Regulation of PrtL of Lactobacillus delbrueckii ssp. lactis crl 581 by the peptide content of the growth medium

BROWN, L.; VILLEGAS, J.; SAVOY DE GIORI, E.; HEBERT, E. M.

San Miguel de Tucumán

Simposio; IV Simposio Internacional de Bacterias Lácticas (SIBAL); 2013

Lactobacillus delbrueckii ssp. lactis CRL 581 is a thermophilic lactic acid bacterium (LAB), used as a starter culture for the manufacture of several fermented dairy products. This strain possess 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 into amino acids. Thus, PrtL has an essential role in bacterial growth as well as it contributes to the development of the organoleptic properties of hard cheeses and the release of bioactive health-beneficial peptides from milk proteins. Previously, we had demonstrated that PrtL activity was remarkably reduced in cells grown in the peptide-rich medium MRS or in a chemically defined medium (CDM) supplemented with 1% Casitone, compared with those found in a peptide-free CDM. In this study, transcriptomic and biochemical analyses were combined to assess the dynamic response of L. delbrueckii ssp. lactis CRL 581 cells growing in media with different peptide content. L. delbrueckii ssp. lactis CRL 581 was grown in CDM, a complex medium MRS and CDM containing 1% casitone and reverse transcription quantitative PCR (RT-PCR) was used to quantify the prtL transcript level, with rpoD (RNA polymerase, sigma 70 factor) and recA (recombinase A) as normalizing genes. The prtL gene was repressed 45-fold and 119-fold when CRL 581 cells were grown in CDM + 1% Casitone and MRS, respectively. These results were confirmed by SDS-PAGE and MALDI-TOF analysis, where PrtL was observed only in the peptide-free medium. This is the first study describing the prtL gene regulation by the peptide content in the growth media in L. delbrueckii ssp. lactis.