1
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Dufour D, Li H, Gong SG, Lévesque CM. Transcriptome Analysis of Streptococcus mutans Quorum Sensing-Mediated Persisters Reveals an Enrichment in Genes Related to Stress Defense Mechanisms. Genes (Basel) 2023; 14:1887. [PMID: 37895236 PMCID: PMC10606796 DOI: 10.3390/genes14101887] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 09/01/2023] [Revised: 09/22/2023] [Accepted: 09/27/2023] [Indexed: 10/29/2023] Open
Abstract
Persisters are a small fraction of growth-arrested phenotypic variants that can survive lethal concentrations of antibiotics but are able to resume growth once antibiotics are stopped. Their formation can be a stochastic process or one triggered by environmental cues. In the human pathogen Streptococcus mutans, the canonical peptide-based quorum-sensing system is an inducible DNA repair system that is pivotal for bacterial survival. Previous work has shown that the CSP-signaling peptide is a stress-signaling alarmone that promotes the formation of stress-induced persisters. In this study, we exposed S. mutans to the CSP pheromone to mimic DNA damage conditions and isolated the antibiotic persisters by treating the cultures with ofloxacin. A transcriptome analysis was then performed to evaluate the differential gene expression between the normal stationary-phase cells and the persisters. RNA sequencing revealed that triggered persistence was associated with the upregulation of genes related to several stress defense mechanisms, notably, multidrug efflux pumps, the arginine deaminase pathway, and the Opu/Opc system. In addition, we showed that inactivation of the VicK kinase of the YycFG essential two-component regulatory system abolished the formation of triggered persisters via the CSP pheromone. These data contribute to the understanding of the triggered persistence phenotype and may suggest new therapeutic strategies for treating persistent streptococcal infections.
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Affiliation(s)
| | | | | | - Céline M. Lévesque
- Faculty of Dentistry, University of Toronto, Toronto, ON M5G 1G6, Canada; (D.D.); (H.L.); (S.-G.G.)
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2
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Li L, Krieger M, Qin H, Zou Z, Kreth J, Merritt J. Adaptation of Prokaryotic Toxins for Negative Selection and Cloning-Independent Markerless Mutagenesis in Streptococcus Species. mSphere 2023:e0068222. [PMID: 37093065 DOI: 10.1128/msphere.00682-22] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 04/25/2023] Open
Abstract
The Streptococcus mutans genetic system offers a variety of strategies to rapidly engineer targeted chromosomal mutations. Previously, we reported the first S. mutans negative selection system that functions in a wild-type background. This system utilizes induced sensitivity to the toxic amino acid analog p-chlorophenylalanine (4-CP) as a negative selection mechanism and was developed for counterselection-based cloning-independent markerless mutagenesis (CIMM). While we have employed this system extensively for our ongoing genetic studies, we have encountered a couple limitations with the system, mainly its narrow host range and the requirement for selection on a toxic substrate. Here, we report the development of a new negative selection system that addresses both limitations, while still retaining the utility of the previous 4-CP-based markerless mutagenesis system. We placed a variety of toxin-encoding genes under the control of the xylose-inducible gene expression cassette (Xyl-S) and found the Fst-sm and ParE toxins to be suitable candidates for inducible negative selection. We combined the inducible toxins with an antibiotic resistance gene to create several different counterselection cassettes. The most broadly useful of these contained a wild-type fst-sm open reading frame transcriptionally fused to a point mutant form of the Xyl-S expression system, which we subsequently named IFDC4. IFDC4 was shown to exhibit exceptionally low background resistance, with 3- to 4-log reductions in cell number observed when plating on xylose-supplemented medium. IFDC4 also functioned similarly in multiple strains of S. mutans as well as with Streptococcus gordonii and Streptococcus sanguinis. We performed CIMM with IFDC4 and successfully engineered a variety of different types of markerless mutations in all three species. The counterselection strategy described here provides a template approach that should be adaptable for the creation of similar counterselection systems in many other bacteria. IMPORTANCE Multiple medically significant Streptococcus species, such as S. mutans, have highly sophisticated genetic systems available, largely as a consequence of their amenability to genetic manipulation via natural competence. Despite this, few options are available for the creation of markerless mutations in streptococci, especially within wild-type strains. Markerless mutagenesis is a critical tool for genetic studies, as it allows the user to explore many fundamental questions that are not easily addressable using marked mutagenesis. Here, we describe a new approach for streptococcal markerless mutagenesis that offers a variety of advantages over the current approach, which employs induced sensitivity to the toxic substrate 4-CP. The approach employed here should be readily adaptable for the creation of similar markerless mutagenesis systems in other organisms.
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Affiliation(s)
- Lena Li
- Department of Restorative Dentistry, Oregon Health and Science University, Portland, Oregon, USA
| | - Madeline Krieger
- Department of Restorative Dentistry, Oregon Health and Science University, Portland, Oregon, USA
| | - Hua Qin
- Department of Restorative Dentistry, Oregon Health and Science University, Portland, Oregon, USA
| | - Zhengzhong Zou
- Department of Restorative Dentistry, Oregon Health and Science University, Portland, Oregon, USA
| | - Jens Kreth
- Department of Restorative Dentistry, Oregon Health and Science University, Portland, Oregon, USA
- Department of Molecular Microbiology and Immunology, Oregon Health and Science University, Portland, Oregon, USA
| | - Justin Merritt
- Department of Restorative Dentistry, Oregon Health and Science University, Portland, Oregon, USA
- Department of Molecular Microbiology and Immunology, Oregon Health and Science University, Portland, Oregon, USA
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3
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Gaio V, Lima T, Vilanova M, Cerca N, França A. mazEF Homologue Has a Minor Role in Staphylococcus epidermidis 1457 Virulence Potential. Front Cell Infect Microbiol 2022; 11:803134. [PMID: 35096651 PMCID: PMC8792614 DOI: 10.3389/fcimb.2021.803134] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 10/27/2021] [Accepted: 12/06/2021] [Indexed: 11/17/2022] Open
Abstract
Staphylococcus epidermidis biofilm cells are characterized by increased antimicrobial tolerance and improved ability to evade host immune system defenses. These features are, in part, due to the presence of viable but non-culturable (VBNC) cells. A previous study identified genes potentially involved in VBNC cells formation in S. epidermidis biofilms, among which SERP1682/1681 raised special interest due to their putative role as a toxin–antitoxin system of the mazEF family. Herein, we constructed an S. epidermidis mutant lacking the mazEF genes homologues and determined their role in (i) VBNC state induction during biofilm formation, (ii) antimicrobial susceptibility, (iii) survival in human blood and plasma, and (iv) activation of immune cells. Our results revealed that mazEF homologue did not affect the proportion of VBNC cells in S. epidermidis 1457, refuting the previous hypothesis that mazEF homologue could be linked with the emergence of VBNC cells in S. epidermidis biofilms. Additionally, mazEF homologue did not seem to influence key virulence factors on this strain, since its deletion did not significantly affect the mutant biofilm formation capacity, antimicrobial tolerance or the response by immune cells. Surprisingly, our data suggest that mazEF does not behave as a toxin–antitoxin system in S. epidermidis strain 1457, since no decrease in the viability and culturability of bacteria was found when only the mazF toxin homologue was being expressed.
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Affiliation(s)
- Vânia Gaio
- Laboratory of Research in Biofilms Rosário Oliveira, Centre of Biological Engineering, University of Minho, Braga, Portugal
| | - Tânia Lima
- Instituto de Investigação e Inovação em Saúde, Universidade do Porto, Porto, Portugal.,Instituto de Biologia Molecular e Celular, Universidade do Porto, Porto, Portugal
| | - Manuel Vilanova
- Instituto de Investigação e Inovação em Saúde, Universidade do Porto, Porto, Portugal.,Instituto de Biologia Molecular e Celular, Universidade do Porto, Porto, Portugal.,Instituto de Ciências Biomédicas de Abel Salazar, Universidade do Porto, Porto, Portugal
| | - Nuno Cerca
- Laboratory of Research in Biofilms Rosário Oliveira, Centre of Biological Engineering, University of Minho, Braga, Portugal
| | - Angela França
- Laboratory of Research in Biofilms Rosário Oliveira, Centre of Biological Engineering, University of Minho, Braga, Portugal
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4
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Genetic Analysis of Mutacin B-Ny266, a Lantibiotic Active against Caries Pathogens. J Bacteriol 2020; 202:JB.00762-19. [PMID: 32229530 DOI: 10.1128/jb.00762-19] [Citation(s) in RCA: 5] [Impact Index Per Article: 1.3] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 12/05/2019] [Accepted: 03/27/2020] [Indexed: 12/18/2022] Open
Abstract
Bacteriocins are ribosomally synthesized proteinaceous antibacterial peptides. They selectively interfere with the growth of other bacteria. The production and secretion of bacteriocins confer a distinct ecological advantage to the producer in competing against other bacteria that are present in the same ecological niche. Streptococcus mutans, a significant contributor to the development of dental caries, is one of the most prolific producers of bacteriocins, known as mutacins in S. mutans In this study, we characterized the locus encoding mutacin B-Ny266, a lantibiotic with a broad spectrum of activity. The chromosomal locus is composed of six predicted operon structures encoding proteins involved in regulation, antimicrobial activity, biosynthesis, modification, transport, and immunity. Mutacin B-Ny266 was purified from semisolid cultures, and two inhibitory peptides, LanA and LanA', were detected. Both peptides were highly modified. Such modifications include dehydration of serine and threonine and the formation of a C-terminal aminovinyl-cysteine (AviCys) ring. While LanA peptide alone is absolutely required for antimicrobial activity, the presence of LanA' enhanced the activity of LanA, suggesting that B-Ny266 may function as a two-peptide lantibiotic. The activation of lanAA' expression is most likely controlled by the conserved two-component system NsrRS, which is activated by LanA peptide but not by LanA'. The chromosomal locus encoding mutacin B-Ny266 was not universally conserved in all sequenced S. mutans genomes. Intriguingly, the genes encoding LanAA' peptides were restricted to the most invasive serotypes of S. mutans IMPORTANCE Although dental caries is largely preventable, it remains the most common and costly infectious disease worldwide. Caries is initiated by the presence of dental plaque biofilm that contains Streptococcus mutans, a species extensively characterized by its role in caries development and formation. S. mutans deploys an arsenal of strategies to establish itself within the oral cavity. One of them is the production of bacteriocins that confer a competitive advantage by targeting and killing closely related competitors. In this work, we found that mutacin B-Ny266 is a potent lantibiotic that is effective at killing a wide array of oral streptococci, including nearly all S. mutans strains tested. Lantibiotics produced by oral bacteria could represent a promising strategy to target caries pathogens embedded in dental plaque biofilm.
