Identification and characterization of the capsular polysaccharide (K-antigen) locus of Porphyromonas gingivalis

Capsular polysaccharides of gram-negative bacteria play an important role in maintaining the structural integrity of the cell in hostile environments and, because of their diversity within a given species, can act as useful taxonomic aids. In order to characterize the genetic locus for capsule biosynthesis in the oral gram-negative bacterium Porphyromonas gingivalis, we analyzed the genome of P. gingivalis W83 which revealed two candidate loci at PG0106-PG0120 and PG1135-PG1142 with sufficient coding capacity and appropriate gene functions based on comparisons with capsule-coding loci in other bacteria. Insertion and deletion mutants were prepared at PG0106-PG0120 in P. gingivalis W50-a K1 serotype. Deletion of PG0109-PG0118 and PG0116-PG0120 both yielded mutants which no longer reacted with antisera to K1 serotypes. Restriction fragment length polymorphism analysis of the locus in strains representing all six K-antigen serotypes and K(-) strains demonstrated significant variation between serotypes and limited conservation within serotypes. In contrast, PG1135-PG1142 was highly conserved in this collection of strains. Sequence analysis of the capsule locus in strain 381 (K(-) strain) demonstrated synteny with the W83 locus but also significant differences including replacement of PG0109-PG0110 with three unique open reading frames, deletion of PG0112-PG0114, and an internal termination codon within PG0106, each of which could contribute to the absence of capsule expression in this strain. Analysis of the Arg-gingipains in the capsule mutants of strain W50 revealed no significant changes to the glycan modifications of these enzymes, which indicates that the glycosylation apparatus in P. gingivalis is independent of the capsule biosynthetic machinery.

Role of the carbohydrate binding site of the Streptococcus pneumoniae capsular polysaccharide type 3 synthase in the transition from oligosaccharide to polysaccharide synthesis

The type 3 synthase catalyzes the formation of the Streptococcus pneumoniae type 3 capsular polysaccharide [-3)-beta-D-GlcUA-(1, 4)-beta-D-Glc-(1-]n. Synthesis is comprised of two distinct catalytic phases separated by a transition step whereby an oligosaccharylphosphatidylglycerol primer becomes tightly bound to the carbohydrate acceptor recognition site of the synthase. Using the recombinant synthase in Escherichia coli membranes, we determined that a critical oligosaccharide length of approximately 8 monosaccharides was required for recognition of the growing chain by the synthase. Upon binding of the oligosaccharide-lipid to the carbohydrate recognition site, the polymerization reaction entered a highly processive phase to produce polymer of high molecular weight. The initial oligosaccharide-synthetic phase also appeared to be processive, the duration of which was enhanced by the concentration of UDP-GlcUA and diminished by an increase in temperature. The overall reaction approached a steady state equilibrium between the polymer- and oligosaccharide-forming phases that was shifted toward the former by higher UDP-GlcUA levels or lower temperatures and toward the latter by lower concentrations of UDP-GlcUA or higher temperatures. The transition step between the two enzymatic phases demonstrated cooperative kinetics, which is predicted to reflect a possible reorientation of the oligosaccharide-lipid in conjunction with the formation of a tight binding complex.

Receptor-mediated clearance of Cryptococcus neoformans capsular polysaccharide in vivo

Cryptococcus neoformans capsular glucuronoxylomannan (GXM) is shed during cryptococcosis and taken up by macrophages. The roles of the putative GXM receptors CD14, CD18, Toll-like receptor 2 (TLR2), and TLR4 in GXM clearance from serum and deposition in the liver and spleen in receptor-deficient mice were studied. While alterations in the kinetics of GXM redistribution were seen in the mutant mice, none of the receptors was absolutely required for serum clearance or hepatosplenic accumulation.

