The Influence Of Environmental Factors On Lipid Metabolism And The Transcription Level Of Thioesterase Of Nannochloropsis Oceanica

With the growth of population and rapid development of world economy, fossil energy consumption is increasing. To solve the energy crisis and environmental issues, the world had to accelerate the development of alternative energy sources of fossil energy. In recent years, biodiesel as a clean and renewable energy gets more and more attention. Although biodiesel has many advantages, its traditional raw materials may cause effect on food security and price of agricultural products. Therefore, choosing a cheap and safe material for the production of biodiesel is the general trend.Nannochloropsis is one of class Eustigmatophyceae and it is a kind of important unicellular economic microalgae. Nannochloropsis is rich in high value-added products, such as protein, polyunsaturated fatty acids, pigments. Nannochloropsis has high photosynthetic efficiency and strong environment adaptability, the lipid content of the algae can reach 30% of the dry weight, it can be cultivated in large-scale, therefore, it is considered to be a promising material for the production of biodiesel. Although microalgae has many advantages over other materials for biodiesel production, fatty acid saturation and length of natural microalgae is not suitable for biodiesel production. In recent years, by changing the medium composition, controlling culture conditions and genetic engineering to improve the quality of fatty acid and lipid content of microalgae has become hot in biodiesel research.This experiment consists of two parts:First part:The cDNA of thioesterase gene was isolated from Nannochloropsis oceanica and named as NoTE. It is 1,314bp in length, encoding 437 amino acids with a molecular mass of 55 kD. To verify its function, it was inserted into pET-30a and expressed in Escherichia coli BL21(DE3). Results showed that expressing NoTE in E. coli BL21(DE3) didn’t change the kinds of fatty acids, but increased the contents of its C14:1, C16:0, C16:1 and C18:1 and total fatty acids by 11%,18%,32%,49% and 30%, respectively, compared with the control strain. This indicated that the isolated gene expressed successfully in E. coli BL21(DE3) and functioned as a thioesterase.Second part:The effects of nitrogen deficiency, phosphorus deficiency and different temperature on lipid contents, fatty acid composition and transcription level of NoTE were explored. Results shouwed that, with the nitrogen deficiency time increasing, the transcription level of NoTE and lipid content increased. Nitrogen deficiency can inhibit the synthesis of polyunsaturated fatty acids and promote the synthesis of monounsaturated fatty acids and saturated fatty acids. The same conclusion was achieved under phosphorus deficiency. With the temperature increasing, the transcription level of NoTE increased. The most lipid content was achieved under 20℃. In the range of experimental temperature, higher temperature promote the synthesis of saturated fatty acids.In general, this study isolated a thioesterase gene from N.oceanica and verified its function by prokaryotic expression system. Exploring the environmental factors on lipid contents, fatty acid composition and transcription level of NoTE were conducted.