[Use of ultrasound to obtain small Escherichia coli cells containing drd plasmids]

Treatment with ultrasound of Escherichia coli K-12 chi 1100 producing mini-cells and containing R factor 100-1 drd depressed in conjugation transfer, prior to defferential and zonal centrifugation, makes it possible to increase the yield and purity of mini-cells. Combination of ultrasound treatment with differential centrifugation produces mini-cells with purity greater than 10(3) per parent cell. Ultrasound has no negative effect on the physiological state of mini-cells and the hydrodynamical characteristics of segregated plasmid DNA.