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Castellani LG, Luchetti A, Nilsson JF, Pérez-Giménez J, Struck B, Schlüter A, Pühler A, Niehaus K, Romero D, Pistorio M, Torres Tejerizo G. RcgA and RcgR, Two Novel Proteins Involved in the Conjugative Transfer of Rhizobial Plasmids. mBio 2022; 13:e0194922. [PMID: 36073816 PMCID: PMC9601222 DOI: 10.1128/mbio.01949-22] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 07/08/2022] [Accepted: 08/12/2022] [Indexed: 11/20/2022] Open
Abstract
Rhizobia are Gram-negative bacteria that are able to establish a nitrogen-fixing symbiotic interaction with leguminous plants. Rhizobia genomes usually harbor several plasmids which can be transferred to other organisms by conjugation. Two main mechanisms of the regulation of rhizobial plasmid transfer have been described: quorum sensing (QS) and the rctA/rctB system. Nevertheless, new genes and molecules that modulate conjugative transfer have recently been described, demonstrating that new actors can tightly regulate the process. In this work, by means of bioinformatics tools and molecular biology approaches, two hypothetical genes are identified as playing key roles in conjugative transfer. These genes are located between conjugative genes of plasmid pRfaLPU83a from Rhizobium favelukesii LPU83, a plasmid that shows a conjugative transfer behavior depending on the genomic background. One of the two mentioned genes, rcgA, is essential for conjugation, while the other, rcgR, acts as an inhibitor of the process. In addition to introducing this new regulatory system, we show evidence of the functions of these genes in different genomic backgrounds and confirm that homologous proteins from non-closely related organisms have the same functions. These findings set up the basis for a new regulatory circuit of the conjugative transfer of plasmids. IMPORTANCE Extrachromosomal DNA elements, such as plasmids, allow for the adaptation of bacteria to new environments by conferring new determinants. Via conjugation, plasmids can be transferred between members of the same bacterial species, different species, or even to organisms belonging to a different kingdom. Knowledge about the regulatory systems of plasmid conjugative transfer is key in understanding the dynamics of their dissemination in the environment. As the increasing availability of genomes raises the number of predicted proteins with unknown functions, deeper experimental procedures help to elucidate the roles of these determinants. In this work, two uncharacterized proteins that constitute a new regulatory circuit with a key role in the conjugative transfer of rhizobial plasmids were discovered.
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Affiliation(s)
- Lucas G. Castellani
- Instituto de Biotecnología y Biología Molecular, CCT-La Plata-CONICET, Departamento de Ciencias Biológicas, Facultad de Ciencias Exactas, Universidad Nacional de La Plata, La Plata, Argentina
| | - Abril Luchetti
- Instituto de Biotecnología y Biología Molecular, CCT-La Plata-CONICET, Departamento de Ciencias Biológicas, Facultad de Ciencias Exactas, Universidad Nacional de La Plata, La Plata, Argentina
| | - Juliet F. Nilsson
- Instituto de Biotecnología y Biología Molecular, CCT-La Plata-CONICET, Departamento de Ciencias Biológicas, Facultad de Ciencias Exactas, Universidad Nacional de La Plata, La Plata, Argentina
| | - Julieta Pérez-Giménez
- Instituto de Biotecnología y Biología Molecular, CCT-La Plata-CONICET, Departamento de Ciencias Biológicas, Facultad de Ciencias Exactas, Universidad Nacional de La Plata, La Plata, Argentina
| | - Ben Struck
- Center for Biotechnology (CeBiTec), Bielefeld University, Genome Research of Industrial Microorganisms, Bielefeld, Germany
| | - Andreas Schlüter
- Center for Biotechnology (CeBiTec), Bielefeld University, Genome Research of Industrial Microorganisms, Bielefeld, Germany
| | - Alfred Pühler
- Center for Biotechnology (CeBiTec), Bielefeld University, Genome Research of Industrial Microorganisms, Bielefeld, Germany
| | - Karsten Niehaus
- Center for Biotechnology (CeBiTec), Bielefeld University, Genome Research of Industrial Microorganisms, Bielefeld, Germany
| | - David Romero
- Programa de Ingeniería Genómica, Centro de Ciencias Genómicas, Universidad Nacional Autónoma de México, Cuernavaca, Morelos, México
| | - Mariano Pistorio
- Instituto de Biotecnología y Biología Molecular, CCT-La Plata-CONICET, Departamento de Ciencias Biológicas, Facultad de Ciencias Exactas, Universidad Nacional de La Plata, La Plata, Argentina
| | - Gonzalo Torres Tejerizo
- Instituto de Biotecnología y Biología Molecular, CCT-La Plata-CONICET, Departamento de Ciencias Biológicas, Facultad de Ciencias Exactas, Universidad Nacional de La Plata, La Plata, Argentina
