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Journal of Bacteriology, September 2007, p. 6101-6108, Vol. 189, No. 17
0021-9193/07/$08.00+0     doi:10.1128/JB.00527-07
Copyright © 2007, American Society for Microbiology. All Rights Reserved.

What Is the Benefit to Escherichia coli of Having Multiple Toxin-Antitoxin Systems in Its Genome?{triangledown}

Virginie Tsilibaris, Geneviève Maenhaut-Michel, Natacha Mine, and Laurence Van Melderen*

Laboratoire de Génétique des Procaryotes, Institut de Biologie et Médecine Moléculaires, Université Libre de Bruxelles, 12 rue des Professeurs Jeener et Brachet, B-6041 Gosselies, Belgium

Received 6 April 2007/ Accepted 7 May 2007

The Escherichia coli K-12 chromosome encodes at least five proteic toxin-antitoxin (TA) systems. The mazEF and relBE systems have been extensively characterized and were proposed to be general stress response modules. On one hand, mazEF was proposed to act as a programmed cell death system that is triggered by a variety of stresses. On the other hand, relBE and mazEF were proposed to serve as growth modulators that induce a dormancy state during amino acid starvation. These conflicting hypotheses led us to test a possible synergetic effect of the five characterized E. coli TA systems on stress response. We compared the behavior of a wild-type strain and its derivative devoid of the five TA systems under various stress conditions. We were unable to detect TA-dependent programmed cell death under any of these conditions, even under conditions previously reported to induce it. Thus, our results rule out the programmed-cell-death hypothesis. Moreover, the presence of the five TA systems advantaged neither recovery from the different stresses nor cell growth under nutrient-limited conditions in competition experiments. This casts a doubt on whether TA systems significantly influence bacterial fitness and competitiveness during non-steady-state growth conditions.

* Corresponding author. Mailing address: Laboratoire de Génétique des Procaryotes, Institut de Biologie et Médecine Moléculaires, Université Libre de Bruxelles, 12 rue des Professeurs Jeener et Brachet, B-6041 Gosselies, Belgium. Phone: 32 2 650 97 78. Fax: 32 2 650 97 70. E-mail: lvmelder{at}ulb.ac.be

{triangledown} Published ahead of print on 18 May 2007.

Journal of Bacteriology, September 2007, p. 6101-6108, Vol. 189, No. 17
0021-9193/07/$08.00+0     doi:10.1128/JB.00527-07
Copyright © 2007, American Society for Microbiology. All Rights Reserved.



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