Summary auto-generated
This study characterizes yersiniabactin (Ybt), a siderophore produced by Yersinia pestis that plays a critical role in pathogenesis by facilitating iron acquisition. Researchers purified Ybt from Y. pestis and confirmed its structure is identical to that previously described in Y. enterocolitica. The purified Ybt demonstrated high affinity for ferric iron (formation constant ~4 × 10^36). In iron-starved cells, purified Ybt enhanced iron uptake and induced expression of Psn, the outer-membrane receptor for Ybt, with regulation occurring at the transcriptional level. The researchers also generated irp2 and psn mutations in Y. pseudotuberculosis using Y. pestis DNA, showing the Ybt systems are functionally interchangeable across these pathogenic Yersinia species. Notably, a psn mutation in Y. pseudotuberculosis partially repressed Ybt synthesis and expression of iron-regulated proteins, whereas the same mutation in Y. pestis did not, revealing species-specific differences in how the Ybt system regulates gene expression.
Key findings
- Yersiniabactin from Y. pestis is chemically identical to that from Y. enterocolitica and has a high ferric iron affinity constant (~4 × 10^36)
- Purified Ybt enhances iron uptake by siderophore-deficient Y. pestis cells and stimulates transcription of the psn gene encoding its outer-membrane receptor
- Ybt-dependent regulation of Psn expression occurs at the transcriptional level in both Y. pestis and Y. pseudotuberculosis
- The Ybt systems in Y. pestis and Y. pseudotuberculosis are functionally interchangeable, but differences exist in how psn mutations affect downstream gene regulation between the two species
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Abstract
A siderophore-dependent iron transport system of the pathogenic yersiniae plays a role in the pathogenesis of these organisms. The structure of the yersiniabactin (Ybt) siderophore produced by Yersinia enterocolitica has been elucidated. This paper reports the purification of Ybt from Yersinia pestis and demonstrates that it has the same structure as Ybt from Y. enterocolitica. Purified Ybt had a formation constant for Fe3+ of approx 4 x 10 to the power of minus 36. Addition of purified Ybt from Y. pestis enhanced iron uptake by a siderophore-negative (irp2) strain of Y. pestis. Maximal expression of the Ybt outer-membrane receptor, Psn, in this strain was dependent upon exogenously supplied Ybt. Regulation of Psn expression by Ybt occurred at the transcriptional level. Y. pestis DNA was used to construct irp2 and psn mutations in Yersinia pseudotuberculosis. The irp2 mutant strain no longer synthesized Ybt and the psn mutant strain could not use exogenously supplied Ybt. As in Y. pestis, Ybt was required for maximal expression of Psn. Regulation by Ybt occurred at the transcriptional level. In contrast to Y. pestis, in which a psn mutation does not repress synthesis of Ybt siderophore or expression of the iron-regulated HMWP1 and HMWP2 proteins, the same mutation in Y. pseudotuberculosis partially repressed these products.