Genetic analysis of expression control of Porphyromonas gingivalis fimbriation

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We transformed porphyromonas gingivalis YH522 with DNA of pYHF2, a chimeric plasmid generated by recombinating fimA gene of strain 381 with pYH420. YH522 used as the recipient is the only known restriction negative strain and pYH420 is the only cloning vector available for this species, both of which had been developed in the previous study. On the cell surface of the YH522 transformants thus obtained, observed were a large number of recombinant fimbriae (r-fimbriae) with a longer shape distinguishable electron-microscopically and serologically from the host's endogenous fimbriae.In these transformants the expression of the host's endogenous fimbriae was markedly suppressed.The r-fimbriae recovered from the transformants were shown to lack some minor components that were detectable on the endogenous fimbriae.By using pYHF2 DNA purified from a YH522 transformant, we could obtain six additional P. gingivalis transformants. Although transformation of this species except for the restriction-negative strain YH522 is known very difficult, the use of YH522 as the donor allowed us to generate these six transformants from about 60 wild strains tested for the recipient ability.The resulted transformants were used for comparison of adhesion activity to bacterial species and mammalial epithelial cells. This series of experiments revealed that the transformants expressing a higher level of r-fimbiae (a relatively lower level of endogenous fimbriae) exhibited a greater decrease in adhesion to other cells. This evidence strongly suggested that the minor component(s) detectable only on the endogenous fimbriae and not on r-fimbiae is an important factor for adhesion of P. gingivalis.