Study On Metabolism Regulation Of DHA-rich Lipid Accumulation In Marine Fungus Schizochytrium Sp.

Docosahexaenoic acid(DHA),a member of ?-3 polyunsaturated fatty acids,plays important roles in reducing blood fat and improving eyesight and brain development.Schizochytrium sp.,an algae-like oleaginous microorganism,produces abundant DHA-rich lipids and therefore is considered to be a promising substitute for DHA production.In this thesis,regulation of lipid accumulation in Schizochytrium sp.DP-16 in response to different nitrogen sources and quorum sensing was investigated.It was found that nitrogen sources had important effects on the biomass,lipid production and DHA percentage in total fatty acids(TFAs).Monosodium glutamate(MSG)helped to improve cell growth,and yeast extract helped to promote lipid production.Compared with sole organic nitrogen source,the combination of 10 g/L MSG and 10 g/L yeast extract greatly enhanced the biomass,total lipids and DHA percentage in TFAs,reaching 55.83 g/L,19.50 g/L and 35.68%respectively at 96 h,but inorganic nitrogen source addition decreased the biomass and total lipids.Lipids accumulation in Schizochytrium sp.was triggered by nitrogen exhaustion in medium.Furthermore,the analysis of isocitrate dehydrogenase(ICDH)and malic enzyme(ME)activities during fermentation process provided insight for the revelation of regulation mechanism of lipid accumulation in Schizochytrium sp.in response to nitrogen exhaustion in broth.The quorum sensing 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,total lipids,lipid-to-biomass ratio were increased by 12.10%,83.30%and 63.55%respectively.The culture supernatant of 40 h was extracted by dichloromethane,chloroform and ethyl acetate respectively and analyzed by GC-MS.It was assumed that the quorum sensing signal molecules might be 4-methyl-5-thiazoleethanol or phthalic acid diisobutyl ester.Pure 4-methyl-5-thiazoleethanol and phthalic acid diisobutyl ester were added to the fermentation broth at 16 h respectively.The fermentation results indicated that there was quorum sensing effect in the fermentation process of Schizochytrium sp.DP-16,and the quorum sensing signal molecule might be phthalic acid diisobutyl ester.