Synthesis of lipopolysaccharide O side chains by Pseudomonas aeruginosa PAO1 requires the enzyme phosphomannomutase.

We have cloned a lipopolysaccharide (LPS) biosynthetic gene from Pseudomonas aeruginosa PAO1 that complements the defect in the production and incorporation of LPS O side chains in the LPS-rough strain AK1012. This gene was characterized by pulsed-field gel electrophoresis, deletion and restriction mapping of the cloned DNA, and biochemical analysis of the protein product. The cloned DNA was found to map to the 7-to-11-min region of the P. aeruginosa chromosome, and the gene needed for complementation of the LPS-rough phenotype was contained on a 2.6-kb HindIII-SacI fragment. This same size restriction fragment contains the alginate gene algC, which encodes the enzyme phosphomannomutase (PMM) and also maps to this region of the P. aeruginosa chromosome. The LPS-rough strain AK1012 was deficient in PMM activity, and this activity was restored to parental levels when the cloned gene was transferred to strain AK1012. In addition, the cloned gene could complement the PMM deficiency in the algC mutant strain 8858, and the cloned algC gene could restore the LPS-smooth phenotype to strain AK1012. These results indicate that the gene we have cloned is equivalent to the alginate gene algC. We designate this gene pmm to emphasize that it encodes the enzyme PMM, which has been shown to be essential for alginate production, and we demonstrate that PMM activity is required for the LPS-smooth phenotype in P. aeruginosa PAO1.     

Presence or absence of lipopolysaccharide O antigens affects type III secretion by Pseudomonas aeruginosa

Pseudomonas aeruginosa is one of the major causative agents of mortality and morbidity in hospitalized patients due to a multiplicity of virulence factors associated with both chronic and acute infections. Acute P. aeruginosa infection is primarily mediated by planktonic bacteria expressing the type III secretion system (TTSS), a surface-attached needle-like complex that injects cytotoxins directly into eukaryotic cells, causing cellular damage. Lipopolysaccharide (LPS) is the principal surface-associated virulence factor of P. aeruginosa. This molecule is known to undergo structural modification (primarily alterations in the A- and B-band O antigen) in response to changes in the mode of life (e.g., from biofilm to planktonic). Given that LPS exhibits structural plasticity, we hypothesized that the presence of LPS lacking O antigen would facilitate eukaryotic intoxication and that a correlation between the LPS O-antigen serotype and TTSS-mediated cytotoxicity would exist. Therefore, strain PAO1 (A+ B+ O-antigen serotype) and isogenic mutants with specific O-antigen defects (A+ B-, A- B+, and A- B-) were examined for TTSS expression and cytotoxicity. A strong association existed in vitro between the absence of the large, structured B-band O antigen and increased cytotoxicity of these strains. In vivo, all three LPS mutant strains demonstrated significantly increased lung injury compared to PAO1. Clinical strains lacking the B-band O antigen also demonstrated increased TTSS secretion. These results suggest the existence of a cooperative association between LPS O-antigen structure and the TTSS in both laboratory and clinical isolates of P. aeruginosa.     

Synthesis of Pseudomonas aeruginosa lipopolysaccharide core antigens containing 7-O-carbamoyl-L-glycero-alpha-D-manno-heptopyranosyl residues.

The monosaccharide allyl 7-O-carbamoyl-L-glycero-alpha-D-manno- heptopyranoside, the reducing disaccharide 7-O-carbamoyl-L-glycero-alpha-D- manno-heptopyranosyl-(1-->3)-L-glycero-D-manno-heptopyranose and the disaccharides allyl 7-O-carbamoyl-L-glycero-alpha-D-manno-heptopyranosyl-(1-->3)-L-glycero- beta- and alpha-D-manno-heptopyranoside were prepared in good yields. The 7-O-carbamoyl substituent was regioselectively introduced via NH3-NH4HCO3 treatment of a 6,7-O-carbonate group. Glycosylation steps were carried out using Me3SiOTf or BF3.Et2O promoted coupling of allyl alcohol with trichloroacetimidate or fluoride glycosyl donors, respectively. The deprotected allyl glycosides were reacted with cysteamine to afford spacer glycosides which were subsequently linked to bovine serum albumin. The artificial antigens which are related to the dephosphorylated heptose region of the lipopolysaccharide core region from Pseudomonas aeruginosa classified into RNA group I may be used for the characterization of monoclonal antibodies directed against inner core epitopes of human-pathogenic Pseudomonas species.     

