Alternative Inverse Metabolic Engineering Based on Transient Acclimation of Yeast Improves Acid-Containing Xylose Fermentation and Tolerance to Formic and Acetic Acids

Improving the production of ethanol from xylose is an important goal in metabolic engineering of Saccharomyces cerevisiae. Furthermore, S. cerevisiae must produce ethanol in the presence of weak acids (formate and acetate) generated during pretreatment of lignocellulosic biomass. In this study, weak acid-containing xylose fermentation was significantly improved using cells that were transiently acclimated to the weak acids during pre-cultivation. Transcriptome analyses showed levels of transcripts for transcriptional/translational machinery–related genes (RTC3 and ANB1) were enhanced by formate and acetate acclimation. Recombinant yeast strains overexpressing RTC3 and ANB1 demonstrated improved ethanol production from xylose in the presence of the weak acids, along with improved tolerance to the acids. Novel metabolic engineering strategy based on the combination of transient acclimation and system-wide analysis was developed, which can develop stress-tolerant strains in a short period of time, although conventional evolutionary engineering approach has required long periods of time to isolate inhibitor-adapted strains.