Properties of the O-specific hapten formed in vivo by mutant strains of Salmonella typhimurium

Polyhydroxyalkanoates as biomaterials

Polyhydroxyalkanoates (PHAs) are biopolymers synthesized by bacteria under unbalanced growth conditions. These biopolymers are considered as potential biomaterials for future applications because they are biocompatible, biodegradable, and easy to produce and functionalize with strong mechanical strength. Currently, PHAs are being extensively innovated for biomedical applications due to their prerequisite properties. The wide range of biomedical applications includes drug delivery systems, implants, tissue engineering, scaffolds, artificial organ constructs, etc. In this article we review the utility of PHAs in various forms (bulk/nano) for biomedical applications so as to bring about the future vision for PHAs as biomaterials for the advancement of research and technology.

Functional characterization of WaaL, a ligase associated with linking O-antigen polysaccharide to the core of Pseudomonas aeruginosa lipopolysaccharide

The O antigen of Pseudomonas aeruginosa B-band lipopolysaccharide is synthesized by assembling O-antigen-repeat units at the cytoplasmic face of the inner membrane by nonprocessive glycosyltransferases, followed by polymerization on the periplasmic face. The completed chains are covalently attached to lipid A core by the O-antigen ligase, WaaL. In P. aeruginosa the process of ligating these O-antigen molecules to lipid A core is not clearly defined, and an O-antigen ligase has not been identified until this study. Using the sequence of waaL from Salmonella enterica as a template in a BLAST search, a putative waaL gene was identified in the P. aeruginosa genome. The candidate gene was amplified and cloned, and a chromosomal knockout of PAO1 waaL was generated. Lipopolysaccharide (LPS) from this mutant is devoid of B-band O-polysaccharides and semirough (SR-LPS, or core-plus-one O-antigen). The mutant PAO1waaL is also deficient in the production of A-band polysaccharide, a homopolymer of D-rhamnose. Complementation of the mutant with pPAJL4 containing waaL restored the production of both A-band and B-band O antigens as well as SR-LPS, indicating that the knockout was nonpolar and waaL is required for the attachment of O-antigen repeat units to the core. Mutation of waaL in PAO1 and PA14, respectively, could be complemented with waaL from either strain to restore wild-type LPS production. The waaL mutation also drastically affected the swimming and twitching motilities of the bacteria. These results demonstrate that waaL in P. aeruginosa encodes a functional O-antigen ligase that is important for cell wall integrity and motility of the bacteria.

Functional analysis of the galactosyltransferases required for biosynthesis of D-galactan I, a component of the lipopolysaccharide O1 antigen of Klebsiella pneumoniae

D-Galactan I is an O-antigenic polymer with the repeat unit structure [-->3)-beta-D-Galf-(1-->3)-alpha-D-Galp-(1-->], that is found in the lipopolysaccharide of Klebsiella pneumoniae O1 and other gram-negative bacteria. A genetic locus containing six genes is responsible for the synthesis and assembly of D-galactan I via an ATP-binding cassette (ABC) transporter-dependent pathway. The galactosyltransferase activities that are required for the processive polymerization of D-galactan I were identified by using in vitro reactions. The activities were determined with endogenous lipid acceptors in membrane preparations from Escherichia coli K-12 expressing individual enzymes (or combinations of enzymes) or in membranes reconstituted with specific lipid acceptors. The D-galactan I polymer is built on a lipid acceptor, undecaprenyl pyrophosphoryl-GlcpNAc, a product of the WecA enzyme that participates in the biosynthesis of enterobacterial common antigen and O-antigenic polysaccharide (O-PS) biosynthesis pathways. This intermediate is directed into D-galactan I biosynthesis by the bifunctional wbbO gene product, which sequentially adds one Galp and one Galf residue from the corresponding UDP-sugars to form a lipid-linked trisaccharide. The two galactosyltransferase activities of WbbO are separable by limiting the UDP-Galf precursor. Galactosyltransferase activity in membranes reconstituted with exogenous lipid-linked trisaccharide acceptor and the known structure of D-galactan I indicate that WbbM catalyzes the subsequent transfer of a single Galp residue to form a lipid-linked tetrasaccharide. Chain extension of the D-galactan I polymer requires WbbM for Galp transferase, together with Galf transferase activity provided by WbbO. Comparison of the biosynthetic pathways for D-galactan I and the polymannose E. coli O9a antigen reveals some interesting features that may reflect a common theme in ABC transporter-dependent O-PS assembly systems.

