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Yang HW, Thapa R, Johnson K, DuPont ST, Khan A, Zhao Y. Examination of Large Chromosomal Inversions in the Genome of Erwinia amylovora Strains Reveals Worldwide Distribution and North America-Specific Types. PHYTOPATHOLOGY 2023; 113:2174-2186. [PMID: 36935376 DOI: 10.1094/phyto-01-23-0004-sa] [Citation(s) in RCA: 3] [Impact Index Per Article: 3.0] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 06/18/2023]
Abstract
Erwinia amylovora is a relatively homogeneous species with low genetic diversity at the nucleotide level. However, phenotypic differences and genomic structural variations among E. amylovora strains have been documented. In this study, we identified 10 large chromosomal inversion (LCI) types in the Spiraeoideae-infecting (SI) E. amylovora strains by combining whole genome sequencing and PCR-based molecular markers. It was found that LCIs were mainly caused by homologous recombination events among seven rRNA operons (rrns) in SI E. amylovora strains. Although ribotyping results identified inter- and intra-variations in the internal transcribed spacer (ITS1 and ITS2) regions among rrns, LCIs tend to occur between rrns transcribed in the opposite directions and with the same tRNA content (tRNA-Glu or tRNA-Ile/Ala) in ITS1. Based on the LCI types, physical/estimated replichore imbalance (PRI/ERI) was examined and calculated. Among the 117 SI strains evaluated, the LCI types of Ea1189, CFBP1430, and Ea273 were the most common, with ERI values at 1.31, 7.87, and 4.47°, respectively. These three LCI types had worldwide distribution, whereas the remaining seven LCI types were restricted to North America (or certain regions of the United States). Our results indicated ongoing chromosomal recombination events in the SI E. amylovora population and showed that LCI events are mostly symmetrical, keeping the ERI less than 15°. These findings provide initial evidence about the prevalence of certain LCI types in E. amylovora strains, how LCI occurs, and its potential evolutionary advantage and history, which might help track the movement of the pathogen.
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Affiliation(s)
- Ho-Wen Yang
- Department of Crop Sciences, University of Illinois at Urbana-Champaign, Urbana, IL 61802
| | - Ranjita Thapa
- School of Integrative Plant Science Plant Pathology and Plant-Microbe Biology, Cornell University, Geneva, NY 14456
| | - Kenneth Johnson
- Department of Botany and Plant Pathology, Oregon State University, Corvallis, OR 97331
| | | | - Awais Khan
- School of Integrative Plant Science Plant Pathology and Plant-Microbe Biology, Cornell University, Geneva, NY 14456
| | - Youfu Zhao
- Department of Crop Sciences, University of Illinois at Urbana-Champaign, Urbana, IL 61802
- Department of Plant Pathology, WSU-IAREC, Prosser, WA 99350
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Gifford I, Dasgupta A, Barrick JE. Rates of gene conversions between Escherichia coli ribosomal operons. G3-GENES GENOMES GENETICS 2021; 11:5974039. [PMID: 33585862 PMCID: PMC8022953 DOI: 10.1093/g3journal/jkaa002] [Citation(s) in RCA: 1] [Impact Index Per Article: 0.3] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Subscribe] [Scholar Register] [Received: 08/03/2020] [Accepted: 11/10/2020] [Indexed: 11/23/2022]
Abstract
Due to their universal presence and high sequence conservation, ribosomal RNA (rRNA) sequences are used widely in phylogenetics for inferring evolutionary relationships between microbes and in metagenomics for analyzing the composition of microbial communities. Most microbial genomes encode multiple copies of rRNA genes to supply cells with sufficient capacity for protein synthesis. These copies typically undergo concerted evolution that keeps their sequences identical, or nearly so, due to gene conversion, a type of intragenomic recombination that changes one copy of a homologous sequence to exactly match another. Widely varying rates of rRNA gene conversion have previously been estimated by comparative genomics methods and using genetic reporter assays. To more directly measure rates of rRNA intragenomic recombination, we sequenced the seven Escherichia coli rRNA operons in 15 lineages that were evolved for ∼13,750 generations with frequent single-cell bottlenecks that reduce the effects of selection. We identified 38 gene conversion events and estimated an overall rate of intragenomic recombination within the 16S and 23S genes between rRNA copies of 3.6 × 10−4 per genome per generation or 8.6 × 10−6 per rRNA operon per homologous donor operon per generation. This rate varied only slightly from random expectations at different sites within the rRNA genes and between rRNA operons located at different positions in the genome. Our accurate estimate of the rate of rRNA gene conversions fills a gap in our quantitative understanding of how ribosomal sequences and other multicopy elements diversify and homogenize during microbial genome evolution.
