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Prophage lambda induction caused by mini-F plasmid genes
Abstract:
When bacterial cells harboring a temperature-sensitive replication plasmid, which carries the particular ccd segment (coupled cell division) containing the ccdA and ccdB genes of a mini-F plasmid, are transferred to 42 degrees C, cell division is inhibited after incubation for an appropriate time. The inhibition occurs, when the copy number of the plasmid decreases to become critically low, about one per cell (Ogura and Hiraga 1983b). In lambda phage lysogens carrying this type of plasmid, the prophage is induced in a small portion of the cell population under the same conditions, in addition to the inhibition of cell division in most of cells. The prophage induction, but not the inhibition of normal cell division, depends on normal recA function. Both induction of prophage and inhibition of cell division are suppressed by the simultaneous presence of a replication proficient plasmid carrying the ccdA gene. We discuss molecular mechanisms of the ccd function that couples host cell division to plasmid proliferation and induces the prophage. Additionally, we propose a hypothesis that the ccd mechanism of F plasmid contributes to indirect induction of prophage lambda by an F plasmid damaged by UV-irradiation and then introduced into a lysogen via conjugation.
Insights
Bacterial cell division halts when plasmids with the ccd segment reach low copy numbers. This coupled cell division (ccd) mechanism also triggers prophage induction, a process influenced by recA function.
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.