Continuous production of mixed alcohols and acids from carbon monoxide

Continuous, steady-state fermentations using carbon monoxide gas as the sole carbon and energy source have been achieved with the CO strain ofButyribacterium methylotrophicum. Fermentation pH was found to regulate carbon monoxide metabolism over the pH range of 6.8 to 5.0. Cell growth diminished at low pH, with washout occurring at pH 5.0. As observed previously in batch culture, lower pH values favored production of butyrate over acetate. The mechanism responsible for this trend is currently being investigated by quantification of key intracellular enzyme activities. At low pH values, direct, steady-state fermentation of carbon monoxide to alcohols has been verified. Of major significance is the production of butanol from carbon monoxide in pure culture. This newly identified pathway provides a potential mechanism for direct bioconversion of synthesis gas to butanol.