Mechanisms of chlorate toxicity and resistance in Pseudomonas aeruginosa

• Published in: Molecular microbiology Vol. 118; no. 4; pp. 321 - 335
• Main Authors: Spero, Melanie A., Jones, Jeff, Lomenick, Brett, Chou, Tsui‐Fen, Newman, Dianne K.
• Format: Journal Article
• Language: English
• Published: Oxford Blackwell Publishing Ltd 01.10.2022
• Subjects: antibiotic tolerance; Antibiotics; Chlorate; DNA biosynthesis; DNA repair; drug resistance; drug toxicity; Hypoxia; Metabolism; Methionine; Mutation; Nitrate reductase; Nitrates; Opportunist infection; Oxidation; Oxidizing agents; Protein turnover; Proteins; Proteomes; Pseudomonas aeruginosa; Reductases; Survival; Toxicity; Transposon mutagenesis
• ISSN: 0950-382X; 1365-2958
• DOI: 10.1111/mmi.14972

Pseudomonas aeruginosa is an opportunistic bacterial pathogen that often encounters hypoxic/anoxic environments within the host, which increases its tolerance to many conventional antibiotics. Toward identifying novel treatments, we explored the therapeutic potential of chlorate, a pro‐drug that kills hypoxic/anoxic, antibiotic‐tolerant P. aeruginosa populations. While chlorate itself is relatively nontoxic, it is enzymatically reduced to the toxic oxidizing agent, chlorite, by hypoxically induced nitrate reductase. To better assess chlorate's therapeutic potential, we investigated mechanisms of chlorate toxicity and resistance in P. aeruginosa. We used transposon mutagenesis to identify genes that alter P. aeruginosa fitness during chlorate treatment, finding that methionine sulfoxide reductases (Msr), which repair oxidized methionine residues, support survival during chlorate stress. Chlorate treatment leads to proteome‐wide methionine oxidation, which is exacerbated in a ∆msrA∆msrB strain. In response to chlorate, P. aeruginosa upregulates proteins involved in a wide range of functions, including metabolism, DNA replication/repair, protein repair, transcription, and translation, and these newly synthesized proteins are particularly vulnerable to methionine oxidation. The addition of exogenous methionine partially rescues P. aeruginosa survival during chlorate treatment, suggesting that widespread methionine oxidation contributes to death. Finally, we found that mutations that decrease nitrate reductase activity are a common mechanism of chlorate resistance. Chlorate is a pro‐drug that kills pathogens in low‐oxygen environments where conventional antibiotics are less effective. This study reveals that chlorate reduction to chlorite (catalyzed by Nar) kills cells by causing proteome‐wide methionine oxidation (MetSO), which can be partially repaired by methionine sulfoxide reductase (Msr) enzymes. Mutations that decrease Nar activity are a primary mechanism of chlorate resistance.