Formation of ethanol from carbon monoxide via a new microbial catalyst

A recently discovered clostridial bacteria converts components of synthesis gas (CO, CO2, H2) into liquid products such as ethanol, butanol and acetic acid. Isolated from an agricultural lagoon, the stability and productivity characteristics of the bacteria were studied in a continuous 4.5 l bubble column bioreactor at 37°C using artificial blends of CO, CO2, and N2. Preliminary results on the rates of cell growth, substrate utilization, product formation, and yields of products and cells from CO are discussed. At steady state, apparent yields (mole C in products per mole CO consumed) of ethanol, butanol, and acetic acid were 0.15, 0.075 and 0.025, respectively, and the cell yield was 0.25 g/mol CO. The theoretical yield of ethanol is 0.33 if CO is only utilized for the production of ethanol. The experimental yield of CO2 from CO was approximately 60% compared to the theoretical yield of 67% with ethanol as the sole product. As a comparison with another ethanol-producing bacteria, the results of a similar fermentation study using batch-grown Clostridium ljungdahlii showed yields of 0.062 for ethanol and 0.094 for acetic acid and a cell yield of 1.378 g/mol.