Several uses for isobutyric Acid-ammonium hydroxide solvent in endotoxin analysis

Structural and biological characteristics of different forms of V. filiformis lipid A: use of MS to highlight structural discrepancies

Vitreoscilla filiformis is a Gram-negative bacterium isolated from spa waters and described for its beneficial effects on the skin. We characterized the detailed structure of its lipopolysaccharide (LPS) lipid A moiety, an active component of the bacterium that contributes to the observed skin activation properties. Two different batches differing in postculture cell recovery were tested. Chemical analyses and mass spectra, obtained before and after mild-alkali treatments, revealed that these lipids A share the common bisphosphorylated β-(1→6)-linked d-glucosamine disaccharide with hydroxydecanoic acid in an amide linkage. Short-chain FAs, hydroxydecanoic and dodecanoic acid, were found in a 2:1 ratio. The two lipid A structures differed by the relative amount of the hexa-acyl molecular species and phosphoethanolamine substitution of the phosphate groups. The two V. filiformis LPS batches induced variable interleukin-6 and TNF-α secretion by stimulated myelomonocytic THP-1 cells, without any difference in reactive oxygen species production or activation of caspase 3/7. Other different well-known highly purified LPS samples were characterized structurally and used as standards. The structural data obtained in this work explain the low inflammatory response observed for V. filiformis LPS and the previously demonstrated beneficial effects on the skin.

Micromethods for Isolation and Structural Characterization of Lipid A, and Polysaccharide Regions of Bacterial Lipopolysaccharides

Lipopolysaccharides (LPS) are major components of the external membrane of most Gram-negative bacteria, providing them with an effective permeability barrier. They are essentially composed of a hydrophilic polysaccharide region (PS) linked to a hydrophobic one, termed lipid A. The LPS polysaccharide moiety is divided into the core oligosaccharide (OS) and O-chain repetitive elements. Depending on their individual variable fine structures, LPS may be potent immunomodulators. The lipid A structure is a key determinant for LPS activity. However, the presence of the core region, or at least of the highly charged 3-deoxy-d-manno-oct-2-ulosonic acid molecules, is also important for preserving the native lipid A conformation within individual LPS molecules. We describe herein four rapid and practical micromethods for LPS, lipid A, and core OS structural analyses. The first method allows the direct isolation of lipid A from whole bacteria cell mass; the second describes conditions for the sequential release of fatty acids enabling the characterization of their substitution position in the lipid A backbone, to be determined by matrix-assisted laser desorption/ionization mass spectrometry (MALDI-MS). The third one is a microscale procedure for the mass spectra screening of LPS, lipid A, and PS using triethylamine and citric acid. The fourth method is a chromatography procedure for Rough-type LPS on thin-layer-chromatography. These methods were developed to be coupled to mass-spectrometry (e.g., MALDI-MS) but can also be used with other analytical techniques (e.g., chromatography). Examples are given with reference to two major human pathogens: Bordetella pertussis and Pseudomonas aeruginosa; to one porcine pathogen: Actinobacillus pleuropneumoniae; and to commercial samples of Salmonella Minnesota Re595 LPS.

Use of mass spectrometry to compare three O-chain-linked and free lipopolysaccharide cores: differences found in Bordetella parapertussis

Plasma desorption mass spectrometry and matrix-assisted laser desorption/ionization mass spectrometry methods were used to investigate the molecular differences between lipopolysaccharide free core molecules and core molecules substituted by O-chains in Bordetella parapertussis, Salmonella ohio, and Escherichia coli 0119. The B. parapertussis analysis indicated a difference in mass of 569 amu corresponding to 3 distal sugars comprising terminal residues of heptose, galactosaminuronic acid, and, N-acetyl-N-methylfucosamine, a result supported by evidence from NMR and serology. No differences were evident in the analyses of cores in either S. ohio or E. coli O119, although the first O-chain unit carried by S. ohio core lacked a terminal glucose present in the residual O-chain repeating units.

