Engineering arabinose-to-arabitol conversion in industrial Saccharomyces cerevisiae for sugar beet pulp valorization

Arabitol, a promising low-calorie sweetener for the food industry, faces production challenges due to the high costs and the environmental impact of conventional chemical methods, as well as the inefficiency of biological approaches using native arabitol-producing yeasts. The Saccharomyces cerevisiae GRE3 gene encodes an NADPH-dependent aldose reductase, capable of converting various aldoses to their respective sugar alcohols. By leveraging the enzyme's broad substrate specificity, the simultaneous conversion of xylose and arabinose into xylitol and arabitol, respectively, was achieved. This study showcases the feasibility of using engineered industrial yeast strains, overexpressing the native GRE3 gene, for the one-step conversion of arabinose to arabitol. Engineered strains (PE2-2-pGRE3, PE2-2-pGRE3-XII5, CA11-pGRE3, CA11-pGRE3-XII5, CAT1- pGRE3 and CAT1- pGRE3-XII5) exhibited successful arabinose-toarabitol conversion, with a 3.5-fold variation in arabitol concentrations across strains. Further enhancement of the best-performing strain through overexpression of the GAL2 gene significantly improved arabinose transport, resulting in a 1.95-fold increase in arabitol productivity. This engineered strain, free of heterologous genes, also demonstrated its potential by converting arabinose-rich sugar-beet pulp hydrolysate into arabitol, reaching a titer of 15 g/L with a yield of 1 g/g. This study represents the first example of arabitol production from agro-food waste using genome-edited S. cerevisiae strains, which contain no foreign genes, as a versatile and efficient host.