The KL24 gene cluster and a genomic island encoding a Wzy polymerase contribute genes needed for synthesis of the K24 capsular polysaccharide by the multiply antibiotic resistant Acinetobacter baumannii isolate RCH51

The whole-genome sequence of the multiply antibiotic resistant Acinetobacter baumannii isolate RCH51 belonging to sequence type ST103 (Institut Pasteur scheme) revealed that the set of genes at the capsule locus, KL24, includes four genes predicted to direct the synthesis of 3-acetamido-3,6-dideoxy-d-galactose (d-Fuc3NAc), and this sugar was found in the capsular polysaccharide (CPS). One of these genes, fdtE, encodes a novel bifunctional protein with an N-terminal FdtA 3,4-ketoisomerase domain and a C-terminal acetyltransferase domain. KL24 lacks a gene encoding a Wzy polymerase to link the oligosaccharide K units to form the CPS found associated with isolate RCH51, and a wzy gene was found in a small genomic island (GI) near the cpn60 gene. This GI is in precisely the same location as another GI carrying wzy and atr genes recently found in several A. baumannii isolates, but it does not otherwise resemble it. The CPS isolated from RCH51, studied by sugar analysis and 1D and 2D 1H and 13C NMR spectroscopy, revealed that the K unit has a branched pentasaccharide structure made up of Gal, GalNAc and GlcNAc residues with d-Fuc3NAc as a side branch, and the K units are linked via a β-d-GlcpNAc-(1→3)-β-d-Galp linkage formed by the Wzy encoded by the GI. The functions of the glycosyltransferases encoded by KL24 were assigned to formation of specific bonds. A correspondence between the order of the genes in KL24 and other KL and the order of the linkages they form was noted, and this may be useful in future predictions of glycosyltransferase specificities.

Genetic diversity of the O antigens of Proteus species and the development of a suspension array for molecular serotyping

Proteus species are well-known opportunistic pathogens frequently associated with skin wound and urinary tract infections in humans and animals. O antigen diversity is important for bacteria to adapt to different hosts and environments, and has been used to identify serotypes of Proteus isolates. At present, 80 Proteus O-serotypes have been reported. Although the O antigen structures of most Proteus serotypes have been identified, the genetic features of these O antigens have not been well characterized. The O antigen gene clusters of Proteus species are located between the cpxA and secB genes. In this study, we identified 55 O antigen gene clusters of different Proteus serotypes. All clusters contain both the wzx and wzy genes and exhibit a high degree of heterogeneity. Potential functions of O antigen-related genes were proposed based on their similarity to genes in available databases. The O antigen gene clusters and structures were compared, and a number of glycosyltransferases were assigned to glycosidic linkages. In addition, an O serotype-specific suspension array was developed for detecting 31 Proteus serotypes frequently isolated from clinical specimens. To our knowledge, this is the first comprehensive report to describe the genetic features of Proteus O antigens and to develop a molecular technique to identify different Proteus serotypes.

Studies on the O-specific polysaccharide of the lipopolysaccharide from the Pseudomonas mediterranea strain C5P1rad1, a bacterium pathogenic of tomato and chrysanthemum

An O-specific polysaccharide (OPS) was isolated from the lipopolysaccharide of Pseudomonas mediterranea strain C5P1rad1, the causal agents of tomato pith necrosis and Chrysanthemum stem rot, and studied by one- and two-dimensional ¹H and ¹³C NMR spectroscopy. The following structure of the trisaccharide repeating unit of the OPS was established, which, to our knowledge, is unique among the known bacterial polysaccharide structures: →4)-β-d-ManpNAc3NAcA-(1 → 4)-β-d-ManpNAc3NAcA-(1 → 3)-α-d-QuipNAc4NAc-(1→ where QuiNAc4NAc and ManNAc3NAcA indicate 2,4-diacetamido-2,4,6-trideoxyglucose and 2,3-diacetamido-2,3-dideoxymannuronic acid, respectively. Pre-treatment of leaves with LPS or OPS preparations at 250 and 50 μg mL^-1 did not inhibit development of a hypersensitivity reaction induced by P. mediterranea C5P1rad1 on tobacco, tomato and chrysanthemum plants. The same preparations at 250 μg mL^-1 partially prevented elicitation of the hypersensitivity reaction by Pseudomonas syringae KVPT7RC on chrysanthemum but not tobacco and tomato.

