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Luchetti A, Castellani LG, Toscani AM, Lagares A, Del Papa MF, Torres Tejerizo G, Pistorio M. Characterization of an accessory plasmid of Sinorhizobium meliloti and its two replication-modules. PLoS One 2023; 18:e0285505. [PMID: 37200389 DOI: 10.1371/journal.pone.0285505] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 12/08/2022] [Accepted: 04/25/2023] [Indexed: 05/20/2023] Open
Abstract
Rhizobia are Gram-negative bacteria known for their ability to fix atmospheric N2 in symbiosis with leguminous plants. Current evidence shows that rhizobia carry in most cases a variable number of plasmids, containing genes necessary for symbiosis or free-living, a common feature being the presence of several plasmid replicons within the same strain. For many years, we have been studying the mobilization properties of pSmeLPU88b from the strain Sinorhizobium meliloti LPU88, an isolate from Argentina. To advance in the characterization of pSmeLPU88b plasmid, the full sequence was obtained. pSmeLPU88b is 35.9 kb in size, had an average GC % of 58.6 and 31 CDS. Two replication modules were identified in silico: one belonging to the repABC type, and the other to the repC. The replication modules presented high DNA identity to the replication modules from plasmid pMBA9a present in an S. meliloti isolate from Canada. In addition, three CDS presenting identity with recombinases and with toxin-antitoxin systems were found downstream of the repABC system. It is noteworthy that these CDS present the same genetic structure in pSmeLPU88b and in other rhizobial plasmids. Moreover, in all cases they are found downstream of the repABC operon. By cloning each replication system in suicide plasmids, we demonstrated that each of them can support plasmid replication in the S. meliloti genetic background, but with different stability behavior. Interestingly, while incompatibility analysis of the cloned rep systems results in the loss of the parental module, both obtained plasmids can coexist together.
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Affiliation(s)
- Abril Luchetti
- Proteome and Metabolome Research, Faculty of Biology, Center for Biotechnology, Bielefeld University, Bielefeld, Germany
- Departamento de Ciencias Biológicas, Facultad de Ciencias Exactas, IBBM (Instituto de Biotecnología y Biología Molecular), CCT-CONICET-La Plata, Universidad Nacional de La Plata, La Plata, Argentina
| | - Lucas G Castellani
- Departamento de Ciencias Biológicas, Facultad de Ciencias Exactas, IBBM (Instituto de Biotecnología y Biología Molecular), CCT-CONICET-La Plata, Universidad Nacional de La Plata, La Plata, Argentina
| | - Andrés Martin Toscani
- Departamento de Ciencias Biológicas, Facultad de Ciencias Exactas, IBBM (Instituto de Biotecnología y Biología Molecular), CCT-CONICET-La Plata, Universidad Nacional de La Plata, La Plata, Argentina
| | - Antonio Lagares
- Departamento de Ciencias Biológicas, Facultad de Ciencias Exactas, IBBM (Instituto de Biotecnología y Biología Molecular), CCT-CONICET-La Plata, Universidad Nacional de La Plata, La Plata, Argentina
| | - María Florencia Del Papa
- Departamento de Ciencias Biológicas, Facultad de Ciencias Exactas, IBBM (Instituto de Biotecnología y Biología Molecular), CCT-CONICET-La Plata, Universidad Nacional de La Plata, La Plata, Argentina
| | - Gonzalo Torres Tejerizo
- Departamento de Ciencias Biológicas, Facultad de Ciencias Exactas, IBBM (Instituto de Biotecnología y Biología Molecular), CCT-CONICET-La Plata, Universidad Nacional de La Plata, La Plata, Argentina
| | - Mariano Pistorio
- Departamento de Ciencias Biológicas, Facultad de Ciencias Exactas, IBBM (Instituto de Biotecnología y Biología Molecular), CCT-CONICET-La Plata, Universidad Nacional de La Plata, La Plata, Argentina
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diCenzo GC, Zamani M, Checcucci A, Fondi M, Griffitts JS, Finan TM, Mengoni A. Multidisciplinary approaches for studying rhizobium–legume symbioses. Can J Microbiol 2019; 65:1-33. [DOI: 10.1139/cjm-2018-0377] [Citation(s) in RCA: 49] [Impact Index Per Article: 9.8] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/10/2023]
Abstract
The rhizobium–legume symbiosis is a major source of fixed nitrogen (ammonia) in the biosphere. The potential for this process to increase agricultural yield while reducing the reliance on nitrogen-based fertilizers has generated interest in understanding and manipulating this process. For decades, rhizobium research has benefited from the use of leading techniques from a very broad set of fields, including population genetics, molecular genetics, genomics, and systems biology. In this review, we summarize many of the research strategies that have been employed in the study of rhizobia and the unique knowledge gained from these diverse tools, with a focus on genome- and systems-level approaches. We then describe ongoing synthetic biology approaches aimed at improving existing symbioses or engineering completely new symbiotic interactions. The review concludes with our perspective of the future directions and challenges of the field, with an emphasis on how the application of a multidisciplinary approach and the development of new methods will be necessary to ensure successful biotechnological manipulation of the symbiosis.
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Affiliation(s)
- George C. diCenzo
- Department of Biology, University of Florence, Sesto Fiorentino, FI 50019, Italy
| | - Maryam Zamani
- Department of Biology, McMaster University, Hamilton, ON L8S 4K1, Canada
| | - Alice Checcucci
- Department of Biology, University of Florence, Sesto Fiorentino, FI 50019, Italy
| | - Marco Fondi
- Department of Biology, University of Florence, Sesto Fiorentino, FI 50019, Italy
| | - Joel S. Griffitts
- Department of Microbiology and Molecular Biology, Brigham Young University, Provo, UT 84602, USA
| | - Turlough M. Finan
- Department of Biology, McMaster University, Hamilton, ON L8S 4K1, Canada
| | - Alessio Mengoni
- Department of Biology, University of Florence, Sesto Fiorentino, FI 50019, Italy
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Checcucci A, diCenzo GC, Ghini V, Bazzicalupo M, Becker A, Decorosi F, Döhlemann J, Fagorzi C, Finan TM, Fondi M, Luchinat C, Turano P, Vignolini T, Viti C, Mengoni A. Creation and Characterization of a Genomically Hybrid Strain in the Nitrogen-Fixing Symbiotic Bacterium Sinorhizobium meliloti. ACS Synth Biol 2018; 7:2365-2378. [PMID: 30223644 DOI: 10.1021/acssynbio.8b00158] [Citation(s) in RCA: 21] [Impact Index Per Article: 3.5] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/22/2022]
Abstract
Many bacteria, often associated with eukaryotic hosts and of relevance for biotechnological applications, harbor a multipartite genome composed of more than one replicon. Biotechnologically relevant phenotypes are often encoded by genes residing on the secondary replicons. A synthetic biology approach to developing enhanced strains for biotechnological purposes could therefore involve merging pieces or entire replicons from multiple strains into a single genome. Here we report the creation of a genomic hybrid strain in a model multipartite genome species, the plant-symbiotic bacterium Sinorhizobium meliloti. We term this strain as cis-hybrid, since it is produced by genomic material coming from the same species' pangenome. In particular, we moved the secondary replicon pSymA (accounting for nearly 20% of total genome content) from a donor S. meliloti strain to an acceptor strain. The cis-hybrid strain was screened for a panel of complex phenotypes (carbon/nitrogen utilization phenotypes, intra- and extracellular metabolomes, symbiosis, and various microbiological tests). Additionally, metabolic network reconstruction and constraint-based modeling were employed for in silico prediction of metabolic flux reorganization. Phenotypes of the cis-hybrid strain were in good agreement with those of both parental strains. Interestingly, the symbiotic phenotype showed a marked cultivar-specific improvement with the cis-hybrid strains compared to both parental strains. These results provide a proof-of-principle for the feasibility of genome-wide replicon-based remodelling of bacterial strains for improved biotechnological applications in precision agriculture.
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Affiliation(s)
- Alice Checcucci
- Department of Biology, University of Florence, 50019 Sesto Fiorentino, Italy
| | - George C. diCenzo
- Department of Biology, University of Florence, 50019 Sesto Fiorentino, Italy
| | - Veronica Ghini
- CERM & CIRMMP, University of Florence, 50019 Sesto Fiorentino, Italy
| | - Marco Bazzicalupo
- Department of Biology, University of Florence, 50019 Sesto Fiorentino, Italy
| | - Anke Becker
- LOEWE − Center for Synthetic Microbiology, 35043 Marburg, Germany
| | - Francesca Decorosi
- Department of Agri-food Production and Environmental Science, University of Florence, 50019 Florence, Italy
| | | | - Camilla Fagorzi
- Department of Biology, University of Florence, 50019 Sesto Fiorentino, Italy
| | - Turlough M. Finan
- Department of Biology, McMaster University, Hamilton, Ontario L8S 4L8, Canada
| | - Marco Fondi
- Department of Biology, University of Florence, 50019 Sesto Fiorentino, Italy
| | - Claudio Luchinat
- CERM & CIRMMP, University of Florence, 50019 Sesto Fiorentino, Italy
- CERM and Department of Chemistry, University of Florence, 50019 Sesto Fiorentino, Italy
| | - Paola Turano
- CERM & CIRMMP, University of Florence, 50019 Sesto Fiorentino, Italy
- CERM and Department of Chemistry, University of Florence, 50019 Sesto Fiorentino, Italy
| | - Tiziano Vignolini
- European Laboratory for Non-Linear Spectroscopy, LENS, 50019 Sesto Fiorentino, Italy
| | - Carlo Viti
- Department of Agri-food Production and Environmental Science, University of Florence, 50019 Florence, Italy
| | - Alessio Mengoni
- Department of Biology, University of Florence, 50019 Sesto Fiorentino, Italy
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diCenzo GC, Finan TM. The Divided Bacterial Genome: Structure, Function, and Evolution. Microbiol Mol Biol Rev 2017; 81:e00019-17. [PMID: 28794225 PMCID: PMC5584315 DOI: 10.1128/mmbr.00019-17] [Citation(s) in RCA: 135] [Impact Index Per Article: 19.3] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/18/2022] Open
Abstract
Approximately 10% of bacterial genomes are split between two or more large DNA fragments, a genome architecture referred to as a multipartite genome. This multipartite organization is found in many important organisms, including plant symbionts, such as the nitrogen-fixing rhizobia, and plant, animal, and human pathogens, including the genera Brucella, Vibrio, and Burkholderia. The availability of many complete bacterial genome sequences means that we can now examine on a broad scale the characteristics of the different types of DNA molecules in a genome. Recent work has begun to shed light on the unique properties of each class of replicon, the unique functional role of chromosomal and nonchromosomal DNA molecules, and how the exploitation of novel niches may have driven the evolution of the multipartite genome. The aims of this review are to (i) outline the literature regarding bacterial genomes that are divided into multiple fragments, (ii) provide a meta-analysis of completed bacterial genomes from 1,708 species as a way of reviewing the abundant information present in these genome sequences, and (iii) provide an encompassing model to explain the evolution and function of the multipartite genome structure. This review covers, among other topics, salient genome terminology; mechanisms of multipartite genome formation; the phylogenetic distribution of multipartite genomes; how each part of a genome differs with respect to genomic signatures, genetic variability, and gene functional annotation; how each DNA molecule may interact; as well as the costs and benefits of this genome structure.
