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The lipid-containing bacteriophage PR4. Effects of altered lipid composition on the virion
Abstract:
Phage PR4 was grown on a variety of Escherichia coli mutants defective in fatty acid and phospholipid metabolism. The composition of the phage lipids was modified by changing the composition of the host membrane phospholipids. The compositions of both the polar and the acyl moieties of the phospholipids were altered. The proportion of saturated fatty acids in the phage phospholipids was increased in increments from 44% of the total fatty acids to 55%, 61% and 69% of the total fatty acids using a host mutant with a temperature-sensitive defect in unsaturated fatty acid biosynthesis. The increase in saturated fatty acids led to a pronounced loss of infectivity when the phage were incubated at temperatures between 2 degrees C and 30 degrees C (temperatures below those at which the phage were grown). The greater the level of saturated fatty acids in the phage phospholipids, the higher the temperature below which the phage were inactivated. Our results strongly suggest that the phage membrane undergoes a lipid phase transition, which can disrupt and inactivate the virion. The phospholipid composition of PR4 was also altered by using host mutants defective in phosphatidylethanolamine and/or cardiolipin synthesis. Phage PR4 grown on wild-type host strains contains 56% phosphatidylethanolamine, 37% phosphatidylglycerol, 4.6% cardiolipin and no detectable phosphatidylserine. However, in response to changes in the host, PR4 preparations were obtained with phospholipid compositions varying from 28% to 60% in phosphatidylethanolamine, from 22% to 39% in phosphatidylglycerol, from 1% to 15% in cardiolipin and containing as much as 35% phosphatidylserine. These changes in phospholipid composition did not affect the infectivity of the phage. Moreover, the increased level of phosphatidylglycerol in the phage relative to the host was not altered by these manipulations. It is concluded that the net charge of the phage membrane phospholipids is not involved in the selection or function of the viral phospholipids. We also present evidence suggesting that the phage and host membranes do not fuse during the course of infection.
Insights
Bacteriophage PR4 lipid composition affects infectivity. Increased saturated fatty acids in phage phospholipids cause inactivation at lower temperatures, suggesting a lipid phase transition. Changes in other phospholipids did not impact infectivity.
Area of Science:
- Microbiology
- Biochemistry
- Molecular Biology
Background:
- Bacteriophages, viruses that infect bacteria, rely on host cell machinery for replication.
- Bacteriophage PR4's lipid envelope composition is influenced by its host, Escherichia coli.
- Understanding viral lipid composition is crucial for comprehending viral assembly and infectivity.
Purpose of the Study:
- To investigate how alterations in host cell phospholipid metabolism affect the lipid composition of bacteriophage PR4.
- To determine the impact of modified phage phospholipid composition on viral infectivity and membrane properties.
Main Methods:
- Culturing bacteriophage PR4 on various Escherichia coli mutants with defects in fatty acid and phospholipid metabolism.
- Analyzing the polar and acyl moieties of phage phospholipids.
- Assessing phage infectivity at different temperatures following lipid composition modifications.
Main Results:
- Increasing saturated fatty acids in phage phospholipids from 44% to 69% led to loss of infectivity below the growth temperature.
- Higher saturated fatty acid content correlated with inactivation at higher temperatures, indicating a lipid phase transition.
- Alterations in phosphatidylethanolamine, cardiolipin, and phosphatidylserine levels did not affect phage infectivity.
- Phage PR4 maintained an increased proportion of phosphatidylglycerol relative to the host, irrespective of host manipulations.
Conclusions:
- The lipid phase transition of the phage membrane, influenced by saturated fatty acid content, is critical for PR4 infectivity.
- The net charge of phage membrane phospholipids is not a primary factor in viral lipid selection or function.
- Evidence suggests that phage and host membranes do not fuse during infection by bacteriophage PR4.