LIPOPOLYSACCHARIDE OF THE GRAM-NEGATIVE CELL WALL

A novel electrophoretic fractionation of Escherichia coli envelopes

Particulate fractions of Escherichia coli have been submitted to electrophoretic fractionation in a buffer stabilized by sucrose gradient. Inner membrane and outer membrane were readily resolved. A combination of electrophoresis, fractional centrifugation and gel filtration can remove remaining contamination by ribosomes and cytoplasm. The presence of particles containing no phospholipids was detected after differential centrifugation. The nature of this fraction is unknown. The inner membrane exhibited heterogeneity on electrophoresis.

Immunological responses of mice to native protoplasmic polysaccharide and lipopolysaccharide: functional separation of the two signals required to stimulate a secondary antibody response

Functional separation of the two signals involved in stimulating immunological responses was achieved through the judicious use of two natural bacterial antigens. Native protoplasmic polysaccharide (NPP) extracted from Escherichia coli was immunochemically identical to the lipopolysaccharide (LPS) extracted from the same organism. However, NPP was not endotoxic, not mitogenic, did not fix complement, and was immunologically independent of T cells. The NPP, which appeared to contain only the antigenic signal, could induce a primary antibody response in mice and could sensitize mice for a secondary response. However, the antigenic signal contained in NPP was insufficient to trigger a secondary response in mice primed with either NPP or LPS. LPS, containing both the antigenic and second signals, was required to trigger a secondary response in primed mice.

Degradative effect of phenol on endotoxin and lipopolysaccharide preparations from Serratia marcescens

It has been established that the well-known deproteinizing action of hot 45% aqueous phenol on whole cells or isolated and purified endotoxin of Serratia marcescens 08 is caused by the cleavage of a phenol-sensitive linkage within the lipid moiety. As a result of this degradation, both the lipopolysaccharide and simple protein fragments retained a part of the lipid moiety. Although not proceeding at the same fast rate as the cleavage of the lipid moiety, such phenol treatment also caused a partial hydrolysis of the O-specific side chain and ester-bound fatty acids. Hydrolysis of the O-specific side chain accounted for 5% of the lipopolysaccharide and that of ester-bound fatty acids accounted for 11% of the total fatty acid content after 60 min of treatment. It is suggested that the presence of these degradation products is one of the main causes of the heterogeneity of endotoxin and lipopolysaccharide preparations.

Susceptibility of whole cells and spheroplasts of Pseudomonas aeruginosa to actinomycin D

Cells of Pseudomonas aeruginosa suspended in 0.2 M Mg(2+), 20% sucrose, 0.01 M tris(hydroxymethyl)aminomethane, or water partially release lipopolysaccharide. The release of alkaline phosphatase from the periplasmic space and the ability to form spheroplasts on lysozyme treatment is directly related to the lipopolysaccharide released during treatment with 0.2 M Mg(2+), 20% sucrose, or other agents. The synthesis of ribonucleic acid (RNA) by intact cells, magnesium-lysozyme spheroplasts, or 20% sucrose-lysozyme spheroplasts is not sensitive to actinomycin D, whereas RNA synthesis by intact cells or spheroplasts in the presence of ethylene-diaminetetraacetic acid (EDTA) is sensitive to actinomycin D. EDTA alone has an inhibitory effect on RNA synthesis by whole cell, by magnesium-lysozyme spheroplasts, and by 20% sucrose-lysozyme spheroplasts. The experimental data indicate that, although the cell wall is damaged by 0.2 M Mg(2+) or 20% sucrose treatment in the presence of lysozyme, the treated cells or spheroplasts are still resistant to actinomycin D. These results suggest that the cytoplasmic membrane should be considered as the final and determinative barrier to this antibiotic in this organism.

Resistance of Escherichia coli to penicillins. IX. Genetics and physiology of class II ampicillin-resistant mutants that are galactose negative or sensitive to bacteriophage C21, or both

Ampicillin-resistant mutants of class II are determined by a doubling of chromosomally and episomally mediated ampicillin resistance on agar plates. Several mutants were isolated from a female as well as from an Hfr strain. The mutants differed from each other in various properties such as response to colicin E2 and sodium cholate, response to the phages T4 and C21, and fermentation of galactose. By conjugation and transduction experiments, it was shown that mutations in at least four loci gave the class II phenotype. The mutations were found to be in the galU gene, the ctr gene, and two new genes close to mtl denoted lpsA and lpsB. The carbohydrate compositions of the lipopolysaccharides of the mutants were investigated and found to be changed compared to the parent strains. GalU mutants lacked rhamnose and galactose and had 11% glucose compared to the parent strain. The lpsA mutant also lacked rhamnose and had only traces of galactose and 58% glucose, whereas the lpsB mutant contained 14% rhamnose, traces of galactose, and 81% glucose compared to the parent strain.

