Peptide utilization by Lactococcus lactis and Leuconostoc mesenteroides.

To explain the competition for nitrogenous nutrients observed in mixed strain cultures of Lactococcus lactis and Leuconostoc mesenteroides, the utilization of peptides as a source of essential amino acids for growth in a chemically defined medium was compared in 12 strains of dairy origin. Both species were multiple amino acid auxotrophs and harboured a large set of intracellular peptidases. Lactococcus lactis can use a wide variety of peptides up to 13 amino acid residues whereas Leuc.

Factors affecting exocellular polysaccharide production by Lactobacillus delbrueckii subsp. bulgaricus grown in a chemically defined medium.

We developed a chemically defined medium (CDM) containing lactose or glucose as the carbon source that supports growth and exopolysaccharide (EPS) production of two strains of Lactobacillus delbrueckii subsp. bulgaricus. The factors found to affect EPS production in this medium were oxygen, pH, temperature, and medium constituents, such as orotic acid and the carbon source.

Isolation and properties of Lactococcus lactis subsp. lactis biovar diacetylactis CNRZ 483 mutants producing diacetyl and acetoin from glucose.

Following treatment with the mutagen N-methyl-N'-nitro-N-nitrosoguanidine, three mutants of Lactococcus lactis subsp. lactis biovar diacetylactis CNRZ 483 that produced diacetyl and acetoin from glucose were isolated. The lactate dehydrogenase activity of these mutants was strongly attenuated, and the mutants produced less lactate than the parental strain.

Specificity of peptide transport systems in Lactococcus lactis: evidence for a third system which transports hydrophobic di- and tripeptides.

A proton motive force-driven di-tripeptide carrier protein (DtpT) and an ATP-dependent oligopeptide transport system (Opp) have been described for Lactococcus lactis MG1363. Using genetically well-defined mutants in which dtpT and/or opp were inactivated, we have now established the presence of a third peptide transport system (DtpP) in L. lactis.

Evidence for Two Bacteriocins Produced by Carnobacterium piscicola and Carnobacterium divergens Isolated from Fish and Active Against Listeria monocytogenes.

Lactic acid bacteria (LAB) isolated from fish products (fresh fish, smoked and marinated fish, fish intestinal tract) were screened for bacteriocin production and immunity in conditions eliminating the effects of organic acids and hydrogen peroxide. Twenty-two isolates which were found to produce bacteriocin-like compounds were identified as Carnobacteria, Lactococci and Enterococci on the basis of morphological examination, gas production from glucose, growth temperatures, configuration of lactic acid, carbohydrates fermentation and deamination of arginine. Two Carnobacteria named V1 and V41 were selected for further studies and identified by DNA-DNA hybridization as Carnobacterium piscicola and Carnobacterium divergens , respectively.