Engineering xylose fermentation in an industrial yeast: continuous cultivation as a tool for selecting improved strains.

This article focuses on engineering and evolving the industrial yeast strain *Saccharomyces cerevisiae* SA-1 to improve its ability to ferment xylose, a pentose sugar derived from lignocellulosic biomass, for second-generation bioethanol production. Using CRISPR-Cas9, the oxidoreductase xylose pathway genes (XYL1, XYL2, XYL3) from *Scheffersomyces stipitis* were integrated into SA-1, creating the SA-1 XR/XDH strain, which was further subjected to adaptive laboratory evolution (ALE) in xylose-limited chemostats to enhance xylose consumption kinetics. The evolved strain, DPY06, demonstrated a 35% higher volumetric ethanol productivity and faster xylose utilization than its parental strain when cultivated in hemicellulosic hydrolysate under microaerobic conditions, although it produced more by-products like xylitol and glycerol and showed reduced biomass formation. These findings illustrate the potential of combining metabolic engineering with ALE to develop robust industrial yeast strains capable of efficiently fermenting xylose from lignocellulosic residues, contributing to sustainable biofuel production.