Acyl lipid metabolism in the oleaginous yeast Rhodotorula gracilis (CBS 3043)

The effects of culture conditions on acyl lipid metabolism in the oleaginous yeast Rhodotorula gracilis (CBS 3043) have been investigated. Growth of R. gracilis under conditions of nitrogen‐limitation resulted in the accumulation of large quantities of triacylglycerols. Thin layer and gas chromatographic analysis of total lipid extracts revealed that the majority of this storage lipid was produced by stationary‐phase cells. In contrast, no such increase in triacylglycerol biosynthesis could be detected in carbon‐limited cells. Freeze‐fracture electron microscopy evidence supported these findings. Growth medium composition was found to have little effect on the relative abundance of the primary phospholipid classes present in R. gracilis . The acyl compositions of triacylglycerols were similarly unchanged by alterations in the composition of the growth medium. In contrast, the degree of unsaturation exhibited by the phospholipid fractions appeared to be particularly sensitive to this external parameter. Acyl quality of triacylglycerol pools extracted from nitrogen‐limited cells were observed to become increasingly saturated as cultures increased in age. Growth of nitrogen‐limited cells at a lower growth temperature was observed to have little effect on triacylglycerol accumulation. However, both triacylglycerol and phospholipid fractions extracted from these cultures were found to contain increased proportions of the polyunsaturated fatty acid, α‐linolenate.