Instability of rRNA operons in Bacillus subtilis

Area of Science:

• Microbiology
• Molecular Biology
• Genetics

Background:

• Laboratory strains of Bacillus subtilis often possess fewer than the typical 10 rRNA operons.
• This reduction is attributed to deletions within specific gene clusters, namely rrnJ-rrnW or rrnI-rrnH-rrnG.
• These gene clusters are part of larger, closely spaced groupings within the cysA-aroI region of the bacterial chromosome.

Purpose of the Study:

• To investigate the mechanisms behind rRNA operon deletions in Bacillus subtilis.
• To understand how the arrangement of rRNA operons influences deletion frequency.
• To elucidate the role of intrachromosomal recombination and integrative plasmids in these genetic events.

Main Methods:

• Analysis of rescued DNA from integrants containing insertions within the rrnG and rrnH operons.
• Investigating spontaneous intrachromosomal recombination events.
• Examining deletions resulting from simultaneous double crossovers with multimeric integrative plasmids.

Main Results:

• The study identified that tandemly arranged rRNA operons within the cysA-aroI region are prone to frequent deletions.
• Evidence suggests these deletions can occur spontaneously through intrachromosomal recombination.
• Simultaneous double crossovers involving multimeric integrative plasmids were also implicated in the deletion process.

Conclusions:

• The specific arrangement of rRNA operons in Bacillus subtilis facilitates the loss of these essential genetic elements.
• Both spontaneous intrachromosomal recombination and integrative plasmid-mediated events contribute to the observed reduction in rRNA operon copy number.
• Understanding these deletion mechanisms is crucial for characterizing laboratory strains and their genetic stability.