Molecular species of mycolic acid subclasses in eight strains of Mycobacterium smegmatis.

Thin layer chromatographic and gas chromatographic separation and mass spectrometric identification of mycolic acid subclasses and molecular species from eight strains of Mycobacterium smegmatis were established. Two major adjacent spots and a lower minor one were detected on silica gel thin layer chromatograms of methyl esters. The most abundant subclass showing the highest Rf value on TLC was that of alpha-mycolic acids (M1), the second was that of alpha-mycolic acids (M1), a shorter homologue than alpha-mycolates, and the third was the hydroxy mycolic acids (M4) derived from epoxy mycolic acids. They were identified by gas chromatography-mass spectrometry as their trimethylsilylether derivatives. alpha'-Mycolic acids were monoenoic acids ranging from C60 to C66 and possessing an alpha-unit of C24:0. Such profiles of alpha'-mycolic acids were common in eight strains. alpha-Mycolates were dienoic acids ranging from C75 to C79 and possessing an alpha-unit of C24:0. In most strains, the major molecular species of alpha-mycolates were odd-carbon-numbered, centering at C77 and C79, possessing a methyl branch in the even-carbon-numbered straight chain. The average carbon number of alpha-mycolates, from seven strains examined, was about 78, but that of the Takeo strain was 76.3. The profiles of epoxy mycolic acid molecular species composition from eight strains ranging from C75 to C81 were very similar to their M1 subclass profiles.