Bartonella Adhesin A Mediates a Proangiogenic Host Cell Response

Bartonella henselae causes vasculoproliferative disorders in humans. We identified a nonfimbrial adhesin of B. henselae designated as Bartonella adhesin A (BadA). BadA is a 340-kD outer membrane protein encoded by the 9.3-kb badA gene. It has a modular structure and contains domains homologous to the Yersinia enterocolitica nonfimbrial adhesin (Yersinia adhesin A). Expression of BadA was restored in a BadA-deficient transposon mutant by complementation in trans. BadA mediates the binding of B. henselae to extracellular matrix proteins and to endothelial cells, possibly via β1 integrins, but prevents phagocytosis. Expression of BadA is crucial for activation of hypoxia-inducible factor 1 in host cells by B. henselae and secretion of proangiogenic cytokines (e.g., vascular endothelial growth factor). BadA is immunodominant in B. henselae–infected patients and rodents, indicating that it is expressed during Bartonella infections. Our results suggest that BadA, the largest characterized bacterial protein thus far, is a major pathogenicity factor of B. henselae with a potential role in the induction of vasculoproliferative disorders

Run-Off Replication of Host-Adaptability Genes Is Associated with Gene Transfer Agents in the Genome of Mouse-Infecting Bartonella grahamii

The genus Bartonella comprises facultative intracellular bacteria adapted to mammals, including previously recognized and emerging human pathogens. We report the 2,341,328 bp genome sequence of Bartonella grahamii, one of the most prevalent Bartonella species in wild rodents. Comparative genomics revealed that rodent-associated Bartonella species have higher copy numbers of genes for putative host-adaptability factors than the related human-specific pathogens. Many of these gene clusters are located in a highly dynamic region of 461 kb. Using hybridization to a microarray designed for the B. grahamii genome, we observed a massive, putatively phage-derived run-off replication of this region. We also identified a novel gene transfer agent, which packages the bacterial genome, with an over-representation of the amplified DNA, in 14 kb pieces. This is the first observation associating the products of run-off replication with a gene transfer agent. Because of the high concentration of gene clusters for host-adaptation proteins in the amplified region, and since the genes encoding the gene transfer agent and the phage origin are well conserved in Bartonella, we hypothesize that these systems are driven by selection. We propose that the coupling of run-off replication with gene transfer agents promotes diversification and rapid spread of host-adaptability factors, facilitating host shifts in Bartonella

Studies of Genome Diversity in Bartonella Populations : A journey through cats, mice, men and lice

Bacteria of the genus Bartonella inhabit the red blood cells of many mammals, including humans, and are transmitted by blood-sucking arthropod vectors. Different species of Bartonella are associated with different mammalian host species, to which they have adapted and normally do not cause any symptoms. Incidental infection of other hosts is however often followed by various disease symptoms, and several Bartonella species are considered as emerging human pathogens. In this work, I have studied the genomic diversity within and between different Bartonella species, with focus on the feline-associated human pathogen B. henselae and its close relatives, the similarly feline-associated B. koehlerae and the trench-fever agent B. quintana which is restricted to humans. In B. henselae, the overall variability in sequence and genome content was modest and well correlated, suggesting low levels of intra-species recombination in the core genome. The variably present genes were located in the prophage and the genomic islands, which are also absent from B. quintana and B. koehlerae, indicating multiple independent excision events. In contrast, diversity of genome structures was immense and probably associated with rearrangements between the repeated genomic islands located around the terminus of replication, possibly to avoid the host’s immune system. In both B. henselae and the mouse-associated species B. grahamii a large portion of the chromosome was manifold amplified in long-time cultures and packaged into phage particles, allowing for different recombination rates for different chromosomal regions. In B. quintana, diversity was studied by sequencing non-coding spacers. The low variability might be due to the recent emergence of this species. Surprisingly, also this species displayed high variability in genome structures, despite its lack of repeated sequences. The results indicate that genome rearrangements and gain or loss of mobile elements are major mechanisms of evolution in Bartonella

Studies of Genome Diversity in Bartonella Populations : A journey through cats, mice, men and lice

Bacteria of the genus Bartonella inhabit the red blood cells of many mammals, including humans, and are transmitted by blood-sucking arthropod vectors. Different species of Bartonella are associated with different mammalian host species, to which they have adapted and normally do not cause any symptoms. Incidental infection of other hosts is however often followed by various disease symptoms, and several Bartonella species are considered as emerging human pathogens. In this work, I have studied the genomic diversity within and between different Bartonella species, with focus on the feline-associated human pathogen B. henselae and its close relatives, the similarly feline-associated B. koehlerae and the trench-fever agent B. quintana which is restricted to humans. In B. henselae, the overall variability in sequence and genome content was modest and well correlated, suggesting low levels of intra-species recombination in the core genome. The variably present genes were located in the prophage and the genomic islands, which are also absent from B. quintana and B. koehlerae, indicating multiple independent excision events. In contrast, diversity of genome structures was immense and probably associated with rearrangements between the repeated genomic islands located around the terminus of replication, possibly to avoid the host’s immune system. In both B. henselae and the mouse-associated species B. grahamii a large portion of the chromosome was manifold amplified in long-time cultures and packaged into phage particles, allowing for different recombination rates for different chromosomal regions. In B. quintana, diversity was studied by sequencing non-coding spacers. The low variability might be due to the recent emergence of this species. Surprisingly, also this species displayed high variability in genome structures, despite its lack of repeated sequences. The results indicate that genome rearrangements and gain or loss of mobile elements are major mechanisms of evolution in Bartonella

