REGULATION OF CARBON AND ELECTRON FLOW IN CLOSTRIDIUM-ACETOBUTYLICUM GROWN IN CHEMOSTAT CULTURE AT NEUTRAL PH ON MIXTURES OF GLUCOSE AND GLYCEROL

The metabolism of Clostridium acetobutylicum was manipulated, at neutr al pH and in chemostat culture, by changing the overall degree of redu ction of the substrate, using mixtures of glucose and glycerol. Cultur es grown on glucose alone produced only acids, and the intracellular e nzymatic pattern indicated the absence of butyraldehyde dehydrogenase activity and very low levels of coenzyme A-transferase, butanol, and e thanol dehydrogenase activities. In contrast, cultures grow?l on mixtu res of glucose and glycerol produced mainly alcohols and low levels of hydrogen. The low production of hydrogen was not associated with a ch ange in the hydrogenase level but was correlated with the induction of a ferredoxin-NAD reductase and a decreased level of NADH-ferredoxin r eductase. The production of alcohols was related to the induction of a NAD-dependent butyraldehyde dehydrogenase and to higher expression of NAD-dependent ethanol and butanol dehydrogenases. The coenzyme A-tran sferase was poorly expressed, and thus no acetone was produced. These changes in the enzymatic pattern, obtained with cultures grown on a mi xture of glucose and glycerol, were associated with a 7-fold increase of the intracellular level of NADH and a 2.5-fold increase of the leve l of ATP.