EmrA 1 membrane fusion protein of F rancisella tularensis LVS is required for resistance to oxidative stress, intramacrophage survival and virulence in mice

Summary F rancisella tularensis is a category A biodefence agent that causes a fatal human disease known as tularaemia. The pathogenicity of F . tularensis depends on its ability to persist inside host immune cells primarily by resisting an attack from host‐generated reactive oxygen and nitrogen species ( ROS / RNS ). Based on the ability of F . tularensis to resist high ROS / RNS levels, we have hypothesized that additional unknown factors act in conjunction with known antioxidant defences to render ROS resistance. By screening a transposon insertion library of F . tularensis   LVS in the presence of hydrogen peroxide, we have identified an oxidant‐sensitive mutant in putative EmrA 1 ( FTL _0687) secretion protein. The results demonstrate that the emrA1 mutant is highly sensitive to oxidants and several antimicrobial agents, and exhibits diminished intramacrophage growth that can be restored to wild‐type F . tularensis   LVS levels by either transcomplementation, inhibition of ROS generation or infection in NADPH oxidase deficient ( gp91Phox −/− ) macrophages. The emrA1 mutant is attenuated for virulence, which is restored by infection in gp91Phox −/− mice. Further, EmrA 1 contributes to oxidative stress resistance by affecting secretion of F rancisella antioxidant enzymes SodB and KatG . This study exposes unique links between transporter activity and the antioxidant defence mechanisms of F . tularensis .