Re-classification within the serogroups O3 and O8 of Citrobacter strains

BACKGROUND

Citrobacter strains are opportunistic pathogens often responsible for serious enteric as well as extra-intestinal diseases, and therefore the O-antigenic scheme, still in use in diagnostic identification, should be set for proper serotyping. The structures of more than 30 different Citrobacter O-antigens (O-polysaccharide chains of the lipopolysaccharides) of 43 Citrobacter O-serogroups have been elucidated so far. However, relationships between strains in several heterogeneous serogroups still need to be clarified by immunochemical studies. These include complex serogroups O3 and O8, represented by 20 and 7 strains, respectively, which are the subject of the present work. Earlier, the O-polysaccharide structures have been determined for Citrobacter O3 strain Be35/57 (PCM 1508) and Citrobacter O8 strain Be64/57 (PCM 1536).

RESULTS

Serological studies (immunoblotting) carried out on Citrobacter lipopolysaccharides from different strains ascribed to serogroups O3 and O8 showed that each of these serogroups should be divided into non-cross-reacting subgroups. Based on the results of chemical analyses and ¹H and ¹³C NMR spectroscopy the structure of Citrobacter O-antigens from strains PCM 1504 (O6) and PCM 1573 (O2) have been established. Chemical data combined with serological analyses showed that several Citrobacter strains should be reclassified into other serogroups.

CONCLUSIONS

Immunochemical studies carried out on Citrobacter LPS, described in this paper, showed the expediency of reclassification of: 1) strains PCM 1504 and PCM 1573 from serogroups O6 and O2 to serogroups O3 and O8, respectively, 2) strains PCM 1503 and PCM 1505 from serogroups O3 and O8 to new serogroups O3a and O8a, respectively.

Function of bacteriophage G7C esterase tailspike in host cell adsorption

Bacteriophages recognize and bind to their hosts with the help of receptor-binding proteins (RBPs) that emanate from the phage particle in the form of fibers or tailspikes. RBPs show a great variability in their shapes, sizes, and location on the particle. Some RBPs are known to depolymerize surface polysaccharides of the host while others show no enzymatic activity. Here we report that both RBPs of podovirus G7C - tailspikes gp63.1 and gp66 - are essential for infection of its natural host bacterium E. coli 4s that populates the equine intestinal tract. We characterize the structure and function of gp63.1 and show that unlike any previously described RPB, gp63.1 deacetylates surface polysaccharides of E. coli 4s leaving the backbone of the polysaccharide intact. We demonstrate that gp63.1 and gp66 form a stable complex, in which the N-terminal part of gp66 serves as an attachment site for gp63.1 and anchors the gp63.1-gp66 complex to the G7C tail. The esterase domain of gp63.1 as well as domains mediating the gp63.1-gp66 interaction is widespread among all three families of tailed bacteriophages.

Structures and gene clusters of the O-antigens of Escherichia albertii O3, O4, O6, and O7

The O-specific polysaccharides (OPSs) called O-antigens were obtained by mild acid degradation of the lipopolysaccharides of Escherichia albertii serotypes O3, O4, O6, and O7 and studied by sugar analysis along with 1D and 2D ¹H and ¹³C NMR spectroscopy. The following structure was established for the OPS of E. albertii O4, which, to our knowledge, is unique among known bacterial polysaccharide structures: →2)-α-l-Rhap-(1 → 2)-α-l-Fucp-(1 → 2)-β-d-Galp-(1 → 3)-α-d-GalpNAc-(1 → 3)-β-d-GlcpNAc-(1→ The OPS structure of the strain of E. albertii O7 studied was identical to that of strain LMG 20973 (= Albert 10457), whose structure has been reported earlier (R. Eserstam et al. Eur. J. Biochem. 269 (2002) 3289-3295). E. albertii O3 and O6 shared the OPS structures with Escherichia coli O181 and O3, respectively, except for the lack of O-acetylation in E. albertii O3, which is present in E. coli O181. The gene clusters driving the O-antigen biosynthesis of the E. albertii strains were sequenced, the genes were annotated by comparison with sequences in the available databases, and the predicted functions of the encoded proteins were found to be consistent with the OPS structures established. In accordance with the relatedness of the OPS structures, the O-antigen gene clusters of E. albertii O3 and O6 contain the same genes and have the same organization as those of E. coli O181 and O3, the entire gene clusters being 83% and 98% identical, respectively.

