Fermentation of glycerol by Clostridium pasteurianum--batch and continuous culture studies

The fermentation of glycerol by Clostridium pasteurianum was studied with respect to product formation as influenced by the culture conditions. In the majority of batch cultures, butanol was the main fermentation product, but a varying fraction of glycerol was also converted to 1,3-propanediol, butyric and acetic acids and ethanol. More than 60 g/l glycerol was utilized, and up to 17 g/l butanol was produced. Fed-batch cultures did not offer an advantage. When molecular nitrogen was used as a nitrogen source, the fermentation time was prolonged by a factor of 1.5. Fermentations at constant pH values between 4.5 and 7.5 did not reveal significant differences in product formation except for an increase in the ethanol content starting at pH 6.5. Chemostat cultures also yielded predominantly n-butanol, but in some fermentations, the 1,3-propanediol fraction was relatively high. The pH auxostat cultures, which were operated at a glycerol excess, contained 1,3-propanediol as the main product. As a whole, the fermentations were characterized by a certain variability in product formation under seemingly equal or slightly varied conditions. It appears that the regulation of the numerous fermentation pathways occurring in this organism is not very strict.