REGULATION OF NITROGEN METABOLISM IN Lactobacillus delbrueckii subsp. lactis

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

San Miguel de Tucumán

Simposio; International Symposium on Lactic Acid Bacteria; 2016

CERELA_CONICET

Lactobacillus delbrueckii subsp. lactis CRL 581 is a thermophilic lactic acid bacterium, usedas a starter culture for the manufacture of several fermented dairy products. This strain possessesa specialized proteolytic system that consists of a cell envelope-associated proteinase,named PrtL, transport systems to allow uptake of the resulting peptides, and severalintracellular peptidases, which degrade peptides to amino acids. The proteolytic system ofLactobacillus has an essential role in bacterial growth, contributes to the flavor developmentof fermented products, and can release bioactive health beneficial peptides during milk fermentation.However, the production of bioactive peptides by L. delbrueckii subsp. lactis CRL581 is repressed by the presence of peptides in the growth medium. Thus, in this work agenomic 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 proteolyticsystem of CRL 581 strain, the transcriptional and proteomic response of this system tothe 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) wereidentified by in silico analysis. The influence of the peptide supply on the transcription of 23genes involved in the proteolytic system of L. delbrueckii subsp. lactis was examined after cellgrowth 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 expressedgenes in CDM; their expression being repressed 6- to 115-fold by addition of Casitone to themedium. The proteomic approach confirmed the transcriptional analysis; an upregulationof PrtL, PepG, OppD and OptF was observed. Growth in CDM also led to the upregulation ofproteins related to glycolysis, amino acids and purine metabolism. Contrariwise, a DNA-bindingprotein (YebC) was up-regulated by Casitone. This is the first report that correlates transcriptionaland proteomic analysis of L. delbrueckii subsp. lactis, and demonstrates that thenitrogen source of the medium modulates the biosynthesis of some components of the proteolyticsystem.