In several micro-organisms, HtrA, a serine periplasmic protease, is considered an important virulence factor that plays a regulatory role in oxidative and temperature stress. The authors have previously shown that the vimA gene product is an important virulence regulator in Porphyromonas gingivalis. Further, purified recombinant VimA physically interacted with the major gingipains and the HtrA from P. gingivalis. To further evaluate a role for HtrA in the pathogenicity of this organism, a 1.5 kb fragment containing the htrA gene was PCR-amplified from the chromosomal DNA of P. gingivalis W83. This gene was insertionally inactivated using the ermF-ermAM antibiotic-resistance cassette and used to create an htrA-deficient mutant by allelic exchange. In one randomly chosen isogenic mutant designated P. gingivalis FLL203, there was increased sensitivity to hydrogen peroxide. Growth of this mutant at an elevated temperature was more inhibited compared to the wild-type. Further, in contrast to the wild-type, there was a significant decrease in Arg-gingipain activity after heat shock in FLL203. However, the gingipain activity in the mutant returned to normal levels after a further 30 min incubation at room temperature. Collectively, these data suggest that HtrA may play a similar role in oxidative and temperature stress in P. gingivalis as observed in other organisms.
