Effect of galactose and glucose on the exopolysaccharide production and the activities of biosynthetic enzymes in Lactobacillus casei CRL 87

Aims: The objective of this work was to study the influence of the sugar so urce on exopolysaccharide (EPS) production and the activities of the enzyme s involved in the synthesis of sugar nucleotides in Lactobacillus casei CRL 87. The relationship between these enzymes and EPS formation was determine d. Methods and Results: The concentration of EPS was estimated by the phenol/s ulphuric acid method while the chemical composition of purified EPS was inv estigated using gas-liquid chromatography, Biosynthetic enzyme activities w ere determined spectrophotometrically by measuring the formation or disappe arance of NAD(P)H at 340 nm, Polysaccharide production by Ld. casei CRL 87 was 1.7 times greater on galactose than on glucose. The isolated polymer wa s composed of rhamnose, glucose and galactose. The activities of uridine-di phosphate (UDP)-glucose-pyrophosphorylase, thymidine-diphosphate (dTFDP)-gl ucose-pyrophosphorylase and the dTDP-rhamnose-synthetic enzyme system were higher in galactose-grown than in glucose-grown cells. When an EPS- mutant strain was used, galactokinase activity was not detected on galactose, this sugar not being available for the formation of sugar nucleotides for furth er EPS production, dTDP-glucose-pyrophosphorylase and dTBP-rhamnose-synthet ic enzyme system activities were lower than the values found for the wild t gpe strain, Conclusions: The carbon source present in the culture medium affects EPS pr oduction by Lb. casei CRL 87. The greater polymer synthesis by galactose-gr own cells is correlated with the higher UDP-glucose-pyrophosphorylase, dTDP -glucose-pyrophosphorylase and dTDP-rhamnose-synthetic enzyme system activi ties. Initial sugar metabolism is also an important step for the synthesis of EPS precursors bq this strain. Significance and Impact of the Study: Knowledge of the effect of the sugar source on EPS production and the activities of biosynthetic enzymes provide s information about the mechanisms of regulation of the synthesis of EPS wh ich can contribute to improving polymer production.