Capsule-negative Staphylococcus aureus induces chronic experimental mastitis in mice

Staphylococcus aureus capsular polysaccharides (CP) have been shown to enhance staphylococcal virulence in numerous animal models of infection. Although serotype 5 CP (CP5) and CP8 predominate among S. aureus isolates from humans, most staphylococcal isolates from bovines with mastitis in Argentina are capsule negative. This study was designed to evaluate the effects of CP5 and CP8 expression on the pathogenesis of experimental murine mastitis. Lactating mice were challenged by the intramammary route with one of three isogenic S. aureus strains producing CP5, CP8, or no capsule. Significantly greater numbers of acapsular mutant cells were recovered from the infected glands 12 days after bacterial challenge compared with the encapsulated strains. Histopathological analyses revealed greater polymorphonuclear and mononuclear leukocyte infiltration and congestion in the mammary glands of mice infected with the encapsulated strains compared with the acapsular mutant, and the serotype 5 strain elicited more inflammation than the serotype 8 strain. In vitro experiments revealed that the acapsular S. aureus strain was internalized by MAC-T bovine epithelial cells in significantly greater numbers than the CP5- or CP8-producing strain. Taken together, the results suggest that S. aureus lacking a capsule was able to persist in the murine mammary gland, whereas encapsulated strains elicited more inflammation and were eliminated faster. Loss of CP5 or CP8 expression may enhance the persistence of staphylococci in the mammary glands of chronically infected hosts.

Biosynthesis and assembly of capsular polysaccharides in Escherichia coli

Capsules are protective structures on the surfaces of many bacteria. The remarkable structural diversity in capsular polysaccharides is illustrated by almost 80 capsular serotypes in Escherichia coli. Despite this variation, the range of strategies used for capsule biosynthesis and assembly is limited, and E. coli isolates provide critical prototypes for other bacterial species. Related pathways are also used for synthesis and export of other bacterial glycoconjugates and some enzymes/processes have counterparts in eukaryotes. In gram-negative bacteria, it is proposed that biosynthesis and translocation of capsular polysaccharides to the cell surface are temporally and spatially coupled by multiprotein complexes that span the cell envelope. These systems have an impact on both a general understanding of membrane trafficking in bacteria and on bacterial pathogenesis.

Capsular polysaccharides secreted by building façade colonisers: characterisation and adsorption to surfaces

Exopolymers secreted by algal and cyanobacterial strains isolated from building façades were imaged by microscopy techniques. They were extracted and characterised to investigate their possible contribution to interactions with solid surfaces. The polymers were polysaccharides, with anionic and hydrophobic properties varying between the various strains. Capsular polysaccharides extracted from a strain of Klebsormidium flaccidum adsorbed in higher amounts on hydrophobic than on hydrophilic surfaces. These results tend to confirm the hypothesis that exopolymers are important in the colonisation process of microorganisms to surfaces.

Escherichia coli K1's capsule is a barrier to bacteriophage T7

Escherichia coli strains that produce the K1 polysaccharide capsule have long been associated with pathogenesis. This capsule is believed to increase the cell's invasiveness, allowing the bacteria to avoid phagocytosis and inactivation by complement. It is also recognized as a receptor by some phages, such as K1F and K1-5, which have virion-associated enzymes that degrade the polysaccharide. In this report we show that expression of the K1 capsule in E. coli physically blocks infection by T7, a phage that recognizes lipopolysaccharide as the primary receptor. Enzymatic removal of the K1 antigen from the cell allows T7 to adsorb and replicate. This observation suggests that the capsule plays an important role as a defense against some phages that recognize structures beneath it and that the K1-specific phages evolved to counter this physical barrier.

Validation of a pXO2-A PCR assay to explore diversity among Italian isolates of Bacillus anthracis strains closely related to the live, attenuated Carbosap vaccine

Several circulating Bacillus anthracis strains isolated in Italy and belonging to the A1.a cluster, genotype 3 (A1.a-3) are genotypically indistinguishable from Carbosap, a live attenuated vaccine strain, containing both pXO1 and pXO2 plasmids. The genotype was assessed by using eight-locus multilocus variable-number tandem repeat analysis. We describe here the use of a ninth locus able to explore variability among strains that have the same genotype. It is important to be able to genotype the wild isolate of B. anthracis strains from outbreaks of anthrax in areas where Carbosap vaccination of cattle and sheep is common practice. A total of 27 representative field strains isolated in Italy and four vaccinal strains, namely, Carbosap, Sterne, Pasteur I, and Pasteur II, were characterized by a ninth marker, called pXO2-A. Twenty-three field strains were genotype 3 and therefore identical to Carbosap. The marker was in the pXO2 plasmid and is based on the polymorphism of the already-known VX2-3 locus. Detection was obtained by PCR with fluorescence-labeled forward primers in order to produce appropriate fragments for capillary electrophoresis with an ABI 310 genetic analyzer. Genetic relationships showed heterogeneity in all of the examined samples. Interestingly, with respect to genotype 3, samples grouped into eight different subtypes, A to H, and the subtype G, had only two samples indistinguishable from Carbosap. The results of the present study confirm the validity of a hierarchical progressive protocol for discrimination among closely related isolates.