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Affiliation(s)
- Isaac Gifford
- Department of Molecular Biosciences, Center for Systems and Synthetic Biology, The University of Texas at Austin, Austin, TX 78712, USA
| | - Aurko Dasgupta
- Department of Molecular Biosciences, Center for Systems and Synthetic Biology, The University of Texas at Austin, Austin, TX 78712, USA
| | - Jeffrey E Barrick
- Department of Molecular Biosciences, Center for Systems and Synthetic Biology, The University of Texas at Austin, Austin, TX 78712, USA
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3
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Libicher K, Hornberger R, Heymann M, Mutschler H. In vitro self-replication and multicistronic expression of large synthetic genomes. Nat Commun 2020; 11:904. [PMID: 32060271 PMCID: PMC7021806 DOI: 10.1038/s41467-020-14694-2] [Citation(s) in RCA: 48] [Impact Index Per Article: 12.0] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 08/07/2019] [Accepted: 01/27/2020] [Indexed: 11/25/2022] Open
Abstract
The generation of a chemical system capable of replication and evolution is a key objective of synthetic biology. This could be achieved by in vitro reconstitution of a minimal self-sustaining central dogma consisting of DNA replication, transcription and translation. Here, we present an in vitro translation system, which enables self-encoded replication and expression of large DNA genomes under well-defined, cell-free conditions. In particular, we demonstrate self-replication of a multipartite genome of more than 116 kb encompassing the full set of Escherichia coli translation factors, all three ribosomal RNAs, an energy regeneration system, as well as RNA and DNA polymerases. Parallel to DNA replication, our system enables synthesis of at least 30 encoded translation factors, half of which are expressed in amounts equal to or greater than their respective input levels. Our optimized cell-free expression platform could provide a chassis for the generation of a partially self-replicating in vitro translation system.
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Affiliation(s)
- K Libicher
- Biomimetic Systems, Max Planck Institute of Biochemistry, Am Klopferspitz 18, 82152, Martinsried, Germany
| | - R Hornberger
- Biomimetic Systems, Max Planck Institute of Biochemistry, Am Klopferspitz 18, 82152, Martinsried, Germany
| | - M Heymann
- Intelligent Biointegrative Systems Group, University of Stuttgart, Pfaffenwaldring 57, 70569, Stuttgart, Germany
| | - H Mutschler
- Biomimetic Systems, Max Planck Institute of Biochemistry, Am Klopferspitz 18, 82152, Martinsried, Germany.