Somatic antigens of Pseudomonas aeruginosa. The structure of O-specific polysaccharide chains of P. aeruginosa O:3a, b and O:3a, d lipopolysaccharides

On mild acid degradation of Pseudomonas aeruginosa O:3a,b and O:3a,d lipopolysaccharides O-specific polysaccharides were isolated. Both polysaccharides were found to contain 2-acetamido-2,6-dideoxy-D-galactose, identified as fucosamine hydrochloride formed after hydrolysis with a very low yield. The other two components of the trisaccharide repeating unit, 2,3-diacetamido-2,3-dideoxy-D-mannuronic acid and 2,3-(1-acetyl-2-methyl-2-imidazolino-5,4)-2,3-dideoxy-D-mannuronic acid, were identified without isolation in their free state directly in the course of structural investigation of the polysaccharides. Both these monosaccharides have never before been found in nature. Solvolysis of either O:3a,b or O:3a,d polysaccharides with liquid hydrogen fluoride resulted in the formation of the same trisaccharide, N-acetylfucosamine residue being the reducing end. The structure of this trisaccharide, which is the repeating unit of both polysaccharides, was deduced from the results of successive chemical modifications and 13C-nuclear magnetic resonance spectra recorded for every oligosaccharide formed. As a result, the acidic diaminosugars were converted into 2,3-diacetamido-2,3-dideoxy-D-mannose indistinguishable from authentic sample. The O-specific polysaccharides O:3a,b and O:3a,d differed in the configuration of the glycosidic bond of N-acetylfucosamine residue only and had the following structures: leads to 4)DManImU(beta 1 leads to 4)DMan(NAc)2U (beta 1 leads to 3)DFucNAc(beta 1- leads to 4)DManImU(beta 1 leads to 4)DMan(NAc)2U (beta 1 leads to 3)DFucNAc(alpha 1- where DManImU = 2.3-(1-acetyl-2-methyl-2-imidazolino-5,4)-2, 3-dideoxy-D-mannuronic acid, DMan(NAc)2U = 2,3-diacetamido-2,3-dideoxy-D-mannuronic acid, DFucNAc = 2-acetamido-2,6-dideoxy-D-galactose. The structures established were in agreement with optical rotations and assignments of all the signals in the 13C-nuclear magnetic resonance spectra of the polysaccharides.     

Somatic antigens of Pseudomonas aeruginosa. The structure of O-specific polysaccharide chains of P. aeruginosa O10 (Lányi) lipopolysaccharides

Mild acid degradation of lipopolysaccharides from Pseudomonas aeruginosa O10a and O10a,b (Lányi classification) resulted in O-specific polysaccharides built up of trisaccharide repeating units containing 2-acetamido-2,6-dideoxy-D-glucose (N-acetylquinovosamine, DQuiNAc), 2-acetamido-2,6-dideoxy-D-galactose (N-acetylfucosamine, DFucNAc), and 5-acetamido-3,5,7,9-tetradeoxy-7-[(R)-3-hydroxybutyramido] -L-glycero-L-manno-nonulosonic acid. The latter is a di-N-acyl derivative of a new sialic-acid-like sugar which was called by us pseudaminic acid (PseN2). A 3-hydroxybutyric acid residue was also found in natural carbohydrates for the first time. In the O10a,b polysaccharide pseudaminic acid carried an O-acetyl group at position 4. For selective cleavage of the O10a polysaccharide, solvolysis with hydrogen fluoride was employed which, owing to the relatively high stability of the glycosidic linkage of pseudaminic acid, led to the disaccharide with this sugar on the non-reducing terminus. Performing the solvolysis in methanol afforded the methyl glycoside of this disaccharide which proved to be more advantageous for further analysis. Carboxyl-reduction made the glycosidic linkage of pseudaminic acid extremely labile, and mild acid hydrolysis of the carboxyl-reduced 010a polysaccharide afforded the trisaccharide with a ketose derivative on the reducing terminus. Establishing the structure of the oligosaccharide fragments obtained and interpreting the 13C nuclear resonance spectra of the polysaccharides allowed to determine the following structure for their repeating units: (formula: see text) In the polysaccharides the N-acetylquinovosamine residue is attached not to pseudaminic acid itself, but to its N-acyl substituent, 3-hydroxybutyryl group, and thus the monomers are linked via both glycosidic and amidic linkages.     

