Programmed cell death in Escherichia coli: some antibiotics can trigger mazEF lethality

Abstract

The discovery of toxin-antitoxin gene pairs (also called addiction modules) on extrachromosomal elements of Escherichia coli, and particularly the discovery of homologous modules on the bacterial chromosome, suggest that a potential for programmed cell death may be inherent in bacterial cultures. We have reported on the E. coli mazEF system, a regulatable addiction module located on the bacterial chromosome. MazF is a stable toxin and MazE is a labile antitoxin. Here we show that cell death mediated by the E. coli mazEF module can be triggered by several antibiotics (rifampicin, chloramphenicol, and spectinomycin) that are general inhibitors of transcription and/or translation. These antibiotics inhibit the continuous expression of the labile antitoxin MazE, and as a result, the stable toxin MazF causes cell death. Our results have implications for the possible mode(s) of action of this group of antibiotics.

FIG. 1

Antibiotics that inhibit transcription and/or translation in E. coli induce mazEF-dependent cell death. Viability plotted against the time of exposure to rifampin (A) and chloramphenicol (B) in M9 medium of E. coli MC4100 relA⁺ (WT) (x) and its ΔmazEF (ΔEF) (O) and ΔclpP (Δ) derivatives is shown. (C) The viability of E. coli MC4100 relA⁺ (WT) and its ΔmazEF (ΔEF) and ΔclpP derivatives in M9 medium either untreated (C, control) or treated for 10 min with rifampin (Rif), chloramphenicol (Cam), spectinomycin (Spc), or ampicillin (Amp). (D) As for panel C but in LB medium. (E) The effects in M9 medium of the antibiotics (untreated cells, □; rifampin, ■; chloram phenicol, ●; spectinomycin, ▴) on protein synthesis in E. coli MC4100 relA⁺. (F) As for panel E but in the derivative strain MC4100 relA⁺ ΔmazEF. The effects of the antibiotics on mazEF-mediated killing and on protein synthesis were measured as described in Materials and Methods.

FIG. 2

Antibiotics that inhibit transcription and/or translation in E. coli affect the level of MazE. (A) The level of E. coli MazE in M9 medium. (B) The level of E. coli MazE in LB medium. (C) The level of E. coli TrpR protein in M9 medium. The experiments were carried out with E. coli strain MC4100 relA⁺ for 90 min in the presence of rifampicin, chloramphenicol, or spectinomycin or without any antibiotics (control) as described in Materials and Methods.

FIG. 3

A schematic representation of the induction of the E. coli mazEF-mediated cell death by antibiotics that inhibit transcription and/or translation (see the text).