Effects Of Regulating MVA Pathway On The Fatty Acids Metabolism In Schizochytrium Sp

Schizochytrium is widely studied for its high production of polyunsaturated fatty acids(PUFAs).Researchers have been working to increase the production of PUFAs by regulating the synthesis pathway of PUFAs for many years.However,due to the synthesis of PUFAs by Schizochytrium is involved in the fatty acid synthase(FAS)and polyketide synthase pathways(PKS),the specific metabolic mechanism is very complicated,which make it difficult to further increase PUFAs productivity by regulating PUFAs biosynthetic pathways.The mevalonate(MVA)pathway exits in all higher eukaryotes and microalgae,which is critical for cell growth and metabolism.In recent years,researchers have found that there are many correlations between MVA pathway and fatty acids metabolism.Furthermore,the metabolites of MVA pathway,such as beta-carotene and squalene,have important commercial value.Therefore,it is significant and meaningful to regulate the MVA pathway of SchizochytriumFirstly,this study selected fluconazole to regulate sterol biosynthesis of the MVA pathway.The results showed when 60 mg/L fluconazole was added at 48 h of fermentation,total lipids yield increased by 16.2 1%,the cholesterol content decreased by 7.80%,and the ?-carotene yield increased by 52.59%at 96 h.The squalene content increased by 44.62%at 72 h.By intracellular NADPH content test and metabolomics analysis,it was found that the inhibition of sterol synthesis channelled more NADPH to fatty acid synthesis,and the increase of squalene and ?-carotene could enhance intracellular oxidative stress reaction,then protecting fatty acids from peroxidation and improving the accumulation of lipidsSecondly,this study selected fluridone to regulate carotene biosynthesis of the MVA pathway.The results showed that when 50 mg/L fluridone was added at 24 h,total lipids yield production showed little increase(7.3%),but arachidonic acid(ARA)and eicosapentaenoic acid(EPA)content increased by 50%and 44.23%,respectively;?-carotene content also increased significantly,which was positively correlated with the change of PUFAs content.It was found that the increase of ?-carotene content decreased the intracellular reactive oxygen species level by tracking intracellular oxidation related parameters,thereby reducing the peroxidation of PUFAs.Gene transcription level analysisindicated that the change of EPA content is positively correlated with the aerobic FAS pathway.Moreover,metabolomics analysis showed the addition of fluridone could delay cell proliferation by inhibiting sterols synthesis,leading to save more oxygen for PUFAs biosynthesis.This work first reported the effect of MVA pathway regulation on fatty acid metabolism in Schizochytrium.It is proposed that increasing content of carotenoids could promote the accumulation of PUFAs,and regulating cell growth and intracellular oxidative stress at earlier stage could improve EPA content.It provided a new perspective and strategy for regulating the production of PUFAs in Schizochytrium.Besides,it also gives new insight for microalgae to produce high-value products,such as pigment and squalene.