The carotenogenesis and lipogenesis of an oleaginous yeast Rhodotorula glutinis NRRL Y-1091 has been comparatively studied, using a HPLC analytical method and several cultivation systems. HPLC provides a powerful method with good reproducibility for the separation and quantification of major carotenoids from R. glutinis, i.e., torularhodin, torulene, γ-carotene and β-carotene. The pigment mixtures on the Novapak $C_{18}$ column could be satisfactorily separated with a good reproducibility in less than 20 min. From the results of environmental factors affecting carotenogenesis and lipogenesis, both biosyntheses were found to be regulated by its own metabolic rate of the cells, and their components were determined by the biosynthetic rates of both compounds. Galactose in culture medium resulted in low cellular growth, low lipid and carotenoid biosyntheses high degree of unsaturation in total lipid and high biosynthetic rate of torulahodin. As the C/N ratio decreased, γ carotene was exclusively converted to torularhodin and the oxygenation leading torularhodin was faster than the cyclization to β-carotene. At the exhaustion of available carbon source, the storage lipid was decomposed to acetyl-CoA accompanied by its utilization as a carbon-skeleton compound for carotenoid biosynthesis. At the time, γ carotene was converted mainly to torulene. Carotenoid destroyed even when the cells still grew and metabolized while lipid began to be decomposed only when the growth rate became nearly zero. Growth rate did not affect the accumulation rate of γ carotene but changed the conversion rate of γ-carotene into either torulene or β-carotene. As the growth rate increased, the cycyclization was faster than the dehydrogenation. When the growth temperature was lowered, both linolenic acid and torularhodin were significantly increased. In addition, torularhodin content tended to be always inversely proportional to torulene content. In a physiological relationship between carotenogenesis and lipogenesis, the yeast could be protected from the destructive free radical reaction by the quantitative metabolic regulation of lipid that degree of unsaturation was decreased with increasing lipid content, and by carotenoids synthesied as antioxidants.
