Saccharomyces Cerevisiae Strains Selected from Nature Significantly Increased the Production of 2-Phenylethanol Through Protoplast Fusion
Abstract Background: 2-Phenylethanol (2-PE) is an aromatic alcohol with rose fragrance, which is widely used as an additive in food, tobacco and daily chemical industries. Yeast is the main microorganism producing natural 2-PE, but it is limited by low production and weak tolerance. Nature and fermented products is a resource treasury of yeasts with excellent traits. Screening strains with good phenotypic traits and conducting breeding by cell fusion for genetic pyramiding is an effective way to improve strains. Results: In this study, 25 strains of 2-PE-producing yeasts were isolated from Chinese brewed samples. Three Saccharomyces cerevisiae strains with good traits in tolerance and 2-PE titre were screened out. The strain LSC-1 produces 2-PE of 3.41 g/L with an increase of 9.3% compared to the industrial strain CWY132. The strain NGER shows good tolerance to 2-PE at the concentration of 3.60 g/L in agar plate, and the thermotolerant strain S.C-1 shows growth ability at 41℃. Two rounds of protoplast fusion were performed with these three parent strains for pyramiding of traits. A fusant strain RH2-16 with high 2-PE titre and increased tolerance was obtained. Using 5g/L L-phenylalanine as the precursor substrate, the maximum titre of 2-PE produced by the RH2-16 strain through fermentation and transformation is 4.31 g/L, and the average titre is 4.04 g/L. The molar conversion rate of L-Phe reached 115% in 36 h. Compared to the parental strain LSC-1 and the industrial strain CWY132, 2-PE titre in RH2-16 increased by 26.4% and 38.1%, respectively.Conclusion: Diversified S. cerevisiae strains with different traits can be isolated from the brewing related samples. Protoplast fusion technology can effectively pyramid excellent genetic traits and breed yeast strains with significantly improved tolerance and 2-PE titre. Our research provided a breeding strategy for S. cerevisiae and a strain for industrial production of 2-PE.