title: What is the benefit to Escherichia coli of having multiple toxin-antitoxin systems in its genome?
abstract: 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.
authors.affiliation: 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.
authors.forename: Virginie
authors.initials: V
authors.lastname: Tsilibaris
authors.forename: Geneviève
authors.initials: G
authors.lastname: Maenhaut-Michel
authors.forename: Natacha
authors.initials: N
authors.lastname: Mine
authors.forename: Laurence
authors.initials: L
authors.lastname: Van Melderen
mesh_terms: D000143:Acids / Q000494:pharmacology; D000222:Adaptation, Physiological; D000596:Amino Acids / Q000378:metabolism; D000900:Anti-Bacterial Agents / Q000494:pharmacology; D017209:Apoptosis; D001427:Bacterial Toxins / Q000235:genetics / Q000633:toxicity*; D015169:Colony Count, Microbial; D004268:DNA-Binding Proteins / Q000235:genetics / Q000502:physiology; D004722:Endoribonucleases / Q000235:genetics / Q000502:physiology; D004926:Escherichia coli / Q000235:genetics / Q000254:growth & development* / Q000502:physiology; D029968:Escherichia coli Proteins / Q000235:genetics / Q000502:physiology*; D017353:Gene Deletion; D050296:Microbial Viability; D012293:Rifampin / Q000494:pharmacology; D051841:Transcription Factor RelB
chemical_list: D000143:Acids; D000596:Amino Acids; D000900:Anti-Bacterial Agents; D001427:Bacterial Toxins; D004268:DNA-Binding Proteins; D004722:Endoribonucleases; D029968:Escherichia coli Proteins; D012293:Rifampin; C523349:DinJ protein, E coli; C422954:MazE protein, E coli; C422955:MazF protein, E coli; C465567:RelB protein, E coli; D051841:Transcription Factor RelB; C465566:RelE protein, E coli; C523350:YafQ protein, E coli; C484519:YefM protein, E coli; C504245:YoeB protein, E coli; C503487:ChpBK protein, E coli