Surface display of pectinesterase on Saccharomyces cerevisiae for efficient bioethanol production from sweet potato starch

Abstract:

[Objective] Bioethanol is a new type of green energy, and predominantly produced currently from starch such as corn and sweet potato. However, pectin contained in the substrates will increase the viscosity of ethanol fermentation broth, which will affect the mass transfer and increase the burden of equipment. In this study, we expressed pectinesterase on the Saccharomyces cerevisiae cell surface and evaluated its effect on fermentation viscosity decrease. [Methods] Pectinesterase gene was fused with the C-terminal-half region of α-agglutinin and then inserted into the downstream of the secretion signal gene, to generate a yeast surface-display expression vector pMGK-AG-PE, which was then transformed into the industrial S. cerevisiae. [Results] Recombinant yeast strain PE successfully displayed pectinesterase on the surface of cells with 2.6 U/g wet cells. The recombinant enzyme performed the maximal activity at 60 ℃, pH 5.0, and this enzyme had high activity and stability from pH 4.0 to 5.5. In the simultaneous saccharification and fermentation of sweet potato, the ethanol production of the PE strain was 95 g/L. The viscosity of fermentation broth using the PE strain was lower than that of the parent strain, 120 mPa.s compared to 145 mPa.s after 12 h of fermentation. [Conclusion] Expressing pectinesterase on yeast cells surface decreased viscosity of fermentation broth, which is beneficial to starch degradation and ethanol production.