Single-Cell Analysis Reveals Cryptic Prophage Protease LfgB ProtectsEscherichia coliDuring Oxidative Stress by Cleaving Antitoxin MqsA

Abstract

ABSTRACTAlthough toxin/antitoxin (TA) systems are ubiquitous, beyond phage inhibition and mobile element stabilization, their role in host metabolism is obscure. One of the best-characterized TA systems is MqsR/MqsA ofEscherichia coli, which has been linked previously to protecting this gastrointestinal species during the stress it encounters from the bile salt deoxycholate as it colonizes humans. However, some recent whole-population studies have challenged the role of toxins such as MqsR in bacterial physiology, since themqsRAlocus is induced over a hundred-fold during stress, but a phenotype was not found upon its deletion. Here, we investigate further the role MqsR/MqsA by utilizing single cells and demonstrate that upon oxidative stress, the TA system MqsR/MqsA has a heterogeneous effect on the transcriptome of single cells. Furthermore, we discovered that MqsR activation leads to induction of the poorly-characterizedyfjXY ypjJ yfjZFoperon of cryptic prophage CP4-57. Moreover, deletion ofyfjYmakes the cells sensitive to H2O2, acid, and heat stress, and this phenotype was complemented. Hence, we recommendyfjYbe renamed tolfgB(less fatalitygeneB). Critically, MqsA represseslfgBby binding the operon promoter, and LfgB is a protease that degrades MqsA to derepressrpoSand facilitate the stress response. Therefore, the MqsR/MqsA TA system facilitates the stress response through cryptic phage protease LfgB.