Biosynthesis of D-threitol from biomass-derived xylose by engineering Trichosporonoides oedocephalis

Xylose is the major pentose and the second most abundant sugar in the lignocellulosic feedstock. Metabolic engineering approaches have been employed to enhance the utilization rate of xylose in yeast. We previously modified Trichosporonoides oedocephalis ATCC 16958 and produced sugar alcohols, including xylitol and erythritol. D-threitol is a rare sugar that cannot be obtained directly from xylose conversion through fermentation. In this study, T. oedocephalis gained xylose assimilation activity by introducing ribulose-5-phosphate isomerase B from Ochrobactrum sp. and xylitol dehydrogenase from the yeast Scheffersomyces stipitis CBS 6054 for D-threitol production. Optimization of the composition of the medium ultimately led to an increase in the yield of D-threitol to 5.18 g/L. In addition, this study also analyzed the kinetics of the fermentation process, including cell growth, D-threitol biosynthesis and xylose consumption. Cell growth conformed to the logistics curve, and D-threitol synthesis and substrate consumption conformed to the Luedeking-Piret curve showing a growth-partially correlated type. This study demonstrated the potential of engineered yeast to synthesize high value-added products from biomass-derived xylose.