Immunity in experimental salmonellosis. II. Basis for the avirulence and protective capacity of gal E mutants of Salmonella typhimurium

Salmonella typhimurium strains which are deficient in uridine diphosphate (UDP)-galactose-4-epimerase (gal E mutants) owe their outstanding protective capacity when used as live vaccine to the fact that when galactose is supplied exogenously, such as occurs in vivo, smooth cell wall lipopolysaccharides are synthesized. The mutants lose most of their protective capacity when this phenotypic curing is prevented by a second mutation of the kind found in strains LT(2)M(1)A (deficient in galactokinase) or E(32) (deficient in UDP-galactose-lipopolysaccharide transferase). Despite such phenotypic reversion, the gal E mutants are rendered avirulent as a result of galactose-induced bacteriolysis. Secondary mutants have been isolated which differ from each other with respect to the extent of galactose-induced lysis. The differences in galactose sensitivity are attributable to different activities of the other Leoloir pathway enzymes, namely, galactokinase and galactose-1-phosphate-uridyl transferase. The influence of these enzymes on lipopolysaccharide composition and galactose sensitivity and thus on virulence and immunogenicity of gal E mutants has been studied.

Properties of a Salmonella typhimurium mutant with an incomplete deficiency of uridinediphosphogalactose-4-epimerase

A galactose-negative mutant, nonleaky in respect to fermentation and utilization, isolated from a smooth Salmonella typhimurium strain by phage selection and inferred deficient of uridine diphosphate (UDP)-galactose-epimerase, was used for experiments on relation of somatic lipopolysaccharide (LPS) character to virulence. Extracts of induced mutant cells retained ca. 1% of wild-type epimerase activity and had only ca. 5% of wild-type kinase and uridyl transferase activities; also, some cultural properties of the mutant differed from those of mutants with complete defects of epimerase only. The mutant was not galactose sensitive, presumably because of its kinase defect. Although the mutant had the phage pattern (including C21-sensitivity) of an epimerase mutant, it was susceptible to transduction by phage P22 and was O-agglutinable, even when grown on defined medium; its LPS must therefore contain some O polymer, including endogenous galactose, resulting from residual epimerase activity. Growth on galactose-supplemented medium restored smooth phage sensitivity; since the mutant was partly inducible this may result, at least in part, from increased endogenous production of UDP-galactose. The mutant was made galactose positive by introduction of an F'-gal(+) plasmid. Base-change and frame-shift mutagens did not increase the frequency of reversion above the spontaneous rate. An insertion into the operator-promoter region of the gal operon seems the most likely mechanism of the mutation.

Bacteriophage attachment sites, serological specificity, and chemical composition of the lipopolysaccharides of semirough and rough mutants of Salmonella typhimurium

Extracted lipopolysaccharides (LPS) from one smooth, one semirough, and five rough mutants of Salmonella typhimurium LT2 or LT7, for which the chemical structure of the polysaccharide chain had been elucidated by using methylation analysis, were characterized with passive hemagglutination inhibition and phage inactivation experiments. Each addition of a sugar residue to a LPS from chemotype Rc was reflected in changed serological reactivity and phage-inhibiting activity of a collection of bacteriophages of the isolated LPS. Thus, certain criteria can be established for a classification of rough mutants of S. typhimurium. The observation that the serological RII specificity corresponds to a completed common core polysaccharide was verified. The serological RI specificity was found in LPS with terminal d-galactose I residues. One of the mutants, SL733, yielded a LPS which cross-reacted with anti-O5 factor serum although the polysaccharide was virtually free from contaminating O-specific material. The O5 reactivity was destroyed by alkaline treatment of SL733 LPS. The smooth- and rough-specific Felix O-l (FO) and the rough-specific 6SR and Br2 phages were shown to have their receptors in the LPS. There was a good correlation between the adsorption rate constant to whole cells and the phage inhibiting activity of isolated LPS suggesting that the LPS exert the major influence on the attachment of these phages to the bacteria. The polysaccharide structures in the LPS necessary for attachment of the 6SR and Br2 phages were defined. It was found that measuring the phage-inhibiting properties of isolated LPS as PhI(50) (LPS concentration required to inactivate 50% of the phages under defined conditions) was a more sensitive method for a characterization of the LPS than the serological and chemical assays used.

