Mutation Screening Of Saccharomyces Cerevisiae Fermenting Xylose To Ethanol And Optimization Of Its Fermentation Conditions

Yeast is a mainly restrict factor of xylose fermentation to produce ethanol. In the study, the yeast strains (Saccharomyces cerevisiae), (CICC-1517RM) which preserved in life science and Technology College of Central South University of Forestry and Technology were mutated by ultraviolet rays and y rays, and screened out with TTC, in order to obtain the yeast strains with the ability to ferment xylose. The molecular identification of mutant strains was carried out with the microscope and 18srDNA. The optimal fermentation conditions were obtained by optimizing the fermentation conditions of the dominant yeast. The results were as follows:1. The compound mutation of UV and gamma rays of Saccharomyces cerevisiae was carried out by TTC. Yeast was treated by 120 s ultraviolet irradiation, and the 0.27 kGy was used to carry out the irradiation. The TTC medium dark culture 2-3 h.Chosen 5 strains with growth well and darker red colonies for further screening. After the comparison of xylose tolerance and ethanol fermentation, a dominant yeast strain was selected, which was LH4. In the medium containing xylose 4%, the final concentration of LH4 was 0.531 g/L, which was much higher than that of the original strain by 0.108 g/L. As a result, the effect of the mutant strain LH4 in the culture medium is better than that of the original strain.2. Observation of the morphology of Mutant by microscope, After staining, it was observed that cells were oval, a few white, mostly blue. There is a small bud by larger maternal cells, parent cells are deep blue, buds are light blue. By 18srDNA amplification and sequencing of the yeast strain of Mutant, and NCBI database is used to carry out the Blast ratio, and the MEGA6.0 software is used to construct the phylogenetic tree. It can be concluded that the strain is a genus of Saccharomyces cerevisiae.3.Using four factor three level orthogonal experiment, the optimal conditions for the production of ethanol from the yeast was liquid loading was 125 ml,inoculation amount was 8%, pH 6.5, temperature was 30℃. Verification experiment of ethanol fermentation by Saccharomyces cerevisiae under optimal conditions, parallel three times. The average yield of ethanol was 0.552 g/L.4.Based on the optimization of fermentation conditions on the shake cultivation, for the amplification experiment fermentation,110 hours’ fermentation of mutant yeast LH4 using 5 L fermentation tank were tested. The final yield of ethanol is 0.180 g/L. Based on the data of the fed batch fermentation, the cell growth, ethanol synthesis and substrate consumption kinetics model of the fermentation process were established, Express as follows:(1) Cell growth kinetics model(2)Kinetic model of ethanol production(3)Matrix depletion kinetics modelThe relevant mathematical model is established and compared, the dynamic process of ethanol production by the fermentation of the mutant strain LH4 was determined, it provide a strong basis for industrial production.