Involvement of the rml locus in core oligosaccharide and O polysaccharide assembly in Pseudomonas aeruginosa

L-Rhamnose (L-Rha) is a component of the lipopolysaccharide (LPS) core, several O antigen polysaccharides, and the cell surface surfactant rhamnolipid of Pseudomonas aeruginosa. In this study, four contiguous genes (rmlBDAC) responsible for the synthesis of dTDP-L-Rha in P. aeruginosa have been cloned and characterized. Non-polar chromosomal rmlC mutants were generated in P. aeruginosa strains PAO1 (serotype O5) and PAK (serotype O6) and LPS extracted from the mutants was analysed by SDS-PAGE and Western immunoblotting. rmlC mutants of both serotype O5 and serotype O6 synthesized a truncated core region which was unable to act as an attachment point for either A-band or B-band O antigen. A rmd rmlC PAO1 double mutant (deficient in biosynthesis of both D-Rha and L-Rha) was constructed to facilitate structural analysis of the mutant core region. This strain has an incomplete core oligosaccharide region and does not produce A-band O antigen. These results provide the genetic and structural evidence that L-Rha is the receptor on the P. aeruginosa LPS core for the attachment of O polysaccharides. This is the first report of a genetically defined mutation that affects the synthesis of a single sugar in the core oligosaccharide region of P. aeruginosa LPS, and provides further insight into the mechanisms of LPS biosynthesis and assembly in this bacterium.

Identification and functional characterization of an ABC transport system involved in polysaccharide export of A-band lipopolysaccharide in Pseudomonas aeruginosa

Pseudomonas aeruginosa coexpresses two distinct lipopolysaccharide (LPS) molecules known as A band and B band. B band is the serospecific LPS, while A band is the common LPS antigen composed of a D-rhamnose O-polysaccharide region. An operon containing eight genes responsible for A-band polysaccharide biosynthesis and export has recently been identified and characterized (H. L. Rocchetta, L. L. Burrows, J. C. Pacan, and J. S. Lam, unpublished data; H. L. Rocchetta, J. C. Pacan, and J. S. Lam, unpublished data). In this study, we report the characterization of two genes within the cluster, designated wzm and wzt. The Wzm and Wzt proteins have predicted sizes of 29.5 and 47.2 kDa, respectively, and are homologous to a number of proteins that comprise ABC (ATP-binding cassette) transport systems. Wzm is an integral membrane protein with six potential membrane-spanning domains, while Wzt is an ATP-binding protein containing a highly conserved ATP-binding motif. Chromosomal wzm and wzt mutants were generated by using a gene replacement strategy in P. aeruginosa PAO1 (serotype 05). Western blot analysis and immunoelectron microscopy using A-band- and B-band-specific monoclonal antibodies demonstrated that the wzm and wzt mutants were able to synthesize A-band polysaccharide, although transport of the polymer to the cell surface was inhibited. The inability of the polymer to cross the inner membrane resulted in the accumulation of cytoplasmic A-band polysaccharide. This A-band polysaccharide is likely linked to a carrier lipid molecule with a phenol-labile linkage. Chromosomal mutations in wzm and wzt were found to have no effect on B-band LPS synthesis. Rather, immunoelectron microscopy revealed that the presence of A-band LPS may influence the arrangement of B-band LPS on the cell surface. These results demonstrate that A-band and B-band O-antigen assembly processes follow two distinct pathways, with the former requiring an ABC transport system for cell surface expression.

