MOLECULAR TOOLS FOR THE GENETIC-MODIFICATION OF DAIRY LACTOBACILLI

The possibility that starter strains of lactic acid bacteria may be de liberately endowed with desired properties by the use of molecular tec hniques is an attractive perspective for the dairy industry. To contri bute to the development of appropriate genetic modification systems fo r lactobacilli, we tested the accessibility of these bacteria to elect rotransformation, and we designed a strategy for the construction and use of food-grade plasmid vectors. Successful electroporation was achi eved with two dairy strains of Lactobacillus casei and Lb. delbrueckii ssp. lactis. Aiming at the construction of safety vectors, replicons of cryptic plasmids from various starter lactobacilli were identified and characterised on the molecular and functional levels. To provide t he resulting vectors with food-grade markers, a number of peptidase an d transport genes of the proteolytic system of Lb. delbrueckii ssp. la ctis DSM7290 were isolated and sequenced, and features of the respecti ve gene products were investigated. Over expression of two of these pe ptidase genes in Lactobacillus had no effects on cell growth, but alte red the composition of the growth medium.