Energy conservation mechanisms in C. ljungdahlii. (A) Shown is the Wood-Ljungdahl pathway with an emphasis on the electron bifurcation in the Wood-Ljungdahl pathway at the methylene-tetrahydrofolate deydrogenase small subunit to generate reduced ferredoxin. The detailed Wood-Ljungdahl pathway is shown in Figure 4. Reaction abbreviations are the same as those in Figure 4. (B) Energy conservation through proton gradient established at the Rnf complex. (C) Identification of a gene encoding the electron bifurcating transhydrogenase for the generation of NADPH during autotrophic growth (Nfn complex). (D) Electron bifurcating hydrogenase for the reduction of ferredoxin from hydrogen during autotrophic growth. Yellow nodes indicate the oxidized form of reducing equivalents and blue nodes indicate the reduced form.