Fig. 4.

Metabolic construction of the putative pathway for AOM coupled to Fe(III) reduction in “M. ferrireducens“. Electrons from methane are generated through the “reverse methanogenesis” pathway and transferred to the menaquinone pool (MK/MKH₂) via the Fpo and Hdr complexes, which oxidise F₄₂₀H₂ and CoM-SH+CoB-SH, respectively. CoM-SH and CoB-SH can be oxidised by the HdrDE complex [53] or the cytoplasmic HdrABC–FrhB complex that also reoxidise ferredoxin and reduce two F₄₂₀ [21]. Reducing equivalents are transferred via the menaquinone:cytochrome c oxidoreductases to MHCs located outside the cytoplasm to reduce the Fe(III) oxides. Abbreviations for enzymes and co-factors: H₄MPT, tetrahydromethanopterin; MFR, methanofuran; Fwd, formyl-methanofuran dehydrogenase; Ftr, formylmethanofuran/H₄MPT formyltransferase; Mch, methenyl-H₄MPT cyclohydrolase; Mtd, F₄₂₀-dependent methylene H₄MPT dehydrogenase; Mer, F₄₂₀-dependent methylene-H₄MPT reductase; Mtr, Na⁺-translocating methyl-H₄MPT:coenzyme M methyltransferase; Mcr, methyl-coenzyme M reductase; Fpo, F₄₂₀H₂ dehydrogenase; MK, menaquinone; CoB-SH, coenzyme B; CoM-SH, coenzyme M; Fd, ferredoxin; Hdr, heterodisulfide reductase; FrhB, F₄₂₀-reducing hydrogenase subunit B; Cytb, b-type cytochrome; NrfD, polysulfide reductase subunit D; FeS, ferredoxin iron sulfur protein. The MHCs are denoted in as blue and the number of hemes are indicated as red diamonds. Normalised gene expression is indicated as TPM. More information on the metabolism in ANME archaea can be found in the previous reviews [61, 62]