(220p) Mechanism of Resistance of a Yeast to Sulfur Dioxide and the Genetic Improvements for Its Application in Advanced Solid-State Fermentation for Fuel Ethanol Production Using Sweet Sorghum

Compared to sugar cane, sweet sorghum has great potentials to be a principal energy crop worldwide due to its supreme agronomics advantages, such as fast growing, broad cultivation regions, and strong tolerance to drought, waterlogging, salinity, and alkalinity. Recently, sweet sorghum has been used as the feedstock for a pilot-scale fuel ethanol production using continuous advanced solid-state fermentation (ASSF) developed by Tsinghua University, China. This first demonstrated the high feasibility of applying ASSF at large scale for fuel ethanol production. For further industrialization and commercialization of ASSF, the sustaining of sugars in sweet sorghum stalks is a prerequisite for year-round production of fuel ethanol using ASSF. Accordingly, extensive studies have focused on the long-term storage strategies of sweet sorghum. However, the high inhibitory activities of antiseptics to yeast fermentation and poor homogenicity between the solid sweet sorghum and the antiseptics result in no effective storage methods so far to support the commercialization of sweet sorghum ethanol using ASSF. Most recently, we developed a storage strategy using sulfur dioxide (SO₂) as the antiseptics that can keep sugars in sweet sorghum stalk with no more than 5% of sugar loss over 6 months. Meanwhile, we obtained a S. cerevisiae strain THS2 that shows a strong tolerance to SO₂. After a serial of SO₂ adaption cultures, TSH2 is capable of growing in the SO2-containing media up to 1600 ppm, which shows much higher tolerance of yeast to SO₂ than that of ever reported. In this study, we investigated the mechanism of TSH2’s tolerance to SO₂, and applied the strategies of genetic and evolutionary engineering to reduce the lag phase of TSH2 in SO₂-containing media. We can expect that this strategy is capable of supporting the commercialization of sweet sorghum ethanol production using ASSF.