ANAEROBIC PATHWAYS OF GLYCEROL DISSIMILATION BY ENTEROBACTER-AGGLOMERANS CNCM-1210 - LIMITATIONS AND REGULATIONS

Continuous cultures of Enterobacter agglomerans CNCM 1210 were perform ed under regulated pH conditions (pH 7.0) with glycerol or glucose (20 g l(-1)) as carbon source. Cultures grown on glucose produced mainly acetate, ethanol and formate. In contrast, 1-3-propanediol (PPD) was t he main product with glycerol. The carbon flow distribution at branchi ng metabolic points was investigated. Higher PPD yields with increased dilution rate were correlated with an important increase in the relat ive ration of glycerol dehydratase to glycerol dehydrogenase. Determin ation of intracellular triose-phosphate and fructose 1,6-biphosphate c oncentrations demonstrated that glyceraldehyde-3-phosphate dehydrogena se is the limiting step in glycerol dissimilation. At the pyruvate bra nching point, pyruvate dehydrogenase (PDH) activity was systematically detected. The pyruvate flow shifted to PDH is suspected to represent up to 22% of the acetyl-CoA formed. In addition, this enzyme pattern c ombined with the enhanced in vivo lactate dehydrogenase activity at hi gh growth rates, was correlated with a decrease in the pyruvate format e-lyase activity. A regulation of this latter enzyme by the accumulati on of triose-phosphate is suspected.