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5
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Tian XL, Li M, Scinocca Z, Rutherford H, Li YH. ClpP is required for proteolytic regulation of type II toxin-antitoxin systems and persister cell formation in Streptococcus mutans. Access Microbiol 2019; 1:e000054. [PMID: 32974554 PMCID: PMC7470404 DOI: 10.1099/acmi.0.000054] [Citation(s) in RCA: 2] [Impact Index Per Article: 0.4] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 07/24/2019] [Accepted: 07/25/2019] [Indexed: 11/18/2022] Open
Abstract
The type II toxin-antitoxin (TA) modules, mazEF and relBE, in Streptococcus mutans have been implicated in stress response, antibiotic tolerance and persister cell formation. However, how S. mutans regulates these systems to prevent unwanted toxin activation and persister cell formation is unclear. In this study, we provide evidence that ClpP is required for the proteolytic regulation of these TA systems and persister cell formation in S. mutans following antibiotic challenge. A persister viability assay showed that S. mutans UA159 (WT) formed a larger quantity of persister cells than its isogenic mutant ΔclpP following antibiotic challenge. However, the lux reporter assay revealed that clpP deletion did not affect the transcriptional levels of mazEF and relBE, since no significant differences (P>0.05) in the reporter activities were detected between the wild-type and ΔclpP background. Instead, all antibiotics tested at a sub-minimum inhibitory concentration (sub-MIC) induced transcriptional levels of mazEF and relBE operons. We then examined the protein profiles of His-tagged MazE and RelB proteins in the UA159 and ΔclpP backgrounds by Western blotting analysis. The results showed that S. mutans strains grown under non-stress conditions expressed very low but detectable levels of MazE and RelB antitoxin proteins. Antibiotics at sub-MICs induced the levels of the MazE and RelB proteins, but the protein levels decreased rapidly in the wild-type background. In contrast, a stable level of MazE and RelB proteins could be detected in the ΔclpP mutant background, suggesting that both proteins accumulated in the ΔclpP mutant. We conclude that ClpP is required for the proteolytic regulation of cellular levels of the MazE and RelB antitoxins in S. mutans , which may play a critical role in modulating the TA activities and persister cell formation of this organism following antibiotic challenge.
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Affiliation(s)
- Xiao-Lin Tian
- Department of Applied Oral Sciences, Dalhousie Universit, Halifax, NS, Canada
| | - Miao Li
- Department of Applied Oral Sciences, Dalhousie Universit, Halifax, NS, Canada.,Lanzhou University, Gansu, PR China
| | - Zachariah Scinocca
- Department of Applied Oral Sciences, Dalhousie Universit, Halifax, NS, Canada
| | - Heather Rutherford
- Department of Applied Oral Sciences, Dalhousie Universit, Halifax, NS, Canada
| | - Yung-Hua Li
- Department of Applied Oral Sciences, Dalhousie Universit, Halifax, NS, Canada.,Department of Microbiology and Immunology, Dalhousie University, Halifax, NS, Canada
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6
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Paul P, Sahu BR, Suar M. Plausible role of bacterial toxin-antitoxin system in persister cell formation and elimination. Mol Oral Microbiol 2019; 34:97-107. [PMID: 30891951 DOI: 10.1111/omi.12258] [Citation(s) in RCA: 14] [Impact Index Per Article: 2.8] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 12/27/2018] [Revised: 02/22/2019] [Accepted: 03/16/2019] [Indexed: 12/11/2022]
Abstract
Although, a large proportion of pathogenic bacteria gets eliminated from hosts after antibiotic treatment, a fraction of population confronts against such effects and undergoes growth arrest to form persisters. Persistence in bacteria is a dormant physiological state where cells escape the effects of antimicrobials as well as other host immune defences without any genetic mutations. The state of dormancy is achieved through various complex phenomena and it is known that a gene pair named as toxin-antitoxin (TA) acts as a key player of persister cell formation where the toxin is activated either stochastically or after an environmental insult, thereby silencing the physiological processes. However, the controversial role of TA modules in persister cell formation has also been documented with reasonable clarity. Persisters may revert back from state of quiescence and regrow when conditions become favourable for their propagation. Therefore, the elimination of dormant bacteria is crucial, and currently, research interest is highly focussed on developing several antipersister strategies that may kill persister bacteria by targeting different molecules. It is worth examining these targets to develop appropriate therapeutic interventions against bacterial infections and it is believed that earmarking TA system can be a novel approach for resuscitation of persisters. In this review, we discussed the role of TA modules in mediating persistence with highlighting on the debatable issues regarding contribution of these modules in dormant bacteria formation. Furthermore, we discussed if these modules in bacteria can be targeted for successful elimination of dormant persister cells.
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Affiliation(s)
- Prajita Paul
- School of Biotechnology, KIIT (Deemed to be University), Bhubaneswar, India
| | - Bikash R Sahu
- School of Biotechnology, KIIT (Deemed to be University), Bhubaneswar, India
| | - Mrutyunjay Suar
- School of Biotechnology, KIIT (Deemed to be University), Bhubaneswar, India
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7
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Xu J, Zhang N, Cao M, Ren S, Zeng T, Qin M, Zhao X, Yuan F, Chen H, Bei W. Identification of Three Type II Toxin-Antitoxin Systems in Streptococcus suis Serotype 2. Toxins (Basel) 2018; 10:toxins10110467. [PMID: 30428568 PMCID: PMC6266264 DOI: 10.3390/toxins10110467] [Citation(s) in RCA: 7] [Impact Index Per Article: 1.2] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 10/22/2018] [Revised: 11/06/2018] [Accepted: 11/07/2018] [Indexed: 01/15/2023] Open
Abstract
Type II toxin-antitoxin (TA) systems are highly prevalent in bacterial genomes and have been extensively studied. These modules involve in the formation of persistence cells, the biofilm formation, and stress resistance, which might play key roles in pathogen virulence. SezAT and yefM-yoeB TA modules in Streptococcus suis serotype 2 (S. suis 2) have been studied, although the other TA systems have not been identified. In this study, we investigated nine putative type II TA systems in the genome of S. suis 2 strain SC84 by bioinformatics analysis and identified three of them (two relBE loci and one parDE locus) that function as typical type II TA systems. Interestingly, we found that the introduction of the two RelBE TA systems into Escherichia coli or the induction of the ParE toxin led to cell filamentation. Promoter activity assays indicated that RelB1, RelB2, ParD, and ParDE negatively autoregulated the transcriptions of their respective TA operons, while RelBE2 positively autoregulated its TA operon transcription. Collectively, we identified three TA systems in S. suis 2, and our findings have laid an important foundation for further functional studies on these TA systems.
