Abstract: A DNA sequence suitable for the controlled transcription and/or expression of a variety of different genes in bacteria, preferably gram positive bacteria is provided. In particular, the DNA sequence includes the promoter and the gene coding for the lac repressor of the lac operon of Lactobacillus delbrueckii with a DNA sequence coding for a gene product of interest being arranged inbetween.

Abstract: The use of a IS-element as a tools for genetically modifying the genome of Lactobacillus delbrueckii or Lactobacillus helveticus. An IS-element, originating from Lactobacillus delbrueckii selected from the DNA sequences SEQ ID NO: 7-10 or functional derivatives thereof. A Lactobacillus delbrueckii or Lactobacillus helveticus providing a gene encoding, or affecting the production of, enzymes producing secondary metabolites, the &bgr;-galactosidase, the cell wall protease, the catabolite control protein A, the lactate dehydrogenase, a glycosyltransferase, a restriction system, a lysogenic prophage, or the permease of the lac operon, wherein the gene is inactivated by insertion of at least one IS-element. The use of the above-mentioned Lactobacillus delbrueckii or Lactobacillus helveticus for the preparation of a fermented product.

Abstract: Recombinant strains of L. johnsonii which have capacities of surviving passage through the intestine, adhering to human intestinal cells and increasing phagocytosis of macrophages and which have a sequence of gene coding which is an L. johnsonii strain sequence of gene coding for D-lactate dehydrogenase modified so that the recombinant strain produces only L(+)-lactate.

Abstract: A recombinant strain of L. johnsonii which has capacities of surviving passage through the intestine, adhering to human intestinal cells and increasing phagocytosis of macrophages and which has a gene sequence code for D-lactate dehydrogenase which is a modified L. johnsonii gene sequence code and which produces only L(+)-lactate.