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Gurtler V, Grando D, Kumar BK, Maiti B, Karunasagar I, Karunasagar I. The Use of Recombined Ribosomal RNA Operon (rrn) Type-Specific Flanking Genes to Investigate rrn Differences Between Vibrio parahaemolyticus Environmental and Clinical Strains. GENE REPORTS 2016. [DOI: 10.1016/j.genrep.2016.02.006] [Citation(s) in RCA: 1] [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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5
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Šmajs D, Paštěková L, Grillová L. Macrolide Resistance in the Syphilis Spirochete, Treponema pallidum ssp. pallidum: Can We Also Expect Macrolide-Resistant Yaws Strains? Am J Trop Med Hyg 2015; 93:678-83. [PMID: 26217043 PMCID: PMC4596581 DOI: 10.4269/ajtmh.15-0316] [Citation(s) in RCA: 30] [Impact Index Per Article: 3.3] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 04/29/2015] [Accepted: 06/05/2015] [Indexed: 11/07/2022] Open
Abstract
Treponema pallidum ssp. pallidum (TPA) causes over 10 million new cases of syphilis worldwide whereas T. pallidum ssp. pertenue (TPE), the causative agent of yaws, affects about 2.5 million people. Although penicillin remains the drug of choice in the treatment of syphilis, in penicillin-allergic patients, macrolides have been used in this indication since the 1950s. Failures of macrolides in syphilis treatment have been well documented in the literature and since 2000, there has been a dramatic increase in a number of clinical samples with macrolide-resistant TPA. Scarce data regarding the genetics of macrolide-resistant mutations in TPA suggest that although macrolide-resistance mutations have emerged independently several times, the increase in the proportion of TPA strains resistant to macrolides is mainly due to the spread of resistant strains, especially in developed countries. The emergence of macrolide resistance in TPA appears to require a two-step process including either A2058G or A2059G mutation in one copy of the 23S rRNA gene and a subsequent gene conversion unification of both rRNA genes. Given the enormous genetic similarity that was recently revealed between TPA and TPE strains, there is a low but reasonable risk of emergence and spread of macrolide-resistant yaws strains following azithromycin treatment.
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Affiliation(s)
- David Šmajs
- Department of Biology, Faculty of Medicine, Masaryk University, Brno, Czech Republic
| | - Lenka Paštěková
- Department of Biology, Faculty of Medicine, Masaryk University, Brno, Czech Republic
| | - Linda Grillová
- Department of Biology, Faculty of Medicine, Masaryk University, Brno, Czech Republic
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Čejková D, Zobaníková M, Pospíšilová P, Strouhal M, Mikalová L, Weinstock GM, Šmajs D. Structure of rrn operons in pathogenic non-cultivable treponemes: sequence but not genomic position of intergenic spacers correlates with classification of Treponema pallidum and Treponema paraluiscuniculi strains. J Med Microbiol 2012; 62:196-207. [PMID: 23082031 PMCID: PMC3755535 DOI: 10.1099/jmm.0.050658-0] [Citation(s) in RCA: 23] [Impact Index Per Article: 1.9] [Reference Citation Analysis] [Abstract] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/18/2022] Open
Abstract
This study examined the sequences of the two rRNA (rrn) operons of pathogenic non-cultivable treponemes, comprising 11 strains of T. pallidum ssp. pallidum (TPA), five strains of T. pallidum ssp. pertenue (TPE), two strains of T. pallidum ssp. endemicum (TEN), a simian Fribourg-Blanc strain and a rabbit T. paraluiscuniculi (TPc) strain. PCR was used to determine the type of 16S–23S ribosomal intergenic spacers in the rrn operons from 30 clinical samples belonging to five different genotypes. When compared with the TPA strains, TPc Cuniculi A strain had a 17 bp deletion, and the TPE, TEN and Fribourg-Blanc isolates had a deletion of 33 bp. Other than these deletions, only 17 heterogeneous sites were found within the entire region (excluding the 16S–23S intergenic spacer region encoding tRNA-Ile or tRNA-Ala). The pattern of nucleotide changes in the rrn operons corresponded to the classification of treponemal strains, whilst two different rrn spacer patterns (Ile/Ala and Ala/Ile) appeared to be distributed randomly across species/subspecies classification, time and geographical source of the treponemal strains. It is suggested that the random distribution of tRNA genes is caused by reciprocal translocation between repetitive sequences mediated by a recBCD-like system.
