Defense Date


Document Type


Degree Name

Master of Science



First Advisor

Janina Lewis


Porphorymonas gingivalis is one of the major bacterial pathogens responsible for the initiation and progression of periodontal disease. The bacterium requires hemin uptake for its growth and has developed sophisticated mechanisms to extract hemin from hemin containing proteins in the oral cavity. Hemin first binds to receptors on the surface of P. gingivalis and is then taken up in an energy dependent manner. TonB is an inner membrane bound protein that spans the periplasm and is believed to be involved in the passage of hemin through the double membrane of P. gingivalis. However, the TonB protein in P. gingivalis is yet to be identified. We identified PG0785 as a possible P. gingivalis TonB based on its bioinformatics data showing similarity to other known TonB proteins. We generated a P. gingivalis mutant lacking a functional PG0785 and then characterized the mutant to determine the role of PG0785. We performed metal content and protease assays, virulence studies and transcriptional and translational analysis of our mutant and wild type P. gingivalis strains. Phenotypic studies showed that the mutant cannot accumulate hemin on its surface. The mutant has significantly lower levels of iron compared to wild type based on metal content assays. The mutant also has significantly lower protease activity compared to the wild type. Virulence studies showed that the mutant interacted and invaded eukaryotic cells at much lower levels than the wild type. These results allowed us to speculate that PG0785 is very important in binding of hemin to surface of P. gingivalis. PG0785 also plays an important role in iron uptake, protease activity and virulence of P. gingivalis. Transcriptional and translational analyses have shown that numerous TonB related genes, metal uptake genes, hemin uptake genes and genes related to virulence have been differentially regulated in the mutant lacking a functional PG0785 gene compared to the wild type strain. In conclusion we believe that based on our results PG0785 is a putative P. gingivalis TonB protein that plays a significant role in the biology of P. gingivalis.


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