Lucia Brown - Academia.edu (original) (raw)

Papers by Lucia Brown

Research paper thumbnail of YebC, a putative transcriptional factor involved in the regulation of the proteolytic system of Lactobacillus

Scientific Reports, 2017

The proteolytic system of Lactobacillus plays an essential role in bacterial growth, contributes ... more The proteolytic system of Lactobacillus plays an essential role in bacterial growth, contributes to the flavor development of fermented products, and can release bioactive health-beneficial peptides during milk fermentation. In this work, a genomic analysis of all genes involved in the proteolytic system of L. delbrueckii subsp. lactis CRL 581 was performed. Genes encoding the cell envelopeassociated proteinase, two peptide transport systems, and sixteen peptidases were identified. 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 supplemented with Casitone. prtL, oppA 1 , optS, optA genes as well as oppDFBC and optBCDF operons were the most highly expressed genes in CDM; their expression being repressed 6-to 115-fold by the addition of peptides. The transcriptional analysis was confirmed by proteomics; the up-regulation of the PrtL, PepG, OppD and OptF proteins in the absence of peptides was observed while the DNA-binding protein YebC was up-regulated by peptides. Binding of YebC to the promoter region of prtL, oppA 1 , and optS, demonstrated by electrophoretic mobility shift assays, showed that YebC acts as a transcriptional repressor of key proteolytic genes. Lactobacillus (L.) delbrueckii subsp. lactis is a homofermentative thermophilic lactic acid bacterium (LAB) widely used as starter culture in dairy fermentation processes, such as fermented sour milks and Swiss-and Italian-type cheeses. Comparative genomic analysis of lactobacilli revealed that amino acid biosynthetic pathways are deficient to a different extent in LAB, resembling the adaptation to specific-niches 1, 2. For instance, dairy LAB such as L. delbrueckii subsp. lactis, L. delbrueckii subsp. bulgaricus and L. helveticus have lost the majority of their amino acid biosynthetic genes 3, 4 , and therefore, depend on the use of exogenous nitrogen sources for optimal growth 5, 6. As the concentration of amino acids and small peptides in milk is very limited 7 , the proteolytic system of LAB is crucial to obtain essential amino acids from caseins during growth in this substrate, thereby ensuring a successful fermentation. This proteolytic system consists of (i) an extracellular cell envelope-associated proteinase (CEP) that hydrolyzes caseins into oligopeptides; (ii) specialized transport systems that take up peptides into the cell; and (iii) several intracellular peptidases, which degrade peptides into amino acids 2, 8, 9. Furthermore, this proteolytic system contributes to the flavor and texture development of fermented products 9, 10 , and may release bioactive health-beneficial peptides during milk fermentation 8-11. Among LAB, the proteolytic system of Lactococcus (Lc.) has received considerably more attention than that of Lactobacillus 2, 9. However, in the last years the proteolytic system of lactobacilli has gained relevance because of their ability to generate bioactive peptides from casein during milk fermentation processes 8, 10. L. delbrueckii subsp. lactis CRL 581, a strain isolated from a homemade Argentinian hard cheese, possesses a CEP (PrtL) that is able to release a series of bioactive health-beneficial peptides (i.e., anti-inflammatory, antihypertensive, and phosphopeptides) from αand β-caseins 11, 12. It was observed that the production of bioactive peptides by PrtL was repressed by the peptide content of the growth medium 7. In Lc. lactis, the transcriptional regulator CodY is responsible for repression of several genes (prtP/prtM, opp-pepO1, pepD, pepN, pepC, and pepX) of the proteolytic

Research paper thumbnail of Lactic Acid Bacteria as Cell Factories for the Generation of Bioactive Peptides

Protein & Peptide Letters, 2017

There is a growing interest in the incorporation of functional foods in the daily diet to achieve... more There is a growing interest in the incorporation of functional foods in the daily diet to achieve health promotion and disease risk reduction. Numerous studies have focused on the production of biologically active peptides as nutraceuticals and functional food ingredients due to their health benefits. These short peptides, displaying antihypertensive, antioxidant, mineral binding, immunomodulatory and antimicrobial activities are hidden in a latent state within the primary sequences of food proteins requiring enzymatic proteolysis for their release. While microbial fermentation is one of the major and economically most convenient processes used to generate bioactive peptides, lactic acid bacteria (LAB) are widely used as starter cultures for the production of diverse fermented foods. This article reviews the current knowledge on LAB as cell factories for the production of bioactive peptides from a variety of food protein sources. These microorganisms depend on a complex proteolytic system to ensure successful fermentation processes. In the dairy industry, LAB containing cell envelope-associated proteinases (CEPs) are employed as biocatalysts for the first step of casein breakdown releasing bioactive peptides during milk fermentation. A better understanding of the functionality and regulation of the proteolytic system of LAB opens up future opportunities for the production of novel food-derived compounds with potential health-promoting properties.

