IDENTIFICATION OF THE SURFACE-EXPOSED LIPIDS ON THE CELL ENVELOPES OFMYCOBACTERIUM-TUBERCULOSIS AND OTHER MYCOBACTERIAL SPECIES

The surface-exposed lipids of Mycobacterium tuberculosis, Mycobacteriu m avium, Mycobacterium kansasii, Mycobacterium gastri, Mycobacterium s megmatis, and Mycobacterium aurum were isolated by gentle mechanical t reatment of cells with glass beads, Analysis of the exposed lipids dem onstrated a selective location of classes of ubiquitous lipids on the surfaces of mycobacteria. While phosphatidylethanolamine and phosphati dylinositol mannosides were exposed in all the species examined, dimyc oloyl trehalose (''cord factor'') was identified in the surface compon ents of M. aurum only, Furthermore, monomycoloyl trehaloses and triacy lglycerides were identified in the surface-exposed lipids of M. avium and M. smegmatis but not in those of the other mycobacterial species e xamined, The species- and type-species specific lipids were present on the mycobacterial cell surface: phenolic glycolipids, dimycocerosates of phthiocerols, and lipooligosaccharides were identified in the surf ace-exposed materials of M. tuberculosis (Canetti), M. kansasii, and M . gastri, whereas glycopeptidolipids were identified in the outermost lipid constituents of M. avium and M. smegmatis. This difference in th e surface exposure of lipids of various mycobacterial species may refl ect differences in their cell envelope organizations, Brief treatments of M. tuberculosis with Tween 80 prior to the use of glass beads led to erosion of regions of the capsule to expose gradually both cord fac tor and other lipids on the cell surface of the tubercle bacillus, dem onstrating that the latter lipids are buried more deeply in the cell e nvelope and leading to the proposal of a scheme for the location of th e capsular lipids of the tubercle bacillus.