Lipid and alkali extractable fatty acids from Mucor rouxii: Effect of thermal changes in growth environment and age of cells

The lipid levels of the fungus Mucor rouxii are affected markedly by both the growth temperature and the age of the cells. Both chloroform-methanol extractable (fraction I) and alkali extractable (fraction II) fatty acids are present in these cells, and the fraction II/fraction I ratio increased significantly with decreasing growth temperature. This ratio was, however, reasonably constant during the entire growth period at each specific growth temperature. In all cases, the unsaturation index of the fraction II fatty acids was significantly lower than the corresponding value for the fraction I fatty acids. Examination of the unsaturation indeces of the two fractions during the early log-phase growth period (48 hrs) indicated that the indeces decreased with increasing growth temperature; however, as the age of the cells increased, this relationship changed dramatically. At the end of 144 hrs growth, the unsaturation index for fraction II has reversed its temperature dependance completely, since the index is a maximum at the higher growth temperature. The degree of unsaturation for fraction I is a maximum at 25 C and is lower for cells grown at 15 and 35 C; this relationship is true between 96-144 hr after inoculation.