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Nayak DD, Metcalf WW. Methylamine-specific methyltransferase paralogs in Methanosarcina are functionally distinct despite frequent gene conversion. THE ISME JOURNAL 2019; 13:2173-2182. [PMID: 31053830 PMCID: PMC6776008 DOI: 10.1038/s41396-019-0428-6] [Citation(s) in RCA: 5] [Impact Index Per Article: 1.0] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Subscribe] [Scholar Register] [Received: 02/06/2019] [Revised: 03/28/2019] [Accepted: 04/03/2019] [Indexed: 11/09/2022]
Abstract
Sequenced archaeal genomes are mostly smaller and more streamlined than typical bacterial genomes; however, members of the Methanosarcina genus within the Euryarchaeaota are a significant exception, with M. acetivorans being the largest archaeal genome (5.8 Mbp) sequenced thus far. This finding is partially explained by extensive gene duplication within Methanosarcina spp. Significantly, the evolutionary pressures leading to gene duplication and subsequent genome expansion have not been well investigated, especially with respect to biological methane production (methanogenesis), which is the key biological trait of these environmentally important organisms. In this study, we address this question by specifically probing the functional evolution of two methylamine-specific methyltransferase paralogs in members of the Methanosarcina genus. Using the genetically tractable strain, M. acetivorans, we first show that the two paralogs have distinct cellular functions: one being required for methanogenesis from methylamine, the other for use of methylamine as a nitrogen source. Subsequently, through comparative sequence analyses, we show that functional divergence of paralogs is primarily mediated by divergent evolution of the 5' regulatory region, despite frequent gene conversion within the coding sequence. This unique evolutionary paradigm for functional divergence of genes post-duplication underscores a divergent role for an enzyme singularly associated with methanogenic metabolism in other aspects of cell physiology.
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Affiliation(s)
- Dipti D Nayak
- Carl R. Woese Institute for Genomic Biology, University of Illinois, 1206 W. Gregory Drive, Urbana, IL, 61801, USA.
| | - William W Metcalf
- Department of Microbiology, University of Illinois, 601 S. Goodwin Avenue, Urbana, IL, 61801, USA
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Hernandez-Salmeron JE, Santoyo G. Phylogenetic analysis reveals gene conversions in multigene families of rhizobia. GENETICS AND MOLECULAR RESEARCH 2011; 10:1383-92. [PMID: 21823087 DOI: 10.4238/vol10-3gmr1118] [Citation(s) in RCA: 7] [Impact Index Per Article: 0.5] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/03/2022]
Abstract
Gene families are an important and intrinsic trait of rhizobial species. These gene copies can participate in non-reciprocal recombination events, also called gene conversions. Gene conversion has diverse roles, but it is usually implicated in the evolution of multigene families. Here, we searched for gene conversions in multigene families of six representative rhizobial genomes. We identified 11 gene families with different numbers of copies, genome location and function in CFN42 and CIAT652 strains of Rhizobium etli, Rhizobium sp NGR234, Mesorhizobium loti MAFF303099, Sinorhizobium meliloti 1021, and Bradyrhizobium japonicum USDA110. Gene conversions were detected by phylogenetic inference in the nifD and nifK gene families in R. etli. Sequence analysis confirmed multiple gene conversions in these two gene families. We suggest that gene conversion events have an important role in homogenizing multigene families in rhizobia.
