Screening Of Microalgae With High PUFAs Yield, Nutrient Stress And Its Application In Hen Feed

Microalgae is a promising source of polyunsaturated fatty acids(PUFAs) and is rich in essential fatty acids required by the human body.The purpose of this study is to screen out microalgae species with high yield of PUFAs from natural ecosystems, and to study the changes of lipid metabolism through nutrient stress treatment, and to further promote the accumulation of PUFAs. At the same time, the selected microalgae strains is applied to large-scale culture with the aim to add microalgae powder in chicken feed and to study the effect of microalgae on the quality of eggs.In this study, 432 microalgae strains were isolated from 29 solid and water samples from northwest China. These strains were screened by Nile red staining preliminarily and by the determination of lipid content and fatty acid composition for the second time. Finally a special strain called S7-M11 was obtained with a high content of lipid accounting for 48.32%of dry weight, and its PUFAs accounted for 22.19% of the total fatty acid composition. The microalgae strain S7-M11 was proved to have a close relationship with Cylindrotheca with 98% homologe to Cylindrotheca closterium through molecular biology identification.The results showed that the nitrogen-repleted condition could promote the biomass accumulation of microalgal cells and increase the proportion of PUFAs in total fatty acids by 12.17%. The nitrogen-depleted condition could inhibit cell growth and promote lipid content. Phosphorus-repleted condition mainly promote the accumulation of MUFAs in algal cells, while the phosphorus-depleted conditions can promote the accumulation of C20:5 and C22:5 long chain polyunsaturated fatty acids while promoting the accumulation of neutral lipids. The content of PUFAs in algal cells increased by 26.84% under the condition of iron deficiency, and the content of three important kinds of PUFAs-C18:3, C20:4 and C20:5 increased in the case of iron deficiency.The microalgae strains S7-M11, Chlorella C4 and Euglena E8 were added to chicken feed for experiment. The results showed that the addition of microalgae to chicken feed did not change the performance of laying hens and the quality of eggs, but could improve the color of egg yolk by 5-7 hue and increase the proportion of PUFAs in total egg yolk. The effect of S7-M11 was most obvious, and omega-6 PUFAs and omega-3 PUFAs in egg yolk were increased by 18.56% and 77.57% respectively, and the three important PUFAs of a-Linolenic acid, Arachidonic acid and Docosahexaenoic acid were also improved.