Hemin-binding surface protein from Bartonella quintana

Genomic properties of a Bartonella quintana strain from Japanese macaque (Macaca fuscata) revealed by genome comparison with human and rhesus macaque strains

Bartonella quintana, the causative agent of trench fever, is an intracellular bacterium that infects human erythrocytes and vascular endothelial cells. For many years, humans were considered the only natural hosts for B. quintana; however, it was recently discovered that wild Japanese macaques (Macaca fuscata) also serve as hosts for B. quintana. To elucidate the genetic characteristics of the B. quintana strain MF1-1 isolated from a Japanese macaque, we determined the complete genome sequence of the strain and compared it with those of strain Toulouse from a human and strain RM-11 from a rhesus macaque. General genomic features and orthologous gene cluster profiles are similar among the three strains, and strain MF1-1 is genetically closer to strain RM-11 than strain Toulouse based on the average nucleotide identity values; however, a significant inversion of approximately 0.68 Mb was detected in the chromosome of strain MF1-1. Moreover, the Japanese macaque strains lacked the bepA gene, which is responsible for anti-apoptotic function, and the trwL2, trwL4, and trwL6 genes, which may be involved in adhesion to erythrocytes of rhesus macaque and human. These features likely represent the genomic traits acquired by Japanese macaque strains in their host-associated evolution.

Bartonella henselae Recombinant Pap31 for the Diagnosis of Canine and Human Bartonelloses

Bartonella spp. comprise a genus of Gram-negative alphaproteobacteria that are slow growing, fastidious, and facultative intracellular pathogens with zoonotic potential. Immunofluorescent antibody assays (IFAs), Western blot (WB), and enzyme-linked immunosorbent assays (ELISAs), the frequently used modalities for the serological diagnosis of canine and human Bartonelloses, generate numerous false negative results. Therefore, the development of a reliable serodiagnostic assay for Bartonelloses is of clinical and epidemiological importance. Pap31, a heme binding surface protein of B. henselae, is associated with bacterial adhesion and related to bacterial colonization. To our knowledge, B. henselae Pap31 and its fragments (N-terminal (NTD), middle (MD), and C-terminal (CTD) domains) have not been investigated for the serodiagnosis of canine and human Bartonelloses. In this study, we evaluate the diagnostic utility of B. henselae recombinant whole Pap31 (rPap31) and Pap31 fragments by ELISA using sera from 70 dogs (36 Bartonella spp. IFA-positive (naturally infected), and 34 Bartonella spp. IFA- and PCR-negative (control dogs)) and 36 humans (18 Bartonella spp. IFA-positive (naturally infected) and 18 controls)). In the dogs, the area under the curve (AUC) score of recombinant whole Pap31 was 0.714 with a sensitivity of 42% and specificity of 94% at an OD cutoff value of 0.8955. Among the evaluated recombinant Pap31 proteins for the diagnosis of canine Bartonelloses, rPap31-NTD yielded the highest AUC score of 0.792 (95% CI 0.688-0.895) with a sensitivity of 44% and specificity of 100% at a cutoff value of 1.198. In concordance with this finding, rPap31-NTD also had the highest AUC score of 0.747 (95% CI 0.581-0.913) among the Pap31 recombinant proteins for the diagnosis of human Bartonelloses, with 39% sensitivity and 94% specificity at a cutoff value of 1.366. Recombinant whole Pap31 (rPap31) resulted in 72% sensitivity and 61% specificity at a cutoff value of 0.215 for human Bartonelloses. Due to either low sensitivity or questionable specificity, our findings indicate that recombinant Pap31 and the selected fragments may not be appropriate diagnostic targets in detecting anti-Bartonella antibodies in Bartonella-infected dogs and humans. The findings from this study can be used to further assess the antigenicity and immunogenicity of B. henselae Pap31 as a diagnostic target.

Immunogenic Peptides from Pap31 and SCS-α of Bartonella bacilliformis: One Step Closer to a Rapid Diagnostic Tool for Carrion's Disease

Bartonella bacilliformis is the causal agent of Carrion’s disease, an overlooked illness endemic in the Andean Mountains with Peru being the most affected country. The diagnostic of this illness is a challenge due to the limited resources and the common symptomatology with other infectious diseases. The goal of this study was to identify immunogenic peptides from Pap31 and succinyl-CoA synthetase α (SCS-α) of B. bacilliformis that might be suitable for developing a serologic tool. The immunodominant character of Pap31 and SCS-α was determined by Western blotting and in-silico analysis. Subsequently, 35 peptides were selected for epitope mapping and their immunoreactivity was tested by enzyme-linked immunosorbent assay (ELISA). A total of 30 sera were tested including pre-exposed people with high IgM levels for Pap31/SCS-α (23 sera), patients (2 sera) as well as 5 sera with no reactivity to Pap31/SCS-α. The results indicate that Pap31-8 (₁₈₇QAIGSAILKGTKDTGT₂₀₂) and SCS-α-12 (₅₉IFASVAEGKEKTGANA₇₄) are the most immunogenic peptides, with Pap31-8 showing potential to discriminate between B. bacilliformis and the remaining Bartonella spp., and SCS-α-12 differentiating Bartonella spp. from other microorganisms.

An Exposed Outer Membrane Hemin-Binding Protein Facilitates Hemin Transport by a TonB-Dependent Receptor in Riemerella anatipestifer

Iron is an essential element for the replication of most bacteria, including Riemerella anatipestifer, a Gram-negative bacterial pathogen of ducks and other birds. R. anatipestifer utilizes hemoglobin-derived hemin as an iron source; however, the mechanism by which this bacterium acquires hemin from hemoglobin is largely unknown. Here, rhuA disruption was shown to impair iron utilization from duck hemoglobin in R. anatipestifer CH-1. Moreover, the putative lipoprotein RhuA was identified as a surface-exposed, outer membrane hemin-binding protein, but it could not extract hemin from duck hemoglobin. Mutagenesis studies showed that recombinant RhuA^Y144A, RhuA^Y177A, and RhuA^H149A lost hemin-binding ability, suggesting that amino acid sites at tyrosine 144 (Y144), Y177, and histidine 149 (H149) are crucial for hemin binding. Furthermore, rhuR, the gene adjacent to rhuA, encodes a TonB2-dependent hemin transporter. The function of rhuA in duck hemoglobin utilization was abolished in the rhuR mutant strain, and recombinant RhuA was able to bind the cell surface of R. anatipestifer CH-1 ΔrhuA rather than R. anatipestifer CH-1 ΔrhuR ΔrhuA, indicating that RhuA associates with RhuR to function. The sequence of the RhuR-RhuA hemin utilization locus exhibits no similarity to those of characterized hemin transport systems. Thus, this locus is a novel hemin uptake locus with homologues distributed mainly in the Bacteroidetes phylum. IMPORTANCE In vertebrates, hemin from hemoglobin is an important iron source for infectious bacteria. Many bacteria can obtain hemin from hemoglobin, but the mechanisms of hemin acquisition from hemoglobin differ among bacteria. Moreover, most studies have focused on the mechanism of hemin acquisition from mammalian hemoglobin. In this study, we found that the RhuR-RhuA locus of R. anatipestifer CH-1, a duck pathogen, is involved in hemin acquisition from duck hemoglobin via a unique pathway. RhuA was identified as an exposed outer membrane hemin-binding protein, and RhuR was identified as a TonB2-dependent hemin transporter. Moreover, the function of RhuA in hemoglobin utilization is RhuR dependent and not vice versa. The homologues of RhuR and RhuA are widely distributed in bacteria in marine environments, animals, and plants, representing a novel hemin transportation system of Gram-negative bacteria. This study not only was important for understanding hemin uptake in R. anatipestifer but also enriched the knowledge about the hemin transportation pathway in Gram-negative bacteria.

Brucella melitensis omp31 Mutant Is Attenuated and Confers Protection Against Virulent Brucella melitensis Challenge in BALB/c Mice

For control of brucellosis in small ruminants, attenuated B. melitensis Rev1 is used but it can be virulent for animals and human. Based on these aspects, it is essential to identify potential immunogens to avoid these problems in prevention of brucellosis. The majority of OMPs in the Omp25/31 family have been studied because these proteins are relevant in maintaining the integrity of the outer membrane but their implication in the virulence of the different species of this genus is not clearly described. Therefore, in this work we studied the role of Omp31 on virulence by determining the residual virulence and detecting lesions in spleen and testis of mice inoculated with the B. melitensis LVM31 mutant strain. In addition, we evaluated the conferred protection in mice immunized with the mutant strain against the challenge with the B. melitensis Bm133 virulent strain. Our results showed that the mutation of omp31 caused a decrease in splenic colonization without generating apparent lesions or histopathological changes apparent in both organs in comparison with the control strains and that the mutant strain conferred similar protection as the B. melitensis Rev1 vaccine strain against the challenge with B. melitensis Bm133 virulent strain. These results allow us to conclude that Omp31 plays an important role on the virulence of B. melitensis in the murine model, and due to the attenuation shown by the strain, it could be considered a vaccine candidate for the prevention of goat brucellosis.

