FIG 4.

Metabolic model of alkane disproportionation proposed for Methanoliparia_GoM. Genes for all the proposed steps were found in the MAGs. Background colors indicate alkane activation and conversion to a CoA-bound fatty acid (red), fatty acid degradation and the ACDS complex (blue), methanogenesis (yellow), and electron cycling (green). The alkanes are activated by forming alkyl-CoM as the primary intermediate by the divergent (div.) MCR. Then, free alcohols form and are sequentially oxidized to fatty acids, which are ligated to CoA and oxidized into acetyl-CoA. This molecule is split into CO₂ and H₄MPT-bound methyl groups. Methyl-H₄MPT is reduced to methane with the canonical (can.) MCR. The surplus reducing equivalents released during this alkane disproportionation are used for additional methane formation through CO₂ reduction. Additional energy-conserving steps are possible via the regeneration of CoM-S-S-CoB and the transfer of electrons from ferredoxin to NADH. A hydrogenase may be present to balance additional electron gradients.