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A method for the isolation of phage mutants altered in their response ot lysogenic induction
Abstract:
Phage lambdacl+ gives clear plaques whereas phage lambdacIind- gives turbid plaques on a lawn of a mutant strain of E. coli K12. This strain, called STS, carries mutation spr in a tif sfi genetic background. I hypothesize that upon temperate phage infection, STS bacteria spontaneously inactivate phage repressor by the same mechanism involved in normal lysogenic induction which results in obligatory lytic growth of lambda+. The use of the STS mutant facilitates the isolation and genetic analysis of phage mutants with an abnormal response to lysogenic induction.
Insights
A new E. coli K12 mutant, STS, spontaneously inactivates phage repressor upon infection, causing obligatory lytic growth. This facilitates studying phage mutants and lysogenic induction mechanisms.
Area of Science:
- Microbiology
- Bacteriology
- Molecular Biology
Background:
- Bacteriophages, like lambda, can exist in lysogenic (dormant) or lytic (active replication) cycles.
- Lysogenic induction involves the inactivation of phage repressor, leading to the lytic cycle.
- The E. coli K12 strain STS, with a spr mutation in a tif sfi background, exhibits unique responses to phage infection.
Purpose of the Study:
- To investigate the mechanism of spontaneous phage repressor inactivation in STS mutant bacteria.
- To utilize the STS mutant for isolating and genetically analyzing phage mutants with altered lysogenic induction responses.
- To understand the interplay between bacterial mutations and phage life cycle regulation.
Main Methods:
- Infecting STS mutant E. coli lawns with different lambda phage variants (e.g., lambdacl+, lambdacIind-).
- Observing plaque morphology (clear vs. turbid) to infer phage behavior.
- Genetic analysis of phage mutants exhibiting abnormal responses to lysogenic induction.
Main Results:
- Phage lambdacl+ produced clear plaques, indicating lytic growth.
- Phage lambdacIind- produced turbid plaques, suggesting a different outcome than expected.
- The STS mutant's genetic background (spr, tif sfi) is implicated in spontaneous repressor inactivation.
Conclusions:
- STS bacteria likely possess a mechanism for spontaneous phage repressor inactivation, mirroring normal lysogenic induction.
- This inactivation leads to obligatory lytic growth of infecting phages like lambda+.
- The STS mutant is a valuable tool for dissecting phage-host interactions and studying lysogenic induction pathways.