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Affiliation(s)
- Jiali Xu
- State Key Laboratory of Agricultural Microbiology, The Cooperative Innovation Center for Sustainable Pig Production, College of Veterinary Medicine, Huazhong Agricultural University, Wuhan 430070, China.
| | - Nian Zhang
- State Key Laboratory of Agricultural Microbiology, The Cooperative Innovation Center for Sustainable Pig Production, College of Veterinary Medicine, Huazhong Agricultural University, Wuhan 430070, China.
| | - Manman Cao
- State Key Laboratory of Agricultural Microbiology, The Cooperative Innovation Center for Sustainable Pig Production, College of Veterinary Medicine, Huazhong Agricultural University, Wuhan 430070, China.
| | - Sujing Ren
- State Key Laboratory of Agricultural Microbiology, The Cooperative Innovation Center for Sustainable Pig Production, College of Veterinary Medicine, Huazhong Agricultural University, Wuhan 430070, China.
| | - Ting Zeng
- State Key Laboratory of Agricultural Microbiology, The Cooperative Innovation Center for Sustainable Pig Production, College of Veterinary Medicine, Huazhong Agricultural University, Wuhan 430070, China.
| | - Minglu Qin
- State Key Laboratory of Agricultural Microbiology, The Cooperative Innovation Center for Sustainable Pig Production, College of Veterinary Medicine, Huazhong Agricultural University, Wuhan 430070, China.
| | - Xigong Zhao
- State Key Laboratory of Agricultural Microbiology, The Cooperative Innovation Center for Sustainable Pig Production, College of Veterinary Medicine, Huazhong Agricultural University, Wuhan 430070, China.
| | - Fangyan Yuan
- Key Laboratory of Prevention and Control Agents for Animal Bacteriosis, Institute of Animal Husbandry and Veterinary Sciences, Hubei Academy of Agricultural Sciences, Wuhan 430064, China.
| | - Huanchun Chen
- State Key Laboratory of Agricultural Microbiology, The Cooperative Innovation Center for Sustainable Pig Production, College of Veterinary Medicine, Huazhong Agricultural University, Wuhan 430070, China.
| | - Weicheng Bei
- State Key Laboratory of Agricultural Microbiology, The Cooperative Innovation Center for Sustainable Pig Production, College of Veterinary Medicine, Huazhong Agricultural University, Wuhan 430070, China.
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8
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Dufour D, Mankovskaia A, Chan Y, Motavaze K, Gong SG, Lévesque CM. A tripartite toxin-antitoxin module induced by quorum sensing is associated with the persistence phenotype in Streptococcus mutans. Mol Oral Microbiol 2018; 33:420-429. [PMID: 30298644 DOI: 10.1111/omi.12245] [Citation(s) in RCA: 5] [Impact Index Per Article: 0.8] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 09/10/2018] [Revised: 09/29/2018] [Accepted: 10/02/2018] [Indexed: 10/28/2022]
Abstract
The oral pathogen Streptococcus mutans communicates using a canonical Gram-positive quorum sensing system, CSP-ComDE. The CSP pheromone already known to be involved in the development of genetic competence positively influences the formation of persisters, dormant variants of regular cells that are highly tolerant to antimicrobial therapy. It is now believed that the persistence phenotype is the end result of a stochastic switch in the expression of toxin-antitoxin (TA) modules. TAs consist of a pair of genes that encode two components, a stable toxin and its cognate labile antitoxin. Transcription analyses revealed that three core genes encoding a putative TA system, called SmuATR, were members of the S. mutans CSP regulon. We hypothesized that S. mutans is using its CSP-ComDE system as a deterministic mechanism for persister formation through the activation of smuATR locus. We showed here that the SmuATR system constitutes a novel tripartite type II TA system in which the smuA and smuT genes encode an antitoxin and a toxin, respectively, while SmuR is a transcriptional repressor involved in the autoregulation of the operon. Ectopic expression of SmuA - SmuT is associated with the CSP-inducible persistence phenotype. In contrast, overexpression of SmuT alone is bactericidal and causes membrane permeabilization. To our knowledge, SmuATR is the first functional chromosomal tripartite TA system shown to be induced by the bacterial quorum sensing system and involved in persister formation.
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Affiliation(s)
- Delphine Dufour
- Faculty of Dentistry, University of Toronto, Toronto, ON, Canada
| | | | - Yuki Chan
- Department of Applied Oral Sciences, Faculty of Dentistry, The University of Hong Kong, Hong Kong, Hong Kong
| | - Kamyar Motavaze
- Faculty of Dentistry, University of Toronto, Toronto, ON, Canada
| | - Siew-Ging Gong
- Faculty of Dentistry, University of Toronto, Toronto, ON, Canada
| | - Céline M Lévesque
- Faculty of Dentistry, University of Toronto, Toronto, ON, Canada.,Department of Applied Oral Sciences, Faculty of Dentistry, The University of Hong Kong, Hong Kong, Hong Kong
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9
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Remodeling of the Streptococcus mutans proteome in response to LrgAB and external stresses. Sci Rep 2017; 7:14063. [PMID: 29070798 PMCID: PMC5656683 DOI: 10.1038/s41598-017-14324-w] [Citation(s) in RCA: 14] [Impact Index Per Article: 2.0] [Reference Citation Analysis] [Abstract] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 06/22/2017] [Accepted: 10/09/2017] [Indexed: 11/24/2022] Open
Abstract
The Streptococcus mutans Cid/Lrg system represents an ideal model to study how this organism withstands various stressors encountered in the oral cavity. Mutation of lrgAB renders S. mutans more sensitive to oxidative, heat, and vancomycin stresses. Here, we have performed a comprehensive proteomics experiment using label-free quantitative mass spectrometry to compare the proteome changes of wild type UA159 and lrgAB mutant strains in response to these same stresses. Importantly, many of identified proteins showed either a strikingly large fold-change, or were completely suppressed or newly induced in response to a particular stress condition. Notable stress proteome changes occurred in a variety of functional categories, including amino acid biosynthesis, energy metabolism, protein synthesis, transport/binding, and transcriptional/response regulators. In the non-stressed growth condition, mutation of lrgAB significantly altered the abundance of 76 proteins (a fold change >1.4, or <0.6, p-value <0.05) and several of these matched the stress proteome of the wild type strain. Interestingly, the statistical correlation between the proteome changes and corresponding RNA-seq transcriptomic studies was relatively low (rho(ρ) <0.16), suggesting that adaptation to a new environment may require radical proteome turnover or metabolic remodeling. Collectively, this study reinforces the importance of LrgAB to the S. mutans stress response.
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10
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Bacusmo JM, Orsini SS, Hu J, DeMott M, Thiaville PC, Elfarash A, Paulines MJ, Rojas-Benítez D, Meineke B, Deutsch C, Iwata-Reuyl D, Limbach PA, Dedon PC, Rice KC, Shuman S, Crécy-Lagard VD. The t 6A modification acts as a positive determinant for the anticodon nuclease PrrC, and is distinctively nonessential in Streptococcus mutans. RNA Biol 2017; 15:508-517. [PMID: 28726545 DOI: 10.1080/15476286.2017.1353861] [Citation(s) in RCA: 8] [Impact Index Per Article: 1.1] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/05/2023] Open
Abstract
Endoribonuclease toxins (ribotoxins) are produced by bacteria and fungi to respond to stress, eliminate non-self competitor species, or interdict virus infection. PrrC is a bacterial ribotoxin that targets and cleaves tRNALysUUU in the anticodon loop. In vitro studies suggested that the post-transcriptional modification threonylcarbamoyl adenosine (t6A) is required for PrrC activity but this prediction had never been validated in vivo. Here, by using t6A-deficient yeast derivatives, it is shown that t6A is a positive determinant for PrrC proteins from various bacterial species. Streptococcus mutans is one of the few bacteria where the t6A synthesis gene tsaE (brpB) is dispensable and its genome encodes a PrrC toxin. We had previously shown using an HPLC-based assay that the S. mutans tsaE mutant was devoid of t6A. However, we describe here a novel and a more sensitive hybridization-based t6A detection method (compared to HPLC) that showed t6A was still present in the S. mutans ΔtsaE, albeit at greatly reduced levels (93% reduced compared with WT). Moreover, mutants in 2 other S. mutans t6A synthesis genes (tsaB and tsaC) were shown to be totally devoid of the modification thus confirming its dispensability in this organism. Furthermore, analysis of t6A modification ratios and of t6A synthesis genes mRNA levels in S. mutans suggest they may be regulated by growth phase.
