Lipid and Carotenoid Production by Rhodotorula glutinis with a Combined Cultivation Mode of Nitrogen, Sulfur, and Aluminium Stress

Torulene is a promising pink pigment, produced only by yeasts and fungi, and its production is still in a developing stage due to the low production rate. Accordingly, this study focuses on maximizing torulene production by Rhodotorula glutinis using shaken flask fermentation. The effect of different nitrogen sources, and C/N and C/S ratios on lipid and carotenoid production by R. glutinis was studied using 60 g/L glucose. The largest cells filled with golden fluorescence lipid bodies were observed using fluorescence microscopy when peptone was used as a nitrogen source. The highest total pigment (0.947 mg/L) and carotenoid relative productivity (Car-RP) (89.04 µg/g) were obtained at C/N 146 and C/S 120, and with ammonium sulfate as a nitrogen source, with 62% torulene domination using High Performance Liquid Chromatography (HPLC) for identification. Under a high C/N ratio, regardless of the C/S ratio, the carotenoid synthesis rate decreased after three days while the lipid synthesis rate kept increasing to the sixth day. Interestingly, after adding 0.7 mM Al2(SO4)3 to the optimized medium, the total pigment and Car-RP (2.2 mg/L and 212.9 µg/g) sharply increased, producing around 2.16 mg/L torulene (98%) with around 50% decrease in lipid yield. This is the first report on the role of Al2(SO4)3 for enhancing torulene production under lipogenesis condition, which could be used as a potential tool for torulene production.