Influence of growth phase and nutrient source on fatty acid composition of Isochrysis galbana CCMP 1324 in a batch photoreactor

The marine microalgal strain Isochrysis galbana CCMP 1324 was cultured in Walne medium to examine the changes in lipid bodies and fatty acid composition, with special emphasis on different iron, nitrogen, and phosphorus sources associated changes in the growth kinetic parameters and fatty acid composition. All the experiments were performed at 20 °C, with the culture medium at pH 9.0, a specific rate of air supply of 1.0 vv−1 m−1 and a continuous illumination of 68 μEm−2 s−1. Lipid bodies in I. galbana CCMP 1324 were observed at different growth phase in Walne medium by light and transmission electron microscopy. Lipid granules from 0.4 to 2.0 μm were observed from exponential growth stage to stationary stage. The I. galbana CCMP 1324 had the highest contents of saturated and monounsaturated fatty acids (SFA + MUFA) as well as polyunsaturated fatty acids (PUFA) in the early stationary phase. The n-3/n-6 value reached a maximal value of 4.9 in the late stationary phase. The Walne medium could be a good iron, nitrogen and phosphorus sources to culture I. galbana to maximize PUFA production and harvesting the biomass at stationary phase may enable better yields in lipid and PUFA composition. The ratio of SFA + MUFA to PUFA was highest in NH4NO3 modified Walne culture and minimal in Walne culture. The n-3 PUFA was predominant in Walne culture. A compromise between the docosahexaenoic acid (DHA) production and growth kinetics can be achieved by using NH4NO3 as N-source in modified Walne medium, which provides the greatest value of DHA production (15.6% of total fatty acids) with the highest maximum specific growth rate (2.34 per day) even though the microalgal cell productivity (43.1 mg l−1 per day) is not the highly attained. The approaches presented in this study could be employed for the design of pilot or full-scale photoreactor for PUFA commercial productions by I. galbana CCMP 1324.