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Affiliation(s)
- J E Hernandez-Salmeron
- Laboratorio de Recombinacion y Diversidad Genomica, Instituto de Investigaciones Quimico Biologicas, Universidad Michoacana de San Nicolas de Hidalgo, Morelia, Michoacan, Mexico
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Orozco-Mosqueda MDC, Altamirano-Hernandez J, Farias-Rodriguez R, Valencia-Cantero E, Santoyo G. Homologous recombination and dynamics of rhizobial genomes. Res Microbiol 2009; 160:733-41. [DOI: 10.1016/j.resmic.2009.09.011] [Citation(s) in RCA: 13] [Impact Index Per Article: 0.9] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 06/01/2009] [Revised: 09/17/2009] [Accepted: 09/21/2009] [Indexed: 10/20/2022]
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The extent of migration of the Holliday junction is a crucial factor for gene conversion in Rhizobium etli. J Bacteriol 2009; 191:4987-95. [PMID: 19502410 DOI: 10.1128/jb.00111-09] [Citation(s) in RCA: 9] [Impact Index Per Article: 0.6] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/11/2023] Open
Abstract
Gene conversion, defined as the nonreciprocal transfer of DNA, is one result of homologous recombination. Three steps in recombination could give rise to gene conversion: (i) DNA synthesis for repair of the degraded segment, (ii) Holliday junction migration, leading to heteroduplex formation, and (iii) repair of mismatches in the heteroduplex. There are at least three proteins (RuvAB, RecG, and RadA) that participate in the second step. Their roles have been studied for homologous recombination, but evidence of their relative role in gene conversion is lacking. In this work, we showed the effect on gene conversion of mutations in ruvB, recG, and radA in Rhizobium etli, either alone or in combination, using a cointegration strategy previously developed in our laboratory. The results indicate that the RuvAB system is highly efficient for gene conversion, since its absence provokes smaller gene conversion segments than those in the wild type as well as a shift in the preferred position of conversion tracts. The RecG system possesses a dual role for gene conversion. Inactivation of recG leads to longer gene conversion tracts than those in the wild type, indicating that its activity may hinder heteroduplex extension. However, under circumstances where it is the only migration activity present (as in the ruvB radA double mutant), conversion segments can still be seen, indicating that RecG can also promote gene conversion. RadA is the least efficient system in R. etli but is still needed for the production of detectable gene conversion tracts.
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Martínez-Salazar JM, Zuñiga-Castillo J, Romero D. Differential roles of proteins involved in migration of Holliday junctions on recombination and tolerance to DNA damaging agents in Rhizobium etli. Gene 2008; 432:26-32. [PMID: 19071199 DOI: 10.1016/j.gene.2008.11.009] [Citation(s) in RCA: 6] [Impact Index Per Article: 0.4] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 06/25/2008] [Revised: 11/07/2008] [Accepted: 11/11/2008] [Indexed: 11/26/2022]
Abstract
The recombination genes involved in Holliday junction migration (ruvB, recG, radA) and heteroduplex editing (mutS) were studied in the alpha-proteobacterium Rhizobium etli. The genes were interrupted with a loxPSp interposon and R. etli mutants, either single or in combination, were constructed by marker exchange. Our results show that these systems play a differential role in sensitivity to DNA damaging agents and recombination in R. etli. RuvB appears to be the main system for tolerance toward agents instigating single- or double-strand breaks (such as UV light, methyl methanesulphonate and nalidixic acid) while the RecG and RadA systems play minor roles in tolerance to these agents. Using five different recombination assays, we have found that a ruvB null mutant showed a notable reduction in recombination proficiency, while a radA mutant was only weakly affected. A null mutation in recG had the opposite effect, enhancing recombination in most of our assays. This effect was more clearly seen in an assay that measured recombination between divergent sequences (i.e. homeologous), but is unaffected by inactivation of mutS. These data indicate that RecG in R. etli limits intra- and intergenomic plasticity.
