title: Dynamics of genome architecture in Rhizobium sp. strain NGR234.
abstract: Bacterial genomes are usually partitioned in several replicons, which are dynamic structures prone to mutation and genomic rearrangements, thus contributing to genome evolution. Nevertheless, much remains to be learned about the origins and dynamics of the formation of bacterial alternative genomic states and their possible biological consequences. To address these issues, we have studied the dynamics of the genome architecture in Rhizobium sp. strain NGR234 and analyzed its biological significance. NGR234 genome consists of three replicons: the symbiotic plasmid pNGR234a (536,165 bp), the megaplasmid pNGR234b (>2,000 kb), and the chromosome (>3,700 kb). Here we report that genome analyses of cell siblings showed the occurrence of large-scale DNA rearrangements consisting of cointegrations and excisions between the three replicons. As a result, four new genomic architectures have emerged. Three consisted of the cointegrates between two replicons: chromosome-pNGR234a, chromosome-pNGR234b, and pNGR234a-pNGR234b. The other consisted of a cointegrate of the three replicons (chromosome-pNGR234a-pNGR234b). Cointegration and excision of pNGR234a with either the chromosome or pNGR234b were studied and found to proceed via a Campbell-type mechanism, mediated by insertion sequence elements. We provide evidence showing that changes in the genome architecture did not alter the growth and symbiotic proficiency of Rhizobium derivatives.
authors.affiliation: Centro de Investigación sobre Fijación de Nitrógeno, Universidad Nacional Autónoma de México, Cuernavaca, Morelos, Mexico. mavingui@cifn.unam.mx
authors.forename: Patrick
authors.initials: P
authors.lastname: Mavingui
authors.forename: Margarita
authors.initials: M
authors.lastname: Flores
authors.forename: Xianwu
authors.initials: X
authors.lastname: Guo
authors.forename: Guillermo
authors.initials: G
authors.lastname: Dávila
authors.forename: Xavier
authors.initials: X
authors.lastname: Perret
authors.forename: William J
authors.initials: WJ
authors.lastname: Broughton
authors.forename: Rafael
authors.initials: R
authors.lastname: Palacios
mesh_terms: D004251:DNA Transposable Elements; D004269:DNA, Bacterial / Q000235:genetics*; D016521:Electrophoresis, Gel, Pulsed-Field; D019143:Evolution, Molecular; D016680:Genome, Bacterial; D010641:Phenotype; D016133:Polymerase Chain Reaction; D011995:Recombination, Genetic; D012093:Replicon; D012231:Rhizobium / Q000235:genetics*; D013559:Symbiosis
chemical_list: D004251:DNA Transposable Elements; D004269:DNA, Bacterial