Structural analysis of the lipopolysaccharide from Vibrio cholerae serotype O22

O-antigen and core carbohydrate of Vibrio fischeri lipopolysaccharide: composition and analysis of their role in Euprymna scolopes light organ colonization

Vibrio fischeri exists in a symbiotic relationship with the Hawaiian bobtail squid, Euprymna scolopes, where the squid provides a home for the bacteria, and the bacteria in turn provide camouflage that helps protect the squid from night-time predators. Like other gram-negative organisms, V. fischeri expresses lipopolysaccharide (LPS) on its cell surface. The structure of the O-antigen and the core components of the LPS and their possible role in colonization of the squid have not previously been determined. In these studies, an O-antigen ligase mutant, waaL, was utilized to determine the structures of these LPS components and their roles in colonization of the squid. WaaL ligates the O-antigen to the core of the LPS; thus, LPS from waaL mutants lacks O-antigen. Our results show that the V. fischeri waaL mutant has a motility defect, is significantly delayed in colonization, and is unable to compete with the wild-type strain in co-colonization assays. Comparative analyses of the LPS from the wild-type and waaL strains showed that the V. fischeri LPS has a single O-antigen repeat composed of yersiniose, 8-epi-legionaminic acid, and N-acetylfucosamine. In addition, the LPS from the waaL strain showed that the core structure consists of L-glycero-D-manno-heptose, D-glycero-D-manno-heptose, glucose, 3-deoxy-D-manno-octulosonic acid, N-acetylgalactosamine, 8-epi-legionaminic acid, phosphate, and phosphoethanolamine. These studies indicate that the unusual V. fischeri O-antigen sugars play a role in the early phases of bacterial colonization of the squid.

Genetic diversity of O-antigen biosynthesis regions in Vibrio cholerae

O-antigen biosynthetic (wbf) regions for Vibrio cholerae serogroups O5, O8, and O108 were isolated and sequenced. Sequences were compared to those of other published V. cholerae O-antigen regions. These wbf regions showed a high degree of heterogeneity both in gene content and in gene order. Genes identified frequently showed greater similarities to polysaccharide biosynthesis genes from species other than V. cholerae. Our results demonstrate the plasticity of O-antigen genes in V. cholerae, the diversity of the genetic pool from which they are drawn, and the likelihood that new pandemic serogroups will emerge.

Structures of the biological repeating units in the O-chain polysaccharides ofHafnia alveistrains having a typical lipopolysaccharide outer core region

Earlier, the structures of the O-chain polysaccharides of the lipopolysaccharides (LPS) of a number of Hafnia 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)-alpha-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-GlcNAc 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.

Molecular and functional characterization of O antigen transfer in Vibrio cholerae

The majority of Gram-negative bacteria transfer O antigen polysaccharides onto the lipid A-core oligosaccharide via the action of surface polymer:lipid A-core ligases (WaaL). Here, we characterize the WaaL proteins of Vibrio cholerae with emphasis on structural and functional characterization of O antigen transfer and core oligosaccharide recognition. We demonstrate that the activity of two distantly related O antigen ligases is dependent on the presence of N-acetylglucosamine, and substitution of an additional sugar, i.e. galactose, alters the site specificity of the core oligosaccharide necessitating discriminative WaaL types. Protein topology analysis and a conserved domain search identified two distinct conserved motifs in the periplasmic domains of WaaL proteins. Site-directed mutagenesis of the two motifs, shown for WaaLs of V. cholerae and Salmonella enterica, caused a loss of O antigen transfer activity. Moreover, analogy of topology and motifs between WaaLs and O polysaccharide polymerases (Wzy) reveals a relationship between the two protein families, suggesting that the catalyzed reactions are related to each other.

Synthesis of cis-(1→3)-glycosides of allyl 2-acetamido-4,6-O-benzylidene-2-deoxy-α-d-glucopyranoside

Syntheses of allyl 2,3,4-tri-O-benzyl-alpha-D-gluco- and D-galactopyranosyluronate-(1-->3)-2-acetamido-4,6-O-benzylidene-2-deoxy-alpha-D-glucopyranoside via oxidation of the hydroxymethyl group of allyl 2,3,4-tri-O-benzyl-alpha-D-gluco- and D-galactopyranosyl-(1-->3)-2-acetamido-4,6-O-benzylidene-2-deoxy-alpha-D-glucopyranoside under Jones conditions are described. Structures of the title compounds were confirmed by (1)H and (13)C NMR spectroscopy.

