Regulation Of DHA-rich Lipid Accumulation Mediated By Auto-inducer In Schizochytrium Sp.

Docosahexaenoic acid(DHA)is a kind of important omega-3 polyunsaturated fatty acid,which has many functions and is widely used in food and medicine industry recently.Because of its rich DHA,schizochytrium fungus is the ideal strain for the commercial production of DHA.In this thesis,the progress of DHA-rich Lipid accumulation regulation produced by Schizochytrium sp was investigated deeply,and the autoinduction efftct in the progress of lipid production was investigated.It was found that the fermentation process was divided into cell proliferation period and lipid accumulation period,the nitrogen source in the medium was quickly consumed in the early stage of fermentation,and the increase of cell number caused the growth of biomass before the nitrogen source was depleted.And when the nitrogen source is completely depleted,the cells continue to absorb carbon sources for the synthesis of lipids,the biomass reached40.50 g/L at 96 h,lipid yield reached 20.36 g/L,lipid content reached 50.28%,DHA percentage in TFAs of 30%.The ME activity was maximum 22559.67 U/g when the nitrogen source was depleted,while the activity of ICDH was gradually decreased by the highest value of11364.63 U/g.The cell count was rapidly increasing before 36 h,the highest in the 84 h,and the cell density was 3.25×10~100 cfu/mL.The autoinduction effect during fermentation process of Schizochytrium sp.DP-16 was investigated.Culture supernatant of 40 h was mixed with cell precipitate of 16 h,and then cultured for 8 h.The biomass and total lipids were increased by 46.10%,28.08%respectively.Further using ethyl acetate to extract the culture supernatant of 40 h,the extraction liquid dissolved after decompression and evaporation,added to 16 h culture solution,and the biomass and lipid yield of 8 h were increased by 13.73%and 13.72%.The culture supernatant of 40 h was extracted by ethyl acetate and analyzed by GC-MS.It was assumed that the autoinducer might be phthalic acid diisobutyl ester and its content is increasing with the increase of fermentation time.Phthalic acid diisobutyl ester and its structural analogues diisooctyl phthalate were added to the fermentation broth at 16 h respectively.The fermentation results was indicated,compared with control group,the lipid yield and biomass of the experimental group were higher,the biomass increased by 7.85%and 4.96%respectively,and the lipid yield increased by 16.42%and 6.35%respectively.Therefore,there was autoinduction effect in the fermentation process of Schizochytrium sp.DP-16,and the autoinducer might be phthalic acid diisobutyl ester.