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Published September 25, 2018 | Supplemental Material + Published
Journal Article Open

Chlorate Specifically Targets Oxidant-Starved, Antibiotic-Tolerant Populations of Pseudomonas aeruginosa Biofilms

Abstract

Nitrate respiration is a widespread mode of anaerobic energy generation used by many bacterial pathogens, and the respiratory nitrate reductase, Nar, has long been known to reduce chlorate to the toxic oxidizing agent chlorite. Here, we demonstrate the antibacterial activity of chlorate against Pseudomonas aeruginosa, a representative pathogen that can inhabit hypoxic or anoxic host microenvironments during infection. Aerobically grown P. aeruginosa cells are tobramycin sensitive but chlorate tolerant. In the absence of oxygen or an alternative electron acceptor, cells are tobramycin tolerant but chlorate sensitive via Nar-dependent reduction. The fact that chlorite, the product of chlorate reduction, is not detected in culture supernatants suggests that it may react rapidly and be retained intracellularly. Tobramycin and chlorate target distinct populations within metabolically stratified aggregate biofilms; tobramycin kills cells on the oxic periphery, whereas chlorate kills hypoxic and anoxic cells in the interior. In a matrix populated by multiple aggregates, tobramycin-mediated death of surface aggregates enables deeper oxygen penetration into the matrix, benefiting select aggregate populations by increasing survival and removing chlorate sensitivity. Finally, lasR mutants, which commonly arise in P. aeruginosa infections and are known to withstand conventional antibiotic treatment, are hypersensitive to chlorate. A lasR mutant shows a propensity to respire nitrate and reduce chlorate more rapidly than the wild type does, consistent with its heightened chlorate sensitivity. These findings illustrate chlorate's potential to selectively target oxidant-starved pathogens, including physiological states and genotypes of P. aeruginosa that represent antibiotic-tolerant populations during infections.

Additional Information

© 2018 Spero and Newman. This is an open-access article distributed under the terms of the Creative Commons Attribution 4.0 International license. Received June 26, 2018. Accepted August 22, 2018. Published online September 25, 2018. This work was supported by grants from the NIH (5R01HL117328-03 and 1R01AI127850-01A1) to D.K.N. We thank Nathan Dalleska and the Environmental Analysis Center (Caltech) for help with metabolite analyses, William DePas for help developing the ABBA protocol, and Elliot Snow for experimental assistance.

Attached Files

Published - e01400-18.full.pdf

Supplemental Material - inline-supplementary-material-1.pdf

Supplemental Material - inline-supplementary-material-2.pdf

Supplemental Material - inline-supplementary-material-3.pdf

Supplemental Material - inline-supplementary-material-4.pdf

Supplemental Material - inline-supplementary-material-5.mov

Supplemental Material - inline-supplementary-material-6.mov

Supplemental Material - inline-supplementary-material-7.mov

Supplemental Material - inline-supplementary-material-8.mov

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