Physical properties of plasmid Mor174, which determines bacteriocin production in Proteus morganii 174

Area of Science:

• Microbiology
• Molecular Biology
• Genetics

Background:

• Plasmids are extrachromosomal DNA molecules crucial for bacterial adaptation and evolution.
• Understanding plasmid characteristics, such as copy number and physical properties, is vital for genetic studies.
• Proteus morganii harbors various plasmids, including Mor174, whose specific attributes require detailed investigation.

Purpose of the Study:

• To characterize the physical properties of Plasmid Mor174.
• To determine the copy number of Plasmid Mor174 per genome equivalent.
• To investigate the effect of chloramphenicol on Plasmid Mor174 copy number.

Main Methods:

• Determination of molecular weight and buoyant density.
• Measurement of sedimentation coefficient for the covalently closed circular form.
• Quantification of plasmid copy number using genome equivalents.
• Analysis of plasmid amplification under chloramphenicol stress.

Main Results:

• Plasmid Mor174 exhibits a molecular weight of 3.6 x 10^6 and a buoyant density of 1.6994 g/cm^3.
• The covalently closed circular form has a sedimentation coefficient of 22S.
• Under normal conditions, 30-40 copies of Plasmid Mor174 exist per genome equivalent.
• Chloramphenicol treatment induced a significant amplification, reaching up to 600 copies per genome equivalent.
• Plasmid Mor174 coexists with a cryptic plasmid (MW 15.8 x 10^6, BD 1.7170 g/cm^3) in Proteus morganii 174.

Conclusions:

• Plasmid Mor174 possesses distinct physical and molecular characteristics.
• The plasmid copy number is subject to significant amplification in response to specific antibiotic stress.
• The coexistence of multiple plasmids in Proteus morganii 174 highlights potential for complex genetic interactions.