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Affiliation(s)
- Jo Marie Bacusmo
- a Department of Microbiology and Cell Science, IFAS , University of Florida , Gainesville , FL , USA
| | - Silvia S Orsini
- a Department of Microbiology and Cell Science, IFAS , University of Florida , Gainesville , FL , USA
| | - Jennifer Hu
- b Center for Environmental Health Sciences, Department of Biological Engineering , Massachusetts Institute of Technology , Cambridge , MA , USA
| | - Michael DeMott
- b Center for Environmental Health Sciences, Department of Biological Engineering , Massachusetts Institute of Technology , Cambridge , MA , USA
| | - Patrick C Thiaville
- a Department of Microbiology and Cell Science, IFAS , University of Florida , Gainesville , FL , USA.,c Genetics and Genomics Graduate Program , University of Florida , Gainesville , USA.,d University of Florida Genetics Institute, University of Florida , Gainesville , FL , USA
| | - Ameer Elfarash
- a Department of Microbiology and Cell Science, IFAS , University of Florida , Gainesville , FL , USA.,e Genetic Department, Faculty of Agriculture , Assiut University , Assuit , Egypt
| | - Mellie June Paulines
- f Rieveschl Laboratories for Mass Spectrometry, Department of Chemistry , University of Cincinnati , Cincinnati OH , USA
| | - Diego Rojas-Benítez
- g Centro de Regulación del Genoma. Facultad de Ciencias - Universidad de Chile , Santiago , Chile
| | - Birthe Meineke
- h Molecular Biology Program , Sloan-Kettering Institute , New York , NY , USA
| | - Chris Deutsch
- i Department of Chemistry , Portland State University , Portland , OR , USA
| | - Dirk Iwata-Reuyl
- i Department of Chemistry , Portland State University , Portland , OR , USA
| | - Patrick A Limbach
- f Rieveschl Laboratories for Mass Spectrometry, Department of Chemistry , University of Cincinnati , Cincinnati OH , USA
| | - Peter C Dedon
- b Center for Environmental Health Sciences, Department of Biological Engineering , Massachusetts Institute of Technology , Cambridge , MA , USA
| | - Kelly C Rice
- a Department of Microbiology and Cell Science, IFAS , University of Florida , Gainesville , FL , USA
| | - Stewart Shuman
- h Molecular Biology Program , Sloan-Kettering Institute , New York , NY , USA
| | - Valérie de Crécy-Lagard
- a Department of Microbiology and Cell Science, IFAS , University of Florida , Gainesville , FL , USA.,d University of Florida Genetics Institute, University of Florida , Gainesville , FL , USA
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11
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Physical and Functional Interplay between MazF 1Bif and Its Noncognate Antitoxins from Bifidobacterium longum. Appl Environ Microbiol 2017; 83:AEM.03232-16. [PMID: 28213540 DOI: 10.1128/aem.03232-16] [Citation(s) in RCA: 6] [Impact Index Per Article: 0.9] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 11/28/2016] [Accepted: 02/09/2017] [Indexed: 11/20/2022] Open
Abstract
Bifidobacterium longum strain JDM301, a widely used commercial strain in China, encodes at least two MazEF-like modules and one RelBE-like toxin-antitoxin (TA) system in its chromosome, designated MazE1F1Bif, MazE2F2Bif, and RelBEBif, respectively. Bacterial TA systems play an important role in several stress responses, but the relationship between these TA systems is largely unknown. In this study, the interactions between MazF1Bif and MazE2Bif or RelBBif were assessed in B. longum strain JDM301. MazF1Bif caused the degradation of tufABif mRNA, and its toxicity was inhibited by forming a protein complex with its cognate antitoxin, MazE1Bif Notably, MazF1Bif toxicity was also partially neutralized when jointly expressed with noncognate antitoxin MazE2Bif or RelBBif Our results show that the two noncognate antitoxins also inhibited mRNA degradation caused by MazF1Bif toxin. Furthermore, the physical interplay between MazF1Bif and its noncognate antitoxins was confirmed by immunoprecipitation. These results suggest that MazF1Bif can arrest cell growth and that MazF1Bif toxicity can be neutralized by its cognate and noncognate antitoxins. These results imply that JDM301 uses a sophisticated toxin-antitoxin interaction network to alter its physiology when coping with environmental stress.IMPORTANCE Although toxin-antitoxin (TA) systems play an important role in several stress responses, the regulatory mechanisms of multiple TA system homologs in the bacterial genome remain largely unclear. In this study, the relationships between MazE1F1Bif and the other two TA systems of Bifidobacterium longum strain JDM301 were explored, and the interactions between MazF1Bif and MazE2Bif or RelBBif were characterized. In addition, the mRNA degradation activity of MazF1Bif was demonstrated. In particular, the interaction of the toxin with noncognate antitoxins was shown, even between different TA families (MazF1Bif toxin and RelBBif antitoxin) in JDM301. This work provides insight into the regulatory mechanisms of TA systems implicated in the stress responses of bifidobacteria.
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Curtis TD, Takeuchi I, Gram L, Knudsen GM. The Influence of the Toxin/Antitoxin mazEF on Growth and Survival of Listeria monocytogenes under Stress. Toxins (Basel) 2017; 9:E31. [PMID: 28098783 PMCID: PMC5308263 DOI: 10.3390/toxins9010031] [Citation(s) in RCA: 29] [Impact Index Per Article: 4.1] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 10/21/2016] [Revised: 12/31/2016] [Accepted: 01/07/2017] [Indexed: 12/11/2022] Open
Abstract
A major factor in the resilience of Listeria monocytogenes is the alternative sigma factor B (σB). Type II Toxin/Antitoxin (TA) systems are also known to have a role in the bacterial stress response upon activation via the ClpP or Lon proteases. Directly upstream of the σB operon in L. monocytogenes is the TA system mazEF, which can cleave mRNA at UACMU sites. In this study, we showed that the mazEF TA locus does not affect the level of persister formation during treatment with antibiotics in lethal doses, but exerts different effects according to the sub-inhibitory stress added. Growth of a ΔmazEF mutant was enhanced relative to the wildtype in the presence of sub-inhibitory norfloxacin and at 42 °C, but was decreased when challenged with ampicillin and gentamicin. In contrast to studies in Staphylococcus aureus, we found that the mazEF locus did not affect transcription of genes within the σB operon, but MazEF effected the expression of the σB-dependent genes opuCA and lmo0880, with a 0.22 and 0.05 fold change, respectively, compared to the wildtype under sub-inhibitory norfloxacin conditions. How exactly this system operates remains an open question, however, our data indicates it is not analogous to the system of S. aureus, suggesting a novel mode of action for MazEF in L. monocytogenes.
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Affiliation(s)
- Thomas D Curtis
- Department of Biotechnology and Biomedicine, Technical University of Denmark, Matematiktorvet Bldg. 301, DK-2800 Kongens Lyngby, Denmark.
| | - Ippei Takeuchi
- Department of Biotechnology and Biomedicine, Technical University of Denmark, Matematiktorvet Bldg. 301, DK-2800 Kongens Lyngby, Denmark.
| | - Lone Gram
- Department of Biotechnology and Biomedicine, Technical University of Denmark, Matematiktorvet Bldg. 301, DK-2800 Kongens Lyngby, Denmark.
| | - Gitte M Knudsen
- Department of Biotechnology and Biomedicine, Technical University of Denmark, Matematiktorvet Bldg. 301, DK-2800 Kongens Lyngby, Denmark.
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Understanding the Streptococcus mutans Cid/Lrg System through CidB Function. Appl Environ Microbiol 2016; 82:6189-6203. [PMID: 27520814 DOI: 10.1128/aem.01499-16] [Citation(s) in RCA: 26] [Impact Index Per Article: 3.3] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 05/16/2016] [Accepted: 08/05/2016] [Indexed: 01/09/2023] Open
Abstract
The Streptococcus mutans lrgAB and cidAB operons have been previously described as a potential model system to dissect the complexity of biofilm development and virulence of S. mutans Herein, we have attempted to further characterize the Cid/Lrg system by focusing on CidB, which has been shown to be critical for the ability of S. mutans to survive and persist in a nonpreferred oxygen-enriched condition. We have found that the expression level of cidB is critical to oxidative stress tolerance of S. mutans, most likely by impacting lrg expression. Intriguingly, the impaired aerobic growth phenotype of the cidB mutant could be restored by the additional loss of either CidA or LrgA. Growth-dependent expression of cid and lrg was demonstrated to be tightly under the control of both CcpA and the VicKR two-component system (TCS), regulators known to play an essential role in controlling major catabolic pathways and cell envelope homeostasis, respectively. RNA sequencing (RNA-Seq) analysis revealed that mutation of cidB resulted in global gene expression changes, comprising major domains of central metabolism and virulence processes, particularly in those involved with oxidative stress resistance. Loss of CidB also significantly changed the expression of genes related to genomic islands (GI) TnSmu1 and TnSmu2, the CRISPR (clustered regularly interspaced short palindromic repeats)-Cas system, and toxin-antitoxin (T/A) modules. Taken together, these data show that CidB impinges on the stress response, as well as the fundamental cellular physiology of S. mutans, and further suggest a potential link between Cid/Lrg-mediated cellular processes, S. mutans pathogenicity, and possible programmed growth arrest and cell death mechanisms. IMPORTANCE The ability of Streptococcus mutans to survive a variety of harmful or stressful conditions and to emerge as a numerically significant member of stable oral biofilm communities are essential elements for its persistence and cariogenicity. In this study, the homologous cidAB and lrgAB operons, previously identified as being highly balanced and coordinated during S. mutans aerobic growth, were further characterized through the functional and transcriptomic analysis of CidB. Precise control of CidB levels is shown to impact the expression of lrg, oxidative stress tolerance, major metabolic domains, and the molecular modules linked to cell death and lysis. This study advances our understanding of the Cid/Lrg system as a key player in the integration of complex environmental signals (such as oxidative stress) into the regulatory networks that modulate S. mutans virulence and cell homeostasis.
