Genetic basis for lipopolysaccharide O-antigen biosynthesis in bordetellae

Genomic plasticity and antibody response of Bordetella bronchiseptica strain HT200, a natural variant from a thermal spring

Classical Bordetella species are primarily isolated from animals and humans causing asymptomatic infection to lethal pneumonia. However, isolation of these bacteria from any extra-host environmental niche has not been reported so far. Here, we have characterized the genomic plasticity and antibody response of Bordetella bronchiseptica strain HT200, isolated from a thermal spring. Genomic ANI value and SNPs-based phylogenetic tree suggest a divergent evolution of strain HT200 from a human-adapted lineage of B. bronchiseptica. Growth and survivability assay showed strain HT200 retained viability for more than 5 weeks in the filter-sterilized spring water. In addition, genes or loci encoding the Bordetella virulence factors such as DNT, ACT and LPS O-antigen were absent in strain HT200, while genes encoding other virulence factors were highly divergent. Phenotypically, strain HT200 was non-hemolytic and showed weak hemagglutination activity, but was able to colonize in the respiratory organs of mice. Further, both infection and vaccination with strain HT200 induced protective antibody response in mouse against challenge infection with virulent B. bronchiseptica strain RB50. In addition, genome of strain HT200 (DSM 26023) showed presence of accessory genes and operons encoding predicted metabolic functions pertinent to the ecological conditions of the thermal spring.

Shotgun proteomic analysis of Bordetella parapertussis provides insights into the physiological response to iron starvation and potential new virulence determinants absent in Bordetella pertussis

Bordetella parapertussis is one of the pathogens that cause whooping cough. Even though its incidence has been rising in the last decades, this species remained poorly investigated. This study reports the first extensive proteome analysis of this bacterium. In an attempt to gain some insight into the infective phenotype, we evaluated the response of B. parapertussis to iron starvation, a critical stress the bacteria face during infection. Among other relevant findings, we observed that the adaptation to this condition involves significant changes in the abundance of two important virulence factors of this pathogen, namely, adenylate cyclase and the O-antigen. We further used the proteomic data to search for B. parapertussis proteins that are absent or classified as pseudogenes in the genome of Bordetella pertussis to unravel differences between both whooping cough causative agents. Among them, we identified proteins involved in stress resistance and virulence determinants that might help to explain the differences in the pathogenesis of these species and the lack of cross-protection of current acellular vaccines. Altogether, these results contribute to a better understanding of B. parapertussis biology and pathogenesis. SIGNIFICANCE: Whooping cough is a reemerging disease caused by both Bordetella pertussis and Bordetella parapertussis. Current vaccines fail to induce protection against B parapertussis and the incidence of this species has been rising over the years. The proteomic analysis of this study provided relevant insights into potential virulence determinants of this poorly-studied pathogen. It further identified proteins produced by B. parapertussis not present in B. pertussis, which might help to explain both the differences on their respective infectious process and the current vaccine failure. Altogether, the results of this study contribute to the better understanding of B. parapertussis pathogenesis and the eventual design of improved preventive strategies against whooping cough.

A comparative study of the complete lipopolysaccharide structures and biosynthesis loci of Bordetella avium, B. hinzii, and B. trematum

A dozen species of human and animal pathogens have been described to date in the Bordetella genus, with the majority being respiratory tract pathogens. Bordetella avium lipopolysaccharides have been shown to be important virulence factors for this bird pathogen. B. hinzii is closely related to the B. avium species, but has also been isolated from humans. B. trematum is associated to ear and blood infections in humans. Its lipid A structure, the biological active moiety of LPS, was found to be closely related to those of B. avium and B. hinzii. It is important to unveil the subtle structural modifications orchestrated during the LPS biosynthetic pathway to better understand host adaptation. The present data are also important in the context of deciphering the virulence pathways of this important genus containing the major pathogens B. pertussis and B. parapertussis, responsible for whooping cough. We recently reported the isolated lipid A structures of the three presented species, following the previously identified O-chain structures. In the present study, we provide details on the free and O-chain-linked core oligosaccharides which were required to characterize the complete LPS structures. Data are presented here in relation to relevant biosynthesis genes. The present characterization of the three species is well illustrated by Matrix Assisted Laser Desorption Mass Spectrometry experiments, and data were obtained mainly on native LPS molecules for the first time.

Ectopic Expression of O Antigen in Bordetella pertussis by a Novel Genomic Integration System

Some bacterial phenotypes emerge through the cooperative functions of a number of genes residing within a large genetic locus. To transfer the phenotype of one bacterium to another, a means to introduce the large genetic locus into the recipient bacterium is needed. Therefore, we developed a novel system by combining the advantages of a bacterial artificial chromosome vector and phage-derived gene integration machinery. In this study, we succeeded for the first time in introducing a gene locus involved in O antigen biosynthesis of Bordetella bronchiseptica into the chromosome of B. pertussis, which intrinsically lacks O antigen, and using this system we analyzed phenotypic alterations in the resultant mutant strain of B. pertussis. The present results demonstrate that this system successfully accomplished the above-described purpose. We consider this system to be applicable to a number of bacteria other than Bordetella.

We describe a novel genome integration system that enables the introduction of DNA fragments as large as 50 kbp into the chromosomes of recipient bacteria. This system, named BPI, comprises a bacterial artificial chromosome vector and phage-derived gene integration machinery. We introduced the wbm locus of Bordetella bronchiseptica, which is required for O antigen biosynthesis, into the chromosome of B. pertussis, which intrinsically lacks O antigen, using the BPI system. After the introduction of the wbm locus, B. pertussis presented an additional substance in the lipooligosaccharide fraction that was specifically recognized by the anti-B. bronchiseptica antibody but not the anti-B. pertussis antibody, indicating that B. pertussis expressed O antigen corresponding to that of B. bronchiseptica. O antigen-expressing B. pertussis was less sensitive to the bactericidal effects of serum and polymyxin B than the isogenic parental strain. In addition, an in vivo competitive infection assay showed that O antigen-expressing B. pertussis dominantly colonized the mouse respiratory tract over the parental strain. These results indicate that the BPI system provides a means to alter the phenotypes of bacteria by introducing large exogenous DNA fragments.

IMPORTANCE Some bacterial phenotypes emerge through the cooperative functions of a number of genes residing within a large genetic locus. To transfer the phenotype of one bacterium to another, a means to introduce the large genetic locus into the recipient bacterium is needed. Therefore, we developed a novel system by combining the advantages of a bacterial artificial chromosome vector and phage-derived gene integration machinery. In this study, we succeeded for the first time in introducing a gene locus involved in O antigen biosynthesis of Bordetella bronchiseptica into the chromosome of B. pertussis, which intrinsically lacks O antigen, and using this system we analyzed phenotypic alterations in the resultant mutant strain of B. pertussis. The present results demonstrate that this system successfully accomplished the above-described purpose. We consider this system to be applicable to a number of bacteria other than Bordetella.

A recombinant iron transport protein from Bordetella pertussis confers protection against Bordetella parapertussis

Whooping cough, which is caused by Bordetella pertussis and B. parapertussis, is a reemerging disease. New protective antigens are needed to improve the efficacy of current vaccines against both species. Using proteomic tools, it was here found that B. parapertussis expresses a homolog of AfuA, a previously reported new vaccine candidate against B. pertussis. It was found that this homolog, named AfuA_Bpp , is expressed during B. parapertussis infection, exposed on the surface of the bacteria and recognized by specific antibodies induced by the recombinant AfuA cloned from B. pertussis (rAfuA). Importantly, the presence of the O-antigen, a molecule that has been found to shield surface antigens on B. parapertussis, showed no influence on antibody recognition of AfuA_Bpp on the bacterial surface. The present study further showed that antibodies induced by immunization with the recombinant protein were able to opsonize B. parapertussis and promote bacterial uptake by neutrophils. Finally, it was shown that this antigen confers protection against B. parapertussis infection in a mouse model. Altogether, these results indicate that AfuA is a good vaccine candidate for acellular vaccines protective against both causative agents of whooping cough.

