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Shen Z, Tang CM, Liu GY. Towards a better understanding of antimicrobial resistance dissemination: what can be learnt from studying model conjugative plasmids? Mil Med Res 2022; 9:3. [PMID: 35012680 PMCID: PMC8744291 DOI: 10.1186/s40779-021-00362-z] [Citation(s) in RCA: 7] [Impact Index Per Article: 3.5] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Received: 07/23/2021] [Accepted: 12/26/2021] [Indexed: 12/12/2022] Open
Abstract
Bacteria can evolve rapidly by acquiring new traits such as virulence, metabolic properties, and most importantly, antimicrobial resistance, through horizontal gene transfer (HGT). Multidrug resistance in bacteria, especially in Gram-negative organisms, has become a global public health threat often through the spread of mobile genetic elements. Conjugation represents a major form of HGT and involves the transfer of DNA from a donor bacterium to a recipient by direct contact. Conjugative plasmids, a major vehicle for the dissemination of antimicrobial resistance, are selfish elements capable of mediating their own transmission through conjugation. To spread to and survive in a new bacterial host, conjugative plasmids have evolved mechanisms to circumvent both host defense systems and compete with co-resident plasmids. Such mechanisms have mostly been studied in model plasmids such as the F plasmid, rather than in conjugative plasmids that confer antimicrobial resistance (AMR) in important human pathogens. A better understanding of these mechanisms is crucial for predicting the flow of antimicrobial resistance-conferring conjugative plasmids among bacterial populations and guiding the rational design of strategies to halt the spread of antimicrobial resistance. Here, we review mechanisms employed by conjugative plasmids that promote their transmission and establishment in Gram-negative bacteria, by following the life cycle of conjugative plasmids.
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Affiliation(s)
- Zhen Shen
- Sir William Dunn School of Pathology, University of Oxford, Oxford, OX1 3RE, UK.,Department of Laboratory Medicine, Ren Ji Hospital, School of Medicine, Shanghai Jiao Tong University, Shanghai, 200127, China
| | - Christoph M Tang
- Sir William Dunn School of Pathology, University of Oxford, Oxford, OX1 3RE, UK
| | - Guang-Yu Liu
- Sir William Dunn School of Pathology, University of Oxford, Oxford, OX1 3RE, UK.
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Crespo I, Bernardo N, Cuppari A, Malfois M, Boer DR. Structural and biochemical characterization of the relaxosome auxiliary proteins encoded on the Bacillus subtilis plasmid pLS20. Comput Struct Biotechnol J 2022; 20:757-765. [PMID: 35198129 PMCID: PMC8829557 DOI: 10.1016/j.csbj.2021.12.041] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 03/14/2021] [Revised: 12/22/2021] [Accepted: 12/30/2021] [Indexed: 12/03/2022] Open
Abstract
Bacterial conjugation is an important route for horizontal gene transfer. The initial step in this process involves a macromolecular protein-DNA complex called the relaxosome, which in plasmids consists of the origin of transfer (oriT) and several proteins that prepare the transfer. The relaxosome protein named relaxase introduces a nick in one of the strands of the oriT to initiate the process. Additional relaxosome proteins can exist. Recently, several relaxosome proteins encoded on the Bacillus subtilis plasmid pLS20 were identified, including the relaxase, named RelpLS20, and two auxiliary DNA-binding factors, named Aux1pLS20 and Aux2pLS20. Here, we extend this characterization in order to define their function. We present the low-resolution SAXS envelope of the Aux1pLS20 and the atomic X-ray structure of the C-terminal domain of Aux2pLS20. We also study the interactions between the auxiliary proteins and the full-length RelpLS20, as well as its separate domains. The results show that the quaternary structure of the auxiliary protein Aux1pLS20 involves a tetramer, as previously determined. The crystal structure of the C-terminal domain of Aux2pLS20 shows that it forms a tetramer and suggests that it is an analog of TraMpF of plasmid F. This is the first evidence of the existence of a TraMpF analog in gram positive conjugative systems, although, unlike other TraMpF analogs, Aux2pLS20 does not interact with the relaxase. Aux1pLS20 interacts with the C-terminal domain, but not the N-terminal domain, of the relaxase RelpLS20. Thus, the pLS20 relaxosome exhibits some unique features despite the apparent similarity to some well-studied G- conjugation systems.
