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J Bacteriol. 1971 May; 106(2): 311-317
Copyright © 1971 American Society for Microbiology. All Rights Reserved.

Isolation and Characterization of Supercoiled Circular Deoxyribonucleic Acid from Beta-Hemolytic Strains of Escherichia coli

Institut für Mikrobiologie und Molekularbiologie, Universität Hohenheim, Stuttgam-Hohenheim, F.R. Germany

ABSTRACT

Covalently closed circular deoxyribonucleic acid (DNA) molecules were isolated by cesium chloride centrifugation in the presence of ethidium bromide from a naturally occurring beta-hemolytic Escherichia coli strain (SC52). The open circular forms have contour lengths of 2.25 ± 0.1 µm, 24.0 ± 0.3 µm, and 29.5 ± 0.5 µm. The beta-hemolytic character of E. coli SC52 can be transferred by conjugation to a nonhemolytic recipient strain. Analysis of the supercoiled DNA of the hemolytic recipient demonstrated that the two large supercoiled DNA molecules of E. coli SC52 are transferred during this event, too. A beta-hemolytic laboratory E. coli strain and several of its derivatives have been shown to contain at least one circular DNA molecule, slightly larger in size than those isolated from E. coli SC52 and its conjugant. The possible significance of these DNA molecules for hemolysin production and transfer is discussed.