A novel pathway for O-polysaccharide biosynthesis in Salmonella enterica serovar Borreze

The plasmid-encoded gene cluster for O:54 O-polysaccharide synthesis in Salmonella enterica serovar Borreze (rfbO:54) contains three genes that direct synthesis of a ManNAc homopolymer with alternating beta1,3 and beta1,4 linkages. In Escherichia coli K-12, RfbAO:54 adds the first ManNAc residue to the Rfe (UDP-GlcpNAc::undecaprenylphosphate GlcpNAc-1-phosphate transferase)- modified lipopolysaccharide core. Hydrophobic cluster analysis of RfbAO:54 indicates this protein belongs to the ExoU family of nonprocessive beta-glycosyltransferases. Two putative catalytic residues and a potential substrate-binding motif were identified in RfbAO:54. Topological analysis of RfbBO:54 predicts four transmembrane domains and a large central cytoplasmic domain. The latter shares homology with a similar domain in the processive beta-glycosyltransferases Cps3S of Streptococcus pneumoniae and HasA of Streptococcus pyogenes. Hydrophobic cluster analysis of RfbBO:54 and Cps3S indicates both possess the structural features characteristic of the HasA family of processive beta-glycosyltransferases. Four potential catalytic residues and a putative substrate-binding motif were identified in RfbBO:54. In Deltarfb E. coli K-12, RfbAO:54 and RfbBO:54 direct synthesis of smooth O:54 lipopolysaccharide, indicating that this O-polysaccharide involves a novel pathway for O-antigen transport. Based on sequence and structural conservation, 15 new ExoU-related and 17 new HasA-related transferases were identified.

C-terminal half of Salmonella enterica WbaP (RfbP) is the galactosyl-1-phosphate transferase domain catalyzing the first step of O-antigen synthesis

We previously showed that the product of the wbaP gene of Salmonella enterica serovar Typhimurium has two functions: it is involved in the first step of O-antigen synthesis (the galactosyltransferase [GT] function) and in a later step (the T function), first thought to be the flipping of the O-antigen subunit on undecaprenyl pyrophosphate from the cytoplasmic face to the periplasmic face of the cytoplasmic membrane. We now locate two wbaP(T) mutations within the first half of the wbaP gene by sequencing. Both mutants retain GT activity, although one was a frameshift mutation resulting in a stop codon 10 codons after the frameshift to give an open reading frame containing only 138 of the 476 codons in WbaP. We also show that there is a secondary translation starting within the wbaP gene resulting in the synthesis of a polypeptide with GT activity. These results indicate that the N- and C-terminal halves of WbaP are the T and GT functional domains, respectively. We now propose that the T block operates prior to the flippase function, probably at the release of undecaprenyl pyrophosphate-linked galactose from WbaP.

Involvement of the galactosyl-1-phosphate transferase encoded by the Salmonella enterica rfbP gene in O-antigen subunit processing

rfbT of Salmonella enterica LT2 was previously thought, together with rfaL, to be involved in the ligation of polymerized O antigen to core-lipid A, and three mutants were known. We report the mapping of the mutations to rfbP, the galactosyl-1-phosphate transferase gene, which is now shown to encode a bifunctional protein. The mutations which have the former rfbT phenotype are referred to as rfbP(T). We also show that rfbP(T) mutants are not blocked in the ligation step as previously believed but in an earlier step, possibly in flipping the O-antigen subunit on undecaprenyl pyrophosphate from the cytoplasmic to periplasmic face of the cytoplasmic membrane.

