Autoregulation of mazEF expression underlies growth heterogeneity in bacterial populations

Abstract

The MazF toxin sequence-specifically cleaves single-stranded RNA upon various stressful conditions, and it is activated as a part of the mazEF toxin–antitoxin module in Escherichia coli. Although autoregulation of mazEF expression through the MazE antitoxin-dependent transcriptional repression has been biochemically characterized, less is known about post-transcriptional autoregulation, as well as how both of these autoregulatory features affect growth of single cells during conditions that promote MazF production. Here, we demonstrate post-transcriptional autoregulation of mazF expression dynamics by MazF cleaving its own transcript. Single-cell analyses of bacterial populations during ectopic MazF production indicated that two-level autoregulation of mazEF expression influences cell-to-cell growth rate heterogeneity. The increase in growth rate heterogeneity is governed by the MazE antitoxin, and tuned by the MazF-dependent mazF mRNA cleavage. Also, both autoregulatory features grant rapid exit from the stress caused by mazF overexpression. Time-lapse microscopy revealed that MazF-mediated cleavage of mazF mRNA leads to increased temporal variability in length of individual cells during ectopic mazF overexpression, as explained by a stochastic model indicating that mazEF mRNA cleavage underlies temporal fluctuations in MazF levels during stress.

Excitable dynamics through toxin-induced mRNA cleavage in bacteria

“…This behavior is shown in Fig. 1B using a similar model and parameters as in [19]. 76 Interestingly, we find that toxin excitations are only present if the cleavage of mRNA by 77 the toxins is included in the model ( Fig.…”

“…Toxin-antitoxin modules have been implicated in plasmid 17 maintenance, abortive phage infections, the response of bacterial cells to nutritional 18 stress and the formation of persister cells [3,10]. These are cells that are tolerant to 19 multiple antibiotics because they are in a temporary state of dormancy [11]. Such a 20 period of persistence has been attributed to an increase in the free toxin concentration.…”

“…In this article we focus on the effect of the cleavage of mRNA in the presence of elevated toxin levels, which has been recently shown to cause toxin excitations [19]. We 48 use a simplified system, where we leave out the formation of the complex TAT and the 49 transcriptional regulation, as this is the simplest toxin-antitoxin model system that still 50 displays the spikes in the free toxin concentration.…”

“…Toxin-induced mRNA cleavage leads to toxin excitations 72 Recently, it has been demonstrated experimentally that MazF toxins cleave mRNA in 73 stressful conditions [19], leading to cell growth heterogeneity. Moreover, using stochastic 74 Gillespie modeling, the authors showed that this mechanism induces toxin excitations.…”

“…The variables and parameters can be found in table 1 and table 2, where most 95 parameters have been experimentally measured or motivated, see [16,19]. DNA is 96 transcribed to mRNA [M] with a constant transcription rate r F .…”