Priliminary Study On The Rapid Growth And Oil Accumulation Of Marine Microalgae

Due to limited stocks of fossil fuels and the production of greenhouse gas carbon dioxide on the combustion, Biodiesel is receiving consideraale attention, as one form of renewable energy with wide resource. Microalge is a primitive plant of Photosynthetic efficiency, have been considered to be a ideal source of biodiesel for its high growth and high lipid content and mass cultivation. As production costs are high, the production of microalgae for biodiesal has not yet been undertaken on a commercial scale. Numerous studies show that the growth and fatty acid accumulation of microalgae could be modified by environmental condition. In this paper, the effect of indole-3-acetic acid on the growth and fatty acid composition of microalgae was investigated. Nitrogen concentration has played a very important role in microalgae fatty acid composition. Compare nitrogen limited culture conditions with medium supplemented with sodium tungstate and sodium molybdae, the different changes in fatty acid composition of microalgae was studied. To optimize the cultural condition for the rapid growth and oil accumulation of marine microalgae, it can provide theoretical basis and technical support for mass production of microalgae biodiesel.Firstly, we selected the microalgae from Chlorella and Chlorococcum which have been reported in high growth and high lipid content. We compared the growth of the six species microalgae, two species microalgae were found with rapid growth and mass cultivation. They were Nannochloropsis oculata and Chlorella sp. C7.As a plant growth hormone, IAA can promote and stimulate the growth of many unicellular algae. Through the comparison of the specific growth rate, final cell density and optical density, Add IAA appropriate algal cells can rapidly achieve exponential growth phase and access the higher biomass. For N. oculata the most significant promotion to the growth was observed when IAA was 0.1mg/L, and 0.25mg/L for Chlorella sp. C7. IAA didn't promote the synthesis of fatty acids in this study. When the concentration was high, IAA most significantly inhibited the synthesis of eicosapentaenoic acid (EPA), making the percentage of EPA the lowest among the analyzed. The total lipid content of two microalgae increased in nitrogen deficiency medium. Under the culture condition of nitrogen starvation, the contents of 16:0,16:1,18:1 were higher while the contents of 14:0,20:4,20:5 became lower, the four main fatty acid content of N. oculata increased by 17.30% with the treatment of 96h; For the Chlorella sp. C7, the contents of 16:(4n-3),18:1 (n-9) were higher while the contents of 18:3(n-3),20:5(n-3) became lower, the four main fatty acid content can increased by 1.18% with the treatment of 96h.Nitrate Reducatase (NR) is a key and rate-limiting eneyme for nitrate assimilation. Through its catalytic reaction regulates nitrate reduction. Sodium tungstate, a nitrate reductase inhibitor, Can inhibit the activity of nitrate reductase, to limit the absorption of nitrogen. The results show that add different concentrations of sodium tungstate the contents of 16:0,16:1,18:0,18:1 increased and the contents of 14:0,20:4,20:5 decreased of N. oculata; For the Chlorella sp. C7, the contents of 16:0,18:1 (n-9) increased and the contents of 18:3 (n-3),0:5 (n-3) decreased. The accumulation of fatty acids in microalgae is consistent with the results of nitrogen deficiency, increase in fatty acid saturation, unsaturated fatty acid content decreased, so adding acid sodium limit the role of nitrogen can be achieved.Sodium molybdate is an activator of nitrate reductase. In this paper we explores the effect on fatty acid composition of microalgae, The experiment of N. oculata show that the contents of 16:0,20:5 increased, especially in the content of EPA was significantly increased, which is contrast with the results of nitrogen deficiency and adding sodium tungstate culture; For the Chlorella sp. C7, the contents of 16:0,18:1 (n-9) increased and the contents of 16:(ln-7),16: (4n-3),18:2 (n-6),18:3 (n-3) decreased. oleic acid increased significantly, a-linolenic acid content decreased, increased intracellular fatty acids, which is similar with the role of nitrogen deficiency and adding sodium tungstate culture on fatty acid synthesis. Sodium tungstate play the opposite role in the fatty acid synthesis of N. oculata and Chlorella sp. C7. Indicating different types of microalgae. The fatty acid metabolism and biosynthesis of different.Finally, compared with Chlorella sp. C7 in high lipid content and effect of nitrogen limit, the N. oculata is more suitable for mass production of microalgae biodiesel. Technical line as follows:initial stage of growth Add 0.1mg/L IAA and cultured to exponential phase (about 8 days), up to a certain biomass, adding lmmol/L sodium tungstate for nitrogen limit processing(about 3 days), fatty acid accumulation, which not only guarantee the biomass, it can increase the lipid content of microalgae. This method is simple and feasible, can provide the experimental basis and technical support for large-scale cultivation of microalgae.