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Journal of Bacteriology, April 2006, p. 2454-2462, Vol. 188, No. 7
0021-9193/06/$08.00+0     doi:10.1128/JB.188.7.2454-2462.2006
Copyright © 2006, American Society for Microbiology. All Rights Reserved.

Role of oxyR in the Oral Anaerobe Porphyromonas gingivalis

Patricia I. Diaz,^1, Nada Slakeski,² Eric C. Reynolds,² Renato Morona,³ Anthony H. Rogers,⁴ and Paul E. Kolenbrander^1*

National Institute of Dental and Craniofacial Research, National Institutes of Health, Bethesda, Maryland,¹ School of Dental Science, The University of Melbourne, VIC, Australia,² Department of Molecular and Life Sciences, The University of Adelaide, SA, Australia,³ Oral Microbiology Laboratory, Dental School, The University of Adelaide, SA, Australia⁴

Received 13 December 2005/ Accepted 20 January 2006

Porphyromonas gingivalis is an anaerobic microorganism that inhabits the oral cavity, where oxidative stress represents a constant challenge. A putative transcriptional regulator associated with oxidative stress, an oxyR homologue, is known from the P. gingivalis W83 genome sequence. We used microarrays to characterize the response of P. gingivalis to H₂O₂ and examine the role of oxyR in the regulation of this response. Most organisms in which oxyR has been investigated are facultative anaerobes or aerobes. In contrast to the OxyR-regulated response of these microorganisms to H₂O₂, the main feature of the response in P. gingivalis was a concerted up-regulation of insertion sequence elements related to IS1 transposases. Common OxyR-regulated genes such as dps and ahpFC were not positively regulated in P. gingivalis in response to H₂O₂. However, their expression was dependent on the presence of a functional OxyR, as revealed by microarray comparison of an oxyR mutant to the wild type. Phenotypic characterization of the oxyR mutant showed that OxyR plays a role in both the resistance to H₂O₂ and the aerotolerance of P. gingivalis. Escherichia coli and other bacteria with more complex respiratory requirements use OxyR for regulating resistance to H₂O₂ and use a separate regulator for aerotolerance. In P. gingivalis, the presence of a single protein combining the two functions might be related to the comparatively smaller genome size of this anaerobic microorganism. In conclusion, these results suggest that OxyR does not act as a sensor of H₂O₂ in P. gingivalis but constitutively activates transcription of oxidative-stress-related genes under anaerobic growth.

Present address: Department of Periodontology, School of Dentistry, University of North Carolina, Chapel Hill, N. C.

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