mazEF : a chromosomal toxin-antitoxin module that triggers programmed cell death in bacteria

481

545

Various mechanisms exist that enable bacteria to resist bacteriophage infection. Resistance strategies include the abortive infection (Abi) systems, which promote cell death and limit phage replication within a bacterial population. A highly effective 2-gene Abi system from the phytopathogen Erwinia carotovora subspecies atroseptica, designated ToxIN, is described. The ToxIN Abi system also functions as a toxin-antitoxin (TA) pair, with ToxN inhibiting bacterial growth and the tandemly repeated ToxI RNA antitoxin counteracting the toxicity. TA modules are currently divided into 2 classes, protein and RNA antisense. We provide evidence that ToxIN defines an entirely new TA class that functions via a novel protein-RNA mechanism, with analogous systems present in diverse bacteria. Despite the debated role of TA systems, we demonstrate that ToxIN provides viral resistance in a range of bacterial genera against multiple phages. This is the first demonstration of a novel mechanistic class of TA systems and of an Abi system functioning in different bacterial genera, both with implications for the dynamics of phage-bacterial interactions.Bacteriophage ͉ Bacteriostasis ͉ Erwinia ͉ plasmid ͉ resistance

Section: Discussionmentioning

confidence: 99%

The phage abortive infection system, ToxIN, functions as a protein–RNA toxin–antitoxin pair

Fineran

Blower

Foulds

et al. 2009

481

545

“…MazE is a labile protein that is degraded by the ClpA protease; thus, in the absence of the genes encoding mazEF, the cellular MazE concentration drops rapidly, leaving MazF to kill or inhibit the growth of the cell (51). The MazF toxin is an endoribonuclease that is specific for ACA sequences (52)(53)(54), and its degradation of mRNA in this manner is believed to lead to the observed bacterial cell death (55). Although mazEF orthologs with varying degrees of homology are present on other bacterial chromosomes (31), including three mazEF homologs on the E. faecalis V583 genome and one on the V583 plasmid pTEF1 (33), the PCR products investigated in this study show surprisingly strong sequence similarity to the mazEF genes from the E. coli K12 genome.…”

Section: Discussionmentioning

confidence: 99%

“…Although mazEF orthologs with varying degrees of homology are present on other bacterial chromosomes (31), including three mazEF homologs on the E. faecalis V583 genome and one on the V583 plasmid pTEF1 (33), the PCR products investigated in this study show surprisingly strong sequence similarity to the mazEF genes from the E. coli K12 genome. Although its role on the E. coli chromosome is not entirely clear, mazEF appears to be a ''stressinduced suicide module'' (55), because it triggers cell death under conditions of amino acid starvation signals (41), antibiotic treatment (56), phage infection (57), thymine starvation (58), oxidative stress, and high temperatures (55). The role of the chromosomally encoded mazEF TA system in E. coli stress response has been reviewed extensively (11,40,55).…”

Section: Discussionmentioning

confidence: 99%

“…Although its role on the E. coli chromosome is not entirely clear, mazEF appears to be a ''stressinduced suicide module'' (55), because it triggers cell death under conditions of amino acid starvation signals (41), antibiotic treatment (56), phage infection (57), thymine starvation (58), oxidative stress, and high temperatures (55). The role of the chromosomally encoded mazEF TA system in E. coli stress response has been reviewed extensively (11,40,55).…”

Section: Discussionmentioning

confidence: 99%

See 1 more Smart Citation

Toxin–antitoxin systems are ubiquitous and plasmid-encoded in vancomycin-resistant enterococci