Structure and gene cluster of a tyvelose-containing O-polysaccharide of an entomopathogenic bacterium Yersinia entomophaga MH96T related to Yersinia pseudotuberculosis

An O-polysaccharide was isolated from the lipopolysaccharide of an entomopathogenic bacterium Yersinia entomophaga MH96^T by mild acid hydrolysis and studied by 2D NMR spectroscopy. The following structure of the branched tetrasaccharide repeating unit of the polysaccharide was established: where Tyv indicates 3,6-dideoxy-d-arabino-hexose (tyvelose). The structure established is consistent with the gene content of the O-antigen gene cluster. The O-polysaccharide structure and gene cluster of Y. entomophaga are related to those of some Y. pseudotuberculosis serotypes.

Acinetobacter baumannii K11 and K83 capsular polysaccharides have the same 6-deoxy-l-talose-containing pentasaccharide K units but different linkages between the K units

Acinetobacter baumannii produces a variety of capsular polysaccharides (CPS) via genes located at the chromosomal K locus and some KL gene clusters include genes for the synthesis of specific sugars. The structures of K11 and K83 CPS produced by isolates LUH5545 and LUH5538, which carry related KL11a and KL83 gene clusters, respectively, were established by sugar analysis and one- and two-dimensional ¹H and ¹³C NMR spectroscopy. Both CPS contain l-rhamnose (l-Rha) and 6-deoxy-l-talose (l-6dTal), and both KL gene clusters include genes for dTDP-l-Rhap synthesis and a tle (talose epimerase) gene encoding an epimerase that converts dTDP-l-Rhap to dTDP-l-6dTalp. The K11 and K83 repeat units are the same pentasaccharide, consisting of d-glucose, l-Rha, l-6dTal, and N-acetyl-d-glucosamine, except that l-6dTal is 2-O-acetylated in K83. However, the K units are linked differently, with l-Rha in the main chain in K11, but as a side-branch in K83. KL11 and KL83 encode unrelated Wzy polymerases that link the K units together and different acetyltransferases, though only Atr8 from KL83 is active. The substrate specificity of each Wzy polymerase was assigned, and the functions of all glycosyltransferases were predicted. The CPS structures produced by three closely related K loci, KL29, KL105 and KL106, were also predicted.

Structure and gene cluster of the O-antigen of Escherichia albertii O1 resembling the O-antigen of Pseudomonas aeruginosa O5

The O-specific polysaccharide (O-antigen) was obtained by mild acid degradation of the lipopolysaccharide of Escherichia albertii serotype O1 strain SP20140089 and studied by sugar analysis along with 1D and 2D ¹H and ¹³C NMR spectroscopy. The following structure was established for the trisaccharide repeating unit of the O-polysaccharide: →4)-β-d-ManpNAc3NAcA-(1 → 4)-β-d-GlcpNAm3NAcA-(1 → 3)-α-d-GlcpNAc-(1→ where ManNAc3NAcA and GlcNAm3NAcA indicate 2,3-diacetamido-2,3-dideoxymannuronic acid and 2-acetimidoylamino-3-acetamido-2,3-dideoxyglucuronic acid, respectively. While showing some similarity with O-polysaccharide structures of a group of Pseudomonas aeruginosa serotypes (O2, O5, O16, O18, and O20), that of E. albertii O1 is unique among known bacterial polysaccharide structures. The gene cluster for biosynthesis of the O1-antigen was sequenced and functions of the genes were predicted by comparison with sequences in the available databases, including those involved in the synthesis of nucleotide precursors of 2,3-diamino-2,3-dideoxyhexuronic acid derivatives in P. aeruginosa O5.

Lipopolysaccharide of Pantoea agglomerans 7969: Chemical identification, function and biological activity

Lipopolysaccharide (LPS) of Pantoea agglomerans 7969 isolated from apple tree was purified and characterized chemically by sugar and fatty acid analysis. Lipid A was analysed by negative-ion mode ESI MS and found to consist mainly of hexa- and tetra-acyl species typical of E. coli lipid A. The O-specific polysaccharide of the LPS was studied by sugar analysis, Smith degradation, and one- and two-dimensional ¹H and ¹³C NMR spectroscopy. The polysaccharide is built up of linear tetrasaccharide repeating units, and about ∼25% repeats contain glycerol 1-phosphate on the GlcNAc residue: →3)-α-l-Rha p-(1→6)-α-d-Man p-(1→3)-α-d-Fuc p-(1→3)-β-d-Glc pNAc-(1→∼25% Gro-1-P-(O→6)^⌋ The LPS showed low levels of toxic and pyrogenic activities and reduced the average adhesion and the index of adhesiveness.

