Fig. 7.

Fe, Zn, and Mn transporters with proven roles in mouse models of bubonic (A), septicemic (B), and pneumonic (C) plague. The Yfe system is shown as “transporting” both Fe³⁺ and Fe²⁺ since there is evidence it functions under aerobic conditions where Fe³⁺ would predominate and under microaerobic or reducing conditions where Fe²⁺ would be prevalent. However, the oxidation state transported is undetermined. Zn binding by Ybt (B) has not been shown; thus Ybt could play an indirect role in Zn uptake.