Selection Of High-level Lipid Microalgae And Effect Of Different Culture Conditions On The Fatty Acid Contents And Components

In this paper, we selected seven species microalgae in our laboratory as the study material. Three species microalgae were found with high content of fatty acids. They were P9, TH6 and CF5 (laboratory number). The total lipid content of P9, CF5 and TH6 were 33.00%, 20.00% and 8.20% respectively.Thus we cultured them in different medium and studied the some facts (nitric nitrogen, IAA, the citric acid and Mg2+ ) which influenced fatty acid contents and components.Nitrogen concentration has played a very important role in microalgae fatty acid percentage composition. The total lipid content of some microalgae does not increase in rich nitrogen medium but others will do. The results indicate that, the nitrogen concentration would influence the total lipid content in three species all. The fatty acid content of P9 had a most significant (P﹤0.01). Along with the nitrogen concentration increased, the total lipid content was also increasing. When the nitrogen concentration was 375 mgL^-1, the total lipid content of P9 increased by 11.21%, compared with the control group. And the palmitic acid, linoleic acid, oleic acid and stearic acid content increased by 18.16%, 11.67%, 10.94% and 11.56% respectively. The total lipid content of TH6 was the highest under the low nitrogen (37.5 mgL^-1). And the palmitic acid, linoleic acid, and oleic acid increased by 19.85%, 3.05% and 3.75% respectively, however, the stearin acid content reduced by 0.07%. The total lipid content of microalgae CF5 did not have the change almost under the different nitrogen concentration medium. It demonstrated that the different microalgae had diffirent reponse to the nitrogen concentration of medium.IAA as a plant growth hormone, can promote and stimulate the growth of many single celled algae. The results showed that, IAA had the obvious promoteraction to microalgae's growth. However IAA did not promote the synthesis of fatty acids in P9 in this study. The highest total lipid content of P9 was 33.12% without another addition IAA. When IAA concentration was 1.0 mgL^-1, the highest total lipid content of TH6 increased about 200%. The palmitic acid, linoleic acid, oleic acid and stearin acid content increased by 13.40%, 0.69%, 1.01% and 4.85% respectively. The total Lipid conten of CF5 increased by16.62 % when IAA concentration was 0.5 mgL^-1. The linoleic acid and oleic acid content increased by 10.03% and16.74%, however the palmitic acid and stearin acid content reduced by 0.39% and 4.05%. Therefore, IAA had played a certain role in microalgae growth and fatty acid synthesis. But different species of algae had different requirements of IAA concentration.Citric acid is an important precursor for fatty acid synthesis. And exogenous citrc acid supplication can elevate the fatty acid synthesis rate. When treated with the citric acid at the concentration of 100 mgL^-1, the highest total lipid content of P9 was 28.04%. Compared with the control group, it increased by13.86%. And the palmitic acid, linoleic acidand oleic acid increased by 0.72%, 3.04% and 3.24% respectively, but the stearin acid content reduced by 2.29%. The total lipid content of TH6 increased by 6.37% with the citric acid at the concentration of 100 mgL^-1, compared with the control group. The linoleic acid, oleic acid and stearin acid content increased by 2.59%, 5.96% and 7.53% respectively, but the palmitic acid reduced by 0.81%. However, when the citric acid concentration was 120 mgL^-1, the highest total lipid content of CF5 was 17.50%. Compared with the control group, it increased by 3.75%. The palmitic acid, linoleic acid and the stearin acid content increased by 0.82%, 0.34% and 4.55% respectively, but the oleic acid reduced by 0.64%.Mg2+ is such a metal element that has certain promotive effect on the proliferation of phytoplanktons, and plays important roles in many physiological process of algae organisms. Mg2+ has some certain promotive effect on the activity of crcial enzyme CoA for plant fatty acid synthesis in a concentration dependent manner. The results show that Mg²⁺ had relativity to synthesis of fatty acids in microalgae. Under the Mg²⁺ 1.8 mmolL^-1 concentration of culture condition, the total lipid content of P9 increased by 13.20%, compared with the control group. The linoleic acid and oleic acid content increased by 2.18% and 8.99% respectively, but the palmitic acid and stearin acid content ruduced by 0.86% and 0.1% respectively. When the Mg²⁺ concentration was 1.5 mmolL^-1, the total lipid content of TH6 increased by 11.14% , compared with the control group. The palmitic acid, linoleic acid, oleic acid and the stearin acid content increased by 3.86%, 4.19%, 6.02% and 7.65% respectively. When the Mg²⁺ concentration was 1.2 mmolL^-1, the total lipid content of CF5 was 20.14%. The linoleic acid, oleic acid and stearin acid content increased by 4.38%, 5.99% and 14.25% respectively, but the palmitic acid reduced by 0.56%.Therefore, P9 which was cultured in the nitrogen concentration at 375 mgL^-1, the citric acid concentration at 100 mgL^-1 and the Mg2+ concentration at 1.8 mmolL^-1 has the optimal growth condition and the highest content of total lipid. TH6 which was cultured in the nitrogen concentration at 37.5 mgL^-1, the concentration of IAA at 1.0 mgL^-1, the citric acid concentration at 100 mgL^-1 and the Mg2+ concentration at 1.2 mmolL^-1 has the highest content of total lipids. CF5 which was cultured in the nitrogen concentration at 150 mgL^-1, the concentration of IAA at 0.5 mgL^-1, the citric acid concentration at 120 mgL^-1 and the Mg2+ concentration at 1.2 mmolL^-1 has the highest content of total lipid. Based on the results above, we draw a conclusion that P9, TH6 and CF5 all have the potential for biodiesel producing.