301
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Blower TR, Short FL, Rao F, Mizuguchi K, Pei XY, Fineran PC, Luisi BF, Salmond GPC. Identification and classification of bacterial Type III toxin-antitoxin systems encoded in chromosomal and plasmid genomes. Nucleic Acids Res 2012; 40:6158-73. [PMID: 22434880 PMCID: PMC3401426 DOI: 10.1093/nar/gks231] [Citation(s) in RCA: 114] [Impact Index Per Article: 9.5] [Reference Citation Analysis] [Abstract] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/22/2022] Open
Abstract
Toxin–antitoxin systems are widespread in bacteria and archaea. They perform diverse functional roles, including the generation of persistence, maintenance of genetic loci and resistance to bacteriophages through abortive infection. Toxin–antitoxin systems have been divided into three types, depending on the nature of the interacting macromolecules. The recently discovered Type III toxin–antitoxin systems encode protein toxins that are inhibited by pseudoknots of antitoxic RNA, encoded by short tandem repeats upstream of the toxin gene. Recent studies have identified the range of Type I and Type II systems within current sequence databases. Here, structure-based homology searches were combined with iterative protein sequence comparisons to obtain a current picture of the prevalence of Type III systems. Three independent Type III families were identified, according to toxin sequence similarity. The three families were found to be far more abundant and widespread than previously known, with examples throughout the Firmicutes, Fusobacteria and Proteobacteria. Functional assays confirmed that representatives from all three families act as toxin–antitoxin loci within Escherichia coli and at least two of the families confer resistance to bacteriophages. This study shows that active Type III toxin–antitoxin systems are far more diverse than previously known, and suggests that more remain to be identified.
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Affiliation(s)
- Tim R Blower
- Department of Biochemistry, University of Cambridge, Cambridge CB2 1QW, UK
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302
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Sevillano L, Díaz M, Yamaguchi Y, Inouye M, Santamaría RI. Identification of the first functional toxin-antitoxin system in Streptomyces. PLoS One 2012; 7:e32977. [PMID: 22431991 PMCID: PMC3303803 DOI: 10.1371/journal.pone.0032977] [Citation(s) in RCA: 31] [Impact Index Per Article: 2.6] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 08/05/2011] [Accepted: 02/03/2012] [Indexed: 11/18/2022] Open
Abstract
Toxin-antitoxin (TA) systems are widespread among the plasmids and genomes of bacteria and archaea. This work reports the first description of a functional TA system in Streptomyces that is identical in two species routinely used in the laboratory: Streptomyces lividans and S. coelicolor. The described system belongs to the YefM/YoeB family and has a considerable similarity to Escherichia coli YefM/YoeB (about 53% identity and 73% similarity). Lethal effect of the S. lividans putative toxin (YoeBsl) was observed when expressed alone in E. coli SC36 (MG1655 ΔyefM-yoeB). However, no toxicity was obtained when co-expression of the antitoxin and toxin (YefM/YoeBsl) was carried out. The toxic effect was also observed when the yoeBsl was cloned in multicopy in the wild-type S. lividans or in a single copy in a S. lividans mutant, in which this TA system had been deleted. The S. lividans YefM/YoeBsl complex, purified from E. coli, binds with high affinity to its own promoter region but not to other three random selected promoters from Streptomyces. In vivo experiments demonstrated that the expression of yoeBsl in E. coli blocks translation initiation processing mRNA at three bases downstream of the initiation codon after 2 minutes of induction. These results indicate that the mechanism of action is identical to that of YoeB from E. coli.