Bordetella parapertussis Circumvents Neutrophil Extracellular Bactericidal Mechanisms

B. parapertussis is a whooping cough etiological agent with the ability to evade the immune response induced by pertussis vaccines. We previously demonstrated that in the absence of opsonic antibodies B. parapertussis hampers phagocytosis by neutrophils and macrophages and, when phagocytosed, blocks intracellular killing by interfering with phagolysosomal fusion. But neutrophils can kill and/or immobilize extracellular bacteria through non-phagocytic mechanisms such as degranulation and neutrophil extracellular traps (NETs). In this study we demonstrated that B. parapertussis also has the ability to circumvent these two neutrophil extracellular bactericidal activities. The lack of neutrophil degranulation was found dependent on the O antigen that targets the bacteria to cell lipid rafts, eventually avoiding the fusion of nascent phagosomes with specific and azurophilic granules. IgG opsonization overcame this inhibition of neutrophil degranulation. We further observed that B. parapertussis did not induce NETs release in resting neutrophils and inhibited NETs formation in response to phorbol myristate acetate (PMA) stimulation by a mechanism dependent on adenylate cyclase toxin (CyaA)-mediated inhibition of reactive oxygen species (ROS) generation. Thus, B. parapertussis modulates neutrophil bactericidal activity through two different mechanisms, one related to the lack of proper NETs-inducer stimuli and the other one related to an active inhibitory mechanism. Together with previous results these data suggest that B. parapertussis has the ability to subvert the main neutrophil bactericidal functions, inhibiting efficient clearance in non-immune hosts.

Structural variability and originality of the Bordetella endotoxins

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

Pertussis: Microbiology, Disease, Treatment, and Prevention

Pertussis is a severe respiratory infection caused by Bordetella pertussis, and in 2008, pertussis was associated with an estimated 16 million cases and 195,000 deaths globally. Sizeable outbreaks of pertussis have been reported over the past 5 years, and disease reemergence has been the focus of international attention to develop a deeper understanding of pathogen virulence and genetic evolution of B. pertussis strains. During the past 20 years, the scientific community has recognized pertussis among adults as well as infants and children. Increased recognition that older children and adolescents are at risk for disease and may transmit B. pertussis to younger siblings has underscored the need to better understand the role of innate, humoral, and cell-mediated immunity, including the role of waning immunity. Although recognition of adult pertussis has increased in tandem with a better understanding of B. pertussis pathogenesis, pertussis in neonates and adults can manifest with atypical clinical presentations. Such disease patterns make pertussis recognition difficult and lead to delays in treatment. Ongoing research using newer tools for molecular analysis holds promise for improved understanding of pertussis epidemiology, bacterial pathogenesis, bioinformatics, and immunology. Together, these advances provide a foundation for the development of new-generation diagnostics, therapeutics, and vaccines.

Host Specificity of Ovine Bordetella parapertussis and the Role of Complement

The classical bordetellae are comprised of three subspecies that differ from broad to very limited host specificity. Although several lineages appear to have specialized to particular host species, most retain the ability to colonize and grow in mice, providing a powerful common experimental model to study their differences. One of the subspecies, Bordetella parapertussis, is composed of two distinct clades that have specialized to different hosts: one to humans (Bpp_hu), and the other to sheep (Bpp_ov). While Bpp_hu and the other classical bordetellae can efficiently colonize mice, Bpp_ov strains are severely defective in their ability to colonize the murine respiratory tract. Bpp_ov genomic analysis did not reveal the loss of adherence genes, but substantial mutations and deletions of multiple genes involved in the production of O-antigen, which is required to prevent complement deposition on B. bronchiseptica and Bpp_hu strains. Bpp_ov lacks O-antigen and, like O-antigen mutants of other bordetellae, is highly sensitive to murine complement-mediated killing in vitro. Based on these results, we hypothesized that Bpp_ov failed to colonize mice because of its sensitivity to murine complement. Consistent with this, the Bpp_ov defect in the colonization of wild type mice was not observed in mice lacking the central complement component C3. Furthermore, Bpp_ov strains were highly susceptible to killing by murine complement, but not by sheep complement. These data demonstrate that the failure of Bpp_ov to colonize mice is due to sensitivity to murine, but not sheep, complement, providing a mechanistic example of how specialization that accompanies expansion in one host can limit host range.

Bordetella parapertussis PagP mediates the addition of two palmitates to the lipopolysaccharide lipid A

Bordetella bronchiseptica PagP (PagPBB) is a lipid A palmitoyl transferase that is required for resistance to antibody-dependent complement-mediated killing in a murine model of infection. B. parapertussis contains a putative pagP homolog (encoding B. parapertussis PagP [PagPBPa]), but its role in the biosynthesis of lipid A, the membrane anchor of lipopolysaccharide (LPS), has not been investigated. Mass spectrometry analysis revealed that wild-type B. parapertussis lipid A consists of a heterogeneous mixture of lipid A structures, with penta- and hexa-acylated structures containing one and two palmitates, respectively. Through mutational analysis, we demonstrate that PagPBPa is required for the modification of lipid A with palmitate. While PagPBB transfers a single palmitate to the lipid A C-3' position, PagPBPa transfers palmitates to the lipid A C-2 and C-3' positions. The addition of two palmitate acyl chains is unique to B. parapertussis. Mutation of pagPBPa resulted in a mutant strain with increased sensitivity to antimicrobial peptide killing and decreased endotoxicity, as evidenced by reduced proinflammatory responses via Toll-like receptor 4 (TLR4) to the hypoacylated LPS. Therefore, PagP-mediated modification of lipid A regulates outer membrane function and may be a means to modify interactions between the bacterium and its human host during infection.

Bordetella parapertussis survives inside human macrophages in lipid raft-enriched phagosomes

Bordetella parapertussis is a human pathogen that causes whooping cough. The increasing incidence of B. parapertussis has been attributed to the lack of cross protection induced by pertussis vaccines. It was previously shown that B. parapertussis is able to avoid bacterial killing by polymorphonuclear leukocytes (PMN) if specific opsonic antibodies are not present at the site of interaction. Here, we evaluated the outcome of B. parapertussis innate interaction with human macrophages, a less aggressive type of cell and a known reservoir of many persistent pathogens. The results showed that in the absence of opsonins, O antigen allows B. parapertussis to inhibit phagolysosomal fusion and to remain alive inside macrophages. The O antigen targets B. parapertussis to lipid rafts that are retained in the membrane of phagosomes that do not undergo lysosomal maturation. Forty-eight hours after infection, wild-type B. parapertussis bacteria but not the O antigen-deficient mutants were found colocalizing with lipid rafts and alive in nonacidic compartments. Taken together, our data suggest that in the absence of opsonic antibodies, B. parapertussis survives inside macrophages by preventing phagolysosomal maturation in a lipid raft- and O antigen-dependent manner. Two days after infection, about 15% of macrophages were found loaded with live bacteria inside flotillin-enriched phagosomes that had access to nutrients provided by the host cell recycling pathway, suggesting the development of an intracellular infection. IgG opsonization drastically changed this interaction, inducing efficient bacterial killing. These results highlight the need for B. parapertussis opsonic antibodies to induce bacterial clearance and prevent the eventual establishment of cellular reservoirs of this pathogen.

Importance of (antibody-dependent) complement-mediated serum killing in protection against Bordetella pertussis

Pertussis is a highly contagious respiratory disease that is caused by Bordetella pertussis. Despite being vaccine preventable, pertussis rates have been rising steadily over the last decades, even in areas with high vaccine uptake. Recently, experiments with infant baboons indicated that although vaccination with acellular pertussis vaccines prevented disease, no apparent effect was observed on infection and transmission. One explanation may be that current acellular pertussis vaccines do not induce high levels of opsonophagocytic and/or bactericidal activity, implying that engineering of vaccines that promote bacterial killing may improve efficacy. Here, we discuss the importance of complement-mediated killing in vaccine-induced protection against B. pertussis. We first examine how B. pertussis may have evolved different complement evasion strategies. Second, we explore the benefits of opsonophagocytic and/or bactericidal killing in vaccine-induced protection and discuss whether or not inclusion of new opsonophagocytic or bactericidal target antigens in pertussis vaccines may benefit efficacy.

