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Isolation and characterization of mutants of colicin plasmids E1 and E2 after Mu bacteriophage infection
Abstract:
Cells colicinogenic for the colicin plasmids E1 or E2 (Col E1 and Col E2, respectively) were selected for a loss of colicin production after infection with bacteriophage Mu. Extrachromosomal deoxyribonucleic acid that was larger than the original colicin plasmids was found in such cells. A small insertion mutant in Col E1 deoxyribonucleic acid affecting active colicin production without affecting either expression of colicin immunity or Col E1 deoxyribonucleic acid replication was found. Cells carrying this Col E1 plasmid mutant do not exhibit the lethal event associated with colicin E1 induction, suggesting that synthesis of active colicin is required for killing during induction. The altered Col E2 plasmid, containing an insertion at least as large as phage Mu, was maintained unstably in the mutants examined.
Insights
Bacteriophage Mu infection disrupted colicin production in Col E1 and Col E2 plasmids. A Col E1 mutant lacking active colicin synthesis prevented cell death during induction, indicating colicin activity is essential for this lethal event.
Area of Science:
- Molecular Biology
- Microbial Genetics
- Bacteriophage Research
Background:
- Colicin plasmids (Col E1, Col E2) confer colicin production in bacteria.
- Bacteriophage Mu is a transposable element known to affect host gene expression.
Purpose of the Study:
- Investigate the impact of bacteriophage Mu infection on colicin plasmid stability and function.
- Characterize genetic alterations in colicin plasmids following Mu integration.
- Determine the role of active colicin synthesis in the lethal effects of colicin induction.
Main Methods:
- Selection of colicin-producing cells (Col E1, Col E2) after bacteriophage Mu infection.
- Analysis of extrachromosomal deoxyribonucleic acid (DNA) in infected cells.
- Identification and characterization of insertion mutants in Col E1 and Col E2 plasmids.
Main Results:
- Infection with bacteriophage Mu led to a loss of colicin production and the appearance of larger extrachromosomal DNA in cells with Col E1 and Col E2 plasmids.
- A Col E1 plasmid insertion mutant was identified that affected active colicin production but not colicin immunity or plasmid replication.
- Cells harboring the Col E1 mutant did not undergo the lethal event associated with colicin E1 induction.
- An altered Col E2 plasmid, containing a large Mu insertion, was found to be unstably maintained.
Conclusions:
- Active colicin synthesis is a prerequisite for the lethal outcome of colicin E1 induction.
- Bacteriophage Mu can cause significant alterations to colicin plasmids, affecting their production and stability.
- The study provides insights into the genetic requirements for colicin activity and its associated cell-killing mechanism.