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Wei Y, Ye L, Li Y, Yang F, Liu D, Guo X, Tang R, Liu C. Functional characterization of RelBE toxin-antitoxin system in probiotic Bifidobacterium longum JDM301. Acta Biochim Biophys Sin (Shanghai) 2016; 48:741-9. [PMID: 27451444 DOI: 10.1093/abbs/gmw056] [Citation(s) in RCA: 7] [Impact Index Per Article: 0.9] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 12/15/2015] [Accepted: 05/16/2016] [Indexed: 12/20/2022] Open
Abstract
Toxin-antitoxin (TA) systems are widespread in bacteria and archaea. However, the roles of chromosomally encoded TA systems in bacterial physiology are still open to debate. In this study, a TA module-relBE in Bifidobacterium longum JDM301 (relBE(Bif)) was identified and its function in stress response was evaluated. Bioinformatics analysis of the whole genome sequences of JDM301 revealed a pair of linked genes encoding a RelBE-like TA system (RelBE(Bif)). Our results revealed a bicistronic operon formed by relBE(Bif) in JDM301. Over-expression of RelE(Bif) had a toxic effect on Escherichia coli, which could be neutralized by co-expression of its cognate antitoxin, RelB(Bif) Our data also demonstrated that RelE(Bif) is an mRNA interferase and that the activity of RelE(Bif) can be inhibited by RelB(Bif) These results suggest that RelE(Bif) is a toxic nuclease which arrests cell growth through mRNA degradation, and that the activity of RelE(Bif) can be abolished by co-expression of RelB(Bif) In addition, we also found that the expression of RelBE(Bif) is increased during osmotic stress, suggesting that RelBE(Bif) is activated under this adverse condition. Our results imply that the RelBE(Bif) TA module may represent a cell growth modulator which helps B. longum to deal with osmotic stress.
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Affiliation(s)
- Yanxia Wei
- Department of Pathogenic Biology and Immunology, Laboratory of Infection and Immunity/School of Stomatology, Xuzhou Medical University, Xuzhou 221004, China
| | - Lu Ye
- Department of Microbiology and Immunity, Shanghai Jiao Tong University School of Medicine, Shanghai 200025, China
| | - Yang Li
- Department of Pathogenic Biology and Immunology, Laboratory of Infection and Immunity/School of Stomatology, Xuzhou Medical University, Xuzhou 221004, China
| | - Fan Yang
- Department of Pathogenic Biology and Immunology, Laboratory of Infection and Immunity/School of Stomatology, Xuzhou Medical University, Xuzhou 221004, China
| | - Dianbin Liu
- Department of Pathogenic Biology and Immunology, Laboratory of Infection and Immunity/School of Stomatology, Xuzhou Medical University, Xuzhou 221004, China
| | - Xiaokui Guo
- Department of Microbiology and Immunity, Shanghai Jiao Tong University School of Medicine, Shanghai 200025, China
| | - Renxian Tang
- Department of Pathogenic Biology and Immunology, Laboratory of Infection and Immunity/School of Stomatology, Xuzhou Medical University, Xuzhou 221004, China
| | - Chang Liu
- Department of Microbiology and Immunity, Shanghai Jiao Tong University School of Medicine, Shanghai 200025, China
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Shields RC, Burne RA. Growth of Streptococcus mutans in Biofilms Alters Peptide Signaling at the Sub-population Level. Front Microbiol 2016; 7:1075. [PMID: 27471495 PMCID: PMC4946182 DOI: 10.3389/fmicb.2016.01075] [Citation(s) in RCA: 21] [Impact Index Per Article: 2.6] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 04/25/2016] [Accepted: 06/27/2016] [Indexed: 11/30/2022] Open
Abstract
Streptococcus mutans activates multiple cellular processes in response to the formation of a complex between comX-inducing peptide (XIP) and the ComR transcriptional regulator. Bulk phase and microfluidic experiments previously revealed that ComR-dependent activation of comX is altered by pH and by carbohydrate source. Biofilm formation is a major factor in bacterial survival and virulence in the oral cavity. Here, we sought to determine the response of S. mutans biofilm cells to XIP during different stages of biofilm maturation. Using flow cytometry and confocal microscopy, we showed that exogenous addition of XIP to early biofilms resulted in robust comX activation. However, as the biofilms matured, increasing amounts of XIP were required to activate comX expression. Single-cell analysis demonstrated that the entire population was responding to XIP with activation of comX in early biofilms, but only a sub-population was responding in mature biofilms. The sub-population response of mature biofilms was retained when the cells were dispersed and then treated with XIP. The proportion and intensity of the bi-modal response of mature biofilm cells was altered in mutants lacking the Type II toxins MazF and RelE, or in a strain lacking the (p)ppGpp synthase/hydrolase RelA. Thus, competence signaling is markedly altered in cells growing in mature biofilms, and pathways that control cell death and growth/survival decisions modulate activation of comX expression in these sessile populations.
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Affiliation(s)
- Robert C Shields
- Department of Oral Biology, College of Dentistry, University of Florida, Gainesville FL, USA
| | - Robert A Burne
- Department of Oral Biology, College of Dentistry, University of Florida, Gainesville FL, USA
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AAU-Specific RNA Cleavage Mediated by MazF Toxin Endoribonuclease Conserved in Nitrosomonas europaea. Toxins (Basel) 2016; 8:toxins8060174. [PMID: 27271670 PMCID: PMC4926141 DOI: 10.3390/toxins8060174] [Citation(s) in RCA: 10] [Impact Index Per Article: 1.3] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 03/22/2016] [Accepted: 05/30/2016] [Indexed: 02/07/2023] Open
Abstract
Nitrosomonas europaea carries numerous toxin-antitoxin systems. However, despite the abundant representation in its chromosome, studies have not surveyed the underlying molecular functions in detail, and their biological roles remain enigmatic. In the present study, we found that a chromosomally-encoded MazF family member, predicted at the locus NE1181, is a functional toxin endoribonuclease, and constitutes a toxin-antitoxin system, together with its cognate antitoxin, MazE. Massive parallel sequencing provided strong evidence that this toxin endoribonuclease exhibits RNA cleavage activity, primarily against the AAU triplet. This sequence-specificity was supported by the results of fluorometric assays. Our results indicate that N. europaea alters the translation profile and regulates its growth using the MazF family of endoribonuclease under certain stressful conditions.
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Li G, Shen M, Lu S, Le S, Tan Y, Wang J, Zhao X, Shen W, Guo K, Yang Y, Zhu H, Rao X, Hu F, Li M. Identification and Characterization of the HicAB Toxin-Antitoxin System in the Opportunistic Pathogen Pseudomonas aeruginosa. Toxins (Basel) 2016; 8:113. [PMID: 27104566 PMCID: PMC4848639 DOI: 10.3390/toxins8040113] [Citation(s) in RCA: 35] [Impact Index Per Article: 4.4] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 03/21/2016] [Revised: 04/06/2016] [Accepted: 04/08/2016] [Indexed: 12/26/2022] Open
Abstract
Toxin-antitoxin (TA) systems are small genetic modules that are widely distributed in the genomes of bacteria and archaea and have been proposed to fulfill numerous functions. Here, we describe the identification and characterization of a type II TA system, comprising the hicAB locus in the human opportunistic pathogen Pseudomonas aeruginosa. The hicAB locus consists of genes hicA and hicB encoding a toxin and its cognate antitoxin, respectively. BLAST analysis revealed that hicAB is prevalent in approximately 36% of P. aeruginosa strains and locates in the same genomic region. RT-PCR demonstrated that hicAB forms a bicistronic operon that is cotranscribed under normal growth conditions. Overproduction of HicA inhibited the growth of Escherichia coli, and this effect could be counteracted by co-expression of HicB. The Escherichia coli kill/rescue assay showed that the effect of HicA is bacteriostatic, rather than bactericidal. Deletion of hicAB had no effect on the biofilm formation and virulence of P. aeruginosa in a mice infection model. Collectively, this study presents the first characterization of the HicAB system in the opportunistic pathogen P. aeruginosa.
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Affiliation(s)
- Gang Li
- Department of Microbiology, Third Military Medical University, Chongqing 400038, China.
| | - Mengyu Shen
- Department of Microbiology, Third Military Medical University, Chongqing 400038, China.
| | - Shuguang Lu
- Department of Microbiology, Third Military Medical University, Chongqing 400038, China.
| | - Shuai Le
- Department of Microbiology, Third Military Medical University, Chongqing 400038, China.
| | - Yinling Tan
- Department of Microbiology, Third Military Medical University, Chongqing 400038, China.
| | - Jing Wang
- Department of Microbiology, Third Military Medical University, Chongqing 400038, China.
| | - Xia Zhao
- Department of Microbiology, Third Military Medical University, Chongqing 400038, China.
| | - Wei Shen
- Department of Microbiology, Third Military Medical University, Chongqing 400038, China.
| | - Keke Guo
- Department of Microbiology, Third Military Medical University, Chongqing 400038, China.
| | - Yuhui Yang
- Department of Microbiology, Third Military Medical University, Chongqing 400038, China.
| | - Hongbin Zhu
- Department of Microbiology, Third Military Medical University, Chongqing 400038, China.
| | - Xiancai Rao
- Department of Microbiology, Third Military Medical University, Chongqing 400038, China.
| | - Fuquan Hu
- Department of Microbiology, Third Military Medical University, Chongqing 400038, China.
| | - Ming Li
- Department of Microbiology, Third Military Medical University, Chongqing 400038, China.