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Protein Transfer through an F Plasmid-Encoded Type IV Secretion System Suppresses the Mating-Induced SOS Response. mBio 2021; 12:e0162921. [PMID: 34253063 PMCID: PMC8406263 DOI: 10.1128/mbio.01629-21] [Citation(s) in RCA: 7] [Impact Index Per Article: 2.3] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/24/2022] Open
Abstract
Bacterial type IV secretion systems (T4SSs) mediate the conjugative transfer of mobile genetic elements (MGEs) and their cargoes of antibiotic resistance and virulence genes. Here, we report that the pED208-encoded T4SS (TrapED208) translocates not only this F plasmid but several plasmid-encoded proteins, including ParA, ParB1, single-stranded DNA-binding protein SSB, ParB2, PsiB, and PsiA, to recipient cells. Conjugative protein translocation through the TrapED208 T4SS required engagement of the pED208 relaxosome with the TraD substrate receptor or coupling protein. T4SSs translocate MGEs as single-stranded DNA intermediates (T-strands), which triggers the SOS response in recipient cells. Transfer of pED208 deleted of psiB or ssb, which, respectively, encode the SOS inhibitor protein PsiB and single-stranded DNA-binding protein SSB, elicited a significantly stronger SOS response than pED208 or mutant plasmids deleted of psiA, parA, parB1, or parB2. Conversely, translocation of PsiB or SSB, but not PsiA, through the TrapED208 T4SS suppressed the mating-induced SOS response. Our findings expand the repertoire of known substrates of conjugation systems to include proteins with functions associated with plasmid maintenance. Furthermore, for this and other F-encoded Tra systems, docking of the DNA substrate with the TraD receptor appears to serve as a critical activating signal for protein translocation. Finally, the observed effects of PsiB and SSB on suppression of the mating-induced SOS response establishes a novel biological function for conjugative protein translocation and suggests the potential for interbacterial protein translocation to manifest in diverse outcomes influencing bacterial communication, physiology, and evolution.
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Costa TRD, Harb L, Khara P, Zeng L, Hu B, Christie PJ. Type IV secretion systems: Advances in structure, function, and activation. Mol Microbiol 2021; 115:436-452. [PMID: 33326642 DOI: 10.1111/mmi.14670] [Citation(s) in RCA: 105] [Impact Index Per Article: 35.0] [Reference Citation Analysis] [Abstract] [Key Words] [Journal Information] [Subscribe] [Scholar Register] [Received: 10/09/2020] [Revised: 12/12/2020] [Accepted: 12/13/2020] [Indexed: 12/14/2022]
Abstract
Bacterial type IV secretion systems (T4SSs) are a functionally diverse translocation superfamily. They consist mainly of two large subfamilies: (i) conjugation systems that mediate interbacterial DNA transfer and (ii) effector translocators that deliver effector macromolecules into prokaryotic or eukaryotic cells. A few other T4SSs export DNA or proteins to the milieu, or import exogenous DNA. The T4SSs are defined by 6 or 12 conserved "core" subunits that respectively elaborate "minimized" systems in Gram-positive or -negative bacteria. However, many "expanded" T4SSs are built from "core" subunits plus numerous others that are system-specific, which presumptively broadens functional capabilities. Recently, there has been exciting progress in defining T4SS assembly pathways and architectures using a combination of fluorescence and cryoelectron microscopy. This review will highlight advances in our knowledge of structure-function relationships for model Gram-negative bacterial T4SSs, including "minimized" systems resembling the Agrobacterium tumefaciens VirB/VirD4 T4SS and "expanded" systems represented by the Helicobacter pylori Cag, Legionella pneumophila Dot/Icm, and F plasmid-encoded Tra T4SSs. Detailed studies of these model systems are generating new insights, some at atomic resolution, to long-standing questions concerning mechanisms of substrate recruitment, T4SS channel architecture, conjugative pilus assembly, and machine adaptations contributing to T4SS functional versatility.