Use of pyrosequencing to differentiate Streptococcus pneumoniae serotypes 6A and 6B

Accurate serotyping of Streptococcus pneumoniae remains important to monitor the changes in seroepidemiology of the organism over time. Though several PCR-based systems have been developed for this purpose, the cross-reactivity within serogroups often limits discrimination between types. All serogroup 6 isolates can be identified using a multiplex PCR system; however, due to the high sequence homology between the cps-6B and cps-6A loci, serotypes 6A and 6B cannot be differentiated by this method. We describe the use of pyrosequencing to reliably differentiate between serotypes 6A and 6B using a previously described single nucleotide polymorphism at codon 195 of the cps locus wciP gene. We observed complete concordance between capsular serotyping results and wciP pyrosequencing among 210 isolates examined, indicating that pyrosequencing is a rapid and accurate technique for deducing serotypes 6A and 6B.

Difficulty in diagnosing chronic meningitis caused by capsule-deficient Cryptococcus neoformans

We report a case of chronic meningitis due to capsule-deficient Cryptococcus neoformans which could not be diagnosed by routine morphological and immunological cerebrospinal fluid (CSF) examination. Repeated CSF examination and culture did not disclose the fungal body, and the cryptococcal antigen tests were always negative. Culture of ventricular fluid showed non-encapsulated cultured cells which were stained positively by indirect immunofluorescence using diluted sera from another patient diagnosed with cryptococcal meningitis. Inoculation of dispersed colonies into mice resulted in encapsulated C neoformans. It is important to suspect capsule-deficient C neoformans when the conventional diagnostic approaches fail to identify the organism or antigens.

Influence of clindamycin on the stability of coa and fnbB transcripts and adherence properties of Staphylococcus aureus Newman

We investigated whether a subinhibitory concentration of clindamycin (Cli), corresponding to 1/2 the strain-specific minimum inhibitory concentration (MIC), could affect expression and stability of transcripts from genes coding for specific adhesins such as fibronectin binding proteins A (fnbA) and B (fnbB) as well as coagulase (coa) in Staphylococcus aureus strain Newman. Furthermore, the effect of 1/2 MIC of Cli on adherence properties and expression of type 5 capsular polysaccharides (CP5) was investigated. Northern slot blot experiments confirmed that the amount of coa- and fnbB-specific mRNA, in contrast to that of fnbA-specific mRNA, was increased 2-fold after treatment of S. aureus Newman with 1/2 MIC of Cli. Analysis of RNA stability revealed that the increased amounts of transcripts of coa and fnbB were due to stabilization of the respective mRNAs. However, when treated with 1/2 MIC of Cli, S. aureus Newman showed no significant changes neither in its adherence patterns to fibrinogen- or fibronectin-coated micotitre plates, nor to epithelial HEp-2 cells and also not in its CP5 expression. Therefore, we conclude that increased mRNA stability of fnbB and coa by 1/2 MIC Cli, in contrast to the situation seen with the protein biosynthesis inhibiting antibiotic florfenicol, does not result in an increase in adherence of S. aureus Newman.

