Relationship between carbon catabolite repression and the biosynthesis regulation of the prolidase PepQ from Lactobacillus delbrueckii ssp bulgaricusCNRZ 397

Lactobacillus delbrueckii ssp. bulgaricus CNRZ 397 (L. bulgaricus) displays several enzymes specific of proline-containing peptides. We focused on the prolidase PepQ which specifically cleaves X-Pro dipeptides. PepQ biosynthe sis was previously shown to be independent of the peptide concentration of the culture medium in contrast to the cell surface proteinase PrtB and seve ral aminopeptidases. Regulation of PepQ biosynthesis can be explained by th e genetic organization of the region pepR1-cre-pepQ. The pepR1 gene encodes a CcpA-like regulator and its promoter harbors a cre site located immediat ely upstream of pepQ. Expression of fusions cre-pepQ-lacZ and pepQ-lacZ in Bacillus subtilis showed that, under glucose conditions, the regulator CcpA acts as a transcriptional activator of pepQ expression. Analysis of PepQ b iosynthesis in L. bulgaricus cells grown in different media is in agreement with a regulation dependent on carbohydrates.