Molecular Mechanisms of Bartonella and Mammalian Erythrocyte Interactions: A Review

Bartonellosis is an infectious disease caused by Bartonella species that are distributed worldwide with animal and public health impact varying according to Bartonella species, infection phase, immunological characteristics, and geographical region. Bartonella is widely present in various mammals including cats, rodents, ruminants, and humans. At least 13 Bartonella species or subspecies are zoonotic. Each species has few reservoir animals in which it is often asymptomatic. Bartonella infection may lead to various clinical symptoms in humans. As described in the B.tribocorum-rat model, when Bartonella was seeded into the blood stream, they could escape immunity, adhered to and invaded host erythrocytes. They then replicated and persisted in the infected erythrocytes for several weeks. This review summarizes the current knowledge of how Bartonella prevent phagocytosis and complement activation, what pathogenesis factors are involved in erythrocyte adhesion and invasion, and how Bartonella could replicate and persist in mammalian erythrocytes. Current advances in research will help us to decipher molecular mechanisms of interactions between Bartonella and mammalian erythrocytes and may help in the development of biological strategies for the prevention and control of bartonellosis.

Identification of Cross-Protective Potential Antigens against Pathogenic Brucella spp. through Combining Pan-Genome Analysis with Reverse Vaccinology

Brucellosis is a zoonotic infectious disease caused by bacteria of the genus Brucella. Brucella melitensis, Brucella abortus, and Brucella suis are the most pathogenic species of this genus causing the majority of human and domestic animal brucellosis. There is a need to develop a safe and potent subunit vaccine to overcome the serious drawbacks of the live attenuated Brucella vaccines. The aim of this work was to discover antigen candidates conserved among the three pathogenic species. In this study, we employed a reverse vaccinology strategy to compute the core proteome of 90 completed genomes: 55 B. melitensis, 17 B. abortus, and 18 B. suis. The core proteome was analyzed by a metasubcellular localization prediction pipeline to identify surface-associated proteins. The identified proteins were thoroughly analyzed using various in silico tools to obtain the most potential protective antigens. The number of core proteins obtained from analyzing the 90 proteomes was 1939 proteins. The surface-associated proteins were 177. The number of potential antigens was 87; those with adhesion score ≥ 0.5 were considered antigen with "high potential," while those with a score of 0.4-0.5 were considered antigens with "intermediate potential." According to a cumulative score derived from protein antigenicity, density of MHC-I and MHC-II epitopes, MHC allele coverage, and B-cell epitope density scores, a final list of 34 potential antigens was obtained. Remarkably, most of the 34 proteins are associated with bacterial adhesion, invasion, evasion, and adaptation to the hostile intracellular environment of macrophages which is adjusted to deprive Brucella of required nutrients. Our results provide a manageable list of potential protective antigens for developing a potent vaccine against brucellosis. Moreover, our elaborated analysis can provide further insights into novel Brucella virulence factors. Our next step is to test some of these antigens using an appropriate antigen delivery system.

Bartonella Species, an Emerging Cause of Blood-Culture-Negative Endocarditis

Since the reclassification of the genus Bartonella in 1993, the number of species has grown from 1 to 45 currently designated members. Likewise, the association of different Bartonella species with human disease continues to grow, as does the range of clinical presentations associated with these bacteria. Among these, blood-culture-negative endocarditis stands out as a common, often undiagnosed, clinical presentation of infection with several different Bartonella species. The limitations of laboratory tests resulting in this underdiagnosis of Bartonella endocarditis are discussed. The varied clinical picture of Bartonella infection and a review of clinical aspects of endocarditis caused by Bartonella are presented. We also summarize the current knowledge of the molecular basis of Bartonella pathogenesis, focusing on surface adhesins in the two Bartonella species that most commonly cause endocarditis, B. henselae and B. quintana. We discuss evidence that surface adhesins are important factors for autoaggregation and biofilm formation by Bartonella species. Finally, we propose that biofilm formation is a critical step in the formation of vegetative masses during Bartonella-mediated endocarditis and represents a potential reservoir for persistence by these bacteria.

Dynamics of Co-Infection with Bartonella henselae Genotypes I and II in Naturally Infected Cats: Implications for Feline Vaccine Development

Bartonella henselae is an emerging bacterial pathogen causing cat-scratch disease and potentially fatal bacillary angiomatosis in humans. Bacteremic cats constitute a large reservoir for human infection. Although feline vaccination is a potential strategy to prevent human infection, selection of appropriate B. henselae strains is critical for successful vaccine development. Two distinct genotypes of B. henselae (type I, type II) have been identified and are known to co-infect the feline host, but very little is known about the interaction of these two genotypes during co-infection in vivo. To study the in vivo dynamics of type I and type II co-infection, we evaluated three kittens that were naturally flea-infected with both B. henselae type I and type II. Fifty individual bloodstream isolates from each of the cats over multiple time points were molecularly typed (by 16S rRNA gene sequencing), to determine the prevalence of the two genotypes over 2 years of persistent infection. We found that both B. henselae genotypes were transmitted simultaneously to each cat via natural flea infestation, resulting in mixed infection with both genotypes. Although the initial infection was predominately type I, after the first 2 months, the isolated genotype shifted to exclusively type II, which then persisted with a relapsing pattern. Understanding the parameters of protection against both genotypes of B. henselae, and the competitive dynamics in vivo between the two genotypes, will be critical in the development of a successful feline vaccine that can ultimately prevent B. henselae transmission to human contacts.

Development of a serum-free liquid medium for Bartonella species

The genus Bartonella comprises numerous species with at least 13 species pathogenic for humans. They are fastidious, aerobic, Gram negative, and facultative intracellular bacteria which cause a variety of human and non-human diseases. This study focused on the development of a serum-free liquid medium for culture of Bartonella species. Some liquid media are available commercially but all of them use undefined supplements such as fetal calf serum or defibrinated sheep blood. Our intention was to create a reproducible liquid medium for Bartonella species that can simply be prepared. We tested several supplements that could potentially support the growth of Bartonella species. Slight growth improvement was achieved with glucose and sucrose. However, hemin in particular improved the growth rate. At a temperature of 37 °C, a CO₂ concentration of 5 %, a humidified atmosphere, and the use of the supplements glucose, sucrose, and hemin, we developed a medium that does not need serum as an undefined supplement any more. In conclusion, the newly developed medium supports growth of Bartonella species equal to the commercially available media but with the advantage that it has a serum-free formulation. It can be prepared fast and easy and is a useful tool in studying these bacteria.

Proteins of Bartonella bacilliformis: Candidates for Vaccine Development

Bartonella bacilliformis is the etiologic agent of Carrión's disease or Oroya fever. B. bacilliformis infection represents an interesting model of human host specificity. The notable differences in clinical presentations of Carrión's disease suggest complex adaptations by the bacterium to the human host, with the overall objectives of persistence, maintenance of a reservoir state for vectorial transmission, and immune evasion. These events include a multitude of biochemical and genetic mechanisms involving both bacterial and host proteins. This review focuses on proteins involved in interactions between B. bacilliformis and the human host. Some of them (e.g., flagellin, Brps, IalB, FtsZ, Hbp/Pap31, and other outer membrane proteins) are potential protein antigen candidates for a synthetic vaccine.

Detection of biological objects using dynamic characteristics of double-walled carbon nanotubes

This study explores double-walled carbon nanotubes as the sensing devices for biological objects including viruses and bacteria. The biological objects studied include alanine with amino terminal residue, deoxyadenosine with free residue, Coronaviridae and Bartonella bacilliformis. An expression has been articulated to identify the mass of biological objects from the shift of frequency. Sensitivity of the sensor has been calculated when subjected to such biological objects. Molecular structural mechanics approach has been used for investigating the vibrational responses of zigzag and armchair double-walled carbon nanotube-based nano biosensors. The elastic properties of beam element are calculated by considering mechanical characteristics of covalent bonds between the carbon atoms in the hexagonal lattice. Spring elements are used to describe the interlayer interactions between the inner and outer tubes caused due to the van der Waals forces. The mass of each beam element is assumed as point mass at nodes coinciding with carbon atoms at inner and outer wall of DWCNT. Based on the sensitivity and the frequency shift it can be concluded that cantilever zigzag DWCNTs are better candidates for detecting the biological objects.