Structural Relationships Between Genetically Closely Related O-Antigens of Escherichia coli and Shigella spp

Gene clusters for biosynthesis of 24 of 34 basic O-antigen forms of Shigella spp. are identical or similar to those of the genetically closely related bacterium Escherichia coli. For 18 of these relatedness was confirmed chemically by elucidation of the O-antigen (O-polysaccharide) structures. In this work, structures of the six remaining O-antigens of E. coli O32, O53, O79, O105, O183 (all related to S. boydii serotypes), and O38 (related to S. dysenteriae type 8) were established using (1)H and (13)C NMR spectroscopy. They were found to be identical to the Shigella counterparts, except for the O32- and O38-polysaccharides, which differ in the presence of O-acetyl groups. The structure of the E. coli O105-related O-polysaccharide of S. boydii type 11 proposed earlier is revised. The contents of the O-antigen gene clusters of the related strains of E. coli and Shigella spp. and different mechanisms of O-antigen diversification in these bacteria are discussed in view of the O-polysaccharide structures established. These data illustrate the value of the O-antigen chemistry and genetics for elucidation of evolutionary relationships of bacteria.

Structures and serospecificity of threonine-containing O polysaccharides of two clinical isolates belonging to the genus Proteus and their classification into O11 subserogroups

Two clinical isolates from Polish patients, Proteus mirabilis 9B-m and Proteus genomospecies 3J-r, were found to be serologically related to P mirabilis O11. However, serological studies involving ELISA and Western blotting methods, using lipopolysaccharides (LPSs) extracted from the strains as antigens and native or adsorbed rabbit polyclonal O antisera, specific to the studied strains, revealed slight differences in the cross-reactivity and specificity of the two studied Proteus isolates, when compared to P. mirabilis O11. Two different O polysaccharides containing N-(d-galacturonoyl)-l-threonine were isolated from the LPSs of the isolates. Their structures were determined by chemical analysis and NMR spectroscopy and found to be related to the P. mirabilis O11 antigen structure established earlier, the 9B-m structure differing in the absence of the lateral glucose residue and the 3J-r structure in non-stoichiometric O-acetylation of the threonine residue only. Thus, the Proteus O11 serogroup should be divided into two subgroups: O11a, represented by the 9B-m isolate and O11a, b possessing the additional b epitope, containing the lateral residue of glucose and formed by the 3J-r isolate as well as P. mirabilis 25/57 belonging to O11 serogroup so far. O11a is the sixth new serotype found in Proteus spp. strains recently isolated from patients in central Poland.

Structure and genetics of the O-antigens of Escherichia coli O182-O187

O-polysaccharides (OPSs) were obtained by mild acid degradation of the lipopolysaccharides of Escherichia coli O182-O187, and their structures were established by sugar analysis, Smith degradation, and ¹H and ¹³C NMR spectroscopy. In addition to the monosaccharides that occur often in E. coli OPSs (d-Glc, d-Gal, d-Man, d-GlcNAc, d-GalNAc, d-GlcA, l-Fuc, d-Rib), a number of less common components were identified as the OPS constituents, including 2-acetamido-2-deoxy-l-quinovose and 4-deoxy-4-[(S)-3-hydroxybutanoyl-l-alanyl]-d-quinovose (O186), 3-acetamido-3-deoxy-d-fucose (O187), 3-deoxy-3-[(R)-3-hydroxybutanoyl]-d-fucose (O184), and 2,3-diacetamido-2,3-dideoxy-l-rhamnose (O182). The OPS structures of E. coli O183 and O182 are identical to those of the OPS of Shigella boydii type 10 and the capsular polysaccharide of E. coli K48, respectively. The OPSs of E. coli O186 and O123 are closely related differing in the presence of a Glc residue in the former in place of a GlcNAc residue in the latter. The O-antigen gene clusters of the bacteria studied were analyzed and their contents were found to be consistent with the OPS structures. Predicted glycosyltransferases encoded in the gene clusters were tentatively assigned to glycosidic linkages based on similarities to sequences of other E. coli O-serogroups available from GenBank and taking into account the OPS structures established.