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Wardell GE, Hynes MF, Young PJ, Harrison E. Why are rhizobial symbiosis genes mobile? Philos Trans R Soc Lond B Biol Sci 2022; 377:20200471. [PMID: 34839705 PMCID: PMC8628070 DOI: 10.1098/rstb.2020.0471] [Citation(s) in RCA: 17] [Impact Index Per Article: 8.5] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 05/14/2021] [Accepted: 07/28/2021] [Indexed: 11/12/2022] Open
Abstract
Rhizobia are one of the most important and best studied groups of bacterial symbionts. They are defined by their ability to establish nitrogen-fixing intracellular infections within plant hosts. One surprising feature of this symbiosis is that the bacterial genes required for this complex trait are not fixed within the chromosome, but are encoded on mobile genetic elements (MGEs), namely plasmids or integrative and conjugative elements. Evidence suggests that many of these elements are actively mobilizing within rhizobial populations, suggesting that regular symbiosis gene transfer is part of the ecology of rhizobial symbionts. At first glance, this is counterintuitive. The symbiosis trait is highly complex, multipartite and tightly coevolved with the legume hosts, while transfer of genes can be costly and disrupt coadaptation between the chromosome and the symbiosis genes. However, horizontal gene transfer is a process driven not only by the interests of the host bacterium, but also, and perhaps predominantly, by the interests of the MGEs that facilitate it. Thus understanding the role of horizontal gene transfer in the rhizobium-legume symbiosis requires a 'mobile genetic element's-eye view' on the ecology and evolution of this important symbiosis. This article is part of the theme issue 'The secret lives of microbial mobile genetic elements'.
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Affiliation(s)
- Grace E. Wardell
- Department of Animal Plant Sciences, University of Sheffield, Western Bank, Sheffield S10 1EA, UK
| | - Michael F. Hynes
- Biological Sciences, University of Calgary, 2500 University Drive NW, Calgary, Alberta, Canada T2N 1N4
| | - Peter J. Young
- Department of Biology, University of York, Wentworth Way, York YO10 5DD, UK
| | - Ellie Harrison
- Department of Animal Plant Sciences, University of Sheffield, Western Bank, Sheffield S10 1EA, UK
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Bañuelos-Vazquez LA, Cazares D, Rodríguez S, Cervantes-De la Luz L, Sánchez-López R, Castellani LG, Tejerizo GT, Brom S. Transfer of the Symbiotic Plasmid of Rhizobium etli CFN42 to Endophytic Bacteria Inside Nodules. Front Microbiol 2020; 11:1752. [PMID: 32849381 PMCID: PMC7403402 DOI: 10.3389/fmicb.2020.01752] [Citation(s) in RCA: 8] [Impact Index Per Article: 2.0] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 04/14/2020] [Accepted: 07/06/2020] [Indexed: 12/27/2022] Open
Abstract
Conjugative transfer is one of the mechanisms allowing diversification and evolution of bacteria. Rhizobium etli CFN42 is a bacterial strain whose habitat is the rhizosphere and is able to form nodules as a result of the nitrogen-fixing symbiotic relationship it may establish with the roots of Phaseolus vulgaris. R. etli CFN42 contains one chromosome and six large plasmids (pRet42a - pRet42f). Most of the genetic information involved in the establishment of the symbiosis is localized on plasmid pRet42d, named as the symbiotic plasmid (pSym). This plasmid is able to perform conjugation, using pSym encoded transfer genes controlled by the RctA/RctB system. Another plasmid of CFN42, pRet42a, has been shown to perform conjugative transfer not only in vitro, but also on the surface of roots and inside nodules, using other rhizobia as recipients. In addition to the rhizobia involved in the formation of nodules, these structures have been shown to contain endophytic bacteria from different genera and species. In this work, we have explored the conjugative transfer of the pSym (pRet42d) from R. etli CFN42 to endophytic bacteria as putative recipients, using as donor a CFN42 derivative labeled with GFP in the pRet42d and RFP in the chromosome. We were able to isolate some transconjugants, which inherit the GFP, but not the RFP marker. Some of them were identified, analyzed and evaluated for their ability to nodulate. We found transconjugants from genera such as Stenotrophomonas, Achromobacter, and Bacillus, among others. Although all the transconjugants carried the GFP marker, and nod, fix, and nif genes from pRet42d, not all were able to nodulate. Ultrastructure microscopy analysis showed some differences in the structure of the nodules of one of the transconjugants. A replicon of the size of pRet42d (371 Kb) could not be visualized in the transconjugants, suggesting that the pSym or a segment of the plasmid is integrated in the chromosome of the recipients. These findings strengthen the proposal that nodules constitute a propitious environment for exchange of genetic information among bacteria, in addition to their function as structures where nitrogen fixation and assimilation takes place.