Oroya fever and verruga peruana: bartonelloses unique to South America

Bartonella bacilliformis is the bacterial agent of Carrión's disease and is presumed to be transmitted between humans by phlebotomine sand flies. Carrión's disease is endemic to high-altitude valleys of the South American Andes, and the first reported outbreak (1871) resulted in over 4,000 casualties. Since then, numerous outbreaks have been documented in endemic regions, and over the last two decades, outbreaks have occurred at atypical elevations, strongly suggesting that the area of endemicity is expanding. Approximately 1.7 million South Americans are estimated to be at risk in an area covering roughly 145,000 km2 of Ecuador, Colombia, and Peru. Although disease manifestations vary, two disparate syndromes can occur independently or sequentially. The first, Oroya fever, occurs approximately 60 days following the bite of an infected sand fly, in which infection of nearly all erythrocytes results in an acute hemolytic anemia with attendant symptoms of fever, jaundice, and myalgia. This phase of Carrión's disease often includes secondary infections and is fatal in up to 88% of patients without antimicrobial intervention. The second syndrome, referred to as verruga peruana, describes the endothelial cell-derived, blood-filled tumors that develop on the surface of the skin. Verrugae are rarely fatal, but can bleed and scar the patient. Moreover, these persistently infected humans provide a reservoir for infecting sand flies and thus maintaining B. bacilliformis in nature. Here, we discuss the current state of knowledge regarding this life-threatening, neglected bacterial pathogen and review its host-cell parasitism, molecular pathogenesis, phylogeny, sand fly vectors, diagnostics, and prospects for control.

Managing iron supply during the infection cycle of a flea borne pathogen, Bartonella henselae

Bartonella are hemotropic bacteria responsible for emerging zoonoses. Most Bartonella species appear to share a natural cycle that involves an arthropod transmission, followed by exploitation of a mammalian host in which they cause long-lasting intra-erythrocytic bacteremia. Persistence in erythrocytes is considered an adaptation to transmission by bloodsucking arthropod vectors and a strategy to obtain heme required for Bartonella growth. Bartonella genomes do not encode for siderophore biosynthesis or a complete iron Fe³⁺ transport system. Only genes, sharing strong homology with all components of a Fe²⁺ transport system, are present in Bartonella genomes. Also, Bartonella genomes encode for a complete heme transport system. Bartonella must face various environments in their hosts and vectors. In mammals, free heme and iron are rare and oxygen concentration is low. In arthropod vectors, toxic heme levels are found in the gut where oxygen concentration is high. Bartonella genomes encode for 3–5 heme-binding proteins. In Bartonella henselae heme-binding proteins were shown to be involved in heme uptake process, oxidative stress response, and survival inside endothelial cells and in the flea. In this report, we discuss the use of the heme uptake and storage system of B. henselae during its infection cycle. Also, we establish a comparison with the iron and heme uptake systems of Yersinia pestis used during its infection cycle.

The Bartonella quintana extracytoplasmic function sigma factor RpoE has a role in bacterial adaptation to the arthropod vector environment

Bartonella quintana is a vector-borne bacterial pathogen that causes fatal disease in humans. During the infectious cycle, B. quintana transitions from the hemin-restricted human bloodstream to the hemin-rich body louse vector. Because extracytoplasmic function (ECF) sigma factors often regulate adaptation to environmental changes, we hypothesized that a previously unstudied B. quintana ECF sigma factor, RpoE, is involved in the transition from the human host to the body louse vector. The genomic context of B. quintana rpoE identified it as a member of the ECF15 family of sigma factors found only in alphaproteobacteria. ECF15 sigma factors are believed to be the master regulators of the general stress response in alphaproteobacteria. In this study, we examined the B. quintana RpoE response to two stressors that are encountered in the body louse vector environment, a decreased temperature and an increased hemin concentration. We determined that the expression of rpoE is significantly upregulated at the body louse (28°C) versus the human host (37°C) temperature. rpoE expression also was upregulated when B. quintana was exposed to high hemin concentrations. In vitro and in vivo analyses demonstrated that RpoE function is regulated by a mechanism involving the anti-sigma factor NepR and the response regulator PhyR. The ΔrpoE ΔnepR mutant strain of B. quintana established that RpoE-mediated transcription is important in mediating the tolerance of B. quintana to high hemin concentrations. We present the first analysis of an ECF15 sigma factor in a vector-borne human pathogen and conclude that RpoE has a role in the adaptation of B. quintana to the hemin-rich arthropod vector environment.

Hemin-binding proteins as potent markers for serological diagnosis of infections with Bartonella quintana

It is difficult to distinguish infections with different Bartonella species using commercially available immunofluorescence (indirect immunofluorescent antibody [IFA]) assay kits. To identify appropriate proteins for serodiagnosis of Bartonella quintana infections, we investigated the antigenicity of B. quintana proteins using sera from homeless people with high B. quintana IgG titers in IFA assay. These sera reacted strongly to an outer membrane protein, hemin-binding protein D (HbpD). Further, serum from an endocarditis patient infected with B. quintana reacted to HbpB and HbpD. To locate the antigenic sites within the proteins, we generated deletion mutants of HbpB and HbpD. Amino acid residues 89 to 220 of HbpB and 151 to 200 of HbpD were identified as the minimum regions required for recognition by these sera. Several oligopeptides comprising parts of the minimum regions of HbpB and HbpD were synthesized, and their immunoreactivity with the above-mentioned sera was tested by enzyme-linked immunosorbent assay (ELISA). Serum from the endocarditis patient reacted similarly to synthetic peptides HbpB2 (amino acid residues 144 to 173 of HbpB) and HbpD3 (151 to 200 residues of HbpD), while sera from the other subjects reacted to HbpD3. These results indicate that synthetic peptides HbpB2 and HbpD3 might be suitable for developing serological tools for differential diagnosis of B. quintana infections from other Bartonella infections.

Heme binding proteins of Bartonella henselae are required when undergoing oxidative stress during cell and flea invasion

Bartonella are hemotropic bacteria responsible for emerging zoonoses. These heme auxotroph alphaproteobacteria must import heme for their growth, since they cannot synthesize it. To import exogenous heme, Bartonella genomes encode for a complete heme uptake system enabling transportation of this compound into the cytoplasm and degrading it to release iron. In addition, these bacteria encode for four or five outer membrane heme binding proteins (Hbps). The structural genes of these highly homologous proteins are expressed differently depending on oxygen, temperature and heme concentrations. These proteins were hypothesized as being involved in various cellular processes according to their ability to bind heme and their regulation profile. In this report, we investigated the roles of the four Hbps of Bartonella henselae, responsible for cat scratch disease. We show that Hbps can bind heme in vitro. They are able to enhance the efficiency of heme uptake when co-expressed with a heme transporter in Escherichia coli. Using B. henselae Hbp knockdown mutants, we show that these proteins are involved in defense against the oxidative stress, colonization of human endothelial cell and survival in the flea.

Heme degrading protein HemS is involved in oxidative stress response of Bartonella henselae

Bartonellae are hemotropic bacteria, agents of emerging zoonoses. These bacteria are heme auxotroph Alphaproteobacteria which must import heme for supporting their growth, as they cannot synthesize it. Therefore, Bartonella genome encodes for a complete heme uptake system allowing the transportation of this compound across the outer membrane, the periplasm and the inner membranes. Heme has been proposed to be used as an iron source for Bartonella since these bacteria do not synthesize a complete system required for iron Fe³⁺uptake. Similarly to other bacteria which use heme as an iron source, Bartonellae must transport this compound into the cytoplasm and degrade it to allow the release of iron from the tetrapyrrole ring. For Bartonella, the gene cluster devoted to the synthesis of the complete heme uptake system also contains a gene encoding for a polypeptide that shares homologies with heme trafficking or degrading enzymes. Using complementation of an E. coli mutant strain impaired in heme degradation, we demonstrated that HemS from Bartonella henselae expressed in E. coli allows the release of iron from heme. Purified HemS from B. henselae binds heme and can degrade it in the presence of a suitable electron donor, ascorbate or NADPH-cytochrome P450 reductase. Knocking down the expression of HemS in B. henselae reduces its ability to face H₂O₂ induced oxidative stress.