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Affiliation(s)
- Laura Sevillano
- Instituto de Biología Funcional y Genómica/Departamento de Microbiología y Genética, Consejo Superior de Investigaciones Científicas, Universidad de Salamanca, Campus Miguel de Unamuno, Salamanca, Spain
| | - Margarita Díaz
- Instituto de Biología Funcional y Genómica/Departamento de Microbiología y Genética, Consejo Superior de Investigaciones Científicas, Universidad de Salamanca, Campus Miguel de Unamuno, Salamanca, Spain
| | - Yoshihiro Yamaguchi
- Department of Biochemistry, Center for Advanced Biotechnology and Medicine, Robert Wood Johnson Medical School, Piscataway, New Jersey, United States of America
| | - Masayori Inouye
- Department of Biochemistry, Center for Advanced Biotechnology and Medicine, Robert Wood Johnson Medical School, Piscataway, New Jersey, United States of America
| | - Ramón I. Santamaría
- Instituto de Biología Funcional y Genómica/Departamento de Microbiología y Genética, Consejo Superior de Investigaciones Científicas, Universidad de Salamanca, Campus Miguel de Unamuno, Salamanca, Spain
- * E-mail:
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303
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Heaton BE, Herrou J, Blackwell AE, Wysocki VH, Crosson S. Molecular structure and function of the novel BrnT/BrnA toxin-antitoxin system of Brucella abortus. J Biol Chem 2012; 287:12098-110. [PMID: 22334680 DOI: 10.1074/jbc.m111.332163] [Citation(s) in RCA: 42] [Impact Index Per Article: 3.5] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 02/03/2023] Open
Abstract
Type II toxin-antitoxin (TA) systems are expressed from two-gene operons that encode a cytoplasmic protein toxin and its cognate protein antitoxin. These gene cassettes are often present in multiple copies on bacterial chromosomes, where they have been reported to regulate stress adaptation and persistence during antimicrobial treatment. We have identified a novel type II TA cassette in the intracellular pathogen Brucella abortus that consists of the toxin gene, brnT, and its antitoxin, brnA. BrnT is coexpressed and forms a 2:2 tetrameric complex with BrnA, which neutralizes BrnT toxicity. The BrnT(2)-BrnA(2) tetramer binds its own promoter via BrnA, and autorepresses its expression; its transcription is strongly induced in B. abortus by various stressors encountered by the bacterial cell during infection of a mammalian host. Although highly divergent at the primary sequence level, an atomic resolution (1.1 Å) crystal structure of BrnT reveals a secondary topology related to the RelE family of type II ribonuclease toxins. However, overall tertiary structural homology to other RelE family toxins is low. A functional characterization of BrnT by site-directed mutagenesis demonstrates a correspondence between its in vitro activity as a ribonuclease and control of bacteriostasis in vivo. We further present an analysis of the conserved and variable features of structure required for RNA scission in BrnT and the RelE toxin family. This structural investigation informs a model of the RelE-fold as an evolutionarily flexible scaffold that has been selected to bind structurally disparate antitoxins, and exhibit distinct toxin activities including RNA scission and DNA gyrase inhibition.
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Affiliation(s)
- Brook E Heaton
- Committee on Microbiology, University of Chicago, Chicago, Illinois 60637, USA
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304
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Short FL, Blower TR, Salmond GPC. A promiscuous antitoxin of bacteriophage T4 ensures successful viral replication. Mol Microbiol 2012; 83:665-8. [PMID: 22283468 DOI: 10.1111/j.1365-2958.2012.07974.x] [Citation(s) in RCA: 12] [Impact Index Per Article: 1.0] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/21/2023]
Abstract
Bacteria are constantly threatened by predation from bacteriophage parasites and, in response, have evolved an array of resistance mechanisms. These resistance mechanisms then place greater selection pressure on the infecting bacteriophages, which develop counter-strategies in a perpetual 'arms race' between virus and host. Toxin-antitoxin (TA) loci are widespread in bacteria and can confer multiple benefits, including resistance to bacteriophages. The study by Otsuka and Yonesaki, published in this issue of Molecular Microbiology, describes a new plasmid-encoded TA system, lsoAB, which confers resistance to a dmd(-) mutant of bacteriophage T4 through the activity of the LsoA toxin. Infections with wild-type T4, however, are unaffected as the Dmd protein acts as an alternative antitoxin to LsoA, thus preventing its anti-bacteriophage activity. Dmd has also been shown to negate the activity of a related toxin, RnlA. This is a striking result indicating that Dmd can act as a promiscuous antitoxin, binding and inhibiting multiple toxin partners, when antitoxin activity is generally considered to be limited to a single cognate toxin. This study is an exciting addition to both the bacteriophage resistance and TA fields, and suggests a greater role for TA system-based resistance and counter-resistance in the world's oldest predator-prey relationship.
