CARBON AND ELECTRON FLOW IN CLOSTRIDIUM-BUTYRICUM GROWN IN CHEMOSTAT CULTURE ON GLUCOSE-GLYCEROL MIXTURES

The metabolism of C. butyricum was manipulated, at neutral pH and in c arbon limited chemostat cultures by changing the overall degree of red uction of the substrate, using mixtures of glucose and glycerol. Cultu res grown on glucose alone produced only acids (acetate, butyrate and lactate). When the glycerol (in C moles)/glucose+glycerol (in C moles) ratio was progressively changed from 0 to 1 a corresponding increase of 1,3-propanediol production occured and an immediate and drastic dec rease of the specific rate of acetate production was observed while th e specific rate of butyrate production only decreased slightly. For gl ycerol (in C moles)/glucose+glycerol (in C moles) ratios higher than 0 .5, the q(NAD(P)H from Fd) and the CO2/H-2 molar ratio increased sharp ly, the first becoming positive and the second higher than 1. This ind icates a complete reversion of the electron flow: part of reduced ferr edoxin produced by the phosphoroclastic cleavage of pyruvate to acetyl -CoA was diverted from H-2 formation toward NAD(P) reduction by the fe rredoxin-NAD(P) reductase(s) in order to produce NAD(P)H. This change in the electron flow was associated to an increase in the specific rat e and the yield of 1,3-propanediol production related to glycerol.