Biochemical studies on the cell wall lipopolysaccharides (O-antigens) of Vibrio cholerae 569 B (Inaba) and El-tor (Inaba)

Elucidation of a novel Vibrio cholerae lipid A secondary hydroxy-acyltransferase and its role in innate immune recognition

Similar to most Gram-negative bacteria, the outer leaflet of the outer membrane of Vibrio cholerae is comprised of lipopolysaccharide. Previous reports have proposed that V. cholerae serogroups O1 and O139 synthesize structurally different lipid A domains, which anchor lipopolysaccharide within the outer membrane. In the current study, intact lipid A species of V. cholerae O1 and O139 were analysed by mass spectrometry. We demonstrate that V. cholerae serogroups associated with human disease synthesize a similar asymmetrical hexa-acylated lipid A species, bearing a myristate (C14:0) and 3-hydroxylaurate (3-OH C12:0) at the 2'- and 3'-positions respectively. A previous report from our laboratory characterized the V. cholerae LpxL homologue Vc0213, which transfers a C14:0 to the 2'-position of the glucosamine disaccharide. Our current findings identify V. cholerae Vc0212 as a novel lipid A secondary hydroxy-acyltransferase, termed LpxN, responsible for transferring the 3-hydroxylaurate (3-OH C12:0) to the V. cholerae lipid A domain. Importantly, the presence of a 3-hydroxyl group on the 3'-linked secondary acyl chain was found to promote antimicrobial peptide resistance in V. cholerae; however, this functional group was not required for activation of the innate immune response.

Lipopolysaccharides of Vibrio cholerae. I. Physical and chemical characterization

Vibrio cholerae is the causative organism of the disease cholera. The lipopolysaccharide (LPS) of V. cholerae plays an important role in eliciting the antibacterial immune response of the host and in classifying the vibrios into some 200 or more serogroups. This review presents an account of our up-to-date knowledge of the physical and chemical characteristics of the three constituents, lipid-A, core-polysaccharide (core-PS) and O-antigen polysaccharide (O-PS), of the LPS of V. cholerae of different serogroups including the disease-causing ones, O1 and O139. The structure and occurrence of the capsular polysaccharide (CPS) on V. cholerae O139 have been discussed as a relevant topic. Similarity and dissimilarity between the structures of LPS of different serogroups, and particularly between O22 and O139, have been analysed with a view to learning their role in the causation of the epidemic form of the disease by avoiding the host defence mechanism and in the evolution of the newer pathogenic strains in future. An idea of the emerging trends of research involving the use of immunogens prepared from synthetic oligosaccharides that mimic terminal epitopes of the O-PS of V. cholerae O1 in the development of a conjugate anti cholera vaccine is also discussed.

Effect of changes in the osmolarity of the growth medium on Vibrio cholerae cells

The rate and extent of lysis of Vibrio cholerae cells under nongrowing conditions were dependent on the osmolarity of the growth medium. Gross alterations in cellular morphology were observed when V. cholerae cells were grown in media of high and low osmolarity. The rate of lysis of V. cholerae cells under nongrowing conditions increased after treatment with chloramphenicol. Chloramphenicol-treated V. cholerae 569B cells showed formation of sphaeroplast-like bodies in medium of high osmolarity, but not in low osmolarity. Changes in the osmolarity of the growth medium also regulated the expression of the outer membrane proteins. This regulation was abolished if V. cholerae cells were grown in Pi-depleted medium. Analysis of the lytic behavior and composition of outer membrane proteins of an osmotically fragile mutant strain revealed a similar dependence on the osmolarity of the growth medium.

Characterization of the lipopolysaccharide from Vibrio cholerae 395 (Ogawa)

The chemical structure and biological properties of the lipopolysaccharide (LPS) from Vibrio cholerae 395 (Ogawa), isolated by the phenol-water procedure, were studied. Upon acid hydrolysis, the LPS was split into its polysaccharide and lipid A moieties. The polysaccharide contained both neutral (glucose, heptose, fructose) and amino (glucosamine, quinovosamine) sugars. The LPS contained the acid-labile amino sugar, 4-amino-arabinose, which was absent in the Inaba serotype of V. cholerae. The LPS differed from the LPSs of Enterobacteriaceae by the absence of 2-keto-3-deoxyoctonate and the presence of fructose. Analysis of the methylated polysaccharide by gas-liquid chromatography and mass spectrometry showed that it had a branched structure with glucose and heptose residues primarily appearing at the nonreducing-end groups. Interactions with lectins, concanavalin A. and wheat germ agglutinin suggested that terminal glucose residues were alpha linked, whereas terminal glucosamine residues were connected by alpha-1,3 linkages. The major fatty acids of the LPS were C14:0, C16:0, C12h:0, and C14h:0 compounds, of which only the C14h:0 were amide linked, the remainder being ester linked to the backbone. Biological studies showed that the LPS possessed endotoxic properties such as lethality, pyrogenicity, limulus lysate gelation, and ability to induce non-specific resistance to infection. Thus, the LPS from V. cholerae 395 (Ogawa) possessed both common and distinct features as compared with the LPSs from the Enterobacteriaceae.

