Engineering of sugar metabolism in Lactococcus lactis

Short English Summary Lactococcus lactis is a lactic acid bacterium used in the dairy industry. This thesis decribes the genetic engineering performed on the sugar metabolism of L. lactis. Besides our fundamental interest for sugar metabolism and its regulation in L. lactis, this project had the interest of the dairy industry. L. lactis strains were made with improved lactose and galactose consumption rates, to produce dairy products with lower (ga)lactose concentrations. This is beneficial for individuals suffering from lactose intolerance of galactosemia. These people cannot consume lactose or galactose respectively, or they will get sick. Therefore they have a life-long dietary restriction for products containing lactose or galactose. Normally, L. lactis prefers the sugar glucose for growth, and the bacterium will first use all the glucose from the growth medium. To make a strain preferring (ga)lactose, resulting in lower (ga)lactose concentrations in the end-product, glucose metabolism was disrupted in L. lactis. The glucose left-over in the medium can be used as natural sweetener. Fundamentally, also some new discoveries were done. This work defined a new glucose transporter and a new galactose transporter in L. lactis. Furthermore, the three different glucose transporters were characterized. Also the regulatory effect of the use of the different transporters on the total glucose metabolism was investigated. Besides this, the gene coding for the enzyme being the bottleneck in galactose metabolism was determined and the enzyme was characterized.