4-16: Effect of pH and temperature on the fermentative production of butanol from glycerol by C. pasteurianum DSM 525

Butanol fermentation was conducted at various pHs and temperatures using C. pasteurianum DSM 525 with a synthetic medium containing glycerol as a sole source of carbon and energy. As the pH of the cultures decreased from 6.5 to 5.0, cell growth rate, the final butanol concentration and butanol yield increased, but glycerol consumption decreased (i.e., with the initial glycerol concentration of 40 g/L, only 29 and 32 g/L of glycerol was consumed at the pHs of 5.0 and 5.5, respectively, while more than 38 g/L of glycerol was consumed at the pHs of 6.0 and 6.5). It seems that the butanol inhibition is more significant at lower pHs. The growth rate and butanol yield increased as the temperature of cultures increased from 25, to 30, and to 37 ^oC. However, more glycerol was consumed and more butanol was produced at lower temperatures at the end of fermentation when fed-batch fermentation was conducted (19, 17, and 13 g/L of butanol were finally produced at the temperatures of 25, 30, and 37 ^oC, respectively). This indicates that butanol inhibition was reduced at lower temperatures.