Energy dependence of O-antigen synthesis in Salmonella typhimurium

The uncoupler 2,4-dinitrophenol prevents in vivo synthesis of O antigen in Salmonella typhimurium by inhibiting the first reaction of the pathway, formation of galactosyl-pyrophosphoryl-undecaprenol. Inhibition was observed only in intact cells; dinitrophenol had no effect on activity of the synthase enzyme in isolated membrane fractions. In vivo inhibition could not be explained by changes in intracellular nucleotide pools or a shift in the equilibrium of the reaction and appeared to be specific for the first step in the pathway. Neither the subsequent mannosyl transferase, which catalyzes formation of the trisaccharide-lipid intermediate, mannosyl-rhamnosyl-galactosyl-pyrophosphoryl-undecaprenol, nor O-antigen polymerase was inhibited. In addition, incorporation of galactose into core lipopolysaccharide was only modestly inhibited under conditions in which O-antigen synthesis was abolished. The results suggest that maintenance of proton motive force is required for access of substrate, UDP-galactose and/or undecaprenyl phosphate, to the active site of the galactosyl-pyrophosphoryl-undecaprenol synthase enzyme.

Localization of the terminal steps of O-antigen synthesis in Salmonella typhimurium

Previous immunoelectron microscopic studies have shown that both the final intermediate in O-antigen synthesis, undecaprenol-linked O polymer, and newly synthesized O-antigenic lipopolysaccharide are localized to the periplasmic face of the inner membrane (C. A. Mulford and M. J. Osborn, Proc. Natl. Acad. Sci. USA 80:1159-1163, 1983). In vivo pulse-chase experiments now provide further evidence that attachment of O antigen to core lipopolysaccharide, as well as polymerization of O-specific polysaccharide chains, takes place at the periplasmic face of the membrane. Mutants doubly conditional in lipopolysaccharide synthesis [kdsA(Ts) pmi] were constructed in which synthesis of core lipopolysaccharide and O antigen are temperature sensitive and mannose dependent, respectively. Periplasmic orientation of O antigen:core lipopolysaccharide ligase was established by experiments showing rapid chase of undecaprenol-linked O polymer, previously accumulated at 42 degrees C in the absence of core synthesis, into lipopolysaccharide following resumption of core formation at 30 degrees C. In addition, chase of the monomeric O-specific tetrasaccharide unit into lipopolysaccharide was found in similar experiments in an O-polymerase-negative [rfc kdsA(Ts) pmi] mutant, suggesting that polymerization of O chains also occurs at the external face of the inner membrane.

An intermediate step in translocation of lipopolysaccharide to the outer membrane of Salmonella typhimurium

Evidence for transient localization of newly synthesized lipopolysaccharide at the periplasmic face of the inner membrane has been obtained by immunoelectron microscopic techniques. Salmonella typhimurium galE mutants in which O-antigen synthesis is dependent on addition of exogenous galactose were employed, and the distribution and fate of pulse-synthesized O antigen was examined by indirect ferritin labeling with anti-O-antigen IgG of spheroplasts prepared by treatment with lysozyme/EDTA. O-reactive lipopolysaccharide appeared rapidly at the exposed periplasmic face of the inner membrane after addition of galactose and was rapidly depleted upon termination of the pulse. Control experiments showed that secondary redistribution of lipopolysaccharide from outer membrane did not occur under the conditions employed for spheroplast formation and immunolabeling, and the pulse-chase kinetics were consistent with those expected for an intermediate in translocation of lipopolysaccharide to the outer membrane. In addition, undecaprenol-linked O antigen was detectable at the periplasmic face of the inner membrane within 30 sec after addition of galactose to a galE deep rough double mutant, and it accumulated stably in that location. The mutation in synthesis of the lipopolysaccharide core in the deep rough strain prevents transfer of O-antigen chains from undecaprenol phosphate to lipopolysaccharide. The result suggests that attachment of O antigen to lipopolysaccharide occurs on the extracytoplasmic side of the inner membrane and supports the conclusion that lipopolysaccharide is translocated to the outer membrane from the periplasmic, rather than the cytoplasmic, face of the inner membrane.

