title: [Demonstration of extrachromosomal DNA in Rhizobium meliloti].
abstract: Seven effective (nitrogen-fixing) strains of Rhizobium meliloti have been studied. By sedimentation analysis of their alkaline lysates in alkaline sucrose gradients, a plasmid was found in four strains. In a strain (2011 str 3) which gave no result with this method, supercoiled DNA was detected by CsCl-dye buoyant density gradient centrifugation. That result was confirmed by analytical Cs2SO4-Ag+ density gradients, which showed a heterogeneity in the average base composition of the DNA extracted from three strains, including the 2011 str 3 strain. Two of those last strains seemed to contain an extrachromosomal DNA of very high molecular weight.
mesh_terms: D002499:Centrifugation, Density Gradient; D004269:DNA, Bacterial / Q000032:analysis*; D005111:Extrachromosomal Inheritance; D008970:Molecular Weight; D010957:Plasmids; D012231:Rhizobium / Q000235:genetics*
chemical_list: D004269:DNA, Bacterial
vernacular_title: Mise en évidence d'ADN extrachromosomique chez Rhizobium meliloti.