Bordetella pertussis pathogenesis: current and future challenges

Pertussis, also known as whooping cough, has recently re-emerged as a major public health threat despite high levels of vaccination against the aetiological agent Bordetella pertussis. In this Review, we describe the pathogenesis of this disease, with a focus on recent mechanistic insights into B. pertussis virulence-factor function. We also discuss the changing epidemiology of pertussis and the challenges facing vaccine development. Despite decades of research, many aspects of B. pertussis physiology and pathogenesis remain poorly understood. We highlight knowledge gaps that must be addressed to develop improved vaccines and therapeutic strategies.

Horizontally acquired divergent O-antigen contributes to escape from cross-immunity in the classical bordetellae

Background

Horizontal gene transfer (HGT) allows for rapid spread of genetic material between species, increasing genetic and phenotypic diversity. Although HGT contributes to adaptation and is widespread in many bacteria, others show little HGT. This study builds on previous work to analyze the evolutionary mechanisms contributing to variation within the locus encoding a prominent antigen of the classical bordetellae.

Results

We observed amongst classical bordetellae discrete regions of the lipopolysaccharide O-antigen locus with higher sequence diversity than the genome average. Regions of this locus had less than 50% sequence similarity, low dN/dS ratios and lower GC content compared to the genome average. Additionally, phylogenetic tree topologies based on genome-wide SNPs were incongruent with those based on genes within these variable regions, suggesting portions of the O-antigen locus may have been horizontally transferred. Furthermore, several predicted recombination breakpoints correspond with the ends of these variable regions. To examine the evolutionary forces that might have selected for this rare example of HGT in bordetellae, we compared in vitro and in vivo phenotypes associated with different O-antigen types. Antibodies against O1- and O2-serotypes were poorly cross-reactive, and did not efficiently kill or mediate clearance of alternative O-type bacteria, while a distinct and poorly immunogenic O-antigen offered no protection against colonization.

Conclusions

This study suggests that O-antigen variation was introduced to the classical bordetellae via HGT through recombination. Additionally, genetic variation may be maintained within the O-antigen locus because it can provide escape from immunity to different O-antigen types, potentially allowing for the circulation of different Bordetella strains within the same host population.

Adaptability and persistence of the emerging pathogen Bordetella petrii

The first described, environmentally isolated, Bordetella petrii was shown to undergo massive genomic rearrangements in vitro. More recently, B. petrii was isolated from clinical samples associated with jaw, ear bone, cystic fibrosis and chronic pulmonary disease. However, the in vivo consequences of B. petrii genome plasticity and its pathogenicity remain obscure. B. petrii was identified from four sequential respiratory samples and a post-mortem spleen sample of a woman presenting with bronchiectasis and cavitary lung disease associated with nontuberculous mycobacterial infection. Strains were compared genetically, phenotypically and by antibody recognition from the patient and from inoculated mice. The successive B. petrii strains exhibited differences in growth, antibiotic susceptibility and recognition by the patient’s antibodies. Antibodies from mice inoculated with these strains recapitulated the specificity and strain dependent response that was seen with the patient’s serum. Finally, we characterize one strain that was poorly recognized by the patient’s antibodies, due to a defect in the lipopolysaccharide O-antigen, and identify a mutation associated with this phenotype. We propose that B. petrii is remarkably adaptable in vivo, providing a possible connection between immune response and bacterial evasion and supporting infection persistence.

Lack of cross-protection against Bordetella holmesii after pertussis vaccination

Vaccines for B. pertussis do not protect against circulating strains of a closely related respiratory pathogen.

Bordetella holmesii, a species closely related to B. pertussis, has been reported sporadically as a cause of whooping cough–like symptoms. To investigate whether B. pertussis–induced immunity is protective against infection with B. holmesii, we conducted an analysis using 11 human respiratory B. holmesii isolates collected during 2005–2009 from a highly B. pertussis–vaccinated population in Massachusetts. Neither whole-cell (wP) nor acellular (aP) B. pertussis vaccination conferred protection against these B. holmesii isolates in mice. Although T-cell responses induced by wP or aP cross-reacted with B. holmesii, vaccine-induced antibodies failed to efficiently bind B. holmesii. B. holmesii–specific antibodies provided in addition to wP were sufficient to rapidly reduce B. holmesii numbers in mouse lungs. Our findings suggest the established presence of B. holmesii in Massachusetts and that failure to induce cross-reactive antibodies may explain poor vaccine-induced cross-protection.

Identification of a CO2 responsive regulon in Bordetella

Sensing the environment allows pathogenic bacteria to coordinately regulate gene expression to maximize survival within or outside of a host. Here we show that Bordetella species regulate virulence factor expression in response to carbon dioxide levels that mimic in vivo conditions within the respiratory tract. We found strains of Bordetella bronchiseptica that did not produce adenylate cyclase toxin (ACT) when grown in liquid or solid media with ambient air aeration, but produced ACT and additional antigens when grown in air supplemented to 5% CO(2). Transcriptome analysis and quantitative real time-PCR analysis revealed that strain 761, as well as strain RB50, increased transcription of genes encoding ACT, filamentous hemagglutinin (FHA), pertactin, fimbriae and the type III secretion system in 5% CO(2) conditions, relative to ambient air. Furthermore, transcription of cyaA and fhaB in response to 5% CO(2) was increased even in the absence of BvgS. In vitro analysis also revealed increases in cytotoxicity and adherence when strains were grown in 5% CO(2). The human pathogens B. pertussis and B. parapertussis also increased transcription of several virulence factors when grown in 5% CO(2), indicating that this response is conserved among the classical bordetellae. Together, our data indicate that Bordetella species can sense and respond to physiologically relevant changes in CO(2) concentrations by regulating virulence factors important for colonization, persistence and evasion of the host immune response.

Bordetella parapertussis survives the innate interaction with human neutrophils by impairing bactericidal trafficking inside the cell through a lipid raft-dependent mechanism mediated by the lipopolysaccharide O antigen

Whooping cough is a reemerging disease caused by two closely related pathogens, Bordetella pertussis and Bordetella parapertussis. The incidence of B. parapertussis in whooping cough cases has been increasing since the introduction of acellular pertussis vaccines containing purified antigens that are common to both strains. Recently published results demonstrated that these vaccines do not protect against B. parapertussis due to the presence of the O antigen on the bacterial surface that impairs antibody access to shared antigens. We have investigated the effect of the lack of opsonization of B. parapertussis on the outcome of its interaction with human neutrophils (polymorphonuclear leukocytes [PMNs]). In the absence of opsonic antibodies, PMN interaction with B. parapertussis resulted in nonbactericidal trafficking upon phagocytosis. A high percentage of nonopsonized B. parapertussis was found in nonacidic lysosome marker (lysosome-associated membrane protein [LAMP])-negative phagosomes with access to the host cell-recycling pathway of external nutrients, allowing bacterial survival as determined by intracellular CFU counts. The lipopolysaccharide (LPS) O antigen was found to be involved in directing B. parapertussis to PMN lipid rafts, eventually determining the nonbactericidal fate inside the PMN. IgG opsonization of B. parapertussis drastically changed this interaction by not only inducing efficient PMN phagocytosis but also promoting PMN bacterial killing. These data provide new insights into the immune mechanisms of hosts against B. parapertussis and document the crucial importance of opsonic antibodies in immunity to this pathogen.