Studies of Genome Diversity in Bartonella Populations : A journey through cats, mice, men and lice

Bacteria of the genus Bartonella inhabit the red blood cells of many mammals, including humans, and are transmitted by blood-sucking arthropod vectors. Different species of Bartonella are associated with different mammalian host species, to which they have adapted and normally do not cause any symptoms. Incidental infection of other hosts is however often followed by various disease symptoms, and several Bartonella species are considered as emerging human pathogens. In this work, I have studied the genomic diversity within and between different Bartonella species, with focus on the feline-associated human pathogen B. henselae and its close relatives, the similarly feline-associated B. koehlerae and the trench-fever agent B. quintana which is restricted to humans. In B. henselae, the overall variability in sequence and genome content was modest and well correlated, suggesting low levels of intra-species recombination in the core genome. The variably present genes were located in the prophage and the genomic islands, which are also absent from B. quintana and B. koehlerae, indicating multiple independent excision events. In contrast, diversity of genome structures was immense and probably associated with rearrangements between the repeated genomic islands located around the terminus of replication, possibly to avoid the host’s immune system. In both B. henselae and the mouse-associated species B. grahamii a large portion of the chromosome was manifold amplified in long-time cultures and packaged into phage particles, allowing for different recombination rates for different chromosomal regions. In B. quintana, diversity was studied by sequencing non-coding spacers. The low variability might be due to the recent emergence of this species. Surprisingly, also this species displayed high variability in genome structures, despite its lack of repeated sequences. The results indicate that genome rearrangements and gain or loss of mobile elements are major mechanisms of evolution in Bartonella

Genome Rearrangements, Deletions, and Amplifications in the Natural Population of Bartonella henselae

Cats are the natural host for Bartonella henselae, an opportunistic human pathogen and the agent of cat scratch disease. Here, we have analyzed the natural variation in gene content and genome structure of 38 Bartonella henselae strains isolated from cats and humans by comparative genome hybridizations to microarrays and probe hybridizations to pulsed-field gel electrophoresis (PFGE) blots. The variation in gene content was modest and confined to the prophage and the genomic islands, whereas the PFGE analyses indicated extensive rearrangements across the terminus of replication with breakpoints in areas of the genomic islands. We observed no difference in gene content or structure between feline and human strains. Rather, the results suggest multiple sources of human infection from feline B. henselae strains of diverse genotypes. Additionally, the microarray hybridizations revealed DNA amplification in some strains in the so-called chromosome II-like region. The amplified segments were centered at a position corresponding to a putative phage replication initiation site and increased in size with the duration of cultivation. We hypothesize that the variable gene pool in the B. henselae population plays an important role in the establishment of long-term persistent infection in the natural host by promoting antigenic variation and escape from the host immune response

Characterization of the Genome Composition of Bartonella koehlerae by Microarray Comparative Genomic Hybridization Profiling

Bartonella henselae is present in a wide range of wild and domestic feline hosts and causes cat-scratch disease and bacillary angiomatosis in humans. We have estimated here the gene content of Bartonella koehlerae, a novel species isolated from cats that was recently identified as an agent of human endocarditis. The investigation was accomplished by comparative genomic hybridization (CGH) to a microarray constructed from the sequenced 1.93-Mb genome of B. henselae. Control hybridizations of labeled DNA from the human pathogen Bartonella quintana with a reduced genome of 1.58 Mb were performed to evaluate the accuracy of the array for genes with known levels of sequence divergence. Genome size estimates of B. koehlerae by pulsed-field gel electrophoresis matched that calculated by the CGH, indicating a genome of 1.7 to 1.8 Mb with few unique genes. As in B. quintana, sequences in the prophage and the genomic islands were reported absent in B. koehlerae. In addition, sequence variability was recorded in the chromosome II-like region, where B. koehlerae showed an intermediate retention pattern of both coding and noncoding sequences. Although most of the genes missing in B. koehlerae are also absent from B. quintana, its phylogenetic placement near B. henselae suggests independent deletion events, indicating that host specificity is not solely attributed to genes in the genomic islands. Rather, the results underscore the instability of the genomic islands even within bacterial populations adapted to the same host-vector system, as in the case of B. henselae and B. koehlerae

The BatR/BatS Two-Component Regulatory System Controls the Adaptive Response of Bartonella henselae during Human Endothelial Cell Infection ▿ † ‡

Here, we report the first comprehensive study of Bartonella henselae gene expression during infection of human endothelial cells. Expression of the main cluster of upregulated genes, comprising the VirB type IV secretion system and its secreted protein substrates, is shown to be under the positive control of the transcriptional regulator BatR. We demonstrate binding of BatR to the promoters of the virB operon and a substrate-encoding gene and provide biochemical evidence that BatR and BatS constitute a functional two-component regulatory system. Moreover, in contrast to the acid-inducible (pH 5.5) homologs ChvG/ChvI of Agrobacterium tumefaciens, BatR/BatS are optimally activated at the physiological pH of blood (pH 7.4). By conservation analysis of the BatR regulon, we show that BatR/BatS are uniquely adapted to upregulate a genus-specific virulence regulon during hemotropic infection in mammals. Thus, we propose that BatR/BatS two-component system homologs represent vertically inherited pH sensors that control the expression of horizontally transmitted gene sets critical for the diverse host-associated life styles of the alphaproteobacteria