A Mycoplasma Mutant Resistant to Lysis by C: Variations in Membrane Composition and Altered Response to the Terminal C Complex

Abstract

Mutant strains of Acholeplasma laidlawii resistant to immune lysis by the classical C pathway have been obtained after the exposure of wild-type cells to nitrosoguanidine. The lysis of one mutant strain, comr-328 is less than 20% of that of the wild-type strain when incubated with antiserum prepared against wild-type cells and guinea pig serum as a source of C. The osmotic stability of comr-328 is similar to that of the wild-type strain. Absorption of anti-wild-type antiserum with mutant or wild-type cells results in the complete loss of C fixing antibody as shown by the inability of the absorbed antiserum to sensitize wild-type cells for immune lysis. Both strains convert 125I-labeled C3 to C3b to the same extent and bind equivalent amounts of 125I-C3b. Whereas the wild-type strain is sensitive to lysis by reactive lysis, comr-328 is resistant. Although both cell types are lysed equally well by amphotericin B, comr-328 is less sensitive than the wild-type strain to lysis by melittin.The membrane lipids of both strains are qualitatively identical, as judged by thin-layer chromatography of chloroform-methanol extracts, but the amount of each lipid varies according to the strain. The most significant variation is found in the glycolipids; the monoglucosyldiglyceride to diglucosyldiglyceride ratio of comr-328 is 2-fold higher than that of the wild-type strain. The difference in the phospholipids is less marked. While more than 35 Coomassie Blue-stained polypeptides are detected by SDS-polyacrylamide gel electrophoresis of solubilized membranes, major quantitative differences occur in only three of these bands. Band 11 is more prominent in comr-328 than in the wild-type strain whereas bands 14 and 26 appear to be less abundant in the mutant.