Nanotransformation of the haemotrophic Mycoplasma suis during in vitro cultivation attempts using modified cell free Mycoplasma media

Mycoplasma suis belongs to haemotrophic mycoplasmas (HMs) which cause infectious anaemia in a large variety of mammals. To date, no in vitro cultivation system for M. suis or other HMs has been established. We hypothesised that M. suis could grow in classical Mycoplasma media supplemented with nutrients (e.g. glucose, iron-binding proteins) which are naturally available from its host environment, the porcine blood. Blood from experimentally M. suis-infected pigs was used to inoculate either standard SP-4 Mycoplasma medium supplemented with iron-binding proteins (transferrin, haemin, and haemoglobin) or glucose-enriched Hayflick Mycoplasma medium. A quantitative M. suis-specific real-time PCR assay was applied to determine and quantify M. suis loads weekly during 12 week-incubation. The first 2 weeks after inoculation M. suis loads decreased remarkably and then persisted at a stationary level over the observation time of 12 weeks in iron-binding protein- or glucose supplemented media variants. Scanning electron microscopic analysis of liquid M. suis sub-cultures on Hayflick agar showed small, densely-packed microcolonies of irregular M. suis cells of reduced size (0.2-0.6μm) indicating nanotransformation. The partial 16S rDNA sequence of these cultured M. suis nanocells was 99.9% identical to M. suis. M. suis cells derived from liquid cultures interact in vitro with porcine erythrocytes by fibril-like structures. We conclude, that the modified Mycoplasma media used for M. suis cultivation are obviously unfavourable for growth but lead to culture persistence. M. suis adapt to inappropriate culture conditions by alteration into nanoforms.

A structurally novel hemopexin fold protein of rice plays role in chlorophyll degradation

Proteins containing hemopexin fold domain are suggested to have diverse functions in various living organisms. In order to investigate the structure and function of this type of protein in rice plant (Oryza sativa), the gene encoding a hemopexin fold protein (OsHFP) was cloned, analyzed in silico and characterized. Molecular modeling revealed that the OsHFP is closely related to other hemopexin fold proteins, but is unique with a cylindrical central tunnel as well as extended N- and C-terminal domains. The recombinant OsHFP was found to bind hemin, the oxidized form of heme in vitro. The expression of the single copy OsHFP gene was detected in rice flower buds. Heterologous expression of OsHFP in green leaf tissues resulted in chlorophyll degradation; however, stable expression of OsHFP was observed in transgenic hairy roots, a non-green tissue. The possible role of OsHFP in regulating programmed cell death in anther green tissues of rice is proposed.

Strategies of exploitation of mammalian reservoirs by Bartonella species

Numerous mammal species, including domestic and wild animals such as ruminants, dogs, cats and rodents, as well as humans, serve as reservoir hosts for various Bartonella species. Some of those species that exploit non-human mammals as reservoir hosts have zoonotic potential. Our understanding of interactions between bartonellae and reservoir hosts has been greatly improved by the development of animal models for infection and the use of molecular tools allowing large scale mutagenesis of Bartonella species. By reviewing and combining the results of these and other approaches we can obtain a comprehensive insight into the molecular interactions that underlie the exploitation of reservoir hosts by Bartonella species, particularly the well-studied interactions with vascular endothelial cells and erythrocytes.

Persistence of Bartonella spp. stealth pathogens: from subclinical infections to vasoproliferative tumor formation

Bartonella spp. are facultative intracellular bacteria that typically cause a long-lasting intraerythrocytic bacteremia in their mammalian reservoir hosts, thereby favoring transmission by blood-sucking arthropods. In most cases, natural reservoir host infections are subclinical and the relapsing intraerythrocytic bacteremia may last weeks, months, or even years. In this review, we will follow the infection cycle of Bartonella spp. in a reservoir host, which typically starts with an intradermal inoculation of bacteria that are superficially scratched into the skin from arthropod feces and terminates with the pathogen exit by the blood-sucking arthropod. The current knowledge of bacterial countermeasures against mammalian immune response will be presented for each critical step of the pathogenesis. The prevailing models of the still-enigmatic primary niche and the anatomical location where bacteria reside, persist, and are periodically seeded into the bloodstream to cause the typical relapsing Bartonella spp. bacteremia will also be critically discussed. The review will end up with a discussion of the ability of Bartonella spp., namely Bartonella henselae, Bartonella quintana, and Bartonella bacilliformis, to induce tumor-like vascular deformations in humans having compromised immune response such as in patients with AIDS.

Hemin binding protein C is found in outer membrane vesicles and protects Bartonella henselae against toxic concentrations of hemin

Bartonella species are gram-negative, emerging bacterial pathogens found in two distinct environments. In the gut of the obligately hematophagous arthropod vector, bartonellae are exposed to concentrations of heme that are toxic to other bacteria. In the bloodstream of the mammalian host, access to heme and iron is severely restricted. Bartonellae have unusually high requirements for heme, which is their only utilizable source of iron. Although heme is essential for Bartonella survival, little is known about genes involved in heme acquisition and detoxification. We developed a strategy for high-efficiency transposon mutagenesis to screen for genes in B. henselae heme binding and uptake pathways. We identified a B. henselae transposon mutant that constitutively expresses the hemin binding protein C (hbpC) gene. In the wild-type strain, transcription of B. henselae hbpC was upregulated at arthropod temperature (28°C), compared to mammalian temperature (37°C). In the mutant strain, temperature-dependent regulation was absent. We demonstrated that HbpC binds hemin and localizes to the B. henselae outer membrane and outer membrane vesicles. Overexpression of hbpC in B. henselae increased resistance to heme toxicity, implicating HbpC in protection of B. henselae from the toxic levels of heme present in the gut of the arthropod vector. Experimental inoculation of cats with B. henselae strains demonstrated that both constitutive expression and deletion of hbpC affect the ability of B. henselae to infect the cat host. Modulation of hbpC expression appears to be a strategy employed by B. henselae to survive in the arthropod vector and the mammalian host.

Intruders below the radar: molecular pathogenesis of Bartonella spp

Bartonella spp. are facultative intracellular pathogens that employ a unique stealth infection strategy comprising immune evasion and modulation, intimate interaction with nucleated cells, and intraerythrocytic persistence. Infections with Bartonella are ubiquitous among mammals, and many species can infect humans either as their natural host or incidentally as zoonotic pathogens. Upon inoculation into a naive host, the bartonellae first colonize a primary niche that is widely accepted to involve the manipulation of nucleated host cells, e.g., in the microvasculature. Consistently, in vitro research showed that Bartonella harbors an ample arsenal of virulence factors to modulate the response of such cells, gain entrance, and establish an intracellular niche. Subsequently, the bacteria are seeded into the bloodstream where they invade erythrocytes and give rise to a typically asymptomatic intraerythrocytic bacteremia. While this course of infection is characteristic for natural hosts, zoonotic infections or the infection of immunocompromised patients may alter the path of Bartonella and result in considerable morbidity. In this review we compile current knowledge on the molecular processes underlying both the infection strategy and pathogenesis of Bartonella and discuss their connection to the clinical presentation of human patients, which ranges from minor complaints to life-threatening disease.

Parallel evolution of a type IV secretion system in radiating lineages of the host-restricted bacterial pathogen Bartonella

Adaptive radiation is the rapid origination of multiple species from a single ancestor as the result of concurrent adaptation to disparate environments. This fundamental evolutionary process is considered to be responsible for the genesis of a great portion of the diversity of life. Bacteria have evolved enormous biological diversity by exploiting an exceptional range of environments, yet diversification of bacteria via adaptive radiation has been documented in a few cases only and the underlying molecular mechanisms are largely unknown. Here we show a compelling example of adaptive radiation in pathogenic bacteria and reveal their genetic basis. Our evolutionary genomic analyses of the α-proteobacterial genus Bartonella uncover two parallel adaptive radiations within these host-restricted mammalian pathogens. We identify a horizontally-acquired protein secretion system, which has evolved to target specific bacterial effector proteins into host cells as the evolutionary key innovation triggering these parallel adaptive radiations. We show that the functional versatility and adaptive potential of the VirB type IV secretion system (T4SS), and thereby translocated Bartonella effector proteins (Beps), evolved in parallel in the two lineages prior to their radiations. Independent chromosomal fixation of the virB operon and consecutive rounds of lineage-specific bep gene duplications followed by their functional diversification characterize these parallel evolutionary trajectories. Whereas most Beps maintained their ancestral domain constitution, strikingly, a novel type of effector protein emerged convergently in both lineages. This resulted in similar arrays of host cell-targeted effector proteins in the two lineages of Bartonella as the basis of their independent radiation. The parallel molecular evolution of the VirB/Bep system displays a striking example of a key innovation involved in independent adaptive processes and the emergence of bacterial pathogens. Furthermore, our study highlights the remarkable evolvability of T4SSs and their effector proteins, explaining their broad application in bacterial interactions with the environment.