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Affiliation(s)
- Jaime M Martínez-Salazar
- Programa de Ingeniería Genómica, Centro de Ciencias Genómicas, Universidad Nacional Autónoma de México, Apartado Postal 565-A, 62210 Cuernavaca, Morelos, México
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6
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STOLL SASCHA, GADAU JÜRGEN, GROSS ROY, FELDHAAR HEIKE. Bacterial microbiota associated with ants of the genus Tetraponera. Biol J Linn Soc Lond 2007. [DOI: 10.1111/j.1095-8312.2006.00730.x] [Citation(s) in RCA: 65] [Impact Index Per Article: 3.8] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/01/2022]
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Santoyo G, Martínez-Salazar JM, Rodríguez C, Romero D. Gene conversion tracts associated with crossovers in Rhizobium etli. J Bacteriol 2005; 187:4116-26. [PMID: 15937174 PMCID: PMC1151741 DOI: 10.1128/jb.187.12.4116-4126.2005] [Citation(s) in RCA: 15] [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
Gene conversion has been defined as the nonreciprocal transfer of information between homologous sequences. Despite its broad interest for genome evolution, the occurrence of this mechanism in bacteria has been difficult to ascertain due to the possible occurrence of multiple crossover events that would mimic gene conversion. In this work, we employ a novel system, based on cointegrate formation, to isolate gene conversion events associated with crossovers in the nitrogen-fixing bacterium Rhizobium etli. In this system, selection is applied only for cointegrate formation, with gene conversions being detected as unselected events. This minimizes the likelihood of multiple crossovers. To track the extent and architecture of gene conversions, evenly spaced nucleotide changes were made in one of the nitrogenase structural genes (nifH), introducing unique sites for different restriction endonucleases. Our results show that (i) crossover events were almost invariably accompanied by a gene conversion event occurring nearby; (ii) gene conversion events ranged in size from 150 bp to 800 bp; (iii) gene conversion events displayed a strong bias, favoring the preservation of incoming sequences; (iv) even small amounts of sequence divergence had a strong effect on recombination frequency; and (v) the MutS mismatch repair system plays an important role in determining the length of gene conversion segments. A detailed analysis of the architecture of the conversion events suggests that multiple crossovers are an unlikely alternative for their generation. Our results are better explained as the product of true gene conversions occurring under the double-strand break repair model for recombination.
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Affiliation(s)
- Gustavo Santoyo
- Programa de Ingeniería Genómica, Centro de Ciencias Genómicas-Universidad Nacional Autónoma de México, Apartado Postal 565-A, 62210 Cuernavaca, Morelos, México
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Zuñiga-Castillo J, Romero D, Martínez-Salazar JM. The recombination genes addAB are not restricted to gram-positive bacteria: genetic analysis of the recombination initiation enzymes RecF and AddAB in Rhizobium etli. J Bacteriol 2004; 186:7905-13. [PMID: 15547262 PMCID: PMC529079 DOI: 10.1128/jb.186.23.7905-7913.2004] [Citation(s) in RCA: 26] [Impact Index Per Article: 1.3] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/20/2022] Open
Abstract
Single-strand gaps (SSGs) and double-strand breaks (DSBs) are the major initiation sites for recombination. In bacteria, the SSGs are repaired by RecFOR, while the DSBs are processed by RecBCD in gram-negative bacteria and AddAB in gram-positive bacteria. Unexpectedly, instead of recBCD genes, the addAB genes were found in members of the alpha-proteobacteria group (gram negative). Taking Rhizobium etli as a model, the role of recF and addAB genes in homologous recombination and repair of damaged DNA was evaluated. Inactivation of either recF or addA provoked strong sensitivity to UV radiation and mitomycin C, while an additive effect was observed in the recF-addA mutant. The DSBs generated by nalidixic acid caused low viability only in the addA mutant. The recombination frequency of large and small plasmids was reduced in the recF mutant (24- and 36-fold, respectively), whereas a slight decrease (threefold) in the addA mutant was observed. Moreover, an additive effect (47- and 90-fold, respectively) was observed in the double mutant, but it was not as dramatic as that in a recA mutant. Interestingly, the frequency of deletion and Campbell-type recombination was slightly affected in either single or double mutants. These results suggest that another pathway exists that allows plasmid and Campbell-type recombination in the absence of recF and addA genes.
