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 has been elucidated. This paper reports the purification of Ybt from and demonstrates that it has the same structure as Ybt from Purified Ybt had a formation constant for Fe of ~ 4×10. Addition of purified Ybt from enhanced iron uptake by a siderophore-negative ()strain of 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. DNA was used to construct and mutations in The mutant strain no longer synthesized Ybt and the mutant strain could not use exogenously supplied Ybt. As in Ybt was required for maximal expression of Psn. Regulation by Ybt occurred at the transcriptional level. In contrast to in which a mutation does not repress synthesis of Ybt siderophore or expression of the iron-regulated HMWP1 and HMWP2 proteins, the same mutation in partially repressed these products.


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