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Affiliation(s)
- Luis Alfredo Bañuelos-Vazquez
- Programa de Ingeniería Genómica, Centro de Ciencias Genómicas, Universidad Nacional Autónoma de México, Cuernavaca, Mexico
| | - Daniel Cazares
- Programa de Ingeniería Genómica, Centro de Ciencias Genómicas, Universidad Nacional Autónoma de México, Cuernavaca, Mexico
| | - Susana Rodríguez
- Programa de Biología de Sistemas y Biología Sintética, Centro de Ciencias Genómicas, Universidad Nacional Autónoma de México, Cuernavaca, Mexico
| | - Laura Cervantes-De la Luz
- Programa de Ingeniería Genómica, Centro de Ciencias Genómicas, Universidad Nacional Autónoma de México, Cuernavaca, Mexico
| | - Rosana Sánchez-López
- Departamento de Biología Molecular de Plantas, Instituto de Biotecnología, Universidad Nacional Autónoma de México, Cuernavaca, Mexico
| | - Lucas G. Castellani
- Departamento de Ciencias Biológicas, Facultad de Ciencias Exactas, Instituto de Biotecnología y Biología Molecular (IBBM) – CCT-CONICET-La Plata, Universidad Nacional de La Plata, La Plata, Argentina
| | - Gonzalo Torres Tejerizo
- Departamento de Ciencias Biológicas, Facultad de Ciencias Exactas, Instituto de Biotecnología y Biología Molecular (IBBM) – CCT-CONICET-La Plata, Universidad Nacional de La Plata, La Plata, Argentina
| | - Susana Brom
- Programa de Ingeniería Genómica, Centro de Ciencias Genómicas, Universidad Nacional Autónoma de México, Cuernavaca, Mexico
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Bañuelos-Vazquez LA, Torres Tejerizo G, Cervantes-De La Luz L, Girard L, Romero D, Brom S. Conjugative transfer between Rhizobium etli endosymbionts inside the root nodule. Environ Microbiol 2019; 21:3430-3441. [PMID: 31037804 DOI: 10.1111/1462-2920.14645] [Citation(s) in RCA: 12] [Impact Index Per Article: 2.4] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 10/16/2018] [Revised: 04/05/2019] [Accepted: 04/26/2019] [Indexed: 11/30/2022]
Abstract
Since the discovery that biological nitrogen fixation ensues in nodules resulting from the interaction of rhizobia with legumes, nodules were thought to be exclusive for hosting nitrogen-fixing and plant growth promoting bacteria. In this work, we uncover a novel function of nodules, as a niche permissive to acquisition of plasmids via conjugative transfer. We used Rhizobium etli CFN42, which nodulates Phaseolus vulgaris. The genome of R. etli CFN42 contains a chromosome and six plasmids. pRet42a is a conjugative plasmid regulated by Quorum-Sensing (QS), and pRet42d is the symbiotic plasmid. Here, using confocal microscopy and flow cytometry, we show that pRet42a transfers on the root's surface, and unexpectedly, inside the nodules. Conjugation still took place inside nodules, even when it was restricted on the plant surface by placing the QS traI regulator under the promoter of the nitrogenase gene, which is only expressed inside the nodules, or by inhibiting the QS transcriptional induction of transfer genes with a traM antiactivator on an unstable vector maintained on the plant surface and lost inside the nodules. These results conclusively confirm the occurrence of conjugation in these structures, defining them as a protected environment for bacterial diversification.
