Acid methanolysates of 104 strains of coryneform and related bacteria were examined for mycolic acids by thin-layer chromatography and mass spectrometry. The mycolic acids of Corynebacterium sensu stricto strains were not uniform in size and structure, and considerable variation existed within the approximate limiting range of C22 to C36. Two species, Corynebacterium bovis and 'Corynebacterium mycetoides', were particularly distinctive; the former had exceptionally low molecular weight mycolic acids (C22 to C32), whereas the latter contained major amounts of mycolates with a side-chain possessing an odd number of carbon atoms. Caseobacter polymorphus contained mycolic acids of a similar size (C30 to C36) to those of true corynebacteria. The mycolates of organisms assigned to the genus Rhodococcus were generally larger (C30 to C56), although a clear distinction between two corynebacteria and rhodococci cannot presently be made by analysis of mycolic acids alone. Strains labelled 'Arthrobacter roseoparaffinus', Corynebacterium equi and Corynebacterium hoagii contained mycolic esters with molecular weights 'intermediate' in size between those of true corynebacteria and rhodococci. The mycolic acid data correlate well with other major trends in coryneform taxonomy and support earlier suggestions that they are of value in the classification of the group.
