Synthesis of oligo- and polysaccharides by Lactobacillus reuteri 121 reuteransucrase at high concentrations of sucrose

GTFA, a glucansucrase enzyme of the probiotic bacterium Lactobacillus reuteri 121, is capable of synthesizing an α-glucan polysaccharide with (1→4) and (1→6) linkages from sucrose. With respect to its biosynthesis, the present study has shown that the ratio of oligosaccharide versus polysaccharide synthesized was directly proportional to the concentration of sucrose. It appears that the size distribution of products is kinetically controlled, but the linkage distribution in the polysaccharide material is not changed. At high sucrose concentrations the sucrose isomers leucrose and trehalulose were synthesized, using the accumulated fructose as acceptor, together with 4′- and 6′-α-d-glucosyl-leucrose and 6′-α-d-glucosyl-trehalulose. The finding of an additional branched hexasaccharide demonstrates that the enzyme is able to introduce branch-points already in relatively short oligosaccharides.