Isolation And Screening Of Marine Microalgae With High Energy Productivity

Energy crisis has caused widespread concern in the world, and scientists have turned to look for renewable new energy source. Due to the large scale use of corn, soybeans and other agricultural products, it is more and more serious that biofuels compete food with human, compete earth with crops and price of the agriculture products fluctuates greatly. Microalgae could grew in water rapidly with high lipid content, and do not occupy cultivated land resources, and they may be used to substitute the traditional fossil fuel as the renewable new energy source. Compared with producing hydrogen from microalgae, the microalga bio-fuels had more practical significance because of the lower cost and security risk advatages. Usually, the two most basic requests for microalgae to product bio-fuels were high growth rate and high lipid productivity. In order to have a better understanding about the present conditions of the microalgae sources in our country, we collected samples from different water areas of China, purified some strains of microalgae, obtained several strains with high lipid productivity and optimized their cultivation parameters in this article, the results in detail were as follows:(1) One thousand of natural water samples were gained from 180 sampling places including Bohai, Huanghai, Donghai, Nanhai and pond etc, and 217 strains of microalgae were isolated and purified.(2) The total lipid content of 52 strains of microalgae was tested by Blight-Dyer method, and the fatty acid compositions of 19 strains of microalgae with higher total lipid content were analyzed by Gas chromatography (GC), and 8 strains of microalgae were proved to be more than 30% lipid content of dry powder.(3) The effects of different growth factors on the net photosynthetic O2 evolution of two strains: No. 01 and No. 40 were studied by testing the changes of dissolved oxygen in the algae medium, the results were as follows: 1. The best growth conditions for No. 01 algae is 200μmol photon m-2s^-1 light intensity, 30-35℃during daytime, 24℃at night, 30‰salinity, pH7-pH9, 75 mg/L nitrate concentration (NaNO₃) and 40 mg/L phosphate concentration (NaH₂PO₄). As a type of carbon source, NaHCO₃ did not affect the growth of this alga significantly. 2. The fastest growth rate for No. 40 strain was under 200 -500μmol photon m^-2s^-1 light intensity, about 35℃during daytime, about 30℃at night, pH7, 160 mg/L nitrate concentration (NaNO₃) and 80 mg/L phosphate concentration (NaH₂PO₄). 3. After the optimization, biomass of No. 01 and No. 40 increased 4.8 and 6.0 times more than those of the first day separately after one week.(4) The results of the oil-producing model optimization were as follows: 1. The composition of fatty acid of No. 01 strain didn't vary under different nutrition deficiencies or different growth phase, but the algae collected in the stationary phase showed higher lipid content than that from the exponential phase. 2. The fatty acid composition of No. 40 microalgae changed after N or P deficiencies in media. And the main change was the content of C16:0 and C18:1 increased, while the content of total fatty acid between C14-C18 did not change significantly. The highest crude lipid content of 55% dcw occurred when the algae was cultured in media with P-deficiency for 2 days. When both N and P were limited in the media, the biomass of No. 40 increased slowly, while the lipid content of the dry algae powder kept a gradual increase, and the highest content of 51% dcw was obtained in the third day. The highest lipid content of 78.75 mg/L was also reached in the third day. 3. A protocol for gaining more lipid product from microalgae was achieved as algae grew under the optimal growth conditions to accumulate biomass first, and then grew in the nutrition limited condition to accumulate best oil production.