Defense Date


Document Type


Degree Name

Master of Science



First Advisor

Janina Lewis


Periodontal disease affects a majority of the US population. Porphyromonas gingivalis is the major etiological agent for development and progression of the disease. P. gingivalis is a hemin-dependent, obligate anaerobe that is found predominantly in periodontal pockets in infected patients. So for, little is known regarding the mechanisms which allow P. gingivalis to survive and sustain itself in the oral cavity. To better understand the adaptive mechanisms of the bacterium to the varying conditions in the oral cavity, regulatory mechanisms must be characterized. Sigma factors (σ) are responsible for initiating transcription by guiding RNA polymerase binding to specific DNA promoter sites. There are several sigma factors present in P. gingivalis, yet their roles have to be identified. Previous unpublished data indicate that a gene coding for an extracytoplasmic function sigma factor (ECF), SigH, is differentially regulated by exposure to molecular oxygen. Different assays were conducted to assess any variation in survival and/or growth between wild-type and SigH deficient strains of P. gingivalis. The ability to grow and survive in the presence of oxidative stress was compared between the mutant deficient in SigH and that of the parental strain. In addition, transcriptional profiles of the two strains were compared. Our assays indicate that growth was slower in the presence of oxygen in the Sigh-deficient mutant with an average difference of 27% compared to the wild-type. Transcriptional profiling showed down-regulation of genes encoding key enzymes associated with oxidative stress protection and oxidative metabolism in the absence of SigH, indicating that the sigma factor is a positive regulator of transcription required for survival of the bacterium in the presence of oxygen. If oxygen sensitivity can be established for this ECF-σ factor, it will aid in better understanding of P. gingivalis’ ability to survive in the oral cavity despite the presence of oxygen.


© The Author

Is Part Of

VCU University Archives

Is Part Of

VCU Theses and Dissertations

Date of Submission

May 2009