Large Plasmids in Different Rhizobium Species

Abstract

Large plasmids were detected in Rhizobium spp. 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 MW. These ranged from 0.7 .times. 108-4.0 .times. 108 daltons. The maximum yield of isolated plasmid DNA relative to chromosomal DNA was 3.8%. [This plasmid may be involved in the initiation of symbiosis with legumes.].