Classification of Vibrio vulnificus strains by the carbohydrate composition of their capsular polysaccharides

Total Synthesis of the Tetrasaccharide Haptens of Vibrio vulnificus MO6-24 and BO62316 and Immunological Evaluation of Their Protein Conjugates

Vibrio vulnificus is a human pathogen that can cause fatal septicemia and necrotizing infections with a high lethal rate exceeding 50%. V. vulnificus MO6-24 and BO62316 are two predominant virulent strains associated with approximately one-third of the clinical infections. The capsular polysaccharides (CPSs) of V. vulnificus consist of several structurally unique sugars and are excellent targets for developing effective glycoconjugate vaccines. This article describes the first total synthesis of the challenging tetrasaccharide repeating units of V. vulnificus MO6-24 and BO62316 CPSs. A key feature of this synthesis was the assembly of the tetrasaccharide skeleton using a 3,4-branched trisaccharide as the glycosyl donor. A modified TEMPO/BAIB oxidation protocol was developed to directly convert α-d-GalN into α-d-GalAN in not only disaccharides but also tri- and tetrasaccharides. The synthetic haptens were covalently coupled with CRM197 carrier protein via a bifunctional linker. Preliminary immunological studies of the resultant glycoconjugates in mice revealed their high efficacy to induce robust T-cell-dependent immune responses, and the IgG antibodies elicited by each glycoconjugate showed weak cross-reactivity with the other synthetic tetrasaccharide.

Structure, Function, and Regulation of the Essential Virulence Factor Capsular Polysaccharide of Vibrio vulnificus

Vibrio vulnificus populates coastal waters around the world, where it exists freely or becomes concentrated in filter feeding mollusks. It also causes rapid and life-threatening sepsis and wound infections in humans. Of its many virulence factors, it is the V. vulnificus capsule, composed of capsular polysaccharide (CPS), that plays a critical role in evasion of the host innate immune system by conferring antiphagocytic ability and resistance to complement-mediated killing. CPS may also provoke a portion of the host inflammatory cytokine response to this bacterium. CPS production is biochemically and genetically diverse among strains of V. vulnificus, and the carbohydrate diversity of CPS is likely affected by horizontal gene transfer events that result in new combinations of biosynthetic genes. Phase variation between virulent encapsulated opaque colonial variants and attenuated translucent colonial variants, which have little or no CPS, is a common phenotype among strains of this species. One mechanism for generating acapsular variants likely involves homologous recombination between repeat sequences flanking the wzb phosphatase gene within the Group 1 CPS biosynthetic and transport operon. A considerable number of environmental, genetic, and regulatory factors have now been identified that affect CPS gene expression and CPS production in this pathogen.

Role of anaerobiosis in capsule production and biofilm formation in Vibrio vulnificus

Vibrio vulnificus, a pervasive human pathogen, can cause potentially fatal septicemia after consumption of undercooked seafood. Biotype 1 strains of V. vulnificus are most commonly associated with human infection and are separated into two genotypes, clinical (C) and environmental (E), based on the virulence-correlated gene. For ingestion-based vibriosis to occur, this bacterium must be able to withstand multiple conditions as it traverses the gastrointestinal tract and ultimately gains entry into the bloodstream. One such condition, anoxia, has yet to be extensively researched in V. vulnificus. We investigated the effect of oxygen availability on capsular polysaccharide (CPS) production and biofilm formation in this bacterium, both of which are thought to be important for disease progression. We found that lack of oxygen elicits a reduction in both CPS and biofilm formation in both genotypes. This is further supported by the finding that pilA, pilD, and mshA genes, all of which encode type IV pilin proteins that aid in attachment to surfaces, were downregulated during anaerobiosis. Surprisingly, E-genotypes exhibited distinct differences in gene expression levels of capsule and attachment genes compared to C-genotypes, both aerobically and anaerobically. The importance of understanding these disparities may give insight into the observed differences in environmental occurrence and virulence potential between these two genotypes of V. vulnificus.

