Characterization of eight excision plasmids of Pseudomonas syringae pv. phaseolicola

Area of Science:

• Microbiology
• Molecular Biology
• Genetics

Background:

• Pseudomonas syringae pv. phaseolicola strain LR719 harbors a 150 kilobase pair (kb) plasmid, pMC7105, integrated into its chromosome.
• Excision plasmids are occasionally observed in single colony isolates of this strain.

Purpose of the Study:

• To characterize eight unique excision plasmids derived from pMC7105.
• To determine the integration site of pMC7105 and identify recombination sites involved in excision.

Main Methods:

• BamHI restriction endonuclease digestion and blot hybridization analyses were used to characterize excision plasmids.
• Restriction mapping of pMC7105 was performed to deduce integration and recombination sites.

Main Results:

• Excision plasmids varied in size from 35 to 270 kb, with the largest containing approximately 130 kb of chromosomal DNA.
• The eight excision plasmids were classified into five groups based on excision sites.
• A conserved 20 kb region of pMC7105, containing the origin of replication, was present in all excision plasmids.
• Integration of pMC7105 occurred within BamHI fragment 8, which showed homology with other plasmid and chromosomal fragments.

Conclusions:

• The integration of pMC7105 into the Pseudomonas syringae chromosome likely occurred at repetitive DNA sequences.
• Homology between plasmid and chromosomal fragments suggests a mechanism for plasmid integration and subsequent excision.