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Isolation of large bacterial plasmids and characterization of the P2 incompatibility group plasmids pMG1 and pMG5
Abstract:
Large plasmids from Agrobacterium tumefaciens, Salmonella typhimurium, Escherichia coli, Pseudomonas putida, and Pseudomonas aeruginosa were routinely and consistently isolated using a procedure which does not require ultracentrifugation but includes steps designed to separate large-plasmid DNA from the bacterial folded chromosome. It also selectively removes fragments of broken chromosome. A variety of large plasmids was readily visualized with agarose gel electorphoresis, including five between 70 and 85 megadaltons (Mdal) in size, six between 90 and 143 Mdal, one that was larger than 200 Mdal, and one that was larger than 300 Mdal. This isolation procedure allowed initial estimation of the molecular sizes of the two IncP2 plasmids, pMG1 and pMG5, which were 312 and 280 Mdal, respectively. A standard curve for size determination by gel electrophoresis including plasmids between 23 and 143 Mdal in size did not extrapolate linearly for plasmids of the 300-Mdal size range. Unique response of different plasmids to the isolation procedure included sensitivity of IncP1 plasmids to high pH and the co-isolation of a 20-Mdal "cryptic" plasmid in conjunction.
Insights
Researchers developed a new method to isolate large bacterial plasmids without ultracentrifugation. This technique effectively separates plasmid DNA from chromosomal DNA, aiding in the study of these important genetic elements.
Area of Science:
- Microbiology
- Molecular Biology
- Genetics
Background:
- Large plasmids play crucial roles in bacterial adaptation and evolution.
- Efficient isolation of large plasmids is essential for their characterization and functional studies.
- Existing methods often involve ultracentrifugation, which can be time-consuming and technically demanding.
Purpose of the Study:
- To develop and validate a novel, ultracentrifugation-free method for isolating large plasmids.
- To demonstrate the efficacy of the method across diverse bacterial species.
- To enable accurate size estimation of large plasmids using standard molecular techniques.
Main Methods:
- A modified DNA isolation procedure was employed, focusing on separating large plasmids from the bacterial folded chromosome.
- Agarose gel electrophoresis was used for visualization and size determination of isolated plasmids.
- Standard curves were generated for plasmid size estimation, with considerations for large molecular weights.
Main Results:
- The method successfully isolated large plasmids from multiple bacterial species including Agrobacterium tumefaciens, Salmonella typhimurium, Escherichia coli, Pseudomonas putida, and Pseudomonas aeruginosa.
- Plasmids ranging from 70 to over 300 Mdal were visualized, including IncP2 plasmids pMG1 (312 Mdal) and pMG5 (280 Mdal).
- Non-linear extrapolation of standard curves was observed for plasmids exceeding 143 Mdal, highlighting challenges in precise size determination for very large plasmids.
Conclusions:
- A robust, ultracentrifugation-free method for large plasmid isolation has been established.
- The procedure is effective for a range of bacterial species and plasmid sizes.
- Further refinement may be needed for precise size determination of plasmids in the >300 Mdal range.