HRURF and bubonic plague: It has previously been shown that the absence of the Yersiniabactin (Ybt) siderophore-dependent system or the Yfe ATP-binding cassette (ABC) iron transporter (but not that of the heme transporter Hmu, the hemin storage system Hms or the ABC iron transporters Yiu and Yfu) attenuates the virulence of Y. pestis in a mouse model of bubonic plague [26], [27], [28], [29], [30].