Adaptive radiation is the rapid origination of an array of species by the divergent colonization of disparate ecological niches. In the case of pathogenic bacteria, radiations can lead to the emergence of novel human pathogens. Being divergently adapted to a range of different mammalian hosts, including humans as reservoir or incidental hosts, the genus Bartonella represents a suitable model to study genomic mechanisms underpinning divergent adaptation of pathogens. Here we show that two distinct lineages of Bartonella have radiated in parallel, resulting in two arrays of evolutionary distinct species adapted to overlapping sets of mammalian hosts. Such parallelisms display excellent models to reveal insights into the genetic mechanisms underlying these independent evolutionary processes. Our genome-wide analysis identifies a striking evolutionary parallelism in a horizontally-acquired protein secretion system in the two lineages. The parallel evolutionary trajectory of this system in the two lineages is characterized by the convergent origination of a wide array of adaptive functions dedicated to the cellular interaction within the mammalian hosts. The parallel evolution of the two radiating lineages on the ecological as well as on the molecular level suggests that the horizontal acquisition and the functional diversification of the secretion system display an evolutionary key innovation underlying adaptive evolution.

Pestilence, persistence and pathogenicity: infection strategies of Bartonella

It has been nearly two decades since the discovery of Bartonella as an agent of bacillary angiomatosis in AIDS patients and persistent bacteremia and 'nonculturable' endocarditis in homeless people. Since that time, the number of Bartonella species identified has increased from one to 24, and 10 of these bacteria are associated with human disease. Although Bartonella is the only genus that infects human erythrocytes and triggers pathological angiogenesis in the vascular bed, the group remains understudied compared with most other bacterial pathogens. Numerous questions regarding Bartonella's molecular pathogenesis and epidemiology remain unanswered. Virtually every mammal harbors one or more Bartonella species and their transmission typically involves a hematophagous arthropod vector. However, many details regarding epidemiology and the public health threat imposed by these animal reservoirs is unclear. A handful of studies have shown that bartonellae are highly-adapted pathogens whose parasitic strategy has evolved to cause persistent infections of the host. To this end, virulence attributes of Bartonella include the subversion of host cells with effector molecules delivered via a type IV secretion system, induction of pathological angiogenesis through various means, including inhibition of apoptosis and activation of hypoxia-inducing factor 1, use of afimbrial adhesins that are orthologs of Yersinia adhesin A, incorporation of lipopolysaccharides with low endotoxic potency in the outer membrane, and several other virulence factors that help Bartonella infect and persist in erythrocytes and endothelial cells of the host circulatory system.

Mixed infections, cryptic diversity, and vector-borne pathogens: evidence from Polygenis fleas and Bartonella species

Coinfections within hosts present opportunities for horizontal gene transfer between strains and competitive interactions between genotypes and thus can be a critical element of the lifestyles of pathogens. Bartonella spp. are Alphaproteobacteria that parasitize mammalian erythrocytes and endothelial cells. Their vectors are thought to be various biting arthropods, such as fleas, ticks, mites, and lice, and they are commonly cited as agents of various emerging diseases. Coinfections by different Bartonella strains and species can be common in mammals, but little is known about specificity and coinfections in arthropod vectors. We surveyed the rate of mixed infections of Bartonella in flea vectors (Polygenis gwyni) parasitizing cotton rats (Sigmodon hispidus) in which previous surveys indicated high rates of infection. We found that nearly all fleas (20 of 21) harbored one or more strains of Bartonella, with rates of coinfection approaching 90%. A strain previously identified as common in cotton rats was also common in their fleas. However, another common strain in cotton rats was absent from P. gwyni, while a rare cotton rat strain was quite common in P. gwyni. Surprisingly, some samples were also coinfected with a strain phylogenetically related to Bartonella clarridgeiae, which is typically associated with felids and ruminants. Finally, a locus (pap31) that is characteristically borne on phage in Bartonella was successfully sequenced from most samples. However, sequence diversity in pap31 was novel in the P. gwyni samples, relative to other Bartonella previously typed with pap31, emphasizing the likelihood of large reservoirs of cryptic diversity in natural populations of the pathogen.

Transcriptional regulation of the heme binding protein gene family of Bartonella quintana is accomplished by a novel promoter element and iron response regulator

We previously identified a five-member family of hemin-binding proteins (Hbp's) of Bartonella quintana that bind hemin on the outer surface but share no homology with known bacterial heme receptors. Subsequently, we demonstrated that expression of the hbp family is significantly influenced by oxygen, heme, and temperature conditions encountered by the pathogen in the human host and the body louse vector; e.g., we observed a dramatic (>100-fold) increase in hbpC transcript levels in response to the "louse-like" temperature of 30 degrees C. The goal of the present study was to identify a transcription factor(s) involved in the coordinated and differential regulation of the hbp family. First, we used quantitative real-time PCR (qRT-PCR) to show that the same environmental conditions generate parallels in the transcript profiles of four candidate transcriptional regulators (Irr, Fur, RirA, and BatR) described in the order Rhizobiales, with the greatest overall change in the transcription of irr (a >5-fold decrease) at a "louse-like" temperature, suggesting that Irr may function as an hbpC repressor. Second, a B. quintana strain hyperexpressing Irr was constructed; it exhibits a "bloodstream-like" hbp transcript profile in the absence of an environmental stimulus (i.e., hbpC is repressed and hbpA, hbpD, and hbpE mRNAs are relatively abundant). Furthermore, when this strain is grown at a "louse-like" temperature, an inversion of the transcript profile occurs, where derepression of hbpC and repression of hbpA, hbpD, and hbpE are readily evident, strongly suggesting that Irr and temperature influence hbp family expression. Third, electrophoretic mobility shift analyses show that recombinant Irr binds specifically to the hbpC promoter region at a sequence that is highly conserved in Bartonella hbp genes, which we designated the hbp family box, or "H-box." Fourth, we used the H-box to search the B. quintana genome and discovered a number of intriguing open reading frames, e.g., five members of a six-member family of cohemolysin autotransporters. Finally, qRT-PCR data regarding the effects of Fur and RirA overexpression on the hbp family are provided; they show that Fur's effect on the hbp family is relatively minor but RirA generates a "bloodstream-like" hbp transcript profile in the absence of an environmental stimulus, as observed for the Irr-hyperexpressing strain.

Role of the Omp25/Omp31 family in outer membrane properties and virulence of Brucella ovis

The genes coding for the five outer membrane proteins (OMPs) of the Omp25/Omp31 family expected to be located in the outer membrane (OM) of rough virulent Brucella ovis PA were inactivated to evaluate their role in virulence and OM properties. The OM properties of the mutant strains and of the mutants complemented with the corresponding wild-type genes were analyzed, in comparison with the parental strain and rough B. abortus RB51, in several tests: (i) binding of anti-Omp25 and anti-Omp31 monoclonal antibodies, (ii) autoagglutination of bacterial suspensions, and (iii) assessment of susceptibility to polymyxin B, sodium deoxycholate, hydrogen peroxide, and nonimmune ram serum. A tight balance of the members of the Omp25/Omp31 family was seen to be essential for the stability of the B. ovis OM, and important differences between the OMs of B. ovis PA and B. abortus RB51 rough strains were observed. Regarding virulence, the absence of Omp25d and Omp22 from the OM of B. ovis PA led to a drastic reduction in spleen colonization in mice. While the greater susceptibility of the Deltaomp22 mutant to nonimmune serum and its difficulty in surviving in the stationary phase might be on the basis of its dramatic attenuation, no defects in the OM able to explain the attenuation of the Deltaomp25d mutant were found, especially considering that the fully virulent Deltaomp25c mutant displayed more important OM defects. Accordingly, Omp25d, and perhaps Omp22, could be directly involved in the penetration and/or survival of B. ovis inside host cells. This aspect, together with the role of Omp25d and Omp22 in the virulence both of B. ovis in rams and of other Brucella species, should be thoroughly evaluated in future studies.

Bartonella bacilliformis GroEL: effect on growth of human vascular endothelial cells in infected cocultures

Bartonella are the only bacteria known to induce angioproliferative lesions of the human vasculature and liver during infection. Previous work from our lab suggests that GroEL participates in the mitogenic response observed in HUVEC cultures supplemented with the soluble fraction of Bartonella bacilliformis. Work in this study shows that exposure to high concentrations of the fraction is actually cytotoxic for HUVECs. To analyze this phenomenon, live B. bacilliformis-HUVEC cocultures were employed to study the effect of excess bacterial GroEL on the host cell during active infection. Four B. bacilliformis strains were generated to produce varying levels of GroEL. HUVEC cocultures with LSS100, a strain that synthesizes markedly greater quantities of GroEL relative to others, significantly accelerates apoptosis of the cocultured HUVECs relative to other strains. Acceleration of apoptosis can be inhibited by Z-VAD-FMK, a pan-caspase inhibitor. Time course data show that, at 18 h of infection, both LSS100 and control strains significantly inhibit spontaneous apoptosis of cocultured HUVECs, as previously reported for other Bartonella species. However, by 48 h, LSS100 significantly increases apoptosis of the host cell. We hypothesize that intracellular Bartonella GroEL functions as an Hsp60 analogue, a eukaryotic orthologue known to accelerate pro-caspase 3 activation by enhancing its vulnerability to upstream activator caspases. These data suggest another strategy whereby Bartonella may regulate host cell growth.