A surface polysaccharide of Escherichia coli O111 contains O-antigen and inhibits agglutination of cells by O-antiserum

The repeating pentasaccharide of O-antigen from Escherichia coli O111 contains galactose, glucose, N-acetylglucosamine, and colitose, the latter representing the major antigenic determinant. Phenol extraction of this strain was previously shown to release two fractions (I and II) containing O-antigen carbohydrate, and both fractions were believed to be lipopolysaccharide. We have now characterized fractions I and II and conclude that only fraction II represents lipopolysaccharide. Fraction II contains phosphate, 2-keto-3-deoxyoctonate, beta-hydroxymyristic acid, and potent endotoxin activity, whereas fraction I was deficient in all of these properties of the lipid A and core oligosaccharide regions of lipopolysaccharide. Fractions I and II each represented 50% of the total cellular O-antigen, and both were present on the cell surface. Both fractions were metabolically stable, and no precursor-product relationship existed between them. Fraction II had a number-average molecular weight of 15,800, corresponding to an average of 12 O-antigen repeats per molecule. In contrast, fraction I had a number-average molecular weight of 354,000, corresponding to an average of 404 O-antigen repeats per molecule. Before heat treatment, cells of E. coli O111 are poorly agglutinated by O-serum; although this indicates the presence of a capsule, the corresponding K-antigen was never detected. We conclude that fraction I, when present on the cell surface, inhibits agglutination of unheated cultures of E. coli O111 by O-serum because: (i) a variant strain which lacks fraction I was agglutinated by O-serum without prior heating; (ii) erythrocytes coated with purified fraction I behaved like bacteria containing fraction I in showing inhibition of O-serum agglutination; and (iii) heat treatment released fraction I and rendered bacterial cells agglutinable in O-serum.

Size heterogeneity of Salmonella typhimurium lipopolysaccharides in outer membranes and culture supernatant membrane fragments

Enterobacteriaceae cells growing in liquid media shed fragments of their outer membranes. These fragments, which may constitute a biologically important form of gram-negative bacterial endotoxin, have been reported to contain proteins, phospholipids, and lipopolysaccharides (LPS). In this study we compared the sizes of LPS molecules in shed membrane fragments and outer membranes from cells growing in broth cultures. Using conditional mutants of Salmonella typhimurium which incorporate specific sugars into LPS, we analyzed radiolabeled LPS by sodium dodecyl sulfate-polyacrylamide gel electrophoresis. This technique revealed that S. typhimurium LPS are more heterogeneous than previously known; molecules possessing from 0 to more than 30 O-chain repeat units were identified in outer membranes, supernatant fragments, and purified LPS. The size distributions of LPS molecules in outer membranes and supernatant fragments were similar; supernatant fragments appeared to be slightly enriched in molecules with long O-polysaccharide chains. Our results indicate the LPS molecules of many sizes are synthesized, translocated to outer membranes, and released into culture supernatants. Since the hydrophilic O-polysaccharides extend from bacterial surfaces into the aqueous environment, our findings suggest that the cell surface topography of this bacterium may be very irregular. We also speculate that heterogeneity in the degree of polymerization of O-antigenic side chains may influence the interactions of the toxic moiety of LPS (lipid A) with host constituents.

Variation in the structure and bacteriophage-inactivating capacity of Salmonella anatum lipopolysaccharide as a function of growth temperature

Growth temperature affects both the structure and the phage-inactivating capacity of Salmonella anatum A1 lipopolysaccharide. Whereas S. anatum cells normally synthesize smooth lipopolysaccharide when grown at physiological temperature (37 degrees C), a partial smooth-rough transition occurs when cells are grown at low temperature (20 to 25 degrees C). The synthesis at low growth temperature of lipopolysaccharide molecules lacking O-antigen was detected both by increased sensitivity of cells to the rough-specific bacteriophage Felix O-1 and by fractionation of oligosaccharides derived from lipopolysaccharide by mild acid hydrolysis. Growth temperature-induced changes in the structure of S. anatum A1 lipopolysaccharide also affected its ability to inactivate epsilon15, a bacteriophage that binds initially to the O-antigen portion of the molecule. Purified lipopolysaccharide prepared from cells grown at low growth temperature exhibited a higher in vitro phage-inactivating capacity than did lipopolysaccharide prepared from cells grown at physiological temperature (37 degrees C).