Immunity to the respiratory pathogen Bordetella pertussis

Bordetella pertussis causes whooping cough, a severe respiratory tract infection in infants and children, and also infects adults. Studies in murine models have shown that innate immune mechanisms involving dendritic cells, macrophages, neutrophils, natural killer cells, and antimicrobial peptides help to control the infection, while complete bacterial clearance requires cellular immunity mediated by T-helper type 1 (Th1) and Th17 cells. Whole cell pertussis vaccines (wP) are effective, but reactogenic, and have been replaced in most developed countries by acellular pertussis vaccines (aP). However, the incidence of pertussis is still high in many vaccinated populations; this may reflect sub-optimal, waning, or escape from immunity induced by current aP. Protective immunity generated by wP appears to be mediated largely by Th1 cells, whereas less efficacious alum-adjuvanted aP induce strong antibody Th2 and Th17 responses. New generation aP that induce Th1 rather than Th2 responses are required to improve vaccine efficacy and prevent further spread of B. pertussis.

sigE facilitates the adaptation of Bordetella bronchiseptica to stress conditions and lethal infection in immunocompromised mice

Background

The cell envelope of a bacterial pathogen can be damaged by harsh conditions in the environment outside a host and by immune factors during infection. Cell envelope stress responses preserve the integrity of this essential compartment and are often required for virulence. Bordetella species are important respiratory pathogens that possess a large number of putative transcription factors. However, no cell envelope stress responses have been described in these species. Among the putative Bordetella transcription factors are a number of genes belonging to the extracytoplasmic function (ECF) group of alternative sigma factors, some of which are known to mediate cell envelope stress responses in other bacteria. Here we investigate the role of one such gene, sigE, in stress survival and pathogenesis of Bordetella bronchiseptica.

Results

We demonstrate that sigE encodes a functional sigma factor that mediates a cell envelope stress response. Mutants of B. bronchiseptica strain RB50 lacking sigE are more sensitive to high temperature, ethanol, and perturbation of the envelope by SDS-EDTA and certain β-lactam antibiotics. Using a series of immunocompromised mice deficient in different components of the innate and adaptive immune responses, we show that SigE plays an important role in evading the innate immune response during lethal infections of mice lacking B cells and T cells. SigE is not required, however, for colonization of the respiratory tract of immunocompetent mice. The sigE mutant is more efficiently phagocytosed and killed by peripheral blood polymorphonuclear leukocytes (PMNs) than RB50, and exhibits decreased cytotoxicity toward macrophages. These altered interactions with phagocytes could contribute to the defects observed during lethal infection.

Conclusions

Much of the work on transcriptional regulation during infection in B. bronchiseptica has focused on the BvgAS two-component system. This study reveals that the SigE regulon also mediates a discrete subset of functions associated with virulence. SigE is the first cell envelope stress-sensing system to be described in the bordetellae. In addition to its role during lethal infection of mice deficient in adaptive immunity, our results indicate that SigE is likely to be important for survival in the face of stresses encountered in the environment between hosts.

Role of pagL and lpxO in Bordetella bronchiseptica lipid A biosynthesis

PagL and LpxO are enzymes that modify lipid A. PagL is a 3-O deacylase that removes the primary acyl chain from the 3 position, and LpxO is an oxygenase that 2-hydroxylates specific acyl chains in the lipid A. pagL and lpxO homologues have been identified in the genome of Bordetella bronchiseptica, but in the current structure for B. bronchiseptica lipid A the 3 position is acylated and 2-OH acylation is not reported. We have investigated the role of B. bronchiseptica pagL and lpxO in lipid A biosynthesis. We report a different structure for wild-type (WT) B. bronchiseptica lipid A, including the presence of 2-OH-myristate, the presence of which is dependent on lpxO. We also demonstrate that the 3 position is not acylated in the major WT lipid A structures but that mutation of pagL results in the presence of 3-OH-decanoic acid at this position, suggesting that lipid A containing this acylation is synthesized but that PagL removes most of it from the mature lipid A. These data refine the structure of B. bronchiseptica lipid A and demonstrate that pagL and lpxO are involved in its biosynthesis.

Bordetella pertussis autotransporter Vag8 binds human C1 esterase inhibitor and confers serum resistance

Bordetella pertussis employs numerous strategies to evade the immune system, including the ability to resist killing via complement. Previously we have shown that B. pertussis binds a complement regulatory protein, C1 esterase inhibitor (C1inh) to its surface in a Bvg-regulated manner (i.e. during its virulence phase), but the B. pertussis factor was not identified. Here we set out to identify the B. pertussis C1inh-binding factor. Using a serum overlay assay, we found that this factor migrates at approximately 100 kDa on an SDS-PAGE gel. To identify this factor, we isolated proteins of approximately 100 kDa from wild type strain BP338 and from BP347, an isogenic Bvg mutant that does not bind C1inh. Using mass spectrometry and bioinformatics, we identified the autotransporter protein Vag8 as the putative C1inh binding protein. To prove that Vag8 binds C1inh, vag8 was disrupted in two different B. pertussis strains, namely BP338 and 18-323, and the mutants were tested for their ability to bind C1inh in a surface-binding assay. Neither mutant strain was capable of binding C1inh, whereas a complemented strain successfully bound C1inh. In addition, the passenger domain of Vag8 was expressed and purified as a histidine-tagged fusion protein and tested for C1inh-binding in an ELISA assay. Whereas the purified Vag8 passenger bound C1inh, the passenger domain of BrkA (a related autotransporter protein) failed to do so. Finally, serum assays were conducted to compare wild type and vag8 mutants. We determined that vag8 mutants from both strains were more susceptible to killing compared to their isogenic wild type counterparts. In conclusion, we have discovered a novel role for the previously uncharacterized protein Vag8 in the immune evasion of B. pertussis. Vag8 binds C1inh to the surface of the bacterium and confers serum resistance.

Virulence determinants, drug resistance and mobile genetic elements of Laribacter hongkongensis: a genome-wide analysis

BACKGROUND

Laribacter hongkongensis is associated with community-acquired gastroenteritis and traveler's diarrhea. In this study, we performed an in-depth annotation of the genes in its genome related to the various steps in the infective process, drug resistance and mobile genetic elements.

RESULTS

For acid and bile resistance, L. hongkongensis possessed a urease gene cassette, two arc gene clusters and bile salt efflux systems. For intestinal colonization, it possessed a putative adhesin of the autotransporter family homologous to those of diffusely adherent Escherichia coli (E. coli) and enterotoxigenic E. coli. To evade from host defense, it possessed superoxide dismutase and catalases. For lipopolysaccharide biosynthesis, it possessed the same set of genes that encode enzymes for synthesizing lipid A, two Kdo units and heptose units as E. coli, but different genes for its symmetrical acylation pattern, and nine genes for polysaccharide side chains biosynthesis. It contained a number of CDSs that encode putative cell surface acting (RTX toxin and hemolysins) and intracellular cytotoxins (patatin-like proteins) and enzymes for invasion (outer membrane phospholipase A). It contained a broad variety of antibiotic resistance-related genes, including genes related to β-lactam (n = 10) and multidrug efflux (n = 54). It also contained eight prophages, 17 other phage-related CDSs and 26 CDSs for transposases.

CONCLUSIONS

The L. hongkongensis genome possessed genes for acid and bile resistance, intestinal mucosa colonization, evasion of host defense and cytotoxicity and invasion. A broad variety of antibiotic resistance or multidrug resistance genes, a high number of prophages, other phage-related CDSs and CDSs for transposases, were also identified.

ABC transporters involved in export of cell surface glycoconjugates

Complex glycoconjugates play critical roles in the biology of microorganisms. Despite the remarkable diversity in glycan structures and the bacteria that produce them, conserved themes are evident in the biosynthesis-export pathways. One of the primary pathways involves representatives of the ATP-binding cassette (ABC) transporter superfamily. These proteins are responsible for the export of a wide variety of cell surface oligo- and polysaccharides in both Gram-positive and Gram-negative bacteria. Recent investigations of the structure and function of ABC transporters involved in the export of lipopolysaccharide O antigens have revealed two fundamentally different strategies for coupling glycan polymerization to export. These mechanisms are distinguished by the presence (or absence) of characteristic nonreducing terminal modifications on the export substrates, which serve as chain termination and/or export signals, and by the presence (or absence) of a discrete substrate-binding domain in the nucleotide-binding domain polypeptide of the ABC transporter. A bioinformatic survey examining ABC exporters from known oligo- and polysaccharide biosynthesis loci identifies conserved nucleotide-binding domain protein families that correlate well with themes in the structures and assembly of glycans. The familial relationships among the ABC exporters generate hypotheses concerning the biosynthesis of structurally diverse oligo- and polysaccharides, which play important roles in the biology of bacteria with different lifestyles.

