DRP1/DMNL-1-mediated mitochondrial fission augments Rickettsia parkeri replication in macrophages

Pathogenic Spotted Fever Group (SFG) Rickettsia species, including Rickettsia parkeri replicate in endothelial cells, monocytes, and macrophages in vitro and during infections in murine models of disease. We demonstrated that R. parkeri survives and proliferates within phagocytes and avoids intracellular killing within lysosomal compartments. We found that infection of human macrophage-like cells with a related SFG Rickettsia, R. conorii, resulted in a significant increase in mitochondria-associated proteins, suggesting that mitochondrial functions are involved in Rickettsia pathogenesis. Several intracellular bacterial pathogens manipulate host cell mitochondrial networks and stimulate mitochondrial fission mediated by a GTP-binding regulatory protein, DRP1/DMNL1, to promote intracellular replication. Here, we investigated the contribution of DRP1 in the growth of R. parkeri in macrophages. Murine immortalized bone marrow derived macrophages (iBMDMs) and primary human monocyte derived macrophages were infected with R. parkeri and mitochondrial dynamics (fission and network) were assessed by immunofluorescence microscopy. R. parkeri proliferated in macrophages, which coincided with a significant increase in mitochondria content and fission compared to uninfected cells. R. parkeri infection led to increases in host cell ATP production primarily due to mitochondrial respiration and bacteria were often found co-localized with mitochondrial fragments. Importantly, R. parkeri growth was significantly impacted in DRP1 deficient macrophages. These results suggest that the modulation of mitochondria content and dynamics are essential for replication and survival of pathogenic SFG Rickettsia species in macrophages and suggest that the metabolic requirements for obligate intracellular pathogens may differ from other pathogenic Gram-negative intracellular bacteria.