Brucella abortus is a causative agent of brucellosis, a chronic bacterial disease with global distribution. The pathogenesis of Brucella remains poorly understood, despite a century of study. During infection, the Brucella bacterium endures numerous environmental and host stresses but establishes a replicative niche in host cells. How the bacterium withstands these host stresses and establishes the replicative niche remains of intense interest. To approach these questions, this thesis probes multiple aspects of Brucella transcriptional regulation. Chapter 1 analyzes historical and current justifying the importance of the work to the Brucella field. Chapter 2 uses a mouse model of infection along with transcriptomics and traditional bacteriological assays to interrogate the quorum sensing system. Major findings include that the LuxR protein BabR contributes to Brucella survival, that 3-OXO-C12 is likely physiologically relevant to the bacterium, and that the quorum sensing system regulates denitrification. Chapter 3 describes a new method for identifying transcription factors controlling expression of regulatory small RNAs (sRNAs) and tests for validity of this method. Chapter 4 develops a screening method to identify the AHL synthesis pathway of Brucella. This pathway is unknown, but as we demonstrate in Chapter 2, controls the activity of the LuxR proteins VjbR and BabR, and thus the transcription of the downstream regulons. Finally, Chapter 5 summarizes several themes that emerged throughout the research in the previous chapters and then proposes several future research directions for Brucella biology.

Brucellosis is a worldwide bacterial disease. Infections are lifelong without antibiotics and treatment is extensive, with many people requiring multiple courses of antibiotics. Understanding how the bacteria avoid dying from immune system activity can eventually improve treatments. This thesis contains my research into how the brucellosis bacteria change their gene expression, which allows bacterial survival during infection. The first research chapter (Chapter 2) examines two proteins that change genetic expression and the chemical signals that the proteins use to function. Chapter 3 finds relationships that had not been appreciated in other datasets by focusing on small segments of RNA that facilitate bacterial gene expression. Finally, Chapter 4 shows a new method for finding the method the bacteria generate the critical chemical signals examined in Chapter 2.

Doctor of Philosophy