The Yersiniabactin Transport System Is Critical for the Pathogenesis of Bubonic and Pneumonic Plague

Abstract

Iron acquisition from the host is an important step in the pathogenic process. While Yersinia pestis has multiple iron transporters, the yersiniabactin (Ybt) siderophore-dependent system plays a major role in iron acquisition in vitro and in vivo. In this study, we determined that the Ybt system is required for the use of iron bound by transferrin and lactoferrin and examined the importance of the Ybt system for virulence in mouse models of bubonic and pneumonic plague. Y. pestis mutants unable to either transport Ybt or synthesize the siderophore were both essentially avirulent via subcutaneous injection (bubonic plague model). Surprisingly, via intranasal instillation (pneumonic plague model), we saw a difference in the virulence of Ybt biosynthetic and transport mutants. Ybt biosynthetic mutants displayed an ϳ24-fold-higher 50% lethal dose (LD 50 ) than transport mutants. In contrast, under iron-restricted conditions in vitro, a Ybt transport mutant had a more severe growth defect than the Ybt biosynthetic mutant. Finally, a ⌬pgm mutant had a greater loss of virulence than the Ybt biosynthetic mutant, indicating that the 102-kb pgm locus encodes a virulence factor, in addition to Ybt, that plays a role in the pathogenesis of pneumonic plague.Nearly all organisms require trace amounts of iron. Pathogens must overcome host iron-and heme-binding proteins to cause an infection and disease. The importance of iron acquisition mechanisms has been demonstrated in a number of bacterial pathogens (14,15,27,32,85). Yersinia pestis, the causative agent of plague, has a number of proven and putative iron and heme transport systems. Of these systems, the yersiniabactin (Ybt) siderophore-dependent iron transport system plays a major role in the virulence of bubonic plague in mice (7,8,38,76,79).All identified genes required for the regulation, synthesis, and transport of Ybt, except for ybtD, are carried within a high-pathogenicity island (HPI) that has been spread among enteric pathogens but is essentially identical in the pathogenic yersiniae (13,59,79). In Y. pestis, the ϳ36-kb HPI is located within the 102-kb pgm locus; the entire pgm locus undergoes spontaneous deletion in vitro at a frequency of about 10 Ϫ5 (25, 39, 62). The Ybt system produces a siderophore composed of one salicylate, one thiazoline, and two thiazolidine rings via a nonribosomal peptide/polyketide synthesis mechanism involving high-molecular-weight protein 1 (HMWP1), HMWP2, YbtD, YbtT, YbtE, YbtU, and YbtS (76, 79, 94). The formation constant of this siderophore with ferric iron is 4 ϫ 10 36 , and the crystal structure of the ferric complex has been solved (68, 78).Iron from the Ybt-Fe complex is transported into the cell via the TonB-dependent outer membrane (OM) receptor Psn (which is also required for sensitivity to the bacteriocin pesticin) and an ABC transporter consisting of two inner membrane (IM), fused-function permease/ATP-binding proteins, YbtP and YbtQ. A mutation in any of these three genes prevents Ybt-dependent uptake of iron but does ...

Resistance of Mice of the 129 Background to Yersinia pestis Maps to Multiple Loci on Chromosome 1

“…The Slc11a1 gene is located at one end of the resistance locus and encodes a divalent metal iron transporter that is recruited to macrophage phagosomes, where it serves to promote killing of intracellular pathogens. Since one of the major ways in which the pgm Ϫ strains of Y. pestis are attenuated is through their loss of the Ybt locus which impacts their ability to acquire iron (24,25), a difference in a gene with the potential to regulate iron availability in the body, such as Slc11a1, could explain the differences in susceptibility to pgm Ϫ plague. Previously, Slc11a1 has been demonstrated to play a role in resistance to pathogens such as Mycobacterium bovis, Leishmania donovani, and Salmonella enterica serovar Typhimurium (20,(26)(27)(28)(29).…”

Yersinia pestisbiovarMicrotusstrain 201, an avirulent strain to humans, provides protection against bubonic plague in rhesus macaques

“…It is suggested that vaccines effectively prime both humoral and cellular immunity could provide superior defense against pneumonic plague. 7,8,41,42 The current study showed that immunization with the Y. pestis strain 201 could induce both cytokine-mediated Th1-type cellular immune response and Th2-type humoral immune response. Therefore, we speculate that the Y. pestis strain 201 might have the potential to provide effective protection against pneumonic plague.…”

Znu Is the Predominant Zinc Importer in Yersinia pestis during In Vitro Growth but Is Not Essential for Virulence

“…instillation of mice have been previously described (31). Briefly, for s.c. infections, cultures of Y. pestis cells were grown in heart infusion broth (HIB; Becton Dickinson) at 26°C and resuspended in mouse isotonic phosphate-buffered saline (PBS).…”

“…Blots were processed using a modified procedure of Towbin et al (98) as previously described (31,38,43). Immunoreactive proteins were detected using horseradish peroxidase-conjugated protein A and the ECL Western blot detection reagent (GE Healthcare) and exposure on Kodak Biomax Light film.…”

“…Iron transport systems in Y. pestis have been extensively characterized and the Ybt siderophore-dependent system has been shown to be essential for the pathogenesis of bubonic plague and to be important for the pathogenesis of pneumonic plague (31,37). A second system, Yfe, transports both Fe and Mn; Fe uptake by this system is inhibited by both Mn and Zn.…”