Microbial production of D-arabitol from D-xylose by engineered Trichosporonoides oedocephalis: Fermentation performance and salt-stress transcriptional responses

D-Arabitol is a naturally occurring pentitol widely used as a low-calorie sweetener and functional ingredient in food formulations. However, microbial production from biomass-derived D-xylose remains constrained by low product titers, limited conversion yields, and the lack of efficient engineered xylose-utilizing strains. In this study, the osmotolerant yeast Trichosporonoides oedocephalis was engineered to produce D-arabitol from D-xylose through the introduction of a heterologous XI (xylose isomerase)-ArDH (arabitol dehydrogenase) pathway. Fermentation conditions relevant to high-sugar food systems were systematically optimized. Compared with the addition of 0.5 g/L KCl (yielding 17.69 g/L D-arabitol), supplementation with 30 g/L KCl significantly increased D-arabitol production, reaching 35.13 g/L in shake flasks and 43.91 g/L in a 5-L bioreactor. Semi-batch fermentation further increased the final titer to 55.21 g/L with a yield of 0.280 g/g. Kinetic analysis indicated predominantly growth-associated D-arabitol formation under these conditions (Luedeking-Piret coefficient, α = 0.61). Comparative transcriptomic analysis revealed that KCl supplementation induced phase-dependent physiological responses, including enrichment of nucleotide metabolism and coordinated transcriptional regulation of central carbon metabolism during exponential growth, as well as increased expression of sugar transport and protein maintenance pathways during the stationary phase. These changes were accompanied by elevated activities of xylose isomerase and arabitol dehydrogenase, suggesting that salt stress is associated with efficient carbon utilization and the biosynthesis of polyols. Importantly, KCl represents a food-compatible and physiologically relevant process regulator, highlighting the potential of salt-mediated metabolic regulation for food-related polyol fermentations. These findings provide an effective strategy for food-related D-arabitol production from xylose and offer insights into salt-associated metabolic regulation in yeast.