Detailed insights into the oligo- and polymeric products formed by three recombinant dextransucrases

The water-soluble exopolysaccharide dextran can be produced from sucrose by various dextransucrases derived from lactic acid bacteria. Many of these enzymes and their corresponding dextrans have been described, but the initially formed products and the compounds which are elongated to dextrans have not been characterized in detail yet. Therefore, we studied the oligo- and polymeric products formed by recombinant dextransucrases from Ligilactobacillus animalis TMW 1.971 (LaniDSΔN), Limosilactobacillus reuteri TMW 1.106 (LreuDSΔN), and Steptococcus salivarius DSM 20560 (SSAL4550) from 0.25 M and 1.5 M sucrose solutions (with and without 1 M glucose) in detail. After incubation of the sucrose solutions, the enzymes mainly elongated sucrose with 1,6-linked glucose units. Erlose and leucrose were identified as additional low molecular weight compounds in the sucrose solutions, whereas glucose addition led to the predominant abundance of isomalto-oligosaccharides and kojibiose. HPSEC analysis demonstrated that glucose addition also influenced the molecular weight of the dextrans produced by LaniDSΔN and SSAL4550. To evaluate which products were used as an acceptor molecule for polysaccharide formation, the products obtained from endo-dextranase hydrolysis of borohydride reduced dextrans were isolated, characterized, and quantified. The quantification of glucitol-containing and theanderose-containing low molecular weight products demonstrated that sucrose and glucose are used as acceptors for dextran formation, whereas erlose or kojibiose are not elongated. At high glucose concentrations, glucose is mostly found at the non-reducing end of the dextran chain. Altogether, our findings provide detailed insights into the course of dextran formation by different dextransucrases.