Global regulation of gene expression by OxyR in an important human opportunistic pathogen

Abstract

Most bacteria control oxidative stress through the H2O2-responsive transactivator OxyR, a member of the LTTR family (LysR Type Transcriptional Regulators), which activates the expression of defensive genes such as those encoding catalases, alkyl hydroperoxide reductases and superoxide dismutases. In the human opportunistic pathogen Pseudomonas aeruginosa, OxyR positively regulates expression of the oxidative stress response genes katA, katB, ahpB and ahpCF. To identify additional targets of OxyR in P. aeruginosa PAO1, we performed chromatin immunoprecipitation in combination with whole genome tiling array analyses (ChIP-chip). We detected 56 genes including all the previously identified defensive genes and a battery of novel direct targets of OxyR. Electrophoretic mobility shift assays (EMSAs) for selected newly identified targets indicated that ∼70% of those were bound by purified oxidized OxyR and their regulation was confirmed by quantitative real-time polymerase chain reaction. Furthermore, a thioredoxin system was identified to enzymatically reduce OxyR under oxidative stress. Functional classification analysis showed that OxyR controls a core regulon of oxidative stress defensive genes, and other genes involved in regulation of iron homeostasis (pvdS), quorum-sensing (rsaL), protein synthesis (rpsL) and oxidative phosphorylation (cyoA and snr1). Collectively, our results indicate that OxyR is involved in oxidative stress defense and regulates other aspects of cellular metabolism as well.

Peroxide-Sensing Transcriptional Regulators in Bacteria

“…OxyR also upregulates the expression of OxyS, a small regulatory RNA that integrates peroxide stress with general stress pathways (34,122). Although there are significant differences, the OxyR regulons of other organisms tend to include similar classes of genes (39,82,96,104,116).…”

“…This dependence on reduction by GrxA also renders OxyR sensitive to the thiol-disulfide redox status (glutathione disulfide [GSSG]/reduced glutathione [GSH] ratio) of the cell (2,123). Recent evidence indicates that a similar reductive recycling of OxyR occurs in Pseudomonas aeruginosa, which utilizes a thioredoxin/thioredoxin reductase system that is part of the OxyR regulon (116).…”

Quorum sensing enhancement of the stress response promotes resistance to quorum quenching and prevents social cheating

“…Also for P. aeruginosa, the H 2 O 2 -responsive transactivator OxyR binds the promoters and may influence the expression of the QS transcriptional regulators rsaL and mvfR (pqsR) (Wei et al, 2012), and nutritional stress by phosphate starvation and QS are linked (Lee et al, 2013).…”

Regulation of virulence gene expression

“…In this Special Focus issue Green and colleagues discuss how bacteria sense and adapt to low oxygen environments, the presence of reactive oxygen species (ROS) and the presence of nitric oxide, each of which may be encountered by the pathogen upon infection of the host and can lead to global changes in gene expression. [16][17][18][19][20] Adaptive responses that result in increased resistance to the action of ROS and nitric oxide are key to the survival of several pathogens in the host. [21][22] Moreover, hypoxia or anoxia is used as a signal not only to trigger changes in expression of genes that allow adaptation to the lack of oxygen but also upregulate the activity of genes that result in obvious damaging consequences for the cell: they encode toxins.…”