Pleiotropic pigmentation mutants of Porphyromonas gingivalis

Porphyromonas gingivalis is a Gram-negative, black pigmented oral anaerobe associated with adult periodontitis. The adherence of the bacterium to junc tional epithelial cells is the first step in infection and colonization. Th e molecular mechanisms and genetics of colonization are, as yet, not well u nderstood, although it has been demonstrated that P. gingivalis fimbriae ar e involved in adhesion. In addition, cell surface cysteine proteinases may play a role either directly as adhesins or indirectly through their involve ment in the biogenesis of fimbriae. A link has been established between cys teine proteinase-hemagglutinating activity and colongy pigmentation on bloo d agar. in this study a P. gingivalis ATCC 33277 transposon library was scr eened for white mutants. Pleiotropic mutants were identified with altered p igmentation, proteinase, hemagglutinin and haemolytic activities. Although the mutants fell into two classes based on the above phenotypes, by electro n microscopy both classes showed increased fimbriation and decreased vesicl e formation. Sequencing of genomic DNA flanking the transposon insertions r evealed that one class of mutants carried disruptions in the gene encoding Lys-gingipain (kgp) and the other in a gene homologous to a glycosyl transf erase. Potential roles for these genes in pigmentation, fimbriation, vesicl e formation and attachment to epithelial cells are discussed. (C) 2000 Acad emic Press.