Environmental Signals Generate a Differential and Coordinated Expression of the Heme Receptor Gene Family of Bartonella quintana

Abstract

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°C relative to 37°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 O 2 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.

The BatR/BatS Two-Component Regulatory System Controls the Adaptive Response ofBartonella henselaeduring Human Endothelial Cell Infection

“…1, cluster 4). Different expression patterns for the members of this gene family have been reported in B. quintana (5), where hbpA and hbpD were expressed at low heme concentrations while hbpB and hbpC were expressed at high heme concentrations. We described a second cluster of genes displaying rapid upregulation after contact with HEC, followed by slower downregulation during the time course of infection (Fig.…”

Intruders below the Radar: Molecular Pathogenesis of Bartonella spp

“…Extracellular deposition of heme is also seen in Yersinia pestis, where efficient transmission by bloodsucking arthropods depends on outer membrane storage of this compound (183,337). Most obviously, such a surface coat would provide a nutritive reservoir for Bartonella, especially as it has to compete with its arthropod vector for heme in the midgut (25). Furthermore, the intrinsic peroxidase activity of heme would make the coat a potent antioxidant barrier (25) and hence constitute a suitable protectant against reactive oxygen species (ROS) as key mediators of antimicrobial defense both in the arthropod gut (169,305) and as part of mammal immune defenses (42).…”

“…The hemin binding proteins (Hbps) of Bartonella are a group of porin-like outer membrane proteins that bind hemin on the bacterial surface, but lack any discernible homology to known bacterial heme receptors (25). Remarkably, Pap31, the first known member of this family in Bartonella, was discovered not as a virulence factor but as being a major protein component of the BLPs that Bartonella releases into culture media, although it is known today that its prevalence in the phagelike particles is rather coincidental (see above).…”

Bartonella and Brucella--Weapons and Strategies for Stealth Attack

“…Hemin-binding proteins (Hbps in Bartonella and OMP25/31 in Brucella) constitute a family of porin-like outer membrane proteins that bind hemin (Battisti et al 2006;Dabo et al 2006;Delpino et al 2006;Caro-Hernandez et al 2007). Hemin is essential for Bartonella growth (Sander et al 2000), rendering these bacteria the most hemin-dependent microbes.…”

“…Examples are the heme HutABC/ HmuV (Parrow et al 2009) and iron FatBCD and Sit/YfeABCd (Battisti et al 2006) uptake systems as well as the ugp-encoded glycerol 3-phosphate importers (Saenz et al 2007) in Bartonella. Such an importer is in Brucella surface protein 41 (SP41), which probably interacts with sialylated host receptors (Castaneda-Roldan et al 2006).…”