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Affiliation(s)
- George C diCenzo
- Department of Biology, McMaster University, Hamilton, Ontario, Canada
| | - Turlough M Finan
- Department of Biology, McMaster University, Hamilton, Ontario, Canada
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Hernández-Tamayo R, Torres-Tejerizo G, Brom S, Romero D. Site-specific bacterial chromosome engineering mediated by IntA integrase from Rhizobium etli. BMC Microbiol 2016; 16:133. [PMID: 27357704 PMCID: PMC4928290 DOI: 10.1186/s12866-016-0755-y] [Citation(s) in RCA: 1] [Impact Index Per Article: 0.1] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 03/16/2016] [Accepted: 06/28/2016] [Indexed: 11/24/2022] Open
Abstract
Background The bacterial chromosome may be used to stably maintain foreign DNA in the mega-base range. Integration into the chromosome circumvents issues such as plasmid replication, stability, incompatibility, and copy number variance. The site-specific integrase IntA from Rhizobium etli CFN42 catalyzes a direct recombination between two specific DNA sites: attA and attD (23 bp). This recombination is stable. The aim of this work was to develop a R. etli derivative that may be used as recipient for the integration of foreign DNA in the chromosome, adapting the IntA catalyzed site-specific recombination system. Results To fulfill our aim, we designed a Rhizobium etli CFN42 derivative, containing a “landing pad” (LP) integrated into the chromosome. The LP sector consists of a green fluorescent protein gene under the control of the lacZ promoter and a spectinomycin resistance gene. Between the lacZ promoter and the GFP gene we inserted an IntA attachment site, which does not affect transcription from the lac promoter. Also, a mobilizable donor vector was generated, containing an attA site and a kanamycin resistance gene; to facilitate insertion of foreign DNA, this vector also contains a multicloning site. There are no promoters flanking the multicloning site. A biparental mating protocol was used to transfer the donor vector into the landing pad strain; insertion of the donor vector into the landing pad sector via IntA-mediated attA X attA recombination thereby interrupted the expression of the green fluorescent protein, generating site-specific cointegrants. Cointegrants were easily recognized by screening for antibiotic sensitivity and lack of GFP expression, and were obtained with an efficiency of 6.18 %. Conclusions Integration of foreign DNA in Rhizobium, lacking any similarity with the genome, can be easily achieved by IntA-mediated recombination. This protocol contains the mating and selection procedures for creating and isolating integrants.
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Affiliation(s)
- Rogelio Hernández-Tamayo
- Programa de Ingeniería Genómica, Centro de Ciencias Genómicas, Universidad Nacional Autónoma de México, Apartado Postal 565-A, 62210, Cuernavaca, Morelos, Mexico
| | - Gonzalo Torres-Tejerizo
- Programa de Ingeniería Genómica, Centro de Ciencias Genómicas, Universidad Nacional Autónoma de México, Apartado Postal 565-A, 62210, Cuernavaca, Morelos, Mexico.,Departamento de Ciencias Biológicas, Instituto de Biotecnología y Biología Molecular, UNLP, CCT-La Plata-CONICET, Facultad de Ciencias Exactas, Universidad Nacional de La Plata, La Plata, Argentina
| | - Susana Brom
- Programa de Ingeniería Genómica, Centro de Ciencias Genómicas, Universidad Nacional Autónoma de México, Apartado Postal 565-A, 62210, Cuernavaca, Morelos, Mexico
| | - David Romero
- Programa de Ingeniería Genómica, Centro de Ciencias Genómicas, Universidad Nacional Autónoma de México, Apartado Postal 565-A, 62210, Cuernavaca, Morelos, Mexico.
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The Plasmid Mobilome of the Model Plant-Symbiont Sinorhizobium meliloti: Coming up with New Questions and Answers. Microbiol Spectr 2016; 2. [PMID: 26104371 DOI: 10.1128/microbiolspec.plas-0005-2013] [Citation(s) in RCA: 8] [Impact Index Per Article: 1.0] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/20/2022] Open
Abstract
Rhizobia are Gram-negative Alpha- and Betaproteobacteria living in the underground which have the ability to associate with legumes for the establishment of nitrogen-fixing symbioses. Sinorhizobium meliloti in particular-the symbiont of Medicago, Melilotus, and Trigonella spp.-has for the past decades served as a model organism for investigating, at the molecular level, the biology, biochemistry, and genetics of a free-living and symbiotic soil bacterium of agricultural relevance. To date, the genomes of seven different S. meliloti strains have been fully sequenced and annotated, and several other draft genomic sequences are also available. The vast amount of plasmid DNA that S. meliloti frequently bears (up to 45% of its total genome), the conjugative ability of some of those plasmids, and the extent of the plasmid diversity has provided researchers with an extraordinary system to investigate functional and structural plasmid molecular biology within the evolutionary context surrounding a plant-associated model bacterium. Current evidence indicates that the plasmid mobilome in S. meliloti is composed of replicons varying greatly in size and having diverse conjugative systems and properties along with different evolutionary stabilities and biological roles. While plasmids carrying symbiotic functions (pSyms) are known to have high structural stability (approaching that of chromosomes), the remaining plasmid mobilome (referred to as the non-pSym, functionally cryptic, or accessory compartment) has been shown to possess remarkable diversity and to be highly active in conjugation. In light of the modern genomic and current biochemical data on the plasmids of S. meliloti, the current article revises their main structural components, their transfer and regulatory mechanisms, and their potential as vehicles in shaping the evolution of the rhizobial genome.
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Characterization of a collection of plasmid-containing bacteria isolated from an on-farm biopurification system used for pesticide removal. Plasmid 2015; 80:16-23. [PMID: 25957823 DOI: 10.1016/j.plasmid.2015.05.001] [Citation(s) in RCA: 14] [Impact Index Per Article: 1.6] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 12/09/2014] [Revised: 04/24/2015] [Accepted: 05/01/2015] [Indexed: 11/21/2022]
Abstract
Biopurification systems (BPS) are complex soil-related and artificially-generated environments usually designed for the removal of toxic compounds from contaminated wastewaters. The present study has been conducted to isolate and characterize a collection of cultivable plasmid-carrying bacterial isolates recovered from a BPS established for the decontamination of wastewater generated in a farmyard. Out of 1400 isolates, a collection of 75 plasmid-containing bacteria was obtained, of which 35 representative isolates comprising in total at least 50 plasmids were chosen for further characterization. Bacterial hosts were taxonomically assigned by 16S ribosomal RNA gene sequencing and phenotypically characterized according to their ability to grow in presence of different antibiotics and heavy metals. The study demonstrated that a high proportion of the isolates was tolerant to antibiotics and/or heavy metals, highlighting the on-farm BPS enrichment in such genetic traits. Several plasmids conferring such resistances in the bacterial collection were detected to be either mobilizable or selftransmissible. Occurrence of broad host range plasmids of the incompatibility groups IncP, IncQ, IncN and IncW was examined with positive results only for the first group. Presence of the IS1071 insertion sequence, frequently associated with xenobiotics degradation genes, was detected in DNA obtained from 24 of these isolates, strongly suggesting the presence of yet-hidden catabolic activities in the collection of isolates. The results showed a remarkable diversity in the plasmid mobilome of cultivable bacteria in the BPS with the presence of abundant resistance markers of different types, thus providing a suitable environment to investigate the genetic structure of the mobile genetic pool in a model on-farm biofilter for wastewater decontamination in intensive agricultural production.
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Morton ER, Merritt PM, Bever JD, Fuqua C. Large deletions in the pAtC58 megaplasmid of Agrobacterium tumefaciens can confer reduced carriage cost and increased expression of virulence genes. Genome Biol Evol 2013; 5:1353-64. [PMID: 23783172 PMCID: PMC3730347 DOI: 10.1093/gbe/evt095] [Citation(s) in RCA: 24] [Impact Index Per Article: 2.2] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/13/2022] Open
Abstract
The accessory plasmid pAtC58 of the common laboratory strain of Agrobacterium tumefaciens confers numerous catabolic functions and has been proposed to play a role in virulence. Genomic sequencing of evolved laboratory strains of A. tumefaciens revealed the presence of multiple deletion events in the At plasmid, with reductions in plasmid size ranging from 25% to 30% (115–194 kb). Flanking both ends of the sites of these deletions is a short-nucleotide repeat sequence that is in a single copy in the deleted plasmids, characteristic of a phage- or transposon-mediated deletion event. This repeat sequence is widespread throughout the C58 genome, but concentrated on the At plasmid, suggesting its frequency to be nonrandom. In this study, we assess the prevalence of the larger of these deletions in multiple C58 derivatives and characterize its functional significance. We find that in addition to elevating virulence gene expression, this deletion is associated with a significantly reduced carriage cost to the cell. These observations are a clear demonstration of the dynamic nature of the bacterial genome and suggest a mechanism for genetic plasticity of these costly but otherwise stable plasmids. Additionally, this phenomenon could be the basis for some of the dramatic recombination events so ubiquitous within and among megaplasmids.
