Rickettsia parkeri forms extensive, stable contacts with the rough endoplasmic reticulum

Abstract

Upon invasion into the host cell, a subset of bacterial pathogens resides exclusively in the cytosol. While previous research revealed how they reshape the plasma membrane during invasion, subvert the immune response, and hijack cytoskeletal dynamics to promote their motility, it was unclear if these pathogens also interacted with the organelles in this crowded intracellular space. Here, we examined if the obligate intracellular pathogen Rickettsia parkeri interacts with the endoplasmic reticulum (ER), a large and dynamic organelle spread throughout the cell. Using live-cell microscopy and transmission and focused-ion-beam scanning electron microscopy, we show that R. parkeri forms extensive contacts with the rough ER that are ∼55 nm apart and cover more than half the bacterial surface. Depletion of the ER-specific tethers VAPA and VAPB reduced rickettsia-ER contacts, and VAPA and VAPB were localized around intracellular rickettsiae. Overall, our findings illuminate an interkingdom ER contact uniquely mediated by rickettsiae that mimics some characteristics of traditional host membrane contact sites.