Superoxide dismutase-encoding gene of the obligate anaerobe Porphyromonas gingivalis is regulated by the redox-sensing transcription activator OxyR

Abstract

Inspection of the genomic DNA sequence of the oral anaerobePorphyromonas gingivalisreveals that the micro-organism possesses the peroxide-sensing transcription activator OxyR, but not the superoxide-sensing transcription factor SoxR. Investigatation of oxidative-stress-responsive proteins inP. gingivalisby two-dimensional gel electrophoresis showed that two proteins were predominantly upregulated in oxidative conditions. In aP. gingivalis oxyRmutant these two proteins were not induced by treatment with hydrogen peroxide under aerobic conditions. By N-terminal amino acid sequencing, the two proteins were found to be superoxide dismutase and alkyl hydroperoxide reductase, encoded bysodandahpC, respectively. Northern blot andlacZfusion analyses revealed thatP. gingivalis sodandahpCwere positively regulated by OxyR. Primer extension analysis located the promoter regions ofsodandahpC, and putative −35 boxes of these promoters were found immediately adjacent to their putative OxyR-binding sequences. Moreover, the promoter regions ofsodandahpChad the ability to bindP. gingivalisOxyR protein. These results demonstrate thatP. gingivalis sodis one of the OxyR regulons, suggesting that OxyR functions as an intracellular redox sensor rather than a peroxide sensor in this organism. Asodgene ofBacteroides fragilis, which is taxonomically related toP. gingivalis, is inducible by redox stresses but not controlled by its OxyR. A DNA fragment including theB. fragilis sodpromoter region could bind theP. gingivalisOxyR protein; however, a putative OxyR binding sequence within the DNA fragment was 14 bases distant from a putative −35 box of its promoter.