title: Natural genomic design in Sinorhizobium meliloti: novel genomic architectures.
abstract: The complete nucleotide sequence of the genome of Sinorhizobium meliloti, the symbiont of alfalfa, was reported in 2001 by an international consortium of laboratories. The genome comprises a chromosome of 3.65 megabases (Mb) and two megaplasmids, pSymA and pSymB, of 1.35 Mb and 1.68 Mb, respectively. Based on the nucleotide sequence of the whole genome, we designed a pathway of consecutive rearrangements leading to novel genomic architectures. In a first step we obtained derivative strains containing two replicons; in a second step we obtained a strain containing the genetic information in one single replicon of 6.68 MB. From this last architecture we isolated revertants containing two replicons, and from these we could return to the original architecture showing the three replicons. We found that the relative frequency of excision of cointegrated replicons is higher at the site used for the cointegration than at other sites. This might conciliate two apparently opposed facts: the highly dynamic state of genomic architecture in S. meliloti and the common observation that different isolates and derived cellular clones of S. meliloti usually present the architecture of one chromosome and two distinct megaplasmids. Different aspects that must be considered to obtain full advantage of the strategy of natural genomic design are discussed.
authors.affiliation: Centro de Investigación sobre Fijación de Nitrógeno, Universidad Nacional Autónoma de México Apdo postal 565-A, Cuernavaca, Morelos, México.
authors.forename: Xianwu
authors.initials: X
authors.lastname: Guo
authors.forename: Margarita
authors.initials: M
authors.lastname: Flores
authors.forename: Patrick
authors.initials: P
authors.lastname: Mavingui
authors.forename: Sara Isabel
authors.initials: SI
authors.lastname: Fuentes
authors.forename: Georgina
authors.initials: G
authors.lastname: Hernández
authors.forename: Guillermo
authors.initials: G
authors.lastname: Dávila
authors.forename: Rafael
authors.initials: R
authors.lastname: Palacios
mesh_terms: D004251:DNA Transposable Elements / Q000235:genetics; D004269:DNA, Bacterial / Q000032:analysis; D016521:Electrophoresis, Gel, Pulsed-Field; D015964:Gene Expression Regulation, Bacterial / Q000235:genetics; D005798:Genes, Bacterial / Q000235:genetics; D016680:Genome, Bacterial; D010957:Plasmids; D011995:Recombination, Genetic / Q000235:genetics; D012093:Replicon / Q000235:genetics; D016962:Sinorhizobium meliloti / Q000235:genetics* / Q000254:growth & development; D013559:Symbiosis / Q000235:genetics
chemical_list: D004251:DNA Transposable Elements; D004269:DNA, Bacterial