Presence of additional peptidases in Streptococcus thermophilus CNRZ 302 compared to Lactococcus lactis

International audienc

PepS from Streptococcus thermophilus

International audienc

Purification and characterization of a general aminopeptidase (St-PepN) from Streptococcus salivarius ssp. thermophilus CNRZ 302

International audienc

St-PepA, a Streptococcus thermophilus aminopeptidase with high specificity for acidic residues

International audienc

Cell-wall proteinases PrtS and PrtB have a different role in <em>Streptococcus thermophilus/Lactobacillus bulgaricus</em> mixed cultures in milk

International audienceThe manufacture of yoghurt relies on the simultaneous utilization of two starters: Streptococcus thermophilus and Lactobacillus delbrueckii subsp. bulgaricus (Lb. bulgaricus). A protocooperation usually takes place between the two species, which often results in enhanced milk acidification and aroma formation compared to pure cultures. Cell-wall proteinases of Lactococcus lactis and lactobacilli have been shown to be essential to growth in milk in pure cultures. In this study, the role of proteinases PrtS from S. thermophilus and PrtB from Lb. bulgaricus in bacterial growth in milk was evaluated; a negative mutant for the prtS gene of S. thermophilus CNRZ 385 was constructed for this purpose. Pure cultures of S. thermophilus CNRZ 385 and its PrtS-negative mutant were made in milk as well as mixed cultures of S. thermophilus and Lb. bulgaricus: S. thermophilus CNRZ 385 or its PrtS-negative mutant was associated with several strains of Lb. bulgaricus, including a PrtB-negative strain. The pH and growth of bacterial populations of the resulting mixed cultures were followed, and the Lactobacillus strain was found to influence both the extent of the benefit of Lb. bulgaricus/S. thermophilus association on milk acidification and the magnitude of S. thermophilus population dominance at the end of fermentation. In all mixed cultures, the sequential growth of S. thermophilus then of Lb. bulgarius and finally of both bacteria was observed. Although proteinase PrtS was essential to S. thermophilus growth in milk in pure culture, it had no effect on bacterial growth and thus on the final pH of mixed cultures in the presence of PrtB. In contrast, proteinase PrtB was necessary for the growth of S. thermophilus, and its absence resulted in a higher final pH. From these results, a model of growth of both bacteria in mixed cultures in milk is proposed

The role of aminopeptidase PepS in the growth of <em>Streptococcus thermophilus</em> is not restricted to nitrogen nutrition

International audienceAims: To investigate the effect of an absence of aminopeptidase PepS on the growth of Streptococcus thermophilus on different media and at different temperatures. Methods and Results: Using gene interruption, a negative mutant of the Strep. thermophilus CNRZ385 strain was constructed for the aminopeptidase PepS (strain D pepS). Checks were first of all made using biochemical assays that the D pepS strain lacks the peptide hydrolase activity of aminopeptidase PepS. It was demonstrated that the absence of the aminopeptidase PepS exerted a negative effect on growth whatever the culture medium (M17, chemically defined medium, milk). The role of aminopeptidase PepS in growth was enhanced at a high temperature (45°C vs 37°C). The D pepS strain was more resistant to lysozyme than the wild-type strain. Conclusions: We were able to demonstrate that aminopeptidase PepS probably plays a pleiotropic role through its involvement in growth via nitrogen nutrition, as well as via other cellular functions⁄metabolisms (such as peptidoglycane metabolism). Significance and Impact of the Study: This study constitutes the first report on the role of a member of the M29 MEROPS family of metallopeptidases (http:// merops.sanger.ac.uk/)

Streptococcus thermophilus cell wall-anchored proteinase: release, purification, and biochemical and genetic characterization

International audienc

4 vertus de la fermentation

Interview par la journaliste Audrey Vaugrent