Chitin-induced carbotype conversion in Vibrio vulnificus

As an etiological agent of bacterial sepsis and wound infections, Vibrio vulnificus is unique among the Vibrionaceae. The most intensely studied of its virulence factors is the capsular polysaccharide (CPS). Over 100 CPS types have been identified, yet little is known about the genetic mechanisms that drive such diversity. Chitin, the second-most-abundant polysaccharide in nature, is known to induce competence in Vibrio species. Here, we show that the frequency of chitin-induced transformation in V. vulnificus varies by strain and that (GlcNAc)(2) is the shortest chitin-derived polymer capable of inducing competence. Transformation frequencies (TFs) increased 8-fold when mixed-culture biofilms were exposed to a strain-specific lytic phage, suggesting that the lysis of dead cells during lytic infection increased the amount of extracellular DNA within the biofilm that was available for transfer. Furthermore, we show that V. vulnificus can undergo chitin-dependent carbotype conversion following the uptake and recombination of complete cps loci from exogenous genomic DNA (gDNA). The acquisition of a partial locus was also demonstrated when internal regions of homology between the endogenous and exogenous loci existed. This suggested that the same mechanism governing the transfer of complete cps loci also contributed to their evolution by generating novel combinations of CPS biosynthesis genes. Since no evidence that cps loci were preferentially acquired during natural transformation (random transposon-tagged DNA was readily taken up in chitin transformation assays) exists, the phenomenon of chitin-induced transformation likely plays an important but general role in the evolution of this genetically promiscuous genus.

Neisseria meningitidis capsular polysaccharides induce inflammatory responses via TLR2 and TLR4-MD-2

CPS are major virulence factors in infections caused by Neisseria meningitidis and form the basis for meningococcal serogroup designation and protective meningococcal vaccines. CPS polymers are anchored in the meningococcal outer membrane through a 1,2-diacylglycerol moiety, but the innate immunostimulatory activity of CPS is largely unexplored. Well-established human and murine macrophage cell lines and HEK/TLR stably transfected cells were stimulated with CPS, purified from an endotoxin-deficient meningococcal serogroup B NMB-lpxA mutant. CPS induced inflammatory responses via TLR2- and TLR4-MD-2. Meningococcal CPS induced a dose-dependent release of cytokines (TNF-α, IL-6, IL-8, and CXCL10) and NO from human and murine macrophages, respectively. CPS induced IL-8 release from HEK cells stably transfected with TLR2/6, TLR2, TLR2/CD14, and TLR4/MD-2/CD14 but not HEK cells alone. mAb to TLR2 but not an isotype control antibody blocked CPS-induced IL-8 release from HEK-TLR2/6-transfected cells. A significant reduction in TNF-α and IL-8 release was seen when THP-1- and HEK-TLR4/MD-2-CD14- but not HEK-TLR2- or HEK-TLR2/6-transfected cells were stimulated with CPS in the presence of Eritoran (E5564), a lipid A antagonist that binds to MD-2, and a similar reduction in NO and TNF-α release was also seen in RAW 264.7 cells in the presence of Eritoran. CD14 and LBP enhanced CPS bioactivity, and NF-κB was, as anticipated, the major signaling pathway. Thus, these data suggest that innate immune recognition of meningococcal CPS by macrophages can occur via TLR2- and TLR4-MD-2 pathways.

Evidence for the horizontal transfer of an unusual capsular polysaccharide biosynthesis locus in marine bacteria

The most intensely studied of the Vibrio vulnificus virulence factors is the capsular polysaccharide (CPS). All virulent strains produce copious amounts of CPS. Acapsular strains are avirulent. The structure of the CPS from the clinical isolate ATCC 27562 is unusual. It is serine modified and contains, surprisingly, N-acetylmuramic acid. We identified the complete 25-kb CPS biosynthesis locus from ATCC 27562. It contained 21 open reading frames and was allelic to O-antigen biosynthesis loci. Two of the genes, murA(CPS) and murB(CPS), were paralogs of the murA(PG) and murB(PG) genes of the peptidoglycan biosynthesis pathway; only a single copy of these genes is present in the strain CMCP6 and YJ016 genomes. Although MurA(CPS) and MurB(CPS) were functional when expressed in Escherichia coli, lesions in either gene had no effect on CPS production, virulence, or growth in V. vulnificus; disruption of 8 other genes within the locus resulted in an acapsular phenotype and attenuated virulence. Thus, murA(CPS) and murB(CPS) were functional but redundant. Comparative genomic analysis revealed that while completely different CPS biosynthesis loci were found in the same chromosomal region in other V. vulnificus strains, most of the CPS locus of ATCC 27562 was conserved in another marine bacterium, Shewanella putrefaciens strain 200. However, the average GC content of the CPS locus was significantly lower than the average GC content of either genome. Furthermore, several of the encoded proteins appeared to be of Gram-positive and archaebacterial origin. These data indicate that the horizontal transfer of intact and partial CPS loci drives CPS diversity in marine bacteria.

