Quantification and Molecular Analysis of Antagonism between Xylose Utilization and Acetic Acid Tolerance in Glucose/Xylose Cofermentation Strains.

For bioethanol production from lignocellulosic materials, an ideal microorganism must possess both excellent xylose utilization and a high tolerance to inhibitory compounds. However, these two traits often exhibit antagonism in recombinant xylose-utilizing strains. In this study, we developed a quantitative metric using an aggregated parameter to evaluate the degree of this antagonism and applied it to evaluate the antagonism of three strains (LF1, LF1-6M, and 6M-15), which had been iteratively evolved in xylose and hydrolyzate environments. Transcriptomic analysis revealed that the yeast strain elevates the alert level to stresses related to DNA replication, unfolded protein, starvation, and hyperosmosis, and reduces the uptake of unimportant nutrients to have a higher acetic acid tolerance during adaptive evolution in hydrolyzate. Additionally, the Snf1p-Mig1p signaling pathway was reprogrammed, enabling the strain to utilize xylose more efficiently during adaptive evolution in xylose. We also confirmed that disruption of the glyceraldehyde-3-phosphate dehydrogenase gene significantly shortened the time required for glucose and/or xylose cofermentation under acetic acid stress by reducing reactive oxygen species accumulation and increasing ATP production. This study offers valuable insights for developing robust and efficient strains capable of glucose/xylose cofermentation.