Response of Porphyrmonas gingivalis to hydrogen peroxide-induced oxidative stress

The inflammatory environment of the periodontal pocket suggests that Porphyromonas gingivalis has properties which are essential for survival through its ability to adapt and resist oxidative stress. Objective: A global approach was used to assess the transcription profile of the cellular response of isogenic mutants of P. gingivalis to varying concentrations of hydrogen peroxide-induced oxidative stress. Methods: Growth of P. gingivalis and a non-black pigmented vimA-defective mutant (FLL92) in the presence of several concentrations of H₂O₂ was monitored spectrophotometrically for 24 hr. For microarray analysis, total RNA, extracted from treated (0.1mM, 0.25mM or 0.5mM for 15min) and untreated samples at mid-log phase were reverse-transcribed, labeled with Cy3 and Cy5 dyes and hybridized to whole-genome DNA microarray slides provided by The Institute for Genomic Research (TIGR). Significance of data was determined as fold change ≥2and P value ≤0.005. Microarray data was confirmed by RT-PCR. Results: At a subinhibitory concentration (0.1mM) of H₂O₂, 38 and 52 genes were upregulated in W83 and FLL92 strains respectively. Only 1 gene was down-regulated in each strain. At 0.25mM, growth was inhibited but without loss of cell viability with 43 and 63 genes up-regulated in W83 and FLL92, respectively. 9 and 6 genes were down-regulated in both strains. Inhibitory concentrations (≥0.5mM) of H₂O₂ resulted in up-regulation of 12 and 9 genes and down-regulation of 8 and 5 genes in W83 and FLL92 respectively. The majority of induced genes are of unknown function. Conclusions: Porphyromonas gingivalis' differential response to varying oxidative stress conditions demonstrates its ability to adapt to the changing conditions of the periodontal pocket. Because only a small subset of induced genes were common to the different conditions, the possibility for multiple mechanisms of oxidative stress resistance exists. This work was supported by Loma Linda University and Public Health Grant DE13664 from NIDCR (to H.M.F.)