Surface Display of Heterologous β -Galactosidase in Food-Grade Recombinant Lactococcus lactis

β -Galactosidase is an essential enzyme for the metabolism of lactose in human beings and has an important role in the treatment of lactose intolerance (LI). β -Galactosidase expressed by intestinal microflora, such as lactic acid bacteria (LAB), also alleviates LI. A promising approach to LI management is to exploit a food-grade LAB delivery system that can inhabit the human intestine and overproduce β -galactosidase. In this study, we constructed a food-grade β -galactosidase surface display delivery system and then integrated into the chromosome of Lactococcus lactis ( L. lactis ) NZ9000 using recombination. Western blot and immunofluorescence analyses confirmed that β -galactosidase was expressed on the cell surface of recombinant L. lactis stain NZ-SDL. The whole-cell biocatalyst exhibits V max and K m values of 121.38 ± 7.17 U ONPG /g and 65.36 ± 5.54 mM, based on ONPG hydrolysis. The optimum temperature for enzyme activity is 37 °C and the optimum pH is 5.0. Activity of the whole-cell biocatalyst is promoted by Mg 2+ , Ca 2+ , and K + , but inhibited by Zn 2+ , Fe 2+ , and Fe 3+ . The system has a thermal stability similar to purified β -galactosidase but better pH stability, and is also more stable in artificial intestinal juice. Oral administration and intraperitoneal injections of NZ-SDL in mice cause no detectable health effects. In conclusion, we have successfully constructed a food-grade gene expression system in L. lactis that displays β -galactosidase on the cell surface. This system exhibits good enzyme activity and stability in vitro, and is safe in vivo. It is therefore a promising candidate for use in LI management.