Plasmid capture by the Bacillus thuringiensis conjugative plasmid pXO16

Area of Science:

• Microbiology
• Bacterial Genetics
• Horizontal Gene Transfer

Background:

• Horizontal gene transfer (HGT) in bacteria, including conjugation, mobilization, and retromobilization, is crucial for bacterial evolution.
• Retromobilization, the capture of DNA from a recipient by a donor cell, has been well-characterized in Gram-negative bacteria.
• Experimental data on retromobilization in Gram-positive bacteria, particularly Bacillus species, are limited.

Purpose of the Study:

• To investigate the mobilization and retromobilization capabilities of the conjugative plasmid pXO16 from Bacillus thuringiensis.
• To determine if a successive model of retromobilization applies to Gram-positive bacteria.
• To assess the ecological impact of these gene transfer events in natural liquid food environments.

Main Methods:

• Utilized mobilizable plasmids (pUB110, pE194) and a non-mobilizable element (pC194) from Staphylococcus aureus.
• Studied the conjugative plasmid pXO16 from Bacillus thuringiensis subsp. israelensis.
• Quantified conjugation, mobilization, and retromobilization frequencies in laboratory media and natural liquid foods (cow milk, soy milk, rice milk).

Main Results:

• Experimental data supported a successive model for retromobilization in Bacillus thuringiensis.
• Retromobilization events were observed to be delayed compared to direct conjugation.
• Gene transfer frequencies in cow and soy milk were comparable to laboratory media, while rice milk showed higher frequencies.

Conclusions:

• Bacillus thuringiensis exhibits plasmid mobilization and retromobilization capabilities.
• The findings support a successive model for retromobilization in Gram-positive bacteria.
• Plasmid capture by Bacillus thuringiensis has potential ecological significance in natural environments, particularly in food matrices.