Global analysis of the proteolytic system of Lactobacillus delbrueckii subsp. lactis

L BROWN; J VILLEGAS; L SAAVEDRA; F. MOZZI; E M HEBERT

Egmond aan Zee

Simposio; 12th International Symposium on Lactic Acid Bacteria; 2017

Lactobacillus delbrueckii subsp. lactis CRL 581 is a thermophilic lactic acid bacterium used as a starter culture in the cheese industry. This strain has a specialized proteolytic system essential for bacterial growth in milk, which is also involved in flavor development of fermented products and can release health-beneficial bioactive peptides. Considering the industrial importance of this system and the scarce information about its regulation in Lactobacillus, we aimed to perform a global analysis of all genes involved in the proteolytic system of L. delbrueckii subsp. lactis CRL 581 and to study the effect of the peptide supply on the expression of several components of this system. Genes encoding the cell envelope-associated proteinase (prtL), peptide transport systems (opp and opt) and sixteen peptidases (pepM, pepP, pepC, pepA, pepO, pepN, pepF, pepR, pepD, pepG, pepI, pepQ, pepT, pepV, pepX and pepL) were identified by in silico analysis. The influence of the peptide supply on the transcription of these 23 genes when L. delbrueckii subsp. lactis grew in a chemically defined medium (CDM) and CDM plus Casitone was examined by qRT-PCR analysis. prtL, oppA1, optS, optA and the oppDFBC and optBCDF operons were the highest expressed genes in CDM; their expression being repressed 6- to 115-fold by the presence of Casitone. Consistently, the proteomic approach showed an upregulation of PrtL, PepG, OppD and OptF. Also, growth in CDM led to the upregulation of proteins related to glycolysis, amino acids and purine metabolism. This is the first report to correlate transcriptional and proteomic analysis of the proteolytic system of L. delbrueckii subsp. lactis demonstrating that the biosynthesis of some components are regulated by the nitrogen source of the medium.