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Affiliation(s)
- Luis Alfredo Bañuelos-Vazquez
- Programa de Ingeniería Genómica, Centro de Ciencias Genómicas, Universidad Nacional Autónoma de México, Cuernavaca, Morelos, Mexico
| | - Gonzalo Torres Tejerizo
- Programa de Ingeniería Genómica, Centro de Ciencias Genómicas, Universidad Nacional Autónoma de México, Cuernavaca, Morelos, Mexico
| | - Laura Cervantes-De La Luz
- Programa de Ingeniería Genómica, Centro de Ciencias Genómicas, Universidad Nacional Autónoma de México, Cuernavaca, Morelos, Mexico
| | - Lourdes Girard
- Programa de Biología de Sistemas y Biología Sintética, Centro de Ciencias Genómicas, Universidad Nacional Autónoma de México, Cuernavaca, Morelos, Mexico
| | - David Romero
- Programa de Ingeniería Genómica, Centro de Ciencias Genómicas, Universidad Nacional Autónoma de México, Cuernavaca, Morelos, Mexico
| | - Susana Brom
- Programa de Ingeniería Genómica, Centro de Ciencias Genómicas, Universidad Nacional Autónoma de México, Cuernavaca, Morelos, Mexico
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Castellani LG, Nilsson JF, Wibberg D, Schlüter A, Pühler A, Brom S, Pistorio M, Torres Tejerizo G. Insight into the structure, function and conjugative transfer of pLPU83a, an accessory plasmid of Rhizobium favelukesii LPU83. Plasmid 2019; 103:9-16. [DOI: 10.1016/j.plasmid.2019.03.004] [Citation(s) in RCA: 8] [Impact Index Per Article: 1.6] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 01/08/2019] [Revised: 03/11/2019] [Accepted: 03/24/2019] [Indexed: 11/26/2022]
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Bañuelos-Vazquez LA, Torres Tejerizo G, Brom S. Regulation of conjugative transfer of plasmids and integrative conjugative elements. Plasmid 2017; 91:82-89. [DOI: 10.1016/j.plasmid.2017.04.002] [Citation(s) in RCA: 38] [Impact Index Per Article: 5.4] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 01/14/2017] [Revised: 04/18/2017] [Accepted: 04/19/2017] [Indexed: 10/25/2022]
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Grohmann E, Goessweiner-Mohr N, Brantl S. DNA-Binding Proteins Regulating pIP501 Transfer and Replication. Front Mol Biosci 2016; 3:42. [PMID: 27563645 PMCID: PMC4981023 DOI: 10.3389/fmolb.2016.00042] [Citation(s) in RCA: 12] [Impact Index Per Article: 1.5] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 06/24/2016] [Accepted: 07/29/2016] [Indexed: 12/21/2022] Open
Abstract
pIP501 is a Gram-positive broad-host-range model plasmid intensively used for studying plasmid replication and conjugative transfer. It is a multiple antibiotic resistance plasmid frequently detected in clinical Enterococcus faecalis and Enterococcus faecium strains. Replication of pIP501 proceeds unidirectionally by a theta mechanism. The minimal replicon of pIP501 is composed of the repR gene encoding the essential rate-limiting replication initiator protein RepR and the origin of replication, oriR, located downstream of repR. RepR is similar to RepE of related streptococcal plasmid pAMβ1, which has been shown to possess RNase activity cleaving free RNA molecules in close proximity of the initiation site of DNA synthesis. Replication of pIP501 is controlled by the concerted action of a small protein, CopR, and an antisense RNA, RNAIII. CopR has a dual function: It acts as transcriptional repressor at the repR promoter and, in addition, prevents convergent transcription of RNAIII and repR mRNA (RNAII), which indirectly increases RNAIII synthesis. CopR binds asymmetrically as a dimer at two consecutive binding sites upstream of and overlapping with the repR promoter. RNAIII induces transcriptional attenuation within the leader region of the repR mRNA (RNAII). Deletion of either control component causes a 10- to 20-fold increase of plasmid copy number, while simultaneous deletions have no additional effect. Conjugative transfer of pIP501 depends on a type IV secretion system (T4SS) encoded in a single operon. Its transfer host-range is considerably broad, as it has been transferred to virtually all Gram-positive bacteria including Streptomyces and even the Gram-negative Escherichia coli. Expression of the 15 genes encoding the T4SS is tightly controlled by binding of the relaxase TraA, the transfer initiator protein, to the operon promoter overlapping with the origin of transfer (oriT). The T4SS operon encodes the DNA-binding proteins TraJ (VirD4-like coupling protein) and the VirB4-like ATPase, TraE. Both proteins are actively involved in conjugative DNA transport. Moreover, the operon encodes TraN, a small cytoplasmic protein, whose specific binding to a sequence upstream of the oriT nic-site was demonstrated. TraN seems to be an effective repressor of pIP501 transfer, as conjugative transfer rates were significantly increased in an E. faecalis pIP501ΔtraN mutant.