CD14/LPS receptor exhibits lectin-like properties

We had previously shown that the specific binding of endotoxin (lipopolysaccharide, LPS) to human monocytes in the presence of serum was mediated by the polysaccharide moiety of the LPS molecule. CD14 has been identified as the main receptor for endotoxin on monocytes/macrophages. In the present report we demonstrate that the CD14 molecule exhibits lectin-like properties. Anti-CD14 monoclonal antibodies inhibited the binding of [3H]-radiolabeled Neisseria meningitidis LPS as efficiently as the homologous unlabeled LPS. Rough Escherichia coli LPS (Rc- and Re-types) could also inhibit the binding of [3H]-LPS to a similar extent, whereas lipid A had no or very weak inhibitory activity. This suggests a major contribution of the inner-core region within the LPS and particularly the Kdo sugars. The lectin-like nature of CD14 was assessed with polyanionic sugars as well as with uncharged polysaccharides. The relative efficiencies in competition were dextran sulfate > fucoidan > mannan > polygalacturonic acid = heparan sulfate ≥ heparin ≥ chondroitin sulfate. Candida albicans phospholipomannan was far more active in the competition experiment than the mannan, indicating that, besides the osidic residues, anionic charges and/or fatty acids may contribute to the interaction with the CD14 molecule. Binding of polysaccharide to CD14 was not sufficient to trigger TNFα and IL-6 production since phospholipomannan and dextran sulfate were unable to induce cytokine release. Taken together, these results demonstrate that the binding of [3H]-LPS to CD14 involves the contribution of sugars and suggest that the signals for cytokine production require additional interactions.

Structural variability and originality of the Bordetella endotoxins

Structural studies of Bordetella endotoxins (LPSs) have revealed remarkable differences: (i) between their LPSs and those of other bacterial pathogens; (ii) among the LPSs of the seven identified Bordetella species; and (iii) among the LPSs of some Bordetella strains. The lipid As have the `classical' bisphosphorylated diglucosamine backbone but tend to have fewer and species-specific fatty acid components compared to those of other genera. Nevertheless, three strains of B. bronchiseptica have at least three different fatty acid distributions; however, the recently identified B. hinzii and B. trematum LPSs had identical lipid A structures. The B. pertussis core is a dodecasaccharide multi-branched structure bearing amino and carboxylic groups. Another unusual feature is the presence of free amino sugars in the central core region and a complex distal trisaccharide unit containing five amino groups of which four are acetylated and one is methylated. The B. pertussis LPS does not have O-chains and that of B. trematum had only a single O-unit, unlike the LPSs of all the other species of the smooth-type. The O-chain-free cores of non- B. pertussis LPSs were always built on the B. pertussis core model but most were species-specifically incomplete. The LPS structures of three B. bronchiseptica strains were found to be different from each other. The O-chains of B. bronchiseptica and B. parapertussis were almost identical and had some features in common with B. hinzii O-chain. Serological analyses are consistent with the determined LPS structures.

Comparison of lipopolysaccharide structures of Bordetella pertussis clinical isolates from pre- and post-vaccine era

Endotoxins are lipopolysaccharides (LPS), and major constituents of the outer membrane of Gram-negative bacteria. Bordetella pertussis LPS were the only major antigens, of this agent of whooping-cough, that were not yet analyzed on isolates from the pre- and post-vaccination era. We compared here the LPS structures of four clinical isolates with that of the vaccine strain BP 1414. All physico-chemical analyses, including SDS-PAGE, TLC, and different MALDI mass spectrometry approaches were convergent. They helped demonstrating that, on the contrary to some other B. pertussis major antigens, no modification occurred in the dodecasaccharide core structure, as well as in the whole LPS molecules. These results are rendering these major antigens good potential vaccine components. Molecular modeling of this conserved LPS structure also confirmed the conclusions of previous experiments leading to the production of anti-LPS monoclonal antibodies and defining the main epitopes of these major antigens.

