Characterization of the Yersinia pestis Yfu ABC inorganic iron transport system

In Yersinia pestis, the causative agent of plague, two inorganic iron trans port systems have been partially characterized. The yersiniabactin (Ybt) sy stem is a siderophore-dependent transport system required for full virulenc e, Yfe is an ABC transport sa stem that accumulates both iron and manganese . We have identified and cloned a Y. pestis yfuABC operon, The YfuABC syste m is a member of the cluster of bacterial ABC iron transporters that includ e Sfu of Serratia, Hit of Haemophilus, and Yfu of Yersinia enterocolitica. The Y, pestis KIM6+ system is most homologous to that in Y. enterocolitica, showing identities of 84% for YfuA (periplasmic binding protein), 87% for YfuB (inner membrane permease), and 75% for YfuC (ATP hydrolase). We constr ucted a yfuABC promoter-lacZ fusion to examine regulation of transcription. This promoter contains a potential Fur binding sequence and is iron and Fu r regulated. Significant expression from the YfuABC promoter occurred durin g iron-deficient growth conditions. In vitro transcription and translation of a recombinant plasmid encoding yfuABC indicates that YfuABC proteins are expressed. Escherichia coli 1017 (an enterobactin-deficient mutant) carryi ng this plasmid was able to grow; in an iron-restrictive complex medium. We constructed a deletion encompassing the yfuABC promoter and most of yfuA, This mutation was introduced into strains with mutations in Ybt, Yfe, or bo th systems to examine the role of Yfu in iron acquisition in I: pestis. Gro wth of the yfu mutants in a deferrated, defined medium (PMH2) at 26 and 37 degreesC failed to identify a growth or iron transport defect due to the yf u mutation. Fifty percent lethal dose studies in mice did not demonstrate a role for the Yfu system in mammalian virulence.