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Wei YX, Ye L, Liu DB, Zhang ZY, Liu C, Guo XK. Activation of the chromosomally encoded mazEF(Bif) locus of Bifidobacterium longum under acid stress. Int J Food Microbiol 2015; 207:16-22. [PMID: 25950853 DOI: 10.1016/j.ijfoodmicro.2015.04.028] [Citation(s) in RCA: 7] [Impact Index Per Article: 0.8] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 11/01/2014] [Revised: 02/18/2015] [Accepted: 04/19/2015] [Indexed: 01/15/2023]
Abstract
Toxin-antitoxin (TA) systems are distributed within the genomes of almost all free-living bacteria. Although the roles of chromosomally encoded TA systems are still under debate, they are suspected to be involved in various stress responses. Here, we provide the first report of a type II TA system in the probiotic bacterium Bifidobacterium longum. Bioinformatic analysis of the B. longum JDM301 genome identified a pair of linked genes encoding a MazEF-like TA system at the locus BLJ_811-BLJ_812. Our results showed that B. longum mazEF(Bif) genes form a bicistronic operon. The over-expression of MazF(Bif) was toxic to Escherichia coli and could be neutralized by the co-expression of its cognate antitoxin MazE(Bif). We demonstrated that MazEF(Bif) was activated during acid stress, which would most likely be encountered in the gastrointestinal tract. In addition, we found that the protease ClpPX(Bif), in addition to MazEF(Bif), was induced under acid stress. Furthermore, we examined antitoxin levels over time for MazEF(Bif) and observed that the antitoxin MazE(Bif) was degraded by ClpPX(Bif), which suggested that MazEF(Bif) was activated through the hydrolysis of MazE(Bif) by ClpP1X(Bif) and ClpP2X(Bif) under acid stress. Our results suggest that the MazEF(Bif) TA module may play an important role in cell physiology and may represent a cell growth modulator that helps bacteria to cope with acid stress in the gastrointestinal tract and environment.
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Affiliation(s)
- Yan-Xia Wei
- Department of Pathogenic Biology and Immunology, Laboratory of Infection and Immunity/School of Stomatology, Xuzhou Medical College, Xuzhou, Jiangsu 221004, China; Department of Medical Microbiology and Parasitology, Institutes of Medical Sciences, Shanghai Jiao Tong University School of Medicine, Shanghai 200025, China
| | - Lu Ye
- Department of Medical Microbiology and Parasitology, Institutes of Medical Sciences, Shanghai Jiao Tong University School of Medicine, Shanghai 200025, China
| | - Dian-Bin Liu
- Department of Pathogenic Biology and Immunology, Laboratory of Infection and Immunity/School of Stomatology, Xuzhou Medical College, Xuzhou, Jiangsu 221004, China
| | - Zhuo-Yang Zhang
- Department of Medical Microbiology and Parasitology, Institutes of Medical Sciences, Shanghai Jiao Tong University School of Medicine, Shanghai 200025, China
| | - Chang Liu
- Department of Medical Microbiology and Parasitology, Institutes of Medical Sciences, Shanghai Jiao Tong University School of Medicine, Shanghai 200025, China.
| | - Xiao-Kui Guo
- Department of Medical Microbiology and Parasitology, Institutes of Medical Sciences, Shanghai Jiao Tong University School of Medicine, Shanghai 200025, China.
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Bertram R, Schuster CF. Post-transcriptional regulation of gene expression in bacterial pathogens by toxin-antitoxin systems. Front Cell Infect Microbiol 2014; 4:6. [PMID: 24524029 PMCID: PMC3905216 DOI: 10.3389/fcimb.2014.00006] [Citation(s) in RCA: 24] [Impact Index Per Article: 2.4] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 12/10/2013] [Accepted: 01/13/2014] [Indexed: 01/27/2023] Open
Abstract
Toxin-antitoxin (TA) systems are small genetic elements ubiquitous in prokaryotic genomes that encode toxic proteins targeting various vital cellular functions. Typically, toxin activity is controlled by adjacently encoded protein or RNA antitoxins and unleashed as a consequence of genetic fluctuations or stressful conditions. Whereas some TA systems interfere with replication or cell wall synthesis, most of them influence transcriptional and post-transcriptional gene regulation. Antitoxin proteins often act as DNA binding transcriptional regulators and many TA toxins exhibit endoribonuclease activity to selectively degrade different RNA species and thus alter gene expression patterns. Some TA RNases cleave tRNA, tmRNAs or rRNAs, whereas most commonly mRNAs either in association with the ribosome or as free transcripts, are targeted. Examples are provided on how TA toxins differentially shape gene expression in bacterial pathogens by creating specialized ribosomes or by altering the transcriptome and how this may be tied in the control of pathogenicity factors.
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Affiliation(s)
- Ralph Bertram
- Department of Microbial Genetics, Faculty of Science, Interfaculty Institute of Microbiology and Infection Medicine Tübingen (IMIT), University of Tübingen Tübingen, Germany
| | - Christopher F Schuster
- Department of Microbial Genetics, Faculty of Science, Interfaculty Institute of Microbiology and Infection Medicine Tübingen (IMIT), University of Tübingen Tübingen, Germany
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20
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A regulatory role for Staphylococcus aureus toxin-antitoxin system PemIKSa. Nat Commun 2013; 4:2012. [PMID: 23774061 DOI: 10.1038/ncomms3012] [Citation(s) in RCA: 43] [Impact Index Per Article: 3.9] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 03/01/2013] [Accepted: 05/15/2013] [Indexed: 11/08/2022] Open
Abstract
Toxin-antitoxin systems were shown to be involved in plasmid maintenance when they were initially discovered, but other roles have been demonstrated since. Here we identify and characterize a novel toxin-antitoxin system (pemIKSa) located on Staphylococcus aureus plasmid pCH91. The toxin (PemKSa) is a sequence-specific endoribonuclease recognizing the tetrad sequence U↓AUU, and the antitoxin (PemISa) inhibits toxin activity by physical interaction. Although the toxin-antitoxin system is responsible for stable plasmid maintenance our data suggest the participation of pemIKSa in global regulation of staphylococcal virulence by alteration of the translation of large pools of genes. We propose a common mechanism of reversible activation of toxin-antitoxin systems based on antitoxin transcript resistance to toxin cleavage. Elucidation of this mechanism is particularly interesting because reversible activation is a prerequisite for the proposed general regulatory role of toxin-antitoxin systems.
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Ning D, Liu S, Xu W, Zhuang Q, Wen C, Tang X. Transcriptional and proteolytic regulation of the toxin-antitoxin locus vapBC10 (ssr2962/slr1767) on the chromosome of Synechocystis sp. PCC 6803. PLoS One 2013; 8:e80716. [PMID: 24260461 PMCID: PMC3834315 DOI: 10.1371/journal.pone.0080716] [Citation(s) in RCA: 12] [Impact Index Per Article: 1.1] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 07/01/2013] [Accepted: 10/07/2013] [Indexed: 12/01/2022] Open
Abstract
VapBC toxin-antitoxin (TA) systems are defined by the association of a PIN-domain toxin with a DNA-binding antitoxin, and are thought to play important physiological roles in bacteria and archaea. Recently, the PIN-associated gene pair PIN-COG2442 was proposed to encode VapBC-family TA system and found to be abundant in cyanobacteria. However, the features of these predicted TA loci remain under investigation. We here report characterization of the PIN-COG2442 locus vapBC10 (ssr2962/slr1767) on the chromosome of Synechocystis sp. PCC 6803. RT-PCR analysis revealed that the vapBC10 genes were co-transcribed under normal growth conditions. Ectopic expression of the PIN-domain protein VapC10 caused growth arrest of Escherichia coli that does not possess vapBC TA locus. Coincidentally, this growth-inhibition effect could be neutralized by either simultaneous or subsequent production of the COG2442-domain protein VapB10 through formation of the TA complex VapBC10 in vivo. In contrast to the transcription repression activity of the well-studied antitoxins, VapB10 positively auto-regulated the transcription of its own operon via specific binding to the promoter region. Furthermore, in vivo experiments in E. coli demonstrated that the Synechocystis protease ClpXP2s, rather than Lons, could cleave VapB10 and proteolytically activate the VapC10 toxicity. Our results show that the PIN-COG2442 locus vapBC10 encodes a functional VapBC TA system with an alternative mechanism for the transcriptional auto-regulation of its own operon.
