Biotechnological applications of D-xylose-fermenting autochthonous yeasts in lignocellulosic biorefineries.

The efficient fermentation of D-xylose by yeasts remains a major bottleneck for the sustainable production of second-generation bioethanol, as this pentose represents a substantial fraction of hemicellulosic sugars in lignocellulosic biomass. While conventional industrial yeasts show limited native capacity for D-xylose utilization, numerous autochthonous (native or wild-derived) yeasts isolated from natural environments harbor metabolic traits that have been naturally selected and enable effective pentose assimilation under challenging conditions. Understanding and harnessing this diversity is essential for advancing lignocellulosic biorefineries. This review synthesizes current knowledge on D-xylose-fermenting yeasts from natural ecosystems, with emphasis on their ecological diversity, taxonomic classification, physiological traits, and biotechnological relevance. Yeasts in genera such as Scheffersomyces, Spathaspora, Candida, and Meyerozyma exhibit efficient D-xylose metabolism via distinct enzymatic strategies, although redox balance, cofactor regeneration, and sugar transport remain key constraints. Many of these yeasts exhibit intrinsic tolerance to inhibitors derived from biomass pretreatment and adaptability to variations in oxygen availability, temperature, and osmotic stress, which are critical attributes for industrial applications. In addition, several species produce hydrolytic enzymes that partially degrade lignocellulosic substrates during fermentation, thereby supporting process integration and consolidation. Beyond ethanol production, D-xylose metabolism in yeasts can be redirected toward value-added bioproducts such as xylitol and organic acids, broadening the economic potential of lignocellulosic feedstocks. Advances in molecular taxonomy, adaptive evolution, metabolic engineering, and omics-based analyses have substantially improved fermentation performance and robustness, enabling more rational strain selection and targeted improvement. By combining phylogenetic-guided strain identification, adaptive and genetic improvement, systems-level characterization, and industrial process integration, this review provides a comprehensive framework for translating natural yeast diversity into efficient platforms for second-generation bioethanol and diversified bioprocesses. Such an integrated perspective is essential for overcoming current technical limitations and for advancing sustainable, biomass-based biorefineries.