SCHEME 2.

Energy diagram for PMF-dependent electrolithoautotrophic carbon fixation in A. ferrooxidans. A. ferrooxidans cell extracts electrons directly from solid electron sources such as conductive minerals and electrodes at a potential of +0.82 V vs. SHE. Electrons are used for O₂ reduction via a down-hill pathway, which in turn generates PMF that is used to elevate the energy of electrons to reduce NAD⁺ to NADH, therefore triggering Calvin cycle. From the energy difference between the input electron and the midpoint potential of NAD+/NADH redox at cytoplasmic pH, it is estimated that A. ferrooxidans elevates the energy of electrons using PMF by 1.14 eV.