Regulation of carbohydrate utilization in Clostridium pasteurianum

Clostridium pasteurianum is capable of fermentative growth on a number of carbohydrate compounds. Several, including glucose, fructose and sorbitol, are accumulated via a phosphoenolpyruvate-dependent phosphotransferase system (PTS), while the uptake of galactose and gluconate is protonmotive-force-dependent. We have examined the utilization of these substrates by cultures of C. pasteurianum growing on carbohydrate mixtures to determine whether the organism displays preferences for one carbon source over the others; such a preference may indicate the operation of specific mechanisms for regulation of carbohydrate metabolism. In most cases the carbohydrates were co-metabolized. Glucose was utilized together with fructose, gluconate and galactose, although galactose appeared to be favoured over glucose. This preference was not due to repression of synthesis of the glucose PTS. On the other hand, glucose prevented induction of the sorbitol PTS, and led to strong inhibition of sorbitol utilization in uninduced cells. Pre-adaptation of cells to growth on sorbitol counteracted the inhibition by glucose resulting in utilization of glucose and sorbitol at approximately equal rates.