Vibrio biofilms: so much the same yet so different

Vibrios are natural inhabitants of aquatic environments and form symbiotic or pathogenic relationships with eukaryotic hosts. Recent studies reveal that the ability of vibrios to form biofilms (i.e. matrix-enclosed, surface-associated communities) depends upon specific structural genes (flagella, pili and exopolysaccharide biosynthesis) and regulatory processes (two-component regulators, quorum sensing and c-di-GMP signaling). Here, we compare and contrast mechanisms and regulation of biofilm formation by Vibrio species, with a focus on Vibrio cholerae, Vibrio parahaemolyticus, Vibrio vulnificus and Vibrio fischeri. Although many aspects are the same, others differ dramatically. Crucial questions that remain to be answered regarding the molecular underpinnings of Vibrio biofilm formation are also discussed.

Identification of a Wzy polymerase required for group IV capsular polysaccharide and lipopolysaccharide biosynthesis in Vibrio vulnificus

The estuarine bacterium Vibrio vulnificus is a human and animal pathogen. The expression of capsular polysaccharide (CPS) is essential for virulence. We used a new mini-Tn10 delivery vector, pNKTXI-SceI, to generate a mutant library and identify genes essential for CPS biosynthesis. Twenty-one acapsular mutants were isolated, and the disrupted gene in one mutant, coding for a polysaccharide polymerase (wzy), is described here. A wecA gene initiating glycosyltransferase was among the genes identified in the region flanking the wzy gene. This, together with the known structure of the CPS, supports a group IV capsule designation for the locus; however, its overall organization mirrored that of group I capsules. This new arrangement may be linked to our finding that the CPS region appears to have been recently acquired by horizontal transfer. Alcian Blue staining and immunoblotting with antisera against the wild-type strain indicated that the wzy::Tn10 mutant failed to produce CPS and was attenuated relative to the wild type in a septicemic mouse model. Interestingly, immunoblotting revealed that the mutant was also defective in lipopolysaccharide (LPS) production. However, the core-plus-one O-antigen pattern typical of wzy mutations was apparent. CPS production, LPS production, and virulence were restored following complementation with the wild-type wzy gene. Hence, Wzy participates in both CPS and LPS biosynthesis and is required for virulence in strain 27562. To our knowledge, this is the first functional demonstration of a Wzy polysaccharide polymerase in V. vulnificus and is the first to show a link between LPS and CPS biosynthesis.

Surface properties of Vibrio vulnificus

AIMS

Vibrio vulnificus adheres to a diverse range of surfaces, ranging from the chitinous exoskeleton of mollusks to human tissue. To determine whether environmental and human clinical isolates exhibit different adhesion traits, we studied the ability of 10 environmental isolates and 10 clinical isolates to adhere to human epithelial cells and hydrocarbons with log P values ranging from 3.1 to 8.2.

METHODS AND RESULTS

All isolates adhered to varying levels to epithelial cells, and were inhibited to various extents from adherence by mannose and fructose. There was a lack of correlation between adherence to either hydrocarbons or cells and colony opacity. Adherence to hydrocarbons was optimal for solvents with a log P < 8.2.

CONCLUSIONS

Vibrio vulnificus clinical and environmental isolates exhibit differential adherence to epithelial cells and hydrocarbons.

SIGNIFICANCE AND IMPACT OF THE STUDY

The differential adherence of organisms to hydrocarbons based on log P may have utility in drug design and enhancement of food safety.

Genetic variation in the Vibrio vulnificus group 1 capsular polysaccharide operon

Vibrio vulnificus produces human disease associated with raw-oyster consumption or wound infections, but fatalities are limited to persons with chronic underlying illness. Capsular polysaccharide (CPS) is required for virulence, and CPS expression correlates with opaque (Op) colonies that show "phase variation" to avirulent translucent (Tr) phenotypes with reduced CPS. The results discussed here confirmed homology of a V. vulnificus CPS locus to the group 1 CPS operon in Escherichia coli. However, two distinct V. vulnificus genotypes or alleles were associated with the operon, and they diverged at sequences encoding hypothetical proteins and also at unique, intergenic repetitive DNA elements. Phase variation was examined under conditions that promoted high-frequency transition of Op to Tr forms. Recovery of Tr isolates in these experiments showed multiple genotypes, which were designated TR1, TR2, and TR3: CPS operons of TR1 isolates were identical to the Op parent, and cells remained phase variable but expressed reduced CPS. TR2 and TR3 showed deletion mutations in one (wzb) or multiple genes, respectively, and deletion mutants were acapsular and locked in the Tr phase. Complementation in trans restored the Op phenotype in strains with the wzb deletion mutation. Allelic variation in repetitive elements determined the locations, rates, and extents of deletion mutations. Thus, different mechanisms are responsible for reversible phase variation in CPS expression versus genetic deletions in the CPS operon of V. vulnificus. Repetitive-element-mediated deletion mutations were highly conserved within the species and are likely to promote survival in estuarine environments.

