Lactic acid bacteria (LAB) are vital members of food microbes. Because they are healthy for human beings and animals, they have important application future in food and medicine fields. The genetic elements, existed outside the chromosome of LAB are excellent material for developing their vector systems. Recent years, with the endogenous plasmids of LAB removed, electrotransformation established and the expression signal elements cloned, a serial of vector-host systems with different usages have b...