Moritz¹,

Hergenrother

2007

125

127

Vancomycin-resistant enterococci (VRE) are common hospital pathogens that are resistant to most major classes of antibiotics. The incidence of VRE is increasing rapidly, to the point where over one-quarter of enterococcal infections in intensive care units are now resistant to vancomycin. The exact mechanism by which VRE maintains its plasmid-encoded resistance genes is ill-defined, and novel targets for the treatment of VRE are lacking. In an effort to identify novel protein targets for the treatment of VRE infections, we probed the plasmids obtained from 75 VRE isolates for the presence of toxin-antitoxin (TA) gene systems. Remarkably, genes for one particular TA pair, the mazEF system (originally identified on the Escherichia coli chromosome), were present on plasmids from 75/75 (100%) of the isolates. Furthermore, mazEF was on the same plasmid as vanA in the vast majority of cases (>90%). Plasmid stability tests and RT-PCR raise the possibility that this plasmidencoded mazEF is indeed functional in enterococci. Given this ubiquity of mazEF in VRE and the deleterious activity of the MazF toxin, disruption of mazEF with pharmacological agents is an attractive strategy for tailored antimicrobial therapy.antibiotics ͉ mazEF ͉ axe-txe ͉ relbE ͉ VRE E nterococci are the leading cause of surgical-site infections and the third leading cause of urinary tract and bloodstream infections (1, 2) and are implicated in bacterial endocarditis, intraabdominal infections, bacteremia, and meningitis (3). The intrinsic resistance of enterococci to cephalosporin and aminoglycoside antibiotics complicates treatment strategies. Historically, vancomycin has been effective in the management of enterococcal infections; however, after nearly 30 years of use, vancomycin-resistant enterococci (VRE) emerged in the mid-1980s. In a short time span, intensive care units in the U.S. have seen a dramatic increase in the percentage of enterococcal infections that are resistant to vancomycin, from 0. 4% in 1989 to 25% in 1999 (3). In fact, in a recent study, 60% of Enterococcus faecium clinical isolates were resistant to vancomycin (4).The genes encoding the elaborate protein systems that mediate vancomycin resistance generally reside on mobile genetic elements within the enterococci. In some cases, plasmids with the various vancomycin resistance gene clusters have been recovered from enterococci (5-8), although the prevalence of plasmid-encoded resistance in VRE has not been defined. Large plasmids often have intricate mechanisms by which they maintain themselves in the bacterial population. Some plasmids contain genes encoding postsegregational killing ''plasmid addiction'' systems (9, 10), in which the plasmid encodes a potent toxin and a labile antitoxin. Provided the plasmid is present, the antitoxin binds to and sequesters the toxin. However, if a plasmid-free daughter cell arises, the unstable antitoxin is degraded, and the toxic protein kills the bacterial cell from within.If toxin-antitoxin (TA) systems are prevalent and functional on ...

“…This quasidormant state can be rapidly reversed if the stressor is removed within a certain window of time, triggering the production of antitoxin that sequesters free toxin. Once cells pass beyond this reversible window of time into a ''point of no return,'' they can no longer be rescued from their quasidormant state (4)(5)(6). Therefore, chromosomal TA toxin action only leads to cell death (proposed to represent a type of programmed cell death distinct from apoptosis in eukaryotic systems) if and when the cell reaches the limit of its capacity to either sustain quasidormancy and/or lose the ability to initiate the synthesis of enough antitoxin to reverse toxin action upon release from stress.…”

mentioning

confidence: 99%

Bacterial addiction module toxin Doc inhibits translation elongation through its association with the 30S ribosomal subunit

Liu¹,

Zhang²,

Inouye³

et al. 2008

119

103

Bacterial toxin-antitoxin (TA) systems (or ''addiction modules'') typically facilitate cell survival during intervals of stress by inducing a state of reversible growth arrest. However, upon prolonged stress, TA toxin action leads to cell death. TA systems have also been implicated in several clinically important phenomena: biofilm formation, bacterial persistence during antibiotic treatment, and bacterial pathogenesis. TA systems harbored by pathogens also serve as attractive antibiotic targets. To date, the mechanism of action of the majority of known TA toxins has not yet been elucidated. We determined the mode of action of the Doc toxin of the Phd-Doc TA system. Doc expression resulted in rapid cell growth arrest and marked inhibition of translation without significant perturbation of transcription or replication. However, Doc did not cleave mRNA as do other addiction-module toxins whose activities result in translation inhibition. Instead, Doc induction mimicked the effects of treatment with the aminoglycoside antibiotic hygromycin B (HygB): Both Doc and HygB interacted with 30S ribosomal subunits, stabilized polysomes, and resulted in a significant increase in mRNA half-life. HygB also competed with ribosome-bound Doc, whereas HygB-resistant mutants suppressed Doc toxicity, suggesting that the Doc-binding site includes that of HygB (i.e., helix 44 region of 16S rRNA containing the A, P, and E sites). Overall, our results illuminate an intracellular target and mechanism of TA toxin action drawn from aminoglycoside antibiotics: Doc toxicity is the result of inhibition of translation elongation, possibly at the translocation step, through its interaction with the 30S ribosomal subunit.antitoxin ͉ hygromycin B ͉ bacteriophage P1 ͉ 16S rRNA ͉ postsegregational killing