Adaptation Strategy to Increase the Tolerance of Scheffersomyces stipitis NRRL Y-7124 to Inhibitors of Sugarcane Bagasse Hemicellulosic Hydrolysate Through Comparative Studies of Proteomics and Fermentation

In this work, we propose an adaptation strategy for Scheffersomyces stipitis NRRL Y-7124 to increase its tolerance to inhibitors of hemicellulosic hydrolysates in the production of bioethanol. Sugarcane bagasse pretreated with 0.5% (v/v) of sulfuric acid at 140 °C for 15 min was used as feedstock. The microorganism was subjected to a cell recycle batch fermentation system with increased inhibitors pressure, characterized by five consecutive batches with 33% of hydrolysate, followed by five subsequent batches with 67% of hydrolysate. The remaining composition of the culture media for each sequential batch (necessary to complete 100% of carbohydrate content) was synthetic substrate. Finally, the strain was used in a fed-batch fermentation with 100% of hydrolysate, resulting in an adapted strain of S. stipitis at the end. In order to validate the adaptation strategy, the fermentative performances of the adapted and non-adapted strains were compared under different acetic acid concentrations using synthetic substrate. 0.7 g/L of acetic acid significantly affected the fermentative performance of the non-adapted strain, while for the adapted strain, this value was 3.7-fold higher (2.6 g/L), confirming the increased tolerance. Through proteomic analysis, genes related to the defense mechanisms of S. stipitis against oxidative stress due to the presence of inhibitory compounds were identified, which plays a key role on the comprehension of the cell adaptation metabolism.