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305
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The ζ toxin induces a set of protective responses and dormancy. PLoS One 2012; 7:e30282. [PMID: 22295078 PMCID: PMC3266247 DOI: 10.1371/journal.pone.0030282] [Citation(s) in RCA: 33] [Impact Index Per Article: 2.8] [Reference Citation Analysis] [Abstract] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 07/06/2011] [Accepted: 12/13/2011] [Indexed: 11/19/2022] Open
Abstract
The ζε module consists of a labile antitoxin protein, ε, which in dimer form (ε2) interferes with the action of the long-living monomeric ζ phosphotransferase toxin through protein complex formation. Toxin ζ, which inhibits cell wall biosynthesis and may be bactericide in nature, at or near physiological concentrations induces reversible cessation of Bacillus subtilis proliferation (protective dormancy) by targeting essential metabolic functions followed by propidium iodide (PI) staining in a fraction (20–30%) of the population and selects a subpopulation of cells that exhibit non-inheritable tolerance (1–5×10−5). Early after induction ζ toxin alters the expression of ∼78 genes, with the up-regulation of relA among them. RelA contributes to enforce toxin-induced dormancy. At later times, free active ζ decreases synthesis of macromolecules and releases intracellular K+. We propose that ζ toxin induces reversible protective dormancy and permeation to PI, and expression of ε2 antitoxin reverses these effects. At later times, toxin expression is followed by death of a small fraction (∼10%) of PI stained cells that exited earlier or did not enter into the dormant state. Recovery from stress leads to de novo synthesis of ε2 antitoxin, which blocks ATP binding by ζ toxin, thereby inhibiting its phosphotransferase activity.
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306
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Jahn N, Preis H, Wiedemann C, Brantl S. BsrG/SR4 from Bacillus subtilis--the first temperature-dependent type I toxin-antitoxin system. Mol Microbiol 2012; 83:579-98. [PMID: 22229825 DOI: 10.1111/j.1365-2958.2011.07952.x] [Citation(s) in RCA: 78] [Impact Index Per Article: 6.5] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/29/2022]
Abstract
Here, we describe bsrG/SR4, a novel type I toxin-antitoxin system from the SPβ prophage region of the Bacillus subtilis chromosome. The 294-nucleotide bsrG RNA encodes a 38-amino-acid toxin, whereas SR4 is a 180-nucleotide antisense RNA that acts as the antitoxin. Both genes overlap by 123 nucleotides. BsrG expression increases at the onset of stationary phase. The sr4 promoter is 6- to 10-fold stronger than the bsrG promoter. Deletion of sr4 stabilizes bsrG mRNA and causes cell lysis on agar plates, which is due to the BsrG peptide and not the bsrG mRNA. SR4 overexpression could compensate cell lysis caused by overexpression of bsrG. SR4 interacts with the 3' UTR of bsrG RNA, thereby promoting its degradation. RNase III cleaves the bsrG RNA/SR4 duplex at position 185 of bsrG RNA, but is not essential for the function of the toxin-antitoxin system. Endoribonuclease Y and 3'-5' exoribonuclease R participate in the degradation of both bsrG RNA and SR4, whereas PnpA processes three SR4 precursors to the mature RNA. A heat shock at 48°C results in faster degradation and, therefore, significantly decreased amounts of bsrG RNA.
