Two Programmed Cell Death Systems in <em>Escherichia coli</em>: An Apoptotic-Like Death Is Inhibited by the <em>mazEF</em>-Mediated Death Pathway

<div><p>In eukaryotes, the classical form of programmed cell death (PCD) is apoptosis, which has as its specific characteristics DNA fragmentation and membrane depolarization. In <em>Escherichia coli</em> a different PCD system has been reported. It is mediated by the toxin–antitoxin system module <em>mazEF</em>. The <em>E. coli mazEF</em> module is one of the most thoroughly studied toxin–antitoxin systems. <em>mazF</em> encodes a stable toxin, MazF, and <em>mazE</em> encodes a labile antitoxin, MazE, which prevents the lethal effect of MazF. <em>mazEF</em>-mediated cell death is a population phenomenon requiring the quorum-sensing pentapeptide NNWNN designated Extracellular Death Factor (EDF). <em>mazEF</em> is triggered by several stressful conditions, including severe damage to the DNA. Here, using confocal microscopy and FACS analysis, we show that under conditions of severe DNA damage, the triggered <em>mazEF</em>-mediated cell death pathway leads to the inhibition of a second cell death pathway. The latter is an apoptotic-like death (ALD); ALD is mediated by <em>recA</em> and <em>lexA</em>. The <em>mazEF</em>-mediated pathway reduces <em>recA</em> mRNA levels. Based on these results, we offer a molecular model for the maintenance of an altruistic characteristic in cell populations. In our model, the ALD pathway is inhibited by the altruistic EDF-<em>mazEF</em>-mediated death pathway.</p> </div>