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Detection and characterization of plasmids in Pseudomonas aeruginosa strain PAO
Abstract:
Using a variety of techniques, it has been established that the sex factor FP2 has a density of 1.717 g/cm(3) (corresponding to a guanine plus cytosine [G + C] content of 58%) and a mean circular contour length of 28.5 +/- 0.6 mum (corresponding to a molecular weight of 59 x 10(6)). Another sex factor FP39 has a density of 1.719 g/cm(3) (corresponding to a G + C content of 60%) and a mean circular contour length of 26.5 +/- 0.5 mum (corresponding to a molecular weight of 55 x 10(6)). 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/cm(3)) and occurring as covalent circular molecules.
Insights
The sex factors FP2 and FP39 in Pseudomonas aeruginosa are primarily circular DNA molecules. These sex factors, along with cryptic plasmids, were characterized by their density and molecular weight.
Area of Science:
- Molecular Biology
- Microbiology
- Genetics
Background:
- Sex factors are plasmids that confer fertility in bacteria.
- Pseudomonas aeruginosa is a Gram-negative bacterium with clinical significance.
- Understanding plasmid properties is crucial for bacterial genetics and evolution.
Purpose of the Study:
- To characterize the biophysical properties of sex factors FP2 and FP39.
- To investigate the nature of cryptic plasmids in Pseudomonas aeruginosa strain PAO.
Main Methods:
- Cesium chloride density gradient centrifugation to determine DNA density and G+C content.
- Electron microscopy to measure contour length and assess molecular form.
- Analysis of DNA from Pseudomonas aeruginosa strain PAO.
Main Results:
- Sex factor FP2 has a density of 1.717 g/cm³ (58% G+C) and a molecular weight of 59 x 10⁶ Da.
- Sex factor FP39 has a density of 1.719 g/cm³ (60% G+C) and a molecular weight of 55 x 10⁶ Da.
- Both FP2 and FP39 DNA predominantly exist as covalently closed circular molecules.
- Strain PAO harbors cryptic plasmids with densities close to chromosomal DNA (1.726 g/cm³), also as circular molecules.
Conclusions:
- FP2 and FP39 are large plasmids with distinct biophysical properties.
- The majority of FP sex factor DNA exists in a circular form.
- Pseudomonas aeruginosa strain PAO contains cryptic plasmids that are physically similar to chromosomal DNA.