Structure and molecular species composition of three homologous series of alpha-mycolic acids from Mycobacterium spp.

SUMMARY: Three homologous series of α-mycolic acids (dicyclopropanoyl acids, monocyclopropanoyl monoenoic acids and dienoic acids) from 16 rapidly growing and 14 slowly growing mycobacteria were separated by argentation thin-layer chromatography and analysed by gas chromatography/mass spectrometry of their trimethylsilyl ether derivatives. Mycobacterial species were separated into five groups. Strains of group A contained similar amounts of even and odd carbon-numbered dienoic acids, with a methyl branch on the odd acids and a C24-α-unit, as typified by Mycobacterium fortuitum and M. chitae. Group B strains possessed similar amounts of even carbon-numbered dicyclopropanoyl α-mycolic acids and odd carbon-numbered unsaturated acids with C22- and C24-α-units, as found in M. phlei and M. diernhoferi. Group C strains contained mainly even carbon-numbered dicyclopropanoyl acids with C22- and C24-α-units, as shown by M. vaccae and M. aurum. Group D strains possessed mainly odd carbon-numbered dienoic acids with a methyl branch and a C24-α-unit, as seen in M. triviale and M. nonchromogenicum. Group E strains had mainly even carbon-numbered dicyclopropanoyl acids with C24- or C26-α-units, as found in M. avium and M. tuberculosis. Many rapidly growing mycobacteria also produced α-mycolic acids which were shorter in the length of the main carbon chain but whose α-units were the same as those in α-mycolic acids from the same species. These α-mycolic acids had either one or two double bonds and showed variations in both their unsaturation and overall size, which may be useful in taxonomic studies.