Pseudomonas aeruginosa Thiol Peroxidase Protects against Hydrogen Peroxide Toxicity and Displays Atypical Patterns of Gene Regulation

Abstract

The Pseudomonas aeruginosa PAO1 thiol peroxidase homolog (Tpx) belongs to a family of enzymes implicated in the removal of toxic peroxides. We have shown the expression of tpx to be highly inducible with redox cycling/superoxide generators and diamide and weakly inducible with organic hydroperoxides and hydrogen peroxide (H 2 O 2 ). The PAO1 tpx pattern is unlike the patterns for other peroxide-scavenging genes in P. aeruginosa. Analysis of the tpx promoter reveals the presence of a putative IscR binding site located near the promoter. The tpx expression profiles in PAO1 and the iscR mutant, together with results from gel mobility shift assays showing that purified IscR specifically binds the tpx promoter, support the role of IscR as a transcriptional repressor of tpx that also regulates the oxidant-inducible expression of the gene. Recombinant Tpx has been purified and biochemically characterized. The enzyme catalyzes thioredoxin-dependent peroxidation and can utilize organic hydroperoxides and H 2 O 2 as substrates. The ⌬tpx mutant demonstrates differential sensitivity to H 2 O 2 only at moderate concentrations (0.5 mM) and not at high (20 mM) concentrations, suggesting a novel protective role of tpx against H 2 O 2 in P. aeruginosa. Altogether, P. aeruginosa tpx is a novel member of the IscR regulon and plays a primary role in protecting the bacteria from submillimolar concentrations of H 2 O 2 .

Multiple antibiotic resistance index, fitness and virulence potential in respiratory Pseudomonas aeruginosa from Jamaica

“…In this study, H 2 O had a greater oxidative stress than t-BOOH at both tested concentrations on biofilm and planktonic cells. The lack of efficacy of t-BOOH could either be as a result of the utilization of this compound as a carbon source by P. aeruginosa (Garnier et al, 1999) or due to the expression of an anti-oxidative resistance mechanism (Somprasong et al, 2012). Consequently, resistant biofilms could conceivably produce more viable cells after treatment with t-BOOH.…”

Gene Expression and Physiological Role of Pseudomonas aeruginosa Methionine Sulfoxide Reductases during Oxidative Stress

“…To survive oxidative stress, P. aeruginosa has evolved a wide variety of mechanisms to protect itself and to repair the damage caused by ROS toxicity. Several antioxidant enzymes capable of degrading ROS, such as catalases, superoxide dismutases, peroxiredoxins, alkyl hydroperoxide reductases, organic hydroperoxide resistance protein, and thiol peroxidase, have been characterized (2)(3)(4)(5)(6). P. aeruginosa also produces a number of enzymes that are required for repairing oxidative DNA damage (7).…”

Copper chloride induces antioxidant gene expression but reduces ability to mediate H2O2 toxicity in Xanthomonas campestris

“…IscR senses changes in the levels of Fe-S clusters and responds by either activating or repressing transcription of target genes (Ayala-Castro et al, 2008). Furthermore, treatments with H 2 O 2 and organic hydroperoxides are able to induce the expression of IscR-regulated genes (Somprasong et al, 2012).…”

“…IscR-regulated genes are predominantly induced by superoxide generators such as plumbagin (Somprasong et al, 2012). Superoxide anions reacted with the Fe-S clusters causing their depletion.…”

“…IscR is an iron-sulfur (Fe-S) cluster-containing transcriptional regulator involved in the oxidative stress response (Somprasong et al, 2012). IscR-regulated genes are predominantly induced by superoxide generators such as plumbagin (Somprasong et al, 2012).…”