Effect of glucose on glycerol bioconversion by Lactobacillus reuteri

The impact of glucose on glycerol metabolism, especially on 3-hydroxypropionaldehyde (3-HPA) accumulation by resting cells of Lactobacillus reuteri has been investigated. Two systems were used in the study: MRS(-) (modified MRS - omitting glucose, acetate and Tween 80) and distilled water (H(2)O). In MRS(-), addition of glucose enhanced glycerol metabolism in resting cells of L. reuteri, consequently increasing the accumulation of 3-HPA by regulating the NAD/NADH ratio. Enhanced glycerol metabolism correlated positively with the concentration of glucose. NADH produced during glucose metabolism was preferentially reoxidized to NAD by the reduction of 3-HPA to 1,3-propanediol; an adequate supply of glycerol therefore outweighed the repression of glucose on the accumulation of 3-HPA. At a molar ratio of glucose to glycerol no greater than 0.33, accumulation of 3-HPA was favored. In non-growing medium (H(2)O), addition of glucose seemed to be counter-productive with respect to 3-HPA accumulation. Lactate had a positive impact on glycerol metabolism, presumably by altering the redox flux, resulting in enhanced 3-HPA accumulation in both MRS(-) and H(2)O systems.