Antigenic Variation among Bordetella: Bordetella bronchiseptica strain MO149 expresses a novel o chain that is poorly immunogenic

The O chain polysaccharide (O PS) of Bordetella bronchiseptica and Bordetella parapertussis lipopolysaccharide is a homopolymer of 2,3-diacetamido-2,3-dideoxygalacturonic acid (GalNAc3NAcA) in which some of the sugars are present as uronamides. The terminal residue contains several unusual modifications. To date, two types of modification have been characterized, and a survey of numerous strains demonstrated that each contained one of these two modification types. Host antibody responses against the O PS are directed against the terminal residue modifications, and there is little cross-reactivity between the two types. This suggests that Bordetella O PS modifications represent a means of antigenic variation. Here we report the characterization of the O PS of B. bronchiseptica strain MO149. It consists of a novel two-sugar repeating unit and a novel terminal residue modification, with the structure Me-4-alpha-L-GalNAc3NAcA-(4-beta-D-GlcNAc3NAcA-4-alpha-L-GalNAc3NAcA-)(5-6)-, which we propose be defined as the B. bronchiseptica O3 PS. We show that the O3 PS is very poorly immunogenic and that the MO149 strain contains a novel wbm (O PS biosynthesis) locus. Thus, there is greater diversity among Bordetella O PSs than previously recognized, which is likely to be a result of selection pressure from host immunity. We also determine experimentally, for the first time, the absolute configuration of the diacetimido-uronic acid sugars in Bordetella O PS.

Substitution of the Bordetella pertussis lipid A phosphate groups with glucosamine is required for robust NF-kappaB activation and release of proinflammatory cytokines in cells expressing human but not murine Toll-like receptor 4-MD-2-CD14

Bordetella pertussis endotoxin is a key modulator of the host immune response, mainly due to the role of its lipid A moiety in Toll-like receptor 4 (TLR4)-mediated signaling. We have previously demonstrated that the lipid A phosphate groups of B. pertussis BP338 can be substituted with glucosamine in a BvgAS-regulated manner. Here we examined the effect of this lipid A modification on the biological activity of B. pertussis endotoxin. We compared purified endotoxin and heat-killed B. pertussis BP338 whole cells that have modified lipid A phosphate groups to an isogenic mutant lacking this modification with respect to their capacities to induce the release of inflammatory cytokines by human and murine macrophages and to participate in the TLR4-mediated activation of NF-kappaB in transfected HEK-293 cells. We found inactivated B. pertussis cells to be stronger inducers of proinflammatory cytokines in THP-1-derived macrophages when lipid A was modified. Most notably, lack of lipid A modification abolished the ability of purified B. pertussis endotoxin to induce the release of inflammatory cytokines by human THP-1-derived macrophages but led to only slightly reduced inflammatory cytokine levels when stimulating murine (RAW 264.7) macrophages. Accordingly, upon stimulation of HEK-293 cells with inactivated bacteria and purified endotoxin, lack of lipid A modification led to impaired NF-kappaB activation only when human, and not when murine, TLR4-MD-2-CD14 was expressed. We speculate that in B. pertussis, lipid A modification has evolved to benefit the bacteria during human infection by modulating immune defenses rather than to evade innate immune recognition.

O antigen allows B. parapertussis to evade B. pertussis vaccine-induced immunity by blocking binding and functions of cross-reactive antibodies

Although the prevalence of Bordetella parapertussis varies dramatically among studies in different populations with different vaccination regimens, there is broad agreement that whooping cough vaccines, composed only of B. pertussis antigens, provide little if any protection against B. parapertussis. In C57BL/6 mice, a B. pertussis whole-cell vaccine (wP) provided modest protection against B. parapertussis, which was dependent on IFN-gamma. The wP was much more protective against an isogenic B. parapertussis strain lacking O-antigen than its wild-type counterpart. O-antigen inhibited binding of wP-induced antibodies to B. parapertussis, as well as antibody-mediated opsonophagocytosis in vitro and clearance in vivo. aP-induced antibodies also bound better in vitro to the O-antigen mutant than to wild-type B. parapertussis, but aP failed to confer protection against wild-type or O antigen-deficient B. parapertussis in mice. Interestingly, B. parapertussis-specific antibodies provided in addition to either wP or aP were sufficient to very rapidly reduce B. parapertussis numbers in mouse lungs. This study identifies a mechanism by which one pathogen escapes immunity induced by vaccination against a closely related pathogen and may explain why B. parapertussis prevalence varies substantially between populations with different vaccination strategies.

The O antigen is a critical antigen for the development of a protective immune response to Bordetella parapertussis

Despite excellent vaccine coverage in developed countries, whooping cough is a reemerging disease that can be caused by two closely related pathogens, Bordetella pertussis and B. parapertussis. The two are antigenically distinct, and current vaccines, containing only B. pertussis-derived antigens, confer efficient protection against B. pertussis but not against B. parapertussis. B. pertussis does not express the O antigen, while B. parapertussis retains it as a dominant surface antigen. Since the O antigen is a protective antigen for many pathogenic bacteria, we examined whether this factor is a potential protective antigen for B. parapertussis. In a mouse model of infection, immunization with wild-type B. parapertussis elicited a strong antibody response to the O antigen and conferred efficient protection against a subsequent B. parapertussis challenge. However, immunization with an isogenic mutant lacking the O antigen, B. parapertussis Deltawbm, induced antibodies that recognized other antigens but did not efficiently mediate opsonophagocytosis of B. parapertussis. The passive transfer of sera raised against B. parapertussis, but not B. parapertussis Deltawbm, reduced B. parapertussis loads in the lower respiratory tracts of mice. The addition of 10 microg of purified B. parapertussis lipopolysaccharide (LPS), which contains the O antigen, but not B. parapertussis Deltawbm LPS drastically improved the efficacy of the acellular vaccine Adacel against B. parapertussis. These data suggest that the O antigen is a critical protective antigen of B. parapertussis and its inclusion can substantially improve whooping cough vaccine efficacy against this pathogen.

Evidence for horizontal gene transfer of two antigenically distinct O antigens in Bordetella bronchiseptica

Host immunity is a major driving force of antigenic diversity, resulting in pathogens that can evade immunity induced by closely related strains. Here we show that two Bordetella bronchiseptica strains, RB50 and 1289, express two antigenically distinct O-antigen serotypes (O1 and O2, respectively). When 18 additional B. bronchiseptica strains were serotyped, all were found to express either the O1 or O2 serotype. Comparative genomic hybridization and PCR screening showed that the expression of either the O1 or O2 serotype correlated with the strain containing either the classical or alternative O-antigen locus, respectively. Multilocus sequence typing analysis of 49 B. bronchiseptica strains was used to build a phylogenetic tree, which revealed that the two O-antigen loci did not associate with a particular lineage, evidence that these loci are horizontally transferred between B. bronchiseptica strains. From experiments using mice vaccinated with purified lipopolysaccharide from strain RB50 (O1), 1289 (O2), or RB50Deltawbm (O antigen deficient), our data indicate that these O antigens do not confer cross-protection in vivo. The lack of cross-immunity between O-antigen serotypes appears to contribute to inefficient antibody-mediated clearance between strains. Together, these data are consistent with the idea that the O-antigen loci of B. bronchiseptica are horizontally transferred between strains and encode antigenically distinct serotypes, resulting in inefficient cross-immunity.

Characterization of WbpB, WbpE, and WbpD and reconstitution of a pathway for the biosynthesis of UDP-2,3-diacetamido-2,3-dideoxy-D-mannuronic acid in Pseudomonas aeruginosa

The lipopolysaccharide of Pseudomonas aeruginosa PAO1 contains an unusual sugar, 2,3-diacetamido-2,3-dideoxy-d-mannuronic acid (d-ManNAc3NAcA). wbpB, wbpE, and wbpD are thought to encode oxidase, transaminase, and N-acetyltransferase enzymes. To characterize their functions, recombinant proteins were overexpressed and purified from heterologous hosts. Activities of His(6)-WbpB and His(6)-WbpE were detected only when both proteins were combined in the same reaction. Using a direct MALDI-TOF mass spectrometry approach, we identified ions that corresponded to the predicted products of WbpB (UDP-3-keto-d-GlcNAcA) and WbpE (UDP-d-GlcNAc3NA) in the coupled enzyme-substrate reaction. Additionally, in reactions involving WbpB, WbpE, and WbpD, an ion consistent with the expected product of WbpD (UDP-d-GlcNAc3NAcA) was identified. Preparative quantities of UDP-d-GlcNAc3NA and UDP-d-GlcNAc3NAcA were enzymatically synthesized. These compounds were purified by high-performance liquid chromatography, and their structures were elucidated by NMR spectroscopy. This is the first report of the functional characterization of these proteins, and the enzymatic synthesis of UDP-d-GlcNAc3NA and UDP-d-GlcNAc3NAcA.

