Structure of the high-molecular weight exopolysaccharide isolated from Lactobacillus pentosus LPS26.

The strain Lactobacillus pentosus LPS26 produces a capsular polymer composed of a high- (2.0x10(6)Da) (EPS A) and a low-molecular mass (2.4x10(4)Da) (EPS B) polysaccharide when grown on semi-defined medium containing glucose as the carbon source. The structure of EPS A and its deacetylated form has been determined by monosaccharide and methylation analysis as well as by 1D/2D NMR studies ((1)H and (13)C). We conclude that EPS A is a charged heteropolymer, with a composition of D-glucose, D-glucuronic acid and L-rhamnose in a molar ratio 1:2:2. The repeating unit is a pentasaccharide with two O-acetyl groups at O-4 of the 3-substituted alpha-D-glucuronic acid and at O-2 of the 3-substituted beta-L-rhamnose, respectively. -->4)-alpha-D-Glcp-(1-->3)-alpha-D-GlcpA4Ac-(1-->3)-alpha-L-Rhap-(1-->4)-alpha-D-GlcpA-(1-->3)-beta-L-Rhap2Ac-(1--> This unbranched structure is not common in EPSs produced by Lactobacilli. Moreover, the presence of acetyl groups in the structure is an unusual feature which has only been reported in L. sake 0-1 [Robijn et al. Carbohydr. Res., 1995, 276, 117-136].