Elucidation of the full O-polysaccharide structure and identification of the core type of the lipopolysaccharide of Providencia alcalifaciens O9

Abstract

Opportunistic human pathogens of the genus Providencia from the family Enterobacteriaceae are serotyped by their O-antigens, which represent the O-polysaccharide chains of the lipopolysaccharides (LPSs) on the cell surface. In this work, the O-polysaccharide of Providencia alcalifaciens O9 was obtained by mild acid degradation of a long-chain S-form LPS. The structure of the hexasaccharide repeat (O-unit) of the O-polysaccharide containing one d-Gal, two d-Glc, and three d-GalNAc residues was established by sugar and methylation analyses along with one- and two-dimensional 1H and 13C NMR spectroscopy. Another degradation product was derived from a short-chain SR-form LPS and found to consist of a core oligosaccharide bearing one O-unit. Its studies by NMR spectroscopy and electrospray ionization mass spectrometry enabled identification of one of the GalNAc residues as the first monosaccharide of the O-unit, whose glycosidic linkage links the O-units to each other and the first O-unit to the core. The core is distinguished by the occurrence of two glycoforms differing in the nature of a lateral monosaccharide, which is either d-Glc or d-GlcNAc. Although composed of common monosaccharides, the O-polysaccharide of P. alcalifaciens O9 has a unique structure among bacterial polysaccharides, whereas the oligosaccharide region belongs to one of several core types recognized in the LPSs of Providencia.