Metabolic adaptation of Lactococcus lactis in the digestive tract: the example of response to lactose.

Lactococcus lactis is a model of food-grade lactic acid bacterium, which can durably colonize the digestive tract of germ-free mice. To study in vivo the bacterial adaptation to a novel nutritional resource brought by alimentation, the lactose-catabolizing strain IL2661 of L. lactis was established in monoxeny in mice.

Beta-glucuronidase in human intestinal microbiota is necessary for the colonic genotoxicity of the food-borne carcinogen 2-amino-3-methylimidazo[4,5-f]quinoline in rats.

2-amino-3-methylimidazo[4,5-f]quinoline (IQ) is a genotoxic/carcinogenic compound formed in meat and fish during cooking. Following absorption in the upper part of the gastrointestinal tract, IQ is mainly metabolized in the liver by xenobiotic-metabolizing enzymes. Among them, UDP-glucuronosyl transferases lead to harmless glucuronidated derivatives that are partly excreted via the bile into the digestive lumen, where they come into contact with the resident microbiota.

Beta-galactosidase production by Streptococcus thermophilus is higher in the small intestine than in the caecum of human-microbiota-associated mice after lactose supplementation.

Transit kinetics and survival rates of a bacterial species from yoghurt (i.e. Streptococcus thermophilus strain FBI3) were examined in different digestive compartments of gnotoxenic and human-microbiota-associated mice.

Conservation of key elements of natural competence in Lactococcus lactis ssp.

Natural competence is active in very diverse species of the bacterial kingdom and probably participates in horizontal gene transfer. Recently, the genome sequence of various species, including Lactococcus lactis, revealed the presence of homologues of competence genes in bacteria, which were not previously identified as naturally transformable. We investigated the conservation among lactococcal strains of key components of the natural competence process in streptococci: (i) comX which encodes a sigma factor, allowing the expression of the late competence genes involved in DNA uptake, (ii) its recognition site, the cin-box and (iii) dprA which encodes a protein shown to determine the fate of incoming DNA.

Lactococcus lactis AbiD1 abortive infection efficiency is drastically increased by a phage protein.

Sensitivity of phage bIL66 to the AbiD1 Lactococcus lactis abortive infection mechanism was previously shown to be determined by the phage middle-time-expressed operon composed of four orfs. Using spontaneous bIL66 mutants resistant to AbiD1, we established that this sensitivity is determined by the orf1 encoded protein. Overproduction of Orf1 in trans in AbiD1(+) cells was shown to increase AbiD1 efficiency on both wild-type phage bIL66 and mutants resistant to AbiD1.

The peptidyl-prolyl isomerase motif is lacking in PmpA, the PrsA-like protein involved in the secretion machinery of Lactococcus lactis.

The prsA-like gene from Lactococcus lactis encoding its single homologue to PrsA, an essential protein triggering the folding of secreted proteins in Bacillus subtilis, was characterized. This gene, annotated pmpA, encodes a lipoprotein of 309 residues whose expression is increased 7- to 10-fold when the source of nitrogen is limited. A slight increase in the expression of the PrsA-like protein (PLP) in L.

Sequence analysis of the lactococcal bacteriophage bIL170: insights into structural proteins and HNH endonucleases in dairy phages.

The complete 31754 bp genome of bIL170, a virulent bacteriophage of Lactococcus lactis belonging to the 936 group, was analysed. Sixty-four ORFs were predicted and the function of 16 of them was assigned by significant homology to proteins in databases. Three putative homing endonucleases of the HNH family were found in the early region.

Streptococcus thermophilus is able to produce a beta-galactosidase active during its transit in the digestive tract of germ-free mice.

This work presents data on the application of a bacterial luciferase used to monitor gene expression of Streptococcus thermophilus in the digestive tract. The main result is that the bacterium was able to produce an active beta-galactosidase in the digestive tract, although it did not multiply during its transit. This production was enhanced when lactose (the inducer) was added to the diet.