Adsorption of mycoplasmavirus MV-L2 to Acholeplasma laidlawii: effects of changes in the acyl-chain composition of membrane lipids.

The enveloped mycoplasmavirus MV-L2 and its host Acholeplasma laidlawii JA1 were used to study the ways in which changes in the membrane lipid bilayer affect virus adsorption. The physical state of the membranes was altered by (i) using viruses and bacteria with different membrane lipid acyl-chain compositions, (ii) using incorporation of cholesterol, and (iii) changing the temperature. Adsorption of viruses was strongly dependent on the acyl-chain composition of the virus and the host. Adsorption to homologous hosts was poor, whereas adsorption to hosts with highly different membrane lipid acyl-chain composition was much stronger. We found a heterogeneity within virus populations produced from hosts with different acyl-chain compositions. In a given virus population, various subpopulations differing in acyl-chain composition were found that differed in their ability to adsorb to cells with a specific acyl-chain composition. The adsorption rate increased slightly when cholesterol was present in the viral membranes but decreased considerably when cholesterol was present in the bacterial membranes. The rate of adsorption was temperature dependent with an increase in adsorption rate above 20 degrees C (for hosts with equal amounts of palmitoyl and oleoyl acyl chains). MV-L2 did not adsorb to the persistently L2-infected strain JA1(2R) but adsorbed very well to the virus-resistant strain A(EF22). The physicochemical properties of the lipid matrix of both virus and host are obviously important factors in the adsorption process.

Effects of acyl chain composition on production of mycoplasmavirus MV-L2 by Acholeplasma laidlawii.

Membrane-enveloped viruses obtain their lipid envelopes from the host cells. Studies with animal viruses and different cell lines have shown that the composition of the virus envelope affects infectivity. In this study, Acholeplasma laidlawii strain JA1 and the membrane-enveloped virus MV-L2 were used. In this system, it is possible to vary the "stiffness" of the host cytoplasmic membrane within a very wide range by adding different fatty acids to the growth medium. Viruses with different envelopes were produced from these hosts. Eleven hosts and 11 viruses with different fatty acyl chain composition were tested in all combinations. The acyl chain composition and presence of cholesterol had a marked influence on the plaque-forming ability of L2. Virus adsorption rates were also dependent on acyl chain composition, but no apparent correlation with plaque-forming ability could be seen. L2 adsorbed equally well to a virus-resistant strain (A EF22).

Membrane composition and virus susceptibility of Acholeplasma laidlawii.

The membrane composition of 11 strains of Acholeplasma laidlawii, including three strains persistently infected with mycoplasmaviruses MVL51, MVL2, and MVL3, was studied and correlated with mycoplasmavirus sensitivity. Membranes of the strains had similiar sodium dodecyl sulfate-polyacrylamide gel electrophoresis patterns, and all strains were inhibited by an antiserum produced against membranes from one of the strains. The amounts of integral membrane proteins solubilized by the nonionic detergent Tween 20 differed considerably. Therefore, characteristic crossed immunoelectrophoresis patterns were obtained for each strain. Strains persistently infected with MVL2 and MVL3 were notably different from the noninfected host. The ability to propagate any of the viruses was not correlated with sodium dodecyl sulfate-polyacrylamide gel electrophoresis or crossed immunoelectrophoresis patterns. The persistently infected strains had a characteristic lipid composition. MVL51-resistant strains, including a resistant clone selected from a sensitive strain, were characterized by a large monoglucosyldiglyceride/diglucosyldiglyceride ratio and trace amounts of diphosphatidylglyceol (as opposed to the sensitive strains). Differences in lipid composition in A. laidlawii seem to affect the relationship between cells and viruses.