Capsule and fimbria interaction in Klebsiella pneumoniae

The capsular polysaccharide and type 1 fimbriae are two of the major surface-located virulence properties associated with the pathogenesis of Klebsiella pneumoniae. The capsule is an elaborate polysaccharide matrix that encases the entire cell surface and provides resistance against many host defense mechanisms. In contrast, type 1 fimbriae are thin adhesive thread-like surface organelles that can extend beyond the capsular matrix and mediate d-mannose-sensitive adhesion to host epithelial cells. These fimbriae are archetypical and consist of a major building block protein (FimA) that comprises the bulk of the organelle and a tip-located adhesin (FimH). It is assumed that the extended major-subunit protein structure permits the FimH adhesin to function independently of the presence of a capsule. In this study, we have employed a defined set of K. pneumoniae capsulated and noncapsulated strains to show that the function of type 1 fimbriae is actually impeded by the concomitant expression of a polysaccharide capsule. Capsule expression had significant effects on two parameters commonly used to define FimH function, namely, yeast cell agglutination and biofilm formation. Our data suggest that this effect is not due to transcriptional/translational changes in fimbrial gene/protein expression but rather the result of direct physical interference. This was further demonstrated by the fact that we could restore fimbrial function by inhibiting capsule synthesis. It remains to be determined whether the expression of these very different surface components occurs simply via random events of phase variation or in a coordinated manner in response to specific environmental cues.

Identification of an Escherichia coli operon required for formation of the O-antigen capsule

Escherichia coli produces polysaccharide capsules that, based on their mechanisms of synthesis and assembly, have been classified into four groups. The group 4 capsule (G4C) polysaccharide is frequently identical to that of the cognate lipopolysaccharide O side chain and has, therefore, also been termed the O-antigen capsule. The genes involved in the assembly of the group 1, 2, and 3 capsules have been described, but those required for G4C assembly remained obscure. We found that enteropathogenic E. coli (EPEC) produces G4C, and we identified an operon containing seven genes, ymcD, ymcC, ymcB, ymcA, yccZ, etp, and etk, which are required for formation of the capsule. The encoded proteins appear to constitute a polysaccharide secretion system. The G4C operon is absent from the genomes of enteroaggregative E. coli and uropathogenic E. coli. E. coli K-12 contains the G4C operon but does not express it, because of the presence of IS1 at its promoter region. In contrast, EPEC, enterohemorrhagic E. coli, and Shigella species possess an intact G4C operon.

Conserved virulence of C to B capsule switched Neisseria meningitidis clinical isolates belonging to ET-37/ST-11 clonal complex

Capsule switching in Neisseria meningitidis is thought to occur by horizontal DNA exchange between meningococcal strains. Antigenic variants may be generated by allelic replacement of the siaD gene; the variants may then be selected by specific immunity against the capsular antigen. There were several vaccination campaigns against serogroup C in France in 2002, following an increase in the prevalence of invasive isolates of serogroup C of the phenotype C:2a:P1.5 and C:2a:P1.5,2 belonging to the ET-37/ST-11 clonal complex. We evaluated the emergence of capsule variants by the detection of B:2a:P1.5 and B:2a:P1.5,2 meningococcal isolates of the ET-37/ST-11 clonal complex. These isolates were significantly more frequent after the year 2002. Pulsed field gel electrophoresis profiles of the serogroup B (ET-37/ST-11) isolates differed from that of serogroup C (ET-37/ST-11) isolates by the bands that harbor the siaD genes responsible for the serogroup specificity. However, serogroup B and C, ET37/ST-11 isolates both express similar virulence as assessed from colonization and invasiveness in a mouse model. Our results indicate that capsule switching events within the same clonal complex can arise frequently with no alteration in virulence. This justifies an enhanced system of surveillance by molecular typing of such isolates, particularly after serogroup-specific vaccination.

Initiation and synthesis of the Streptococcus pneumoniae type 3 capsule on a phosphatidylglycerol membrane anchor

