title: Adaptation to high salt in Lactobacillus: role of peptides and proteolytic enzymes.
abstract: OBJECTIVE
  To study the influence of peptides and proteolytic enzymes in the osmotic adaptation of Lactobacillus casei.
  
  
  RESULTS
  Di- and tri-peptides added individually increased the osmotolerance of Lact. casei when grown in a chemically defined medium (CDM) containing NaCl. Growth stimulation and the re-establishment in their presence of plasmid DNA supercoiling (recovery of the linking number) in hyperosmotic medium indicated that they are used as osmocompatible solutes as carnithine a known osmoprotector does. The investigation of the proteolytic system showed that in high osmolarity medium, the cell envelope-associated proteinase (PrtP), and PepX (X-prolyl-dipeptidyl aminopeptidase) increased activity and lost repression by peptides. PepI, an iminopeptidase was also derepressed. PepQ, a prolidase that specifically liberated proline from dipeptides, was almost unaffected. Derepression in the presence of peptides took place at the transcriptional level. However, the twofold activation of PrtP in CDM hyperosmotic medium was essentially through an increase of the apparent Vmax of the enzyme.
  
  
  CONCLUSIONS
  These results strongly suggest a contribution of the proteolytic system peptide supply in the osmotic adaptation.
  
  
  CONCLUSIONS
  Advances in understanding the role of peptides in the adaptation to high osmolarity particularly involved in dairy processes.
authors.affiliation: Departamento de Química Biológica. Facultad Ciencias Exactas y Naturales, Universidad de Buenos Aires, Buenos Aires, Argentina.
authors.forename: M
authors.initials: M
authors.lastname: Piuri
authors.forename: C
authors.initials: C
authors.lastname: Sanchez-Rivas
authors.forename: S M
authors.initials: SM
authors.lastname: Ruzal
mesh_terms: D003470:Culture Media; D005516:Food Microbiology; D005798:Genes, Bacterial / Q000502:physiology; D006801:Humans; D007780:Lacticaseibacillus casei / Q000187:drug effects* / Q000254:growth & development / Q000502:physiology; D009994:Osmolar Concentration; D010447:Peptide Hydrolases / Q000502:physiology*; D010455:Peptides / Q000502:physiology*; D020133:Reverse Transcriptase Polymerase Chain Reaction; D012697:Serine Endopeptidases / Q000235:genetics; D012965:Sodium Chloride / Q000494:pharmacology*; D014158:Transcription, Genetic; D014882:Water-Electrolyte Balance / Q000502:physiology
chemical_list: D003470:Culture Media; D010455:Peptides; D012965:Sodium Chloride; D010447:Peptide Hydrolases; D012697:Serine Endopeptidases; C085783:lactocepin