Transcriptional Analysis of the Bacteroides fragilis Starch Utilization Operon, osuA

Abstract

The opportunistic pathogen Bacteroides fragilis is a symbiotic organism that inhabits the human gastrointestinal tract where it utilizes dietary and host-derived polysaccharides as carbon and energy sources. If abdominal injury occurs, this otherwise commensal organism can migrate from the anaerobic environment of the large intestine to the more aerobic peritoneum. In this new extraintestinal environment, B. fragilis frequently contributes to the development of intra-abdominal abscesses, and is often the most common isolate from such anaerobic infections which can lead to systemic infections and death if left untreated. The organism's ability to shift from commensalist to pathogen is inextricably linked with the complex oxidative stress response (OSR) it has evolved. The studies described in this thesis have focused on the characterization of the promoter for the oxidative starch utilization operon, osu, and the identification of regulatory sequences involved in transcription activation during growth in maltose or exposure to oxygen. The results of this promoter deletional analysis study have demonstrated that the osu promoter is indeed responsive to both maltose and oxygen, and that regulatory regions important for activation of transcription in response to both stimuli are likely found within the same 50 bp region of the promoter. Consistent with this observation was the discovery of a LacI-type binding region in this site. In addition, studies demonstrated that there is the possibility of an additional weak oxygen-responsive promoter that exists in a separate region of the osu promoter. The previously identified transcriptional activator, OsuR, may also play a critical role in transcription activation of the osu promoter, regardless of whether the inducing agent is maltose or oxygen. The mechanism of osu protection during oxidative stress is not fully understood, but results of this thesis offer a more complex model of transcriptional activation of the osu operon than was initially theorized. More studies will be necessary to further elucidate the role of osu in maintaining the OSR of B. fragilis during oxygen exposure.