Biotechnological production of d-tagatose from lactose using metabolically engineering Lactiplantibacillus plantarum

d-Tagatose is a low-calorie sweetener with health benefits. To produce d-tagatose from lactose, a metabolic engineering Lactiplantibacillus plantarum was constructed. The galactokinase gene galK was inactivated and the original promoter of β-galactosidase gene lacLM was replaced by a strong lactose/galactose-inducible promoter PlacLM-35-10 in Lpb. plantarum WCFS1. Subsequently, the l-arabinose isomerase gene AraA derived from Lactobacillus casei SDMCC050286 was over-expressed. A recombinant strain with the potential of d-tagatose production was obtained. Its galactose metabolism pathway was blocked, and β-galactosidase activity was increased by 5.4-folds. Meanwhile, the heterogeneous l-arabinose isomerase was highly expressed in this strain. The optimal conditions for d-tagatose production by resting cells of the recombinant strain were at 65 °C and pH 7.5. Furthermore, the conversion rate of d-tagatose from 175 g/L lactose reached 33% at 56 h. This study verified the feasibility of one-pot production of d-tagatose from lactose by engineering strain of Lpb. plantarum, thereby laying down the foundation for industrial usage of lactose.