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Cell growth inhibition upon deletion of four toxin-antitoxin loci from the megaplasmids of Sinorhizobium meliloti. J Bacteriol 2013; 196:811-24. [PMID: 24317400 DOI: 10.1128/jb.01104-13] [Citation(s) in RCA: 36] [Impact Index Per Article: 3.3] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/18/2022] Open
Abstract
Toxin and antitoxin (TA) gene pairs are addiction systems that are present in many microbial genomes. Sinorhizobium meliloti is an N2-fixing bacterial symbiont of alfalfa and other leguminous plants, and its genome consists of three large replicons, a circular chromosome (3.7 Mb) and the megaplasmids pSymA (1.4 Mb) and pSymB (1.7 Mb). S. meliloti carries 211 predicted type II TA genes, each encoding a toxin or an antitoxin. We constructed defined deletion strains that collectively removed the entire pSymA and pSymB megaplasmids except for their oriV regions. Of approximately 100 TA genes on pSymA and pSymB, we identified four whose loss was associated with cell death or stasis unless copies of the genes were supplied in trans. Orthologs of three of these loci have been characterized in other organisms (relB/E [sma0471/sma0473], Fic [DOC] [sma2105], and VapC [PIN] [orf2230/sma2231]), and this report contains the first experimental proof that RES/Xre (smb21127/smb21128) loci can function as a TA system. Transcriptome sequencing (RNA-seq) analysis did not reveal transcriptional differences between the TA systems to account for why deletion of the four "active" systems resulted in cell toxicity. These data suggest that severe cell growth phenotypes result from the loss of a few TA systems and that loss of most TA systems may result in more subtle phenotypes. These four TA systems do not appear to play a direct role in the S. meliloti-alfalfa symbiosis, as strains lacking these TA systems had a symbiotic N2 fixation phenotype that was indistinguishable from the wild type.
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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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Laranjo M, Alexandre A, Rivas R, Velázquez E, Young JPW, Oliveira S. Chickpea rhizobia symbiosis genes are highly conserved across multiple Mesorhizobium species. FEMS Microbiol Ecol 2008; 66:391-400. [DOI: 10.1111/j.1574-6941.2008.00584.x] [Citation(s) in RCA: 65] [Impact Index Per Article: 4.1] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/01/2022] Open
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Pistorio M, Giusti MA, Del Papa MF, Draghi WO, Lozano MJ, Torres Tejerizo G, Lagares A. Conjugal properties of the Sinorhizobium meliloti plasmid mobilome. FEMS Microbiol Ecol 2008; 65:372-82. [DOI: 10.1111/j.1574-6941.2008.00509.x] [Citation(s) in RCA: 22] [Impact Index Per Article: 1.4] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/30/2022] Open
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Plasmid content of salt stress-tolerant Rhizobium strains from Egyptian soils nodulating common bean (Phaseolus vulgaris L.). World J Microbiol Biotechnol 2007. [DOI: 10.1007/s11274-007-9618-x] [Citation(s) in RCA: 2] [Impact Index Per Article: 0.1] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 10/22/2022]
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Stiens M, Schneiker S, Keller M, Kuhn S, Pühler A, Schlüter A. Sequence analysis of the 144-kilobase accessory plasmid pSmeSM11a, isolated from a dominant Sinorhizobium meliloti strain identified during a long-term field release experiment. Appl Environ Microbiol 2006; 72:3662-72. [PMID: 16672515 PMCID: PMC1472397 DOI: 10.1128/aem.72.5.3662-3672.2006] [Citation(s) in RCA: 53] [Impact Index Per Article: 2.9] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/20/2022] Open
Abstract
The genome of Sinorhizobium meliloti type strain Rm1021 consists of three replicons: the chromosome and two megaplasmids, pSymA and pSymB. Additionally, many indigenous S. meliloti strains possess one or more smaller plasmids, which represent the accessory genome of this species. Here we describe the complete nucleotide sequence of an accessory plasmid, designated pSmeSM11a, that was isolated from a dominant indigenous S. meliloti subpopulation in the context of a long-term field release experiment with genetically modified S. meliloti strains. Sequence analysis of plasmid pSmeSM11a revealed that it is 144,170 bp long and has a mean G+C content of 59.5 mol%. Annotation of the sequence resulted in a total of 160 coding sequences. Functional predictions could be made for 43% of the genes, whereas 57% of the genes encode hypothetical or unknown gene products. Two plasmid replication modules, one belonging to the repABC replicon family and the other belonging to the plasmid type A replicator region family, were identified. Plasmid pSmeSM11a contains a mobilization (mob) module composed of the type IV secretion system-related genes traG and traA and a putative mobC gene. A large continuous region that is about 42 kb long is very similar to a corresponding region located on S. meliloti Rm1021 megaplasmid pSymA. Single-base-pair deletions in the homologous regions are responsible for frameshifts that result in nonparalogous coding sequences. Plasmid pSmeSM11a carries additional copies of the nodulation genes nodP and nodQ that are responsible for Nod factor sulfation. Furthermore, a tauD gene encoding a putative taurine dioxygenase was identified on pSmeSM11a. An acdS gene located on pSmeSM11a is the first example of such a gene in S. meliloti. The deduced acdS gene product is able to deaminate 1-aminocyclopropane-1-carboxylate and is proposed to be involved in reducing the phytohormone ethylene, thus influencing nodulation events. The presence of numerous insertion sequences suggests that these elements mediated acquisition of accessory plasmid modules.
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Affiliation(s)
- M Stiens
- Fakultät für Biologie, Lehrstuhl für Genetik, Universität Bielefeld, Postfach 100131, D-33501 Bielefeld, Germany
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Xiong J, Hynes MF, Ye H, Chen H, Yang Y, M'zali F, Hawkey PM. bla(IMP-9) and its association with large plasmids carried by Pseudomonas aeruginosa isolates from the People's Republic of China. Antimicrob Agents Chemother 2006; 50:355-8. [PMID: 16377710 PMCID: PMC1346779 DOI: 10.1128/aac.50.1.355-358.2006] [Citation(s) in RCA: 36] [Impact Index Per Article: 2.0] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/20/2022] Open
Abstract
A novel plasmid-mediated metallo-beta-lactamase (IMP-9) is described in seven isolates of Pseudomonas aeruginosa from Guangzhou, China, isolated in 2000. The gene was carried on a large (approximately 450-kb) IncP-2 conjugative plasmid. This is the first report of carriage of bla(IMP) genes on such large plasmids.
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Affiliation(s)
- Jianhui Xiong
- Division of Immunity and Infection, University of Birmingham, Edgbaston, United Kingdom
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Perrine FM, Hocart CH, Hynes MF, Rolfe BG. Plasmid-associated genes in the model micro-symbiont Sinorhizobium meliloti 1021 affect the growth and development of young rice seedlings. Environ Microbiol 2005; 7:1826-38. [PMID: 16232297 DOI: 10.1111/j.1462-2920.2005.00927.x] [Citation(s) in RCA: 17] [Impact Index Per Article: 0.9] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/30/2022]
Abstract
Sinorhizobium meliloti strain 1021 and its closely related strain Rm2011 inhibit rice seedling (Oryza sativa L. cv. Pelde) growth and development under certain rice-growing conditions. Experiments showed that inoculation of seedlings with approximately less than 10 cells of 1021 was sufficient to cause this inhibition. By using a series of plasmid-cured and plasmid-deleted derivatives of Rm2011, it was found that interactions between genes encoded on pSymA, and possibly pSymB, of Rm2011, affected rice growth and development by affecting both/either the plant and/or the bacteria. Further studies found that genes potentially related to indole-3-acetic acid (IAA) synthesis and nitrate metabolism, encoded on pSymA, were involved in rice growth inhibition in Sm1021- and Sm2011-treated rice seedlings. We conclude that the rice growth inhibition by S. meliloti Sm1021 is pSymA-associated and is induced by environmental nitrate.
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Affiliation(s)
- Francine M Perrine
- Genomic Interactions Group, Research School of Biological Sciences, The Australian National University, GPO Box 475, Canberra, ACT 2601, Australia
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17
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Wong K, Golding GB. A phylogenetic analysis of the pSymB replicon from the Sinorhizobium meliloti genome reveals a complex evolutionary history. Can J Microbiol 2003; 49:269-80. [PMID: 12897836 DOI: 10.1139/w03-037] [Citation(s) in RCA: 25] [Impact Index Per Article: 1.2] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/22/2022]
Abstract
Microbial genomes are thought to be mosaic, making it difficult to decipher how these genomes have evolved. Whole-genome nearest-neighbor analysis was applied to the Sinorhizobium meliloti pSymB replicon to determine its origin, the degree of horizontal transfer, and the conservation of gene order. Prediction of the nearest neighbor based on contextual information, i.e., the nearest phylogenetic neighbor of adjacent genes, provided useful information for genes for which phylogenetic relationships could not be established. A large portion of pSymB genes are most closely related to genes in the Agrobacterium tumefaciens linear chromosome, including the rep and min genes. This suggests a common origin for these replicons. Genes with the nearest neighbor from the same species tend to be grouped in "patches". Gene order within these patches is conserved, but the content of the patches is not limited to operons. These data show that 13% of pSymB genes have nearest neighbors in species that are not members of the Rhizobiaceae family (including two archaea), and that these likely represent genes that have been involved in horizontal transfer.
