The gas chromatographic separation and mass spectrometric identification of mycolic acids ranging from Czs to CaS in Nocardia and related acid-fast groups of bacteria was established. Using this method, the molecular species of mycolic acids were clearly separated as the trimethylsilyl (TMS) derivatives of the methyl esters, according to their total carbon numbers. From the [Mlt, [M-15]+ and [M-90]t ions produced by gas chromatography mass spectrometry, the total carbon and double bond numbers were determined, while the straight and branched chain structures were identified by the mass fragment ions due to C2-C3 cleavageBased on the molecular species composition, the average carbon numbers of the mycolic acids from 16 strains of Nocardia and related taxa (Mycobacterium rhodochrous complex and Gordona bronchialis) were determined. Each species of bacteria was demonstrated to possess a characteristic profile of mycolic acid composition, and they were shown to be classified approximately into at least four groups: (1) CZs to C48 (average carbon numbers C3,-,,) mostly saturated for Nocardia erythropolis and several 'Mycobacterium rhodochrous complex'; ( 2 ) CM to Cs0 (average C43-45) monoenoic and dienoic for N. rubra, N. corallina and N. lutea; (3) C44 to CS8 (average C5,-5z) monoenoic to tetraenoic for N. asteroides and 'true' nocardiae; (4) c 5 6 to Css (average c62-a) monoenoic to pentaenoic for N. polychromogenes and Gordona bronchialis. The results indicate that the structural determination of mycolic acids by gas chromatography mass spectrometry can be one of the most useful criteria for the chemotaxonomy of Nocardia and related bacteria.

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