Yersinia pestis, the causative agent of bubonic, septicemic and
pneumonic plague, encodes a multitude of Fe transport systems. Some of these are defective due to frameshift or
IS element insertions, while others are functional in vitro but have no established role in causing
infections. Indeed only 3 Fe transporters (Ybt, Yfe and Feo) have been shown to be important in at least one form of
plague. The
yersiniabactin (Ybt) system is essential in the early dermal/lymphatic stages of
bubonic plague, irrelevant in the septicemic stage, and critical in
pneumonic plague. Two Mn transporters have been characterized (Yfe and MntH). These two systems play a role in
bubonic plague but the double yfe mntH mutant is fully virulent in a mouse model of
pneumonic plague. The same in vivo phenotype occurs with a mutant lacking two (Yfe and Feo) of four ferrous transporters. A role for the Ybt
siderophore in Zn acquisition has been revealed. Ybt-dependent Zn acquisition uses a transport system completely independent of the Fe-Ybt uptake system. Together Ybt components and ZnuABC play a critical role in Zn acquisition in vivo. Single mutants in either system retain high virulence in a mouse model of
septicemic plague while the double mutant is completely avirulent.