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Affiliation(s)
- Tiago R D Costa
- MRC Centre for Molecular Bacteriology and Infection, Department of Life Sciences, Imperial College London, London, UK
| | - Laith Harb
- Department of Biochemistry and Biophysics and Center for Phage Technology, Texas A&M University, College Station, TX, USA
| | - Pratick Khara
- Department of Microbiology and Molecular Genetics, McGovern Medical School at UTHealth, Houston, TX, USA
| | - Lanying Zeng
- Department of Biochemistry and Biophysics and Center for Phage Technology, Texas A&M University, College Station, TX, USA
| | - Bo Hu
- Department of Microbiology and Molecular Genetics, McGovern Medical School at UTHealth, Houston, TX, USA
| | - Peter J Christie
- Department of Microbiology and Molecular Genetics, McGovern Medical School at UTHealth, Houston, TX, USA
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Hancock SJ, Phan MD, Luo Z, Lo AW, Peters KM, Nhu NTK, Forde BM, Whitfield J, Yang J, Strugnell RA, Paterson DL, Walsh TR, Kobe B, Beatson SA, Schembri MA. Comprehensive analysis of IncC plasmid conjugation identifies a crucial role for the transcriptional regulator AcaB. Nat Microbiol 2020; 5:1340-1348. [PMID: 32807890 DOI: 10.1038/s41564-020-0775-0] [Citation(s) in RCA: 15] [Impact Index Per Article: 3.8] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 12/08/2018] [Accepted: 07/16/2020] [Indexed: 01/05/2023]
Abstract
The IncC family of broad-host-range plasmids enables the spread of antibiotic resistance genes among human enteric pathogens1-3. Although aspects of IncC plasmid conjugation have been well studied4-9, many roles of conjugation genes have been assigned based solely on sequence similarity. We applied hypersaturated transposon mutagenesis and transposon-directed insertion-site sequencing to determine the set of genes required for IncC conjugation. We identified 27 conjugation genes, comprising 19 that were previously identified (including two regulatory genes, acaDC) and eight not previously associated with conjugation. We show that one previously unknown gene, acaB, encodes a transcriptional regulator that has a crucial role in the regulation of IncC conjugation. AcaB binds upstream of the acaDC promoter to increase acaDC transcription; in turn, AcaDC activates the transcription of IncC conjugation genes. We solved the crystal structure of AcaB at 2.9-Å resolution and used this to guide functional analyses that reveal how AcaB binds to DNA. This improved understanding of IncC conjugation provides a basis for the development of new approaches to reduce the spread of these multi-drug-resistance plasmids.
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Affiliation(s)
- Steven J Hancock
- School of Chemistry and Molecular Biosciences, The University of Queensland, Brisbane, Queensland, Australia
- Australian Infectious Diseases Research Centre, The University of Queensland, Brisbane, Queensland, Australia
| | - Minh-Duy Phan
- School of Chemistry and Molecular Biosciences, The University of Queensland, Brisbane, Queensland, Australia.
- Australian Infectious Diseases Research Centre, The University of Queensland, Brisbane, Queensland, Australia.
