Relationship between glycolysis and exopolysaccharide biosynthesis in Lactococcus lactis

The relationships between glucose metabolism and exopolysaccharide (EPS) pr oduction in a Lactococcus lactis strain containing the EPS gene cluster (Ep s(+)) and in nonproducer strain MG5267 (Eps(-)) were characterized. The con centrations of relevant phosphorylated intermediates in EPS and cell wall b iosynthetic pathways or glycolysis were determined by P-31 nuclear magnetic resonance. The concentrations of two EPS precursors, UDP-glucose and UDP-g alactose, were significantly lower in the Eps(+) strain than in the Eps(-) strain. The precursors of the peptidoglycan pathway, UDP-N-acetylglucosamin e and UDP-N-acetylmuramoylpentapeptide, were the major UDP-sugar derivative s detected in the two strains examined, but the concentration of the latter ,vas greater in the Eps(+) strain, indicating that there is competition bet ween EPS synthesis and cell growth, An intermediate in biosynthesis of hist idine and nucleotides, 5-phospharylribose l-pyrophosphate, accumulated at c oncentrations in the millimolar range, showing that the pentose phosphate p athway was operating. Fructose 1,6-bisphosphate and glucose 6-phosphate wer e the prominent glycolytic intermediates during exponential growth of both strains, whereas in the stationary phase the main metabolites were 3-phosph oglyceric acid, 2-phosphoglyceric acid, and phosphoenolpyruvate. The activi ties of relevant enzymes, such as phosphoglucose isomerase, or-phosphogluco mutase, and UDP-glucose pyrophosphorylase, were identical in the two strain s. C-13 enrichment on the sugar moieties of pure EPS showed that glucose 6- phosphate is the key metabolite at the branch point between glycolysis and EPS biosynthesis and ruled out involvement of the triose phosphate pool. Th is study provided clues for ways to enhance EPS production by genetic manip ulation.