Acetogenic bacteria grow by the oxidation of various substrates coupled to the reduction of carbon dioxide (acetogenesis) or other electron acceptors but the mechanisms of energy conservation are still enigmatic. Here, we report the presence of a rnf gene cluster rnfCDGEAB in Acetobacterium woodii that is speculated to encode a novel, energy-conserving ferredoxin:NAD(+)-oxidoreductase complex composed of at least six different subunits. Transcriptional analysis revealed that the genes constitute an operon. RnfC and RnfG were heterologously produced and antibodies were generated. Western blot analyses demonstrated that these subunits were produced and are associated with the cytoplasmic membrane. The subunits were present in cells respiring with either carbon dioxide or caffeate. A preparation with NADH dehydrogenase activity was obtained from detergent solubilized membranes that contained RnfC and RnfG.