| | - Zhenyao Luo
- School of Chemistry and Molecular Biosciences, The University of Queensland, Brisbane, Queensland, Australia
- Australian Infectious Diseases Research Centre, The University of Queensland, Brisbane, Queensland, Australia
- Institute for Molecular Bioscience, The University of Queensland, Brisbane, Queensland, Australia
| | - Alvin W Lo
- School of Chemistry and Molecular Biosciences, The University of Queensland, Brisbane, Queensland, Australia
- Australian Infectious Diseases Research Centre, The University of Queensland, Brisbane, Queensland, Australia
| | - Kate M Peters
- School of Chemistry and Molecular Biosciences, The University of Queensland, Brisbane, Queensland, Australia
- Australian Infectious Diseases Research Centre, The University of Queensland, Brisbane, Queensland, Australia
| | - Nguyen Thi Khanh Nhu
- School of Chemistry and Molecular Biosciences, The University of Queensland, Brisbane, Queensland, Australia
- Australian Infectious Diseases Research Centre, The University of Queensland, Brisbane, Queensland, Australia
| | - Brian M Forde
- School of Chemistry and Molecular Biosciences, The University of Queensland, Brisbane, Queensland, Australia
- Australian Infectious Diseases Research Centre, The University of Queensland, Brisbane, Queensland, Australia
| | - Jason Whitfield
- Institute for Molecular Bioscience, The University of Queensland, Brisbane, Queensland, Australia
- Australian Institute for Bioengineering and Nanotechnology, The University of Queensland, Brisbane, Queensland, Australia
| | - Ji Yang
- Department of Microbiology and Immunology, The University of Melbourne at the Peter Doherty Institute for Infection and Immunity, Melbourne, Victoria, Australia
| | - Richard A Strugnell
- Department of Microbiology and Immunology, The University of Melbourne at the Peter Doherty Institute for Infection and Immunity, Melbourne, Victoria, Australia
| | - David L Paterson
- The University of Queensland Centre for Clinical Research, Brisbane, Queensland, Australia
| | | | - Bostjan Kobe
- School of Chemistry and Molecular Biosciences, The University of Queensland, Brisbane, Queensland, Australia.
- Australian Infectious Diseases Research Centre, The University of Queensland, Brisbane, Queensland, Australia.
- Institute for Molecular Bioscience, The University of Queensland, Brisbane, Queensland, Australia.
| | - Scott A Beatson
- School of Chemistry and Molecular Biosciences, The University of Queensland, Brisbane, Queensland, Australia
- Australian Infectious Diseases Research Centre, The University of Queensland, Brisbane, Queensland, Australia
| | - Mark A Schembri
- School of Chemistry and Molecular Biosciences, The University of Queensland, Brisbane, Queensland, Australia.
- Australian Infectious Diseases Research Centre, The University of Queensland, Brisbane, Queensland, Australia.
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Li YG, Christie PJ. The TraK accessory factor activates substrate transfer through the pKM101 type IV secretion system independently of its role in relaxosome assembly. Mol Microbiol 2020; 114:214-229. [PMID: 32239779 DOI: 10.1111/mmi.14507] [Citation(s) in RCA: 12] [Impact Index Per Article: 3.0] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 02/02/2020] [Revised: 03/24/2020] [Indexed: 12/12/2022]
Abstract
A large subfamily of the type IV secretion systems (T4SSs), termed the conjugation systems, transmit mobile genetic elements (MGEs) among many bacterial species. In the initiating steps of conjugative transfer, DNA transfer and replication (Dtr) proteins assemble at the origin-of-transfer (oriT) sequence as the relaxosome, which nicks the DNA strand destined for transfer and couples the nicked substrate with the VirD4-like substrate receptor. Here, we defined contributions of the Dtr protein TraK, a predicted member of the Ribbon-Helix-Helix (RHH) family of DNA-binding proteins, to transfer of DNA and protein substrates through the pKM101-encoded T4SS. Using a combination of cross-linking/affinity pull-downs and two-hybrid assays, we determined that TraK self-associates as a probable tetramer and also forms heteromeric contacts with pKM101-encoded TraI relaxase, VirD4-like TraJ receptor, and VirB11-like and VirB4-like ATPases, TraG and TraB, respectively. TraK also promotes stable TraJ-TraB complex formation and stimulates binding of TraI with TraB. Finally, TraK is required for or strongly stimulates the transfer of cognate (pKM101, TraI relaxase) and noncognate (RSF1010, MobA relaxase) substrates. We propose that TraK functions not only to nucleate pKM101 relaxosome assembly, but also to activate the TrapKM101 T4SS via interactions with the ATPase energy center positioned at the channel entrance.