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Affiliation(s)
- Kim Wong
- McMaster University, Department of Biology, Hamilton, ON L8S 4K1, Canada
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18
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Roumiantseva ML, Andronov EE, Sharypova LA, Dammann-Kalinowski T, Keller M, Young JPW, Simarov BV. Diversity of Sinorhizobium meliloti from the Central Asian Alfalfa Gene Center. Appl Environ Microbiol 2002; 68:4694-7. [PMID: 12200335 PMCID: PMC124126 DOI: 10.1128/aem.68.9.4694-4697.2002] [Citation(s) in RCA: 45] [Impact Index Per Article: 2.0] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/20/2022] Open
Abstract
Sinorhizobium meliloti was isolated from nodules and soil from western Tajikistan, a center of diversity of the host plants (Medicago, Melilotus, and Trigonella species). There was evidence of recombination, but significant disequilibrium, between and within the chromosome and megaplasmids. The most frequent alleles matched those in the published genome sequence.
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Affiliation(s)
- Marina L Roumiantseva
- Research Institute for Agricultural Microbiology, St.-Petersburg-Pushkin 8, 196608, Russia.
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19
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Finan TM, Weidner S, Wong K, Buhrmester J, Chain P, Vorhölter FJ, Hernandez-Lucas I, Becker A, Cowie A, Gouzy J, Golding B, Pühler A. The complete sequence of the 1,683-kb pSymB megaplasmid from the N2-fixing endosymbiont Sinorhizobium meliloti. Proc Natl Acad Sci U S A 2001; 98:9889-94. [PMID: 11481431 PMCID: PMC55548 DOI: 10.1073/pnas.161294698] [Citation(s) in RCA: 249] [Impact Index Per Article: 10.8] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/18/2022] Open
Abstract
Analysis of the 1,683,333-nt sequence of the pSymB megaplasmid from the symbiotic N(2)-fixing bacterium Sinorhizobium meliloti revealed that the replicon has a high gene density with a total of 1,570 protein-coding regions, with few insertion elements and regions duplicated elsewhere in the genome. The only copies of an essential arg-tRNA gene and the minCDE genes are located on pSymB. Almost 20% of the pSymB sequence carries genes encoding solute uptake systems, most of which were of the ATP-binding cassette family. Many previously unsuspected genes involved in polysaccharide biosynthesis were identified and these, together with the two known distinct exopolysaccharide synthesis gene clusters, show that 14% of the pSymB sequence is dedicated to polysaccharide synthesis. Other recognizable gene clusters include many involved in catabolic activities such as protocatechuate utilization and phosphonate degradation. The functions of these genes are consistent with the notion that pSymB plays a major role in the saprophytic competence of the bacteria in the soil environment.
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Affiliation(s)
- T M Finan
- Department of Biology, McMaster University, Hamilton, ON, Canada.
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20
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Rogel MA, Hernández-Lucas I, Kuykendall LD, Balkwill DL, Martinez-Romero E. Nitrogen-fixing nodules with Ensifer adhaerens harboring Rhizobium tropici symbiotic plasmids. Appl Environ Microbiol 2001; 67:3264-8. [PMID: 11425750 PMCID: PMC93009 DOI: 10.1128/aem.67.7.3264-3268.2001] [Citation(s) in RCA: 79] [Impact Index Per Article: 3.4] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/20/2022] Open
Abstract
Ensifer adhaerens is a soil bacterium that attaches to other bacteria and may cause lysis of these other bacteria. Based on the sequence of its small-subunit rRNA gene, E. adhaerens is related to Sinorhizobium spp. E. adhaerens ATCC 33499 did not nodulate Phaseolus vulgaris (bean) or Leucaena leucocephala, but with symbiotic plasmids from Rhizobium tropici CFN299 it formed nitrogen-fixing nodules on both hosts. The nodule isolates were identified as E. adhaerens isolates by growth on selective media.
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Affiliation(s)
- M A Rogel
- Centro de Investigación sobre Fijación de Nitrógeno, UNAM. Ap. P. 565-A, Cuernavaca, México
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21
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Garinot-Schneider C, Lellouch AC, Geremia RA. Identification of essential amino acid residues in the Sinorhizobium meliloti glucosyltransferase ExoM. J Biol Chem 2000; 275:31407-13. [PMID: 10908566 DOI: 10.1074/jbc.m004524200] [Citation(s) in RCA: 35] [Impact Index Per Article: 1.5] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/06/2022] Open
Abstract
ExoM is a beta(1-4)-glucosyltransferase involved in the assembly of the repeat unit of the exopolysaccharide succinoglycan from Sinorhizobium meliloti. By comparing the sequence of ExoM to those of other members of the Pfam Glyco Domain 2 family, most notably SpsA (Bacillus subtilis) for whom the three-dimensional structure has been resolved, three potentially important aspartic acid residues of ExoM were identified. Single substitutions of each of the Asp amino acids at positions 44, 96, and 187 with Ala resulted in the loss of mutant recombinant protein activity in vitro as well as the loss of succinoglycan production in an in vivo rescue assay. Mutants harboring Glu instead of Asp-44 or Asp-96 possessed no in vitro activity but could restore succinoglycan production in vivo. However, replacement of Asp-187 with Glu completely inactivated ExoM as judged by both the in vitro and in vivo assays. These results indicate that Asp-44, Asp-96, and Asp-187 are essential for the activity of ExoM. Furthermore, these data are consistent with the functions proposed for each of the analogous aspartic acids of SpsA based on the SpsA-UDP structure, namely, that Asp-44 and Asp-96 are involved in UDP substrate binding and that Asp-187 is the catalytic base in the glycosyltransferase reaction.
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Affiliation(s)
- C Garinot-Schneider
- Centre de Recherches sur les Macromolécules Végétales, CNRS, Affiliated with the Joseph Fourier University, BP 53X, Grenoble 38041, Cedex 9, France
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22
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Chain PS, Hernandez-Lucas I, Golding B, Finan TM. oriT-directed cloning of defined large regions from bacterial genomes: identification of the Sinorhizobium meliloti pExo megaplasmid replicator region. J Bacteriol 2000; 182:5486-94. [PMID: 10986253 PMCID: PMC110993 DOI: 10.1128/jb.182.19.5486-5494.2000] [Citation(s) in RCA: 19] [Impact Index Per Article: 0.8] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/20/2022] Open
Abstract
We have developed a procedure to directly clone large fragments from the genome of the soil bacterium Sinorhizobium meliloti. Specific regions to be cloned are first flanked by parallel copies of an origin of transfer (oriT) together with a plasmid replication origin capable of replicating large clones in Escherichia coli but not in the target organism. Supplying transfer genes in trans specifically transfers the oriT-flanked region, and in this process, site-specific recombination at the oriT sites results in a plasmid carrying the flanked region of interest that can replicate in E. coli from the inserted origin of replication (in this case, the F origin carried on a BAC cloning vector). We have used this procedure with the oriT of the plasmid RK2 to clone contiguous fragments of 50, 60, 115, 140, 240, and 200 kb from the S. meliloti pExo megaplasmid. Analysis of the 60-kb fragment allowed us to identify a 9-kb region capable of autonomous replication in the bacterium Agrobacterium tumefaciens. The nucleotide sequence of this fragment revealed a replicator region including homologs of the repA, repB, and repC genes from other Rhizobiaceae, which encode proteins involved in replication and segregation of plasmids in many organisms.
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Affiliation(s)
- P S Chain
- Department of Biology, McMaster University, Hamilton, Ontario, Canada L8S 4K1
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23
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García-Rodríguez FM, Toro N. Sinorhizobium meliloti nfe (nodulation formation efficiency) genes exhibit temporal and spatial expression patterns similar to those of genes involved in symbiotic nitrogen fixation. MOLECULAR PLANT-MICROBE INTERACTIONS : MPMI 2000; 13:583-591. [PMID: 10830257 DOI: 10.1094/mpmi.2000.13.6.583] [Citation(s) in RCA: 22] [Impact Index Per Article: 0.9] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 05/23/2023]
Abstract
The nfe genes (nfeA, nfeB, and nfeD) are involved in the nodulation efficiency and competitiveness of the Sinorhizobium meliloti strain GR4 on alfalfa roots. The nfeA and nfeB genes are preceded by functional nif consensus sequences and NifA binding motifs. Here, we determined the temporal and spatial expression patterns of the nfe genes in symbiosis with alfalfa. Translational fusions of the nfe promoters with the gusA gene and reverse transcription-polymerase chain reaction analyses indicate that they are expressed and translated within mature nitrogen-fixing nodules and not during early steps of nodule development. Within the nodules the three nfe genes exhibit a spatial expression pattern similar to that of genes involved in symbiotic nitrogen fixation. We show that nfeB and nfeD genes are expressed not only from their own promoters but also from the upstream nfe promoter sequences. Furthermore, with the use of specific antibodies the NfeB and NfeD proteins were detected within the root nodule bacteroid fraction. Finally, NfeB was inmunolocalized in the bacteroid cell membrane whereas NfeD was detected in the bacteroid cytoplasm.
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Affiliation(s)
- F M García-Rodríguez
- Departamento de Microbiología del Suelo y Sistemas Simbióticos, Estación Experimental del Zaidín, Consejo Superior de Investigaciones Científicas, Granada, Spain
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24
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Oresnik IJ, Liu SL, Yost CK, Hynes MF. Megaplasmid pRme2011a of Sinorhizobium meliloti is not required for viability. J Bacteriol 2000; 182:3582-6. [PMID: 10852892 PMCID: PMC101967 DOI: 10.1128/jb.182.12.3582-3586.2000] [Citation(s) in RCA: 80] [Impact Index Per Article: 3.3] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/20/2022] Open
Abstract
We report the curing of the 1,360-kb megaplasmid pRme2011a from Sinorhizobium meliloti strain Rm2011. With a positive selection strategy that utilized Tn5B12-S containing the sacB gene, we were able to cure this replicon by successive rounds of selecting for deletion formation in vivo. Subsequent Southern blot, Eckhardt gel, and pulsed-field gel electrophoresis analyses were consistent with the hypothesis that the resultant strain was indeed missing pRme2011a. The cured derivative grew as well as the wild-type strain in both complex and defined media but was unable to use a number of substrates as a sole source of carbon on defined media.