Identification of the Vibrio vulnificus wbpP gene and evaluation of its role in virulence

A wbpP gene encoding a putative UDP-N-acetyl-D-glucosamine C(4) epimerase was identified and cloned from Vibrio vulnificus. The functions of the wbpP gene, assessed by the construction of an isogenic mutant and by evaluating its phenotype changes, demonstrated that WbpP is essential in both the pathogenesis and the capsular polysaccharide biosynthesis of V. vulnificus.

Expression of Vibrio vulnificus capsular polysaccharide inhibits biofilm formation

Vibrio vulnificus is a human pathogen that produces lethal septicemia in susceptible persons, and the primary virulence factor for this organism is capsular polysaccharide (CPS). The role of the capsule in V. vulnificus biofilms was examined under a variety of conditions, by using either defined CPS mutants or spontaneous CPS expression phase variants derived from multiple strains. CPS expression was shown to inhibit attachment and biofilm formation, which contrasted with other studies describing polysaccharides as integral to biofilms in related species.

Fingerprint profiling of acid hydrolyzates of polysaccharides extracted from the fruiting bodies and spores of Lingzhi by high-performance thin-layer chromatography

Modern extraction and planar chromatographic instrumentation were employed for the fingerprint profiling of carbohydrates from an important and popular medicinal mushroom commonly known as Lingzhi. For the first time, the feasibility of employing the high-performance thin-layer chromatography (HPTLC) peak profiles (fingerprints) of carbohydrates for the screening of various Lingzhi species/products was demonstrated. An analytical procedure was developed such that upon acid hydrolysis of the polysaccharides extracted from various Lingzhi samples, fingerprint profiles that reveal the relative amounts of the degradation products, such as mono- and oligosaccharides, can be obtained using HPTLC plates (Si 50000) for separation and 4-aminobenzoic acid as the post-chromatographic derivatization reagent for detection. Also, using automated multiple development (AMD), the acid hydrolyzates from Lingzhi, consisting of simple and more complex sugars, can be separated simultaneously with high degree of automation. An important finding was that unique fingerprint patterns were observed in the monosaccharide profiles between two highly valued Lingzhi species, Ganoderma applanatum and Ganoderma lucidum, under total or partial acid hydrolysis conditions. Additionally, the HPTLC fingerprint profiles of carbohydrates were obtained from the extracts of the spores and fruiting bodies of Lingzhi and compared.

Cholera and other types of vibriosis: a story of human pandemics and oysters on the half shell

Vibrios are ubiquitous in the aquatic environment and are commonly present in or on shellfish and other seafood. A small subset of strains/species are able to cause human disease, including the cholera toxin-producing strains of Vibrio cholerae that are responsible for epidemic/pandemic cholera; thermostable direct hemolysin-producing strains of Vibrio parahaemolyticus; and Vibrio vulnificus, which can cause fulminant sepsis. Cholera outbreaks can be initiated by transmission of "epidemic" V. cholerae strains from their environmental reservoir to humans through seafood or other environmentally related food or water sources. "Nonepidemic" strains of V. cholerae and strains of other Vibrio species, including V. parahaemolyticus and V. vulnificus, are generally acquired by eating seafood (particularly raw oysters/oysters on the half shell). Although the primary clinical manifestation of infection with these strains is gastroenteritis, they can also cause wound infections and (particularly for V. vulnificus) septicemia in persons who have liver disease or are immunocompromised.

Identification of genetic loci required for capsular expression in Vibrio vulnificus

Transposon mutagenesis of an encapsulated, virulent strain of Vibrio vulnificus 1003(O) led to the identification of four genetic regions that are essential to capsular polysaccharide (CPS) expression and virulence. Of the four regions, three are believed to be part of a capsule gene locus comprised of biosynthesis, polymerization, and transport genes clustered on a single chromosomal fragment. Genes indicating a Wzy-dependent system of polymerization and transmembrane export are present, suggesting that the CPS of V. vulnificus is lipid linked. The fourth region, while it contains a gene essential for CPS expression, is characteristic of an integron-gene cassette region, similar to the super integron of V. cholerae. It is not believed to be part of a CPS gene locus and is located in a region of the chromosome separate from the putative CPS loci. It is comprised of open reading frames (ORFs) carrying genes of unknown function surrounded by direct repeats. This region also contains IS492, an insertion sequence located numerous times throughout a region of the genome, demonstrating a restriction fragment length polymorphism among an encapsulated and nonencapsulated morphotype of V. vulnificus. Collectively, 22 ORFs were recognized: 13 capsule synthesis genes, 4 insertion sequences, 1 truncated biosynthesis gene, and 4 genes of unknown function. This study has led to the identification of previously unrecognized genetic loci that may help to increase the understanding of capsular genetics and antigenic diversity among V. vulnificus strains.