Structural characterization of bacterial lipopolysaccharides with mass spectrometry and on- and off-line separation techniques

The focus of this review is the application of mass spectrometry to the structural characterization of bacterial lipopolysaccharides (LPSs), also referred to as "endotoxins," because they elicit the strong immune response in infected organisms. Recently, a wide variety of MS-based applications have been implemented to the structure elucidation of LPS. Methodological improvements, as well as on- and off-line separation procedures, proved the versatility of mass spectrometry to study complex LPS mixtures. Special attention is given in the review to the tandem mass spectrometric methods and protocols for the analyses of lipid A, the endotoxic principle of LPS. We compare and evaluate the different ionization techniques (MALDI, ESI) in view of their use in intact R- and S-type LPS and lipid A studies. Methods for sample preparation of LPS prior to mass spectrometric analysis are also described. The direct identification of intrinsic heterogeneities of most intact LPS and lipid A preparations is a particular challenge, for which separation techniques (e.g., TLC, slab-PAGE, CE, GC, HPLC) combined with mass spectrometry are often necessary. A brief summary of these combined methodologies to profile LPS molecular species is provided.

Roles of predicted glycosyltransferases in the biosynthesis of the Rhizobium etli CE3 O antigen

The Rhizobium etli CE3 O antigen is a fixed-length heteropolymer. The genetic regions required for its synthesis have been identified, and the nucleotide sequences are known. The structure of the O antigen has been determined, but the roles of specific genes in synthesizing this structure are relatively unclear. Within the known O-antigen genetic clusters of this strain, nine open reading frames (ORFs) were found to contain a conserved glycosyltransferase domain. Each ORF was mutated, and the resulting mutant lipopolysaccharide (LPS) was analyzed. Tricine SDS-PAGE revealed stepwise truncations of the O antigen that were consistent with differences in mutant LPS sugar compositions and reactivity with O-antigen-specific monoclonal antibodies. Based on these results and current theories of O-antigen synthesis, specific roles were deduced for each of the nine glycosyltransferases, and a model for biosynthesis of the R. etli CE3 O antigen was proposed. In this model, O-antigen biosynthesis is initiated with the addition of N-acetyl-quinovosamine-phosphate (QuiNAc-P) to bactoprenol-phosphate by glycosyltransferase WreU. Glycosyltransferases WreG, WreE, WreS, and WreT would each act once to attach mannose, fucose, a second fucose, and 3-O-methyl-6-deoxytalose (3OMe6dTal), respectively. WreH would then catalyze the addition of methyl glucuronate (MeGlcA) to complete the first instance of the O-antigen repeat unit. Four subsequent repeats of this unit composed of fucose, 3OMe6dTal, and MeGlcA would be assembled by a cycle of reactions catalyzed by two additional glycosyltransferases, WreM and WreL, along with WreH. Finally, the O antigen would be capped by attachment of di- or tri-O-methylated fucose as catalyzed by glycosyltransferase WreB.

Development of a new trend conjugate vaccine for the prevention of Klebsiella pneumoniae

Klebsiella pneumoniae is a major cause of nosocomial pneumonia, septicemia and urinary tract infections, especially in newborns, blood cancer patients, and other immunocompromised candidates. The control of K. pneumoniae is a complicated issue due to its tight pathogenesis. Immuno-prophylactic preparations, especially those directed toward the bacterium O-antigen, showed to be the most successful way to prevent the infection incidence. However, all previously proposed preparations were either of limited spectrum or non-maternal, and hence not targeting the main Klebsiella patients. Moreover, all preparations were directed only to prevent the respiratory diseases due to that pathogen. This article addresses the development of a method originally used to purify the non-capsular bacterial-endotoxins, as a new and easy method for vaccine production against K. pneumoniae. The application of this method was preceded by a biotechnological control of capsular polysaccharide production in K. pneumoniae. The new produced natural conjugate between the bacterial O-antigen and its outer membrane proteins was evaluated by physicochemical and immunological methods to investigate its purity, integrity, safety and immunogenicity. It showed to be pure, stable, safe for use, and able to elicit a protective immunoglobulin titer against different Klebsiella infections. This immune-response proved to be transferable to the offspring of the vaccinated experimental rabbits via placenta.

