Electrochemical regulation of the end-product profile in Propionibacterium freudenreichii ET-3 with an endogenous mediator.

The end-product profile of the glucose fermentation by Propionibacterium freudenreichii ET-3 changed on an electrochemical treatment, in which the culture vessel was filled with a carbon felt anode. Acetate and propionate were produced as final end products in a molar ratio of 2:3 without any electrochemical treatments at the point of the consumption of lactate as an intermediate of the glucose fermentation. The ratio was changed to 1:1 at the point of the lactate consumption by the electrochemical incubation at an electrode potential of 0.4 V versus Ag|AgCl for 100 h. During further electrochemical incubation, propionate was oxidized to acetate as a final end-product in the microbe-containing anode chamber. 1,4-Dihydroxy-2-naphthoic acid produced by P. freudenreichii ET-3 itself would receive electrons from the metabolic pathway and serve as an electron transfer mediator from the microbial cells to the electrode.