Somatic antigens of Pseudomonas aeruginosa. The structure of the O-specific polysaccharide chain of the lipopolysaccharide from P. aeruginosa O13 (Lányi)

The O-specific polysaccharide, obtained on mild acid degradation of lipopolysaccharide of Pseudomonas aeruginosa O13 (Lányi classification), is built up of trisaccharide repeating units involving 2-acetamidino-2,6-dideoxy-D-glucose (N-acetyl-D-quinovosamine, D-QuiNAc), 2-acetamidino-2,6-dideoxy-L-galactose (L-fucosacetamidine, L-FucAm), and a new sialic-acid-like sugar, 5,7-diacetamido-3,5,7,9-tetradeoxy-D-glycero-L-galacto-nonuloso n ic acid (Sug), and thus contains simultaneously both acidic and basic functions. Cleavage of the polysaccharide with hydrogen fluoride in methanol revealed the high stability of the glycosidic linkage of the ulosonic acid and afforded methyl glycosides of a disaccharide and a trisaccharide. The structures of the new ulosonic acid and acetamidino group were established by analysing the oligosaccharide fragments by 1H, 13C nuclear magnetic resonance spectrometry, as well as on the basis of their chemical conversions: alkaline hydrolysis of the acetamidino group into acetamido group, reductive deamination with lithium borohydride into the ethylamino group and acetylation with acetic anhydride in pyridine accompanied by intramolecular acylation of the acetamidino function by the ulosonic acid to form a six-membered lactam ring. Identification of the oligosaccharide fragments and comparative analysis of the 13C nuclear magnetic resonance spectra of the oligosaccharides and polysaccharide revealed the following structure of the repeating unit: ----3)D-QuiNAcp(alpha 1----3)Sugp(alpha 2----3)L-FucAmp(alpha 1----.     

Antibodies against the common polysaccharide and protein protective antigens of Pseudomonas aeruginosa in normal blood donors.

Screening of normal plasma obtained from 172 blood donors from the Helsinki area and from 46 blood donors from the Moscow area was performed in order to reveal 'natural' antibodies to the common polysaccharide (rhamnan) and protein antigens of P. aeruginosa. Antibodies were detected by ELISA. Among blood donors from the Helsinki area high titres of antibodies to the protein antigens were detected in 42 active blood donors (24.4%) and very high titres in nine (5.3%) highly-active blood donors, whereas in the Moscow area in 15 (34.9%) and in one case (2.3%), respectively. Antibodies to the common polysaccharide antigen were determined in the Helsinki area in 23 active blood donors (13.4%) and in one (0.5%) highly active blood donor, whereas in the Moscow area in four active blood donors (8.6%). The plasma contained both polysaccharide and anti-protein antibodies. The level of antibodies to the polysaccharide antigen was lower than the level of antibodies to the protein antigens. There was no statistically significant difference between the corresponding values of blood donor groups from the Helsinki and Moscow areas.     

The effect of lipopolysaccharide composition on the ultrastructure of Pseudomonas aeruginosa.

The surface structure of Pseudomonas aeruginosa PACl and PAClR and of lipopolysaccharide-defective mutants derived from them was studied by negative-staining and thin-section electron microscopy and compared with that of a rough mutant with wild-type lipopolysaccharide. The rough mutant and the parent strains had fairly smooth outer layers. Negatively stained preparations of all the mutants lacking polymerized O-antigenic sidechains, including a semi-rough mutant, showed numerous blebs on the surface. In thin sections of these mutants occasional extrusions from the surface were seen. They appeared to consist of material extruded from the outer membrane, but there was no evidence to suggest they were complete unit membranes. Polymerized O-antigenic side-chains in the lipopolysaccharide appear to be required to produce the wild-type appearance of the outer membrane in P. aeruginosa.     

Computer simulation of the rough lipopolysaccharide membrane of Pseudomonas aeruginosa.

Lipopolysaccharides (LPSs) form the major constituent of the outer membrane of Gram-negative bacteria, and are believed to play a key role in processes that govern microbial metal binding, microbial adsorption to mineral surfaces, and microbe-mediated oxidation/reduction reactions at the bacterial exterior surface. A computational modeling capability is being developed for the study of geochemical reactions at the outer bacterial envelope of Gram-negative bacteria. A molecular model for the rough LPS of Pseudomonas aeruginosa has been designed based on experimentally determined structural information. An electrostatic model was developed based on Hartree-Fock SCF calculations of the complete LPS molecule to obtain partial atomic charges. The exterior of the bacterial membrane was assembled by replication of a single LPS molecule and a single phospholipid molecule. Molecular dynamics simulations of the rough LPS membrane of P. aeruginosa were carried out and trajectories were analyzed for the energetic and structural factors that determine the role of LPS in processes at the cell surface.     