Development of immunization trials against Klebsiella pneumoniae

Klebsiella pneumoniae is the most common cause of nosocomial respiratory tract and premature intensive care infections, and the second most frequent cause of Gram-negative bacteraemia and urinary tract infections. Drug resistant isolates remain an important hospital-acquired bacterial pathogen, add significantly to hospital stays, and are especially problematic in high impact medical areas such as intensive care units. Many investigations worldwide proved the increasing resistance of such pathogen, resulting in an average rate of 1.63 outbreak every year. A variety of preventive measures were applied to reduce such incidences. Immunotherapy and passive immunization researches as well found their way to the treatment of Klebsiella. During the last 40 years, many trials for constructing effective vaccines were followed. This up-to-date review classifies such trials and documents them in a progressive way. A following comment discusses each group benefits and defects.

Micromethods for lipid A isolation and structural characterization

Lipopolysaccharides (LPSs) are major components of the external membrane of Gram-negative bacteria, and act as an effective permeability barrier. They are essentially composed of a hydrophilic polysaccharide region linked to an hydrophobic one, termed lipid A. Depending on their individual variable fine structures, they may be potent immunomodulators. Because of the structural importance and role of lipid A in bacterial pathogenesis, herein we describe two rapid practical micromethods for structural analysis. The first method allows the direct isolation of lipid A from whole bacteria cell mass; the second describes conditions for the sequential release of fatty acids, enabling the determination of their substitution position in the lipid A structure to be determined by matrix-assisted laser desorption/ionization mass spectrometry. Examples are given with reference to two major pathogens: Bordetella pertussis and Pseudomonas aeruginosa.

SOLID2: an antibody array-based life-detector instrument in a Mars Drilling Simulation Experiment (MARTE)

A field prototype of an antibody array-based life-detector instrument, Signs Of LIfe Detector (SOLID2), has been tested in a Mars drilling mission simulation called MARTE (Mars Astrobiology Research and Technology Experiment). As one of the analytical instruments on the MARTE robotic drilling rig, SOLID2 performed automatic sample processing and analysis of ground core samples (0.5 g) with protein microarrays that contained 157 different antibodies. Core samples from different depths (down to 5.5 m) were analyzed, and positive reactions were obtained in antibodies raised against the Gram-negative bacterium Leptospirillum ferrooxidans, a species of the genus Acidithiobacillus (both common microorganisms in the Río Tinto area), and extracts from biofilms and other natural samples from the Río Tinto area. These positive reactions were absent when the samples were previously subjected to a high-temperature treatment, which indicates the biological origin and structural dependency of the antibody-antigen reactions. We conclude that an antibody array-based life-detector instrument like SOLID2 can detect complex biological material, and it should be considered as a potential analytical instrument for future planetary missions that search for life.

A rapid, small-scale procedure for the structural characterization of lipid A applied to Citrobacter and Bordetella strains: discovery of a new structural element

Endotoxins [lipopolysaccharides (LPSs)] are part of the outer cell membrane of Gram-negative bacteria. Their biological activities are associated mainly with the lipid component (lipid A) and even more specifically with discrete aspects of their fine structure. The need for a rapid and small-scale analysis of lipid A motivated us to develop a procedure that combines direct isolation of lipids A from bacterial cells with sequential release of their ester-linked fatty acids by a mild alkali treatment followed by MALDI-MS analysis. This method avoids the multiple-step LPS extraction procedure and lipid A isolation. The whole process can be performed in a working day and applied to lyophilized bacterial samples as small as 1 mg. We illustrate the method by applying it to the analysis of lipids A of three species of Citrobacter that were found to be identical. On the other hand, when applied to two batches of Bordetella bronchiseptica strain 4650, it highlighted the presence, in one of them, of hitherto unreported hexosamine residues substituting the lipid A phosphate groups, possibly a new camouflage opportunity to escape a host defense system.

Simple method for repurification of endotoxins for biological use

A method for obtaining highly purified endotoxin (lipopolysaccharide [LPS]) in a few hours by repurification of commercial or laboratory preparations was devised. It avoids the use of phenol, which is not suitable for phenol-soluble lipopolysaccharides nor for some industrial purposes. Sodium dodecyl sulfate-polyacrylamide gel electrophoresis and matrix-assisted laser desorption ionization mass spectrometry analysis confirmed the integrity of the purified LPSs. The purified products did not activate Toll-like receptor 2 (TLR2), nuclear oligomerization domain 1 (NOD1), or NOD2 but did activate TLR4. Applied to different lipopolysaccharides, the method also improved their mass spectra, thus facilitating their structural analysis.

