Structures of the biological repeating units in the O-chain polysaccharides of Hafnia alvei strains having a typical lipopolysaccharide outer core region

Earlier, the structures of the O-chain polysaccharides of the lipopolysaccharides (LPS) of a number of Hafitia alvei strains have been established. However, it remained unknown, which is the first and the last monosaccharide of the O-chain. This is defined by the structure of the so-called biological repeating unit (O-unit), which is pre-assembled and then polymerised in the course of biosynthesis of bacterial polysaccharides by the Wzy-dependent pathway. Now we report on the structures of the O-units in 10 H. alvei strains. The LPS were cleaved by mild acid hydrolysis and oligosaccharide fractions IIIa and IIIb were isolated by gel chromatography subsequently on Sephadex G-50 and BioGel P-2 and studied by methylation analysis and NMR spectroscopy. Fraction IIIb was found to represent the core oligosaccharide containing a terminal upstream alpha-D-Glc-(1 -> 3)-alpha-D-Glc or alpha-D-Gal-(1 -> 3)-a-D-Glc disaccharide in the outer region that is typical of H. alvei. Fraction IIIa consists of the LPS core with one O-unit linked by a 3-substituted beta-D-GalNAc residue (in strains PCM 1189 and PCM 1546) or a 3-substituted beta-D-GleNAc residue (in the other strains studied). In most strains examined the beta-configuration of the D-GlcNAc linkage in the first O-unit attached to the core is the same and in some strains is opposite to that found in the interior O-units of the O-chain polysaccharide. Various monosaccharides, including D-Glc, D-Gal, D-GlcA and acyl derivatives of 3-amino-3,6-dideoxy-D-glucose or 4-amino-4,6-dideoxy-D-glucose, occupy the non-reducing end of the O-unit. (c) 2005 Federation of European Microbiological Societies. Published by Elsevier B.V. All rights reserved.