Analysis of plasmid deletional instability in Bacillus subtilis

Area of Science:

• Molecular Biology
• Genetics
• Microbiology

Background:

• Deletion formation is a critical process influencing genome stability.
• Understanding recombination mechanisms in bacteria like Bacillus subtilis is essential for genetic engineering and evolutionary studies.

Purpose of the Study:

• To investigate the mechanisms of deletion formation in Bacillus subtilis.
• To identify the sequence requirements and conditions for intramolecular recombination between plasmids.

Main Methods:

• Ligation of staphylococcal plasmids pSA2100 and pUB110 at their XbaI sites.
• Transformation into rec+ and recE4 strains of Bacillus subtilis.
• Restriction enzyme analysis of isolated recombinant plasmids.

Main Results:

• Intramolecular recombination consistently occurred between ligated plasmids, forming new plasmids of 2.6 and 9.0 kilobases.
• Recombination was mediated by short, 18-base-pair homologous sequences oriented as direct repeats, bounded by dyad symmetry.
• The recombination event was biased towards intramolecular occurrence and did not require specific DNA repair or competence factors.

Conclusions:

• Specific homologous sequences and their orientation are key drivers of illegitimate intramolecular recombination.
• The identified recombination mechanism in Bacillus subtilis is robust, occurring across various genetic mutant backgrounds.
• This study provides insights into the precise molecular events underlying plasmid recombination and deletion formation.