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Affiliation(s)
- I J Oresnik
- Department of Biological Sciences, University of Calgary, Calgary, Alberta, Canada
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25
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Mendrygal KE, González JE. Environmental regulation of exopolysaccharide production in Sinorhizobium meliloti. J Bacteriol 2000; 182:599-606. [PMID: 10633091 PMCID: PMC94320 DOI: 10.1128/jb.182.3.599-606.2000] [Citation(s) in RCA: 89] [Impact Index Per Article: 3.7] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/20/2022] Open
Abstract
Exopolysaccharide production by Sinorhizobium meliloti is required for invasion of root nodules on alfalfa and successful establishment of a nitrogen-fixing symbiosis between the two partners. S. meliloti wild-type strain Rm1021 requires production of either succinoglycan, a polymer of repeating octasaccharide subunits, or EPS II, an exopolysaccharide of repeating dimer subunits. The reason for the production of two functional exopolysaccharides is not clear. Earlier reports suggested that low-phosphate conditions stimulate the production of EPS II in Rm1021. We found that phosphate concentrations determine which exopolysaccharide is produced by S. meliloti. The low-phosphate conditions normally found in the soil (1 to 10 microM) stimulate EPS II production, while the high-phosphate conditions inside the nodule (20 to 100 mM) block EPS II synthesis and induce the production of succinoglycan. Interestingly, the EPS II produced by S. meliloti in low-phosphate conditions does not allow the invasion of alfalfa nodules. We propose that this invasion phenotype is due to the lack of the active molecular weight fraction of EPS II required for nodule invasion. An analysis of the function of PhoB in this differential exopolysaccharide production is presented.
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Affiliation(s)
- K E Mendrygal
- Department of Molecular and Cell Biology, University of Texas at Dallas, Richardson, Texas 75083-0688, USA
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26
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Abstract
A cluster of genes on megaplasmid pRmeSU47b, bhbA-D, is required for growth on the polyhydroxyalkanoate degradation pathway intermediates 3-hydroxybutyrate and acetoacetate as sole carbon source. DNA sequence analysis of the bhbA gene indicated that it encoded a protein of 712 amino acids (aa) (78kDa) which appeared to be a homodimeric methylmalonyl-CoA mutase enzyme (EC 5.4.99.2). Cell-free extract of a bhbA::Tn5 mutant was devoid of methylmalonyl-CoA mutase activity, thus confirming the identity of the bhbA-encoded enzyme. The reason for the requirement of methylmalonyl-CoA mutase activity for operation of the polyhydroxyalkanoate degradation pathway is not immediately apparent. Situated immediately upstream of bhbA, in the same orientation, is a gene which is predicted to encode a protein that exhibits remarkable sequence similarity to the alpha subunit of propionyl-CoA carboxylase (EC 6.4.1.3). A mutation in this gene did not affect ability to grow on 3-hydroxybutyrate as sole carbon source. Downstream of, and oriented towards bhbA, was identified a member of the GNTR class of transcriptional regulator-encoding genes. It is not yet known whether this regulatory protein is directly involved in modulation of bhbA expression.
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Affiliation(s)
- T C Charles
- Department of Natural Resource Sciences, McGill University, Ste-Anne-de-Bellevue, Que. H9X 3V9, Canada.
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27
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Niehaus K, Becker A. The role of microbial surface polysaccharides in the Rhizobium-legume interaction. Subcell Biochem 1998; 29:73-116. [PMID: 9594645 DOI: 10.1007/978-1-4899-1707-2_3] [Citation(s) in RCA: 41] [Impact Index Per Article: 1.6] [Reference Citation Analysis] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 02/07/2023]
Affiliation(s)
- K Niehaus
- Lehrstuhl für Genetik, Fakultät für Biologie, Universität Bielefeld, Germany
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28
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Schlüter A, Patschkowski T, Quandt J, Selinger LB, Weidner S, Krämer M, Zhou L, Hynes MF, Priefer UB. Functional and regulatory analysis of the two copies of the fixNOQP operon of Rhizobium leguminosarum strain VF39. MOLECULAR PLANT-MICROBE INTERACTIONS : MPMI 1997; 10:605-616. [PMID: 9204566 DOI: 10.1094/mpmi.1997.10.5.605] [Citation(s) in RCA: 38] [Impact Index Per Article: 1.4] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 05/22/2023]
Abstract
DNA corresponding to two copies of the Rhizobium leguminosarum bv. viciae strain VF39 fixNOQP operon coding for a putative symbiotic terminal oxidase of the heme-copper oxidase superfamily was cloned, sequenced, and genetically analyzed. The first copy is located upstream of the fixK-fixL region on plasmid pRleVF39c, whereas the second copy resides on the nodulation plasmid pRleVF39d. Insertional mutagenesis with antibiotic resistance cassettes confirmed that both copies were functional, and that the presence of at least one functional copy was required for nitrogen fixation. The deduced amino acid sequences of both fixN genes are highly similar (95% identity) and contain 15 putative transmembrane helices, suggesting that the fixN gene products are integral membrane proteins. Furthermore, six histidine residues predicted to be the ligands for a heme-copper binuclear center and a low-spin heme b are conserved in both R. leguminosarum fixN proteins. The deduced fixO and fixP gene products show characteristics of membrane-bound monoheme and diheme cytochrome c, respectively. Upstream of both fixN copies putative Fnr-consensus binding sites (anaeroboxes) were found that differ in certain base pairs. As R. leguminosarum VF39 possesses two members of the Fnr/FixK regulator family, FnrN and FixK, the possible differential regulation of both fixN copies was analyzed with fixN-gusA reporter gene fusions. Both fixN fusions were induced under free-living microaerobic conditions and in the symbiotic zone of the root nodule. Induction of the expression of fixNc and fixNd was highly reduced in a fnrN mutant background and in a fixL mutant background, whereas fixK was only marginally involved in fixN regulation. Residual expression of fixN was observed in an fnrN/fixK double mutant.
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Affiliation(s)
- A Schlüter
- Okologie des Bodens, Botanisches Institut, RWTH Aachen, Germany
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29
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Mazurier SI, Laguerre G. Unusual localization of nod and nif genes in Rhizobium leguminosarum bv. viciae. Can J Microbiol 1997. [DOI: 10.1139/m97-056] [Citation(s) in RCA: 4] [Impact Index Per Article: 0.1] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/22/2022]
Abstract
Genomic DNA from seven strains of Rhizobium leguminosarum bv. viciae isolated from nodules of field-grown lentils showed homology to nod and nif gene probes, whereas plasmid DNA did not hybridize with these probes. The results suggest that symbiotic genes could be located on the chromosome or perhaps on a very large plasmid that could not be resolved in Eckhardt gels. Each strain contained one plasmid that hybridized with a pSym isolated from a R. leguminosarum strain of the same field population. This finding led us to hypothesize that the nod and nif genes of the seven strains might have originated from a Sym plasmid and have been integrated into another replicon. The ability to nodulate vetch was confirmed for all of the seven strains. Thus, wild strains of R. leguminosarum bv. viciae that nodulate vetch carry nod and nif genes either on the chromosome or on an extrachromosomal replicon of size much larger than the pSyms hitherto described.Key words: Rhizobium leguminosarum, nod genes, nif genes, chromosome, symbiotic plasmid, megaplasmid.
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30
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Bardin S, Dan S, Osteras M, Finan TM. A phosphate transport system is required for symbiotic nitrogen fixation by Rhizobium meliloti. J Bacteriol 1996; 178:4540-7. [PMID: 8755882 PMCID: PMC178221 DOI: 10.1128/jb.178.15.4540-4547.1996] [Citation(s) in RCA: 94] [Impact Index Per Article: 3.4] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 02/02/2023] Open
Abstract
The bacterium Rhizobium meliloti forms N2-fixing root nodules on alfalfa plants. The ndvF locus, located on the 1,700-kb pEXO megaplasmid of R. meliloti, is required for nodule invasion and N2 fixation. Here we report that ndvF contains four genes, phoCDET, which encode an ABC-type transport system for the uptake of Pi into the bacteria. The PhoC and PhoD proteins are homologous to the Escherichia coli phosphonate transport proteins PhnC and PhnD. The PhoT and PhoE proteins are homologous to each other and to the E. coli phosphonate transport protein PhnE. We show that the R. meliloti phoD and phoE genes are induced in response to phosphate starvation and that the phoC promoter contains two elements which are similar in sequence to the PHO boxes present in E. coli phosphate-regulated promoters. The R. meliloti ndvF mutants grow poorly at a phosphate concentration of 2 mM, and we hypothesize that their symbiotic phenotype results from their failure to grow during the nodule infection process. Presumably, the PhoCDET transport system is employed by the bacteria in the soil environment, where the concentration of available phosphate is normally 0.1 to 1 microM.
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Affiliation(s)
- S Bardin
- Department of Biology, McMaster University, Hamilton, Ontario, Canada
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31
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Becker A, Küster H, Niehaus K, Pühler A. Extension of the Rhizobium meliloti succinoglycan biosynthesis gene cluster: identification of the exsA gene encoding an ABC transporter protein, and the exsB gene which probably codes for a regulator of succinoglycan biosynthesis. MOLECULAR & GENERAL GENETICS : MGG 1995; 249:487-97. [PMID: 8544814 DOI: 10.1007/bf00290574] [Citation(s) in RCA: 59] [Impact Index Per Article: 2.0] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 01/31/2023]
Abstract
Two new genes, designated exsA and exsB, were identified adjacent to the 24 kb exo gene cluster of Rhizobium meliloti, which is involved in succinoglycan (EPS I) biosynthesis. The derived amino acid sequence of ExsA displayed significant homologies to ATP binding cassette (ABC) transporter proteins. R. meliloti strains mutated in exsA were characterized by a decreased ratio of HMW to LMW EPS I, indicating a function for ExsA in EPS I biosynthesis. The R. meliloti NdvA protein, which is involved in the transport of cyclic beta-(1,2)-glucans, was identified as the closest homologue of ExsA. R. meliloti exsB mutants produced a three-fold increased amount of EPS I in comparison to the wild-type strain. In contrast, high copy number of exsB resulted in a decrease in the EPS I level to 20% of wild type, indicating that the exsB gene product can negatively influence EPS I biosynthesis. It was demonstrated that this influence is not due to transcriptional regulation of the exo genes by the exsB gene product. By plasmid integration it was shown that exsA and exsB represent monocistronic transcription units.