Interactions between lipopolysaccharide and phosphatidylethanolamine in molecular monolayers

Lipopolysaccharide and phosphatidylethanolamine are the two major lipid constituents of the membrane of Salmonella typhimurium. Interactions between the purified lipopolysaccharide and phosphatidylethanolamine were studied in molecular monolayers at air-water interfaces. The equilibrium surface pressures of mixed films of lipopolysaccharide and phosphatidylethanolamine were determined as a function of the film composition. The plot of the equilibrium surface pressrue vs. the area occupied by phosphatidylethanolamine molecules exhibited two distinct regions. Below a phosphatidylethanolamine surface concentration at which 55% of the surface was occupied by phosphatidylethanolamine molecules, the equilibrium pressure was invariant and had the value of a pure lipopolysaccharide monolayer at maximum compression. At phosphatidylethanolamine surface concentrations in excess of 55% surface area occupation (phosphatidylethanolamine/lipopolysaccharide (mol/mol) greater than 16), the equilibrium surface pressure was a function of the surface concentration of phosphatidylethanolamine. The results suggest a simple model in which lipopolysaccharide and phosphatidylethanolamine form a complex in which each lipopolysaccharide molecule is surrounded ("lipidated") by a shell of approx. 16 phosphatidylethanolamine molecules.

Purification of the O antigen of Bacteroides fragilis ss. fragilis NCTC 9343 from phenol-water extracts by gel filtration and chromatography on deae-cellulose and hydroxylapatite

O antigen extracted from whole cells of Bacteroides fragilis ss. fragilis NCTC 9343 with 45 per cent aqueous phenol has been purified by gel filtration and chromatography. First, the water phase was treated with RNase and DNase and passed through a column of agarose. The chromatographic procedures included ion exchange on a column of DEAE-cellulose and adsorption to hydroxylapatite. The O antigen was eluted from the DEAE-cellulose with a gradient of NaCl, and from the column of hydroxylapatite with 1 M phosphate buffer, pH 6.8. Inhibition of indirect haemagglutination was used to detect the O antigen in the eluates.

The isolation of two different lipopolysaccharide fractions from various Proteus mirabilis strains

Four distinct Proteus mirabilis strains were extracted by the phenol/water procedure. After ultracentrifugation of the dialyzed water phase, the pelleted lipopolysaccharide was purified and analyzed. The sugar composition of this lipopolysaccharide fraction I was similar for all four strains, containing only small amounts of strain-specific constituents. A second lipopolysaccharide fraction was isolated from the supernatant above (termed L1 fraction) after removal of nucleic acids. DEAE-cellulose chromatography indicated that this material is not a polysaccharide but rather a water-soluble lipopolysaccharide containing strain-specific constituents such as uronic acids, amino acids, amino sugars, neutral sugars, ethanolamine and phosphate, depending on the strain from which lipopolysaccharide II was isolated.

Glyceraldehyde phosphate at the reducing terminus of Salmonella Q haptens. Salmonella montevideo