Identification of a group 1-like capsular polysaccharide operon for Vibrio vulnificus

Virulence of Vibrio vulnificus correlates with changes in colony morphology that are indicative of a reversible phase variation for expression of capsular polysaccharide (CPS). Encapsulated variants are virulent with opaque colonies, whereas phase variants with reduced CPS expression are attenuated and are translucent. Using TnphoA mutagenesis, we identified a V. vulnificus CPS locus, which included an upstream ops element, a wza gene (wza(Vv)), and several open reading frames with homology to CPS biosynthetic genes. This genetic organization is characteristic of group 1 CPS operons. The wza gene product is required for transport of CPS to the cell surface in Escherichia coli. Polar transposon mutations in wza(Vv) eliminated expression of downstream biosynthetic genes, confirming operon structure. On the other hand, nonpolar inactivation of wza(Vv) was specific for CPS transport, did not alter CPS biosynthesis, and could be complemented in trans. Southern analysis of CPS phase variants revealed deletions or rearrangements at this locus. A survey of environmental isolates indicated a correlation between deletions in wza(Vv) and loss of virulent phenotype, suggesting a genetic mechanism for CPS phase variation. Full virulence in mice required surface expression of CPS and supported the essential role of capsule in the pathogenesis of V. vulnificus.

Epidemiology and pathogenesis of Vibrio vulnificus

Vibrio vulnificus is capable of causing severe and often fatal infections in susceptible individuals. It causes two distinct disease syndromes, a primary septicemia and necrotizing wound infections. This review discusses the interaction of environmental conditions, host factors, and bacterial virulence determinants that contribute to the epidemiology and pathogenesis of V. vulnificus.

Differential expression of Vibrio vulnificus capsular polysaccharide

Vibrio vulnificus is a human pathogen whose virulence has been associated with the expression of capsular polysaccharide (CPS). Multiple CPS types have been described; however, virulence does not appear to correlate with a particular CPS composition. Reversible-phase variation for opaque and translucent colony morphologies is characterized by changes in CPS expression, as suggested by electron microscopy of cells stained nonspecifically with ruthenium red. Isolates with opaque colony morphologies are virulent and appear to be more thickly encapsulated than naturally occurring translucent-phase variants, which have reduced, patchy, or absent CPS. Previously, we have shown that the virulence of translucent-phase variants was intermediate between opaque-phase variants and acapsular transposon mutants, suggesting a correlation between virulence and the amount of CPS expressed. In the present study, CPS expression of phase variants and genetically defined mutants of V. vulnificus M06-24/O was examined by using a CPS-specific monoclonal antibody with an enzyme-linked immunosorbent assay, flow cytometry, and immunoelectron microscopy. Semiquantitative analyses of CPS expression correlated well among these assays, confirming that the translucent-phase variant was intermediate in CPS expression and retained type I CPS-specific epitopes. Cell surface expression of CPS varied with the growth phase, increasing during logarithmic growth and declining in stationary culture. Significantly greater CPS expression (P = 0.026) was observed for cells grown at 30 degrees C than for those at 37 degrees C. These studies confirm that phase variation and virulence in V. vulnificus correlate with the amount of CPS expressed and demonstrate the fluidity of bacterial polysaccharide expression in response to environmental conditions.

Structure of a muramic acid containing capsular polysaccharide from the pathogenic strain of Vibrio vulnificus ATCC 27562

Vibrio vulnificus strains isolated from septicemia cases and from the environment show a wide variety of capsular types. In an attempt to find common structural features which can be correlated with pathogenicity and toxicity, we have determined structures of the capsular polysaccharides (CPS) from several pathogenic strains. We report the complete structure of the polysaccharide from the pathogenic V. vulnificus strain ATCC 27562 using a combination of homonuclear and heteronuclear one-dimensional and two dimensional NMR experiments. The 13C and 1H NMR spectra, including the exchangeable amide proton resonances, have been completely assigned. The amide linkage between Ser and C6 of GalA has been unambiguously determined by water-suppressed 2D NOESY. To verify the structure established by NMR, we have fragmented the polymer employing the Smith degradation procedure. The Smith product identified by NMR and matrix-assisted laser desorption mass spectrometry is consistent with the proposed structure for the CPS, which is composed of D-GlcNAc, MurNAc, D-GalA, L-Rha and is serine-linked as shown: [formula: see text]