Rathin Datta

Evidence for Production of n-Butanol from Carbon Monoxide by Butyribacterium methylotrophicum

Abstract Biological conversion of synthesis gas, primarily a mixture of carbon monoxide (CO) and hydrogen gases, is a potential alternative to chemical processing for production of fuels and chemicals. In addition to acetate and butyrate as metabolic end products, Butyribacterium methylotrophicum has now exhibited n-butanol production directly from CO gas. A butanol concentration as high as 2.7 g/l has been achieved using the CO strain of this organism. These findings suggest the existence of a unique metabolic pathway for butanol production from CO in this strain.

Butyrate production from carbon monoxide byButyribacterium methylotrophicum

Carbon monoxide is produced in high concentrations by gasification of coal or biomass, and is a potentially inexpensive feedstock for biological processes. A number of anaerobic microorganisms metabolize carbon monoxide, with acetate, hydrogen, or methane being the primary reduced products. The CO strain ofButyribacterium methylotrophicum was previously shown to grow on carbon monoxide as the sole carbon and energy source, with acetate being the primary product. This paper demonstrates that by modifying culture conditions, the carbon and electron flow ofB. methylotrophicum can be manipulated to yield butyrate as the major product. A butyrate concentration of 6 g/L was obtained in batch culture with continuous addition of 100% carbon monoxide. The significance of this fermentation for fuels and chemicals production from carbon monoxide is discussed.

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.