February 8, 2008
As millions of Americans with periodontal disease well know, oral bacteria tend to accumulate in the shallow fluid-filled crevices between a tooth and the surrounding gingiva. Among them is the gram-negative pathogen, Porphyromonas gingivalis. Decades of research has established that, when left to its own opportunistic devices, P. gingivalis will attach to the gingiva and slip undetected into its surface cells. Once inside, the bacterium quietly adapts its lifestyle to its new surroundings, establishing a latent infection that can spread to cells deeper within the gingiva. In the December 2007 issue of the journal Proteomics, a team of NIDCR grantees published for the first time a quantitative comparison of protein expression inside and outside of gingival cells for a common strain of P. gingivalis. They found that 385 proteins were overexpressed in the internalized bacterium, or roughly 28 percent of its protein-encoding DNA. This suggests a massive - and perhaps therapeutically exploitable - downshifting of its behavior inside gingival cells. As the authors concluded, their initial data sets forth “a biologically consistent picture of an organism that down-regulates production of destructive proteases, coordinates responses to elevated oxygen tension and iron availability, dispenses with production of energetically costly surface molecules that have outlived their use, and ramps up production to thrive in a nutritionally rich intracellular environment.”