O-antigen modifications providing antigenic diversity of Shigella flexneri and underlying genetic mechanisms

O-Antigens (O-specific polysaccharides) of Shigella flexneri, a primary cause of shigellosis, are distinguished by a wide diversity of chemical modifications following the oligosaccharide O-unit assembly. The present review is devoted to structural, serological, and genetic aspects of these modifications, including O-acetylation and phosphorylation with phosphoethanolamine that have been identified recently. The modifications confer the host with specific immunodeterminants (O-factors or O-antigen epitopes), which accounts for the antigenic diversity of S. flexneri considered as a virulence factor of the pathogen. Totally, 30 O-antigen variants have been recognized in these bacteria, the corresponding O-factors characterized using specific antibodies, and a significant extension of the serotyping scheme of S. flexneri on this basis is suggested. Multiple genes responsible for the O-antigen modifications and the resultant serotype conversions of S. flexneri have been identified. The genetic mechanisms of the O-antigen diversification by acquisition of mobile genetic elements, including prophages and plasmids, followed occasionally by gene mobilization and inactivation have been revealed. These findings further our understanding of the genetics and antigenicity of S. flexneri and assist control of shigellosis.

Structure elucidation and gene cluster characterization of the O-antigen of Escherichia coli O80

Mild alkaline degradation of the lipopolysaccharide of Escherichia coli O80 afforded a polysaccharide, which was studied by sugar analysis, selective cleavage of glycosidic linkages, and (1)H and (13)C NMR spectroscopy. Solvolysis of the polysaccharide with CF3CO2H cleaved the linkages of α-Fuc and β-linked GlcNAc and GalNAc residues to give two disaccharides. The following structure of the hexasaccharide repeating unit of the O-polysaccharide was established: The polysaccharide repeat also contains a minor O-acetyl group but its position was not determined. The O-antigen gene cluster of E. coli O80 between the conserved galF and gnd genes was analyzed and found to be consistent with the O-polysaccharide structure established.

Dectin-2 Recognizes Mannosylated O-antigens of Human Opportunistic Pathogens and Augments Lipopolysaccharide Activation of Myeloid Cells

LPS consists of a relatively conserved region of lipid A and core oligosaccharide and a highly variable region of O-antigen polysaccharide. Whereas lipid A is known to bind to the Toll-like receptor 4 (TLR4)-myeloid differentiation factor 2 (MD2) complex, the role of the O-antigen remains unclear. Here we report a novel molecular interaction between dendritic cell-associated C-type lectin-2 (Dectin-2) and mannosylated O-antigen found in a human opportunistic pathogen, Hafnia alvei PCM 1223, which has a repeating unit of [-Man-α1,3-Man-α1,2-Man-α1,2-Man-α1,2-Man-α1,3-]. H. alvei LPS induced higher levels of TNFα and IL-10 from mouse bone marrow-derived dendritic cells (BM-DCs), when compared with Salmonella enterica O66 LPS, which has a repeat of [-Gal-α1,6-Gal-α1,4-[Glc-β1,3]GalNAc-α1,3-GalNAc-β1,3-]. In a cell-based reporter assay, Dectin-2 was shown to recognize H. alvei LPS. This binding was inhibited by mannosidase treatment of H. alvei LPS and by mutations in the carbohydrate-binding domain of Dectin-2, demonstrating that H. alvei LPS is a novel glycan ligand of Dectin-2. The enhanced cytokine production by H. alvei LPS was Dectin-2-dependent, because Dectin-2 knock-out BM-DCs failed to do so. This receptor cross-talk between Dectin-2 and TLR4 involved events including spleen tyrosine kinase (Syk) activation and receptor juxtaposition. Furthermore, another mannosylated LPS from Escherichia coli O9a also bound to Dectin-2 and augmented TLR4 activation of BM-DCs. Taken together, these data indicate that mannosylated O-antigens from several Gram-negative bacteria augment TLR4 responses through interaction with Dectin-2.

