| Eicosapentaenoic acid(EPA)is a kind of polyunsaturated fatty acids(PUFAs)which is very important for human body,especially for treating and preventing cardiovascular,anti-inflammatory and anti-cancer.However,the main source of EPA is still deep-sea fish oil,which cannot meet the increasing market demand owing to the depletion of marine resources and environmental pollution.The quality of fish oil is not satisfactory either.At present,main microalgae producing EPA are photoautotrophic.The growth process is inseparable from light.The cultivation conditions are complex,and the biomass and lipid yield are low,which greatly limits the industrial development of microalgae produced EPA.Schizochytrium sp.,a heterotrophic marine fungal,grows fast with high lipid yield and riches in DHA.Schizochytrium sp.can be used as a potential strain for EPA production.In this paper,Schizochytrium sp.ATCC 20888 was used to investigate the EPA production under different culture conditions.A high-yield EPA fermentation strategy was established and the pilot-scale experiment was realized.The related pathways of fatty acid synthesis of Schizochytrium sp.were analyzed by transcriptome sequencing analysis.The metabolic regulation mechanism of Schizochytrium sp.producing EPA was studied.This paper provided a theoretical basis for overcoming the bottleneck of EPA fermentation technology and industrial production.The main contents and conclusions of this paper are as follows:(1)Study on the conditions of producing EPA by Schizochytrium sp..The effect of fermentation media and conditions were optimized at the shaking flask level.The results showed that glucose,yeast extract and monosodium glutamate were the best carbon and nitrogen sources for Schizochytrium sp.to produce EPA,and the optimal carbon nitrogen ratio was 11:1.The EPA content reached the highest at 34?,and the highest content was 4.67%.The production of EPA increased by 109.09% when cultured at 28? under two-stage temperature control(28??34?).Dissolved oxygen had a significant effect on the growth and EPA accumulation of Schizochytrium sp..the yield of EPA was the highest at 180 rpm,reaching 0.28 g / L.(2)Study on the metabolic mechanism of Schizochytrium sp.producing EPA.The results showed that the changes of fatty acid composition showed a certain regularity under constant temperature 28? and stage-controlled temperature(28??34?).According to the changes of fatty acid,it was speculated that there might be differences in the metabolic pathways of EPA and DHA.Temperature stress promoted the transformation of saturated fatty acids to EPA and other polyunsaturated fatty acids.The differential genes closely related to fatty acid synthesis were analyzed by transcriptome analysis.It was speculated that saturated fatty acids could be converted into EPA and DHA by FAS pathway under the condition of abundant fatty acid synthesis precursor acetyl-Co A.(3)Study on pilot-scale experiment.The fermentation conditions of EPA production were optimized in 5 L fermentor,including temperature changing time,p H and dissolved oxygen.The optimal fermentation process was established: the temperature was controlled at28?(0 h-24 h)in the initial stage of fermentation,Schizochytrium sp.increased rapidly,and the synthesis of EPA was promoted when the fermentation temperature was increased to 34?in the middle logarithmic growth period(24 h).Under the optimal fermentation conditions,EPA yield reached 1.15 g/L when it was fermented for 96 h,and biomass,lipid yield and EPA content were 56.60 g/L,9.62 g/L and 12.50%,respectively.The optimal fermentation process was verified in 500 L fermentor.The biomass and lipid yield reached the highest at 84 h,which were 72.69 g/L and 25.88 g/L,respectively.Compared with the optimal fermentation process in the laboratory,the biomass and lipid yield increased by 27.36% and 146.48%.The EPA yield reached 1.91 g/L at 96 h.Compared with the optimal fermentation process in the laboratory,the fermentation result increased by 80.19%. |
PDF Full Text Request