Indirect selection of bacterial plasmids lacking identifiable phenotypic properties

Area of Science:

• Bacterial genetics
• Molecular biology
• Plasmid biology

Background:

• Identifying bacteria with specific plasmids is crucial for genetic studies.
• Co-transformation of multiple plasmids can be challenging to track, especially for non-phenotypic plasmids.
• Previous methods lacked efficiency in isolating specific plasmid combinations.

Purpose of the Study:

• To develop an efficient method for identifying bacterial cells co-transformed with a selectable and a non-selectable plasmid.
• To isolate and characterize the P15A cryptic plasmid from Escherichia coli strain 15.
• To demonstrate the independent replicative capability of the P15A plasmid.

Main Methods:

• Utilized an indicator plasmid (pSC201) for indirect selection of co-transformed bacteria.
• Employed a temperature-sensitive mutation in the indicator plasmid for its subsequent elimination.
• Applied selective conditions to isolate bacteria containing only the target non-selectable plasmid.

Main Results:

• Achieved 50-85% efficiency in co-transformant identification using the indicator plasmid system.
• Successfully isolated the P15A cryptic plasmid, a small genetic element of 2,300 base pairs.
• Confirmed that the P15A plasmid functions as an independent replicon in Escherichia coli.

Conclusions:

• The described indirect selection procedure is effective for isolating bacteria carrying non-phenotypic plasmids.
• The P15A plasmid is a functional and independent replicon in Escherichia coli.
• This method facilitates the study of small, cryptic plasmids and their replication mechanisms.