dAcetogenic bacteria can grow by the oxidation of various substrates coupled to the reduction of CO 2 in the Wood-Ljungdahl pathway. Here, we show that growth of the acetogen Acetobacterium woodii on 1,2-propanediol (1,2-PD) as the sole carbon and energy source is independent of acetogenesis. Enzymatic measurements and metabolite analysis revealed that 1,2-PD is dehydrated to propionaldehyde, which is further oxidized to propionyl coenzyme A (propionyl-CoA) with concomitant reduction of NAD. NADH is reoxidized by reducing propionaldehyde to propanol. The potential gene cluster coding for the responsible enzymes includes genes coding for shell proteins of bacterial microcompartments. Electron microscopy revealed the presence of microcompartments as well as storage granules in cells grown on 1,2-PD. Gene clusters coding for the 1,2-PD pathway can be found in other acetogens as well, but the distribution shows no relation to the phylogeny of the organisms.A cetogenic bacteria are a diverse group of anaerobic bacteria able to reduce two molecules of CO 2 to acetate by the WoodLjungdahl pathway (WLP) (1-4). Electrons may derive from molecular hydrogen (autotrophic growth) or from organic donors (heterotrophic growth), such as hexoses, pentoses, formate, lactate, alcohols, and methyl group donors (1). This not only provides the cell with organic material for biomass formation, but the pathway is also coupled to energy conservation for ATP supply (2, 5). The energy-conserving reactions remained an enigma for a long time, but recent discoveries in the model acetogen Acetobacterium woodii provided insights into the energy metabolism of this group of anaerobic bacteria (6, 7). In A. woodii, the reactions for the oxidation of the substrate can in general be regarded as isolated modules separate from the reactions of the WLP for the reoxidation of the electron carriers by the reduction of CO 2 . One has to emphasize that all enzymes of the WLP are soluble and located in the cytoplasm (6). With molecular hydrogen as the electron donor, only one enzyme is necessary for its oxidation, providing the reducing equivalents as reduced ferredoxin (Fd) and NADH in a 1:1 stoichiometry (8). Oxidation of organic substrates, such as hexoses, also yields reduced ferredoxin and NADH that are reoxidized in the WLP. The WLP in A. woodii does not use both electron carriers in equal amounts; therefore, a membranebound Fd:NAD oxidoreductase (presumably the Rnf complex) provides NADH from reduced ferredoxin, thereby translocating sodium ions across the cytoplasmic membrane that are used for subsequent ATP synthesis by a membrane-bound, sodium iondependent ATP synthase (7, 9, 10). The reaction is reversible, and the enzyme can drive Fd reduction at the expense of the electrochemical sodium ion potential.Besides CO 2 , acetogenic bacteria can use different alternative electron acceptors, e.g., nitrate (Moorella thermoacetica [11]) or phenylacrylates (A. woodii [12]). These acceptors have a more positive redox potential than the CO 2 -acetate pair,...