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.

The Vibrio cholerae O139 O-antigen polysaccharide is essential for Ca2+-dependent biofilm development in sea water

Vibrio cholerae is both an inhabitant of estuarine environments and the etiologic agent of the diarrheal disease cholera. Previous work has demonstrated that V. cholerae forms both an exopolysaccharide-dependent biofilm and a Ca2+-dependent biofilm. In this work, we demonstrate a role for the O-antigen polysaccharide of V. cholerae in Ca2+-dependent biofilm development in model and true sea water. Interestingly, V. cholerae biofilms, as well as the biofilms of several other Vibrio species, disintegrate when Ca2+ is removed from the bathing medium, suggesting that Ca2+ is interacting directly with the O-antigen polysaccharide. In the Bay of Bengal, cholera incidence has been correlated with increased sea surface height. Because of the low altitude of this region, increases in sea surface height are likely to lead to transport of sea water, marine particulates, and marine biofilms into fresh water environments. Because fresh water is Ca2+-poor, our results suggest that one potential outcome of an increase is sea surface height is the dispersal of marine biofilms with an attendant increase in planktonic marine bacteria such as V. cholerae. Such a phenomenon may contribute to the correlation of increased sea surface height with cholera.

Identification of a novel inner-core oligosaccharide structure in Neisseria meningitidis lipopolysaccharide

The structure of the lipopolysaccharide (LPS) from three Neisseria meningitidis strains was elucidated. These strains were nonreactive with mAbs that recognize common inner-core epitopes from meningococcal LPS. It is well established that the inner core of meningococcal LPS consists of a diheptosyl-N-acetylglucosamine unit, in which the distal heptose unit (Hep II) can carry PEtn at the 3 or 6 position or not at all, and the proximal heptose residue (Hep I) is substituted at the 4 position by a glucose residue. Additional substitution at the 3 position of Hep II with a glucose residue is also a common structural feature in some strains. The structures of the O-deacylated LPSs and core oligosaccharides of the three chosen strains were deduced by a combination of monosaccharide analysis, NMR spectroscopy and MS. These analyses revealed the presence of a structure not previously identified in meningococcal LPS, in which an additional beta-configured glucose residue was found to substitute Hep I at the 2 position. This provided the structural basis for the nonreactivity of LPS with these mAbs. The determination of this novel structural feature identified a further degree of variability within the inner-core oligosaccharide of meningococcal LPS which may contribute to the interaction of meningococcal strains with their host.

Comparative and genetic analyses of the putative Vibrio cholerae lipopolysaccharide core oligosaccharide biosynthesis (wav) gene cluster

We identified five different putative wav gene cluster types, which are responsible for the synthesis of the core oligosaccharide (OS) region of Vibrio cholerae lipopolysaccharide. Preliminary evidence that the genes encoded by this cluster are involved in core OS biosynthesis came from analysis of the recently released O1 El Tor V. cholerae genome sequence and sodium dodecyl sulfate-polyacrylamide gel electrophoresis analysis of O1 El Tor mutant strains defective in three genes (waaF, waaL, and wavB). Investigations of 38 different V. cholerae strains by Southern blotting, PCR, and sequencing analyses showed that the O1 El Tor wav gene cluster type is prevalent among clinical isolates of different serogroups associated with cholera and environmental O1 strains. In contrast, we found differences in the wav gene contents of 19 unrelated non-O1, non-O139 environmental and human isolates not associated with cholera. These strains contained four new wav gene cluster types that differ from each other in distinct gene loci, providing evidence for horizontal transfer of wav genes and for limited structural diversity of the core OS among V. cholerae isolates. Our results show genetic diversity in the core OS biosynthesis gene cluster and predominance of the type 1 wav gene locus in strains associated with clinical cholera, suggesting that a specific core OS structure could contribute to V. cholerae virulence.