Microextraction of bacterial lipid A: easy and rapid method for mass spectrometric characterization

Endotoxins (lipopolysaccharides) are the main components of Gram-negative bacterial outer membranes. A quick and simple way to isolate their lipid region (lipid A) directly from whole bacterial cells was devised. This method using hot ammonium-isobutyrate solvent was applied to small quantities of cells and proved to be indispensable when a rapid characterization of lipid A structure by mass spectrometry was required. Biological activities of endotoxins are directly related to the lipid A structures, which vary greatly with cell growth conditions. This method is suitable for rough- and smooth-type bacteria and very efficient for screening variations in lipid A structures. Data are acquired in a few hours and avoid the use of phenol in extraction.

Structure of theBordetella trematumLPS O-chain subunit

Analysis of the O-chain subunit of the lipopolysaccharide (LPS, endotoxin) isolated from Bordetella trematum, a recently identified human pathogen, was undertaken. The polysaccharide (PS) moiety was shown to contain only two O-chain subunits, which differed in the anomeric bond of their first sugar. A trisaccharide fragment resulting from the cleavage of a FucNAc glycosidic bond was isolated after treatment of the PS with anhydrous HF. Nitrous deamination of the LPS led to the release of the following heptasaccharide corresponding to two trisaccharide subunits linked to an anhydromannitol residue. beta-ManNAc3NAmA-(1-4)-beta-ManNAc3NAmA-(1-3)-alpha-FucNAc-(1-4)-beta-ManNAc3NAmA-(1-4)-beta-ManNAc3NAmA-(1-3)-beta-FucNAc-(1-6)-2,5-anhManol.

Structure of bacterial lipopolysaccharides

Bacterial lipopolysaccharides are the major components of the outer surface of Gram-negative bacteria They are often of interest in medicine for their immunomodulatory properties. In small amounts they can be beneficial, but in larger amounts they may cause endotoxic shock. Although they share a common architecture, their structural details exert a strong influence on their activity. These molecules comprise: a lipid moiety, called lipid A, which is considered to be the endotoxic component, a glycosidic part consisting of a core of approximately 10 monosaccharides and, in "smooth-type" lipopolysaccharides, a third region, named O-chain, consisting of repetitive subunits of one to eight monosaccharides responsible for much of the immunospecificity of the bacterial cell.

Structural characterization of the O-chain polysaccharide isolated from Bordetella avium ATCC 5086: variation on a theme(1)

The O-chain polysaccharide (O-PS) of Bordetella avium was isolated from the lipopolysaccharide by mild acid hydrolysis to remove the lipid A, followed by hydrofluorolysis to remove the lipopolysaccharide core oligosaccharide leaving a residual O-PS for structural analysis. High resolution (1)H and (13)C NMR and MALDI studies showed the O-chain to be a polymer composed of 1,4-linked 2-acetamidino-3-[3-hydroxybutanamido]-2,3-dideoxy-beta-D-glucopyranosyluronic acid residues.

Direct microextraction and analysis of rough-type lipopolysaccharides by combined thin-layer chromatography and MALDI mass spectrometry

A rapid method for the microscale extraction of lipopolysaccharides (endotoxins, LPSs) from rough-type Gram-negative bacteria was developed using thin-layer chromatography (TLC) combined with improved conditions for LPS analysis by mass spectrometry. TLC of intact bacteria on silica gel plates in an appropriate solvent selectively extracted and separated their LPS components. The bands of molecular species were scraped from the plates after nondestructive visualization, directly mixed with matrix, and analyzed by laser desorption time-of-flight mass spectrometry. Lipids A and Re-type LPSs were analyzed after transfer to a membrane. Adding citric acid to the matrix gave greatly improved mass spectra. The system allows characterization of bacterial LPS at the microscale level and is equally well applicable to heterogeneous LPS and lipid A preparations (Escherichia coli lipid A and Bordetella lipopolysaccharides were used). The technique provides a rapid determination of the heterogeneity of unmodified preparations and the determination of the molecular weight of each separated component.

