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Isolation and Characterization of the Fertility Factor P of Vibrio cholerae

^a Department of Bacterial Immunology, Division of Communicable Disease and Immunology, Walter Reed Army Institute of Research, Washington, D.C. 20012

ABSTRACT

Vibrio cholerae strains with the transmissible fertility factor P contained a supercoiled circular deoxyribonucleic acid (DNA) component amounting to between 2 and 6% of the total DNA obtained from the cells. Such a component was not observed in V. cholerae strains lacking the fertility factor. This supercoiled circular DNA was isolated from P⁺ cells, and the molecular weight was determined by sedimentation velocity experiments and electron microscopy to be approximately 80 million daltons. These supercoiled circular DNA molecules, which have a guanine plus cytosine (G + C) composition of 42%, were concluded to be the extrachromosomal P factor. It was calculated that there is approximately one copy of the P factor per chromosome. A small amount of supercoiled circular DNA was occasionally isolated from the P^– strains of V. cholerae. The function of this component, which has a molecular weight of 40 million daltons, is not known. The molecules found in the P^– strains were readily distinguished from the P⁺ circular molecules by their smaller molecular weight and different G + C composition.

¹ World Health Organization Senior Research Fellow, on leave from Cholera Research Centre, Calcutta-16, India.

² On leave from Department of Bacteriology, U.C.L.A., Los Angeles, Calif. 90024.