The chemical structure of the lipid A component of lipopolysaccharides from Vibrio cholerae

The chemical structure of the lipid A component of the lipopolysaccharide from Vibrio cholerae 95R was studied. After sequential degradation a reduced D-glucosamine disaccharide was isolated from lipid A and, after permethylation, shown by combined gas-liquid chromatography/mass spectrometry to be beta 1,6-linked. The disaccharide is substituted with a phosphate group, ester-bound to the non-reducing glucosamine (GlcN) residue and a pyrophosphorylethanolamine group (PP-Etn) linked to C-1 of the reducing glucosamine residue. This backbone structure is shown in the following formula: P-GlcN(beta 1-6)GlcN-1-PP-Etn. The amino groups of the glucosamine disaccharide are substituted by D-3-hydroxytetradecanoic acid; tetradecanoic, hexadecanoic and a D-3-O-(D-3-hydroxydodecanoyl)-dodecanoic acid residue are linked to hydroxyl groups. A similar fatty acid composition was detected in lipopolysaccharides from Inaba, Ogawa and NAG strains of V. cholerae.

Identification and preliminary characterization of Vibrio cholerae outer membrane proteins

Outer membrane proteins of Vibrio cholerae were purified by sucrose density centrifugation and Triton X-100 extraction at 10 mM Mg2+. The proteins were separated by polyacrylamide gel electrophoresis in the presence of sodium dodecyl sulfate. V. cholerae outer membrane proteins presented a unique pattern when compared with the patterns of other gram-negative rods. There were 8 to 10 major bands (Mr 94,000 to 27,000), with most of the protein located in band 5 (Mr approximately 45,000), which thus appears to be the major structural protein of the outer membrane. Lipid and carbohydrate were associated with band 6.

Biological activities of chemically modified endotoxins from Vibrio cholerae

Lipopolysaccharides from Vibrio cholerae, NIH 41, Ogawa 5321 and Inaba 66/64 were treated with succinic anhydride, phthalic anhydride and dinitrophenyl ethylene diamine, and the resultant derivatives, sodium succinyl lipopolysaccharide, sodium phthalyl lipopolysaccharide, and dinitrohpenyl lipopolysaccharide obtained respectively were investigated for various biological activities. The succinylation and phthalylation of lipopolysaccharide decreased the 3-hydroxy lauric acid, a major ester-linked fatty acid of these bacteria, and as a result of which these modified products exhibited lower toxic activities in chick embryos, mouse and in generalized local Shwartzmann reaction in rabbits than their parent lipopolysaccharides. The dinitrophenylation of lipopolysaccharide increased its toxicity in chick embryos and mice, but dinitrophenyl lipopolysaccharide was completely inactive in Shwartzmann reaction in rabbits. However, despite the loss of these biological activities, these modified derivatives of lipopolysaccharide retained and increased the activities in pyrogenecity and in various immunological properties.

Immunochemical studies of the lipopolysaccharides of Vibrio cholerae: constitution of O specific side chain and core polysaccharide

Lipopolysaccharides from various strains of Vibrio cholerae have been found to consist of distinct O-specific side chain and core polysaccharide regions in their degraded polysaccharides. The major identifiable components in the core polysaccharide were phosphorus, glucose, heptose, fructose, and ethanolamine phosphate, with small amounts or traces of mannose, rhamnose, and D-perosamine. On the other hand, glucose, fructose, mannose, rhamnose, glucosamine, D-quinovosamine, and D-perosamine were identified from O-specific side chain polysaccharide. The amounts of each component have been determined from O-specific side chain and core polysaccharides of the lipopolysaccharides from these bacterial strains.

Structural investigations of the lipopolysaccharide isolated from Vibrio cholera, Inaba 569 B

On hydrolysis, the purified lipopolysaccharide (LPS) isolated from Vibrio cholera, Inaba 569 B, yielded glucose, mannose, a heptose behaving like D-glycero-L-manno-heptose and one behaving like D-glycero-L-gluco-heptose, 2-amino-2-deoxyglucose, and glucuronic acid in the molar ratios of approximately 9:4:5:1:2:5. Studies on the LPS, the polysaccharide (PS), and carboxyl-reduced LPS showed that the PS has a branched structure, with (1 leads to 2)-linked mannopyranosyl and a heptopyranosyl, and (1 leads to 4)-linked glucopyranosyluronic and 2-amino-2-deoxyglucopyranosyl residues in the interior part of the molecule, and glucopyranosyl and heptopyranosyl residues as nonreducing end-groups.

Fatty acid composition of lipopolysaccharides of Vibrio cholerae 35A3 (Inaba), NIB 90 (Ogawa), and 4715 (Nag)

Considerable amounts of odd-numbered fatty acids, such as non-hydroxy C15 and C17 and 3-hydroxy C11 and C13 acids, were found in lipopolysaccharides from Vibrio cholerae 35A3 (Inaba).

Characterization of lipid A and polysaccharide moieties of the lipopolysaccharides from Vibrio cholerae

Lipid A and polysaccharide moieties obtained by mild acid hydrolysis of the lipopolysaccharides from Vibrio cholerae 569 B (Inaba) and Vibrio el-tor (Inaba) were characterized. Heterogeneity of lipid A fractions was indicated by t.l.c. and by gel filtration of the de-O-acylated products from mild alkaline methanolysis of the lipids. Presumably lipid A contains a glucosamine backbone, and the fatty acids are probably bound to the hydroxyl and amino groups of glucosamine residues. Approximately equal amounts of fatty acids C16:0, C18:1 and 3-hydroxylauric acid were involved in ester linkages, but 3-hydroxymyristic acid was the only amide-linked fatty acid. Sephadex chromatography of the polysaccharide moiety showed the presence of a high-molecular-weight heptose-free fraction and a low-molecular-weight heptose-containing fraction. Haemagglutination-inhibition assays of these fractions showed the heptose-free fraction to be an O-specific side-chain polysaccharide, whereas the heptose-containing fraction was the core polysaccharide region of the lipopolysaccharides. Identical results were obtained for both organisms.