Bacteriophage receptor development and synthesis of O-specific side chains after addition of D-galactose to the uridine diphosphate-galactose-4-epimeraseless mutant Salmonella typhimurium LT2-M1

The formation of complete cell wall core lipopolysaccharide (LPS) and O-antigenic side chains after addition of d-galactose to the uridine diphosphate-galactose-4-epimeraseless mutant, Salmonella typhimurium LT2-M1, has been studied by (i) determination of adsorption rates of smooth and rough specific bacteriophages, (ii) passive hemagglutination inhibition, and (iii) qualitative and quantitative determination of the polysaccharide composition and structure. A rapid synthesis of the complete core LPS and O side chains occurred in bacteria in the log phase and the early stationary phase. Phage C21, which attaches to unsubstituted Rc structures, was adsorbed by the bacteria for only 10 min after the addition of d-galactose. Unsubstituted Rc structures, however, could still be detected after 160 min by immunological and chemical assays. Attachment of the P22 phage, which requires O-specific side chains with more than one repeating unit for adsorption, was demonstrated 10 min after the addition of d-galactose. Attachment of the Felix O-1 phage, which requires a complete core, was observed between 20 and 80 min after the addition of d-galactose. The rough specific phages 6SR and Br2 did not adsorb to the bacteria at any time after the addition of d-galactose. By passive hemagglutination inhibition, the presence of O-specific structures could be demonstrated after 10 min. No antigenic activity of the Ra and Rb structures was observed in the LPS preparations isolated at any time after the addition of d-galactose. Methylation analysis of LPS preparations isolated at 10 and 160 min after the addition of d-galactose showed that the O-specific side chains contained an average of 11 and 15 repeating units, respectively. In the 10-min sample, every 25th "Rc structure" carried a side chain, compared to every 3rd residue in the 160-min sample.

Direction of chain growth in polysaccharide synthesis

The biosynthesis of a bacterial polysaccharide-the surface O-antigen of Salmonella newington-differs in several respects from the more classical example of glycogen synthesis. Sugars are not transferred directly to the antigen from sugar nucleotide precursors but are transferred first into lipid-linked oligosaccharides. Growth of the polysaccharide chain then occurs by assembly of these lipid-linked precursors at the reducing end of the polymer rather than at its nonreducing end as in glycogen. This method of assembly, in which nascent chains are transferred to the next subunit, is analogous to the growth of proteins or fatty acids. It seems possible that these differences reflect the more complex requirements of a surface polysaccharide synthesized by membrane-bound enzymes. If this is the case, then several other polysaccharide systems may be synthesized by comparable mechanisms.

Somatic antigen 2 inheritance in Salmonella groups B and D

Somatic (O) antigen 2 of Salmonella paratyphi A replaced somatic antigen 4 of an S. typhimurium recipient as the consequence of mating with an S. paratyphi A var. durazzo Hfr strain. The genetic determinants of these O antigens behaved in this cross as alleles of a common O locus, which is linked to the determinant of histidine biosynthesis, his. By employing phage lysates obtained by growth of P22 on an S. typhimurium hybrid which had received his and O-factor 2 determinants from the S. paratyphi A Hfr, it was possible to cotransduce the his and O-antigen 2 genes to both S. typhimurium and S. typhosa. S. typhimurium transductants which received somatic antigen 2 concurrently lost O-antigen 4, and S. typhosa transductants receiving O-antigen 2, lost their native O-antigen 9. These results indicate that the genetic determinants of O-antigens 2, 4, and 9 occupy the same O locus in S. paratyphi A, S. typhimurium, and S. typhosa, respectively, and are probably allelic.

