Yersinia pestis Resists Predation by Acanthamoeba castellanii and Exhibits Prolonged Intracellular Survival

Plague is a flea-borne rodent-associated zoonotic disease caused byYersinia pestis . The disease is characterized by epizootics with high rodent mortalities, punctuated by interepizootic periods when the bacterium persists in an unknown reservoir. This study investigates the interaction betweenY. pestis and the ubiquitous soil free-living amoeba (FLA)Acanthamoeba castellanii to assess if the bacterium can survive within soil amoebae and whether intracellular mechanisms are conserved between infection of mammalian macrophages and soil amoebae. The results demonstrate that during coculture with amoebae, representativeY. pestis strains of epidemic biovars Medievalis, Orientalis, and Antiqua are phagocytized and able to survive within amoebae for at least 5 days. KeyY. pestis determinants of the intracellular interaction ofY. pestis and phagocytic macrophages, PhoP and the type three secretion system (T3SS), were then tested for their roles in theY. pestis -amoeba interaction. Consistent with a requirement for the PhoP transcriptional activator in the intracellular survival ofY. pestis in macrophages, a PhoP mutant is unable to survive when cocultured with amoebae. Additionally, induction of the T3SS blocks phagocytic uptake ofY. pestis by amoebae, similar to that which occurs during macrophage infection. Electron microscopy revealed that inA. castellanii ,Y. pestis resides intact within spacious vacuoles which were characterized using lysosomal trackers as being separated from the lysosomal compartment. This evidence for prolonged survival and subversion of intracellular digestion ofY. pestis within FLA suggests that protozoa may serve as a protective soil reservoir forY. pestis .IMPORTANCE Yersinia pestis is a reemerging flea-borne zoonotic disease. Sylvatic plague cycles are characterized by an epizootic period during which the disease spreads rapidly, causing high rodent mortality, and an interepizootic period when the bacterium quiescently persists in an unknown reservoir. An understanding of the ecology ofY. pestis in the context of its persistence in the environment and its reactivation to initiate a new epizootic cycle is key to implementing novel surveillance strategies to more effectively predict and prevent new disease outbreaks. Here, we demonstrate prolonged survival and subversion of intracellular digestion ofY. pestis within a soil free-living amoeba. This suggests the potential role for protozoa as a protective soil reservoir forY. pestis , which may help explain the recrudescence of plague epizootics.