Overview of the flux distributions under various growth conditions. Figure shows the flow of electrons during aerobic (light blue dashed arrows) and photosynthetic (black dashed arrows) growth. During anaerobic growth electrons flow from the photosynthetic reaction center (RC), along the electron transport chain (ETC) and back to the RC via reduced cytcochrome (C2red) in a cyclic photosynthetic system , with protons pumped into the periplasm. NADH dehydrogenase is predicted to function in the reverse direction, reducing NAD to NADH while oxidizing ubiquinol (QH) to ubiquinone (Q). Under these conditions, excess electrons obtained from the oxidation of electron rich carbon sources (CnHmOp) would be dissipated via the alternative electron consuming pathways or via carbon fixation. During aerobic growth either cytochrome oxidase (Cox) or quinol oxidase (Qox) can be used in the oxidation of QH to Q, with the Cox reaction favored as more protons are pumped across the cytoplasmic membrane. Under these conditions, NADH dehydrogenase functions in the forward direction oxidizing NADH to NAD. ATP synthase is omitted from the ETC for simplicity. C2ox - oxidized cytochrome; Fred - reduced ferredoxin; Fox - oxidized ferredoxin.