Involvement of an Skp-Like Protein, PGN_0300, in the Type IX Secretion System of Porphyromonas gingivalis.

The oral Gram-negative anaerobic bacterium Porphyromonas gingivalis is an important pathogen involved in chronic periodontitis. Among its virulence factors, the major extracellular proteinases, Arg-gingipain and Lys-gingipain, are of interest given their abilities to degrade host proteins and process other virulence factors. Gingipains possess C-terminal domains (CTDs) and are translocated to the cell surface or into the extracellular milieu by the type IX secretion system (T9SS). Gingipains contribute to the colonial pigmentation of the bacterium on blood agar. In this study, Omp17, the PGN_0300 gene product, was found in the outer membrane fraction. A mutant lacking Omp17 did not show pigmentation on blood agar and showed reduced proteolytic activity of the gingipains. CTD-containing proteins were released from bacterial cells without cleavage of the CTDs in the omp17 mutant. Although synthesis of the anionic polysaccharide (A-LPS) was not affected in the omp17 mutant, the processing of and A-LPS modification of CTD-containing proteins was defective. PorU, a C-terminal signal peptidase that cleaves the CTDs of other CTD-containing proteins, was not detected in any membrane fraction of the omp17 mutant, suggesting that the defective maturation of CTD-containing proteins by impairment of Omp17 is partly due to loss of function of PorU. In the mouse subcutaneous infection experiment, the omp17 mutant was less virulent than the wild type. These results suggested that Omp17 is involved in P. gingivalis virulence.

Characterization of the tripartite drug efflux pumps of Porphyromonas gingivalis aTCC 33277.

The periodontal pathogen, Porphyromonas gingivalis ATCC 33277 has six gene clusters that encode tripartite drug efflux pumps. To examine the effects of the drug efflux pumps on its antibiotic sensitivity, six mutants were constructed, each defective in the membrane fusion protein gene of each gene cluster. Compared to the wild-type strain, all mutants exhibited an elevated sensitivity to tetracycline, and two mutants with deletions in the PGN_1431 and PGN_1680 genes showed an increased sensitivity to various types of antibiotics. These results suggest that the activity of drug efflux systems may affect antibiotic sensitivity in P. gingivalis.