K19 capsular polysaccharide of Acinetobacter baumannii is produced via a Wzy polymerase encoded in a small genomic island rather than the KL19 capsule gene cluster

Polymerization of the oligosaccharides (K units) of complex capsular polysaccharides (CPSs) requires a Wzy polymerase, which is usually encoded in the gene cluster that directs K unit synthesis. Here, a gene cluster at the Acinetobacter K locus (KL) that lacks a wzy gene, KL19, was found in Acinetobacter baumannii ST111 isolates 28 and RBH2 recovered from hospitals in the Russian Federation and Australia, respectively. However, these isolates produced long-chain capsule, and a wzy gene was found in a 6.1 kb genomic island (GI) located adjacent to the cpn60 gene. The GI also includes an acetyltransferase gene, atr25, which is interrupted by an insertion sequence (IS) in RBH2. The capsule structure from both strains was →3)-α-d-GalpNAc-(1→4)-α-d-GalpNAcA-(1→3)-β-d-QuipNAc4NAc-(1→, determined using NMR spectroscopy. Biosynthesis of the K unit was inferred to be initiated with QuiNAc4NAc, and hence the Wzy forms the β-(1→3) linkage between QuipNAc4NAc and GalpNAc. The GalpNAc residue is 6-O-acetylated in isolate 28 only, showing that atr25 is responsible for this acetylation. The same GI with or without an IS in atr25 was found in draft genomes of other KL19 isolates, as well as ones carrying a closely related CPS gene cluster, KL39, which differs from KL19 only in a gene for an acyltransferase in the QuiNAc4NR synthesis pathway. Isolates carrying a KL1 variant with the wzy and atr genes each interrupted by an ISAba125 also have this GI. To our knowledge, this study is the first report of genes involved in capsule biosynthesis normally found at the KL located elsewhere in A. baumannii genomes.

O antigen of FranconibacterpulverisG3872 (O1) is a 4-deoxy-d-arabino-hexose-containing polysaccharide synthesized by the ABC-transporter-dependent pathway

Franconibacter (Enterobacter, Cronobacter) pulveris bacteria share several typical characteristics with, and hence pose a challenge for the detection of, Cronobacter sakazakii, an emerging opportunistic pathogen, which can cause severe infections in neonates. A structurally variable O-specific polysaccharide (OPS) called O antigen provides the major basis for the typing of Gram-negative bacteria. We investigated the structure and genetics of the O antigen of F. pulveris G3872 (designated O1). An OPS was isolated by mild alkaline degradation of the LPS, whereas the same polysaccharide and its oligosaccharide fragments were obtained by mild acid degradation. Studies by sugar analysis and NMR spectroscopy showed that the OPS contained d-ribose, l-rhamnose (l-Rha) and a rarely occurring monosaccharide 4-deoxy-d-arabino-hexose, and the OPS structure was established. The O-antigen gene cluster of F. pulveris G3872 between JUMPStart and gnd genes includes putative genes for glycosyltransferases, ATP-binding cassette (ABC)-transporter genes wzm and wzt, and genes for the synthesis of l-Rha, but no genes for the synthesis of 4-deoxy-d-arabino-hexose. A mutation test with the wzm gene confirmed that the OPS is synthesized and exported by the ABC-transporter-dependent pathway. A trifunctional transferase was suggested to catalyse formation of two glycosidic linkages and add a methyl group to the non-reducing end of the OPS to terminate the chain elongation. A carbohydrate-binding module that presumably recognizes the terminal methyl-modified monosaccharide was found at the C-terminus of Wzt. Primers specific for F. pulveris G3872 were designed based on the wzm gene, which has potential to be used for identification and detection of the O1 serogroup.

Structure and gene cluster of the O-antigen of Escherichia coli O133

The O-specific polysaccharide (O-antigen) of Escherichia coli O133 was obtained by mild acid hydrolysis of the lipopolysaccharide of E. coli O133. The structure of the hexasaccharide repeating unit of the polysaccharide was elucidated by (1)H and (13)C NMR spectroscopy, including a two-dimensional (1)H-(1)H ROESY experiment: Functions of genes in the O-antigen gene cluster were putatively identified by comparison with sequences in the available databases and, particularly, an encoded predicted multifunctional glycosyltransferase was assigned to three α-l-rhamnosidic linkages.

Structure and gene cluster of the O-antigen of Escherichia coli O156 containing a pyruvic acid acetal

The lipopolysaccharide of Escherichia coli O156 was degraded under mild acidic and alkaline conditions and the resulting polysaccharides were studied by sugar analysis and (1)H and (13)C NMR spectroscopy. The following structure of the pentasaccharide repeating unit of the O-polysaccharide was established: where Rpyr indicates R-configurated pyruvic acid acetal. Minor O-acetyl groups also were present and tentatively localized on the Gal residues. The gene cluster for biosynthesis of the O-antigen of E. coli O156 was analyzed and shown to be consistent with the O-polysaccharide structure.