The type 3 synthase from Streptococcus pneumoniae is a processive beta-glycosyltransferase that assembles the type 3 polysaccharide [3)-beta-D-GlcUA-(1-->4)-beta-D-Glc-(1-->] by a multicatalytic process. Polymer synthesis occurs via alternate additions of Glc and GlcUA onto the nonreducing end of the growing polysaccharide chain. In the presence of a single nucleotide sugar substrate, the type 3 synthase ejects its nascent polymer and also adds a single sugar onto a lipid acceptor. Following single sugar incorporation from either UDP-[(14)C]Glc or UDP-[(14)C]GlcUA, we found that phospholipase D digestion of the Glc-labeled lipid yielded a product larger than a monosaccharide, while digestion of the GlcUA-labeled lipid resulted in a product larger than a disaccharide. These data indicated that the lipid acceptor contained a headgroup and that the order of addition to the lipid acceptor was Glc followed by GlcUA. Higher-molecular-weight product synthesized in vitro was also sensitive to phospholipase D digestion, suggesting that the same lipid acceptor was being used for single sugar additions and for polymer formation. Mass spectral analysis of the anionic lipids of a type 3 S. pneumoniae strain demonstrated the presence of glycosylated phosphatidylglycerol. This lipid was also observed in Escherichia coli strains expressing the recombinant type 3 synthase. The presence of the lipid primer in S. pneumoniae membranes explained both the ability of the synthase to reinitiate polysaccharide synthesis following ejection of its nascent chain and the association of newly synthesized polymer with the membrane. Unlike most S. pneumoniae capsular polysaccharides, the type 3 capsule is not covalently linked to the cell wall. The present data indicate that phosphatidylglycerol may anchor the type 3 polysaccharide to the cell membrane.

Sialylation of group B streptococcal capsular polysaccharide is mediated by cpsK and is required for optimal capsule polymerization and expression

Several bacterial pathogens have evolved the means to escape immune detection by mimicking host cell surface carbohydrates that are crucial for self/non-self recognition. Sialic acid, a terminal residue on these carbohydrates, inhibits activation of the alternate pathway of complement by recruiting the immune modulating molecule factors H, I, and iC3b. Sialylation of capsular polysaccharide (CPS) is important for virulence of group B streptococci (GBS), a significant human pathogen. We previously reported that cpsK, a gene within the cps locus of type III GBS, could complement a sialyltransferase deficient lst mutant of Haemophilus ducreyi, implicating its role in sialylation of the GBS capsule. To explore the function of cpsK in GBS capsule production, we created a mutant in cpsK. Immunoblot analysis and enzyme-linked immunosorbent assay using anti-type III CPS antisera demonstrated that the mutant CPS did not contain sialic acid. This was confirmed by high-performance liquid chromatography after mild acid hydrolysis of the CPS. Although increased CPS chain length was seen for this strain, CPS production was <20% of the parental isolate. An episomal cpsK copy restored synthesis of sialo-CPS to wild-type levels. These data support our hypothesis that cpsK encodes the GBS CPS sialyltransferase and provide further evidence that lack of CPS oligosaccharide sialylation reduces the amount of CPS expressed on the cell surface. These observations also imply that one or more of the components involved in synthesis or transport of oligosaccharide repeating units requires a sialo-oligosaccharide for complete activity.

[Influence of nicotinamide adenine dinucleotide and hemin concentrations on the growth of Haemophilus influanzae type b and the synthesis of capsular polysaccharide]

In the process the cultivation of H. influenzae, type b, in semisynthetic nutrient medium with aminopeptide base the growth of the bacteria and the synthesis of capsular polysaccharide were shown to depend on the concentrations of aminopeptide, nicotinamide adenine nucleotide (NAD) and hemin. An increase in the concentrations of NAD and hemin stimulated the growth of H. influenzae and inhibited the synthesis of capsular polysaccharide. Similar effect was observed in the simultaneous increase of NAD and hemin concentrations. At elevated concentrations of NAD and hemin and the content of aminopeptide equal to 350 mI/l the maximum weight of biomass was achieved. The increase of hemin concentration had no influence on the growth of H. influenzae, type b, and the synthesis of capsular polysaccharide.

The capsular polysaccharide biosynthesis of Streptococcus pneumoniae serotype 8: functional identification of the glycosyltransferase WciS (Cap8H)

