Regulation of cell wall mycolic acid biosynthesis in acid-fast bacteria. I. Temperature-induced changes in mycolic acid molecular species and related compounds in Mycobacterium phlei.

Molecular species of two major subclasses of mycolic acids from Mycobacterium phlei, alpha-mycolic acids (M1) and dicarboxy mycolic acids (M3), were separated gas-chromatographically and identified mass-spectrometrically. The mycolic acid compositions of extractable and cell wall bound lipids were markedly influenced by growth temperature. Increasing growth temperature from 20 degrees C to 50 degrees C resulted in an increase in longer chain species of both mycolisc acid subclasses with a concomitant decrease in shorter chain homologues. The most abundant molecular species were C76 and C58 of M1 and M3 in the 20 degrees C grown cells, while the 50 degrees C grown cells contained C80 in M1 and C62 in M3, most abundantly. Changes in mycolic acid composition occurred rapidly after growth temperature was raised from 20 degrees C to 50 degrees C with an increase in C62 and a concomitant decrease in C58. Mass fragmentographic analysis revealed that an increase in total carbon numbers of mycolic acids was caused by the elongation of straight chain alkyl unit, without any changes in alpha-branch. Changes in the molecular species composition of secondary alcohols presumably derived from the ester mycolic acids were also observed and an increase in longer species (C20-ol-2) with a concomitant decrease in shorter ones (C18-ol-2) was noted as the temperature rose. An increase in the growth temperature also resulted in a decrease in unsaturated fatty acids in extractable lipids. These observations suggest that mycobacteria alter the molecular species composition of mycolic acid subclasses and phospholipids, in response to growth temperature, to maintain a suitable membrane function.