(341c) Improving Acetic Acid and Ethanol Resistance of S. Cerevisiae 424A(LNH-ST) During the Co-Fermentation of Glucose and Xylose

Efficient conversion of hemicellulose-derived sugars to ethanol at high yields and titers are goals toward commercializing cellulosic ethanol production. S. cerevisiae 424A (LNH-ST) developed at Purdue University can efficiently ferment glucose and xylose. However, inhibitors present in cellulosic feedstocks (acetic acid) and the desired fermentation product (ethanol) reduce yeast growth rate and fermentation rates, especially during xylose fermentation.

Through adaptation we have developed new strains with improved xylose fermentation compared to the original strain. The new strain has 500% higher ethanol volumetric productivity on xylose in the presence of higher ethanol concentrations (above 6%) than the original strain. An acetic acid-resistant yeast strain co-fermenting glucose and xylose in the presence of acetic acid (10 g/L) when compared to the original strain has 3 times the rate of xylose utilization (1.05 g/L/h from 0.32 g/L/h) and results in a higher final ethanol titer (76.3 g/L from 61.2 g/L). We present the results from a system biology approach to analyzing differences between our original strain and newly developed strains. We focus not only on expression profiling (transcriptomics), but also report changes in metabolic intermediates and fluxes, and lipid membrane composition to elucidate the basis for improved yeast performance.