Post-assembly modification of Bordetella bronchiseptica O polysaccharide by a novel periplasmic enzyme encoded by wbmE

Bordetella bronchiseptica is a pathogen of humans and animals that colonizes the respiratory tract. It produces a lipopolysaccharide O antigen that contains a homopolymer of 2,3-dideoxy-2,3-diacetamido-l-galacturonic acid (l-GalNAc3NAcA). Some of these sugars are found in the uronamide form (l-GalNAc3NAcAN), and there is no discernible pattern in the distribution of amides along the chain. A B. bronchiseptica wbmE mutant expresses an O polysaccharide unusually rich in uronamides. The WbmE protein localizes to the periplasm and catalyzes the deamidation of uronamide-rich O chains in lipopolysaccharide purified from the mutant, to attain a wild-type uronamide/uronic acid ratio. WbmE is a member of the papain-like transglutaminase superfamily, and this categorization is consistent with a deamidase role. The periplasmic location of WbmE and its acceptance of complete lipopolysaccharide as substrate indicate that it operates at a late stage in lipopolysaccharide biosynthesis, after polymerization and export of the O chain from the cytoplasm. This is the first report of such a modification of O antigen after assembly. The expression of wbmE is controlled by the Bordetella virulence gene two-component regulatory system, BvgAS, suggesting that this deamidation is a novel mechanism by which these bacteria modify their cell surface charge in response to environmental stimuli.

Biosynthesis of a rare di-N-acetylated sugar in the lipopolysaccharides of both Pseudomonas aeruginosa and Bordetella pertussis occurs via an identical scheme despite different gene clusters

Pseudomonas aeruginosa and Bordetella pertussis produce lipopolysaccharide (LPS) that contains 2,3-diacetamido-2,3-dideoxy-D-mannuronic acid (D-ManNAc3NAcA). A five-enzyme biosynthetic pathway that requires WbpA, WbpB, WbpE, WbpD, and WbpI has been proposed for the production of this sugar in P. aeruginosa, based on analysis of genes present in the B-band LPS biosynthesis cluster. In the analogous B. pertussis cluster, homologs of wbpB to wbpI were present, but a putative dehydrogenase gene was missing; therefore, the biosynthetic mechanism for UDP-D-ManNAc3NAcA was unclear. Nonpolar knockout mutants of each P. aeruginosa gene were constructed. Complementation analysis of the mutants demonstrated that B-band LPS production was restored to P. aeruginosa knockout mutants when the relevant B. pertussis genes were supplied in trans. Thus, the genes that encode the putative oxidase, transaminase, N-acetyltransferase, and epimerase enzymes in B. pertussis are functional homologs of those in P. aeruginosa. Two candidate dehydrogenase genes were located by searching the B. pertussis genome; these have 80% identity to P. aeruginosa wbpO (serotype O6) and 32% identity to wbpA (serotype O5). These genes, wbpO(1629) and wbpO(3150), were shown to complement a wbpA knockout of P. aeruginosa. Capillary electrophoresis was used to characterize the enzymatic activities of purified WbpO(1629) and WbpO(3150), and mass spectrometry analysis confirmed that the two enzymes are dehydrogenases capable of converting UDP-D-GlcNAc, UDP-D-GalNAc, to a lesser extent, and UDP-D-Glc, to a much lesser extent. Together, these results suggest that B. pertussis produces UDP-D-ManNAc3NAcA through the same pathway proposed for P. aeruginosa, despite differences in the genomic context of the genes involved.

Replacement of adenylate cyclase toxin in a lineage of Bordetella bronchiseptica

Bordetella bronchiseptica is a gram-negative respiratory pathogen that infects a wide range of hosts and causes a diverse spectrum of disease. This diversity is likely affected by multiple factors, such as host immune status, polymicrobial infection, and strain diversity. In a murine model of infection, we found that the virulence of B. bronchiseptica strains, as measured by the mean lethal dose, varied widely. Strain 253 was less virulent than the typically studied strain, RB50. Transcriptome analysis showed that cyaA, the gene encoding adenylate cyclase toxin (CyaA), was the most downregulated transcript identified in strain 253 compared to that in strain RB50. Comparative genomic hybridization and genome sequencing of strain 253 revealed that the cya locus, which encodes, activates, and secretes CyaA, was replaced by an operon (ptp) predicted to encode peptide transport proteins. Other B. bronchiseptica strains from the same phylogenetic lineage as that of strain 253 also lacked the cya locus, contained the ptp genes, and were less virulent than strain RB50. Although the loss of CyaA would be expected to be counterselected since it is conserved among the classical bordetellae and believed to be important to their success, our data indicate that the loss of this toxin and the gain of the ptp genes occurred in an ancestral strain that then expanded into a lineage. This suggests that there may be ecological niches in which CyaA is not critical for the success of B. bronchiseptica.

O antigen protects Bordetella parapertussis from complement

Bordetella pertussis, a causative agent of whooping cough, expresses BrkA, which confers serum resistance, but the closely related human pathogen that also causes whooping cough, Bordetella parapertussis, does not. Interestingly, B. parapertussis, but not B. pertussis, produces an O antigen, a factor shown in other models to confer serum resistance. Using a murine model of infection, we determined that O antigen contributes to the ability of B. parapertussis to colonize the respiratory tract during the first week of infection, but not thereafter. Interestingly, an O antigen-deficient strain of B. parapertussis was not defective in colonizing mice lacking the complement cascade. O antigen prevented both complement component C3 deposition on the surface and complement-mediated killing of B. parapertussis. In addition, O antigen was required for B. parapertussis to systemically spread in complement-sufficient mice, but not complement-deficient mice. These data indicate that O antigen enables B. parapertussis to efficiently colonize the lower respiratory tract by protecting against complement-mediated control and clearance.

Predicting protein function from structure--the roles of short-chain dehydrogenase/reductase enzymes in Bordetella O-antigen biosynthesis

The pathogenic bacteria Bordetella parapertussis and Bordetella bronchiseptica express a lipopolysaccharide O antigen containing a polymer of 2,3-diacetamido-2,3-dideoxy-l-galacturonic acid. The O-antigen cluster contains three neighbouring genes that encode proteins belonging to the short-chain dehydrogenase/reductase (SDR) family, wbmF, wbmG and wbmH, and we aimed to elucidate their individual functions. Mutation and complementation implicate each gene in O-antigen expression but, as their putative sugar nucleotide substrates are not currently available, biochemical characterisation of WbmF, WbmG and WbmH is impractical at the present time. SDR family members catalyse a wide range of chemical reactions including oxidation, reduction and epimerisation. Because they typically share low sequence conservation, however, catalytic function cannot be predicted from sequence analysis alone. In this context, structural characterisation of the native proteins, co-crystals and small-molecule soaks enables differentiation of the functions of WbmF, WbmG and WbmH. These proteins exhibit typical SDR architecture and coordinate NAD. In the substrate-binding domain, all three enzymes bind uridyl nucleotides. WbmG contains a typical SDR catalytic TYK triad, which is required for oxidoreductase function, but the active site is devoid of additional acid-base functionality. Similarly, WbmH possesses a TYK triad, but an otherwise feature-poor active site. Consequently, 3,5-epimerase function can probably be ruled out for these enzymes. The WbmF active site contains conserved 3,5-epimerase features, namely, a positionally conserved cysteine (Cys133) and basic side chain (His90 or Asn213), but lacks the serine/threonine component of the SDR triad and therefore may not act as an oxidoreductase. The data suggest a pathway for synthesis of the O-antigen precursor UDP-2,3-diacetamido-2,3-dideoxy-l-galacturonic acid and illustrate the usefulness of structural data in predicting protein function.

