Defense Date


Document Type


Degree Name

Master of Science


Microbiology & Immunology

First Advisor

Lewis Janina P


Porphyromonas gingivalis is a major etiological agent that is responsible for the cause and progression of periodontal diseases. The bacterium is exposed to various environmental conditions and oxidative stress conditions while it is in the oral cavity. So, P. gingivalis should have an efficient regulatory system in order to adjust and survive in the oral cavity. But little is known about the regulatory mechanisms that help the bacteria to survive in the oral cavity. So, it is essential to understand and characterize these regulatory mechanisms. The response and adaptation of P. gingivalis to environmental stress conditions occur at the level of transcription which involves the alternative sigma factors. Extracytoplasmic function (ECF) sigma factors are the largest group of alternative sigma factors that play a major role in bacterial response to environmental stress conditions. Here we characterize the σ-70 factor, SigH and SigG, the extracytoplasmic function sigma factors encoded in P. gingivalis genome. Our results show that the expression of SigH is upregulated when P. gingivalis is grown in the presence of oxygen. However, there is no change in the expression of SigG when grown in the presence of oxygen. Furthermore several genes involved in oxidative stress protection such as sod, trx, tpx, ftn, feOB and the hemin uptake locus, hmu, are downregulated in the mutant deficient in SigH designated as V2948. Our RNA-seq analysis of SigG showed that there is no change in the regulation of genes involved in oxidative stress protection and metal homeostasis in SigG deficient mutant designated as V3085. Our survival studies showed that both SigH and SigG are essential for P. gingivalis to grow in host cells. Collectively our studies demonstrate that SigH is a positive regulator of gene expression required for survival of the bacterium in the presence of oxygen and oxidative stress, hemin uptake and virulence. However our studies show that SigG is essential for the bacteria to grow in host cells and hence helps in the virulence of P. gingivalis.


© The Author

Is Part Of

VCU University Archives

Is Part Of

VCU Theses and Dissertations

Date of Submission


Available for download on Sunday, May 14, 2023