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Affiliation(s)
- Elisabeth Grohmann
- Division of Infectious Diseases, University Medical Center FreiburgFreiburg im Breisgau, Germany; Life Sciences and Technology, Beuth University of Applied Sciences BerlinBerlin, Germany
| | - Nikolaus Goessweiner-Mohr
- Center for Structural System Biology, University Medical Center Hamburg-EppendorfHamburg, Germany; Deutsches Elektronen-SynchrotronHamburg, Germany; Institute of Molecular Biotechnology, Austrian Academy of SciencesVienna, Austria; Research Institute of Molecular PathologyVienna, Austria
| | - Sabine Brantl
- Lehrstuhl für Genetik, Biologisch-Pharmazeutische Fakultät, AG Bakteriengenetik, Friedrich-Schiller-Universität Jena Jena, Germany
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Fernández-González E, Bakioui S, Gomes MC, O'Callaghan D, Vergunst AC, Sangari FJ, Llosa M. A Functional oriT in the Ptw Plasmid of Burkholderia cenocepacia Can Be Recognized by the R388 Relaxase TrwC. Front Mol Biosci 2016; 3:16. [PMID: 27200362 PMCID: PMC4853378 DOI: 10.3389/fmolb.2016.00016] [Citation(s) in RCA: 5] [Impact Index Per Article: 0.6] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 03/11/2016] [Accepted: 04/14/2016] [Indexed: 12/14/2022] Open
Abstract
Burkholderia cenocepacia is both a plant pathogen and the cause of serious opportunistic infections, particularly in cystic fibrosis patients. B. cenocepacia K56-2 harbors a native plasmid named Ptw for its involvement in the Plant Tissue Watersoaking phenotype. Ptw has also been reported to be important for survival in human cells. Interestingly, the presence of PtwC, a homolog of the conjugative relaxase TrwC of plasmid R388, suggests a possible function for Ptw in conjugative DNA transfer. The ptw region includes Type IV Secretion System genes related to those of the F plasmid. However, genes in the adjacent region shared stronger homology with the R388 genes involved in conjugative DNA metabolism. This region included the putative relaxase ptwC, a putative coupling protein and accessory nicking protein, and a DNA segment with high number of inverted repeats and elevated AT content, suggesting a possible oriT. Although we were unable to detect conjugative transfer of the Ptw resident plasmid, we detected conjugal mobilization of a co-resident plasmid containing the ptw region homologous to R388, demonstrating the cloned ptw region contains an oriT. A similar plasmid lacking ptwC could not be mobilized, suggesting that the putative relaxase PtwC must act in cis on its oriT. Remarkably, we also detected mobilization of a plasmid containing the Ptw oriT by the R388 relaxase TrwC, yet we could not detect PtwC-mediated mobilization of an R388 oriT-containing plasmid. Our data unambiguously show that the Ptw plasmid harbors DNA transfer functions, and suggests the Ptw plasmid may play a dual role in horizontal DNA transfer and eukaryotic infection.
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Affiliation(s)
- Esther Fernández-González
- Departamento de Biología Molecular, Instituto de Biomedicina y Biotecnología de Cantabria, Universidad de Cantabria, UC-SODERCAN-Consejo Superior de Investigaciones Científicas Santander, Spain
| | - Sawsane Bakioui
- Institut National de la Santé et de la Recherche Médicale, U1047Nimes, France; UFR de Médecine Site de Nimes, U1047, Université de MontpellierFrance
| | - Margarida C Gomes
- Institut National de la Santé et de la Recherche Médicale, U1047Nimes, France; UFR de Médecine Site de Nimes, U1047, Université de MontpellierFrance
| | - David O'Callaghan
- Institut National de la Santé et de la Recherche Médicale, U1047Nimes, France; UFR de Médecine Site de Nimes, U1047, Université de MontpellierFrance
| | - Annette C Vergunst
- Institut National de la Santé et de la Recherche Médicale, U1047Nimes, France; UFR de Médecine Site de Nimes, U1047, Université de MontpellierFrance
| | - Félix J Sangari
- Departamento de Biología Molecular, Instituto de Biomedicina y Biotecnología de Cantabria, Universidad de Cantabria, UC-SODERCAN-Consejo Superior de Investigaciones Científicas Santander, Spain
| | - Matxalen Llosa
- Departamento de Biología Molecular, Instituto de Biomedicina y Biotecnología de Cantabria, Universidad de Cantabria, UC-SODERCAN-Consejo Superior de Investigaciones Científicas Santander, Spain
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Torres Tejerizo G, Pistorio M, Althabegoiti MJ, Cervantes L, Wibberg D, Schlüter A, Pühler A, Lagares A, Romero D, Brom S. Rhizobial plasmid pLPU83a is able to switch between different transfer machineries depending on its genomic background. FEMS Microbiol Ecol 2014; 88:565-78. [PMID: 24646299 DOI: 10.1111/1574-6941.12325] [Citation(s) in RCA: 18] [Impact Index Per Article: 1.8] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 11/14/2013] [Revised: 02/20/2014] [Accepted: 03/07/2014] [Indexed: 12/01/2022] Open
Abstract
Plasmids have played a major role in bacterial evolution, mainly by their capacity to perform horizontal gene transfer (HGT). Their conjugative transfer (CT) properties are usually described in terms of the plasmid itself. In this work, we analyzed structural and functional aspects of the CT of pLPU83a, an accessory replicon from Rhizobium sp. LPU83, able to transfer from its parental strain, from Ensifer meliloti, or from Rhizobium etli. pLPU83a contains a complete set of transfer genes, featuring a particular organization, shared with only two other rhizobial plasmids. These plasmids contain a TraR quorum-sensing (QS) transcriptional regulator, but lack an acyl-homoserine lactone (AHL) synthase gene. We also determined that the ability of pLPU83a to transfer from R. etli CFN42 genomic background was mainly achieved through mobilization, employing the machinery of the endogenous plasmid pRetCFN42a, falling under control of the QS regulators from pRetCFN42a. In contrast, from its native or from the E. meliloti background, pLPU83a utilized its own machinery for conjugation, requiring the plasmid-encoded traR. Activation of TraR seemed to be AHL independent. The results obtained indicate that the CT phenotype of a plasmid is dictated not only by the genes it carries, but by their interaction with its genomic context.
