Transformation of sterols by Mycobacterium vaccae: Effect of lecithin on the permeability of cell envelopes to sterols

An enhancement of beta-sitosterol transformation to androstendione by Mycobacterium vaccae observed in medium containing egg-yolk lecithin, was associated with the incorporation of a considerable amount of lecithin into the cell envelope lipids, By GC/MS measurements, fatty acids ranging from 14 to 22 carbon atoms were identified in the lipids removed from the cells by organic solvents. Octadecenoic (18:1), 2-methyl-octadecenoic (2-Me 18:1), and hexadecanoic (16:0) acids were the major components of the lipid preparation obtained from both the control cells, and the cells grown in lecithin-containing medium. However, in the fatty acid pattern of the latter a distinct increase in the C-18:1 component, concomitant with the decrease in the 2-Me 18:1 fatty acid was demonstrated. The C-16 fatty acid fraction also showed a higher content of methyl-branched components in the control cell preparation, The enrichment in unsaturated fatty acids increases fluidity of lipids, whereas the decrease in methyl-branched fatty acids may affect the conformation of the surface lipidic components, which may result in enhanced sterol penetration through the cell wall barrier in the presence of lecithin.