Regulation of nitrogen metabolism in Lactobacillus delbrueckii subsp. lactis

BROWN, L.; VILLEGAS, J.M.; FADDA, S.; SAVOY DE GIORI, G.; SAAVEDRA, L.; MOZZI, F.; HEBERT, E.M.

Simposio; SIBAL 2016. V International Symposium on Lactic Acid Bacteria. Benefitting from Lactic Acid Bacteria. Progress in Health and Food.; 2016

Lactobacillus delbrueckii subsp. lactis CRL 581 is a thermophilic lactic acid bacterium, used as a starter culture for the manufacture of several fermented dairy products. This strain possesses a specialized proteolytic system that consists of a cell envelope-associated proteinase, named PrtL, transport systems to allow uptake of the resulting peptides, and several intracellular peptidases, which degrade peptides to amino acids. The proteolytic system of Lactobacillus has an essential role in bacterial growth, contributes to the flavor development of fermented products, and can release bioactive health beneficial peptides during milk fermentation. However, the production of bioactive peptides by L. delbrueckii subsp. lactis CRL 581 is repressed by the presence of peptides in the growth medium. Thus, in this work a genomic analysis of all genes involved in the proteolytic system of L. delbrueckii subsp. lactisCRL 581 was performed. In order to understand the effect of peptide supply on the proteolytic system of CRL 581 strain, the transcriptional and proteomic response of this system to the peptide supply was analyzed. 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 23 genes involved in the proteolytic system of L. delbrueckii subsp. lactis was examined after cell growth in a chemically defined medium (CDM) and CDM plus Casitone by qRT-PCR analysis.prtL, oppA1, optS, optA as well as oppDFBC and optBCDF operons were the highest expressed genes in CDM; their expression being repressed 6- to 115-fold by addition of Casitone to the medium. The proteomic approach confirmed the transcriptional analysis; an upregulation of PrtL, PepG, OppD and OptF was observed. Growth in CDM also led to the upregulation of proteins related to glycolysis, amino acids and purine metabolism. Contrariwise, a DNA-binding protein (YebC) was up-regulated by Casitone. This is the first report that correlates transcriptionaland proteomic analysis of L. delbrueckii subsp. lactis, and demonstrates that the nitrogen source of the medium modulates the biosynthesis of some components of the proteolytic system.