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Effect of lipid alkyl chain perturbations on the assembly of bacteriophage PM2
Abstract:
The lipid-containing bacteriophage PM2 can produce infectious virus in cultures infected at temperatures up to 31.5 degrees C, but not at 34 degrees C. Its host, Pseudomonas BAL-31, grows at 34 degrees C and cultures infected at that temperature undergo lysis. Sucrose-gradient analysis shows that 34 degrees C lysates contain no PM2-like particles. Temperature-shift experiments establish that the thermally sensitive process is late in infection when virus assembly is taking place. Adamantanone, a small hydrophobic molecule that perturbs membrane hydrocarbon zones, prevents the production of infective virus. Concentrations which prevent virus production have no effect on host-cell growth or stability of mature virions. Adamantanone exerts its effects late in the infectious cycle, and lysates amde in its presence contain no PM2-like particles. These experiments, carried out at 25 degrees C, indicate that adamantanone prevents the assembly of stable PM2 virus. Spin-label studies suggest that the lipid alkyl chains of the host-cell membrane are in an "ordered" state at temperatures below about 33 degrees C and undergo a transition to a "disordered" state above that temperature. Furthermore, the addition of adamantanone perturbs the hydrocarbon zones, producing a greater degree of disorder even below 25 degrees C. Our findings suggest that the cell membrane can function and grow with the lipid alkyl chains in either the "ordered" or "disordered" state, but that the "ordered" state must be maintanined for PM2 assembly to occur.
Insights
Bacteriophage PM2 assembly requires an ordered cell membrane, which is disrupted by higher temperatures or adamantanone. This study reveals the critical role of membrane fluidity in viral replication.
Area of Science:
- Virology
- Microbiology
- Biochemistry
Background:
- The lipid-containing bacteriophage PM2 infects Pseudomonas BAL-31.
- PM2 replication is sensitive to temperature, failing above 31.5°C.
- Host cell growth and lysis occur at higher temperatures.
Purpose of the Study:
- To investigate the temperature-dependent process limiting bacteriophage PM2 production.
- To determine the effect of membrane perturbation on PM2 assembly.
Main Methods:
- Temperature-shift experiments in Pseudomonas BAL-31 cultures.
- Sucrose-gradient analysis of viral particles.
- Effect of adamantanone on viral production and host cell viability.
- Spin-label studies of cell membrane fluidity.
Main Results:
- PM2 assembly is inhibited at temperatures above 31.5°C, with no infectious virus produced at 34°C.
- Adamantanone prevents infectious virus production by inhibiting viral assembly, without affecting host cell growth.
- Membrane lipid alkyl chains transition from an ordered to a disordered state around 33°C.
- Adamantanone induces membrane disorder even at lower temperatures.
Conclusions:
- PM2 assembly is dependent on maintaining an ordered state of the host cell membrane.
- Temperature and hydrophobic molecules like adamantanone can disrupt membrane order, inhibiting viral replication.
- The cell membrane can accommodate both ordered and disordered states for growth, but ordered state is essential for PM2 assembly.