Mycolic acid composition and thermally adaptative changes in Nocardia asteroides

Abstract

The nocardomycolic acid compositions of extractable and the cell wall-bound lipids from five strains of N. asteroides (A-23007, A-23094, B-23006, B-23095, and IFO 3384) were compared by using gas chromatography-mass spectrometry. The molecular species composition of mycolic acid differed significantly among the strains of N. asteroides. The A-23007 strain possessed the shortest species, centering at C44(46), and the A-23094 and IFO-3384 strains followed, each centering at C52. The B-23006 and B-23095 strains possessed the longest species, centering at C56 or C54, thus indicating that N. asteroides strains accommodate a heterogeneous group in respect to carbon numbers of mycolic acids. The double-bond isomers of mycolic acids from the representative strain IFO 3384 were fully separated and analyzed by argentation thin-layer chromatography, followed by gas chromatography-mass spectrometry. The reference strain (IFO 3384) possessed up to four double bonds on the straight chain of mycolic acids ranging from C46 to C60. All of the species possessed a C14 alkyl branch at C-2. The more highly unsaturated subclasses consisted of the longer-chain mycolic acids. Marked changes in mycolic acid composition were induced by altering the growth temperature of strain IFO 3384. The cells grown at the higher temperature (50°C) contained more saturated mycolic acids, whereas those grown at the lower temperature (17°C) had more polyunsaturated (up to tetraenoic) mycolic acids, although a significant difference in carbon chain length was not detected. These changes in the degree of unsaturation of mycolic acids occurred shortly after shifting the growth temperature from 17 to 50°C at logarithmic stages of the bacterial growth, thus indicating that N. asteroides can adapt to changes in the environmental temperature by altering the structure of mycolic acids of the cell walls.