title: Tyramine biosynthesis is transcriptionally induced at low pH and improves the fitness of Enterococcus faecalis in acidic environments.
abstract: Enterococcus faecalis is a commensal bacterium of the human gut that requires the ability to pass through the stomach and therefore cope with low pH. E. faecalis has also been identified as one of the major tyramine producers in fermented food products, where they also encounter acidic environments. In the present work, we have constructed a non-tyramine-producing mutant to study the role of the tyramine biosynthetic pathway, which converts tyrosine to tyramine via amino acid decarboxylation. Wild-type strain showed higher survival in a system that mimics gastrointestinal stress, indicating that the tyramine biosynthetic pathway has a role in acid resistance. Transcriptional analyses of the E. faecalis V583 tyrosine decarboxylase cluster showed that an acidic pH, together with substrate availability, induces its expression and therefore the production of tyramine. The protective role of the tyramine pathway under acidic conditions appears to be exerted through the maintenance of the cytosolic pH. Tyramine production should be considered important in the adaptability of E. faecalis to acidic environments, such as fermented dairy foods, and to survive passage through the human gastrointestinal tract.
authors.affiliation: Instituto de Productos Lácteos de Asturias (IPLA-CSIC), Paseo Rio Linares s/n, 33300, Villaviciosa, Spain.
authors.forename: Marta
authors.initials: M
authors.lastname: Perez
authors.forename: Marina
authors.initials: M
authors.lastname: Calles-Enríquez
authors.forename: Ingolf
authors.initials: I
authors.lastname: Nes
authors.forename: Maria Cruz
authors.initials: MC
authors.lastname: Martin
authors.forename: Maria
authors.initials: M
authors.lastname: Fernandez
authors.forename: Victor
authors.initials: V
authors.lastname: Ladero
authors.forename: Miguel A
authors.initials: MA
authors.lastname: Alvarez
mesh_terms: D013293:Enterococcus faecalis / Q000235:genetics* / Q000378:metabolism*; D020869:Gene Expression Profiling; D015964:Gene Expression Regulation, Bacterial / Q000187:drug effects*; D055786:Gene Knockout Techniques; D006801:Humans; D006863:Hydrogen-Ion Concentration; D050296:Microbial Viability / Q000187:drug effects; D005810:Multigene Family; D014158:Transcription, Genetic / Q000187:drug effects*; D014439:Tyramine / Q000096:biosynthesis*; D014445:Tyrosine Decarboxylase / Q000096:biosynthesis / Q000235:genetics
chemical_list: D014445:Tyrosine Decarboxylase; D014439:Tyramine