Enzymes involved in carbohydrate metabolism and their role onexopolysaccharide production in Streptococcus thermophilus

摘要

The role of the enzymes uridine-5'-diphospho-(UDP) glucose pyrophosphorylase and UDP galactose 4-epimerase in exopolysaccharide production of Gal(-) ropy and non-ropy strains of Streptococcus thermophila in a batch culture was investigated, Growth of the ropy and non-ropy strains was accompanied by total release of the galactose moiety from lactose hydrolysis in modified Bellinker broth with lactose as the only carbon source. This was associated with a greater exopolysaccharide production by the ropy strain. The polymer produced by both strains in cultures with lactose or glucose as cal bon sources contained glucose, galactose and rhamnose, indicating that glucose a as used as a carbon source for bacterial growth and for exopolysaccharide formation. UDP-glucose pyrophosphorylase activity was associated with polysaccharide production during the first 12 h in a 20 h culture in the ropy strain, but not in the non-ropy strain, UDP-galactose 4-epimerase nas not associated with exopolysaccharide synthesis in any strain. The evidence presented suggests that the glucose moiety from lactose hydrolysis is the source of sugar for heteropolysaccharide synthesis, due to a high UBP-glucose pyrophosphorylase activity.