Somatic antigens of Pseudomonas aeruginosa. The structure of O-specific polysaccharide chains of the lipopolysaccharides from P. aeruginosa O5 (Lányi) and immunotype 6 (Fisher)

Lipopolysaccharides were isolated from dry bacterial cells of Pseudomonas aeruginosa O5a,b,c, O5a,b,d, O5a,d (Lányi classification) and immunotype 6 (Fisher classification) by the Westphal procedure. Their polysaccharide chains were built up of trisaccharide repeating units containing D-xylose, 2-acetamido-2,6-dideoxy-D-galactose and a new sialic acid-like sugar, the di-N-acyl derivative of 5,7-diamino-3,5,7,9-tetradeoxy-L-glycero-L-manno-nonulosonic (pseudaminic) acid. Formyl, acetyl and (R)-3-hydroxybutyryl groups were identified as the N-acyl substituents of the last monosaccharide; O5a,b,c and O5a,b,d lipopolysaccharides also contained O-acetyl groups. The glycosidic linkage of pseudaminic acid was extremely labile towards acids, and mild acid degradation of the lipopolysaccharides produced, instead of the O-specific polysaccharides, their trisaccharide fragments with pseudaminic acid at the reducing terminus. Similar degradation of immunotype 6 lipopolysaccharides, followed by oxidation with sodium metaperiodate, resulted in a disaccharide fragment due to destruction of xylose. In contrast the glycosidic linkage of pseudaminic acid proved to be more stable towards treatment with hydrogen fluoride than those of xylose and N-acetylfucosamine. As a result, solvolysis of immunotype 6 lipopolysaccharide with hydrogen fluoride in methanol gave methyl glycosides of a disaccharide and a trisaccharide with pseudaminic acid at the non-reducing terminus. Mild acid hydrolysis of these oligosides afforded free 5-N-acetyl-7-N-formylpseudaminic acid, which was identified by the 1H ande 13C nuclear magnetic resonance data, as well as by the mass spectrum of the corresponding fully methylated aldonic acid. As a result of the identification of all oligosaccharides obtained and comparative analysis of the 13C nuclear magnetic resonance spectra of the oligosaccharides and lipopolysaccharides the following structures were established for the repeating units of the polysaccharide chains of the lipopolysaccharides: (Formula: see text) where D-Xyl = D-xylose, D-FucNAc = 2-acetamido-2,6-dideoxy-D-galactose, Pse5N7NFm = 5-amino-3,5,7,9-tetradeoxy-7-formamido-L-glycero-L-manno-nonulosonic+ ++ acid (7-N-formylpseudaminic acid). All the polysaccharides have an identical carbohydrate skeleton and differ from each other by the acyl substituent at N-5 of pseudaminic acid [acetyl or (R)-3-hydroxybutyryl group] or by the presence or absence of the O-acetyl group at position 4 of N-acetylfucosamine. The data obtained account properly for the O specificity of the studied P. aeruginosa strains.     

Somatic antigens of Pseudomonas aeruginosa. The structure of O-specific polysaccharide chains of lipopolysaccharides of P. aeruginosa O3 (Lányi), O25 (Wokatsch) and Fisher immunotypes 3 and 7

O-specific polysaccharides, obtained on mild acid degradation of lipopolysacchrides of the serologically related strains Pseudomonas aeruginosa O3 (Lányi classification), O25 (Wokatsch classification) and immunotypes 3 and 7 (Fisher classification), are built up of trisaccharide repeating units involving 2-acetamido-2,6-dideoxy-D-galactose (N-acetyl-D-fucosamine), 2,3-diacetamido-2,3-dideoxy-D-mannuronic acid or 2,3-diacetamido-2,3-dideoxy-L-guluronic acid and 3-acetamidino-2-acetamido-2,3-dideoxy-D-mannuronic acid or 3-acetamidino-2-acetamido-2,3-dideoxy-L-guluronic acid. Lányi O3(a),3d,3f and Wokatsch O25 polysaccharides contain also O-acetyl groups. On the basis of solvolysis with anhydrous hydrogen fluoride, resulting in trisaccharide fragments with N-acetylfucosamine residue at the reducing terminus, chemical modifications of the acetamidino group (alkaline hydrolysis to the acetamido group or reductive deamination to the ethylamino group), as well as analysis by 1H-NMR (including nuclear Overhauser effect experiments) and 13C-NMR spectroscopy, and fast-atom bombardment mass spectrometry, it was concluded that the repeating units of the polysaccharides have the following structures: (Formula: see text) where HexNAcAmA = alpha-L-GulNAcAmA (approximately 70%) or beta-D-ManNacAMA (approximately 30%). Lányi O3(a),3d,3f polysaccharide involves two types of repeating units, which differ from each other only in the configuration at C-5 of the 3-acetamidino-2-acetamido-2,3-dideoxyuronic acid residue. Lányi O3(a),3c,O3a,3d,3e and Fisher immunotypes 3 and 7 polysaccharides contain, together with the major repeating units shown above, a small proportion of units in which the derivative of alpha-L-guluronic acid is replaced by the corresponding beta-D-manno isomer. The data obtained provide the opportunity to substantiate the serological interrelations between these strains of P. aeruginosa by the presence in the O-specific polysaccharides of common monosaccharides or disaccharide fragments. The distinctions between them stem from the presence or absence of the O-acetyl group, a different configuration of the glycosidic linkage of the N-acetylfucosamine residue and/or a different configuration at C-5 of one or both derivatives of diaminouronic acids.     

