Porphyromonas gingivalis genes involved in fimA regulation.

Porphyromonas gingivalis is an important component of the complex plaque biofilm that is a direct precursor of periodontal disease. The major fimbriae are required for attachment to oral surfaces and are an important virulence factor. Fimbrillin (FimA) expression in P. gingivalis is inhibited by surface molecule of Streptococcus cristatus, an early colonizer of dental plaque. In this study, differential display PCR was used to identify P. gingivalis genes that are regulated in response to S. cristatus. Of several differentially expressed genes, pg2131 and pg2167 were upregulated by S. cristatus signaling molecules. A null mutant of pg2167 did not transcriptionally regulate fimA following exposure to S. cristatus. In fact, fimA transcription was enhanced in the pg2167 mutant, suggesting that pg2167 may act to repress fimA expression. In contrast, a mutation in pg2131 did not affect transcription of fimA in the presence of S. cristatus. However, production of fimbrillin was significantly diminished in the pg2131 mutant, implicating involvement in posttranscriptional regulation in fimbriation. These data suggest that P. gingivalis fimbriation is controlled by more than one regulation mechanism, involving both transcriptional and posttranscriptional processes.