Yersiniabactin from Yersinia pestis: biochemical characterization of the siderophore and its role in iron transport and regulation

A siderophore-dependent iron transport system of the pathogenic yersiniae p lays a role in the pathogenesis of these organisms. The structure of the ye rsiniabactin (Ybt) siderophore produced by Yersinia enterocolitica has been elucidated. This paper reports the purification of Ybt from Yersinia pesti s and demonstrates that it has the same structure as Ybt from Y. enterocoli tica. Purified Ybt had a formation constant for Fe3+ of similar to 4 x 10(- 36). Addition of purified Ybt from Y. pestis enhanced iron uptake by a side rophore-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 transcri ptional level. Y, pestis DNA was used to construct irp2 and psn mutations i n Yersinia pseudotuberculosis. The irp2 mutant strain no longer synthesized Ybt and the psn mutant strain could not use exogenously supplied Ybt. As i n Y. pestis, Ybt was required for maximal expression of Psn. Regulation by Ybt occurred at the transcriptional level. In contrast to Y. pestis, in whi ch a psn mutation does not repress synthesis of Ybt siderophore or expressi on of the iron-regulated HMWP1 and HMWP2 proteins, the same mutation in Y. pseudotuberculosis partially repressed these products.