Helicobacter mustelae lipid A structure differs from that of Helicobacter pylori

The lipid A structure of the Gram-negative bacterium Helicobacter mustelae, a ferret gastric pathogen responsible for the onset of gastric diseases in its host, was investigated. Two variant lipid A structures were found in the same strain. One structure contained a bisphosphorylated beta-(1-->6)-linked D-glucosamine backbone disaccharide with hydroxytetradecanoic acid in amide linkages. Unlike the structure described for the lipid A of the related human Helicobacter pylori gastric pathogen, which contains a C1 phosphate moiety, this lipid A presented phosphate groups at both the C1 and C4' positions, and contained no octadecanoyl fatty acid, which is present in H. pylori. The second lipid A structure had a different fatty acid composition in that 3-OH C(16) replaced most of the amide-linked 3-OH C(14).

Chemical and serological characterization of the Bordetella hinzii lipopolysaccharides

Bordetella hinzii has recently been isolated from immunocompromised human hosts. The polysaccharides isolated from its endotoxin (lipopolysaccharide, LPS) were investigated using chemical analyses, NMR, gas-liquid chromatography/mass spectrometry and mass spectrometry by plasma desorption, matrix-assisted laser desorption/ionization and electrospray. The following structure for the O-chain-free LPS was deduced from the experimental results: carbohydrate structure [see text] Mass spectrometry and serology revealed that the O-chains were different from the homopolymer common to Bordetella bronchiseptica and Bordetella parapertussis strains and were composed of a trisaccharide repeating unit. Masses up to 8 kDa were obtained for native LPS molecular species.

Structure of the Bordetella pertussis 1414 endotoxin

The endotoxin (lipopolysaccharide) of Bordetella pertussis, the agent of whooping cough, consists of a lipid A linked to a highly branched dodecasaccharide containing several acid and amino sugars. The elucidation of the polysaccharide structure was accomplished by first analyzing the structures of fragments obtained by hydrolysis and nitrous deamination and then piecing the fragments together. The fine structure of the antigenic distal pentasaccharide, presented here, was determined by chemical analyses as well as by high-resolution nuclear magnetic resonance and mass spectrometry. The complete structure was reconstituted and confirmed by matrix-assisted laser desorption/ionization mass spectrometry. The following structure was derived from the combined experimental data:The detailed structure combined with previously reported serological data now allows the synthesis of its epitopes for potential vaccines.

Novel variation of lipid A structures in strains of different Yersinia species

The Yersinia genus includes human and animal pathogens (plague, enterocolitis). The fine structures of the endotoxin lipids A of seven strains of Yersinia enterocolitica, Yersinia ruckeri and Yersinia pestis were determined and compared using mass spectrometry. These lipids differed in secondary acylation at C-2': this was dodecanoic acid (C(12)) for two strains of Y. enterocolitica and Y. ruckeri, tetradecanoic acid (C(14)) in two other Y. enterocolitica and hexadecenoic acid (C(16:1)) in Y. pestis. The enterocolitica lipids having a mass identical to that of Escherichia coli were found to be structurally different. The results supported the idea of a relation between membrane fluidity and environmental adaptability in Yersinia.

Structure of the lipid A of Bordetella hinzii ATCC 51730

Bordetella hinzii has recently been isolated from immunocompromised human hosts. The structure of the lipid A of its endotoxin was investigated using chemical analyses, nuclear magnetic resonnance (NMR), gas liquid chromatography/mass spectrometry (GC/MS), plasma desorption mass spectrometry (PDMS) and matrix-assisted laser desorption/ionization (MALDI) mass spectrometry. The lipid A contains the classical bisphosphorylated beta-(1-->6)-linked D-glucosamine disaccharide with hydroxytetradecanoic acid (C14OH) in amide linkages. The lipid A components of B. pertussis, B. bronchiseptica, and B. parapertussis all differ in their acylation pattern but share a residue of tetradecanoyl-3-hydroxytetradecanoic acid in amide linkage at the C-2' position. However, in the B. hinzii species, the tetradecanoic acid (C14) is stoichiometrically replaced by a 2-hydroxytetradecanoic acid (2-C14OH). In the few reported examples of a hydroxylated fatty acid in this position, the substitutions were only partial. The B. hinzii lipid A differs from that of B. pertussis also by replacement of the hydroxydecanoic acid (C10OH) by hydroxydodecanoic acid (C12OH) and by the presence of a hexadecanoic acid (C16) to give a sixth fatty acid. The lipid A was heterogeneous, being composed of three major molecular species: tetra-, penta- and hexaacylated. The fatty acids in ester linkage were localized by PDMS of the native and alkali-treated lipid A. The lipid A components isolated from the O-chain-linked lipopolysaccharides (LPSs) were shown to be more acylated than those from the O-chain-free LPSs.

