| Quorum sensing is a phenomenon defined as gene regulation in response to cell density. It regulates various functions in multiple bacterial species. Porphyromonas gingivalis possesses a luxS encoded AI-2 system. Microarray analysis was done using RNA samples from W83 and a luxS mutant, LY2001. The results indicated that 17 genes or ORFs in LY2001 are upregulated while 2 are downregulated. A group of stress related genes are upregulated in the mutant, including htrA, clpB, groEL, dnaK and F subunit of alkyl hydroperoxide reductase (Real time PCR confirmed the microarray results). This indicates that luxS is involved in stress gene regulation. Strain LY2001 had a significantly higher survival rate than W83 when stressed at 50°C, 0.35 mM H2O 2 and pH 9. These results suggest that the stress genes regulated by luxS might be involved in response to temperature stress, H 2O2 stress and pH stress. Three luxS regulated genes including clpB, htrA and a gene encoding a hypothetical protein were chosen for further analysis. Mutants of each gene were constructed, and physiological and virulence studies were performed on these mutants. The ClpB mutant, LY2003, showed increased sensitivity to heat but not to H2O2 and pH 9. An invasion assay indicated that the clpB mutant had significantly less invasion of KB, HCAE and GE cells. Also, the virulence of the clpB mutant was severely impaired. The htrA mutant, JD2003, did not show any difference as compared to the wild type parent strain during heat stress, H2O2 stress and pH stress. The virulence of JD2003 was not different from W83 in a mouse abscess model. But interestingly, JD2003 showed increased invasion of KB and GE cells, but not of HCAE cells. The third mutant, PG1102, did not show any difference in invasion or virulence, indicating no virulent activity with this gene. These data suggest that quorum sensing regulates stress gene expression in P. gingivalis and the stress gene clpB is involved in virulence of this bacterium. |
