RICKETTSIA MODULATION OF HOST PHYSIOLOGY FOR INTRACELLULAR INHABITATION

Abstract

Rickettsia is an obligate intracellular bacterium that parasitizes the eukaryotic cytoplasm. Rickettsia species have evolved highly reduced genomes to exclusively proliferate within eukaryotic host cells, particularly within endothelial cells of the mammalian vasculature. Through evolution in this very specific niche, Rickettsia has developed an inextricable dependence on multiple host functions. However, much of the Rickettsia–mammalian host interactions remain to be deciphered due to technological constraints. Understanding which host pathways are exploited during infection is therefore critical for identifying mechanisms of pathogenesis and potential therapeutic targets. In this dissertation, we investigated the role of host calcium during rickettsial infection and determined that disruption of the host calcium gradient significantly reduced Rickettsia load in endothelial cells and diminished the ability of the bacteria to polymerize host actin for motility, thereby likely impacting dissemination. To further characterize the host pathways Rickettsia exploits for its benefit, we employed CRISPR/Cas9-based knockout screening with a library of sgRNAs targeting human metabolism and lipid droplets, as Rickettsia relies on at least 51 host metabolites for its core functions. The screen revealed 54 potential host factors utilized by Rickettsia, many of which clustered around mitochondrial activity, fatty acid metabolism, and calcium-related signaling pathways. Together, these findings suggest that Rickettsia exploits multiple host metabolic and signaling networks to establish and maintain its intracellular niche. The combined evidence from calcium inhibition experiments and CRISPR-based screening highlights the importance of host calcium signaling and metabolic regulation during infection. These results provide insight into host–Rickettsia interactions and support the potential for host-targeted therapeutic strategies that complement traditional antibiotic treatment.