Alterations of the outer membrane composition in Escherichia coli lacking the histone-like protein HU

Escherichia coli cells lacking the histone-like protein HU form filaments and have an abnormal number of anucleate cells. Furthermore, their phenotype resembles that of rfa mutants, the well-characterized deep-rough phenotype, as they show an enhanced permeability that renders them hypersensitive to chloramphenicol, novobiocin, and detergents. We show that, unlike rfa mutants, hupAB mutants do not have a truncated lipopolysaccharide but do have an abnormal abundance of OmpF porin in their outer membrane. While the complete absence of HU does not abolish the osmoregulation of OmpF protein synthesis, the steady-state level of micF RNA, the negative regulator of OmpF, decreases in bacteria lacking HU, increasing the basal level of this membrane protein. These findings demonstrate a novel link between a bacterial chromosomal protein and the outer membrane composition.

Antigenic polymorphism of the lipopolysaccharides from human and animal isolates of Bordetella bronchiseptica

Six monoclonal antibodies (mAbs) against lipopolysaccharides (LPS) from Bordetella pertussis (P1P3, 60.5), B. parapertussis (PP2, PP6, PPB) and B. bronchiseptica (BRg1) were used to examine the presence of antigenic determinants of LPS on B. bronchiseptica cells. Forty-eight clinical isolates of this Gram-negative bacterium (4 canine, 3 equine, 6 porcine, 4 rabbit and 31 human) were examined. Significant cross-reactivities with the heterologous anti-pertussis and anti-parapertussis mAbs were observed. The isolates also exhibited marked antigenic polymorphism. The 48 isolates could be classified in six immunogroups. Purified LPS preparations extracted from some isolates were analysed by ELISA, thin-layer chromatography, and tricine-SDS-PAGE. The results show that four main types of antigenic polymorphism of B. bronchiseptica LPSs exist: (a) heterogeneity of the core, (b) presence or absence of O-chains, (c) differences in the hinge region between O-chain and core, and (d) differences in interactions of LPS with other cell-surface constituents. Smooth-type LPS molecules, detectable with mAb PP6, were more frequently observed in animal isolates (94%) than in human isolates (52%). Reverse frequencies were found with mAb 60.5 (48% of human isolates, 18% of animal isolates), which is unable to react with long-chain LPSs. This observation could be due to the general absence of some lectin-like receptor, specific to the O-chain, on human bronchoalveolar tissues.

Epitopes of Bordetella pertussis lipopolysaccharides as potential markers for typing of isolates with monoclonal antibodies

Three hybridomas (P1P3, D7 and 60.5) producing monoclonal antibodies (mAbs) against Bordetella pertussis lipopolysaccharide (LPS) were established. All reacted with the LPS from a typical, vaccine strain of B. pertussis (1414), but not with that of a variant strain (A100). Two of these mAbs (P1P3 and 60.5) cross-reacted with a B. bronchiseptica LPS; only one (P1P3) reacted with a B. parapertussis LPS. ELISA reactivities with intact LPSs, and defined partial structures covalently linked to bovine serum albumin, were compared. mAb 60.5 bound to the terminal region of a distal trisaccharide consisting of N-acetylated amino sugars. D7 reacted with a substructure which can be modified in the B. parapertussis and B. bronchiseptica LPSs by addition of a polymeric O-chain. P1P3 bound to a nonacetylated glucosamine substituted with L-glycero-D-manno-heptose, present in the 'core' of the B. pertussis LPS. These mAbs may be useful for rapid typing of Bordetella in clinical isolates.