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Affiliation(s)
- Darina Čejková
- The Genome Institute, Washington University in St Louis, 4444 Forest Park Avenue, St Louis, MO 63108, USA.,Department of Biology, Faculty of Medicine, Masaryk University, Kamenice 5, Building A6, 62500 Brno, Czech Republic
| | - Marie Zobaníková
- Department of Biology, Faculty of Medicine, Masaryk University, Kamenice 5, Building A6, 62500 Brno, Czech Republic
| | - Petra Pospíšilová
- Department of Biology, Faculty of Medicine, Masaryk University, Kamenice 5, Building A6, 62500 Brno, Czech Republic
| | - Michal Strouhal
- The Genome Institute, Washington University in St Louis, 4444 Forest Park Avenue, St Louis, MO 63108, USA.,Department of Biology, Faculty of Medicine, Masaryk University, Kamenice 5, Building A6, 62500 Brno, Czech Republic
| | - Lenka Mikalová
- Department of Biology, Faculty of Medicine, Masaryk University, Kamenice 5, Building A6, 62500 Brno, Czech Republic
| | - George M Weinstock
- The Genome Institute, Washington University in St Louis, 4444 Forest Park Avenue, St Louis, MO 63108, USA
| | - David Šmajs
- Department of Biology, Faculty of Medicine, Masaryk University, Kamenice 5, Building A6, 62500 Brno, Czech Republic
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7
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DNA profiling of complex bacterial populations: toxic cyanobacterial blooms. Appl Microbiol Biotechnol 2009; 85:237-52. [DOI: 10.1007/s00253-009-2180-8] [Citation(s) in RCA: 15] [Impact Index Per Article: 1.0] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 06/22/2009] [Revised: 08/03/2009] [Accepted: 08/03/2009] [Indexed: 11/25/2022]
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8
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Treangen TJ, Abraham AL, Touchon M, Rocha EPC. Genesis, effects and fates of repeats in prokaryotic genomes. FEMS Microbiol Rev 2009; 33:539-71. [PMID: 19396957 DOI: 10.1111/j.1574-6976.2009.00169.x] [Citation(s) in RCA: 111] [Impact Index Per Article: 7.4] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 02/06/2023] Open
Abstract
DNA repeats are causes and consequences of genome plasticity. Repeats are created by intrachromosomal recombination or horizontal transfer. They are targeted by recombination processes leading to amplifications, deletions and rearrangements of genetic material. The identification and analysis of repeats in nearly 700 genomes of bacteria and archaea is facilitated by the existence of sequence data and adequate bioinformatic tools. These have revealed the immense diversity of repeats in genomes, from those created by selfish elements to the ones used for protection against selfish elements, from those arising from transient gene amplifications to the ones leading to stable duplications. Experimental works have shown that some repeats do not carry any adaptive value, while others allow functional diversification and increased expression. All repeats carry some potential to disorganize and destabilize genomes. Because recombination and selection for repeats vary between genomes, the number and types of repeats are also quite diverse and in line with ecological variables, such as host-dependent associations or population sizes, and with genetic variables, such as the recombination machinery. From an evolutionary point of view, repeats represent both opportunities and problems. We describe how repeats are created and how they can be found in genomes. We then focus on the functional and genomic consequences of repeats that dictate their fate.
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Abstract
The chromosome structure of lactic acid bacteria has been investigated only recently. The development of pulsed-field gel electrophoresis (PFGE) combined with other DNA-based techniques enables whole-genome analysis of any bacterium, and has allowed rapid progress to be made in the knowledge of the lactic acid bacteria genome. Lactic acid bacteria possess one of the smallest eubacterial chromosomes. Depending on the species, the genome sizes range from 1.1 to 2.6 Mb. Combined physical and genetic maps of several species are already available or close to being achieved. Knowledge of the genomic structure of these organisms will serve as a basis for future genetic studies. Macrorestriction fingerprinting by PFGE is already one of the major tools for strain differentiation, identification of individual strains, and the detection of strain lineages. The genome data resulting from these studies will be of general application strain improvement.
