Natural sweetening of food products by engineering Lactococcus lactis for glucose production.

We show that sweetening of food products by natural fermentation can be achieved by a combined metabolic engineering and transcriptome analysis approach. A Lactococcus lactis ssp. cremoris strain was constructed in which glucose metabolism was completely disrupted by deletion of the genes coding for glucokinase (glk), EII(man/glc) (ptnABCD), and the newly discovered glucose-PTS EII(cel) (ptcBAC). After introducing the lactose metabolic genes, the deletion strain could solely ferment the galactose moiety of lactose, while the glucose moiety accumulated extracellularly. Additionally, less lactose remained in the medium after fermentation. The resulting strain can be used for in situ production of glucose, circumventing the need to add sweeteners as additional ingredients to dairy products. Moreover, the enhanced removal of lactose achieved by this strain could be very useful in the manufacture of products for lactose intolerant individuals.