Structure of a hexasaccharide proximal to the hydrophobic region of lipopolysaccharides present in Bordetella pertussis endotoxin preparations

A branched-chain hexasaccharide containing 3-deoxy-D-manno-oct-2-ulosonic acid was released by detergent-promoted hydrolysis from Bordetella pertussis endotoxin preparations that were first dephosphorylated with aqueous HF and then treated with nitrous acid. Its structure (2) [Formula: See text] was determined by chemical and physical methods. This hexasaccharide is present in all four lipopolysaccharides that make up the B. pertussis strain 1414 (phase 1) endotoxin preparations analysed, and is situated near to the hydrophobic domains. An analogous structure reported previously (ref 7) is erroneous and should be disregarded.

Effects of sub-minimal inhibitory concentrations of EDTA on growth of Escherichia coli and the release of lipopolysaccharide

Release of lipopolysaccharide from E. coli was studied in the presence of sub-minimal inhibitory concentrations of ethylenediaminetetraacetic acid (EDTA). In untreated cells no release was detected with 50 mM Mg2+ in the medium, but a steady release of over 50% of the synthesized lipopolysaccharide was observed with 0.1 mM Mg2+. EDTA at MIC/8 led to a 2- to 3-fold higher release, presumably by an adjustment of the concentration of unchelated Mg2+ to a value still sustaining normal growth but giving rise to a highly unstable outer membrane. No structural difference was observed between cell-bound and released lipopolysaccharide.

Structural features involved in the mitogenic activity of Bordetella pertussis lipopolysaccharides for spleen cells of C3H/HeJ mice

Spleen cells from the C3H/HeJ mouse strain cannot be stimulated by many smooth-type lipopolysaccharides (LPSs), and by the main biologically-active region (lipid A) of these molecules. The genetic origin of this defect (expression of the mutant allele Lpsd at the chromosome 4 locus) was established over 20 years ago, but its biochemical nature has remained undefined. Several investigators have noted, however, that some particular LPSs can bypass this defect, and stimulate the proliferation of C3H/HeJ B lymphocytes. In this study we compare the mitogenic activities of the LPSs isolated from a wild strain (1414) and from a mutant 'rough' strain (A100) of Bordetella pertussis. Both LPS-1414 and LPS-A100 were mitogenic for C3H/HeJ spleen cells, but their lipid A fragments were not. This indicates that a carbohydrate structure proximal to lipid A is involved in the mitogenic activity. However, the isolated polysaccharides were not mitogenic. Four sugars are common to both LPS-1414 and LPS-A100: an heptose, and three sugars bearing free amino groups. After removal of these four sugars from the LPSs by nitrous acid treatment, the recovered lipooligosaccharides were not mitogenic in Lpsd spleen cells. The results suggest that substructures present in lipid A and in this group of four sugars are both required for induction of a mitogenic effect in Lpsd splenocytes, whereas lipid A alone can stimulate Lpsn spleen cells.

Identification, isolation, and structural studies of the outer membrane lipopolysaccharide of Caulobacter crescentus

The lipopolysaccharide (LPS) of the outer membrane of Caulobacter crescentus was purified and analyzed. Two distinct strains of the species, NA 1000 and CB2A, were examined; despite differences in other membrane-related polysaccharides, the two gave similar LPS composition profiles. The LPS was the equivalent of the rough LPS described for other bacteria in that it lacked the ladder of polysaccharide-containing species that results from addition of variable amounts of a repeated sequence of sugars, as detected by gel electrophoresis in smooth LPS strains. The purified LPS contained two definable regions: (i) an oligosaccharide region, consisting of an inner core of three residues of 2-keto-3-deoxyoctonate, two residues of alpha-L-glycero-D-mannoheptose, and one alpha-D-glycero-D-mannoheptose unit and an outer core region containing one residue each of alpha-D-mannose, alpha-D-galactose, and alpha-D-glucose, with the glucose likely phosphorylated and (ii) a region equivalent to the lipid A region of the archetype, consisting primarily of an esterified fatty acid, 3-OH-dodecanoate. The lipid A-like region was resistant to conclusive analysis; in particular, although a variety of analytical methods were used, no amino sugars were detected, as is found in the lipid A of the LPS of most bacteria.