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Affiliation(s)
- Gonzalo Torres Tejerizo
- Programa de Ingeniería Genómica, Centro de Ciencias Genómicas, Universidad Nacional Autónoma de México, Cuernavaca, Morelos, México; Instituto de Biotecnología y Biología Molecular, CCT-La Plata-CONICET, Departamento de Ciencias Biológicas, Facultad de Ciencias Exactas, Universidad Nacional de La Plata, La Plata, Argentina
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Characterization of IntA, a bidirectional site-specific recombinase required for conjugative transfer of the symbiotic plasmid of Rhizobium etli CFN42. J Bacteriol 2013; 195:4668-77. [PMID: 23935046 DOI: 10.1128/jb.00714-13] [Citation(s) in RCA: 3] [Impact Index Per Article: 0.3] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/20/2022] Open
Abstract
Site-specific recombination occurs at short specific sequences, mediated by the cognate recombinases. IntA is a recombinase from Rhizobium etli CFN42 and belongs to the tyrosine recombinase family. It allows cointegration of plasmid p42a and the symbiotic plasmid via site-specific recombination between attachment regions (attA and attD) located in each replicon. Cointegration is needed for conjugative transfer of the symbiotic plasmid. To characterize this system, two plasmids harboring the corresponding attachment sites and intA were constructed. Introduction of these plasmids into R. etli revealed IntA-dependent recombination events occurring at high frequency. Interestingly, IntA promotes not only integration, but also excision events, albeit at a lower frequency. Thus, R. etli IntA appears to be a bidirectional recombinase. IntA was purified and used to set up electrophoretic mobility shift assays with linear fragments containing attA and attD. IntA-dependent retarded complexes were observed only with fragments containing either attA or attD. Specific retarded complexes, as well as normal in vivo recombination abilities, were seen even in derivatives harboring only a minimal attachment region (comprising the 5-bp central region flanked by 9- to 11-bp inverted repeats). DNase I-footprinting assays with IntA revealed specific protection of these zones. Mutations that disrupt the integrity of the 9- to 11-bp inverted repeats abolish both specific binding and recombination ability, while mutations in the 5-bp central region severely reduce both binding and recombination. These results show that IntA is a bidirectional recombinase that binds to att regions without requiring neighboring sequences as enhancers of recombination.
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Nogales J, Blanca-Ordóñez H, Olivares J, Sanjuán J. Conjugal transfer of the Sinorhizobium meliloti 1021 symbiotic plasmid is governed through the concerted action of one- and two-component signal transduction regulators. Environ Microbiol 2013; 15:811-21. [PMID: 23336126 DOI: 10.1111/1462-2920.12073] [Citation(s) in RCA: 22] [Impact Index Per Article: 2.0] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 07/12/2012] [Revised: 11/08/2012] [Accepted: 12/04/2012] [Indexed: 11/30/2022]
Abstract
Conjugal transfer of Sinorhizobium meliloti and Rhizobium etli symbiotic plasmids are repressed by the transcriptional regulator RctA. Here we report on new key players in the signal transduction cascade towards S. meliloti pSym conjugation. We have identified S. meliloti pSymA gene SMa0974 as an orthologue of the R. etli rctB gene which is required to antagonize repression by RctA. In S. meliloti two additional genes, rctR and rctC participate in control of rctB expression. rctR (SMa0955) encodes a protein of the GntR family of transcriptional regulators involved in repression of rctB. A rctR mutant promotes pSymA conjugal transfer and displays increased transcription of tra, virB and rctB genes even in presence of wild-type rctA gene. Among genes repressed by RctR, rctC (SMa0961) encodes a response regulator required to activate rctB transcription and therefore for derepression of plasmid conjugative functions. We conclude that in both R. etli and S. meliloti pSym conjugal transfer is derepressed via rctB, however the regulatory cascades to achieve activation of rctB are probably different. Upstream of rctB, the S. meliloti pSym conjugal transfer is regulated through the concerted action of genes representing one- (rctR) and two-component (rctC) signal transduction systems in response to yet unidentified signals.