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Affiliation(s)
- A Becker
- Lehrstuhl für Genetik, Fakultät für Biologie, Universität Bielefeld, Federal Republic of Germany
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32
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Becker A, Niehaus K, Pühler A. Low-molecular-weight succinoglycan is predominantly produced by Rhizobium meliloti strains carrying a mutated ExoP protein characterized by a periplasmic N-terminal domain and a missing C-terminal domain. Mol Microbiol 1995; 16:191-203. [PMID: 7565082 DOI: 10.1111/j.1365-2958.1995.tb02292.x] [Citation(s) in RCA: 80] [Impact Index Per Article: 2.8] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/26/2023]
Abstract
The membrane topology of the Rhizobium meliloti 2011 ExoP protein involved in polymerization and export of succinoglycan was analysed by translational fusions of lacZ and phoA reporter genes to the exoP gene. Based on this analysis, the ExoP protein could be divided into an N-terminal domain mainly located in the periplasmic space and a C-terminal domain located in the cytoplasm. Whereas the C-terminal domain of ExoP is characterized by a potential nucleotide-binding motif, the N-terminal ExoP domain contains the sequence motif 'PX2PX4SPKX11GXMXG', which is also present in proteins involved in the determination of O-antigen chain length. R. meliloti strains carrying mutated exoP* genes, exclusively encoding the N-terminal ExoP domain, produced a reduced amount of succinoglycan. This reduction could be suppressed by a mutation in the regulatory gene exoR. The ratio of low-molecular-weight to high-molecular-weight succinoglycan was significantly increased in the exoP* mutant strain. In the exoP*/exoR mutant strain only low-molecular-weight succinoglycan could be detected. Based on sequence homologies and similar hydropathic profiles, the N-terminal domain of ExoP was proposed to be a member of a protein family thought to be involved in polysaccharide chain-length determination.
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Affiliation(s)
- A Becker
- Lehrstuhl für Genetik, Fakultät für Biologie, Universität Bielefeld, Germany
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33
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Selbitschka W, Dresing U, Hagen M, Niemann S, Pühler A. A biological containment system for Rhizobium meliloti based on the use of recombination-deficient (recAâ) strains. FEMS Microbiol Ecol 1995. [DOI: 10.1111/j.1574-6941.1995.tb00286.x] [Citation(s) in RCA: 6] [Impact Index Per Article: 0.2] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/30/2022] Open
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34
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Becker A, Kleickmann A, Keller M, Arnold W, Pühler A. Identification and analysis of the Rhizobium meliloti exoAMONP genes involved in exopolysaccharide biosynthesis and mapping of promoters located on the exoHKLAMONP fragment. MOLECULAR & GENERAL GENETICS : MGG 1993; 241:367-79. [PMID: 8246891 DOI: 10.1007/bf00284690] [Citation(s) in RCA: 71] [Impact Index Per Article: 2.3] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 01/29/2023]
Abstract
Sequence analysis of a 7.494 kb DNA fragment from megaplasmid 2 of Rhizobium meliloti 2011 involved in exopolysaccharide I (EPS I) biosynthesis revealed the presence of five exo genes designated exoA, exoM, exoN, exoO, and exoP. ExoN was found to show strong homology to a UDP-glucose pyrophosphorylase from Acetobacter xylinum, whereas ExoO displayed weak homologies to the NodC proteins from R. meliloti and R. loti. Surprisingly, different mutations in exoP resulted in divergent phenotypes. One exoP mutant was able to establish an effective symbiosis with alfalfa, although no EPS I polymer could be detected. In contrast, other exoP mutations prevented the formation of an effective symbiosis. The transcriptional organization of the exoA-exoP gene region has been analysed in conjunction with the exoH, exoK and exoL genes. Using exo-lacZ transcription fusions in association with plasmid integration mutagenesis a strong promoter was identified upstream of exoH, which is able to direct transcription of the whole exoHKLAMONP gene cluster. A much weaker promoter upstream of exoL was found to be involved in the transcription of the exoLAMONP genes. In addition, weak promoters were identified upstream of exoK, exoA, exoN and exoP.
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Affiliation(s)
- A Becker
- Lehrstuhl für Genetik, Fakultät für Biologie, Universität Bielefeld, Germany
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35
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Glucksmann MA, Reuber TL, Walker GC. Genes needed for the modification, polymerization, export, and processing of succinoglycan by Rhizobium meliloti: a model for succinoglycan biosynthesis. J Bacteriol 1993; 175:7045-55. [PMID: 8226646 PMCID: PMC206832 DOI: 10.1128/jb.175.21.7045-7055.1993] [Citation(s) in RCA: 157] [Impact Index Per Article: 5.1] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/29/2023] Open
Abstract
The major acidic exopolysaccharide of Rhizobium meliloti, termed succinoglycan, is required for nodule invasion and possibly nodule development. Succinoglycan is a polymer of octasaccharide subunits composed of one galactose residue, seven glucose residues, and acetyl, succinyl, and pyruvyl modifications, which is synthesized on an isoprenoid lipid carrier. A cluster of exo genes in R. meliloti are required for succinoglycan production, and the biosynthetic roles of their gene products have recently been determined (T.L. Reuber and G. C. Walker, Cell 74:269-280, 1993). Our sequencing of 16 kb of this cluster of exo genes and further genetic analysis of this region resulted in the discovery of several new exo genes and has allowed a correlation of the genetic map with the DNA sequence. In this paper we present the sequences of genes that are required for the addition of the succinyl and pyruvyl modifications to the lipid-linked intermediate and genes required for the polymerization of the octasaccharide subunits or the export of succinoglycan. In addition, on the basis of homologies to known proteins, we suggest that ExoN is a uridine diphosphoglucose pyrophosphorylase and that ExoK is a beta(1,3)-beta (1,4)-glucanase. We propose a model for succinoglycan biosynthesis and processing which assigns roles to the products of nineteen exo genes.
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Affiliation(s)
- M A Glucksmann
- Department of Biology, Massachusetts Institute of Technology, Cambridge 02139
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36
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Glucksmann MA, Reuber TL, Walker GC. Family of glycosyl transferases needed for the synthesis of succinoglycan by Rhizobium meliloti. J Bacteriol 1993; 175:7033-44. [PMID: 8226645 PMCID: PMC206831 DOI: 10.1128/jb.175.21.7033-7044.1993] [Citation(s) in RCA: 82] [Impact Index Per Article: 2.6] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/29/2023] Open
Abstract
Rhizobium meliloti produces an acidic exopolysaccharide, termed succinoglycan or EPS I, that is important for invasion of the nodules that it elicits on its host, Medicago sativa. Succinoglycan is a high-molecular-weight polymer composed of repeating octasaccharide subunits. These subunits are synthesized on membrane-bound isoprenoid lipid carriers, beginning with a galactose residue followed by seven glucose residues, and modified by the addition of acetate, succinate, and pyruvate. Biochemical characterizations of lipid-linked succinoglycan biosynthetic intermediates from previously identified exo mutant strains have been carried out in our laboratory (T. L. Reuber and G. C. Walker, Cell 74:269-280, 1993) to determine where each mutation blocks the biosynthetic pathway. We have carried out a fine structure genetic analysis of a portion of the cluster of exo genes present on the second symbiotic megaplasmid of R. meliloti and have identified several new genes. In addition, the DNA sequence of 16 kb of the exo cluster was determined and the genetic map was correlated with the DNA sequence. In this paper we present the sequence of a family of glycosyl transferases required for the synthesis of succinoglycan and discuss their functions.
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Affiliation(s)
- M A Glucksmann
- Department of Biology, Massachusetts Institute of Technology, Cambridge 02139
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37
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Reuber TL, Walker GC. Biosynthesis of succinoglycan, a symbiotically important exopolysaccharide of Rhizobium meliloti. Cell 1993; 74:269-80. [PMID: 8343955 DOI: 10.1016/0092-8674(93)90418-p] [Citation(s) in RCA: 232] [Impact Index Per Article: 7.5] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/30/2023]
Abstract
The exo genes of Rhizobium meliloti are needed for the synthesis of an acidic exopolysaccharide, succinoglycan. We have assigned biosynthetic roles to the products of the exo genes by characterizing succinoglycan biosynthetic intermediates from exo mutant strains. We propose a model of succinoglycan biosynthesis in which the products of the exoY and exoF genes function in the addition of the first sugar, galactose, to the lipid carrier; the products of the exoA, exoL, exoM, exoO, exoU, and exoW genes function in subsequent sugar additions; and the product of the exoV gene functions in the addition of pyruvate. The products of the exoP, exoQ, and exoT genes are required for polymerization of the octasaccharide subunits or transport of the completed polymer.
