| The application of EPA in human health care has received increasing attention in recent years, and the global consumption of EPA has increased. Microalgae are consider to be potential sources for EPA production due to its stable and high lipid content and without cholesterol, pollution, pleasant fishy smell and heavy metals pollution. In this study, ten microalgae strains with promising lipids content were isolated by Nile Red staining initial screening from mangrove forest in the north Gulf of Guangxi Zhuang Autonomous and five of ten strains with EPA content were determined by gas chromatography. Among five algae, the strain HD02 with the EPA yield of 33.4 μg · L-1 · d-1 and 2.7 d doubling time, and the strain HE06 with the EPA yield of 25.8 μg · L-1 · d-1 and 2.5 d doubling time were selected. The stain HD02 was identified as cymbella and the algae HE06 was identified as nitzschia according to morphological characteristics and18 s DNA sequence.In order to enhance EPA content of HD02 and HE06, the cultivation conditions on the two algae growth and EPA accumulated had been studied. The optimal concentration of silicon, sodium nitrate, vitamin B1, vitamin B12, biotin,IAA, 6-BA, gibberellin, glycerol, glucose and sodium bicarbonate in the culture of cymbella HD02 were 80 mg·L-1, 65 mg·L-1, 50 μg·L-1, 2 μg·L-1, 4 μg·L-1, 4 mg·L-1,0.8 mg·L-1, 0.4 mg·L-1, 2.4 g·L-1, 1.8 g·L-1 and 1.2 g·L-1, respectively. Under the optimal culture condition, the max biomass productivity of cymbella HD02 had reached 34.8 mg·L-1·d-1 and the yield of EPA in cymbella HD02 was 930.1μg·L-1·d-1. The final EPA content of cymbella HD02 had reached 2.66 percent of dry biomass which had increased 21 times than what in f/2 culture condition. The optimal concentration of sodium nitrate, ammonium chloride, urea, vitamin B1,vitamin B12, biotin, glucose, glycerol, sodium bicarbonate in the culture of nitzschia HE06 were 77 mg·L-1,75 mg·L-1, 5 mg·L-1, 30 mg·L-1, 1.5 mg·L-1, 6μg·L-1, 10 μg·L-1, 1.2 g·L-1, 2.4 g·L-1, 1.2 g·L-1, respectively. Under the optimal conditions, the productivity of EPA had reached 504.8 μg · L-1 · d-1 and 16-fold increased from the initial culture condition. The final EPA content of nitzschia HE06 had reached 2.66 percent(dry biomass) and the biomass yield of nitzschia HE06 had increase 67.2 percent and reached 32.4 mg · L-1 · d-1.In order to increase the total lipid content of algae, the algae strain HE07 weremutated by UV-light. The Nile Red dye were added to heterotrophic culture dish and labeled algae colonies with strong fluorescence under a microscope on agar.Ten mutant strains with strong fluorescence were selected, and the total lipids content of eight mutant strains among them increased between 33.0 percent to 53.3percent. The strain with highest lipids content was UV-7 and its total lipids yield was 15.6 mg·L-1·d-1. |
