Detection and Characterization of Plasmids in Pseudomonas aeruginosa Strain PAO

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Abstract
Using a variety of techniques, it has been established that the sex factor FP2 has a density of 1.717 g/cm3 (corresponding to a guanine plus cytosine [G + C] content of 58%) and a mean circular contour length of 28.5 ± 0.6 μm (corresponding to a molecular weight of 59 × 106). Another sex factor FP39 has a density of 1.719 g/cm3 (corresponding to a G + C content of 60%) and a mean circular contour length of 26.5 ± 0.5 μm (corresponding to a molecular weight of 55 × 106). It appears that all, or nearly all, of the FP sex factor deoxyribonucleic acid occurs as covalent circular molecules under the conditions employed. In addition, these procedures have been used to demonstrate that strain PAO, a naturally occurring female (i.e., FP−) strain of Pseudomonas aeruginosa, harbors a number of cryptic plasmids having similar densities to the bulk of the cell deoxyribonucleic acid (1.726 g/cm3) and occurring as covalent circular molecules.