1,9-PROPANEDIOL FORMATION WITH PRODUCT-TOLERANT MUTANTS OF CLOSTRIDIUM-BUTYRICUM DSM-5431 IN CONTINUOUS-CULTURE - PRODUCTIVITY, CARBON AND ELECTRON FLOW

Glycerol fermentation and product formation of two product-tolerant mu tants of Clostridium butyricum DSM 5431 were investigated in continuou s culture at increasing glycerol feed concentrations. Under conditions of glycerol excess (above 55 g l(-1) at D = 0.15 h(-1)), the mutants maintained a constant level of glycerol consumption and product format ion, whereas the parent strain exhibited a substantial decrease in sub strate conversion, 1,3-propanediol and butyrate formation, and an incr ease in acetate formation. The activities of the glycerol dehydrogenas e, the glycerol dehydratase and the 1,3-propanediol dehydrogenase show ed only slight changes with glycerol concentrations in the mutants, bu t dropped markedly at high concentrations in the wild type. Intracellu lar concentrations of NADH, NAD(+) and acetyl-CoA remained at a relati vely constant level in the mutants, but increased sharply with the wil d type strain. The NADH content was always higher than the NAD(+) cont ent in the mutants as well as in the wild type.