Environmental signals generate a differential and coordinated expression of the heme receptor gene family of Bartonella quintana

Of all bacteria, Bartonella quintana has the highest reported in vitro hemin requirement, yet an explanation for this remains elusive. To produce diseases such as trench fever, endocarditis, and bacillary angiomatosis, B. quintana must survive and replicate in the disparate environments of the Pediculus humanus corporis (body louse) gut and the human vasculature. We previously identified a five-member family of hemin binding proteins (Hbps) synthesized by B. quintana that bind hemin on the outer surface but share no similarity to known bacterial heme receptors. In the present study, we examine the transcription, regulation, and synthesis of this virulence factor family by cultivation of the bacterium in environments that simulate natural heme, oxygen, and temperature conditions encountered in the host and insect vector. First, quantitative real-time PCR data show that hbpC expression is regulated by temperature, where a >100-fold increase in transcript quantity was seen at 30 degrees C relative to 37 degrees C, suggesting that HbpC synthesis would be greatest in the cooler temperature of the louse. Second, cultivation at human bloodstream oxygen concentration (5% relative to 21% atmospheric) significantly decreases the transcript quantity of all hbp genes, indicating that expression is influenced by O2 and/or reactive oxygen species. Third, a differential expression pattern within the hbp family is revealed when B. quintana is grown in a range of hemin concentrations: subgroup I (hbpC and hbpB) predominates in a simulated louse environment (high heme), and subgroup II (hbpA, hbpD, and hbpE) is preferentially expressed in a simulated human background (low heme). By using two-dimensional sodium dodecyl sulfate-polyacrylamide gel electrophoresis, immunoblotting, and matrix-assisted laser desorption ionization-time of flight mass spectrometry fingerprinting, we demonstrate that synthesis of HbpA correlates with hbpA transcript increases observed at low hemin concentrations. Finally, an hbpA promoter-lacZ reporter construct in B. quintana demonstrates that a transcriptional regulator(s) is controlling the expression of hbpA through a cis-acting regulatory element located in the hbpA promoter region.

Bartonella henselae Pap31, an extracellular matrix adhesin, binds the fibronectin repeat III13 module

Bartonella henselae wound-associated infections suggest involvement of extracellular matrix molecules in adhesion and invasion. Pap31 was previously identified as a hemin-binding protein. Our recent studies suggest the protein is an adhesin that is recognized by the host's immune systems. In this study we examined the interactions of B. henselae Pap31 with fibronectin (Fn), heparin (Hep), and human umbilical vein endothelial cells (HUVECs). The cloned gene was expressed in Escherichia coli, and the purified Pap31 protein elicited strong antibody responses in mice and was reactive with rabbit anti-live B. henselae and mouse anti-Pap31 antibodies by Western blotting. Pap31 bound to immobilized Fn and to HUVECs in a dose-dependent manner and to Hep. Fn fragment-binding assays identified the Hep-1 and Hep-2 binding domains of human Fn and in particular the (12-13)FnIII repeat module as primary binding sites for this adhesin. Furthermore, Pap31 binding to the above Fn fragments could be inhibited by Hep, suggesting a common binding site involving the 13FnIII repeat module on the Hep-2 domain of Fn. Adherence of intact B. henselae to HUVECs was inhibited by increasing concentrations of anti-Pap31 antibodies. In addition, purified Pap31 coprecipitated effectively with Fn and anti-Fn antibodies. Taken together, these data suggest that Pap31 is an Fn-binding protein mediating the B. henselae-host interaction(s), and they implicate the 13FnIII repeat module as an important binding site for this adhesin on the Fn molecule. These interactions may be important initial steps leading to bacterial attachment and colonization that promote the establishment of B. henselae infections in vivo.

Brucella outer membrane protein Omp31 is a haemin-binding protein

The expression of haemin-binding proteins (HBPs) in the outer membrane is one of the strategies used by Gram-negative bacteria to obtain iron from the host. No HBP has been described in Brucella spp. We investigated whether Omp31, an outer membrane protein from Brucella with homology to HBPs from Bartonella quintana, is an HBP. Soluble recombinant Omp31 bound specifically to haemin-agarose, while an unrelated Brucella protein (SurA) did not. A similar experiment showed that native Omp31 found in the Brucella suis membrane fraction also binds to haemin-agarose. Recombinant Omp31 was electrophoresed by SDS-PAGE, transferred to nitrocellulose, and incubated with a haemin solution. Haemin bound to Omp31 and to albumin (positive control) but not to SurA. IPTG-induced recombinant Escherichia coli cells expressing Omp31 on their membrane bound significantly more haemin than uninduced cells or controls carrying a similar plasmid without the omp31 gene, showing that Omp31 also binds haemin in a bacterial membrane environment. Viable Brucella ovis cells bound haemin in solution, and this binding was markedly inhibited by preincubation of cells with antibodies to Omp31 and to an exposed prominent loop of the protein, thus showing that Omp31 functions as an HBP in brucellae. To test whether the expression of Omp31 is iron-regulated, B. suis was grown in trypticase-soy broth (TSB) and in iron-depleted TSB. The expression of Omp31, as assessed by Western blot, was significantly higher in bacteria grown under iron limitation. Overall, these results show that Omp31 from B. suis, B. melitensis and B. ovis is an HBP, whose expression seems to be induced by iron limitation.

Genetic variability of the heme uptake system among different strains of the fish pathogen Vibrio anguillarum: identification of a new heme receptor

The ability to utilize heme compounds as iron sources was investigated in Vibrio anguillarum strains belonging to serotypes O1 to O10. All strains, regardless of their serotype or isolation origin could utilize hemin and hemoglobin as sole iron sources. Similarly, all of the isolates could bind hemin and Congo red, and this binding was mediated by cell envelope proteins. PCR and Southern hybridization were used to assay the occurrence of heme transport genes huvABCD, which have been previously described in serotype O1. Of 23 strains studied, two serotype O3 isolates proved negative for all huvABCD genes, whereas nine strains included in serotypes O2, O3, O4, O6, O7, and O10 tested negative for the outer membrane heme receptor gene huvA. A gene coding for a novel outer membrane heme receptor was cloned and characterized in a V. anguillarum serotype O3 strain lacking huvA. The new heme receptor, named HuvS, showed significant similarity to other outer membrane heme receptors described in Vibrionaceae, but little homology (39%) to HuvA. This heme receptor was present in 9 out of 11 of the V. anguillarum strains that tested negative for HuvA. Furthermore, complementation experiments demonstrated that HuvS could substitute for the HuvA function in Escherichia coli and V. anguillarum mutants. The huvS and huvA sequences alignment, as well as the analysis of their respective upstream and downstream DNA sequences, suggest that horizontal transfer and recombination might be responsible for generating this genetic diversity.

Isolation of Bacteriophages from Bartonella vinsonii subsp. berkhoffii and the Characterization of Pap31 Gene Sequences from Bacterial and Phage DNA

Bacteriophages enhance bacterial survival, facilitate bacterial adaptation to new environmental conditions, assist in the adaptation to a new host species, and enhance bacterial evasion or inactivation of host defense mechanisms. We describe the detection and purification of a novel tailed bacteriophage from Bartonella vinsonii subsp. berkhoffii, which was previously described as a bacteriophage-negative species. We also compare B. vinsonii subsp. berkhoffi Pap31 bacteriophage gene sequences to B. henselae (Houston I), and B. quintana (Fuller) bacteriophage Pap31 sequences. Negative staining electron microscopy of log phase culturesof B. vinsonii subsp. berkhoffii identified bacteriophages, possessing a 50-nm icosahedric head diameter and a 60- to 80-nm contractile tail. Sequence analysis of the bacteriophage Pap31 gene from B. vinsonii subsp. berkhoffii showed three consensus sequences and a 12-bp insertion when compared with Pap31 gene sequences from B. henselae (Houston I) and B. quintana (Fuller) bacteriophages. Isolation of B. vinsonii subsp. berkhoffii bacteriophages containing a Pap31 gene suggests that this heme-binding protein gene might play an important role in bacterial virulence through the genetic exchange of DNA within this subspecies. Defining phage-associated genes may also contribute to the enhanced understanding of the evolutionary relationships among members of the genus Bartonella.