Research paper thumbnail of YebC, a putative transcriptional factor involved in the regulation of the proteolytic system of Lactobacillus

Scientific Reports, 2017

The proteolytic system of Lactobacillus plays an essential role in bacterial growth, contributes ... more The proteolytic system of Lactobacillus plays an essential role in bacterial growth, contributes to the flavor development of fermented products, and can release bioactive health-beneficial peptides during milk fermentation. In this work, a genomic analysis of all genes involved in the proteolytic system of L. delbrueckii subsp. lactis CRL 581 was performed. Genes encoding the cell envelopeassociated proteinase, two peptide transport systems, and sixteen peptidases were identified. 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 supplemented with Casitone. prtL, oppA 1 , optS, optA genes as well as oppDFBC and optBCDF operons were the most highly expressed genes in CDM; their expression being repressed 6-to 115-fold by the addition of peptides. The transcriptional analysis was confirmed by proteomics; the up-regulation of the PrtL, PepG, OppD and OptF proteins in the absence of peptides was observed while the DNA-binding protein YebC was up-regulated by peptides. Binding of YebC to the promoter region of prtL, oppA 1 , and optS, demonstrated by electrophoretic mobility shift assays, showed that YebC acts as a transcriptional repressor of key proteolytic genes. Lactobacillus (L.) delbrueckii subsp. lactis is a homofermentative thermophilic lactic acid bacterium (LAB) widely used as starter culture in dairy fermentation processes, such as fermented sour milks and Swiss-and Italian-type cheeses. Comparative genomic analysis of lactobacilli revealed that amino acid biosynthetic pathways are deficient to a different extent in LAB, resembling the adaptation to specific-niches 1, 2. For instance, dairy LAB such as L. delbrueckii subsp. lactis, L. delbrueckii subsp. bulgaricus and L. helveticus have lost the majority of their amino acid biosynthetic genes 3, 4 , and therefore, depend on the use of exogenous nitrogen sources for optimal growth 5, 6. As the concentration of amino acids and small peptides in milk is very limited 7 , the proteolytic system of LAB is crucial to obtain essential amino acids from caseins during growth in this substrate, thereby ensuring a successful fermentation. This proteolytic system consists of (i) an extracellular cell envelope-associated proteinase (CEP) that hydrolyzes caseins into oligopeptides; (ii) specialized transport systems that take up peptides into the cell; and (iii) several intracellular peptidases, which degrade peptides into amino acids 2, 8, 9. Furthermore, this proteolytic system contributes to the flavor and texture development of fermented products 9, 10 , and may release bioactive health-beneficial peptides during milk fermentation 8-11. Among LAB, the proteolytic system of Lactococcus (Lc.) has received considerably more attention than that of Lactobacillus 2, 9. However, in the last years the proteolytic system of lactobacilli has gained relevance because of their ability to generate bioactive peptides from casein during milk fermentation processes 8, 10. L. delbrueckii subsp. lactis CRL 581, a strain isolated from a homemade Argentinian hard cheese, possesses a CEP (PrtL) that is able to release a series of bioactive health-beneficial peptides (i.e., anti-inflammatory, antihypertensive, and phosphopeptides) from αand β-caseins 11, 12. It was observed that the production of bioactive peptides by PrtL was repressed by the peptide content of the growth medium 7. In Lc. lactis, the transcriptional regulator CodY is responsible for repression of several genes (prtP/prtM, opp-pepO1, pepD, pepN, pepC, and pepX) of the proteolytic

Research paper thumbnail of Lactic Acid Bacteria as Cell Factories for the Generation of Bioactive Peptides

Protein & Peptide Letters, 2017

There is a growing interest in the incorporation of functional foods in the daily diet to achieve... more There is a growing interest in the incorporation of functional foods in the daily diet to achieve health promotion and disease risk reduction. Numerous studies have focused on the production of biologically active peptides as nutraceuticals and functional food ingredients due to their health benefits. These short peptides, displaying antihypertensive, antioxidant, mineral binding, immunomodulatory and antimicrobial activities are hidden in a latent state within the primary sequences of food proteins requiring enzymatic proteolysis for their release. While microbial fermentation is one of the major and economically most convenient processes used to generate bioactive peptides, lactic acid bacteria (LAB) are widely used as starter cultures for the production of diverse fermented foods. This article reviews the current knowledge on LAB as cell factories for the production of bioactive peptides from a variety of food protein sources. These microorganisms depend on a complex proteolytic system to ensure successful fermentation processes. In the dairy industry, LAB containing cell envelope-associated proteinases (CEPs) are employed as biocatalysts for the first step of casein breakdown releasing bioactive peptides during milk fermentation. A better understanding of the functionality and regulation of the proteolytic system of LAB opens up future opportunities for the production of novel food-derived compounds with potential health-promoting properties.