PHYSIOLOGICAL-MECHANISMS INVOLVED IN ACCUMULATION OF 3-HYDROXYPROPIONALDEHYDE DURING FERMENTATION OF GLYCEROL BY ENTEROBACTER-AGGLOMERANS

When grown in 700 mM glycerol within the pH range 6.0 to 7.5, anaerobi c pH-regulated cultures of Enterobacter agglomerans exhibited an extra cellular accumulation of 3-hydroxypropionaldehyde (3-HPA), This phenom enon, which causes fermentation cessation, occurred earlier when pH wa s low, In contrast, substrate consumption was complete at pH 8, Levels of glycerol-catabolizing enzymes, i,e,, glycerol dehydrogenase and di hydroxyacetone kinase for the oxidative route and glycerol dehydratase and 1,3-propanediol dehydrogenase for the reductive route, as well as the nucleotide pools were determined periodically in the pH 7- and pH 8-regulated cultures, A NAD/NADH ratio of 1.7 was correlated with the beginning of the production of the inhibitory metabolite, Further acc umulation was dependent on the ratio of glycerol dehydratase activity to 1,3-propanediol dehydrogenase activity, For a ratio higher than 1,3 -HPA was produced until fermentation ceased, which occurred for the pH 7-regulated culture, At pH 8, a value below 1 was noticed and 3-HPA a ccumulation was transient, while the NAD/NADH ratio decreased, The low rate of glycerol dissimilation following the appearance of 3-HPA in t he culture medium was attributed to the strong inhibitory effect exert ed by 3-HPA on glycerol dehydrogenase activity.