The Bartonella vinsonii subsp. arupensis immunodominant surface antigen BrpA gene, encoding a 382-kilodalton protein composed of repetitive sequences, is a member of a multigene family conserved among bartonella species

Bartonella proteins that elicit an antibody response during an infection are poorly defined; therefore, to characterize antigens recognized by the host, a Bartonella genomic expression library was screened with serum from an infected mouse. This process led to the discovery of a Bartonella vinsonii subsp. arupensis gene encoding a 382-kDa protein, part of a gene family encoding large proteins, each containing multiple regions of repetitive segments. The genes were termed brpA to -C (bartonella repeat protein) and bore significant similarity to genes encoding the BadA adhesin protein and members of the variably expressed outer membrane protein family of proteins from Bartonella henselae and Bartonella quintana, respectively.

Molecular and Cellular Basis ofBartonellaPathogenesis

The genus Bartonella comprises several important human pathogens that cause a wide range of clinical manifestations: cat-scratch disease, trench fever, Carrion's disease, bacteremia with fever, bacillary angiomatosis and peliosis, endocarditis, and neuroretinitis. Common features of bartonellae include transmission by blood-sucking arthropods and the specific interaction with endothelial cells and erythrocytes of their mammalian hosts. For each Bartonella species, the invasion and persistent intracellular colonization of erythrocytes are limited to a specific human or animal reservoir host. In contrast, endothelial cells are target host cells in probably all mammals, including humans. Bartonellae subvert multiple cellular functions of human endothelial cells, resulting in cell invasion, proinflammatory activation, suppression of apoptosis, and stimulation of proliferation, which may cumulate in vasoproliferative tumor growth. This review summarizes our understanding of Bartonella-host cell interactions and the molecular mechanisms of bacterial virulence and persistence. In addition, current controversies and unanswered questions in this area are highlighted.

Heme-iron increases levels of AP65-mediated adherence by Trichomonas vaginalis

Trichomonas vaginalis is a protozoan responsible for the number one, non-viral sexually transmitted disease. Surface proteins (AP65, AP51, AP33 and AP23) mediate adherence to vaginal epithelial cells (VECs). Iron increases growth of trichomonads and synthesis and surface placement of adhesins. We observed by immunofluorescence using monoclonal antibody (mAb) 12G4 the placement of AP65 on surfaces of trichomonads supplemented with hemoglobin or hemin as a source of iron. We, therefore, tested the hypothesis that heme-bound iron is an alternative source of iron important to trichomonal growth and regulation of expression of the adhesin genes. Here we show that the inhibition of parasite growth by the iron chelator 2,2-dipyridal is rescued by hemoglobin or hemin, but not protoporphyrin IX. Importantly, trichomonads grown in iron-limiting medium supplemented with free iron, hemoglobin and hemin had elevated levels of ap65 transcript that were 12.6-, 12.3- and 9.2-fold higher, respectively, than low-iron organisms, as determined by RT-PCR. Similarly, the amounts of AP65 were 8.9-, 11.2-, and 4.8-fold higher in parasites grown in free iron, hemoglobin and hemin, respectively, than organisms in low-iron medium. The heme-iron-regulated AP65 increased adherence of parasites to immortalized VECs. Not surprisingly, parasites pretreated with anti-AP65 serum IgG had decreased adherence compared to organisms incubated with prebleed serum IgG. These data illustrate that heme-bound iron is a source of iron similar to lactoferrin. This work extends our findings about the multiple sources of iron for regulating virulence genes of T. vaginalis.

Predominant outer membrane antigens of Bartonella henselae

A hallmark of Bartonella henselae is persistent bacteremia in cats despite the presence of a vigorous host immune response. To understand better the long-term survival of B. henselae in cats, we examined the feline humoral immune response to B. henselae outer membrane (OM) proteins in naturally and experimentally infected cats. Initially, a panel of sera (n = 42) collected throughout North America from naturally infected cats was used to probe B. henselae total membranes to detect commonly recognized antigens. Twelve antigens reacted with sera from at least 85% of cats, and five were recognized by sera from all cats. To localize these antigens further, OMs were purified on discontinuous sucrose density step gradients. Each membrane fraction (OM, hybrid or inner membrane [IM]) contained less than 1% of the total malate dehydrogenase activity (soluble marker), indicating very little contamination by cytoplasmic proteins. FtsI, an integral IM cell division protein, was used to identify the low-density fraction (rho = 1.13 g/cm3) as putative IM (<5% of the total FtsI localized to the high-density fraction) while lipopolysaccharide (LPS) and Pap31, a homolog of the Bartonella quintana heme-binding protein A (HbpA), defined the high-density fraction (rho = 1.20 g/cm3) as putative OM. Additionally, little evidence of cross-contamination between the IM and OM was evident by two-dimensional gel electrophoresis. When purified OMs were probed with feline sera, antigenic proteins profiles were very similar to those observed with total membranes, indicating that many, but not all, of the immunoreactive proteins detected in the initial immunoblots were OM components. Interestingly, two-dimensional immunoblots indicated that B. henselae LPS and members of the Hbp family of proteins did not appear to stimulate an humoral response in any infected cats. Seven proteins were recognized by at least 70% of sera tested, but only three were recognized by all sera. Nanospray-tandem mass spectrometry was used to identify OM components, including the immunodominant OM proteins. Recognition of the nonimmunogenic nature of the major OM components, such as LPS, and identification of the predominant immunogens should elucidate the mechanisms by which B. henselae establishes persistent bacteremic infections within cats. Additionally, the common antigens may serve as potential feline vaccine candidates to eliminate the pathogen from its animal reservoir.

Mitogenic effect of Bartonella bacilliformis on human vascular endothelial cells and involvement of GroEL

Bartonellae are bacterial pathogens for a wide variety of mammals. In humans, bartonellosis can result in angioproliferative lesions that are potentially life threatening to the patient, including bacillary angiomatosis, bacillary peliosis, and verruga peruana. The results of this study show that Bartonella bacilliformis, the agent of Oroya fever and verruga peruana, produces a proteinaceous mitogen for human vascular endothelial cells (HUVECs) that acts in a dose-dependent fashion in vitro with maximal activity at >or=72 h of exposure and results in a 6- to 20-fold increase in cell numbers relative to controls. The mitogen increases bromodeoxyuridine (BrdU) incorporation into HUVECs by almost twofold relative to controls. The mitogen is sensitive to heat and trypsin but is not affected by the lipopolysaccharide inhibitor polymyxin B. The mitogen does not affect caspase 3 activity in HUVECs undergoing serum starvation-induced apoptosis. The Bartonella mitogen was found in bacterial culture supernatants, the soluble cell lysate fraction, and, to a lesser degree, in insoluble cell fractions of the bacterium. In contrast, soluble cell lysate fractions from closely related B. henselae, although possessing significant mitogenicity for HUVECs, resulted in only about a twofold increase in cell numbers. Biochemical and immunological analyses identified GroEL as a participant in the observed HUVEC mitogenicity. A B. bacilliformis strain containing the intact groES-groEL operon on a multicopy plasmid was generated and used to demonstrate a correlation between HUVEC mitogenicity and GroEL levels in the lysate (r(2) = 0.85). Antiserum to GroEL significantly inhibited mitogenicity of the lysate. Data also show that GroEL is located in the soluble and insoluble fractions (including inner and outer membranes) of the cell and is actively secreted by B. bacilliformis.

Characterization of new members of the group 3 outer membrane protein family of Brucella spp

Impairment of the omp25 gene in Brucella spp. leads to attenuated strains and confers protection to the host. Omp25 and Omp31, whose functions remain unknown, were the first characterized members of group 3 outer membrane proteins (Omps) (25 to 34 kDa). Recently, genomic and proteomic approaches identified five new putative members of this family, some of which are produced in B. melitensis or B. abortus. In the present study, using protein microsequencing, we identified new members of group 3 Omps proteins produced in B. suis. Since several monoclonal antibodies (MAbs) against Omp25 cross-reacted with other members of group 3 Omps, we also performed Western immunoblotting to compare wild-type B. suis with mutants systematically having B. suis omp25-related genes knocked out. We demonstrate the production of three paralogs of Omp31 and/or Omp25 in B. suis, and the existence of a common site of signal peptide cleavage (AXAAD), which is very similar to that present in the five homologous Omps of Bartonella quintana. The seven group 3 Omps were classified in four-subgroups on the basis of percentage amino acid sequence identities: Omp25 alone, the Omp25b-Omp25c-Omp25d cluster, the Omp31/31b subgroup, and the less related Omp22 protein (also called Omp3b). Together with previous data, our results demonstrate that all new members of group 3 Omps are produced in B. suis or in other Brucella species and we propose a nomenclature that integrates all of these proteins to facilitate the understanding of future Brucella interspecies study results.