CPS (capsular polysaccharide) is a major virulence factor in Streptococcus pneumoniae. Biosynthesis of CPS RU (repeat unit) proceeds by sequential transfer of sugar residues from the appropriate sugar donor to an activated lipid carrier by committed GTs (glycosyltransferases). While the nucleotide sequence of many cps loci is already known, the real substrate specificity of the hypothetical GTs, as well as the sequence of sugar addition is unclear. In the present paper, we report the biochemical characterization of one alpha-galactosyltransferase, WciS (Cap8H), a member of GT family 4. This enzyme is implicated in the tetrasaccharide RU biosynthetic pathway of Strep. pneumoniae CPS 8 ([-->4)-alpha-D-Glcp-(1-->4)-alpha-D-Galp-(1-->4)-beta-D-GlcAp-(1-->4)-beta-D-Glcp-(1-->]n). Expression of WciS-His6 in Escherichia coli BL21 (DE3) strains or BL21 (DE3)/DeltagalU strain resulted in synthesis of a 39 kDa membrane-associated protein identified by N-terminal sequencing and recognized by anti-His6-tag antibody. This protein was capable of adding a galactose residue cellobiuronic acid [beta-D-GlcAp-(1-->4)-D-Glcp]-pyrophosphate-polyprenol from UDP-Gal. The newly added galactose residue is removed by alpha-galactosidase, indicating that WciS is a retaining GT. Our results suggest that WciS catalyses the addition of the third sugar residue of the CPS 8 RU. The recombinant WciS-His6 was solubilized and purified as a soluble multimer, opening the way for structural studies.

Bacillus anthracis CapD, belonging to the γ-glutamyltranspeptidase family, is required for the covalent anchoring of capsule to peptidoglycan

Several examples of bacterial surface-structure anchoring have been described, but they do not include polyglutamate capsule. Bacillus anthracis capsule, which is composed only of poly-gamma- d-glutamate, is one of the two major virulence factors of the bacterium. We analysed its anchoring. We report that the polyglutamate is anchored directly to the peptidoglycan and that the bond is covalent. We constructed a capD mutant strain, capD being the fourth gene of the capsule biosynthetic operon. The mutant bacilli are surrounded by polyglutamate material that is not covalently anchored. Thus, CapD is required for the covalent anchoring of polyglutamate to the peptidoglycan. Sequence similarities suggest that CapD is a gamma-glutamyltranspeptidase. Furthermore, CapD is cleaved at the gamma-glutamyltranspeptidase consensus cleavage site, and the two subunits remain associated, as necessary for gamma-glutamyltranspeptidase activity. Other Gram-positive gamma-glutamyltranspeptidases are secreted, but CapD is located at the Bacillus surface, associated both with the membrane and the peptidoglycan. Polyglutamate is hydrolysed by CapD indicating that it is a CapD substrate. We suggest that CapD catalyses the capsule anchoring reaction. Interestingly, the CapD(-) strain is far less virulent than the parental strain.

Characterization and quantification of C-polysaccharide in Streptococcus pneumoniae capsular polysaccharide preparations

Purified capsular polysaccharide preparations from Streptococcus pneumoniae that are used for vaccine production typically contain residual levels of C-polysaccharide (C-Ps). Residual C-Ps is typically found in one of two forms, either chemically linked to the capsular polysaccharide (bound) or present by itself (free). Two analytical methods have been developed and applied to determine the relative percentages of the two C-Ps forms present in various capsular polysaccharide preparations. Both methods differentiate the two forms of C-Ps according to the difference of their hydrodynamic sizes. One method is based on labeling C-Ps with a fluorescent tag and separating the two forms of C-Ps by high-performance size exclusion chromatography with on-line refractive index and fluorescence detection, and the other method is based on measuring self-diffusion rates of the two forms of C-Ps by nuclear magnetic resonance (NMR) and quantifying each form with deconvolution. Both methods were evaluated for relative accuracy, precision, and ease of application, and they were found to provide comparable results for a large number of pneumococcal polysaccharide preparations. These analyses, combined with other quantitative NMR measurement of total C-Ps in the polysaccharide powder, provide a more refined means of evaluating the amount of each form of C-Ps in polysaccharide preparations targeted for vaccine production.

[Influence of the aminopeptide concentration on the growth of Haemophilus influenzae, type b, and the synthesis of its capsular polysaccharide]

The influence of the aminopeptide concentration on the growth of H. influenzae b culture and the synthesis of H. influenzae b capsular polysaccharide was determined. The maximum amount of capsular polysaccharide was accumulated at the concentration of aminopeptide in the culture fluid reaching 50 ml/l. An increase in the aminopeptide concentration led to a decreased amount of synthesized polysaccharide and an increased amount of biomass. The decrease of the aminopeptide concentration to 10 ml/l resulted in decreased amounts of both biomass and synthesized polysaccharide.