The genes responsible for O-antigen synthesis of vibrio cholerae O139 are closely related to those of vibrio cholerae O22

Several studies have shown that the emergence of the O139 serogroup of Vibrio cholerae is a result of horizontal gene transfer of a fragment of DNA from a serogroup other than O1 into the region responsible for O-antigen biosynthesis of the seventh pandemic V. cholerae O1 biotype El Tor strain. In this study, we show that the gene cluster responsible for O-antigen biosynthesis of the O139 serogroup of V. cholerae is closely related to those of O22. When DNA fragments derived from O139 O-antigen biosynthesis gene region were used as probes, the entire O139 O-antigen biosynthesis gene region could be divided into five classes, designated as I-V based on the reactivity pattern of the probes against reference strains of V. cholerae representing serogroups O1-O193. Class IV was specific to O139 serogroup, while classes I-III and class V were homologous to varying extents to some of the non-O1, non-O139 serogroups. Interestingly, the regions other than class IV were also conserved in the O22 serogroup. Long and accurate PCR was employed to determine if a simple deletion or substitution was involved to account for the difference in class IV between O139 and O22. A product of approx. 15kb was amplified when O139 DNA was used as the template, while a product of approx. 12.5kb was amplified when O22 DNA was used as the template, indicating that substitution but not deletion could account for the difference in the region between O22 and O139 serogroups. In order to precisely compare between the genes responsible for O-antigen biosynthesis of O139 and O22, the region responsible for O-antigen biosynthesis of O22 serogroup was cloned and analyzed. In concurrence with the results of the hybridization test, all regions were well conserved in O22 and O139 serogroups, although wbfA and the five or six genes comprising class IV in O22 and O139 serogroups, respectively, were exceptions. Again the genes in class IV in O22 were confirmed to be specific to O22 among the 155 'O' serogroups of V. cholerae. These data suggest that the gene clusters responsible for O139 O-antigen biosynthesis are most similar to those of O22 and genes within class IV of O139, and O22 defines the unique O antigen of O139 or O22.

Structural and functional characterization of IS1358 from Vibrio cholerae

The new epidemic serovar O139 of Vibrio cholerae has emerged from the pandemic serovar O1 biotype El Tor through the replacement of a 22-kbp DNA region by a 40-kbp O139-specific DNA fragment. This O139-specific DNA fragment contains an insertion sequence that was described previously (U. H. Stroeher, K. E. Jedani, B. K. Dredge, R. Morona, M. H. Brown, L. E. Karageorgos, J. M. Albert, and P. A. Manning, Proc. Natl. Acad. Sci. USA 92:10374-10378, 1995) and designated IS1358O139. We studied the distribution of the IS1358 element in strains from various serovars by Southern analysis. Its presence was detected in strains from serovars O1, O2, O22, O139, and O155 but not in strains from serovars O15, O39, and O141. Furthermore, IS1358 was present in multiple copies in strains from serovars O2, O22, and O155. We cloned and sequenced four copies of IS1358 from V. cholerae O22 and one copy from V. cholerae O155. A comparison of their nucleotide sequences with those of O1 and O139 showed that they were almost identical. We constructed a transposon consisting of a kanamycin resistance gene flanked by two directly oriented copies of IS1358 to study the functionality of this element. Transposition of this element from a nonmobilizable plasmid onto the conjugative plasmid pOX38-Gen was detected in an Escherichia coli recA donor at a frequency of 1.2 x 10(-8). Sequence analysis revealed that IS1358 duplicates 10 bp at its insertion site.

More on the structure of Vibrio cholerae O22 lipopolysaccharide

The structure of a short-chain lipopolysaccharide (LPS) of Vibrio cholerae O22 strain 169-68, that cross-reacts with V. cholerae O139 Bengal, was elucidated. The structure differs in detail from that reported on another strain of O22 [A.D. Cox, J-R. Brisson, P. Thibault and M.B. Perry, Carbohydr. Res., 304 (1997) 191-208]. The similarity and difference between the LPS structures of the two strains as well as between O22 and O139 are discussed.

Vibrio cholerae O22 might be a putative source of exogenous DNA resulting in the emergence of the new strain of Vibrio cholerae O139

The new epidemic strain O139 of Vibrio cholerae, the etiologic agent of cholera, has probably emerged from the pandemic strain O1 E1 Tor through a genetic rearrangement involving the horizontal transfer of exogenous O-antigen- and capsule-encoding genes of unknown origin. In V. cholerae O139, these genes are associated with an insertion sequence designated IS1358O139. In this work, we studied the distribution of seven genes flanking the IS1358O139 element in 13 serovars of V. cholerae strains. All these O139 genes and an IS1358 element designated IS1358O22-1 were only found in V. cholerae O22 with a similar genetic organization. Sequence analysis of a 4.5-kb fragment containing IS1358O22-1 and the adjacent genes revealed that these genes are highly homologous to those of V. cholerae O139. These results suggest that strains of V. cholerae O22 from the environment might have been the source of the exogenous DNA resulting in the emergence of the new epidemic strain O139.