Alpha-proteobacteria represent a diverse group of Gram-negative bacteria that inhabit a wide range of ecological niches, including associations with animals and plants, and exhibit lifestyles ranging from intracellular parasitism and endosymbiosis to free-living proliferation. This group has been extensively studied in the context of bacterial cell cycle regulation, particularly through the free-living model Caulobacter crescentus, which has provided foundational insights into the coordination of bacterial growth and division. In contrast, Orientia tsutsugamushi, a member of the Rickettsiales order, is an obligatory intracellular bacterium and the causative agent of scrub typhus, a neglected tropical disease of increasing public health concern. Despite its clinical relevance and highly specialized lifestyle, the regulatory mechanisms that govern gene expression in O. tsutsugamushi remain largely uncharacterized. This thesis aims to shed light on how transcriptional regulators participate to orchestrate gene expression across the two distinct stages of O. tsutsugamushi’s life cycle, intracellular and extracellular, with a particular focus on two signature proteins, TrcR and CtrA, originally identified in C. crescentus and highly conserved among Alpha-proteobacteria but whose regulon remains largely unknown Rickettsiales.