Hemin binding, functional expression, and complementation analysis of Pap 31 from Bartonella henselae

Growth of Bartonella henselae is strongly heme dependent, and B. henselae is unable to synthesize heme itself. At least five outer membrane-associated proteins from B. henselae bind hemin, including the 31-kDa protein designated Pap31. The gene of this protein was heterologously expressed in Escherichia coli M15(pREP4) and detected with monoclonal antibodies in the outer membrane fraction. Complementation of the hemA-deficient mutant E. coli K-12 EB53 (aroB tsx malT hemA) with pap31 demonstrated that this protein is involved in heme acquisition and may be an important virulence factor in the pathogenesis of B. henselae.

Five-member gene family of Bartonella quintana

Bartonella quintana, the agent of trench fever and an etiologic agent of bacillary angiomatosis, has an extraordinarily high hemin requirement for growth compared to other bacterial pathogens. We previously identified the major hemin receptor of the pathogen as a 30-kDa surface protein, termed HbpA. This report describes four additional homologues that share approximately 48% amino acid sequence identity with hbpA. Three of the genes form a paralagous cluster, termed hbpCAB, whereas the other members, hbpD and hbpE, are unlinked. Secondary structure predictions and other evidence suggest that Hbp family members are beta-barrels located in the outer membrane and contain eight transmembrane domains plus four extracellular loops. Homologs from a variety of gram-negative pathogens were identified, including Bartonella henselae Pap31, Brucella Omp31, Agrobacterium tumefaciens Omp25, and neisserial opacity proteins (Opa). Family members expressed in vitro-synthesized proteins ranging from ca. 26.5 to 35.1 kDa, with the exception of HbpB, an approximately 55.9-kDa protein whose respective gene has been disrupted by a approximately 510 GC-rich element containing variable-number tandem repeats. Transcription analysis by quantitative reverse transcriptase-PCR (RT-PCR) indicates that all family members are expressed under normal culture conditions, with hbpD and hbpB transcripts being the most abundant and the rarest, respectively. Mutagenesis of hbpA by allelic exchange produced a strain that exhibited an enhanced hemin-binding phenotype relative to the parental strain, and analysis by quantitative RT-PCR showed elevated transcript levels for the other hbp family members, suggesting that compensatory expression occurs.

gyrA mutations in ciprofloxacin-resistant Bartonella bacilliformis strains obtained in vitro

We isolated and characterized mutants of Bartonella bacilliformis that are resistant to the fluoroquinolone antibiotic ciprofloxacin, which targets the A subunit of DNA gyrase. Mutants had single point mutations in the gyrA gene that changed either Asp-90 to Gly or Asp-95 to Asn and had 3- or 16-fold higher resistance, respectively, to ciprofloxacin than did wild-type B. bacilliformis. Asp-95 is homologous to Asp-87 of Escherichia coli GyrA and is a common residue mutated in fluoroquinolone-resistant strains of other bacteria. This is the first report of a mutation at an Asp-90 homologue, which corresponds to Asp-82 in E. coli GyrA.

Major outer membrane proteins of Brucella spp.: past, present and future

The major outer membrane proteins (OMPs) of Brucella spp. were initially identified in the early 1980s and characterised as potential immunogenic and protective antigens. They were classified according to their apparent molecular mass as 36-38 kDa OMPs or group 2 porin proteins and 31-34 and 25-27 kDa OMPs which belong to the group 3 proteins. The genes encoding the group 2 porin proteins were identified in the late 1980s and consist of two genes, omp2a and omp2b, which are closely linked in the Brucella genome, and which share a great degree of identity (>85%). In the 1990s, two genes were identified coding for the group 3 proteins and were named omp25 and omp31. The predicted amino acid sequences of omp25 and omp31 share 34% identity. The recent release of the genome sequence of B. melitensis 16 M has revealed the presence of five additional gene products homologous to Omp25 and Omp31. The use of recombinant protein technology and monoclonal antibodies (MAbs) has shown that the major OMPs appear to be of little relevance as antigens in smooth (S) B. abortus or B. melitensis infections i.e. low or no protective activity in the mouse model of infection and low or no immunogenicity during host infection. However, group 3 proteins, in particular Omp31, appear as immunodominant antigen in the course of rough (R) B. ovis infection in rams and as important protective antigen in the B. ovis mouse model of infection. The major OMP genes display diversity and specific markers have been identified for Brucella species, biovars, and strains, including the recent marine mammal Brucella isolates for which new species names have been proposed. Recently, Omp25 has been shown to be involved in virulence of B. melitensis, B. abortus and B. ovis. Mutants lacking Omp25 are indeed attenuated in animal models of infection, and moreover provide levels of protection similar or better than currently used attenuated vaccine strain B. melitensis Rev.1. Therefore, these mutant strains appear interesting vaccine candidates for the future. The other group 3 proteins identified in the genome merit also further investigation related to the development of new vaccines.

The Brucella suis genome reveals fundamental similarities between animal and plant pathogens and symbionts

The 3.31-Mb genome sequence of the intracellular pathogen and potential bioterrorism agent, Brucella suis, was determined. Comparison of B. suis with Brucella melitensis has defined a finite set of differences that could be responsible for the differences in virulence and host preference between these organisms, and indicates that phage have played a significant role in their divergence. Analysis of the B. suis genome reveals transport and metabolic capabilities akin to soil/plant-associated bacteria. Extensive gene synteny between B. suis chromosome 1 and the genome of the plant symbiont Mesorhizobium loti emphasizes the similarity between this animal pathogen and plant pathogens and symbionts. A limited repertoire of genes homologous to known bacterial virulence factors were identified.

Processing of heme and heme-containing proteins by bacteria

An extensive amount of new knowledge on bacterial systems involved in heme processing has been accumulated in the last 10 years. We discuss common themes in heme transport across bacterial outer and inner membranes, emphasizing proteins and mechanisms involved. The processing of heme in the bacterial cytoplasm is extensively covered, and a new hypothesis about the fate of heme in the bacterial cell is presented. Auxiliary genes involved in heme utilization, i.e., TonB, proteases, proteins involved in heme storage and pigmentation, as well as genes involved in regulation of heme assimilation are reviewed.

Establishing a direct role for the Bartonella bacilliformis invasion-associated locus B (IalB) protein in human erythrocyte parasitism

The invasion-associated locus A and B genes (ialAB) of Bartonella bacilliformis were previously shown to confer an erythrocyte-invasive phenotype upon Escherichia coli, indirectly implicating their role in virulence. We report the first direct demonstration of a role for ialB as a virulence factor in B. bacilliformis. The presence of a secretory signal sequence and amino acid sequence similarity to two known outer membrane proteins involved in virulence suggested that IalB was an outer membrane protein. To develop an antiserum for protein localization, the ialB gene was cloned in frame into an expression vector with a six-histidine tag and under control of the lacZ promoter. The IalB fusion protein was purified by nickel affinity chromatography and used to raise polyclonal antibodies. IalB was initially localized to the bacterial membrane fraction. To further localize IalB, B. bacilliformis inner and outer membranes were fractionated by sucrose density gradient centrifugation and identified by appearance, buoyant density (rho), and cytochrome b content. Inner and outer membrane proteins were analyzed by sodium dodecyl sulfate-polyacrylamide gel electrophoresis (SDS-PAGE), and IalB was positively identified by Western blot. Contrary to expectations, IalB was localized to the inner membrane of the pathogen. To directly demonstrate a role for IalB in erythrocyte parasitism, the B. bacilliformis ialB gene was disrupted by insertional mutagenesis. The resulting ialB mutant strain was complemented in trans with a replicative plasmid encoding the full-length ialB gene. PCR and high-stringency DNA hybridization confirmed mutagenesis and transcomplementation events. Abrogation and restoration of ialB expression was verified by SDS-PAGE and immunoblotting. In vitro virulence assays showed that mutagenesis of ialB decreased bacterial association and invasion of human erythrocytes by 47 to 53% relative to controls. Transcomplementation of ialB restored erythrocyte association and invasion rates to levels observed in the parental strain. These data provide direct evidence for IalB's role in erythrocyte parasitism and represent the first demonstration of molecular Koch's postulates for a Bartonella species.