Chemical composition of cell envelopes from Agrobacterium tumefaciens

Cell envelopes from logarithmic phase cells of eight strains of Agrobacterium tumefaciens were isolated and examined qualitatively and quantitatively for various components. Envelopes, 6 to 9% of the total dry weight of the bacteria, were composed of approximately 23 to 27% lipid, 3.1 to 6.0% total nitrogen, and 6.3 to 11.2% carbohydrates. Cytochrome was present in envelopes obtained from logarithmic phase cells.The glycosaminopeptide was composed of glutamic acid, alanine, 2,6-diaminopimelic acid, and amino sugars. Leucine, phenylalanine, serine, and aspartic acid were found in relatively high levels in several of the strains investigated.In addition to ubiquinones, four phospholipids, phosphatidylethanolamine, phosphatidyl-N-methylethanolamine, phosphatidyl-N,N-dimethylethanolamine, and phosphatidyl-choline, were observed in the lipid fraction of all eight strains of A. tumefaciens examined.Glucose, fucose, and 2-keto-3-deoxyoctulosonic acid were present in the lipopolysaccharide of all strains tested.There appears to be no correlation between the virulence of this plant pathogen and the mucopeptide or lipid–protein–polysaccharide components of the cell envelope.

Interferon production in mice by cell wall mutants of Salmonella typhimurium

The interferon response elicited by Salmonella typhimurium mutants in mice is not dependent on the presence of a complete cell wall lipopolysaccharide. In fact, a mutant (G30/C21) which has lost all the polysaccharide side chains and sugars of the O antigen and contains only 2-keto-3-deoxyoctonate and lipid is indistinguishable in its interferon-stimulating ability from the wild type which possesses a complete O antigen with polysaccharide side chains.

Lipopolysaccharides of Salmonella T mutants

The composition of lipopolysaccharides derived from various Salmonella T forms was studied. All T1-form lipopolysaccharides examined contained 14 to 22% each of both d-galactose and pentose in addition to 4 to 9% each of ketodeoxyoctonic acid, heptose, d-glucosamine, and d-glucose. The pentose was identified as d-ribose. The T2-form lipopolysaccharide examined did not contain a significant amount of pentose, nor more than the usual amounts of d-galactose. Periodate oxidation of T1 (lipo) polysaccharides followed by NaBH(4) reduction revealed that ribose was almost quantitatively protected, galactose was destroyed, and threitol and mannose were newly formed. The latter two products probably originated from 4-linked galactose and heptose, respectively. Ribose and galactose were found in specific precipitates of T1 lipopolysaccharide with anti-T1 antiserum but were not found in specific precipitates of alkali-treated T1 lipopolysaccharide and of Freeman degraded polysaccharide with anti-T1 serum Ribose and galactose are present in these degraded preparations in the form of nondialyzable polymers. The T1-form mutant lipopolysaccharides lacked the O-specific sugars constituting the side-chains in the wild-type antigens. They did not produce the soluble O-specific haptenic polysaccharide known to be accumulated in RI strains. With these properties, T1 lipopolysaccharides resemble RII lipopolysaccharides. Like RII degraded polysaccharides, T1-degraded polysaccharides also contained glucosamine. Furthermore, strong cross-reactions were found to exist between T1 and RII lipopolysaccharides in both hemagglutination inhibition assays and in precipitation tests. It is proposed that T1 lipopolysaccharides represent RII lipopolysaccharides to which polymers consisting of ribose and galactose are attached.

Biologically active endotoxins from Salmonella mutants deficient in O- and R-polysaccharides and heptose

Well-characterized Salmonella mutants formerly used in biosynthetic studies of lipopolysaccharides were used to study the toxic portion of the complex endotoxin. Endotoxins prepared from wild types and their mutants were tested for their biological activities, including pyrogenicity, lethality, and immunogenicity. There was little difference either in the endotoxin yields or in the toxicities between endotoxins from the wild-type and O-antigen deficient mutants. Endotoxin containing mostly lipid A and keto-deoxyoctonate (KDO) prepared from the mutant deficient in both O- and R-antigens and the backbone sugar, heptose, was biologically active. Possibly because of the difference in solubility in water, the yield of endotoxin from the heptoseless mutant was about 10% of the wild type. There was complete reciprocal cross-immunity between all endotoxins tested. These observations suggest that the common toxic moiety is not present in the O- and R-polysaccharides or the backbone sugar heptose, but rather is associated with the lipid portion of the molecule which includes mostly lipid A and KDO.