Structural characterization of the outer core and the O-chain linkage region of lipopolysaccharide from Pseudomonas aeruginosa serotype O5.

The point of attachment of the O-chain in the outer core region of Pseudomonas aeruginosa serotype O5 lipopolysaccharide (LPS) was determined following a detailed analysis of the extended core oligosaccharide, containing one trisaccharide O-chain repeating unit, present in both the wild-type strain PAO1 and O-chain deficient mutant strains AK1401 and PAO-rfc. The structure of the extended core oligosaccharide was determined by various mass spectrometric methods as well as one-dimensional and two-dimensional NMR spectroscopy. Furthermore, the one-dimensional analogues of NOESY and TOCSY experiments were applied to confirm the structure of the outer core region in the O-chain polysaccharide. In both the extended core oligosaccharide and the core of the smooth LPS, a loss of one of the beta-glucosyl residues and the translocation of the alpha-rhamnosyl residue, followed by the attachment of the first O-chain repeating unit was observed. This process is complicated and could involve two distinct rhamnosyltransferases, one with alpha-1, 6-linkage specificity and another with alpha-1,3-linkage specificity. It is also plausible that an alpha-1,3 rhamnosyltransferase facilitates the addition of the 'new' alpha-rhamnosyl residue that will act as a receptor for the attachment of the single O-antigen repeating unit in the LPS of the semi-rough mutant. The 2-amino-2-deoxy-fucosyl residue of the first O-chain repeating unit directly attached to the core was found to have a beta-anomeric configuration instead of an alpha configuration, characteristic for this residue as a component of the O-chain polysaccharide. The results of this study provide the first example of the mechanistic implications of the structure of the outer core region in a fully assembled O-chain containing LPS, differing from the O-chain deficient rough LPS.     

Heterogeneity of lipopolysaccharides from Pseudomonas aeruginosa: analysis of lipopolysaccharide chain length.

Lipopolysaccharide (LPS) from smooth strains of Pseudomonas aeruginosa 503, PAZ1, PAO1715, PAO1716, and Z61 was fractionated by gel filtration chromatography. LPS samples from the first four strains, all PAO1 derivatives, separated into three major size populations, whereas LPS from strain Z61, a Pac K799/WT mutant strain, separated into two size populations. When column fractions were applied to sodium dodecyl sulfate-polyacrylamide gels in their order of elution, molecules of decreasing size were resolved, and the ladder of molecules with different-length O antigens formed a diagonal across the gel. The LPS from the PAO1 derivatives contained two distinct sets of bands, distinguished on the gels as two sets of diagonals. The set of bands with the faster mobility, the B bands, was found in column fractions comprising the three major amino sugar-containing peaks. In the sample from strain 503, a fourth minor peak which contained B bands was resolved. The slower-moving set of bands, the A bands, were recovered in a minor peak. LPS from strain Z61 contained only one set of bands, with the higher-molecular-weight molecules eluting from the column in a volume similar to that of the B bands of the PAO1 strains. Analysis of the fractions of LPS from all strains indicated that less than 8% of the LPS molecules had a long, attached O antigen. Analysis of the peak that contained mainly A bands indicated a lack of reactive amino sugar and phosphate, although heptose and 2-keto-3-deoxyoctulosonic acid were detected. Reaction of isolated fractions with monoclonal antibody specific for the PAO1 O-antigen side chain indicated that only the B bands from the PAO1 strains were antigenically reactive. The bands from strain Z61 showed no reactivity. The data suggest that the A and B bands from the PAO1 strains are antigenically distinct. We propose that PAO1 strains synthesize two types of molecules that are antigenically different.