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Summary
Bacteriophage P1 exists in three head size variants (P1B, P1S, P1M), determined by its genome, not the host. These variants, differing in genome content, can infect and kill host cells.
Area of Science:
- Molecular Biology
- Virology
- Microbiology
Background:
- Bacteriophage P1 exhibits morphological variations in head size.
- These variants, designated P1B, P1S, and P1M, were observed across multiple hosts.
Purpose of the Study:
- To investigate the origin and characteristics of bacteriophage P1 head size variants.
- To determine the role of the host versus the phage genome in variant production.
Main Methods:
- Electron microscopy was used to measure head diameters and analyze morphology.
- Banding in CsCl gradients was employed to separate and analyze phage particles based on density and genome content.
- Infectivity assays and genetic marker rescue experiments were performed.
Main Results:
- Three distinct head sizes (icosadeltahedra) were identified: 86 nm (P1B), 65 nm (P1S), and 47 nm (P1M).
- Variant production was confirmed to be a function of the P1 genome.
- P1S particles contained partial P1B genomes (40-60%) and could infect host cells, injecting DNA and causing cell death.
- Defective P1B particles with 60% genome content were also identified.
- Genetic markers from P1S could be rescued by infectious P1B, confirming the presence of P1 DNA.
Conclusions:
- Bacteriophage P1 exhibits intrinsic genome-controlled morphological variation.
- Smaller variants (P1S) possess partial genomes and are capable of host cell infection and DNA injection.
- These findings contribute to understanding phage genome-host interactions and genome packaging mechanisms.