Influence of the carbohydrate source on β-glucan production and enzyme activities involved in sugar metabolism in Pediococcus parvulus 2.6

The influence of carbohydrate source on growth, exopolysaccharide (EPS) production and on the activity of the enzymes implicated in energy generation and UDP-glucose synthesis in Pediococcus parvulus 2.6 was evaluated. The highest EPS production was obtained on glucose, while fructose was a poor substrate for EPS synthesis. HPLC and NMR analysis on monomer composition and structure of the EPS showed that this strain produced the same β-glucan, regardless of the carbohydrate source. The α-phosphoglucomutase specific activities were dependent on the carbohydrate source and a high correlation between the activity of this enzyme and the amount of EPS was found in glucose- and maltose-grown cultures. α-UDP-glucose pyrophosphorylase activity, necessary for the activation of glucose, was very low, but significantly higher on glucose as sugar source. In vitro phosphorylation assays and transport activities showed that glucose is taken up by a proton motive force-dependent permease, while fructose is internalized by an inducible phosphotransferase system, which renders fructose-6-phosphate. The levels of 6-phosphofructokinase activity and α-phosphoglucomutase activities determined on fructose were higher and lower, than those found on glucose or maltose, respectively. This suggests that fructose-6-phosphate is mainly diverted to glycolysis and explains the low EPS synthesis on fructose. Results indicate that α-phosphoglucomutase and/or α-UDP-glucose pyrophosphorylase might be the bottlenecks for EPS biosynthesis, opening the field for metabolic-engineering strategies aimed to improve EPS production.