Bistable Expression of a Toxin-Antitoxin System Located in a Cryptic Prophage of Escherichia coli O157:H7
Dukas Jurėnas, Nathan Fraikin, Frédéric Goormaghtigh, Pieter De Bruyn, Alexandra Vandervelde, Safia Zedek, Thomas Jové, Daniel Charlier, Remy Loris, Laurence Van Melderen
Abstract
Transcriptional regulation of bacterial toxin-antitoxin (TA) systems allows compensation of toxin and antitoxin proteins to maintain a neutral state and avoid cell intoxication unless TA genes are lost. Such models have been primarily studied in plasmids, but TAs are equally present in other mobile genetic elements, such as transposons and prophages. Here, we demonstrate that the expression of a TA system located in a lambdoid cryptic prophage is transcriptionally coupled to the prophage immunity region and relies on phage transcription factors. Moreover, competition between transcription factors results in bistable expression, which generates cell-to-cell heterogeneity in the population, but without, however, leading to any detectable phenotype, even in cells expressing the TA system. We show that despite the lack of protein sequence similarity, this locus retains major lambda prophage regulation features.