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Affiliation(s)
- Jacobo Zuñiga-Castillo
- Programa de Genética Molecular de Plásmidos Bacterianos, Centro de Investigación sobre Fijación de Nitrógeno-UNAM, 62210 Cuernavaca, Morelos, México
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Toledo I, Lloret L, Martínez-Romero E. Sinorhizobium americanus sp. nov., a new Sinorhizobium species nodulating native Acacia spp. in Mexico. Syst Appl Microbiol 2003; 26:54-64. [PMID: 12747410 DOI: 10.1078/072320203322337317] [Citation(s) in RCA: 89] [Impact Index Per Article: 4.2] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/18/2022]
Abstract
The sinorhizobia isolated from root nodules of Acacia species native of Mexico constitute a diverse group of bacteria on the basis of their metabolic enzyme electromorphs but share restriction patterns of the PCR products of 16S rRNA genes and a common 500 kb symbiotic plasmid. They are distinguished from other Sinorhizobium species by their levels of DNA-DNA hybridization and the sequence of 16S rRNA and nifH genes. nolR gene hybridization patterns were found useful to identify sinorhizobia and characterize species. A new species, Sinorhizobium americanus, is described and the type strain is CFNEI 156 from Acacia acatlensis.
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Affiliation(s)
- Ivonne Toledo
- Centro de Investigación sobre Fijación de Nitrógeno, Universidad Nacional Autónoma de México, Cuernavaca, Morelos, México
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Silva C, Vinuesa P, Eguiarte LE, Martínez-Romero E, Souza V. Rhizobium etli and Rhizobium gallicum nodulate common bean (Phaseolus vulgaris) in a traditionally managed milpa plot in Mexico: population genetics and biogeographic implications. Appl Environ Microbiol 2003; 69:884-93. [PMID: 12571008 PMCID: PMC143635 DOI: 10.1128/aem.69.2.884-893.2003] [Citation(s) in RCA: 48] [Impact Index Per Article: 2.3] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/20/2022] Open
Abstract
The stability of the genetic structure of rhizobial populations nodulating Phaseolus vulgaris cultivated in a traditionally managed milpa plot in Mexico was studied over three consecutive years. The set of molecular markers analyzed (including partial rrs, glnII, nifH, and nodB sequences), along with host range experiments, placed the isolates examined in Rhizobium etli bv. phaseoli and Rhizobium gallicum bv. gallicum. Cluster analysis of multilocus enzyme electrophoresis and plasmid profile data separated the two species and identified numerically dominant clones within each of them. Population genetic analyses showed that there was high genetic differentiation between the two species and that there was low intrapopulation differentiation of the species over the 3 years. The results of linkage disequilibrium analyses are consistent with an epidemic genetic structure for both species, with frequent genetic exchange taking place within conspecific populations but not between the R. etli and R. gallicum populations. A subsample of isolates was selected and used for 16S ribosomal DNA PCR-restriction fragment length polymorphism analysis, nifH copy number determination, and host range experiments. Plasmid profiles and nifH hybridization patterns also revealed the occurrence of lateral plasmid transfer among distinct multilocus genotypes within species but not between species. Both species were recovered from nodules of the same plants, indicating that mechanisms other than host, spatial, or temporal isolation may account for the genetic barrier between the species. The biogeographic implications of finding an R. gallicum bv. gallicum population nodulating common bean in America are discussed.
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Affiliation(s)
- Claudia Silva
- Laboratorio de Evolución Molecular y Experimental, Instituto de Ecología, Universidad Nacional Autónoma de México, México D. F. 04510, Mexico.
