B. methylotrophicum has the ability to convert syngas into acetic acid, butyric acid, and buta­nol. Shen et al. (1999) compared the physiological differences between the wild-type and the CO-adapted strains of B. methylotrophicum, and the production of both butyrate and butanol from CO. The authors found that the activity of the wild-type B. methylotrophicum was completely inhibited by the presence of CO. The study further reported that the CO-adapted strain produced significant amount of butyrate, while the wild-type produced only trace amounts of butyrate. The CO-adapted strain produced 0.33 g/L of butanol and 0.5 g/L etha­nol at pH 6.0 from the microbes grown at 100% CO.

In a different study, Worden et al. (1989) studied the possibilities of ethanol and butanol production via syngas fermentation. The authors found an increase electron flow of 6-70% from CO into butyrate when the pH was lowered from 6.8 to 6.0. The high level of butyrate essentially increased the butanol yield in a two-stage fermentation process (Worden et al.,

1991) . During the two-stage process including acidogenic and solventogenic bioconversions, Worden et al. (1991) used two different biocatalysts, B. methylotrophicum and Clostridium acetobutylicum, in a two-stage process. The authors reported high butyrate (4 g/L) and acetate (8 g/L) concentrations while the biomass recirculation was maintained. The authors further reported a butanol concentration of 2.7 g/L from the continuous operation. Eqs (6) and (7) show the change in Gibbs free energy (AG°) for the reactions of CO bioconversion to butyric acid (C3H7COOH) and butanol (C4H9OH) (Worden et al., 1991).

10CO + 4H2O! C3H7COOH + 6CO2 AG° = -40.61kJ/gmole CO (6)

12CO + 5H2O! C4H9OH + 8CO2 AG° = —37.68kJ/gmole CO (7)