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Affiliation(s)
- T L Reuber
- Department of Biology, Massachusetts Institute of Technology, Cambridge 02139
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38
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O'connell KP, Handelsman J. Foliar Chlorosis in Symbiotic Host and Nonhost Plants Induced by
Rhizobium tropici
Type B Strains. Appl Environ Microbiol 1993; 59:2184-9. [PMID: 16348994 PMCID: PMC182255 DOI: 10.1128/aem.59.7.2184-2189.1993] [Citation(s) in RCA: 1] [Impact Index Per Article: 0.0] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/20/2022] Open
Abstract
Rhizobium tropici
CIAT899 induced chlorosis in the leaves of its symbiotic hosts, common bean (
Phaseolus vulgaris
L.), siratro (
Macroptilium atropurpureum
Urb.), and
Leucaena leucocephala
(Lam.) de Wit. Chlorosis induction by strains CIAT899 and CT9005, an exopolysaccharide-deficient mutant of CIAT899, required carbon substrate. When the bacteria were added at planting in a solution of mannitol (50 g/liter), as few as 10
3
cells of CIAT899 were sufficient to induce chlorosis in bean plants. All carbon sources tested, including organic acids and mono- and disaccharides, supported chlorosis induction. The addition of a carbon source did not affect the growth rate or the population density of CT9005 in the bean plant rhizosphere. Cell-free filtrates of cultures of CT9005 did not induce detectable chlorosis. All type B strains of
R. tropici
tested also induced chlorosis in common bean. Type A strains of
R. tropici
and all other species of bacteria tested did not induce chlorosis. Several lines of evidence indicated that nodulation was not required for chlorosis induction. Strain RSP900, a pSym-cured derivative of CIAT899, induced chlorosis in wild-type
P. vulgaris
. In addition, NOD125, a nodulation-defective line of common bean, developed chlorosis when inoculated with CIAT899, but did not develop nodules. CIAT899 consistently induced severe chlorosis in the leaves of the nonhost legumes alfalfa (
Medicago sativa
L.) and Berseem clover (
Trifolium alexandrinum
L.), and induced chlorosis in 29 to 58% of the plants tested of sunflower, cucumber, and tomato seedlings, but it did not induce chlorosis in the leaves of corn or wheat. Chlorosis induction in nonhost plants also required carbon substrate. The data are consistent with the hypothesis that
R. tropici
type B strains produce a chlorosis-inducing factor that affects a wide range of plant species.
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Affiliation(s)
- K P O'connell
- Department of Bacteriology, University of Wisconsin-Madison, 1630 Linden Drive, Madison, Wisconsin 53706
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39
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Reuber TL, Walker GC. The acetyl substituent of succinoglycan is not necessary for alfalfa nodule invasion by Rhizobium meliloti Rm1021. J Bacteriol 1993; 175:3653-5. [PMID: 8501069 PMCID: PMC204767 DOI: 10.1128/jb.175.11.3653-3655.1993] [Citation(s) in RCA: 50] [Impact Index Per Article: 1.6] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/31/2023] Open
Abstract
Rhizobium meliloti Rm1021 requires a Calcofluor-binding exopolysaccharide, termed succinoglycan or EPS I, to invade alfalfa nodules. We have determined that a strain carrying a mutation in the exoZ locus produces succinoglycan that lacks the acetyl substituent. The exoZ mutant nodules alfalfa normally.
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Affiliation(s)
- T L Reuber
- Department of Biology, Massachusetts Institute of Technology, Cambridge 02139
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40
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Becker A, Kleickmann A, Arnold W, Pühler A. Analysis of the Rhizobium meliloti exoH/exoK/exoL fragment: ExoK shows homology to excreted endo-beta-1,3-1,4-glucanases and ExoH resembles membrane proteins. MOLECULAR & GENERAL GENETICS : MGG 1993; 238:145-54. [PMID: 8479421 DOI: 10.1007/bf00279541] [Citation(s) in RCA: 44] [Impact Index Per Article: 1.4] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 01/31/2023]
Abstract
Nucleotide sequencing of a 4.15 kb DNA fragment from megaplasmid 2 of Rhizobium meliloti 2011 revealed the location of the genes exoH, exoK and exoL. The putative proteins encoded by these genes have molecular weights of 41, 30, and 44 kDa, respectively. The hydrophobicity profile of the ExoH amino acid sequence resembles that of transmembrane proteins. The predicted exoL gene product does not contain hydrophobic regions, indicating a cytoplasmic localization. The exoK gene product is characterized by a putative signal peptide and exhibits significant homology to endo-beta-1,3-1,4-glucanases of bacilli and Clostridium thermocellum. R. meliloti exoK mutants induced pink nodules and synthesized a reduced amount of exopolysaccharide (EPS). Colonies of this mutant showed a delay in the appearance of the Calcofluor white fluorescence. In addition, the formation of the characteristic halo was strongly delayed. R. meliloti exoL and exoH mutants induced pseudonodules. The exoH, but not the exoL mutant, synthesized an EPS that could be precipitated by cetyl pyridinium chloride (CPC) and also by ethanol. Plasmid integration mutagenesis revealed promoter regions preceding exoH, exoK and exoL.
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Affiliation(s)
- A Becker
- Lehrstuhl für Genetik, Fakultät für Biologie, Universität Bielefeld, FRG
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41
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Brom S, García de los Santos A, Stepkowsky T, Flores M, Dávila G, Romero D, Palacios R. Different plasmids of Rhizobium leguminosarum bv. phaseoli are required for optimal symbiotic performance. J Bacteriol 1992; 174:5183-9. [PMID: 1644746 PMCID: PMC206350 DOI: 10.1128/jb.174.16.5183-5189.1992] [Citation(s) in RCA: 87] [Impact Index Per Article: 2.7] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/28/2022] Open
Abstract
Rhizobium leguminosarum bv. phaseoli CFN42 contains six plasmids (pa to pf), and pd has been shown to be the symbiotic plasmid. To determine the participation of the other plasmids in cellular functions, we used a positive selection scheme to isolate derivatives cured of each plasmid. These were obtained for all except one (pe), of which only deleted derivatives were recovered. In regard to symbiosis, we found that in addition to pd, pb is also indispensable for nodulation, partly owing to the presence of genes involved in lipopolysaccharide synthesis. The positive contribution of pb, pc, pe, and pf to the symbiotic capacity of the strain was revealed in competition experiments. The strains that were cured (or deleted for pe) were significantly less competitive than the wild type. Analysis of the growth capacity of the cured strains showed the participation of the plasmids in free-living conditions: the pf- strain was unable to grow on minimal medium, while strains cured of any other plasmid had significantly reduced growth capacity in this medium. Even on rich medium, strains lacking pb or pc or deleted for pe had a diminished growth rate compared with the wild type. Complementation of the cured strains with the corresponding wild-type plasmid restored their original phenotypes, thus confirming that the effects seen were due only to loss of plasmids. The results indicate global participation of the Rhizobium genome in symbiotic and free-living functions.
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Affiliation(s)
- S Brom
- Departamento de Genética Molecular, Universidad Nacional Autónoma de México, Cuernavaca, Morelos
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42
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Novikova N, Safronova V. Transconjugants ofAgrobacterium radiobacterharbouring sym genes ofRhizobium galegaecan form an effective symbiosis withMedicago sativa. FEMS Microbiol Lett 1992. [DOI: 10.1111/j.1574-6968.1992.tb05107.x] [Citation(s) in RCA: 30] [Impact Index Per Article: 0.9] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/01/2022] Open
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43
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SELBITSCHKA W, POHLER A, SIMON R. The construction of recA–deficient Rhizobium meliloti and R. leguminosarum strains marked with gusA or luc cassettes for use in risk–assessment studies. Mol Ecol 1992. [DOI: 10.1111/j.1365-294x.1992.tb00150.x] [Citation(s) in RCA: 23] [Impact Index Per Article: 0.7] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/28/2022]
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44
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Masepohl B, Kutsche M, Riedel KU, Schmehl M, Klipp W, Pühler A. Functional analysis of the cysteine motifs in the ferredoxin-like protein FdxN of Rhizobium meliloti involved in symbiotic nitrogen fixation. MOLECULAR & GENERAL GENETICS : MGG 1992; 233:33-41. [PMID: 1603075 DOI: 10.1007/bf00587558] [Citation(s) in RCA: 20] [Impact Index Per Article: 0.6] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 12/27/2022]
Abstract
The Rhizobium meliloti fdxN gene, which is part of the nifA-nifB-fdxN operon, is absolutely required for symbiotic nitrogen fixation. The deduced sequence of the FdxN protein is characterized by two cysteine motifs typical of bacterial-type ferredoxins. The Fix-phenotype of an R. meliloti fdxN::[Tc] mutant could be rescued by the R. leguminosarum fdxN gene, whereas no complementation was observed with nif-associated genes encoding ferredoxins from Bradyrhizobium japonicum, Azotobacter vinelandii, A. chroococcum and Rhodobacter capsulatus. In addition to these heterologous genes, several R. meliloti fdxN mutant genes constructed by site-directed mutagenesis were analyzed. Not only a cysteine residue within the second cysteine motif (position 42), which is known to coordinate the Fe-S cluster in homologous proteins, but also a cysteine located down-stream of this motif (position 61), was found to be essential for the activity of the R. meliloti FdxN protein. Changing the amino acid residue proline in position 56 into methionine resulted in a FdxN mutant protein with decreased activity, whereas changes in positions 35 (Asp35Glu) and 45 (Gly45Glu) had no significant effect on the function of the FdxN mutant proteins. In contrast to bacterial-type ferredoxins, which contain two identical cysteine motifs of the form C-X2-C-X2-C-X3-C, nif-associated ferredoxins, including R. meliloti FdxN, are characterized by two different cysteine motifs. Six "additional" amino acids separate the second (Cys42) and the third cysteine (Cys51) in the C-terminal motif (C-X2-C-X8-C-X3-C).(ABSTRACT TRUNCATED AT 250 WORDS)
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Affiliation(s)
- B Masepohl
- Lehrstuhl für Genetik, Fakultät für Biologie, Universität Bielefeld, FRG
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45
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Aguilar OM, Grasso DH. The product of the Rhizobium meliloti ilvC gene is required for isoleucine and valine synthesis and nodulation of alfalfa. J Bacteriol 1991; 173:7756-64. [PMID: 1744032 PMCID: PMC212565 DOI: 10.1128/jb.173.24.7756-7764.1991] [Citation(s) in RCA: 26] [Impact Index Per Article: 0.8] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/28/2022] Open
Abstract
Tn5-induced mutants of Rhizobium meliloti that require the amino acids isoleucine and valine for growth on minimal medium were studied. In one mutant, 1028, the defect is associated with an inability to induce nodules on alfalfa. The Tn5 mutation in 1028 is located in a chromosomal 5.5-kb EcoRI fragment. Complementation analysis with cloned DNA indicated that 2.0 kb of DNA from the 5.5-kb EcoRI fragment restored the wild-type phenotype in the Ilv- Nod- mutant. This region was further characterized by DNA sequence analysis and was shown to contain a coding sequence homologous to those for Escherichia coli IlvC and Saccharomyces cerevisiae Ilv5. Genes ilvC and ilv5 code for the enzyme acetohydroxy acid isomeroreductase (isomeroreductase), the second enzyme in the parallel pathways for the biosynthesis of isoleucine and valine. Enzymatic assays confirmed that strain 1028 was a mutant defective in isomeroreductase activity. In addition, it was shown that the ilvC genes of Rhizobium meliloti and E. coli are functionally equivalent. We demonstrated that in ilvC mutant 1028 the common nodulation genes nodABC are not activated by the inducer luteolin. E. coli ilvC complemented both defective properties (Ilv- and Nod-) found in mutant 1028. These findings demonstrate that R. meliloti requires an active isomeroreductase enzyme for successful nodulation of alfalfa.