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González V, Bustos P, Ramírez-Romero MA, Medrano-Soto A, Salgado H, Hernández-González I, Hernández-Celis JC, Quintero V, Moreno-Hagelsieb G, Girard L, Rodríguez O, Flores M, Cevallos MA, Collado-Vides J, Romero D, Dávila G. The mosaic structure of the symbiotic plasmid of Rhizobium etli CFN42 and its relation to other symbiotic genome compartments. Genome Biol 2003; 4:R36. [PMID: 12801410 PMCID: PMC193615 DOI: 10.1186/gb-2003-4-6-r36] [Citation(s) in RCA: 129] [Impact Index Per Article: 6.1] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 11/01/2002] [Revised: 03/06/2003] [Accepted: 04/02/2003] [Indexed: 11/20/2022] Open
Abstract
BACKGROUND Symbiotic bacteria known as rhizobia interact with the roots of legumes and induce the formation of nitrogen-fixing nodules. In rhizobia, essential genes for symbiosis are compartmentalized either in symbiotic plasmids or in chromosomal symbiotic islands. To understand the structure and evolution of the symbiotic genome compartments (SGCs), it is necessary to analyze their common genetic content and organization as well as to study their differences. To date, five SGCs belonging to distinct species of rhizobia have been entirely sequenced. We report the complete sequence of the symbiotic plasmid of Rhizobium etli CFN42, a microsymbiont of beans, and a comparison with other SGC sequences available. RESULTS The symbiotic plasmid is a circular molecule of 371,255 base-pairs containing 359 coding sequences. Nodulation and nitrogen-fixation genes common to other rhizobia are clustered in a region of 125 kilobases. Numerous sequences related to mobile elements are scattered throughout. In some cases the mobile elements flank blocks of functionally related sequences, thereby suggesting a role in transposition. The plasmid contains 12 reiterated DNA families that are likely to participate in genomic rearrangements. Comparisons between this plasmid and complete rhizobial genomes and symbiotic compartments already sequenced show a general lack of synteny and colinearity, with the exception of some transcriptional units. There are only 20 symbiotic genes that are shared by all SGCs. CONCLUSIONS Our data support the notion that the symbiotic compartments of rhizobia genomes are mosaic structures that have been frequently tailored by recombination, horizontal transfer and transposition.
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Affiliation(s)
- Víctor González
- Centro de Investigación Sobre Fijación de Nitrógeno, Universidad Nacional Autónoma de México, Cuernavaca, Morelos, México 62210
| | - Patricia Bustos
- Centro de Investigación Sobre Fijación de Nitrógeno, Universidad Nacional Autónoma de México, Cuernavaca, Morelos, México 62210
| | - Miguel A Ramírez-Romero
- Centro de Investigación Sobre Fijación de Nitrógeno, Universidad Nacional Autónoma de México, Cuernavaca, Morelos, México 62210
| | - Arturo Medrano-Soto
- Centro de Investigación Sobre Fijación de Nitrógeno, Universidad Nacional Autónoma de México, Cuernavaca, Morelos, México 62210
| | - Heladia Salgado
- Centro de Investigación Sobre Fijación de Nitrógeno, Universidad Nacional Autónoma de México, Cuernavaca, Morelos, México 62210
| | - Ismael Hernández-González
- Centro de Investigación Sobre Fijación de Nitrógeno, Universidad Nacional Autónoma de México, Cuernavaca, Morelos, México 62210
| | - Juan Carlos Hernández-Celis
- Centro de Investigación Sobre Fijación de Nitrógeno, Universidad Nacional Autónoma de México, Cuernavaca, Morelos, México 62210
| | - Verónica Quintero
- Centro de Investigación Sobre Fijación de Nitrógeno, Universidad Nacional Autónoma de México, Cuernavaca, Morelos, México 62210
| | - Gabriel Moreno-Hagelsieb
- Centro de Investigación Sobre Fijación de Nitrógeno, Universidad Nacional Autónoma de México, Cuernavaca, Morelos, México 62210
| | - Lourdes Girard
- Centro de Investigación Sobre Fijación de Nitrógeno, Universidad Nacional Autónoma de México, Cuernavaca, Morelos, México 62210
| | - Oscar Rodríguez
- Centro de Investigación Sobre Fijación de Nitrógeno, Universidad Nacional Autónoma de México, Cuernavaca, Morelos, México 62210
| | - Margarita Flores
- Centro de Investigación Sobre Fijación de Nitrógeno, Universidad Nacional Autónoma de México, Cuernavaca, Morelos, México 62210
| | - Miguel A Cevallos
- Centro de Investigación Sobre Fijación de Nitrógeno, Universidad Nacional Autónoma de México, Cuernavaca, Morelos, México 62210
| | - Julio Collado-Vides
- Centro de Investigación Sobre Fijación de Nitrógeno, Universidad Nacional Autónoma de México, Cuernavaca, Morelos, México 62210
| | - David Romero
- Centro de Investigación Sobre Fijación de Nitrógeno, Universidad Nacional Autónoma de México, Cuernavaca, Morelos, México 62210
| | - Guillermo Dávila
- Centro de Investigación Sobre Fijación de Nitrógeno, Universidad Nacional Autónoma de México, Cuernavaca, Morelos, México 62210
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Omelchenko MV, Makarova KS, Koonin EV. Recurrent intragenomic recombination leading to sequence homogenization during the evolution of the lipoyl-binding domain. FEMS Microbiol Lett 2002; 209:255-60. [PMID: 12007814 DOI: 10.1111/j.1574-6968.2002.tb11140.x] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/29/2022] Open
Abstract
The lipoyl-binding domain is often present, in one or several copies, in the E2 subunit and, less often, in the E1 and E3 subunits of 2-oxo acid dehydrogenase complexes. Phylogenetic analysis shows evidence of multiple, independent intragenomic recombination events between different versions of the lipoyl-binding domain in various bacteria and eukaryotic mitochondria, leading to homogenization of the sequences of the lipoyl-binding domain within the same enzymatic complex in several bacterial lineages. This appears to be the first case of sequence homogenization at the level of an individual domain in prokaryotes.