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Affiliation(s)
- Natalie Jahn
- Friedrich-Schiller-Universität Jena, Biologisch-Pharmazeutische Fakultät, AG Bakteriengenetik, Philosophenweg 12, Jena, Germany
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307
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Hong SH, Wang X, O'Connor HF, Benedik MJ, Wood TK. Bacterial persistence increases as environmental fitness decreases. Microb Biotechnol 2012; 5:509-22. [PMID: 22221537 PMCID: PMC3323757 DOI: 10.1111/j.1751-7915.2011.00327.x] [Citation(s) in RCA: 112] [Impact Index Per Article: 9.3] [Reference Citation Analysis] [Abstract] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/21/2023] Open
Abstract
Since persister cells cause chronic infections and since Escherichia coli toxin MqsR increases persisters, we used protein engineering to increase the toxicity of MqsR to gain insights into persister cell formation. Through two amino acid replacements that increased the stability of MqsR, toxicity and persistence were increased. A whole‐transcriptome study revealed that the MqsR variant increased persistence by repressing genes for acid resistance, multidrug resistance and osmotic resistance. Corroborating these microarray results, deletion of rpoS, as well as the genes that the master stress response regulator RpoS controls, increased persister formation dramatically to the extent that nearly the whole population became persistent. Furthermore, wild‐type cells stressed by prior treatment to acid or hydrogen peroxide increased persistence 12 000‐fold. Whole‐transcriptome analyses of persister cells generated by two different methods (wild‐type cells pretreated with hydrogen peroxide and the rpoS deletion) corroborated the importance of suppressing RpoS in persister cell formation. Therefore, the more toxic MqsR increases persistence by decreasing the ability of the cell to respond to antibiotic stress through its RpoS‐based regulation of acid resistance, multidrug resistance and osmotic resistance systems.
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Affiliation(s)
- Seok Hoon Hong
- Departments of Chemical Engineering Biology, Texas A&M University, College Station, TX 77843-3122, USA
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308
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The Proteolytic Activation of the relNEs (ssr1114/slr0664) Toxin–Antitoxin System by Both Proteases Lons and ClpP2s/Xs of Synechocystis sp. PCC 6803. Curr Microbiol 2011; 63:496-502. [DOI: 10.1007/s00284-011-0011-5] [Citation(s) in RCA: 16] [Impact Index Per Article: 1.2] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 07/20/2011] [Accepted: 08/25/2011] [Indexed: 10/17/2022]
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309
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Wang X, Wood TK. Toxin-antitoxin systems influence biofilm and persister cell formation and the general stress response. Appl Environ Microbiol 2011; 77:5577-83. [PMID: 21685157 PMCID: PMC3165247 DOI: 10.1128/aem.05068-11] [Citation(s) in RCA: 314] [Impact Index Per Article: 24.2] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/29/2023] Open
Abstract
In many genomes, toxin-antitoxin (TA) systems have been identified; however, their role in cell physiology has been unclear. Here we examine the evidence that TA systems are involved in biofilm formation and persister cell formation and that these systems may be important regulators of the switch from the planktonic to the biofilm lifestyle as a stress response by their control of secondary messenger 3',5'-cyclic diguanylic acid. Specifically, upon stress, the sequence-specific mRNA interferases MqsR and MazF mediate cell survival. In addition, we propose that TA systems are not redundant, as they may have developed to respond to specific stresses.
