Fig. 7: Main methanogenesis pathways in the animal gut.
From: Factors shaping the abundance and diversity of the gut archaeome across the animal kingdom
a Proportion of the total archaeal reads that are assigned to taxa with a predicted hydrogenotrophic CO2-reducing methanogenesis (H2 + CO2; blue) or hydrogenotrophic methyl-reducing methanogenesis (CH3-R + H2; orange) pathway. Methanosarcina spp. can have diverse methanogenesis pathways (i.e., the two above-mentioned pathways and the methyl-dismutation (or methylotrophic) and acetoclastic pathways). b Diagram indicating the methanogenesis pathways with the highest energy yield depending on methanol concentration (C(methanol) in mol/l) and hydrogen partial pressure (p(H2) in bar). The three methanogenesis pathways considered are methyl-compound dismutation (CH3-R dismut.), hydrogenotrophic methyl-reducing methanogenesis (CH3-R + H2) or hydrogenotrophic CO2-reducing methanogenesis (CO2 + H2). Coloured areas on the map indicate which pathway(s) yield(s) the highest amount of energy per mole of methane, i.e., concentrations and pressures for which the associated ∆G expressed in kJ/mol CH4 is the lowest (see “Gibbs free energies of methanogenic pathways” in Materials and Methods). In central areas of the diagram, energy yields of two or three (*in this case none is yielding more energy) of the pathways are comparable with differences in ∆G of less than 10 kJ/mol CH4. This is shown in light red, grey and light blue areas. The dotted line indicates values of C(methanol) and p(H2) for which all three catabolisms have exactly the same ∆G. Ranges of C(methanol) and p(H2) found in the literature for rumen (1), human colon (2) and cockroach hindgut (3), and marine sediments (4–8; Supplementary Table 3) were mapped on the graph: dots correspond to mean values and bars indicate minimal and maximal values.
