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 R f value on TLC was that of α‐mycolic acids (M 1 ), the second was that of α′‐mycolic acids (M 1 ′) a shorter homologue than α‐mycolates, and the third was the hydroxy mycolic acids (M 4 ) derived from epoxy mycolic acids. They were identified by gas chromatography‐mass spectrometry as their trimethylsilylether derivatives. α′‐Mycolic acids were monoenoic acids ranging from C 60 to C 66 and possessing an α‐unit of C 24∶0 . Such profiles of α′‐mycolic acids were common in eight strains. α‐Mycolates were dienoic acids ranging from C 75 to C 79 and possessing an α‐unit of C 24∶0 . In most strains, the major molecular species of α‐mycolates were odd‐carbon‐numbered, centering at C 77 and C 79 , possessing a methyl branch in the even‐carbon‐numbered straight chain. The average carbon number of α‐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 C 75 to C 81 were very similar to their M 1 subclass profiles.