Figure 1.

Pathways for native and engineered ethanol production in Pyrococcus furiosus.

Glycolysis to pyruvate (0.5 glucose) yields no ATP and produces 2 Fd_red (net 2 e⁻). Ethanol production from: (A) pyruvate via the pyruvate decarboxylase activity of pyruvate ferredoxin oxidoreductase (POR) and an alcohol dehydrogenase (ADH) results in no net ATP, produces 2 Fd_red and uses 1 NAD(P)H (net 2 e⁻); (B) acetyl‐CoA via AdhE yields no net ATP, produces 4 Fd_red and uses 2 NADH (net 0 e⁻); (C) acetate via aldehyde ferredoxin oxidoreductase (AOR, here also representing other oxidoreductases with aldehyde oxidizing activity), and AdhA results in 1 net ATP via acetyl‐CoA synthase (ACS), produces 2 Fd_red and uses 1 NADPH (net 0 e⁻). P. furiosus enzymes are shown in orange, AdhA is shown in red, and AdhE is shown in blue. Proposed physiological reactions are indicated with solid arrows, and engineered pathways in recombinant strains are indicated with dashed arrows.