Fig. 7. Schematic view of the proposed interaction between the bacterial endosymbionts and P. schiedti.
The eukaryote uses a complex array of GHs to digest starch, cellulose and glycogen generating monosaccharides. The eukaryote ferments these sugars to acetate (Ac) H2 and formate (For). Sugars are also used by Ca. Vesiculincola pelomyxae that ferments them to acetate (Ac) and H2. Ca. Syntrophus pelomyxae uses isovalerate, butyrate and succinate (Succ) to fuel its metabolism. Isovalerate and butyrate is most probably taken from the environment, while succinate is obtained from the host. The host with the two bacteria generates a H2, acetate and formate pool that is used by the methanogen for methanogenesis and biosynthesis, keeping the overall concentration of the fermentation products low to facilitate the metabolic flux in the other community members. The question marks indicate the uncertainty of how the formate gets imported by the methanogen, or if is produced using the formate hydrogenlyase and FdhA. AA amino acids, CH3-S-CoM methyl coenzyme M, F420H2 reduced coenzyme F420, Fdred reduced ferredoxin.