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Front. Microbiol. | doi: 10.3389/fmicb.2018.00337

A metabolic trade-off modulates policing of social cheaters in populations of Pseudomonas aeruginosa

Huicong Yan1,  Meizhen Wang1*, Feng Sun1,  Ajai A. Dandekar2*, Dongsheng Shen1 and Na Li1
  • 1Zhejiang Gongshang University, China
  • 2Department of Microbiology, University of Washington, United States

Pseudomonas aeruginosa uses quorum sensing (QS) to regulate the production of public goods such as the secreted protease elastase. P. aeruginosa requires the LasI-LasR QS circuit to induce elastase and enable growth on casein as the sole carbon and energy source. The LasI-LasR system also induces a second quorum-sensing circuit, the RhlI-RhlR system. During growth on casein, LasR-mutant social cheaters emerge, and this can lead to a population collapse. In a minimal medium containing ammonium sulfate as a nitrogen source populations do not collapse, cheaters and cooperators reach a stable equilibrium; however, without ammonium sulfate, cheaters overtake the cooperators and populations collapse. We show that ammonium sulfate enhances activity of the RhlI-RhlR system in casein medium and this leads to increased production of cyanide, which serves to control levels of cheaters. This enhancement of cyanide production occurs because of a trade-off in the metabolism of glycine: exogenous ammonium ion inhibits the transformation of glycine to 5,10-methylenetetrahydrofolate (5,10-methylene-THF) through a reduction in expression of the glycine cleavage genes gcvP1 and gcvP2, thereby increasing the availability of glycine as a substrate for RhlR-regulated hydrogen cyanide synthesis. Thus, environmental ammonia enhances cyanide production and stabilizes QS in populations of P. aeruginosa.

Keywords: Quorum Sensing, LASR, rhlR, sociomicrobiology, Hydrogen Cyanide

Received: 24 Dec 2017; Accepted: 12 Feb 2018.

Edited by:

Frank Schreiber, Bundesanstalt für Materialforschung und prüfung (BAM), Germany

Reviewed by:

Rolf Kümmerli, University of Zurich, Switzerland
R Fredrik Inglis, Washington University in St. Louis, United States  

Copyright: © 2018 Yan, Wang, Sun, Dandekar, Shen and Li. This is an open-access article distributed under the terms of the Creative Commons Attribution License (CC BY). The use, distribution or reproduction in other forums is permitted, provided the original author(s) and the copyright owner are credited and that the original publication in this journal is cited, in accordance with accepted academic practice. No use, distribution or reproduction is permitted which does not comply with these terms.

* Correspondence:
Prof. Meizhen Wang, Zhejiang Gongshang University, Hangzhou, China, wmz@zjgsu.edu.cn
Prof. Ajai A. Dandekar, Department of Microbiology, University of Washington, Seattle, United States, dandekar@uw.edu