Role of oxyR in the Oral Anaerobe Porphyromonas gingivalis

Abstract

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 H 2 O 2 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 H 2 O 2 , 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 H 2 O 2 . 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 H 2 O 2 and the aerotolerance of P. gingivalis. Escherichia coli and other bacteria with more complex respiratory requirements use OxyR for regulating resistance to H 2 O 2 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 H 2 O 2 in P. gingivalis but constitutively activates transcription of oxidative-stress-related genes under anaerobic growth.

Identification of bistable populations of Porphyromonas gingivalis that differ in epithelial cell invasion

“…This might be explained by cross-talk in their regulatory pathways, as it has been established in several organisms that sodB is regulated by Fur (Thompson et al, 2002;Fee, 1991;Ernst et al, 2005) and oxyR (Diaz et al, 2006). These transcriptomic observations implicate the involvement of global transcriptional regulators in the control of this adaptation, which might indicate the existence of a stochastic fluctuation in gene expression levels that gives rise to these subtypes.…”

“…The OxyR (PG0270) protein is known to regulate several oxidative stress genes in P. gingivalis (Diaz & Rogers, 2004;Diaz et al, 2006), and although they were not present in our signature set, a selection were regulated in the invasive/ non-invasive and protease strains, including ahpC (alkylhydroperoxidase, PG0430) and uspA (oxidative stress resistance, PG0245), which are known to be key genes for stress resistance in P. gingivalis (Ueshima et al, 2003;Johnson et al, 2004;Chen et al, 2006). These data indicate that the invasive subtypes are likely to be well adapted to their intracellular environment, and indeed we found that they retained greater viability after exposure to hydrogen peroxide (Fig.…”

Gingipain-dependent interactions with the host are important for survival of Porphyromonas gingivalis

“…Transcriptome analysis of P. gingivalis in the presence of hydrogen peroxide has further extended our understanding of the complex response of this organism to oxidative stress (8,46,184). Diaz,et al (46) in their DNA microarray analysis of P. gingivalis isogenic mutants, have demonstrated that common OxyR-regulated genes such as dps and ahpFC were not positively regulated in response to H 2 O 2, although, their expression was dependent on the presence of a functional OxyR protein.…”

“…In P. gingivalis, oxidative stress was found to modulate the expression of several proteins including HtpG, GroEL, DnaK, AhpC, FeoB2, TPR domain protein, and trigger factor (8,46,77,82,101,149,184). Since several of these proteins are also involved in heat shock, it implies that the organism uses a multifunctional approach that may involve the gingipains to maintain cell viability under adverse environmental conditions.…”

Differential response of Porphyromonas gingivalis to varying levels and duration of hydrogen peroxide-induced oxidative stress

“…Oxidative stress defence is an important cellular protective mechanism(s) which plays a crucial role in the survival of all bacteria especially anaerobic bacteria (Brioukhanov & Netrusov, 2004) such as P. gingivalis (Henry et al, 2012;Diaz et al, 2006). In the periodontal pocket, the presence of periodontal pathogens including P. gingivalis triggers a massive host immune response including the release of reactive oxygen species (ROS) such as hydrogen peroxide (H 2 O 2 ) and superoxide (O neutrophils and macrophages (Chapple, 1996).…”