Highly phosphorylated core oligosaccharides and those substituted with one O-antigen repeating unit were obtained by mild acid degradation or strong alkaline hydrolysis of lipopolysaccharide samples from 23 reference strains representing all Pseudomonas aeruginosa O-serogroups. Studies by high-resolution electrospray ionization mass spectrometry and two-dimensional NMR spectroscopy revealed both conserved and variable structural features of the lipopolysaccharides of various O-serogroups. The upstream terminal saccharide of the O-antigen, which contributes most to the immunospecificity of the bacteria, was defined in 11 from a total of 13 O-serogroups. The data obtained link together the known biosynthesis pathways, genetics and serology of the P. aeruginosa lipopolysaccharide.

The review is devoted to recent progress in the structural elucidation of the lipopolysaccharide of the bacterium Pseudomonas aeruginosa, including O-antigen biological repeats, core oligosaccharide, and lipid A. Data on biosynthesis, genetics and serology of the lipopolysaccharide isolated from various P. aeruginosa O-serogroups are discussed in relation to the chemical structures.

Lipopolysaccharide (LPS) expressed by isolates of Pseudomonas aeruginosa from cystic fibrosis patients lacks the O-polysaccharide chain but the degree to which the rest of the molecule changes has not been determined. We analyzed, for the first time, the core structure of an LPS from a rough, cystic fibrosis isolate of P. aeruginosa. The products of mild acid hydrolysis and strong alkaline degradation of the LPS were studied by ESI MS, MALDI MS, and NMR spectroscopy. The following structure was determined for the highest-phosphorylated core-lipid A backbone oligosaccharide isolated after alkaline deacylation of the LPS:where Kdo and Hep are 3-deoxy-D-manno-octulosonic acid and L-glycero-D-manno-heptose, respectively; all sugars are in the pyranose form and have the D configuration unless stated otherwise. The outer core region occurs as two isomeric glycoforms differing in the position of rhamnose (Rha). The inner core region carries four phosphorylation sites at two Hep residues, Hep I being predominantly bisphosphorylated and Hep II monophosphorylated. In the intact LPS, both Hep residues carry monophosphate and diphosphate groups in nonstoichiometric quantities, GalN is N-acylated by an L-alanyl group, Hep II is 7-O-carbamoylated, and the outer core region is nonstoichiometrically O-acetylated at four sites. Therefore, the switch to the LPSrough phenotype in cystic fibrosis isolates of P. aeruginosa is not accompanied by losses of core monosaccharide, phosphate or acyl components. The exact positions of the O-acetyl groups and the role of the previously undescribed O-acetylation in the LPS core of P. aeruginosa remain to be determined.

The structure of the lipopolysaccharide (LPS) of Pseudomonas aeruginosa immunotype 1 was studied after mild acid and strong alkaline degradations by MS and NMR spectroscopy. Three types of LPS molecules were found, including those with an unsubstituted glycoform 1 core (A) or an isomeric glycoform 2 core substituted with one O‐polysaccharide repeating unit (B) or with a long‐chain O‐polysaccharide. Therefore, of two core glycoforms, only glycoform 2 accepts the O‐polysaccharide. In the structures A and B, Kdo, Hep, Hep7Cm, GalNAcAN3Ac, GalNFoAN, QuiNAc, GalNAla represent 3‐deoxy‐d‐manno‐octulosonic acid, l‐glycero‐d‐manno‐heptose, 7‐O‐carbamoyl‐l‐glycero‐d‐manno‐heptose, 2‐acetamido‐3‐O‐acetyl‐2‐deoxygalacturonamide, 2‐formamido‐2‐deoxygalacturonamide, 2‐acetamido‐2,6‐dideoxyglucose and 2‐(l‐alanylamino)‐2‐deoxygalactose, respectively; all sugars are in the pyranose form and have the d configuration unless otherwise stated. One or more phosphorylation sites may be occupied by diphosphate groups. In a minority of the LPS molecules, an O‐acetyl group is present in the outer core region at unknown position.  The site and the configuration of the linkage between the O‐polysaccharide and the core and the structure of the O‐polysaccharide repeating unit were defined in P. aeruginosa immunotype 1. The QuiNAc residue linked to the Rha residue of the core was found to have the β configuration, whereas in the interior repeating units of the O‐polysaccharide this residue is in the α‐configuration. The data obtained are in accordance with the initiation of biosynthesis of the O‐polysaccharide of P. aeruginosa O6, which is closely related to immunotype 1, by transfer of d‐QuiNAc‐1‐P to undecaprenyl phosphate followed by synthesis of the repeating O‐antigen tetrasaccharide.