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Affiliation(s)
- Degang Ning
- Department of Environment Sciences, School of the Environment, Jiangsu University, Zhenjiang, Jiangsu, China
| | - Shuibing Liu
- Department of Environment Sciences, School of the Environment, Jiangsu University, Zhenjiang, Jiangsu, China
| | - Weidong Xu
- Department of Pharmaceutical engineering, School of Pharmacy, Jiangsu University, Xuefu Road, Zhenjiang, Jiangsu, China
| | - Qiang Zhuang
- Department of Environment Sciences, School of the Environment, Jiangsu University, Zhenjiang, Jiangsu, China
| | - Chongwei Wen
- Department of Pharmaceutical engineering, School of Pharmacy, Jiangsu University, Xuefu Road, Zhenjiang, Jiangsu, China
| | - Xiaoxia Tang
- Department of Environment Sciences, School of the Environment, Jiangsu University, Zhenjiang, Jiangsu, China
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Development of a tunable wide-range gene induction system useful for the study of streptococcal toxin-antitoxin systems. Appl Environ Microbiol 2013; 79:6375-84. [PMID: 23934493 DOI: 10.1128/aem.02320-13] [Citation(s) in RCA: 25] [Impact Index Per Article: 2.3] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/29/2023] Open
Abstract
Despite the plethora of genetic tools that have been developed for use in Streptococcus mutans, the S. mutans genetic system still lacks an effective gene induction system exhibiting low basal expression and strong inducibility. Consequently, we created two hybrid gene induction cassettes referred to as Xyl-S1 and Xyl-S2. Both Xyl-S cassettes are xylose inducible and controlled by the Bacillus megaterium xylose repressor. The Xyl-S cassettes each demonstrated >600-fold-increased reporter activity in the presence of 1.2% (wt/vol) xylose. However, the Xyl-S1 cassette yielded a much higher maximum level of gene expression, whereas the Xyl-S2 cassette exhibited much lower uninduced basal expression. The cassettes also performed similarly in Streptococcus sanguinis and Streptococcus gordonii, which suggests that they are likely to be useful in a variety of streptococci. We demonstrate how both Xyl-S cassettes are particularly useful for the study of toxin-antitoxin (TA) modules using both the previously characterized S. mutans mazEF TA module and a previously uncharacterized HicAB TA module in S. mutans. HicAB TA modules are widely distributed among bacteria and archaea, but little is known about their function. We show that HicA serves as the toxin component of the module, while HicB serves as the antitoxin. Our results suggest that, in contrast to that of typical TA modules, HicA toxicity in S. mutans is modest at best. The implications of these results for HicAB function are discussed.
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Ramisetty BCM, Natarajan B, Santhosh RS. mazEF-mediated programmed cell death in bacteria: "what is this?". Crit Rev Microbiol 2013; 41:89-100. [PMID: 23799870 DOI: 10.3109/1040841x.2013.804030] [Citation(s) in RCA: 38] [Impact Index Per Article: 3.5] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/18/2022]
Abstract
Toxin-antitoxin (TA) systems consist of a bicistronic operon, encoding a toxin and an antitoxin. They are widely distributed in the prokaryotic kingdom, often in multiple numbers. TAs are implicated in contradicting phenomena of persistence and programmed cell death (PCD) in bacteria. mazEF TA system, one of the widely distributed type II toxin-antitoxin systems, is particularly implicated in PCD of Escherichia coli. Nutrient starvation, antibiotic stress, heat shock, DNA damage and other kinds of stresses are shown to elicit mazEF-mediated-PCD. ppGpp and extracellular death factor play a central role in regulating mazEF-mediated PCD. The activation of mazEF system is achieved through inhibition of transcription or translation of mazEF loci. Upon activation, MazF cleaves RNA in a ribosome-independent fashion and subsequent processes result in cell death. It is hypothesized that PCD aids in perseverance of the population during stress; the surviving minority of the cells can scavenge the nutrients released by the dead cells, a kind of "nutritional-altruism." Issues regarding the strains, reproducibility of experimental results and ecological plausibility necessitate speculation. We review the molecular mechanisms of the activation of mazEF TA system, the consequences leading to cell death and the pros and cons of the altruism hypothesis from an ecological perspective.
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Ning D, Jiang Y, Liu Z, Xu Q. Characterization of a chromosomal type II toxin-antitoxin system mazEaFa in the Cyanobacterium Anabaena sp. PCC 7120. PLoS One 2013; 8:e56035. [PMID: 23451033 PMCID: PMC3581536 DOI: 10.1371/journal.pone.0056035] [Citation(s) in RCA: 14] [Impact Index Per Article: 1.3] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 10/11/2012] [Accepted: 01/04/2013] [Indexed: 01/04/2023] Open
Abstract
Cyanobacteria have evolved to survive stressful environmental changes by regulating growth, however, the underlying mechanism for this is obscure. The ability of chromosomal type II toxin-antitoxin (TA) systems to modulate growth or cell death has been documented in a variety of prokaryotes. A chromosomal mazEaFa locus of Anabaena sp. PCC 7120 has been predicted as a putative mazEF TA system. Here we demonstrate that mazEaFa form a bicistronic operon that is co-transcribed under normal growth conditions. Overproduction of MazFa induced Anabaena growth arrest which could be neutralized by co-expression of MazEa. MazFa also inhibited the growth of Escherichia coli cells, and this effect could be overcome by simultaneous or subsequent expression of MazEa via formation of the MazEa-MazFa complex in vivo, further confirming the nature of the mazEaFa locus as a type II TA system. Interestingly, like most TA systems, deletion of mazEaFa had no effect on the growth of Anabaena during the tested stresses. Our data suggest that mazEaFa, or together with other chromosomal type II TA systems, may promote cells to cope with particular stresses by inducing reversible growth arrest of Anabaena.
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Affiliation(s)
- Degang Ning
- Department of Environment Sciences, School of the Environment, Jiangsu University, Zhenjiang, Jiangsu, China
| | - Yan Jiang
- Institute of Life Sciences, Jiangsu University, Zhenjiang, Jiangsu, China
| | - Zhaoying Liu
- Department of Environment Sciences, School of the Environment, Jiangsu University, Zhenjiang, Jiangsu, China
| | - Qinggang Xu
- Institute of Life Sciences, Jiangsu University, Zhenjiang, Jiangsu, China
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Koyanagi S, Lévesque CM. Characterization of a Streptococcus mutans intergenic region containing a small toxic peptide and its cis-encoded antisense small RNA antitoxin. PLoS One 2013; 8:e54291. [PMID: 23326602 PMCID: PMC3543317 DOI: 10.1371/journal.pone.0054291] [Citation(s) in RCA: 34] [Impact Index Per Article: 3.1] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 10/25/2012] [Accepted: 12/10/2012] [Indexed: 12/21/2022] Open
Abstract
Toxin-antitoxin (TA) modules consist of a pair of genes that encode two components: a protein toxin and an antitoxin, which may be in the form of either a labile protein or an antisense small RNA. Here we describe, to the best of our knowledge, the first functional chromosomal type I TA system in streptococci. Our model organism is the oral pathogen Streptococcus mutans. Our results showed that the genome of S. mutans UA159 reference strain harbors a previously unannotated Fst-like toxin (Fst-Sm) and its cis-encoded small RNA antitoxin (srSm) converging towards the end of the toxin gene in IGR176, a small intergenic region of 318 nt. Fst-Sm is a small hydrophobic peptide of 32 amino acid residues with homology to the Fst toxin family. Transcripts of ∼200 nt and ∼70 nt specific to fst-Sm mRNA and srSm RNA, respectively, were detected by Northern blot analysis throughout S. mutans growth. The toxin mRNA was considerably more stable than its cognate antitoxin. The half-life of srSm RNA was determined to be ∼30 min, while fst-Sm mRNA had a half-life of ∼90 min. Both fst-Sm and srSm RNAs were transcribed across direct tandem repeats providing a region of complementarity for inhibition of toxin translation. Overproduction of Fst-Sm had a toxic effect on E. coli and S. mutans cells which can be neutralized by coexpression of srSm RNA. Deletion of fst-Sm/srSm locus or overexpression of Fst-Sm/srSm had no effect on S. mutans cell growth in liquid medium and no differences in the total biofilm biomass were noted. In contrast, mild-overproduction of Fst-Sm/srSm type I TA system decreases the levels of persister cells tolerant to bacterial cell wall synthesis inhibitors.
