The Process And Mechanism Of Oil Accumulation Promoted By 2,4-D And Salt Stress In Microalgae

Microalgae is considered as a potential biomass alternative energy because its cells are rich in nutrients such as oil,protein and pigment.To realize the largescale production of biodiesel in microalgae,the first thing to be solved is the problem of low yield and high cost in the steps of planting,harvesting and extraction.Therefore,the optimization of microalgae production and oil productivity is the key in microalgae biofuel production.In this study,Chlorella vulgaris was cultured by the combination of plant hormone 2,4-Dichlorophenoxyacetic acid and salt stress.The changes of Chlorella vulgaris growth,intracellular biochemical components,fatty acid synthesis,ROS level and antioxidant system were studied,and the process and mechanism of Chlorella vulgaris growth and intracellular oil production and accumulation were further analyzed.The main work and research results of this paper are as follows:(1)The effects of environmental conditions such as different initial cell density,light intensity and aeration on the biomass,oil content and yield of Chlorella vulgaris were studied by single factor experiment.It was found that under the suitable growth environment,the maximum biomass of Chlorella vulgaris can reach about 0.75 g/L and the oil content can also reach 19%.(2)Chlorella vulgaris was cultured by Na Cl,2,4-Dichlorophenoxyacetic acid(2,4-D)and 2,4-D combined with Na Cl.Through the indexes of biomass and oil content,the combination of 2,4-D and Na Cl was determined as the best culture method.Furthermore,the cell morphology,biochemical components,fatty acid composition and quality of Chlorella vulgaris under these four culture methods were analyzed.It was found that under the condition of combined culture of 2,4-D and Na Cl,the contents of chlorophyll a,carotenoid and soluble egg white of Chlorella vulgaris increased with the increase of culture days,the content of carbohydrate decreased first and then increased,and the content of fatty acid in C16 ～ C18 increased further,it reached 88.63% of the total fatty acid content.In addition,the combustion,ignition and oxidation stability of Chlorella fatty acids were significantly improved under this culture mode.(3)By detecting the content of ROS in Chlorella vulgaris,the effects of the above four culture methods on the oxidation degree of Chlorella vulgaris were studied.The correlation between intracellular ROS level and fatty acid content was studied.The Pearson correlation coefficient was r = 0.73,P < 0.01.The data confirmed that there was a positive correlation between intracellular ROS level and fatty acid content.At the same time,the concentrations of SOD and cat were measured under different conditions.It was found that a large number of SOD and CAT were produced under salt stress,which further showed that the large accumulation of ROS caused the oxidative stress response of Chlorella vulgaris under nutrient salt stress.