Carbon monoxide metabolism of the methylotrophic acidogen Butyribacterium methylotrophicum

The Marburg strain of Butyribacterium methylotrophicum did not grow on CO alone but did consume CO during growth on a variety of substrates in the presence of a 100% CO gas phase. We selected a strain (the CO strain) that grew vigorously on CO alone. The ability of the CO strain to grow on CO was stable through multiple transfers in the absence of CO. CO dehydrogenase activity was lower in the CO strain grown on CO (13.3 micromol/min per mg of protein) than in the Marburg strain grown on methanol-acetate (47.2 mumol/min per mg of protein); thus, the levels of this enzyme did not explain the growth on CO. CO was dissimilated to acetate and CO2 with the following stoichiometry: 4 CO leads to 2.17 CO2 + 0.74 acetate. We observed a growth rate of 0.05 h-1, a final optical density at 660 nm of 0.8, and a cell yield of 3.0 g of cells per mol of CO during growth of the CO strain. Growing cultures of the CO strain displayed a Ks for CO of 28 to 56 microM. The apparent thermodynamic efficiency of cell synthesis from CO was 57%. Energetic and biochemical aspects of CO metabolism are described.