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Affiliation(s)
- P Le Bourgeois
- Laboratoire de Microbiologie et Génétique Moléculaire du CNRS, Toulouse, France
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10
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Hashimoto JG, Stevenson BS, Schmidt TM. Rates and consequences of recombination between rRNA operons. J Bacteriol 2003; 185:966-72. [PMID: 12533472 PMCID: PMC142796 DOI: 10.1128/jb.185.3.966-972.2003] [Citation(s) in RCA: 63] [Impact Index Per Article: 3.0] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 06/25/2002] [Accepted: 11/11/2002] [Indexed: 11/20/2022] Open
Abstract
A mutant strain of Escherichia coli was created by inserting a cassette encoding sucrose sensitivity and neomycin resistance (sacB-neo) into the small-subunit rRNA-encoding gene rrs in the rrnB operon. During growth in a complex medium, the cassette was lost from the population, and a complete rrs gene was restored at a rate of 5 x 10(-9) per cell division. Repair of this lesion required flanking regions of DNA that were similar to the six remaining intact rRNA operons and reestablished the full complement of seven rRNA operons. The relative fitness of strains with restored rrnB operons was 1 to 2% higher than that of the mutant strain. The rrnB operon normally contains a spacer region between the 16S and 23S rRNA-encoding genes that is similar in length and tRNA gene content to the spacer in rrnC, -E, and -G. In 2 of the 14 strains in which rrnB was restored, the spacer region had the same length as the spacer region in rrnA, -D, and -H. The requirement for flanking regions of nearly identical DNA and the replication of the spacer region from other rRNA operons during the repair of rrnB suggest that the restoration was accomplished via gene conversion. The rate of gene conversion was 10-fold less than the fixation of point mutations in the same region of the chromosome but was apparently sufficient to homogenize the sequences of rRNA genes in E. coli. These findings are discussed in the context of a conceptual model describing the presence of sequence heterogeneity in coevolving rRNA genes.
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Affiliation(s)
- Joel G Hashimoto
- Department of Microbiology and Molecular Genetics, Michigan State University, East Lansing, MI 48823-4320, USA
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11
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Adrian PV, Mendrick C, Loebenberg D, McNicholas P, Shaw KJ, Klugman KP, Hare RS, Black TA. Evernimicin (SCH27899) inhibits a novel ribosome target site: analysis of 23S ribosomal DNA mutants. Antimicrob Agents Chemother 2000; 44:3101-6. [PMID: 11036030 PMCID: PMC101610 DOI: 10.1128/aac.44.11.3101-3106.2000] [Citation(s) in RCA: 33] [Impact Index Per Article: 1.4] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 06/05/2000] [Accepted: 08/21/2000] [Indexed: 11/20/2022] Open
Abstract
Spontaneous mutants of susceptible clinical and laboratory isolates of Streptococcus pneumoniae exhibiting reduced susceptibility to evernimicin (SCH27899; MIC, 0.5 to 4.0 mg/liter) were selected on plates containing evernimicin. Four isolates that did not harbor mutations in rplP (which encodes ribosomal protein L16) were further analyzed. Whole chromosomal DNA or PCR products of the 23S ribosomal DNA (rDNA) operons from these mutants could be used to transform the susceptible S. pneumoniae strain R6 to resistance at frequencies of 10(-5) and 10(-4), respectively, rates 10- to 100-fold lower than that for a single-allele chromosomal marker. The transformants appeared slowly (48 to 72 h) on selective medium, and primary transformants passaged on nonselective medium produced single colonies that displayed heterogeneous susceptibilities to evernimicin. A single passage on selective medium of colonies derived from a single primary transformant homogenized the resistance phenotype. Sequence analysis of the 23S rDNA and rRNA from the resistant mutants revealed single, unique mutations in each isolate at the equivalent Escherichia coli positions 2469 (A --> C), 2480 (C --> T), 2535 (G --> A), and 2536 (G --> C). The mutations map within two different stems of the peptidyltransferase region of domain V. Because multiple copies of rDNA are present in the chromosome, gene conversion between mutant and wild-type 23S rDNA alleles may be necessary for stable resistance. Additionally, none of the characterized mutants showed cross-resistance to any of a spectrum of protein synthesis inhibitors, suggesting that the target site of evernimicin may be unique.
