(228ba) Understanding the Metabolism of Scheffersomyces Stipitis during the Transition from Aerobic Growth to Fermentation Condition

Xylose fermentation is essential in converting lignocellulosic material to biofuels in order to make an economically feasible process. Scheffersomyces stipitis is a native strain with the highest known capability of converting xylose to ethanol by fermentation. Since S. stipitis is a respiratory yeast strain, the oxygen availability is a critical parameter to consider for ethanol optimization due to the redox balance. Many other studies showed the effects of oxygenation conditions on ethanol yield and productivity; however, these studies have not look at the metabolism shifts occurred during the transition stage, where the oxygen condition changed from aerobic to oxygen-limited conditions. In order to systematically understand the metabolic states of S. stipitis during this transition period, we conducted experiments under controlled chemostat to achieve aerobic growth with no product and by-products, then it was switched to fermentation conditions by switching the oxygen condition from aerobic to oxygen-limitation. During this transition, we took samples frequently to capture the rapid changes of genome expression and metabolites. To doing this, we manipulated carbon-to-oxygen ratio (C/O2) to reach desired metabolic states of aerobic and oxygen-limited conditions. Different ranges of C/O2 ratio define different phenotypes of S. stipitis to produce different product and by-products. During the transitions stage, the experiments showed that the specific rates of substrate consumption, products and by-products profiles were changed within 1.5 hours to switch their metabolic states. This study allows us to understand the mechanisms of shifting metabolism of S. stipitis.