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Affiliation(s)
- Xiaoxue Wang
- Department of Chemical Engineering, Texas A&M University, College Station, Texas 77843-3122
- Key Laboratory of Marine Bio-Resource Sustainable Utilization, the South China Sea Institute of Oceanology, Chinese Academy of Sciences, Guangzhou 510301, People's Republic of China
| | - Thomas K. Wood
- Department of Chemical Engineering, Texas A&M University, College Station, Texas 77843-3122
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310
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Mutschler H, Meinhart A. ε/ζ systems: their role in resistance, virulence, and their potential for antibiotic development. J Mol Med (Berl) 2011; 89:1183-94. [PMID: 21822621 PMCID: PMC3218275 DOI: 10.1007/s00109-011-0797-4] [Citation(s) in RCA: 66] [Impact Index Per Article: 5.1] [Reference Citation Analysis] [Abstract] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 06/20/2011] [Revised: 07/19/2011] [Accepted: 07/22/2011] [Indexed: 12/17/2022]
Abstract
Cell death in bacteria can be triggered by activation of self-inflicted molecular mechanisms. Pathogenic bacteria often make use of suicide mechanisms in which the death of individual cells benefits survival of the population. Important elements for programmed cell death in bacteria are proteinaceous toxin-antitoxin systems. While the toxin generally resides dormant in the bacterial cytosol in complex with its antitoxin, conditions such as impaired de novo synthesis of the antitoxin or nutritional stress lead to antitoxin degradation and toxin activation. A widespread toxin-antitoxin family consists of the ε/ζ systems, which are distributed over plasmids and chromosomes of various pathogenic bacteria. In its inactive state, the bacteriotoxic ζ toxin protein is inhibited by its cognate antitoxin ε. Upon degradation of ε, the ζ toxin is released allowing this enzyme to poison bacterial cell wall synthesis, which eventually triggers autolysis. ε/ζ systems ensure stable plasmid inheritance by inducing death in plasmid-deprived offspring cells. In contrast, chromosomally encoded ε/ζ systems were reported to contribute to virulence of pathogenic bacteria, possibly by inducing autolysis in individual cells under stressful conditions. The capability of toxin-antitoxin systems to kill bacteria has made them potential targets for new therapeutic compounds. Toxin activation could be hijacked to induce suicide of bacteria. Likewise, the unique mechanism of ζ toxins could serve as template for new drugs. Contrarily, inhibition of virulence-associated ζ toxins might attenuate infections. Here we provide an overview of ε/ζ toxin-antitoxin family and its potential role in the development of new therapeutic approaches in microbial defense.
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Affiliation(s)
- Hannes Mutschler
- Department of Biomolecular Mechanisms, Max Planck Institute for Medical Research, Heidelberg, Germany
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311
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Hayes F, Van Melderen L. Toxins-antitoxins: diversity, evolution and function. Crit Rev Biochem Mol Biol 2011; 46:386-408. [PMID: 21819231 DOI: 10.3109/10409238.2011.600437] [Citation(s) in RCA: 196] [Impact Index Per Article: 15.1] [Reference Citation Analysis] [Abstract] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/16/2022]
Abstract
Genes for toxin-antitoxin (TA) complexes are widespread in prokaryote genomes, and species frequently possess tens of plasmid and chromosomal TA loci. The complexes are categorized into three types based on genetic organization and mode of action. The toxins universally are proteins directed against specific intracellular targets, whereas the antitoxins are either proteins or small RNAs that neutralize the toxin or inhibit toxin synthesis. Within the three types of complex, there has been extensive evolutionary shuffling of toxin and antitoxin genes leading to considerable diversity in TA combinations. The intracellular targets of the protein toxins similarly are varied. Numerous toxins, many of which are sequence-specific endoribonucleases, dampen protein synthesis levels in response to a range of stress and nutritional stimuli. Key resources are conserved as a result ensuring the survival of individual cells and therefore the bacterial population. The toxin effects generally are transient and reversible permitting a set of dynamic, tunable responses that reflect environmental conditions. Moreover, by harboring multiple toxins that intercede in protein synthesis in response to different physiological cues, bacteria potentially sense an assortment of metabolic perturbations that are channeled through different TA complexes. Other toxins interfere with the action of topoisomersases, cell wall assembly, or cytoskeletal structures. TAs also play important roles in bacterial persistence, biofilm formation and multidrug tolerance, and have considerable potential both as new components of the genetic toolbox and as targets for novel antibacterial drugs.
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Affiliation(s)
- Finbarr Hayes
- Faculty of Life Sciences and Manchester Interdisciplinary Biocentre, The University of Manchester, Manchester, UK.
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