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Affiliation(s)
- Yang Grace Li
- Department of Microbiology and Molecular Genetics, McGovern Medical School, Houston, TX, USA
| | - Peter J Christie
- Department of Microbiology and Molecular Genetics, McGovern Medical School, Houston, TX, USA
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Cooperative Function of TraJ and ArcA in Regulating the F Plasmid tra Operon. J Bacteriol 2018; 201:JB.00448-18. [PMID: 30322855 DOI: 10.1128/jb.00448-18] [Citation(s) in RCA: 7] [Impact Index Per Article: 1.2] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 07/25/2018] [Accepted: 10/03/2018] [Indexed: 11/20/2022] Open
Abstract
The F plasmid tra operon encodes most of the proteins required for bacterial conjugation. TraJ and ArcA are known activators of the tra operon promoter PY, which is subject to H-NS-mediated silencing. Donor ability and promoter activity assays indicated that PY is inactivated by silencers and requires both TraJ and ArcA for activation to support efficient F conjugation. The observed low-level, ArcA-independent F conjugation is caused by tra expression from upstream alternative promoters. Electrophoretic mobility shift assays showed that TraJ alone weakly binds to PY regulatory DNA; however, TraJ binding is significantly enhanced by ArcA binding to the same DNA, indicating cooperativity of the two proteins. Analysis of binding affinities between ArcA and various DNA fragments in the PY regulatory region defined a 22-bp tandem repeat sequence (from -76 to -55 of PY) sufficient for optimal ArcA binding, which is immediately upstream of the predicted TraJ-binding site (from -54 to -34). Deletion analysis of the PY promoter in strains deficient in TraJ, ArcA, and/or H-NS determined that sequences upstream of -103 are required by silencers including H-NS for PY silencing, whereas sequences downstream of -77 are targeted by TraJ and ArcA for activation. TraJ and ArcA appear not only to counteract PY silencers but also to directly activate PY in a cooperative manner. Our data reveal the cooperativity of TraJ and ArcA during PY activation and provide insights into the regulatory circuit controlling F-family plasmid-mediated bacterial conjugation.IMPORTANCE Conjugation is a major mechanism for dissemination of antibiotic resistance and virulence among bacterial populations. The tra operon in the F family of conjugative plasmids encodes most of the proteins involved in bacterial conjugation. This work reveals that activation of tra operon transcription requires two proteins, TraJ and ArcA, to bind cooperatively to adjacent sites immediately upstream of the major tra promoter PY The interaction of TraJ and ArcA with the tra operon not only relieves PY from silencers but also directly activates it. These findings provide insights into the regulatory circuit of the F-family plasmid-mediated bacterial conjugation.
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Miguel-Arribas A, Hao JA, Luque-Ortega JR, Ramachandran G, Val-Calvo J, Gago-Córdoba C, González-Álvarez D, Abia D, Alfonso C, Wu LJ, Meijer WJJ. The Bacillus subtilis Conjugative Plasmid pLS20 Encodes Two Ribbon-Helix-Helix Type Auxiliary Relaxosome Proteins That Are Essential for Conjugation. Front Microbiol 2017; 8:2138. [PMID: 29163424 PMCID: PMC5675868 DOI: 10.3389/fmicb.2017.02138] [Citation(s) in RCA: 8] [Impact Index Per Article: 1.1] [Reference Citation Analysis] [Abstract] [Key Words] [Grants] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 08/03/2017] [Accepted: 10/19/2017] [Indexed: 12/15/2022] Open
Abstract
Bacterial conjugation is the process by which a conjugative element (CE) is transferred horizontally from a donor to a recipient cell via a connecting pore. One of the first steps in the conjugation process is the formation of a nucleoprotein complex at the origin of transfer (oriT), where one of the components of the nucleoprotein complex, the relaxase, introduces a site- and strand specific nick to initiate the transfer of a single DNA strand into the recipient cell. In most cases, the nucleoprotein complex involves, besides the relaxase, one or more additional proteins, named auxiliary proteins, which are encoded by the CE and/or the host. The conjugative plasmid pLS20 replicates in the Gram-positive Firmicute bacterium Bacillus subtilis. We have recently identified the relaxase gene and the oriT of pLS20, which are separated by a region of almost 1 kb. Here we show that this region contains two auxiliary genes that we name aux1LS20 and aux2LS20 , and which we show are essential for conjugation. Both Aux1LS20 and Aux2LS20 are predicted to contain a Ribbon-Helix-Helix DNA binding motif near their N-terminus. Analyses of the purified proteins show that Aux1LS20 and Aux2LS20 form tetramers and hexamers in solution, respectively, and that they both bind preferentially to oriTLS20 , although with different characteristics and specificities. In silico analyses revealed that genes encoding homologs of Aux1LS20 and/or Aux2LS20 are located upstream of almost 400 relaxase genes of the RelLS20 family (MOBL) of relaxases. Thus, Aux1LS20 and Aux2LS20 of pLS20 constitute the founding member of the first two families of auxiliary proteins described for CEs of Gram-positive origin.
