Fig. 5
The proposed methanogenesis pathway in ISO4-H5 growing with hydrogen and methanol, mono-, di-, tri-methylamine, or methyl-3-methylthiopropionate. Two methyl groups are needed from the methyl donors for every two methane formed. Methyl groups from methanol (MeOH), monomethylamine (MMA), dimethylamine (DMA), trimethylamine (TMA) and methyl-3-methylthiopropionate (M3MTP) are transferred onto methyl-binding corrinoid proteins CH3-MtaC, CH3-MtmC, CH3-MtbC, CH3-MttC and CH3-MtsB by specific corrinoid methyl transferases MtaB, MtmB, MtbB, MttB and MtsA respectively. The methyl groups are then transferred from the corrinoid proteins to CoM by CoM methyltransferase MtaA, MtmA, and bifunctional MtsA. Methyl-CoM is reduced to methane by the methyl coenzyme M reductase Mrt complex with cofactor HS-CoB. Heterodisulfide reductase complex Hdr and hydrogenase complex Mvh couple electron bifurcation to cofactor regeneration, and are coupled to the Fpo-like complex to generate a membrane potential for ATP production. The H+ (or Na+) ratio to ATP is not known, and the reconstruction of the pathway is based on the schemes proposed by Lang et al. [28]. The presence or absence of each gene or the complete pathway for coenzyme M synthesis, in members of Methanomassiliicoccales is highlighted by colored circles; a white circle indicates absence in a genome. The fpoF and fpoO genes that are not found in members of Methanomassiliicoccales but exist in M. barkeri are represented by dotted red circles in the Fpo-like complex