Amyloids--a functional coat for microorganisms

Amyloids are filamentous protein structures approximately 10 nm wide and 0.1-10 mum long that share a structural motif, the cross-beta structure. These fibrils are usually associated with degenerative diseases in mammals. However, recent research has shown that these proteins are also expressed on bacterial and fungal cell surfaces. Microbial amyloids are important in mediating mechanical invasion of abiotic and biotic substrates. In animal hosts, evidence indicates that these protein structures also contribute to colonization by activating host proteases that are involved in haemostasis, inflammation and remodelling of the extracellular matrix. Activation of proteases by amyloids is also implicated in modulating blood coagulation, resulting in potentially life-threatening complications.

Escherichia coli K1 polysialic acid O-acetyltransferase gene, neuO, and the mechanism of capsule form variation involving a mobile contingency locus

Potential O-acetylation of the sialic acid residues of Escherichia coli K1, groups W-135, Y, and C meningococci, and group B Streptococcus capsular polysaccharides modifies their immunogenicity and susceptibility to glycosidases. Despite the biological importance of O-acetylation, no sialic or polysialic acid O-acetyltransferase has been identified in any system. Here we show that the E. coli K1 O-acetyltransferase encoded by neuO is genetically linked to the endo-neuraminidase tail protein gene of a chromosomal accretion element, designated CUS-3, with homology to lambdoid bacteriophage. Molecular epidemiological analysis established concordance between O-acetyltransferase and CUS-3 in a set of E. coli K1 strains. Deleting neuO eliminated enzymatic activity, which was restored by complementation in trans, and confirmed by (13)C-NMR analysis of the acetylated product. Analysis of mutants that accumulate intracellular polysialic acid because of export defects (kpsM and kpsS) or an inability to synthesize the sialic acid precursor, N-acetylmannosamine (neuC), indicated that NeuO does not require constant association with its substrate for activity. DNA sequencing and PCR analysis of neuO from strains that had undergone random capsule form variation showed that slip strand DNA mispairing or unequal recombination resulted in gain or loss of (5'-AAGACTC-3')(n) heptanucleotide repeats (where n approximately equals 14-39) located in the neuO 5' region. These repeats code for a previously undescribed structure designated the poly(Psi) motif. The unexpected discovery of the neuO contingency locus (hypervariable gene controlling expression of a surface epitope) in E. coli, and of a potential phage for redistributing variant neuO alleles, provides a robust system for investigating the functions of localized hypermutability in pathogen evolution.

Translocation and surface expression of lipidated serogroup B capsular Polysaccharide in Neisseria meningitidis

The capsule of N. meningitidis serogroup B, (alpha2-->8)-linked polysialic acid and the capsules of other meningococcal serogroups and of other gram-negative bacterial pathogens are anchored in the outer membrane through a 1,2-diacylglycerol moiety. Previous work on the meningococcal cps complex in Escherichia coli K-12 indicated that deletion of genes designated lipA and lipB caused intracellular accumulation of hyperelongated capsule polymers lacking the phospholipid substitution. To better understand the role of lip and lipB in capsule expression in a meningococcal background, the location, sequence, and relationship to related bacterial capsule genes were defined and specific mutations in lipA and lipB were generated in the serogroup B meningococcal strain NMB. The lipA and lipB genes are located on the 3' end of the ctr operon and are most likely transcribed independently. Inactivation of lipA, lipB, and both resulted in the same total levels of capsular polymer production as in the parental controls; however, these mutants were as sensitive as an unencapsulated mutant to killing by normal human serum. Immunogold electron microscopy and flow cytometric analyses revealed intracellular inclusions of capsular polymers in lipA, lipB, and lipA lipB mutants. Capsular polymers purified from lipA, lipB, and lipA lipB mutants were lipidated. The phospholipid anchor was shown by gas chromatography-mass spectroscopy analysis to be a phosphodiester-linked 1,2-dipalmitoyl (C16:0) glycerol moiety and was identical in structure to that found on the wild-type meningococcal capsule polymers. Thus, lipA and lipB do not encode proteins responsible for diacylglycerophosphatidic acid substitution of the meningococcal capsule polymer; rather, they are required for proper translocation and surface expression of the lipidated polymer.