FIG 4.

Diverse physiology in methane-producing and methane-consuming archaea. (A) Hydrogenotrophic methanogenesis by Methanosarcina barkeri; (B) methylotrophy by M. acetivorans; (C) methanotrophy by ANME-2 with direct interspecies electron exchange (DIET). Red arrows indicate electron transfer, and dashed black arrows represent ion translocation steps for energy conservation. Enzyme abbreviations: Frh, F₄₂₀-reducing hydrogenase; Ech, ferredoxin-dependent hydrogenase; Vho, methanophenazine-reducing hydrogenase; Fpo/Fqo, F₄₂₀H₂:phenazine/quinone oxidoreductase; HdrDE, heterodisulfide reductase; Mhc, multiheme cytochrome; Rnf, Na⁺-translocating ferredoxin:NAD oxidoreductase; Mtr, Na⁺-translocating methyl-H₄MPT:coenzyme M methyltransferase. The figure is based on reports from McGlynn (108), Timmers et al. (92), Thauer et al. (204), and references therein.