Fig. 3.

Model of syntrophic scFA oxidation coupled to CO₂ reduction in S. aciditrophicus. The model scFA butyrate is oxidized to two acetates coupled to the reduction of two CO₂ to formate. Alternatively, the NADH formed by 3-hydroxybutyryl-CoA DH is regenerated by a soluble hydrogenase, and the H₂ formed diffuses across the membrane without the involvement of a transporter. Protons that contribute to proton motive force (pmf) generation are shown in green; those that diminish pmf are shown in red. Note that transport of protons during uptake and excretion is based on assumptions and has not been studied in this work.