Genetic basis for divergent virulence of P. gingivalis strains 33277 and 381

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Abstract Porphyromonas ginigvalis is a Gram negative bacterium that displays unique distinguishing characteristics among the oral microbial community. It is capable of indirectly promoting a periodontal disease outcome via a community dysbiosis mechanism. In addition, the bacterium exerts a number of direct immunomodulatory effects on the host innate immune response machinery to dampen the ability of the host to resolve both extracellular and intracellular infections. Consequently, P. gingivalis maintains the ability to survive, infect host cells, disperse systemically, and either exacerbate or evade select host inflammatory responses. A number of bacterial factors including fimbriae, lipid A phosphatases, gingipains, polysaccharide capsule, and adhesins have been strongly implicated in contributing to the pathogenic phenotype associated with P. gingivalis. However, it is unclear how these factors are coordinated with each other, or with additional uncharacterized immunomodulatory factors to confer disease-related phenotypes associated with particular strains. In this application we propose an innovative approach to identify a novel virulence attribute of P. gingivalis by comparing the genomes of two highly related strains, 33277 and 381, which display significantly different inflammasome activation and Toll-like receptor 2 responses, two key innate immune response pathways. Our preliminary comparisons, using laboratory and publicly available sequence information indicate that the number of genomic differences between P. gingivalis 33277 and 381 is surprisingly limited (less than 150 polymorphisms). In Aim 1 we will systematically evaluate genomic sequence data and RNA expression data from 33277 and 381 strains that have been tested for their abilities to activate host cell inflammasome and TLR2, in order to obtain high priority candidate gene sequences encoding products that exhibit features predicted to confer the strain-specific inflammatory effects, such as bacterial factors having demonstrated roles in immunomodulation. In Aim 2 we will create mutant strains bearing targeted deletions in high priority candidates in both the 33277 and 381 backgrounds. The mutant strains will be assessed for their abilities to activate the macrophage inflammasome or TLR2 signaling in order to identify the genetic factor(s) that determine the distinct immunogenic characteristics strains 33277 and 381. The use of functional genomics to elucidate the basis P. gingivalis' strain-specific immunogenicity will lay the foundation for further studies aimed at determining correlations between strain type, disease associations, and potential therapeutic interventions in inflammatory disorders that significantly impact human health.