Abstract
Lactococcus lactis is frequently used in food production. It will be a great benefit to us, if Lactococcus lactis can produce large amount of wanted proteins, and secrete them into the medium. We use tandem promoter (PnisR, PnisA) to enhance the expression of nisI. PnisR-PnisA-nisI showed higher nisin resistence than PnisA-nisI did. PnisA can not be induced by galactose and lactose in lactococcus lactis MG1363. In fact, galactose and lactose may inhibit PnisA in high concentration of nisin. We fused signal sequence usp45 to lipid-free nisI, which could secrete into medium, but neither PnisR-PnisA or PnisA is strong enough to express more proteins, according to the result of SDS-PAGE.