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MESH Headings
- Alleles
- Aminoglycosides
- Anti-Bacterial Agents/pharmacology
- Bacterial Proteins/genetics
- Base Sequence
- DNA, Bacterial/genetics
- Drug Resistance, Microbial
- Humans
- Microbial Sensitivity Tests
- Molecular Sequence Data
- Mutation
- Nucleic Acid Conformation
- RNA, Bacterial/analysis
- RNA, Bacterial/genetics
- RNA, Ribosomal, 23S/chemistry
- RNA, Ribosomal, 23S/drug effects
- RNA, Ribosomal, 23S/genetics
- Streptococcus pneumoniae/drug effects
- Streptococcus pneumoniae/genetics
- Transformation, Bacterial
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Affiliation(s)
- P V Adrian
- Pneumococcal Diseases Research Unit, South African Institute for Medical Research, University of the Witwatersrand, and the Medical Research Council, Johannesburg, South Africa.
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Rodríguez C, Romero D. Multiple recombination events maintain sequence identity among members of the nitrogenase multigene family in Rhizobium etli. Genetics 1998; 149:785-94. [PMID: 9611191 PMCID: PMC1460202 DOI: 10.1093/genetics/149.2.785] [Citation(s) in RCA: 17] [Impact Index Per Article: 0.7] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/14/2022] Open
Abstract
A distinctive characteristic of the Rhizobium genome is the frequent finding of reiterated sequences, which often constitute multigene families. Interestingly, these families usually maintain a high degree of nucleotide sequence identity. It is commonly assumed that apparent gene conversion between reiterated elements might lead to concerted variation among members of a multigene family. However, the operation of this mechanism has not yet been demonstrated in the Rhizobiaceae. In this work, we employed different genetic constructions to address the role of apparent gene conversion as a homogenizing mechanism between members of the plasmid-located nitrogenase multigene family in Rhizobium etli. Our results show that a 28-bp insertion into one of the nitrogenase reiterations can be corrected by multiple recombination events, including apparent gene conversion. The correction process was dependent on the presence of both a wild-type recA gene and wild-type copies of the nitrogenase reiterations. Frequencies of apparent gene conversion to the wild-type nitrogenase reiterations were the same when the insertion to be corrected was located either in cis or in trans, indicating that this event frequently occurs through intermolecular interactions. Interestingly, a high frequency of multiple crossovers was observed, suggesting that these large plasmid molecules are engaging repeatedly in recombination events, in a situation akin to phage recombination or recombination among small, high-copy number plasmids.
