ENVIRONMENTAL-REGULATION OF FIMBRIAL GENE-EXPRESSION IN PORPHYROMONAS-GINGIVALIS

Porphyromonas gingivalis fimbriae are an important virulence factor in volved in attachment and invasion. Fimbrillin, encoded by the fimA gen e, is the major subunit protein of the fimbriae, To elucidate the infl uence of environmental signals on the expression of the fimA gene, a s train of P. gingivalis (designated PLE) containing a chromosomal trans criptional fusion between a promoterless lacZ gene and the fimA promot er region was constructed. Promoter activity was assessed by measureme nt of beta-galactosidase activity of PLE. An 11-fold increase in activ ity of fimA promoter was found as growth temperature declined from 39 to 34 degrees C. Promoter activity decreased by approximately 50% in r esponse to hemin limitation and upon culture on solid medium. In addit ion, the presence of serum or saliva in the growth medium decreased fi mA promoter activity by similar amounts, A correlation between fi prom oter activity and phenotypic properties dependent upon fimbriae was es tablished. P. gingivalis grown al 34 degrees C, compared to 39 degrees C, Showed an increased ability to adhere to Streptococcus gordonii an d to invade primary cultures of gingival epithelial cells, These studi es indicate that expression of the P. gingivalis fimA gene is regulate d at the transcriptional level in response to several environmental co nditions and that altered fim expression can also modulate the adheren ce and invasion abilities of P. gingivalis.