Characterization of the Yersinia pestis Yfu ABC inorganic iron transport system

In Yersinia pestis, the causative agent of plague, two inorganic iron transport systems have been partially characterized. The yersiniabactin (Ybt) system is a siderophore-dependent transport system required for full virulence. Yfe is an ABC transport system that accumulates both iron and manganese. We have identified and cloned a Y. pestis yfuABC operon. The YfuABC system is a member of the cluster of bacterial ABC iron transporters that include 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 constructed a yfuABC promoter-lacZ fusion to examine regulation of transcription. This promoter contains a potential Fur binding sequence and is iron and Fur regulated. Significant expression from the yfuABC promoter occurred during 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) carrying 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 both systems to examine the role of Yfu in iron acquisition in Y. pestis. Growth of the yfu mutants in a deferrated, defined medium (PMH2) at 26 and 37 degrees C failed to identify a growth or iron transport defect due to the yfu mutation. Fifty percent lethal dose studies in mice did not demonstrate a role for the Yfu system in mammalian virulence.