Identification of diffusible small molecules that regulate replication of Porphyromonas gingivalis

Project Summary Porphyromonas gingivalis (Pg) is a late-colonizer with a demonstrated role in the etiology of periodontitis and implicated as a risk factor in several systemic conditions. Our previous work showed that population size, which determines the availability of a still unidentified endogenous diffusible small molecule(s), limits the in vitro growth and the in vivo colonization and virulence of Pg. Our work also showed that the inability of Pg to grow in vitro and colonize in vivo from a small inoculum was overcome by forming a partnership with the ubiquitous Gram- negative early colonizer Veillonella parvula (Vp). In preliminary studies we show that intermediates of menaquinone biosynthesis may play a role stimulating growth of low cell-density Pg and may be produced by certain strains of Pg and by Vp. However, other strains of Pg capable of supporting their own growth via small diffusible cues present in their spent media may utilize a different strategy as they do not have the machinery for menaquinone biosynthesis. Accordingly, the overall goal of this application is to establish the identity of the growth-promoting cues produced by different strains of Pg and by Vp that support Pg replication from a low cell density population. Therefore, in this proposal we will utilize chemical and molecular genetic strategies to identify the soluble cues produced by Pg 381, Pg W83 and Vp that stimulate growth of Pg from low cell density inocula. We anticipate this work will elucidate the mechanisms regulating cell density-dependent replication in different strains of Pg and the manner in which inter-species interactions with early biofilm colonizers, such as Vp, can help Pg overcome the growth barrier and allow its replication and establishment in the oral cavity.