An evolving view of methane metabolism in the Archaea
Methane is a key compound in the global carbon cycle that influences both nutrient cycling and the Earth's climate. A limited number of microorganisms control the flux of biologically generated methane, including methane metabolizing archaea that either produce or consume methane. Methanogenic and methanotrophic archaea belonging to the phylum Euryarchaeota share a genetically similar, interrelated pathway for methane metabolism. The key enzyme in this pathway, the methyl coenzyme M reductase (Mcr) complex, catalyses the last step in methanogenesis and the first step in methanotrophy. The discovery of mcr and divergent mcr like genes in new euryarchaeotal lineages and novel archaeal phyla challenges long held views of the evolutionary origin of this metabolism within the Euryarchaeota. Divergent mcr like genes have recently been shown to oxidize short chain alkanes, indicating that these complexes have evolved to metabolize substrates other than methane. In this Review, we examine the diversity, metabolism and evolutionary history of mcr containing archaea in light of these recent discoveries.Methane metabolism has a central role in the global carbon cycle. In the Review, Tyson and colleagues discuss the enzymatic pathways responsible for archaeal methane metabolism and highlight the evolutionary relationships of key enzymes with recently discovered alkane oxidizing archaea.
Nature Reviews Microbiology