METABOLIC FLEXIBILITY OF CLOSTRIDIUM-ACETOBUTYLICUM IN RESPONSE TO METHYL VIOLOGEN ADDITION

Batch cultures of Clostridium acetobutylicum, were examined with 0, 0. 1 and 1 mM methyl viologen addition at four different controlled pH va lues (between 4.5 and 6.5). Methyl viologen addition diverted the elec tron flow: reducing equivalents normally released as molecular hydroge n were directed towards NAD(P)H formation. Production of butanol, the most reduced non-gaseous product, was sharply increased (0.65 mol/mol glucose) at the expense of acetone and butyric and acetic acids. In ad dition to butanol and lactate production, NADH excess induced the form ation of glycerol, a product that has never been reported to be formed by C. acetobutylicum. Metabolic perturbation brought about by the ele ctron carrier led to a reduction of the growth rate and an increase of the lag phase. A correlation between the shape of the redox potential curve and the switch from an acidogenic to a solventogenic metabolism is reported.