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Affiliation(s)
- O M Aguilar
- Quimica Biologica I, Facultad de Ciencias Exactas, Universidad Nacional de La Plata, Argentina
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46
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Selbitschka W, Arnold W, Priefer UB, Rottschäfer T, Schmidt M, Simon R, Pühler A. Characterization of recA genes and recA mutants of Rhizobium meliloti and Rhizobium leguminosarum biovar viciae. MOLECULAR & GENERAL GENETICS : MGG 1991; 229:86-95. [PMID: 1896024 DOI: 10.1007/bf00264217] [Citation(s) in RCA: 30] [Impact Index Per Article: 0.9] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 12/29/2022]
Abstract
DNA fragments carrying the recA genes of Rhizobium meliloti and Rhizobium leguminosarum biovar viciae were isolated by complementing a UV-sensitive recA- Escherichia coli strain. Sequence analysis revealed that the coding region of the R. meliloti recA gene consists of 1044 bp coding for 348 amino acids whereas the coding region of the R. leguminosarum bv. viciae recA gene has 1053 bp specifying 351 amino acids. The R. meliloti and R. leguminosarum bv. viciae recA genes show 84.8% homology at the DNA sequence level and of 90.1% at the amino acid sequence level. recA- mutant strains of both Rhizobium species were constructed by inserting a gentamicin resistance cassette into the respective recA gene. The resulting recA mutants exhibited an increased sensitivity to UV irradiation, were impaired in their ability to perform homologous recombination and showed a slightly reduced growth rate when compared with the respective wild-type strains. The Rhizobium recA strains did not have altered symbiotic nitrogen fixation capacity. Therefore, they represent ideal candidates for release experiments with impaired strains.
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Affiliation(s)
- W Selbitschka
- Lehrstuhl für Genetik, Universität Bielefeld, Federal Republic of Germany
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47
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Charles TC, Newcomb W, Finan TM. ndvF, a novel locus located on megaplasmid pRmeSU47b (pEXO) of Rhizobium meliloti, is required for normal nodule development. J Bacteriol 1991; 173:3981-92. [PMID: 1648074 PMCID: PMC208044 DOI: 10.1128/jb.173.13.3981-3992.1991] [Citation(s) in RCA: 29] [Impact Index Per Article: 0.9] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/28/2022] Open
Abstract
Rhizobium meliloti strains carrying either of two overlapping deletions (delta 5408 and delta F114) of the megaplasmid pRmeSU47b form nodules on alfalfa which fail to fix N2 (Fix-). Strains carrying these deletions also fail to fluoresce on media containing calcofluor, indicating a defect in synthesis of the acidic exopolysaccharide (Exo-) of R. meliloti. We have isolated cosmid clones (pTH21 and pTH22) which complement the Fix- but not the Exo- phenotype of the strains carrying the delta 5408 and delta F114 deletions. In addition, cosmid clones which complement the Exo- phenotype fail to complement the Fix- phenotype of these deletions; thus, the Exo- phenotype is not related to the Fix- phenotype. A 5-kb region within a 7.3-kb BamHI restriction fragment was found to be required for complementation of the Fix- phenotype of the delta 5408 and delta F114 deletion strains. Tn5 insertions in the 5-kb region generated a Fix- phenotype when recombined into the wild-type genome. We have designated this locus ndvF, for nodule development. TnphoA mutagenesis of this region generated active alkaline-phosphatase gene fusions, indicating that ndvF encodes extracytoplasmic protein(s). Induction of nodules by the ndvF mutants was delayed by 2 to 3 days compared with induction by the wild-type strain. Light microscopy of nodules elicited by strains carrying the large 150-kb delta F114 deletion, a 12-kb deletion removing ndvF, or an individual ndvF::Tn5 insertion mutation demonstrated that many nodules contained few infected cortical cells, indicating that nodule development was blocked early in the infection process, before the release of bacteria from the infection threads.
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Affiliation(s)
- T C Charles
- Department of Biology, McMaster University, Hamilton, Ontario, Canada
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48
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Buendia AM, Enenkel B, Köplin R, Niehaus K, Arnold W, Pühler A. The Rhizobium meliloti exoZl exoB fragment of megaplasmid 2: ExoB functions as a UDP-glucose 4-epimerase and ExoZ shows homology to NodX of Rhizobium leguminosarum biovar viciae strain TOM. Mol Microbiol 1991; 5:1519-30. [PMID: 1787800 DOI: 10.1111/j.1365-2958.1991.tb00799.x] [Citation(s) in RCA: 84] [Impact Index Per Article: 2.5] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/28/2022]
Abstract
A 2.6 kb ClaI-BamHI DNA fragment of megaplasmid 2 of Rhizobium meliloti 2011 was found to carry genes involved in exopolysaccharide synthesis and infection of alfalfa nodules. The analysis of the nucleotide sequence of this DNA fragment revealed the existence of two open reading frames (ORFs) running in opposite directions. Plasmid integration mutagenesis showed that these ORFs are organized as two monocistronic transcription units. One of the ORFs represents a new exo gene designated exoZ, which is involved in, but not essential for, the production of acidic exopolysaccharide. However, exoZ is not necessary for nodule formation with alfalfa. The ExoZ protein was found to show homology (23.3%) to the NodX protein of the R. leguminosarum biovar viciae strain TOM, known to be essential for nodulating the primitive Afghanistan pea. The second identified ORF corresponds to the exoB locus. The deduced amino acid sequence of the ExoB protein is homologous (39.6%) to that of the Escherichia coli GalE protein. In R. meliloti, exoB codes for a UDP-glucose 4-epimerase. A deficiency in the activity of this enzyme fully accounts for all the multiple carbohydrate defects that have been observed in exoB mutants.
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Affiliation(s)
- A M Buendia
- Lehrstuhl für Genetik, Universität Bielefeld, Germany
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49
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Reed JW, Glazebrook J, Walker GC. The exoR gene of Rhizobium meliloti affects RNA levels of other exo genes but lacks homology to known transcriptional regulators. J Bacteriol 1991; 173:3789-94. [PMID: 1711027 PMCID: PMC208009 DOI: 10.1128/jb.173.12.3789-3794.1991] [Citation(s) in RCA: 58] [Impact Index Per Article: 1.8] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/28/2022] Open
Abstract
Rhizobium meliloti strains mutant in the exoR gene overproduce an exopolysaccharide called succinoglycan or EPS I. Protein fusions to several different exo genes required for EPS I biosynthesis are expressed at a higher level in an exoR strain than in a wild-type strain, showing that the overproduction of EPS I in exoR strains results at least in part from increased gene expression. This regulation is important to nodulation, since exoR mutants fail to invade alfalfa nodules unless secondary suppressor mutations that cause a decrease in EPS I production occur. Here, we show that an exoR strain contains higher levels of mRNA for other exo genes than does the wild-type parental strain. ExoR therefore most probably exerts its regulatory effect at the level of transcription. In addition, we have localized, subcloned, and sequenced the exoR gene. A newly constructed insertion allele of exoR has the same phenotype as the original mutant. The deduced sequence of ExoR is 268 amino acids long but does not show homology to other sequenced genes.
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Affiliation(s)
- J W Reed
- Department of Biology, Massachusetts Institute of Technology, Cambridge 02139
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50
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Sobral BW, Honeycutt RJ, Atherly AG. The genomes of the family Rhizobiaceae: size, stability, and rarely cutting restriction endonucleases. J Bacteriol 1991; 173:704-9. [PMID: 1846148 PMCID: PMC207062 DOI: 10.1128/jb.173.2.704-709.1991] [Citation(s) in RCA: 25] [Impact Index Per Article: 0.8] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/29/2022] Open
Abstract
The lack of high-resolution genetic or physical maps for the family Rhizobiaceae limits our understanding of this agronomically important bacterial family. On the basis of statistical analyses of DNA sequences of the Rhizobiaceae and direct evaluation by pulsed-field agarose gel electrophoresis (PFE), five restriction endonucleases with AT-rich target sites were identified as the most rarely cutting: AseI (5'-ATTAAT-3'), DraI (5'-TTTAAA-3'), SpeI (5'-ACTAGT-3'), SspI (5'-AATAAT-3'), and XbaI (5'-TCTAGA-3'). We computed the sizes of the genomes of Bradyrhizobium japonicum USDA 424 and Rhizobium meliloti 1021 by adding the sizes of DNA fragments generated by SpeI digests. The genome sizes of R. meliloti 1021 and B. japonicum USDA 424 were 5,379 +/- 282.5 kb and 6,195 +/- 192.4 kb, respectively. We also compared the organization of the genomes of free-living and bacteroid forms of B. japonicum. No differences between the PFE-resolved genomic fingerprints of free-living and mature (35 days after inoculation) bacteroids of B. japonicum USDA 123 and USDA 122 were observed. Also, B. japonicum USDA 123 genomic fingerprints were unchanged after passage through nodules and after maintenance on a rich growth medium for 100 generations. We conclude that large-scale DNA rearrangements are not seen in mature bacteroids or during free-living growth on rich growth media under laboratory conditions.
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Affiliation(s)
- B W Sobral
- Department of Genetics, Iowa State University, Ames 50011
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