Summary: Continuous cultures of CNCM 1210 were performed under regulated pH conditions (pH 7.0) with glycerol or glucose (20 gl) as carbon source. Cultures grown on glucose produced mainly acetate, ethanol and formate. In contrast, 1,3-propanediol (PPD) was the main product with glycerol. The carbon flow distribution at branching metabolic points was investigated. Higher PPD yields with increased dilution rate were correlated with an important increase in the relative ratio of glycerol dehydratase to glycerol dehydrogenase. Determination of intracellular triose-phosphate and fructose 1,6-biphosphate concentrations demonstrated that glyceraldehyde-3-phosphate dehydrogenase is the limiting step in glycerol dissimilation. At the pyruvate branching 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 combined with the enhanced lactate dehydrogenase activity at high growth rates, was correlated with a decrease in the pyruvate formate-lyase activity. A regulation of this latter enzyme by the accumulation of triose-phosphate is suspected.


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