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Affiliation(s)
- Andrés Miguel-Arribas
- Department of Virology and Microbiology, Centro de Biología Molecular “Severo Ochoa” (CSIC-UAM), Instituto de Biología Molecular “Eladio Viñuela” (CSIC), Autonomous University of Madrid, Madrid, Spain
| | - Jian-An Hao
- Department of Virology and Microbiology, Centro de Biología Molecular “Severo Ochoa” (CSIC-UAM), Instituto de Biología Molecular “Eladio Viñuela” (CSIC), Autonomous University of Madrid, Madrid, Spain
- The Institute of Seawater Desalination and Multipurpose Utilization (SOA), Tianjin, China
| | | | - Gayetri Ramachandran
- Department of Virology and Microbiology, Centro de Biología Molecular “Severo Ochoa” (CSIC-UAM), Instituto de Biología Molecular “Eladio Viñuela” (CSIC), Autonomous University of Madrid, Madrid, Spain
| | - Jorge Val-Calvo
- Department of Virology and Microbiology, Centro de Biología Molecular “Severo Ochoa” (CSIC-UAM), Instituto de Biología Molecular “Eladio Viñuela” (CSIC), Autonomous University of Madrid, Madrid, Spain
| | - César Gago-Córdoba
- Department of Virology and Microbiology, Centro de Biología Molecular “Severo Ochoa” (CSIC-UAM), Instituto de Biología Molecular “Eladio Viñuela” (CSIC), Autonomous University of Madrid, Madrid, Spain
| | - Daniel González-Álvarez
- Department of Virology and Microbiology, Centro de Biología Molecular “Severo Ochoa” (CSIC-UAM), Instituto de Biología Molecular “Eladio Viñuela” (CSIC), Autonomous University of Madrid, Madrid, Spain
| | - David Abia
- Department of Virology and Microbiology, Centro de Biología Molecular “Severo Ochoa” (CSIC-UAM), Instituto de Biología Molecular “Eladio Viñuela” (CSIC), Autonomous University of Madrid, Madrid, Spain
| | - Carlos Alfonso
- Centro de Investigaciones Biológicas (CSIC), Madrid, Spain
| | - Ling J. Wu
- Centre for Bacterial Cell Biology, Institute for Cell and Molecular Biosciences, Newcastle University, Newcastle Upon Tyne, United Kingdom
| | - Wilfried J. J. Meijer
- Department of Virology and Microbiology, Centro de Biología Molecular “Severo Ochoa” (CSIC-UAM), Instituto de Biología Molecular “Eladio Viñuela” (CSIC), Autonomous University of Madrid, Madrid, Spain
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O'Brien FG, Yui Eto K, Murphy RJT, Fairhurst HM, Coombs GW, Grubb WB, Ramsay JP. Origin-of-transfer sequences facilitate mobilisation of non-conjugative antimicrobial-resistance plasmids in Staphylococcus aureus. Nucleic Acids Res 2015; 43:7971-83. [PMID: 26243776 PMCID: PMC4652767 DOI: 10.1093/nar/gkv755] [Citation(s) in RCA: 59] [Impact Index Per Article: 6.6] [Reference Citation Analysis] [Abstract] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 05/26/2015] [Accepted: 07/14/2015] [Indexed: 11/17/2022] Open
Abstract
Staphylococcus aureus is a common cause of hospital, community and livestock-associated infections and is increasingly resistant to multiple antimicrobials. A significant proportion of antimicrobial-resistance genes are plasmid-borne, but only a minority of S. aureus plasmids encode proteins required for conjugative transfer or Mob relaxase proteins required for mobilisation. The pWBG749 family of S. aureus conjugative plasmids can facilitate the horizontal transfer of diverse antimicrobial-resistance plasmids that lack Mob genes. Here we reveal that these