Complete Title of Thesis: "The Mycobacterium tuberculosis DosR regulon and metabolism under oxygen-restricted conditions."
Prepared under the direction of Martin Voskuil
Mycobacterium tuberculosis (Mtb) infects a third of the world and survives in latently infected individuals, likely in a non-respiring and non-replicating state. How Mtb achieves this dormant-like state is poorly understood. The goal of this thesis was to investigate Mtb mechanisms that contribute to respiration-restricted survival and metabolism in the hope that they may shed light on Mtb persistence in necrotic lesions and latently infected hosts. The Mtb DosR regulon is a genetic program induced by conditions that inhibit aerobic respiration and prevent bacilli replication. In this study, we used a mutant incapable of DosR regulon induction to investigate the contribution of the regulon to bacterial metabolism during hypoxia and anaerobiosis. We also investigated the contribution of non-DosR regulon factors to metabolism and respiration. Our results show the DosR regulon is essential for Mtb survival during prolonged anaerobiosis and also that it is required for metabolic processes that occur upon entry into and throught a non-respiring state. Specifically, we show that regulon mechanisms shift metabolism away from aerobic respiration in the face of dwindling oxygen availability and are required for maintaining energy levels and redox balance as the culture becomes anaerobic. We demonstrated that the DosR regulon is crucial for rapid resumption of aerobic growth once Mtb exits an anaerobic or nitric oxide-induced non-replicating state. We also show that under anaerobic conditions, the DosR regulon components are required for resistance to type II dehydrogenase inhibition, resistance to ATP synthase inhibition as well as for CO2 assimilation and conversion of CO2 to succinate in what is most likely a novel reductive metabolic pathway. We also suggest carbohydrate catabolite repression may be missing or altered in Mtb and that Mtb catabolizes cholesterol to survive long term anaerobiosis. In summary, the DosR regulon encodes novel metabolic mechanisms essential for Mtb to survive in respiration-restricted environments reminiscent of the host envrionment.