Photosynthetic and hybrid photosynthetic schemes. (A) Conventional photosynthetic microbes. (B) Biotic fixation of carbon with H2-oxidizing microbes that use a hydrogenase enzyme to oxidize H2 to provide a source of intracellular reducing equivalents for carbon fixation and fuel synthesis. (C) Biotic fixation of carbon with EET capable electroactive microbes that are able to absorb electricity directly into carbon fixing metabolism. (D) Abiotic fixation of carbon with H2-oxidizing microbes that use a hydrogenase enzyme to oxidize H2 to provide a source of intracellular reducing equivalents for carbon fixation and fuel synthesis. (E) Abiotic fixation of carbon with EET capable electroactive microbes that are able to absorb electricity directly into carbon fixing metabolism. (F) Model of electron uptake by H2 oxidizing  microbes. (G) Model of electron uptake by EET microbes. A denotes MtrA, B denotes MtrB, C denotes MtrC,  D denotes OmcA and Q denotes CymA.