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Affiliation(s)
- Joaquina Nogales
- Dpto. Microbiología del Suelo y Sistemas Simbióticos, Estación Experimental del Zaidín, Consejo Superior de Investigaciones Científicas (CSIC), Granada, Spain
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Genetic characterization of a novel rhizobial plasmid conjugation system in Rhizobium leguminosarum bv. viciae strain VF39SM. J Bacteriol 2012; 195:328-39. [PMID: 23144250 DOI: 10.1128/jb.01234-12] [Citation(s) in RCA: 27] [Impact Index Per Article: 2.3] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/20/2022] Open
Abstract
Rhizobium leguminosarum strain VF39SM contains two plasmids that have previously been shown to be self-transmissible by conjugation. One of these plasmids, pRleVF39b, is shown in this study to carry a set of plasmid transfer genes that differs significantly from conjugation systems previously studied in the rhizobia but is similar to an uncharacterized set of genes found in R. leguminosarum bv. trifolii strain WSM2304. The entire sequence of the transfer region on pRleVF39b was determined as part of a genome sequencing project, and the roles of the various genes were examined by mutagenesis. The transfer region contains a complete set of mating pair formation (Mpf) genes, a traG gene, and a relaxase gene, traA, all of which appear to be necessary for plasmid transfer. Experimental evidence suggested the presence of two putative origins of transfer within the gene cluster. A regulatory gene, trbR, was identified in the region between traA and traG and was mutated. TrbR was shown to function as a repressor of both trb gene expression and plasmid transfer.
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Giusti MDLÁ, Pistorio M, Lozano MJ, Tejerizo GAT, Salas ME, Martini MC, López JL, Draghi WO, Del Papa MF, Pérez-Mendoza D, Sanjuán J, Lagares A. Genetic and functional characterization of a yet-unclassified rhizobial Dtr (DNA-transfer-and-replication) region from a ubiquitous plasmid conjugal system present in Sinorhizobium meliloti, in Sinorhizobium medicae, and in other nonrhizobial Gram-negative bacteria. Plasmid 2012; 67:199-210. [PMID: 22233546 DOI: 10.1016/j.plasmid.2011.12.010] [Citation(s) in RCA: 21] [Impact Index Per Article: 1.8] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 09/15/2011] [Revised: 11/24/2011] [Accepted: 12/01/2011] [Indexed: 11/15/2022]
Abstract
Rhizobia are Gram-negative bacteria that live in soils and associate with leguminous plants to establish nitrogen-fixing symbioses. The ability of these bacteria to undergo horizontal gene transfer (HGT) is thought to be one of the main features to explain both the origin of their symbiotic life-style and the plasticity and dynamics of their genomes. In our laboratory we have previously characterized at the species level the non-pSym plasmid mobilome in Sinorhizobium meliloti, the symbiont of Medicago spp., and have found a high incidence of conjugal activity in many plasmids (Pistorio et al., 2008). In this work we characterized the Dtr (DNA-transfer-and-replication) region of one of those plasmids, pSmeLPU88b. This mobilization region was found to represent a previously unclassified Dtr type in rhizobia (hereafter type-IV), highly ubiquitous in S. meliloti and found in other genera of Gram-negative bacteria as well; including Agrobacterium, Ochrobactrum, and Chelativorans. The oriT of the type-IV Dtr described here could be located by function within a DNA fragment of 278 bp, between the divergent genes parA and mobC. The phylogenetic analysis of the cognate relaxase MobZ indicated that this protein groups close to the previously defined MOB(P3) and MOB(P4) type of enzymes, but is located in a separate and novel cluster that we have designated MOB(P0). Noteworthy, MOB(P0) and MOB(P4) relaxases were frequently associated with plasmids present in rhizospheric soil bacteria. A comparison of the nod-gene locations with the phylogenetic topology of the rhizobial relaxases revealed that the symbiotic genes are found on diverse plasmids bearing any of the four Dtr types, thus indicating that pSym plasmids are not specifically associated with any particular mobilization system. Finally, we demonstrated that the type-IV Dtr promoted the mobilization of plasmids from S. meliloti to Sinorhizobium medicae as well as from these rhizobia to other bacteria by means of their own helper functions. The results present an as-yet-unclassified and seemingly ubiquitous conjugal system that provides a mechanistic support for the HGT between sympatric rhizobia of Medicago roots, and between other soil and rhizospheric bacteria.
