Expression of Lactobacillus casei ATCC 393 beta-galactosidase encoded by plasmid pLZ15 in Lactococcus lactis CNRZ 1123.

Lactococcus lactis subsp. lactis CNRZ 1123, a Lac- derivative of CNRZ 1122 was transformed by electroporation with the Lactobacillus casei ATCC 393 plasmid pLZ15, which bears a beta-galactosidase gene. The transformants expressed a constitutive beta-galactosidase activity at a higher level than in Lact. casei, and in the cell-free extract two additional protein bands were detected by SDS-PAGE which could correspond to lactose metabolism enzymes. Both plasmid and beta-gal activity were stable in Lactococcus after 100 generations in glucose-containing medium.