The O antigen enables Bordetella parapertussis to avoid Bordetella pertussis-induced immunity

Bordetella pertussis and Bordetella parapertussis are closely related endemic human pathogens which cause whooping cough, a disease that is reemerging in human populations. Despite how closely related these pathogens are, their coexistence and the limited efficacy of B. pertussis vaccines against B. parapertussis suggest a lack of cross-protective immunity between the two. We sought to address the ability of infection-induced immunity against one of these pathogens to protect against subsequent infection by the other using a mouse model of infection. Immunity induced by B. parapertussis infection protected against subsequent infections by either species. However, immunity induced by B. pertussis infection prevented subsequent B. pertussis infections but did not protect against B. parapertussis infections. The O antigen of B. parapertussis inhibited binding of antibodies to the bacterial surface and was required for B. parapertussis to colonize mice convalescent from B. pertussis infection. Thus, the O antigen of B. parapertussis confers asymmetrical cross-immunity between the causative agents of whooping cough. We propose that these findings warrant investigation of the relative role of B. parapertussis in the resurgence of whooping cough.

Cloning, expression, purification and preliminary crystallographic analysis of the short-chain dehydrogenase enzymes WbmF, WbmG and WbmH from Bordetella bronchiseptica

The short-chain dehydrogenase enzymes WbmF, WbmG and WbmH from Bordetella bronchiseptica were cloned into Escherichia coli expression vectors, overexpressed and purified to homogeneity. Crystals of all three wild-type enzymes were obtained using vapour-diffusion crystallization with high-molecular-weight PEGs as a primary precipitant at alkaline pH. Some of the crystallization conditions permitted the soaking of crystals with cofactors and nucleotides or nucleotide sugars, which are possible substrate compounds, and further conditions provided co-complexes of two of the proteins with these compounds. The crystals diffracted to resolutions of between 1.50 and 2.40 A at synchrotron X-ray sources. The synchrotron data obtained were sufficient to determine eight structures of the three enzymes in complex with a variety of cofactors and substrate molecules.

Comparative role of immunoglobulin A in protective immunity against the Bordetellae

The genus Bordetella includes a group of closely related mammalian pathogens that cause a variety of respiratory diseases in a long list of animals (B. bronchiseptica) and whooping cough in humans (B. pertussis and B. parapertussis). While past research has examined how these pathogens are eliminated from the lower respiratory tract, the host factors that control and/or clear the bordetellae from the upper respiratory tract remain unclear. We hypothesized that immunoglobulin A (IgA), the predominant mucosal antibody isotype, would have a protective role against these mucosal pathogens. IgA(-/-) mice were indistinguishable from wild-type mice in their control and clearance of B. pertussis or B. parapertussis, suggesting that IgA is not crucial to immunity to these organisms. However, naïve and convalescent IgA(-/-) mice were defective in reducing the numbers of B. bronchiseptica in the upper respiratory tract compared to wild-type controls. Passively transferred serum from convalescent IgA(-/-) mice was not as effective as serum from convalescent wild-type mice in clearing this pathogen from the tracheae of naive recipient mice. IgA induced by B. bronchiseptica infection predominantly recognized lipopolysaccharide-containing O-antigen, and antibodies against O-antigen were important to bacterial clearance from the trachea. Since an IgA response contributes to the control of B. bronchiseptica infection of the upper respiratory tract, immunization strategies aimed at inducing B. bronchiseptica-specific IgA may be beneficial to preventing the spread of this bacterium among domestic animal populations.

Comparison of the genome sequence of the poultry pathogen Bordetella avium with those of B. bronchiseptica, B. pertussis, and B. parapertussis reveals extensive diversity in surface structures associated with host interaction

Bordetella avium is a pathogen of poultry and is phylogenetically distinct from Bordetella bronchiseptica, Bordetella pertussis, and Bordetella parapertussis, which are other species in the Bordetella genus that infect mammals. In order to understand the evolutionary relatedness of Bordetella species and further the understanding of pathogenesis, we obtained the complete genome sequence of B. avium strain 197N, a pathogenic strain that has been extensively studied. With 3,732,255 base pairs of DNA and 3,417 predicted coding sequences, it has the smallest genome and gene complement of the sequenced bordetellae. In this study, the presence or absence of previously reported virulence factors from B. avium was confirmed, and the genetic bases for growth characteristics were elucidated. Over 1,100 genes present in B. avium but not in B. bronchiseptica were identified, and most were predicted to encode surface or secreted proteins that are likely to define an organism adapted to the avian rather than the mammalian respiratory tracts. These include genes coding for the synthesis of a polysaccharide capsule, hemagglutinins, a type I secretion system adjacent to two very large genes for secreted proteins, and unique genes for both lipopolysaccharide and fimbrial biogenesis. Three apparently complete prophages are also present. The BvgAS virulence regulatory system appears to have polymorphisms at a poly(C) tract that is involved in phase variation in other bordetellae. A number of putative iron-regulated outer membrane proteins were predicted from the sequence, and this regulation was confirmed experimentally for five of these.

Complete structures of Bordetella bronchiseptica and Bordetella parapertussis lipopolysaccharides

The structures of the lipopolysaccharide (LPS) core and O antigen of Bordetella bronchiseptica and Bordetella parapertussis are known, but how these two regions are linked to each other had not been determined. We have studied LPS from several strains of these microorganisms to determine the complete carbohydrate structure of the LPS. LPS was analyzed using different chemical degradations, NMR spectroscopy, and mass spectrometry. This identified a novel pentasaccharide fragment that links the O chain to the core in all the LPS studied. In addition, although the O chain of these bacteria was reported as a homopolymer of 1,4-linked 2,3-diacetamido-2,3-dideoxy-alpha-galacturonic acid, we discovered that the polymer contains several amidated uronic acids, the number of which varies between strains. These new data describe the complete structure of the LPS carbohydrate backbone for both Bordetella species and help to explain the complex genetics of LPS biosynthesis in these bacteria.

Bordetella pertussis, the causative agent of whooping cough, evolved from a distinct, human-associated lineage of B. bronchiseptica

Bordetella pertussis, B. bronchiseptica, B. parapertussis(hu), and B. parapertussis(ov) are closely related respiratory pathogens that infect mammalian species. B. pertussis and B. parapertussis(hu) are exclusively human pathogens and cause whooping cough, or pertussis, a disease that has resurged despite vaccination. Although it most often infects animals, infrequently B. bronchiseptica is isolated from humans, and these infections are thought to be zoonotic. B. pertussis and B. parapertussis(hu) are assumed to have evolved from a B. bronchiseptica-like ancestor independently. To determine the phylogenetic relationships among these species, housekeeping and virulence genes were sequenced, comparative genomic hybridizations were performed using DNA microarrays, and the distribution of insertion sequence elements was determined, using a collection of 132 strains. This multifaceted approach distinguished four complexes, representing B. pertussis, B. parapertussis(hu), and two distinct B. bronchiseptica subpopulations, designated complexes I and IV. Of the two B. bronchiseptica complexes, complex IV was more closely related to B. pertussis. Of interest, while only 32% of the complex I strains were isolated from humans, 80% of the complex IV strains were human isolates. Comparative genomic hybridization analysis identified the absence of the pertussis toxin locus and dermonecrotic toxin gene, as well as a polymorphic lipopolysaccharide biosynthesis locus, as associated with adaptation of complex IV strains to the human host. Lipopolysaccharide structural diversity among these strains was confirmed by gel electrophoresis. Thus, complex IV strains may comprise a human-associated lineage of B. bronchiseptica from which B. pertussis evolved. These findings will facilitate the study of pathogen host-adaptation. Our results shed light on the origins of the disease pertussis and suggest that the association of B. pertussis with humans may be more ancient than previously assumed.

