Prophage lambda induction caused by mini-F plasmid genes

Area of Science:

• Molecular Biology
• Genetics
• Microbiology

Background:

• The coupled cell division (ccd) system of mini-F plasmids, including ccdA and ccdB genes, regulates plasmid replication and host cell division.
• Low plasmid copy numbers trigger inhibition of bacterial cell division.

Purpose of the Study:

• To investigate the molecular mechanisms of the ccd function in coupling host cell division to plasmid proliferation.
• To explore the role of the ccd system in prophage induction.
• To propose a hypothesis on the indirect induction of prophage lambda by F plasmids.

Main Methods:

• Utilizing temperature-sensitive replication plasmids carrying the ccd segment in bacterial cells.
• Incubating cells at 42°C to observe effects on cell division and prophage induction.
• Analyzing the role of recA function in prophage induction.
• Assessing the effect of a replication-proficient ccdA-carrying plasmid on these processes.

Main Results:

• Transferring bacteria with temperature-sensitive plasmids to 42°C inhibits cell division when plasmid copy number drops critically low.
• In lambda phage lysogens, prophage induction occurs alongside cell division inhibition under the same conditions.
• Prophage induction requires functional recA, while cell division inhibition does not.
• Both phenomena are suppressed by a co-existing replication-proficient plasmid carrying the ccdA gene.

Conclusions:

• The ccd system couples host cell division to plasmid proliferation, potentially through mechanisms involving plasmid copy number.
• The ccd mechanism contributes to prophage induction in lysogenic bacteria.
• A hypothesis is proposed suggesting the F plasmid's ccd mechanism mediates indirect prophage lambda induction after UV damage and conjugation.