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Affiliation(s)
- María de los Ángeles Giusti
- Instituto de Biotecnología y Biología Molecular (IBBM)-CCT-CONICET-La Plata, Departamento de Ciencias Biológicas, Facultad de Ciencias Exactas, Universidad Nacional de La Plata, La Plata, Argentina
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Mruk I, Liu Y, Ge L, Kobayashi I. Antisense RNA associated with biological regulation of a restriction-modification system. Nucleic Acids Res 2011; 39:5622-32. [PMID: 21459843 PMCID: PMC3141266 DOI: 10.1093/nar/gkr166] [Citation(s) in RCA: 15] [Impact Index Per Article: 1.2] [Reference Citation Analysis] [Abstract] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/14/2022] Open
Abstract
Restriction–modification systems consist of a modification enzyme that methylates a specific DNA sequence and a restriction endonuclease that cleaves DNA lacking this epigenetic signature. Their gene expression should be finely regulated because their potential to attack the host bacterial genome needs to be controlled. In the EcoRI system, where the restriction gene is located upstream of the modification gene in the same orientation, we previously identified intragenic reverse promoters affecting gene expression. In the present work, we identified a small (88 nt) antisense RNA (Rna0) transcribed from a reverse promoter (PREV0) at the 3′ end of the restriction gene. Its antisense transcription, as measured by transcriptional gene fusion, appeared to be terminated by the PM1,M2 promoter. PM1,M2 promoter-initiated transcription, in turn, appeared to be inhibited by PREV0. Mutational inactivation of PREV0 increased expression of the restriction gene. The biological significance of this antisense transcription is 2-fold. First, a mutation in PREV0 increased restriction of incoming DNA. Second, the presence of the antisense RNA gene (ecoRIA) in trans alleviated cell killing after loss of the EcoRI plasmid (post-segregational killing). Taken together, these results strongly suggested the involvement of an antisense RNA in the biological regulation of this restriction–modification system.
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Affiliation(s)
- Iwona Mruk
- Department of Microbiology, University of Gdansk, Kladki 24, Gdansk, 80-822, Poland
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pSymA-dependent mobilization of the Sinorhizobium meliloti pSymB megaplasmid. J Bacteriol 2010; 192:6309-12. [PMID: 20889746 DOI: 10.1128/jb.00549-10] [Citation(s) in RCA: 24] [Impact Index Per Article: 1.7] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/20/2022] Open
Abstract
Sinorhizobium meliloti 1021 carries two megaplasmids, pSymA of 1,354 kb and pSymB of 1,683 kb, which are essential in establishing symbiosis with its legume hosts and important for bacterial fitness in the rhizosphere. We have previously shown that pSymA is self-transmissible and that its conjugal functions are regulated by the transcriptional repressor RctA. Here, we show conjugal transfer of pSymB as an in trans mobilization event that requires the type IV secretion system encoded by pSymA. pSymB carries a functional oriT and an adjacent relaxase gene, traA2, that is also transcriptionally repressed by rctA. Both symbiotic megaplasmids would require the relaxase genes in cis with their respective oriTs to achieve the highest transfer efficiencies.
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Plasmids of the Rhizobiaceae and Their Role in Interbacterial and Transkingdom Interactions. ACTA ACUST UNITED AC 2010. [DOI: 10.1007/978-3-642-14512-4_12] [Citation(s) in RCA: 7] [Impact Index Per Article: 0.5] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 02/17/2023]
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Abstract
Rhizobia are agriculturally important bacteria that can form nitrogen-fixing nodules on the roots of leguminous plants. Agricultural application of rhizobial inoculants can play an important role in increasing leguminous crop yields. In temperate rhizobia, genes involved in nodulation and nitrogen fixation are usually located on one or more large plasmids (pSyms) or on symbiotic islands. In addition, other large plasmids of rhizobia carry genes that are beneficial for survival and competition of rhizobia in the rhizosphere. Conjugative transfer of these large plasmids thus plays an important role in the evolution of rhizobia. Therefore, understanding the mechanism of conjugative transfer of large rhizobial plasmids provides foundations for maintaining, monitoring, and predicting the behaviour of these plasmids during field release events. In this minireview, we summarize two types of known rhizobial conjugative plasmids, including quorum sensing regulated plasmids and RctA-repressed plasmids. We provide evidence for the existence of a third type of conjugative plasmid, including pRleVF39c in Rhizobium leguminosarum bv. viciae strain VF39SM, and we provide a comparison of the different types of conjugation genes found in members of the rhizobia that have had their genomes sequenced so far.
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Affiliation(s)
- Hao Ding
- Department of Biological Sciences, University of Calgary, AB, Canada
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