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Affiliation(s)
- Stephanie Koyanagi
- Dental Research Institute, Faculty of Dentistry, University of Toronto, Toronto, Ontario, Canada
| | - Céline M. Lévesque
- Dental Research Institute, Faculty of Dentistry, University of Toronto, Toronto, Ontario, Canada
- * E-mail:
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Cell death of Streptococcus mutans induced by a quorum-sensing peptide occurs via a conserved streptococcal autolysin. J Bacteriol 2012; 195:105-14. [PMID: 23104806 DOI: 10.1128/jb.00926-12] [Citation(s) in RCA: 38] [Impact Index Per Article: 3.2] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/01/2023] Open
Abstract
Streptococcus mutans, a member of the human indigenous oral microbiome, produces a quorum-sensing peptide called the competence-stimulating peptide (CSP) pheromone. We previously demonstrated that S. mutans expresses its CSP pheromone under specific stresses and responds to high levels of CSP by inducing cell death in a fraction of the bacterial population. Streptococci lack the classical SOS response, and the induction of the SigX regulon has been proposed to act as a general stress response in Gram-positive bacteria. We show here that inactivation of SigX abolished the CSP-induced cell death phenotype. Among SigX-regulated genes, SMU.836 (now named lytF(Sm)), encoding a conserved streptococcal protein, is a functional peptidoglycan hydrolase involved in CSP-induced cell lysis. We also demonstrated that LytF(Sm) is most likely a self-acting autolysin, since LytF(Sm) produced by attacker cells cannot trigger CSP-induced lysis of LytF(Sm)-deficient target cells present in the same environment. Electron microscopy revealed important morphological changes accompanying autolysis of CSP-induced wild-type cultures that were absent in the LytF(Sm)-deficient mutant. The LytF(Sm) promoter was activated in the physiological context of elevated concentrations of the CSP pheromone under stress conditions, such as exposure to heat, hydrogen peroxide, and acid. In a long-term survival assay, the viability of a mutant deficient in LytF(Sm) autolysin was significantly lower than that observed for the wild-type strain. The results of this study suggest that cell death of S. mutans induced by its quorum-sensing CSP pheromone may represent a kind of altruistic act that provides a way for the species to survive environmental stresses at the expense of some of its cells.
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Characterization of a mazEF toxin-antitoxin homologue from Staphylococcus equorum. J Bacteriol 2012; 195:115-25. [PMID: 23104807 DOI: 10.1128/jb.00400-12] [Citation(s) in RCA: 30] [Impact Index Per Article: 2.5] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/20/2022] Open
Abstract
Toxin-antitoxin (TA) systems encoded in prokaryotic genomes fall into five types, typically composed of two distinct small molecules, an endotoxic protein and a cis-encoded antitoxin of ribonucleic or proteinaceous nature. In silico analysis revealed seven putative type I and three putative type II TA systems in the genome of the nonpathogenic species strain Staphylococcus equorum SE3. Among these, a MazEF system orthologue termed MazEF(seq) was further characterized. 5' rapid amplification of cDNA ends (RACE) revealed the expression and the transcriptional start site of mazE(seq), indicating an immediately upstream promoter. Heterologous expression of the putative toxin-encoding mazF(seq) gene imposed growth cessation but not cell death on Escherichia coli. In vivo and in vitro, MazF(seq) was shown to cleave at UACAU motifs, which are remarkably abundant in a number of putative metabolic and regulatory S. equorum gene transcripts. Specific interaction between MazF(seq) and the putative cognate antitoxin MazE(seq) was demonstrated by bacterial two-hybrid analyses. These data strongly suggest that MazEF(seq) represents the first characterized TA system in a nonpathogenic Staphylococcus species and indicate that MazEF modules in staphylococci may also control processes beyond pathogenicity.
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Abstract
Most prokaryotic chromosomes contain a number of toxin-antitoxin (TA) modules consisting of a pair of genes that encode 2 components, a stable toxin and its cognate labile antitoxin. TA systems are also known as addiction modules, since the cells become "addicted" to the short-lived antitoxin product (the unstable antitoxin is degraded faster than the more stable toxin) because its de novo synthesis is essential for their survival. While toxins are always proteins, antitoxins are either RNAs (type I, type III) or proteins (type II). Type II TA systems are widely distributed throughout the chromosomes of almost all free-living bacteria and archaea. The vast majority of type II toxins are mRNA-specific endonucleases arresting cell growth through the mechanism of RNA cleavage, thus preventing the translation process. The physiological role of chromosomal type II TA systems still remains the subject of debate. This review describes the currently known type II toxins and their characteristics. The different hypotheses that have been proposed to explain their role in bacterial physiology are also discussed.
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Affiliation(s)
- Mohammad Adnan Syed
- Dental Research Institute, Faculty of Dentistry, University of Toronto, 124 Edward Street, Toronto, ON M5G 1G6, Canada
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Myxococcus xanthus developmental cell fate production: heterogeneous accumulation of developmental regulatory proteins and reexamination of the role of MazF in developmental lysis. J Bacteriol 2012; 194:3058-68. [PMID: 22493014 DOI: 10.1128/jb.06756-11] [Citation(s) in RCA: 42] [Impact Index Per Article: 3.5] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/20/2022] Open
Abstract
Myxococcus xanthus undergoes a starvation-induced multicellular developmental program during which cells partition into three known fates: (i) aggregation into fruiting bodies followed by differentiation into spores, (ii) lysis, or (iii) differentiation into nonaggregating persister-like cells, termed peripheral rods. As a first step to characterize cell fate segregation, we enumerated total, aggregating, and nonaggregating cells throughout the developmental program. We demonstrate that both cell lysis and cell aggregation begin with similar timing at approximately 24 h after induction of development. Examination of several known regulatory proteins in the separated aggregated and nonaggregated cell fractions revealed previously unknown heterogeneity in the accumulation patterns of proteins involved in type IV pilus (T4P)-mediated motility (PilC and PilA) and regulation of development (MrpC, FruA, and C-signal). As part of our characterization of the cell lysis fate, we set out to investigate the unorthodox MazF-MrpC toxin-antitoxin system which was previously proposed to induce programmed cell death (PCD). We demonstrate that deletion of mazF in two different wild-type M. xanthus laboratory strains does not significantly reduce developmental cell lysis, suggesting that MazF's role in promoting PCD is an adaption to the mutant background strain used previously.
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A stress-inducible quorum-sensing peptide mediates the formation of persister cells with noninherited multidrug tolerance. J Bacteriol 2012; 194:2265-74. [PMID: 22366415 DOI: 10.1128/jb.06707-11] [Citation(s) in RCA: 116] [Impact Index Per Article: 9.7] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/20/2022] Open
Abstract
Within a given microbial population, a small subpopulation known as dormant persister cells exists. This persistence property ensures the survival of the population as a whole in the presence of lethal factors. Although persisters are highly important in antibiotic therapy, the mechanism for persistence is still not thoroughly understood. We show here that the cariogenic organism Streptococcus mutans forms persister cells showing noninherited multidrug tolerance. We demonstrated that the ectopic expression of the type II toxin-antitoxin systems, MazEF and RelBE, caused an increase in the number of persisters. In a search for additional persistence genes, an expression library was constructed, and several clones exhibiting a significant difference in persister formation after prolonged antibiotic treatment were selected. The candidate persister genes include genes involved in transcription/replication, sugar metabolism, cell wall synthesis, and energy metabolism, clearly pointing to redundant pathways for persister formation. We have previously reported that the S. mutans quorum-sensing peptide, CSP pheromone, was a stress-inducible alarmone capable of conveying sophisticated messages in the bacterial population. In this study, we demonstrate the involvement of the intraspecies quorum-sensing system during the formation of stress-induced multidrug-tolerant persisters. To the best of our knowledge, this is the first study reporting the induction of bacterial persistence using a quorum-sensing regulatory system.
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Frampton R, Aggio RBM, Villas-Bôas SG, Arcus VL, Cook GM. Toxin-antitoxin systems of Mycobacterium smegmatis are essential for cell survival. J Biol Chem 2011; 287:5340-56. [PMID: 22199354 DOI: 10.1074/jbc.m111.286856] [Citation(s) in RCA: 52] [Impact Index Per Article: 4.0] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/06/2022] Open
Abstract
The role of chromosomal toxin-antitoxin (TA) modules in bacterial physiology remains enigmatic despite their abundance in the genomes of many bacteria. Mycobacterium smegmatis contains three putative TA systems, VapBC, MazEF, and Phd/Doc, and previous work from our group has shown VapBC to be a bona fide TA system. In this study, we show that MazEF and Phd/Doc are also TA systems that are constitutively expressed, transcribed as leaderless transcripts, and subject to autoregulation, and expression of the toxin component leads to growth inhibition that can be rescued by the cognate antitoxin. No phenotype was identified for deletions of the individual TA systems, but a triple deletion strain (ΔvapBC, mazEF, phd/doc), designated ΔTA(triple), exhibited a survival defect in complex growth medium demonstrating an essential role for these TA modules in mycobacterial survival. Transcriptomic analysis revealed no significant differences in gene expression between wild type and the ΔTA(triple) mutant under these conditions suggesting that the growth defect was not at a transcriptional level. Metabolomic analysis demonstrated that in response to starvation in complex medium, both the wild type and ΔTA(triple) mutant consumed a wide range of amino acids from the external milieu. Analysis of intracellular metabolites revealed a significant difference in the levels of branched-chain amino acids between the wild type and ΔTA(triple) mutant, which are proposed to play essential roles in monitoring the nutritional supply and physiological state of the cell and linking catabolic with anabolic reactions. Disruption of this balance in the ΔTA(triple) mutant may explain the survival defect in complex growth medium.
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Affiliation(s)
- Rebekah Frampton
- Department of Microbiology and Immunology, Otago School of Medical Sciences, University of Otago, Dunedin 9054, New Zealand
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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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