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.