Cell suspensions of Acetobacterium woodii produced CO from H 2 and COe. Depending on the conditions, more than 1,000 ppm CO were measured in the gas phase. This concentration was more than 10-fold higher than the thermodynamic equilibrium concentration that can be calculated to be 83.5 ppm for the experimental conditions used. This finding is taken as evidence that, besides the activation of formate, also CO production from CO2 is an energy-dependent step in the reduction of CO2 to acetate. Studies on the influence of ionophores and dicyclohexylcarbodiimide (DCCD) as well as that of CO and formaldehyde on acetate synthesis were undertaken in order to determine whether ATP or A ~tn + is the driving force for CO2 reduction to CO.
Cells of A. woodii also catalyzed the conversion of CO (5% in the gas phase) to CO2 and Ha. This process was coupled to the generation of metabolic energy, which could be used by the cells to drive the uptake of histidine into the cells; histidine uptake was almost completely inhibited by the ionophores valinomycin plus nigericin. The data were taken to indicate that in this acetogen the energy derived from CO oxidation can be converted to metabolic energy.