The O antigen polysaccharide of Salmonella montevideo was isolated from a core-defective mutant by the phenol/water procedure, and was suspected to contain phosphomonester and cyclic phosphodiester at its reducing end in anology to the O hapten from Salmonella typhimurium (Kent and Obsborn, 1968. Therefore, it was chromatographed on a DEAE-cellulose column. Whereas one part eluted with water the other part of the polysaccharide could only be eluted with buffer. Both fractions were further purified on Sephadex G100 and contained mannose, glucose, N-acetylglucosamine and phosphate in a molar ratio of 4:1:1: less than 0.1. In order to specifically label the reducing end phosphate was removed enzymatically, or the presumed cyclic diester was cleaved by mild hydrolysis, and the fractions were reduced with sodium horo[3H]hydride. Both fractions yield mainly [3H]glycerol after hydrolysis and paper chromatogaphy. In addition, [3H]mannitol and [H]monohydroxyacetone could be identified by paper chromatography and were concluded to be the result of phosphate migration and beta-elimination reactions taking place during the isolation procedure and the various treatments prior to sodium boro[3H]hydride reduction. These findings in addition to periodate oxidation studies indicated that the O antigen polysaccharide of Salmonella montevideo had glyceraldehyde phosphate at its reducing end. From the incorporation of 3H into the polysaccharide the O antigen was calculated to consist of about 19 repeating units of 6 sugar residues each.

Glucose transfer from dolichol monophosphate glucose: the product formed with endogenous microsomal acceptor

The product formed by incubation of dolichol monophosphate glucose with liver microsomes was studied. It is insoluble in most solvents, but is soluble in a chloroform-methanol mixture with a high content of water. Treatment with ammonia gave rise to the formation of a water soluble, negatively charged compound of molecular weight 3550. The negative charge could be removed by treatment with phosphatase. Acid hydrolysis of the original compound led to the liberation of an uncharged, water-soluble compound (molecular weight 3550). Acetolysis of the latter gave rise to the formation of a series of products, which appeared to be oligosaccharides when chromatographed on paper or silica plates. The original substance behaved like a polyprenol pyrophosphate when chromatographed on DEAE-cellulose. Molecular weight measurements of the deoxycholate inclusion compound gave a value of 14,300, while dolichol monophosphate glucose under the same conditions gave 11,300. It is tentatively suggested that the compound is dolichol joined through a phosphate or pyrophosphate bridge to an oligosaccharide containing about 20 monosaccharide residues.

Role of lipids in the biosynthesis of the bacterial cell envelope

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Biosynthesis of T1 antigen in Salmonella: biosynthesis in a cell-free system

A particulate fraction from a T1 form of Salmonella typhimurium incorporated radioactivity from uridine diphosphate (UDP)-(14)C-glucose into products associated with the particulate enzyme. A major fraction of the incorporated radioactivity was found in the cell wall lipopolysaccharide fraction. Acid hydrolysis of incorporation products produced labeled galactose, ribose, and also glucose. The incorporation of glucose could be dissociated from the incorporation of galactose and ribose under certain conditions, and was assumed to represent incorporation into a polymer not related to T1 antigen. The incorporation of galactose and ribose probably represented the synthesis of T1 side chains of lipopolysaccharide, because (i) particulate fractions from non-T1 strains incorporated much less of these sugars and (ii) periodate oxidation and borohydride reduction converted a large portion of incorporated galactose residues into arabinose. The latter finding indicates that the galactose residues are galactofuranosides substituted either at C2 or C3; about 70% of the galactose residues in T1 side chains are known to be galactofuranosides substituted at C3. UDP-(14)C-galactose preparation used was not contaminated by UDP-(14)C-galactofuranose; therefore pyranose-to-furanose conversion must have taken place at some step during the reactions described above. The mechanism of conversion of galactose to ribose is not clear, but it was not found to involve a selective elimination of C1 or C6 of galactose or glucose.

Mechanism of conversion of the salmonella O antigen by bacteriophageepsilon 34

The structural determinants for antigen 34 in the E group salmonella are glucosyl substituents on the galactosyl units of the O antigen which has a mannosylrhamnosylgalactose repeating sequence. The temperate bacteriophage epsilon(34) brings about the production of antigen 34. It has been shown here that glucose is transferred from uridine diphosphate glucose to the O antigen via a glucosyl-lipid intermediate in a two-step reaction. Glucose is linked through carbon 1 to the lipid by a phosphodiester bridge, the glucosyl bond having the beta-anomeric configuration. The lipid is a C(55)-polyisoprenoid alcohol, each isoprene unit having one double bond. It is the same lipid which is involved in the synthesis of the O antigen repeating sequence.