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Affiliation(s)
- C Rodríguez
- Departamento de Genética Molecular, Centro de Investigación sobre Fijación de Nitrógeno, Universidad Nacional Autónoma de México, Cuernavaca, Morelos, México
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Specific Amplification and Restriction Polymorphisms of the Cyanobacterial rRNA Operon Spacer Region. Syst Appl Microbiol 1997. [DOI: 10.1016/s0723-2020(97)80033-1] [Citation(s) in RCA: 29] [Impact Index Per Article: 1.1] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/22/2022]
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14
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Mattatall NR, Sanderson KE. Salmonella typhimurium LT2 possesses three distinct 23S rRNA intervening sequences. J Bacteriol 1996; 178:2272-8. [PMID: 8636028 PMCID: PMC177935 DOI: 10.1128/jb.178.8.2272-2278.1996] [Citation(s) in RCA: 56] [Impact Index Per Article: 2.0] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 02/01/2023] Open
Abstract
The rrl genes for 23S rRNA of Salmonella typhimurium LT2 are known to carry intervening sequences (IVSs) at two sites, helix-25 and helix-45, which are excised by RNase III during rRNA maturation, resulting in rRNA which is fragmented but nevertheless functional. We isolated DNA fragments containing the seven rrl genes from BlnI, I-CeuI, and SpeI genomic digests following pulsed-field gel electrophoresis and used these DNA fragments as templates for PCRs utilizing primers upstream and downstream of helix-25 and helix-45. Variance in amplicon length and cycle sequencing indicated that rrlG and rrlH have IVSs in helix-25 of approximately 110 bp which are only 56% identical. rrnA, rrnB, rrnC, rrnD, rrnE, and rrnH have IVSs of approximately 90 bp in helix-45, and all have the same nucleotide sequence. Twenty-one independent wild-type strains of S. typhimurium from Salmonella Reference Collection A were analyzed for IVSs by using PCRs with genomic DNAs and by denaturing agarose electrophoresis of RNAs. Many strains resemble LT2, but some have no IVSs in helix-25 and others have IVSs in helix-45 in all seven rrl genes. However, the IVSs in individual wild-type lines are relatively stable, for several LT2 isolates separated over many years by many single-colony isolations are indistinguishable from one another, with the exception of line LB5010, which differs by one helix-25 IVS. We postulate that IVSs have entered strain LT2 by three independent lateral-transfer events and that the IVS in helix-45 was dispersed to and maintained in the same sequence in six of the seven rrl genes by the mechanism of gene conversion.
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Affiliation(s)
- N R Mattatall
- Salmonella Genetic Stock Centre, Uniersity of Calgary, Alberta, Canada.
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15
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Okazaki N, Matsuo S, Saito K, Tominaga A, Enomoto M. Conversion of the Salmonella phase 1 flagellin gene fliC to the phase 2 gene fljB on the Escherichia coli K-12 chromosome. J Bacteriol 1993; 175:758-66. [PMID: 8423149 PMCID: PMC196215 DOI: 10.1128/jb.175.3.758-766.1993] [Citation(s) in RCA: 23] [Impact Index Per Article: 0.7] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/30/2023] Open
Abstract
The Escherichia coli-Salmonella typhimurium-Salmonella abortus-equi hybrid strain EJ1420 has the two Salmonella flagellin genes fliC (antigenic determinant i) and fljB (determinant e,n,x) at the same loci as in the Salmonella strains and constitutively expresses the fliC gene because of mutations in the genes mediating phase variation. Selection for motility in semisolid medium containing anti-i flagellum serum yielded 11 motile mutants, which had the active fliC(e,n,x) and silent fljB(e,n,x) genes. Genetic analysis and Southern hybridization indicated that they had mutations only in the fliC gene, not in the fljB gene or the control elements for phase variation. Nucleotide sequence analysis of the fliC(e,n,x) genes from four representative mutants showed that the minimum 38% (565 bp) and maximum 68% (1,013 bp) sequences of the fliC(i) gene are replaced with the corresponding sequences of the fljB(e,n,x) gene. One of the conversion endpoints between the two genes lies somewhere in the 204-bp homologous sequence in the 5' constant region, and the other lies in the short homologous sequence of 6, 8, or 38 bp in the 3' constant region. The conversions include the whole central variable region of the fljB gene, resulting in fliC(e,n,x) genes with the same number of nucleotides (1,503 bp) as the fljB gene. We discuss the mechanisms for gene conversion between the two genes and also some intriguing aspects of flagellar antigenic specificities in various Salmonella serovars from the viewpoint of gene conversion.
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Affiliation(s)
- N Okazaki
- Department of Biology, Faculty of Science, Okayama University, Japan
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