Yersinia pestis is a facultative intracellular pathogen that causes the disease known as plague. During infection of macrophages Y. pestis actively evades the normal phagosomal maturation pathway to establish a replicative niche within the cell. However, the mechanisms used by Y. pestis to subvert killing by the macrophage are unknown. Host Rab GTPases are central mediators of vesicular trafficking and are commonly targeted by bacterial pathogens to alter phagosome maturation and killing by macrophages. Here we demonstrate for the first time that host Rab1b is required for Y. pestis to effectively evade killing by macrophages. We also show that Rab1b is specifically recruited to the Yersinia containing vacuole (YCV) and that Y. pestis is unable to subvert YCV acidification when Rab1b expression is knocked down in macrophages. Furthermore, Rab1b knockdown also altered the frequency of association between the YCV with the lysosomal marker Lamp1, suggesting that Rab1b recruitment to the YCV directly inhibits phagosome maturation. Finally, we show that Rab1b knockdown also impacts the pH of the Legionella pneumophila containing vacuole, another pathogen that recruits Rab1b to its vacuole. Together these data identify a novel role for Rab1b in the subversion of phagosome maturation by intracellular pathogens and suggest that recruitment of Rab1b to the pathogen containing vacuole may be a conserved mechanism to control vacuole pH.
Yersinia pestis is the bacterial agent that causes the human disease known as plague. While often considered a historic disease, Y. pestis is endemic in rodent populations on several continents and the World Health Organization considers plague to be a reemerging disease. Much of the success of this pathogen comes from its ability to evade clearance by the innate immune system of its host. One weapon in the Y. pestis arsenal is its ability to resist killing when engulfed by macrophages. Upon invasion of macrophages, Y. pestis actively manipulates the cell to generate a protective vacuolar compartment, called the Yersinia containing vacuole (YCV) that allows the bacterium to evade the normal pathogen killing mechanisms of the macrophage. Here we demonstrate that the host protein Rab1b is recruited to the YCV and is required for Y. pestis to inhibit both the acidification and normal maturation of the phagosome to establish a protective niche within the cell. Rab1b is the first protein, either from the host or Y. pestis, shown to contribute to the biogenesis of the YCV. Furthermore, our data suggest a previously unknown impact of Rab1b recruitment in the phagosome maturation pathway.