A patatin-like phospholipase mediates Rickettsia parkeri escape from host membranes

Abstract

Spotted fever group Rickettsia species are arthropod-borne obligate intracellular bacteria that can cause mild to severe human disease. These bacteria invade host cells, replicate in the cell cytosol, and then spread from cell to cell. To access the host cytosol and avoid detection by immune surveillance mechanisms, these pathogens must have evolved efficient ways to escape membrane-bound vacuoles. Although Rickettsia are predicted to express factors that disrupt host membranes, little is known about how and when these proteins function during infection. Here, we investigated the role of a Rickettsia patatin-like phospholipase A2 enzyme (Pat1) during host cell infection by characterizing a Rickettsia parkeri mutant with a transposon insertion in the pat1 gene. We show that Pat1 is important for infection in a mouse model and in host cells. We further show that Pat1 is critical for efficiently escaping from the single and double membrane-bound vacuoles into the host cytosol, and for avoiding host galectins that mark damaged membranes. In the host cytosol, Pat1 is important for avoiding host polyubiquitin, preventing recruitment of autophagy receptor p62, and promoting actin-based motility and cell-cell spread. Our results show that Pat1 plays critical roles in escaping host membranes and promoting cell-cell spread during R. parkeri infection and suggest diverse roles for patatin-like phospholipases in facilitating microbial infection. ImportanceSpotted fever group Rickettsia are bacteria that reside in ticks and can be transmitted to mammalian hosts, including humans. Severe disease is characterized by high fever, headache, and rash, and results in occasional mortality despite available treatment. Rickettsia interact with host cell membranes while invading cells, escaping into the cytosol, and evading cellular defenses. Bacterial phospholipase enzymes have been proposed as critical factors for targeting host cell membranes, however the specific roles of rickettsial phospholipases are not well defined. We investigated the contribution of one conserved patatin-like phospholipase, Pat1, in Rickettsia parkeri. We observed that Pat1 is important for virulence in an animal model. Moreover, Pat1 plays critical roles in host cells by facilitating access to the cell cytosol, inhibiting detection by host defense pathways, and promoting cell-cell spread. Our study indicates that Pat1 performs several critical functions, suggesting a broad role for phospholipases throughout the Rickettsia lifecycle.