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Published on: March 27, 2011
[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.
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