Production of Optically Pure ()-3-Hydroxy-γ-butyrolactone from d-Xylose Using Engineered .

Biocatalysis has advantages in asymmetric synthesis due to the excellent stereoselectivity of enzymes. The present study established an efficient biosynthesis pathway for optically pure ()-3-hydroxy-γ-butyrolactone [()-3HγBL] production using engineered . We mimicked the 1,2,4-butanetriol biosynthesis route and constructed a five-step pathway consisting of d-xylose dehydrogenase, d-xylonolactonase, d-xylonate dehydratase, 2-keto acid decarboxylase, and aldehyde dehydrogenase. The engineered strain harboring the five enzymes could convert d-xylose to 3HγBL with glycerol as the carbon source. Stereochemical analysis by chiral GC proved that the microbially synthesized product was a single isomer, and the enantiomeric excess (ee) value reached 99.3%. ()-3HγBL production was further enhanced by disrupting the branched pathways responsible for d-xylose uptake and intermediate reduction. Fed-batch fermentation of the best engineered strain showed the highest ()-3HγBL titer of 3.5 g/L. The volumetric productivity and molar yield of ()-3HγBL on d-xylose reached 50.6 mg/(L·h) and 52.1%, respectively. The final fermentation product was extracted, purified, and confirmed by NMR. This process utilized renewable d-xylose as the feedstock and offered an alternative approach for the production of the valuable chemical.