Highly Efficient Synthesis of Rare Sugars from Glycerol in Endotoxin-Free by Fermentation.

Rare sugars possess potential applications as low-calorie sweeteners, especially for anti-obesity and anti-diabetes. In this study, a fermentation biosystem based on the "DHAP-dependent aldolases strategy" was established for D-allulose and D-sorbose production from glycerol in endotoxin-free BL21 (DE3). Several engineering strategies were adopted to enhance rare sugar production. Firstly, the combination of different plasmids for , and expression was optimized. Then, the artificially constructed ribosomal binding site (RBS) libraries of , and genes were assembled individually and combinatorially. In addition, a peroxidase was overexpressed to eliminate the damage or toxicity from hydrogen peroxide generated by alditol oxidase (AldO). Finally, stepwise improvements in rare sugar synthesis were elevated to 15.01 g/L with a high yield of 0.75 g/g glycerol in a 3 L fermenter. This research enables the effective production of rare sugars from raw glycerol in high yields.