Sterol and Squalene Content of a Docosahexaenoic-Acid-Producing Thraustochytrid: Influence of Culture Age, Temperature, and Dissolved Oxygen

Thraustochytrid strain ACEM 6063, rich in omega-3 polyunsaturated fatty acids, was cultured at 15°C and 20°C in high (>40%) and low (<5%) dissolved oxygen (DO), and at 25°C in low-DO media. Samples were taken 4, 2, and 0 days before each culture reached peak biomass (T-4, T-2, and Tp, respectively). Twenty sterols, 13 of which were identified, were detected. Predominant were cholest-5-en-3β-ol, 24-ethylcholesta-5,22E-dien-3β-ol, 24-methylcholesta-5,22E-dien-3β-ol, and 2 coeluting sterols, one of which was 24-ethylcholesta-5,7,22-trien-3β-ol. These 4 sterols comprised 50% to 90% of total sterols. Cultures grown at high DO had simpler sterol profiles than those grown at low DO. Only the 4 sterols mentioned above were present at more than 3% of total sterols in high-DO cultures. In low-DO cultures, up to 6 additional sterols were present at more than 3% of total sterols. Culture age, temperature, and DO influenced squalene and sterol content. Total sterols (as a proportion of total lipids) decreased with increasing culture age. If organisms such as ACEM 6063 are to be used for commercial production of lipid products for human consumption, both their sterol content and factors influencing sterol production need to be characterized thoroughly.