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Isolation and properties of Escherichia coli mutants which are nonpermissive for the growth of phage lambda
Abstract:
By selecting survivors of lambda phage infection, mutants of Escherichia coli K12 that block reproduction cycle of the phage have been isolated. Fourteen of these phage-tolerant mutants (lam mutants) were chosen and characterized biochemically and genetically. It was shown that these mutants were tolerant to infection by all the lambdoid phages, except for few cases, but they were susceptible to infection by a non-lambdoid temperate phage (phi299), P1 or T phages. The mutants can be divided into at least three groups: (1) A mutant (lam 16) strain that seems to block normal penetration of phage DNA: (2) Three mutant (lam 64, lam 67 and lam 71) strains that block an "early" step(s) of phage growth, including phage DNA synthesis: (3) Six mutant (lam 24, lam 25, lam 26, lam 27, lam 646 and lam 6) strains that block normal functioning of the gene E products and produce unusual head structures. Some lambdoid phages and lambda mutants that overcome the interference by the lam mutations have been obtained, and were used as tools for characterizing the host mutations. Two (lam 12 and lam 13) mutant strains and one (lam 1) mutant were inferred as affecting the expression of "late" genes, and early gene, respectively, by this test.
Insights
Researchers isolated Escherichia coli K12 mutants (lam mutants) that block lambda phage reproduction. These mutants offer insights into phage-host interactions and phage DNA replication, synthesis, and assembly processes.
Area of Science:
- Microbiology
- Molecular Biology
- Genetics
Background:
- Bacteriophages, particularly lambda phage, are vital tools for studying bacterial genetics.
- Understanding phage-host interactions is crucial for controlling phage infections and developing phage therapy.
Purpose of the Study:
- To isolate and characterize mutants of Escherichia coli K12 that exhibit tolerance to lambda phage infection.
- To elucidate the specific stages of the lambda phage reproductive cycle that are blocked by these host mutations.
Main Methods:
- Isolation of phage-tolerant mutants from Escherichia coli K12 survivors of lambda phage infection.
- Biochemical and genetic characterization of fourteen isolated lambda-tolerant (lam) mutants.
- Testing mutant susceptibility to various lambdoid and non-lambdoid phages.
- Utilizing specific lambdoid phages and lambda mutants to overcome host mutations for further characterization.
Main Results:
- Fourteen lam mutants were identified, exhibiting tolerance to most lambdoid phages but susceptibility to non-lambdoid phages.
- Mutants were categorized into three main groups based on the blocked stage: phage DNA penetration, early phage growth (including DNA synthesis), and gene E product function leading to abnormal head structures.
- Further analysis suggested specific mutants affected late gene expression (lam 12, lam 13) and early gene expression (lam 1).
Conclusions:
- The isolated lam mutants represent valuable tools for dissecting the lambda phage life cycle at the host level.
- These mutants provide genetic evidence for distinct steps in phage DNA replication, synthesis, and assembly within Escherichia coli.
- The study highlights the complex interplay between phage and host during infection and offers avenues for future research into phage-host interactions.