2020 Volume 58 Issue 2 Pages 33-38
Prevotella melaninogenica is a gram-negative anaerobic commensal bacterium present in the human oral cavity and has been isolated as a pathogen from suppurative diseases inside and outside the oral cavity. However, little is known about the virulence factors of P. melaninogenica. Periodontal pathogens, Porphyromonas gingivalis and Tanerella forsythia, secrete virulence factors such as proteases and bacterial cell surface proteins via the type IX secretion system (T9SS) involved in virulence. P. melaninogenica also possesses all known orthologs of T9SS. In this study, P. melaninogenica GAI 07411 mutant was con structed that lacked the ortholog of porK, the gene encoding a major component of T9SS. The porK mutant has reduced hemagglutination and biofilm formation. In addition, after growth on medium containing skim milk, the diameter of the halo surrounding the porK mutant was smaller than that of the wild-type strain, suggesting a reduction in extracellular protease secretion. To investigate this in detail, the culture supernatants of the wild-type strain and the porK mutant strain were purified and compared by two-dimen sional electrophoresis. In the mutant, the number of spots detected was low, indicating a decrease in the number of secreted proteins. In infection experiments, the mortality rate of mice inoculated with the porK mutant was statistically significantly reduced compared to the wild-type strain. These results suggested that P. melaninogenica secretes potent virulence factors via T9SS, which contributes to the pathogenesis of this bacterium.
