Intrinsic silver resistance of Pseudomonas aeruginosa in simulated human wound fluid
Date
2020-10-19
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Abstract
A meta-analysis of randomized clinical trials using silver suggests that it does not improve patient outcomes and that the opportunistic pathogen Pseudomonas aeruginosa can persist in wounds treated with silver-impregnated bandages. However, little is known about how this microorganism withstands silver toxicity. Using strand-specific RNA-sequencing of burn-wound isolated P. aeruginosa in tandem with susceptibility testing of transposon mutants in simulated human wound fluid, we identified 46 differentially expressed genes that are bona fide silver resistance determinants. We focused on the most highly differentially expressed gene identified in the screen, copZ2. This gene is a paralog of P. aeruginosa copZ1, which encodes a copper-binding chaperone protein. CopZ2 is a small protein (65 amino acids, 6.9 kDa) that contains a M-X-C-X-H-C metal-binding motif that is essential for its function. Although CopZ1 is a putative cytoplasmic protein regulated by the copper-responsive regulator, CueR, we provide evidence that CopZ2 is enriched in the outer membrane of P. aeruginosa and that its transcription is regulated by both the putative envelope stress-response regulator, CpxR, and CueR. Purified CopZ2 binds to silver (Ag+) with an equilibrium dissociation constant (Kd) of 7.7 µM, providing it with higher affinity for silver ions than copper ions (Cu2+, Kd = 37.0 µM) in the same milieu. CopZ2 orthologues are widely distributed in Pseudomonas species, and heterologous expression of these genes confers silver tolerance to Escherichia coli. Taken together, these data begin to define the determinants of P. aeruginosa intrinsic silver resistance in environments with complex organics, and identify that CopZ2 is an evolutionarily conserved, membrane-associated, silver-binding protein that may account for a widespread ability of Pseudomonads to withstand silver toxicity.
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Keywords
Silver tolerance, Pseudomonas aeruginosa
Citation
Ostaszewski, A. (2020). Intrinsic silver resistance of Pseudomonas aeruginosa in simulated human wound fluid (Doctoral thesis, University of Calgary, Calgary, Canada). Retrieved from https://prism.ucalgary.ca.