia

Methanotrophs play an important role in controlling methane balance in the biosphere. For over 100 years, methanotrophs of the Proteobacteria phylum have been studied under oxic conditions, with molecular oxygen serving as the major electron acceptor. However, recent metagenomic data suggest that proteobacterial methanotrophs may be more metabolically versatile. In this work, we demonstrate methane-dependent ferrihydrite reduction by a methanotroph of the Methylomonas genus (Gammaproteobacteria) as well as by a methanotroph of the Methylosinus genus (Alphaproteobacteria). This suggests that solid minerals may serve as alternative electron acceptors for aerobic methanotrophs, under hypoxia. This novel type of energy metabolism likely serves as a survival strategy in the absence of molecular oxygen. Our findings expand the range of known microorganisms capable of methane-dependent mineral reduction and provide a deeper understanding of microbial methane metabolism across redox niches.