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Affiliation(s)
- Marina V Omelchenko
- Department of Pathology, F.E. Hebert School of Medicine, Uniformed Services University of the Health Sciences, Bethesda, MD 20814-4799, USA
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Abstract
Studies in several organisms show that recombination and replication interact closely. Recombinational repair usually requires associated replication at some stage; moreover, additional replication can induce recombination through either homologous or illegitimate events. In prokaryotes, stimulation of recombination by replication is more dramatic when rolling circle replication is employed. In contrast, theta-type replication induces only a modest increase in recombination frequency. In this article, we show that induction of theta-type replication from a supernumerary origin in the symbiotic plasmid (pSym) of Rhizobium etli leads to a 1000-fold increase in deletion formation on this plasmid. These deletions span 120 kb (the symbiotic region) and have as endpoints the reiterated nitrogenase operons. We have named this phenomenon RER, for recombination enhancement by replication. RER is not affected by the position of the replication origin in the pSym, the direction of advance of the replication fork, or the distance from the origin to the recombining repeats. On the other hand, RER is dependent on an active recA allele, indicating that it is due to homologous recombination. RER displays a strong regionality restricted to the symbiotic region. The similarities and differences of RER with the recombination process observed at the terminus of replication of the Escherichia coli chromosome are discussed.
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Affiliation(s)
- E Valencia-Morales
- Programa de Genética Molecular de Plásmidos Bacterianos, Centro de Investigación sobre Fijación de Nitrógeno, Universidad Nacional Autónoma de México, 62210 Cuernavaca, Morelos, México
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Romero D, Martínez-Salazar J, Ortiz E, Rodríguez C, Valencia-Morales E. Repeated sequences in bacterial chromosomes and plasmids: a glimpse from sequenced genomes. Res Microbiol 1999; 150:735-43. [PMID: 10673011 DOI: 10.1016/s0923-2508(99)00119-9] [Citation(s) in RCA: 25] [Impact Index Per Article: 1.0] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/26/2022]
Abstract
To gain insight into the extent of exact DNA repeats in sequenced bacterial genomes and their plasmids, we analyzed the collection of completely sequenced bacterial genomes available at GenBank using the program Miropeats. This program draws graphical representations of exact DNA repeats in whole genomes. In this work, we present maps showing the extent and type (inverted or direct) of exact DNA repeats longer than 300 bp for the whole collection. These repeats may participate in a variety of events relevant for bacterial genome plasticity, such as amplifications, deletions, inversions, and translocations (via homologous recombination), as well as transposition. Additionally, we review recent data showing that high-frequency architectural variations in genomic structure occur at both the interspecies and interstrain levels.
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Affiliation(s)
- D Romero
- Programa de Genética Molecular de Plásmidos Bacterianos, Centro de Investigación sobre Fijación de Nitrógeno, Universidad Nacional Autónoma de México, Morelos, Mexico.
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