Thermophilic fungi: II. Fatty acid composition of polar and neutral lipids of thermophilic and mesophilic fungi.

The relative per cents of polar and neutral lipids and the fatty acid profile of the polar and neutral lipids of nine thermophilic and nine mesophilic fungi were examined and compared. The polar lipids of the thermophiles contained an average of 0.89 double bonds per mole fatty acid (unsaturation index, USI) and were considerably more saturated than the corresponding lipids of the mesophiles (average 1.32 USI). Within the thermophilic species the polar lipids were generally more saturated than the neutral lipids (average 0.95 USI) and in the mesophilic species the polar lipids were usually more saturated than the neutral lipids (average 1.14 USI). The mesophiles produced higher levels of 16∶1, 18∶2 and 18∶3 fatty acids than the thermophiles and preferentially incorporated 16∶1 and 16∶2 into their polar lipids. The thermophiles produce higher levels of saturated fatty acids and 18∶1 than the mesophiles and preferentially incorporated the saturated fatty acids into their polar lipids.