SCHEME 1.

Bifurcated electron and proton transfer model of Fe(II) oxidation in Acidithiobacillus ferrooxidans (Sugio et al., 1981; Ingledew, 1982; Elbehti et al., 1999, 2000; Brasseur et al., 2004; Valdés et al., 2008; Quatrini et al., 2009; Bird et al., 2011). A small periplasmic blue copper protein (rusticyanin, Rus) has been proposed as a branch point to switch an electron flow between NAD⁺ and O₂. Proton circuit for a down-hill and an up-hill electron-transfer reaction is indicated by blue and red dotted line, respectively. Electron and energy delivery to the cells for carbon fixation is based on the diffusion and/or convection of soluble Fe²⁺ ions.