Metabolic Engineering Of Saccharomyces Cerevisiae For Lycopene Biosynthesis

Lycopene is one of very important carotenoids.It has a series of excellent physical functions which makes it have extensive application and huge market value in the field of food and pharmaceuticals,including anti-aging,prevention of cancer,relieving atherosclerosis,enhancing ability to resist radiation and so on.Lycopene can be obtained by natural plant extraction,chemical synthesis and microbial fermentation.But the natural plant extract can be obstructed by external factors such as season,producing area,in addition,high extraction cost going with disappointing supply hindering the performance of meeting the demand of market.Chemical synthesis method of low cost,but will produce more side products,which greatly limits its industrial applications.Using microorganism fermentation to produce lycopene has low cost,high production rate and the advantages of the controllable product quality,which is considered the most promising method.Saccharomyces cerevisae is recognized as a safety strain which can be used for large-scale fermentation of food,this study selected saccharomyces cerevisiae as the setting strain of the metabolic engineering lycopene production.Based on previous studies,we found that the early accumulation of lycopene would affect cell growth and ultimately affect the yield of lycopene,so we chose the GAL control system to achieve the balance between cell growth and lycopene production.First,we compared the strength of the galactose-inducible promoters and selected the stronger to control the expression of key genes of lycopene synthesis.And knocking out the gene GAL1/7/10 to reduce the waste of GAL series promoter resources and to eliminate the use of galactose.Increasing the synthesis of IPP(isopentenyl pyrophosphate)and DMAPP(dimethylallyl pyrophosphate)by overexpressing the rate-limiting enzyme HMG-CoA reductase in MVA pathway.Through screening downstream genes CrtE,CrtB and CrtI from different species,the higher lycopene biosynthesis strain was obtained.Then adjusting the copy number of the key gene and optimizing the culture medium,the strain could produce 210 mg/L lycopene in shake flask fermentation.Eventually,a titer of 1.61 g/L(66 mg/g DCW)lycopene was achieved in 5 L fed-batch fermentation.