Escherichia coli Stress, Multi-cellularity, and the Generation of the Quorum Sensing Peptide EDF.

Bacterial communication via quorum sensing (QS) molecules, as well as toxin-antitoxin (TA) gene modules located on bacterial chromosomes are well-studied mechanisms. Escherichia coli mazEF is a stress-induced TA system mediating cell death requiring a QS extracellular death factor (EDF), the pentapeptide NNWNN. MazF is an endoribonuclease specific for ACA sites. During adverse conditions, the activated MazF generates a stress induced translation machinery, composed of MazF-processed mRNAs and selective ribosomes that specifically translate these processed mRNAs. Moreover, we identified the molecular mechanism underlying the formation of EDF from the zwf mRNA that involves distinct steps comprising the activity of MazF, the trans-translation system as well as the protease ClpPX. Bacterial trans-translation is generally known as a quality control process that rescues stalled translation complexes at the 3'-terminus of non-stop mRNAs. Our results indicate that trans-translation has a similar role in EDF generation from zwf mRNA. However, our data reveal that the trans-translation system may also provide a regulatory mechanism to attenuate EDF generation in the single cells. Thereby, the required threshold of EDF molecules is only achieved by the entire bacterial population, as expected for a genuine QS process.