In order to improve the yield of 1,3-propanediol (1,3-PPD) in Clostridium butyricum E5, we carried out cofermentation experiments on glucose/glycerol mixtures in chemostat culture. The results showed the influence of the ratio of the two carbon substrates on the production of the required diol. The progressive increase of glucose in culture medium containing a given concentration of glycerol made it possible to highlight the deviation of carbon flow from the oxidative towards the reducing pathway, in order to maintain the oxidation/reduction balance in the cell. The conversion of glycerol into 1,3-PPD thus increased from 0.63 mol mol(-1), without the addition of glucose, to a maximum of 0.89 mol mol(-1) for a molar glucose/glycerol ratio of 0.2 for the wild-type strain. The same experiments carried out with the mutant MD strain, which is resistant to allyl alcohol, led to similar results but with a maximum of 0.84 mol mol(-1) for a glucose/glycerol molar ratio of 0.1. Beyond a molar ratio of 0.2, the biosynthesis of enzymes for the glycerol metabolism was less subject to catabolic repression by glucose in the mutant MD strain than in the wild-type strain.