Interactions of pulmonary collectins with Bordetella bronchiseptica and Bordetella pertussis lipopolysaccharide elucidate the structural basis of their antimicrobial activities

Surfactant proteins A (SP-A) and D (SP-D) play an important role in the innate immune defenses of the respiratory tract. SP-A binds to the lipid A region of lipopolysaccharide (LPS), and SP-D binds to the core oligosaccharide region. Both proteins induce aggregation, act as opsonins for neutrophils and macrophages, and have direct antimicrobial activity. Bordetella pertussis LPS has a branched core structure and a nonrepeating terminal trisaccharide. Bordetella bronchiseptica LPS has the same structure, but lipid A is palmitoylated and there is a repeating O-antigen polysaccharide. The ability of SP-A and SP-D to agglutinate and permeabilize wild-type and LPS mutants of B. pertussis and B. bronchiseptica was examined. Previously, wild-type B. pertussis was shown to resist the effects of SP-A; however, LPS mutants lacking the terminal trisaccharide were susceptible to SP-A. In this study, SP-A was found to aggregate and permeabilize a B. bronchiseptica mutant lacking the terminal trisaccharide, while wild-type B. bronchiseptica and mutants lacking only the palmitoyl transferase or O antigen were resistant to SP-A. Wild-type B. pertussis and B. bronchiseptica were both resistant to SP-D; however, LPS mutants of either strain lacking the terminal trisaccharide were aggregated and permeabilized by SP-D. We conclude that the terminal trisaccharide protects Bordetella species from the bactericidal functions of SP-A and SP-D. The O antigen and palmitoylated lipid A of B. bronchiseptica play no role in this resistance.

Structure of theBordetella trematumLPS O-chain subunit

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

Strain-dependent role of BrkA during Bordetella pertussis infection of the murine respiratory tract

Bordetella pertussis, the causative agent of whooping cough, expresses many virulence factors believed to be involved in infection and disease progression. While these factors as a group are required for infection, deletion of individual virulence factor genes generally has limited effects on the ability of B. pertussis to efficiently infect the respiratory tract of mice, suggesting they may perform noncritical or redundant functions. We have recently observed that a B. pertussis strain, putatively with a mutation of a single gene, brkA, results in a severe defect in vivo. Although BrkA has been shown to be required for B. pertussis to resist complement-mediated killing in vitro, the relevance of these findings to the in vivo role of BrkA during infection has not been examined. Transducing this mutation into multiple wild-type B. pertussis strains allowed us to confirm the in vitro phenotype of reduced resistance to serum complement. All DeltabrkA mutants were increased in their sensitivity to complement in vitro, both in the presence and absence of antibodies. However, these strains differed substantially in their phenotypes in vivo. DeltabrkA mutants of recent clinical isolates were indistinguishable from wild-type strains in their efficient infection of respiratory organs, suggesting that the function of BrkA in these strains is noncritical or redundant. In contrast, multiple DeltabrkA strains derived from Tohama I were severely defective during the first week postinoculation compared to their wild-type parent. This defect was present even in complement-deficient mice, revealing a complement-independent phenotype for the DeltabrkA mutant in respiratory tract infection.

Nonreducing Terminal Modifications Determine the Chain Length of Polymannose O Antigens of Escherichia coli and Couple Chain Termination to Polymer Export via an ATP-binding Cassette Transporter

The chain length of bacterial lipopolysaccharide O antigens is regulated to give a modal distribution that is critical for pathogenesis. This paper describes the process of chain length determination in the ATP-binding cassette (ABC) transporter-dependent pathway, a pathway that is widespread among Gram-negative bacteria. Escherichia coli O8 and O9/O9a polymannans are synthesized in the cytoplasm, and an ABC transporter exports the nascent polymer across the inner membrane prior to completion of the LPS molecule. The polymannan O antigens have nonreducing terminal methyl groups. The 3-O-methyl group in serotype O8 is transferred from S-adenosylmethionine by the WbdD(O8) enzyme, and this modification terminates polymerization. Methyl groups are added to the O9a polymannan in a reaction dependent on preceding phosphorylation. The bifunctional WbdD(O9a) catalyzes both reactions, but only the kinase activity controls chain length. Chain termination occurs in a mutant lacking the ABC transporter, indicating that it precedes export. An E. coli wbdD(O9a) mutant accumulated O9a polymannan in the cytoplasm, indicating that WbdD activity coordinates polymannan chain termination with export across the inner membrane.

Biochemical characterization of WbpA, a UDP-N-acetyl-D-glucosamine 6-dehydrogenase involved in O-antigen biosynthesis in Pseudomonas aeruginosa PAO1

WbpA (PA3159) is an enzyme involved in the biosynthesis of unusual di-N-acetyl-d-mannosaminuronic acid-derived sugar nucleotides found in the O antigen of Pseudomonas aeruginosa PAO1 (serotype O5). The wbpA gene that encodes this enzyme was cloned into pET-28a, overexpressed as a histidine-tagged fusion protein, and purified by nickel chelation chromatography. Capillary electrophoresis was used to examine substrate conversion by WbpA, and the data revealed that WbpA is a UDP-N-acetyl-D-glucosamine 6-dehydrogenase (EC 1.1.1.136), which uses NAD(+) as a coenzyme. The enzyme reaction product was purified by HPLC and analyzed using NMR spectroscopy. Our results showed unequivocally that the product of the WbpA reaction is UDP-N-acetyl-d-glucosaminuronic acid. WbpA requires either NH(4)(+) or K(+) for activity and the accompanying anions exert secondary effects on activity consistent with their ranking in the Hofmeister series. Kinetic analysis showed positive cooperativity with respect to UDP-N-acetyl-d-glucosamine binding with a K(0.5) of 94 microM, a k(cat) of 86 min(-1), and a Hill coefficient of 1.8. In addition, WbpA has a K(0.5) for NAD(+) of 220 microM, a k(cat) of 86 min(-1), and a Hill coefficient of 1.1. The oligomerization state of WbpA was analyzed by gel filtration, dynamic light scattering, and analytical ultracentrifugation, with all three techniques indicating that WbpA exists as a trimer in solution. However, tertiary structure predictions suggested a tetramer, which was supported by data from transmission electron microscopy. The electron micrograph of negatively stained WbpA samples revealed structures with 4-fold symmetry.

Bordetella species are distinguished by patterns of substantial gene loss and host adaptation

Pathogens of the bacterial genus Bordetella cause respiratory disease in humans and animals. Although virulence and host specificity vary across the genus, the genetic determinants of this diversity remain unidentified. To identify genes that may underlie key phenotypic differences between these species and clarify their evolutionary relationships, we performed a comparative analysis of genome content in 42 Bordetella strains by hybridization of genomic DNA to a microarray representing the genomes of three Bordetella species and by subtractive hybridization. Here we show that B. pertussis and B. parapertussis are predominantly differentiated from B. bronchiseptica by large, species-specific regions of difference, many of which encode or direct synthesis of surface structures, including lipopolysaccharide O antigen, which may be important determinants of host specificity. The species also exhibit sequence diversity at a number of surface protein-encoding loci, including the fimbrial major subunit gene, fim2. Gene loss, rather than gene acquisition, accompanied by the proliferation of transposons, has played a fundamental role in the evolution of the pathogenic bordetellae and may represent a conserved evolutionary mechanism among other groups of microbial pathogens.

Structure of bacterial lipopolysaccharides

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

Comparative analysis of the genome sequences of Bordetella pertussis, Bordetella parapertussis and Bordetella bronchiseptica

Bordetella pertussis, Bordetella parapertussis and Bordetella bronchiseptica are closely related Gram-negative beta-proteobacteria that colonize the respiratory tracts of mammals. B. pertussis is a strict human pathogen of recent evolutionary origin and is the primary etiologic agent of whooping cough. B. parapertussis can also cause whooping cough, and B. bronchiseptica causes chronic respiratory infections in a wide range of animals. We sequenced the genomes of B. bronchiseptica RB50 (5,338,400 bp; 5,007 predicted genes), B. parapertussis 12822 (4,773,551 bp; 4,404 genes) and B. pertussis Tohama I (4,086,186 bp; 3,816 genes). Our analysis indicates that B. parapertussis and B. pertussis are independent derivatives of B. bronchiseptica-like ancestors. During the evolution of these two host-restricted species there was large-scale gene loss and inactivation; host adaptation seems to be a consequence of loss, not gain, of function, and differences in virulence may be related to loss of regulatory or control functions.