OxyR controls H2O2-dependent gene expression in Pseudomonas aeruginosa. Without OxyR, diluted (<107/ml) organisms are easily killed by micromolar H2O2. The goal of this study was to define proteins that contribute to oxyR mutant survival in the presence of H2O2. We identified proteins in an oxyR mutant that were oxidized by using 2,4-dinitrophenylhydrazine for protein carbonyl detection, followed by identification using a two-dimensional gel/matrix-assisted laser desorption ionization-time of flight approach. Among these was the peptidoglycan-associated lipoprotein, OprL. A double oxyR oprL mutant was constructed and was found to be more sensitive to H2O 2 than the oxyR mutant. Provision of the OxyR-regulated alkyl hydroperoxide reductase, AhpCF, but not AhpB or the catalase, KatB, helped protect this strain against H2O2. Given the sensitivity of oxyR oprL bacteria to planktonic H2O2, we next tested the hypothesis that the biofllm mode of growth might protect such organisms from H2O2-mediated killing. Surprisingly, biofllm-grown oxyR oprL mutants, which (in contrast to planktonic cells) possessed no differences in catalase activity compared to the oxyR mutant, were sensitive to killing by as little as 0.5 mM H2O2. Transmission electron microscopy studies revealed that the integrity of both cytoplasmic and outer membranes of oxyR and oxyR oprL mutants were compromised. These studies suggest that sensitivity to the important physiological oxidant H2O2 in the exquisitely sensitive oxyR mutant bacteria is based not only upon the presence and location of OxyR-controlled antioxidant enzymes such as AhpCF but also on structural reinforcement by the peptidoglycan-associated lipoprotein OprL, especially during growth in biofllms.
ASJC Scopus subject areas
- Molecular Biology