mobilisable plasmids carry copies of the pWBG749 origin-of-transfer (oriT) sequence and that these oriT sequences facilitate mobilisation by pWBG749. Sequences resembling the pWBG749 oriT were identified on half of all sequenced S. aureus plasmids, including the most prevalent large antimicrobial-resistance/virulence-gene plasmids, pIB485, pMW2 and pUSA300HOUMR. oriT sequences formed five subfamilies with distinct inverted-repeat-2 (IR2) sequences. pWBG749-family plasmids encoding each IR2 were identified and pWBG749 mobilisation was found to be specific for plasmids carrying matching IR2 sequences. Specificity of mobilisation was conferred by a putative ribbon-helix-helix-protein gene smpO. Several plasmids carried 2–3 oriT variants and pWBG749-mediated recombination occurred between distinct oriT sites during mobilisation. These observations suggest this relaxase-in trans mechanism of mobilisation by pWBG749-family plasmids is a common mechanism of plasmid dissemination in S. aureus.
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Affiliation(s)
- Frances G O'Brien
- CHIRI Biosciences Precinct, School of Biomedical Sciences, Faculty of Health Sciences, Curtin University, Bentley WA 6102, Australia Australian Collaborating Centre for Enterococcus and Staphylococcus Species (ACCESS) Typing and Research, School of Veterinary Sciences and Life Sciences, Murdoch University and School of Biomedical Sciences, Curtin University, Perth, Western Australia, Australia
| | - Karina Yui Eto
- CHIRI Biosciences Precinct, School of Biomedical Sciences, Faculty of Health Sciences, Curtin University, Bentley WA 6102, Australia
| | - Riley J T Murphy
- CHIRI Biosciences Precinct, School of Biomedical Sciences, Faculty of Health Sciences, Curtin University, Bentley WA 6102, Australia
| | - Heather M Fairhurst
- CHIRI Biosciences Precinct, School of Biomedical Sciences, Faculty of Health Sciences, Curtin University, Bentley WA 6102, Australia
| | - Geoffrey W Coombs
- CHIRI Biosciences Precinct, School of Biomedical Sciences, Faculty of Health Sciences, Curtin University, Bentley WA 6102, Australia Australian Collaborating Centre for Enterococcus and Staphylococcus Species (ACCESS) Typing and Research, School of Veterinary Sciences and Life Sciences, Murdoch University and School of Biomedical Sciences, Curtin University, Perth, Western Australia, Australia PathWest Laboratory Medicine, Fiona Stanley Hospital, Perth, Western Australia, Australia
| | - Warren B Grubb
- CHIRI Biosciences Precinct, School of Biomedical Sciences, Faculty of Health Sciences, Curtin University, Bentley WA 6102, Australia Australian Collaborating Centre for Enterococcus and Staphylococcus Species (ACCESS) Typing and Research, School of Veterinary Sciences and Life Sciences, Murdoch University and School of Biomedical Sciences, Curtin University, Perth, Western Australia, Australia
| | - Joshua P Ramsay
- CHIRI Biosciences Precinct, School of Biomedical Sciences, Faculty of Health Sciences, Curtin University, Bentley WA 6102, Australia Australian Collaborating Centre for Enterococcus and Staphylococcus Species (ACCESS) Typing and Research, School of Veterinary Sciences and Life Sciences, Murdoch University and School of Biomedical Sciences, Curtin University, Perth, Western Australia, Australia
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