The extraction of cell walls of Pseudomonas aeruginosa with aqueous phenol. The insoluble residue and material from the aqueous layers

1. The insoluble residue and material present in the aqueous layers resulting from treatment of cell walls of Pseudomonas aeruginosa with aqueous phenol were examined. 2. The products (fractions AqI and AqII) isolated from the aqueous layers from the first and second extractions respectively account for approx. 25% and 12% of the cell wall and consist of both lipopolysaccharide and muropeptide. 3. The lipid part of the lipopolysaccharide is qualitatively similar to the corresponding material (lipid A) from other Gram-negative organisms, as is the polysaccharide part. 4. The insoluble residue (fraction R) contains sacculi, which also occur in fraction AqII. On hydrolysis, the sacculi yield glucosamine, muramic acid, alanine, glutamic acid and 2,6-diaminopimelic acid, together with small amounts of lysine, and they are therefore similar to the murein sacculi of other Gram-negative organisms. Fraction R also contains substantial amounts of protein, which differs from that obtained from the phenol layer. 5. The possible association or aggregation of lipopolysaccharide, murein and murein sacculi is discussed.

The immunochemistry of Shigella flexneri O-antigens. The biochemical basis of smooth to rough mutation

1. Smooth to rough mutation has the same biochemical basis in Shigella as in Salmonella. It is the result of enzyme defects blocking the incorporation of the O-specific side chains that characterize the smooth lipopolysaccharide with the consequent exposure of the underlying basal structures that determine ;rough'-specificity. 2. The Shigella flexneri basal structure resembles its Salmonella analogue in that it has the same qualitative sugar composition, and enzyme defects in its biosynthetic pathway give rise to ;rough'-lipopolysaccharides that are indistinguishable from those of Salmonella chemotypes Ra, Rb, Rc and Rd. However, the Salmonella and Shigella basal structures are not identical as judged by quantitative analysis and the absence of serological cross-reaction. 3. The Sh. flexneri basal structure side chain has been isolated and characterized as an alpha-N-acetylglucosaminyl-(1-->4)-galactosyl-(1-->3)-glucose sequence with alpha-glucosyl radicals substituted on the 3- and 4-positions of the galactose and glucose respectively. The different sugar types in this side chain are incorporated into the growing molecule in the same order as in Salmonella, which explains why the enzyme defects associated with smooth to rough mutation produce the same series of R-chemotypes from both genera. The terminal alpha-glucosyl and alpha-N-acetylglucosaminyl-(1-->4)-galactosyl residues of the Sh. flexneri basal structure are sufficiently different from the terminal alpha-galactosyl and alpha-N-acetylglucosaminylglucosyl residues of the Salmonella analogue that they offer an explanation for the absence of serological cross-reaction between these two basal structures.

Reassociation of purified lipopolysaccharide and phospholipid of the bacterial cell envelope: electron microscopic and monolayer studies

Phosphatidyl ethanolamine and lipopolysaccharide were extracted and purified from the cell envelope fractions of Escherichia coli and Salmonella typhimurium. The two components were studied separately and after recombination, by use of electron microscopy and monolayer techniques, and by measuring their ability to participate in the enzyme-catalyzed uridine diphosphate-galactose:lipopolysaccharide alpha, 3 galactosyl transferase reaction, which requires a lipopolysaccharide-phospholipid complex as substrate. Electron microscopy of purified lipopolysaccharide showed a uniform population of hollow spheres, with each sphere bounded by a continuous leaflet. The diameter of the spheres was approximately 500 to 1,000 A, and the thickness of the enveloping leaflet was approximately 30 A. Phosphatidyl ethanolamine showed a regular lamellar structure. When lipopolysaccharide and phosphatidyl ethanolamine were mixed under conditions of heating and slow-cooling, the leaflet of the lipopolysaccharide spheroids appeared to extend directly into the phosphatidyl ethanolamine structure, with continuity between the two leaflets. Various stages of penetration were seen. At high concentrations of lipopolysaccharide, there were disruptive changes in phosphatidyl ethanolamine leaflets similar to those seen when saponin acts on cholesterol-lecithin leaflets. Monolayer experiments indicated that lipopolysaccharide penetrated a monomolecular film of phosphatidyl ethanolamine at an air-water interface, as revealed by an increase in surface pressure. The results indicate that a common leaflet structure containing lipopolysaccharide and phosphatidyl ethanolamine may be formed in vitro, and suggest that a similar leaflet may exist in the intact bacterial cell envelope.