Screening Of Three Excellent Microalgae, Optimizating Culture Conditions And Preliminary Study Of PEPCase

Microalgae absorb carbon dioxide in the air mainly by using solar energy to generatesubstances for the growth of itself. With the advantages of easy to cultivate, fast growth, highbiomass production and rich in lipids and astaxanthin, microalgae are important resources ofbio-energy and high-value co-products in the field of energy and health care sector. Thus,microalgae have been attracting a lot of attention in the world.The purpose of this thesis is screening the high-lipid microglgal strains with highbiomass from In Wuliangsuhai、Dongjiang port Tianjin and three oil-rich strains wereobtained,next they were named based on the morphological and molecularindentification.Then their lipid production performance were evaluated,the culture conditionswere optimized to improve the lipid yield.At last,the PEPCase activity ofNannochoropsis sp. was measured to research the lipid metabolism in microalgae.Themajor results are shown as follows:1. The biomass and lipid content of the three oil-rich strains named XJ307、XJ308、XJ309were1.2g/L（50.3%）、0.86g/L（34.6%）、0.48g/L（40.5%） respectively. XJ307wasisolated from In Wuliangsuhai, XJ308and XJ309were obtained form Dongjiang portTianjin. AA and EPA is rich in XJ307,accounted for0.52%and5.12%of the total lipid;astaxanthin,a high-value co-product was found in XJ308, ccounted for0.43%dry cell weight;the fatty acids of the three microalgae,with a majority as oleic acids and palmitic acids,weresuitable feedstock for biodiesel production.2. Cells of XJ307are unicellular, swelled in the middle, small in the two ends, and thereare two chromatophores existed in two sides. And cells of XJ308、XJ309are unicellular,atrichosis spheroidal and green. However the cells of XJ308will become red in late stablephase.With the morphological and molecular identification, XJ307was named Nitzschia sp.XJ307, XJ308was named Scenedesmus sp. XJ308, XJ309was named Chlorococcum sp.XJ309. 3. Based on f/2medium and seawater-BG11, the optimal results were optimized asfollows:the highest lipid production rate of XJ308was about100.27mg/L/day when theinitial NaNO₃is0.6g/L in seawater-BG11medium,while the astasxanthin yield was19.61mg/L. The highest lipid production rate of XJ309was22.74mg/L/day when the initialNaNO₃was0.1g/L in f/2medium. Comparing with f/2medium, the biomass of XJ309wasimproved significantly from open race-pond with seawater-BG11that the initial NaNO₃wasjust750mg/L,and the final biomass was2g/L, lipid content reached25.425%,the productionrate reached21.6818g/m²/day.Moreover, a mathematical model was established based on therelationship between the illumination intesity, temperature, NaNO₃consumption and thegrowth of microlage,which can reveal the growth of microalgae with illumination intesity,temperature, and NaNO₃consumption.4. Nile Red straining as a rapid method was used for lipid determination in differentinitial NaNO₃concentration. The highest PEPCase activity was29.77U/mL when the initialNaNO₃concentration was150mg/L, and on the contrary the lipid content was just540mg/L.The highest lipid content was1306.9mg/L when the initial NaNO₃concentration was30mg/L, however, the PEPCase activity was only13.73U/mL.The PEPCase activity andlipid content were14.91U/mL,1182.0mg/L respectively when the initial NaNO₃concentration was75mg/L.The utilization of the three isolated oil-rich algae will definitely lay the foundation forlarge-scale biodiesel production, polyunsaturated fatty acids production and high valuedpigments production, and it has broad prospects in the future.