Escherichia coli MazF Leads to the Simultaneous Selective Synthesis of Both “Death Proteins” and “Survival Proteins”

Abstract

The Escherichia coli mazEF module is one of the most thoroughly studied toxin–antitoxin systems. mazF encodes a stable toxin, MazF, and mazE encodes a labile antitoxin, MazE, which prevents the lethal effect of MazF. MazF is an endoribonuclease that leads to the inhibition of protein synthesis by cleaving mRNAs at ACA sequences. Here, using 2D-gels, we show that in E. coli, although MazF induction leads to the inhibition of the synthesis of most proteins, the synthesis of an exclusive group of proteins, mostly smaller than about 20 kDa, is still permitted. We identified some of those small proteins by mass spectrometry. By deleting the genes encoding those proteins from the E. coli chromosome, we showed that they were required for the death of most of the cellular population. Under the same experimental conditions, which induce mazEF-mediated cell death, other such proteins were found to be required for the survival of a small sub-population of cells. Thus, MazF appears to be a regulator that induces downstream pathways leading to death of most of the population and the continued survival of a small sub-population, which will likely become the nucleus of a new population when growth conditions become less stressful.

MazEF toxin-antitoxin proteins alter Escherichia coli cell morphology and infrastructure during persister formation and regrowth

“…Our findings disfavour the hypothesis that MazF may stimulate stress-induced mutagenesis that could lead to antibiotic-resistant cells [19]. We found that MazFexpressing persisters remained largely viable, in agreement with some studies [8,16,17] but at variance to others [5,18,20,21]. However, only a fraction of persisters could resume growth after expressing MazE to neutralize MazF.…”

“…It was only after cells resumed growth that they became susceptible to lysis and their nucleoids unravelled. Ribosomes were observed outside of the nucleoid region, suggesting that translation is largely shut down in MazF-expressing persisters [20].…”

“…In seeking an explanation for the resumed growth of MazF-expressing cells, we hypothesized that the resumed growth may be caused by DNA mutagenesis (Fig. 1), since MazF stimulates ROS production [19,20]. Mutations in the plasmid-encoded mazF gene seemed to be a good possibility.…”

“…However, other studies suggest that MazF-expressing cells can become irreversibly dormant [18]. MazF has been proposed to elevate cellular mutagenesis through ROS production [19,20] and the SOS response [21]. MazF may induce programmed cell death, dependent on quorum sensing [22], for the benefit of a bacterial population exposed to antibiotics.…”

The ParE2–PaaA2 toxin–antitoxin complex fromEscherichia coliO157 forms a heterodocecamer in solution and in the crystal

“…Various roles have been attributed to TA modules, including selfish entities and the stabilization of labile chromosomal segments (Magnuson, 2007;Van Melderen, 2010). Most researchers nevertheless agree on an involvement in stress response, given that various internal and external stresses lead to their activation (Christensen et al, 2001;Amitai et al, 2009;Kolodkin-Gal et al, 2009) and that at least in some cases differential activation is observed based on the type of stress encountered (Fiebig et al, 2010). However, since knocking out of individual TA modules does not seem to affect bacterial survival upon stress exposure in most bacteria, this may be a secondary effect (Tsilibaris et al, 2007).…”