Heterologous Biosynthesis Of Taraxerol By Engineered Saccharomyces Cerevisiae

Taraxerol is an oleanane type pentacyclic triterpenoid compound,which has good effects in the treatment of inflammatory,tumor and oxidation,and also has good effects in the treatment of diabetes and liver protection.At present,the most commonly used method for obtaining taraxerol is chemical extraction.There are few studies on the synthesis of taraxerol by chemical synthesis or biosynthesis.Saccharomyces cerevisiae is a commonly used model microorganism.In this study,two different sources of taraxerol synthase genes were codon-optimized and introduced into strain W303,combined with the overexpression of ERG1 gene,a strain WKd E2 was constructed.Strain WKd E2 is able to produce taraxerol with a titer of 1.85 mg/L.Then,by overexpressing the key genes t HMG1,ERG20,and ERG9 in the biosynthesis pathway of taraxerol,the production of taraxerol was increased to 17.02 mg/L.Then,by knocking out the GAL80 gene,a strain WTK15 was constructed.Although the titer of taraxerol drops to 12.51mg/L,there is no need to add the galactose during fermentation,which greatly reduces the fermentation cost.The HXT1 p promoter was used to weaken the expression of ERG7 to control the synthesis of sterols.As a result,the production of dandelion cyperol did not increase but decreased.Next,we modified the endoplasmic reticulum of strain WTK15.First,PGK1 p promoter and ADH2 p promoter were used to overexpress the gene INO2 which activates phospholipid synthesis,and strains WTK17 and WTK18 were constructed.The titer of taraxerol of strains WTK17 and WTK18 were 16.12 mg/L and 14.80 mg/L,respectively.We knocked out the OPI1 gene in WTK17 and constructed the strain WTK19.The titer of taraxerol of strains WTK19 further increased to 17.35mg/l.By optimizing fermentation conditions,the titer of taraxerol in batch fermentation was25.79 mg/L and in fed-batch fermentation further increased 59.55mg/L.