Pyruvate effects on the metabolism of Clostridium acetobutylicum during glucose fermentation were studied. After addition to the culture medium, the pyruvate was rapidly used, provoking several changes in the metabolic pattern of the bacteria. When pyruvate addition occurred early in the fermentation, the glucose utilization decreased and the solventogenic phase was not induced. When pyruvate was added during solventogenesis, glucose consumption was slightly affected and the cells fermented both substrates simultaneously: however, the acidogenic phase started again to the detriment of solvent formation. Usually, during the solvent phase, the cells remetabolized acetic and butyric acids into solvents, but when pyruvate was added, the utilization of acids was stopped and the specific rates of acetate and butyrate formation increased immediately. The acidogenic growth phase was characterized by high levels of acetate and butyrate kinase which dropped during the solvent phase. Addition of pyruvate limited the down shift of these two enzymes and the levels of the activities remained constant during the course of the fermentation. Conversely, the acetoacetate decarboxylase, which is characteristic of the solvent phase, decreased sharply in the presence of pyruvate. The fact that the specific rate of glucose consumption was not decreased by the pyruvate metabolism, a cosubstrate, proves that the phosphoroclastic reaction is not a limiting step. Furthermore, the pyruvate utilization represented a promising approach to obtain useful data on the intracellular compounds implicated in the mechanism for switching from the acidogenic to the solventogenic phase.

Clostridium↗

PubMedDate not supplied

[Selection of mutants of Clostridium acetobutylicum defective in production of acetone].

The butyrate analogue 2-bromobutyrate is toxic toward Clostridium acetobutylicum. After mutation using nitrosoguanidine, mutants resistant to the suicide co-substrate 2-bromobutyrate were selected. Such mutants no longer produced acetone, whereas the synthesis of butanol and ethanol was unaffected. Enzymatic analysis of a 2-bromobutyrate-resistant mutant showed a low level of coenzyme A transferase and of acetoacetate decarboxylase, the two enzymes implicated in the biosynthesis of acetone, whereas the level of hydrogenase was unaffected.

Acetone↗

PubMedDate not supplied

Regulation of coenzyme A transferase and acetoacetate decarboxylase activities in Clostridium acetobutylicum.

The activity of two enzymes involved in acetone production in Clostridium acetobutylicum, acetoacetate decarboxylase and coenzyme A transferase, was studied under acidogenic or solventogenic conditions. Acetoacetate decarboxylase activity was low under acidogenic conditions and after pyruvate addition. Under the same conditions, coenzyme A transferase activity was high. A mutant which lacked acetoacetate decarboxylase activity but was positive for coenzyme A transferase activity was isolated.

Acetone↗