Optimization of Culture Conditions for Thraustochytrid F24-2 Biomass Production

Thraustochytrid strain F24-2 is capable of producing oil rich in palmitic and docosahexaenoic acid (DHA). As increasing biomass concentration leads to the accumulation of oil and fatty acids, the objective of this work was to apply a 2-factorial Plackett-Burman design with central points to identify the significant culture conditions influencing biomass production by F24-2. Factors and levels included in the design were: glucose (5-20 g/L), soy peptone (2-20 g/L), sea salt (9-18 g/L), ammonium sulfate (0.2-2 g/L), vitamin B solution (1-3 mL/L), initial pH (4-7) and temperature (25-31ºC). Five milliliters of pure F24-2 inocula (OD600nm= 1) were added into 95 mL of test media and incubated for 4 d at 25ºC and 2000 rpm followed by harvest of cells by centrifugation. Pellets were frozen, freeze-dried, weighed and stored prior to dry weight biomass evaluation and fatty acid analysis by gas chromatography. The most significant factors (p<0.05) on biomass production were initial pH and sea salt concentration. F24-2 strain showed highest biomass (10.7 g/L) at an incubation temperature of 25ºC, neutral pH, low concentration of ammonium sulfate (0.2 g/L) and high concentrations of glucose (20 g/L), soy peptone (20 g/L), sea salt (18 g/L) and vitamin solution (3 mL/L). At the optimum culture conditions, the most abundant fatty acids were (mg/g): DHA (85.9), palmitic acid (60.5), docosapentaenoic acid n-6 (26.1), myristic acid (9.7), eicosapentaenoic (EPA) (4.4), stearic acid (2.5) and pentadecanoic acid (2.0). Our results showed that F24-2 strain could be a promising thraustochytrid for DHA and palmitic acid production