Large Plasmids in Different Rhizobium Species

Abstract

Summary Large plasmids were detected in Rhizobium species by sedimentation analysis of lysates on alkaline sucrose gradients and by dye buoyant density centrifugation. Mitomycin C treatment did not increase the amount of plasmid DNA in the bacteria. Renaturation kinetics were used to confirm that these large DNA molecules had the molecular complexity of plasmids and to estimate their molecular weights. These ranged from 0·7 × 108 to 4·0 × 108 daltons. The maximum yield of isolated plasmid DNA relative to chromosomal DNA was 3·8%.