Efficient one-step conversion of low-cost lactose to high-yield D-tagatose in Corynebacterium glutamicum using L-arabinose isomerase

D-tagatose, a functional rare sugar, has physiological effects such as lowering blood sugar and anti-caries. However, research on the industrial production of D-tagatose has primarily focused on Escherichia coli , limiting application in the food field. In this study, a cell factory for efficient synthesis of D-tagatose was constructed using the GRAS strain Corynebacterium glutamicum . Firstly, the key enzyme L-arabinose isomerase from Lactobacillus fermentum was screened. Secondly, by rational design, the optimal mutant D390V/H339P significantly enhanced enzyme activity by 40.65 % and improved thermostability. Subsequently, a dual-enzyme coupled whole-cell system was established by regulating the ratio of β-galactosidase and L-arabinose isomerase by RBS optimization. After optimizing the catalytic system, 101.42 g/L D-tagatose was produced from 400 g/L lactose, and the conversion rate reached 25.12 % in 5 L fermenter, which is the highest yield using lactose as substrate and GRAS strain as chassis cells. This research laid a foundation for the industrial application of food-grade D-tagatose.