Biochemistry and physiology of Clostridium acetobutylicum relative to its fermentation shift and to culture degeneration

Experiments were conducted in physiological parameters associated with the fermentation shift in C. acetobutylicum using a wild-type strain, ATCC 824, and several strains defective in solvent production (a butanol tolerant, low butanol producing derivative, SA-2; a butanol dehydrogenase minus derivative, AA-115; a degenerative derivative, DG; and C. butyricum ATCC 19398).C. acetobutylicum ATCC 824 was grown in defined media with several different buffering capacities. While the concentration of the butyrate ion at the initiation of solventogenesis could vary, the concentration of protonated butyric acid remained relatively constant, indicating protonated butyric acid plays a role in the initiation of solventogenesis.Strains SA-2 and DG show similar activity to the parent strain in the terminal enzymes in the butanol pathway, attain comparable levels of reducing equivalents during acidogenesis and take up butyrate in a similar manner. C. acetobutylicum AA-115 is similar in all these respects except that it lacks butanol hydrogenase activity. C. acetobutylicum DG accumulates relatively high levels of lactate, indicating a blockage in the carbon flow. The flow of electrons through the metabolic pathway in the strains defective in solvent production is different from the wild type. C. acetobutylicum DG produces higher amounts of hydrogen gas, produces hydrogen later into the growth cycle and maintains hydrogenase activity later into the fermentation than does C. acetobutylicum ATCC 824. C. acetobutylicum strains SA-2 and AA-115 also show higher peak hydrogen production. C. butyricum displays higher hydrogen gas production than C. acetobutylicum ATCC 824. It is suggested that the increased hydrogen production and hydrogen activity are compensation for the loss of the production of butanol as a hydrogen sink.A high concentration of butyrate present in the medium leads to butanol and acetone production in C. acetobutylicum DG at levels comparable to the parent strain. It is suggested that the degeneration process in C. acetobutylicum leads to the loss of acyl-CoA transferase activity, the butanol synthesis pathway is no longer present to act as an electron sink, and the cell compensates by increased hydrogen and lactate production. It is also suggested that the fermentation shift is dependent on the regulatory event that governs the activity of acyl-CoA transferase. (Abstract shortened with permission of author.)U of I OnlyETDs are only available to UIUC Users without author permissio