Ethanol production by a newly isolated anaerobe, Clostridium saccharolyticum: effects of culture medium and growth conditions

Abstract

Clostridium saccharolyticum was shown to ferment glucose, cellobiose, and xylose to CO2, H2, ethanol, acetate, and lactate. The addition of 0.12 M CaCO3 and 1% yeast extract (w/v) to the glucose medium was found to shift the ethanol–acetate mole ratio from 1.36 to 2.6. Although the addition of exogenous H2 (240 kPa) did not affect the growth of C. saccharolyticum, it did alter the pattern of fermentation products. Both H2 and acetate formation decreased, while ethanol production increased. Ethanol production also increased at the expense of H2 and acetate when C. saccharolyticum was incubated without shaking. Stationary incubation under a H2 headspace (standard temperature and pressure) resulted in an ethanol concentration, at 25 °C, of 1.7% (v/v), an efficiency of conversion of 1.8 mol ethanol/mol glucose, and ethanol–acetate ratios of 7.6 at 35 °C and 9.4 at 20 °C. These results indicate that H2 concentration plays a significant role in the regulation of C. saccharolyticum catabolism.