The synthesis of exopolysaccharide by Klebsiella aerogenes membrane preparations and the involvement of lipid intermediates

1. Membrane preparations from Klebsiella aerogenes type 8 were shown to transfer glucose and galactose from their uridine diphosphate derivatives to a lipid and to polymer. The ratio of glucose to galactose transfer in both cases was 1:2. This is the same ratio in which these sugars occur in native polysaccharide. Galactose transfer was dependent on prior glucosylation of the lipid. Mutants were obtained lacking (a) glucosyltransferase and (b) galactosyltransferase. The transferase activities in a number of non-mucoid mutants was examined. 2. Glucose transfer was partially inhibited by uridine monophosphate, and incorporation of either glucose or galactose into lipid was decreased in the presence of uridine diphosphate. The sugars are thought to be linked to a lipid through a pyrophosphate bond, and treatment of the lipid intermediates with phenol yielded water-soluble compounds. These could be dephosphorylated with alkaline phosphatase. Transfer of glucuronic acid to lipid or polymer from uridine diphosphate glucuronic acid was much lower than that of the other two sugars. 3. The fate of sugars incorporated into polymer was also followed. Some conversion of glucose into galactose and glucuronic acid occurred. Mutants unable to transfer glucose or galactose to lipid were unable to form polymer. Other mutants capable of lipid glycosylation were in some cases unable to form polymer. A model for capsular polysaccharide synthesis is proposed and its similarity to the formation of other polymers outside the cell membrane is discussed.

Resistance of Salmonella typhimurium mutants to galactose death

A class of galactose-resistant mutants has been derived from strains of Salmonella typhimurium which are defective in uridine diphosphoglucose-4-epimerase. Resistant strains are phenotypically similar to parent organisms but do not lyse in the presence of galactose. Low levels of functional epimerase can be detected in induced cells grown at 20 C but not at 37 C, and acid is not produced from galactose. Sufficient galactose is synthesized at reduced temperatures to fabricate smooth lipopolysaccharide and acceptor sites for phage P22 from galactose-deficient media. The leaky nature of these mutants may account for resistance to galactose death by maintaining galactose metabolites at a subcritical level. Glucose protects sensitive strains by control of levels of toxic metabolites by catabolite repression.

Biosynthesis of cell wall lipopolysaccharide in mutants of Salmonella. V. A mutant of Salmonella typhimurium defective in the synthesis of cytidine diphosphoabequose

A mutant of Salmonella typhimurium LT2 was found to be unable to convert cytidine diphospho-4-keto-6-deoxy-d-glucose into cytidine diphosphoabequose. The mutation maps in the rfb gene cluster, which is known to be involved in the biosynthesis of the peripheral, "O side-chain" portion of cell wall lipopolysaccharide. In spite of the fact that, in the O side chains, abequose is not a part of the main chain but occurs as short branches, the mutant appears to be unable to polymerize oligosaccharide "repeat units" into long O side chains. The following evidence indicates that this failure is the result of the absence of cytidine diphosphoabequose rather than that of a superimposed second mutation in other genes of the rfb cluster. (i) The mutant does not behave like a multisite mutant in genetic crosses, and it gives rise, at a high frequency, to "revertants" where the ability to synthesize cytidine diphosphoabequose and the ability to synthesize normal lipopolysaccharide with O side chains are both restored. (ii) The mutant strain has normal levels of activity of all of the other enzymes known to be involved in O side-chain synthesis, except that the levels of several enzymes were lowered by about 30% owing to the polarity effect of the mutation. That the lowering of these enzymes is not responsible for the failure of the mutant to synthesize O side chains is clear from the fact that there were revertants which had regained some ability to synthesize abequose but still had lowered levels of these other enzymes, and that this type of revertant produced lipopolysaccharide with considerable amounts of O side chains.