Detection and characterization of plasmids in Pseudomonas glycinea

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Abstract
Pathogenic strains of P. glycinea [causative organism of soybean blight] possessed plasmid DNA by dye-buoyant density gradient centrifugation. The size and number of plasmids of 4 different isolates were determined by neutral sucrose gradient centrifugation. Two isolates harbored a single plasmid, but they differed in size, having MW of 43 .times. 106 and 54 .times. 106. Two other isolates each contained 2 different plasmids. Plasmids with MW of 43 .times. 106 and 73 .times. 106 were observed in 1 isolate, and the other carried plasmids with MW of 25 .times. 106 and 87 .times. 106. An auxotrophic mutant derived from the latter strain contained plasmids of identical size. The plasmids were under stringent control of replication, having plasmid copies of 1.0-2.7/chromosome equivalent. By the dye CsCl technique, the mutant showed twice as much covalently closed circular DNA as did the parental strain.