Abstract
BackgroundThe tyramine producer Enterococcus durans IPLA655 contains all the necessary genes for tyramine biosynthesis, grouped in the TDC cluster. This cluster includes tyrS, an aminoacyl-tRNA synthetase like gene.ResultsThis work shows that tyrS was maximally transcribed in absence of tyrosine at acidic pH, showing a greater than 10-fold induction in mRNA levels over levels occurring in presence of tyrosine. Mapping of the tyrS transcriptional start site revealed an unusually long untranslated leader region of 322 bp, which displays the typical features of the T box transcriptional attenuation mechanism. The tyrosine concentration regulation of tyrS was found to be mediated by a transcription antitermination system, whereas the specific induction at acidic pH was regulated at transcription initiation level.ConclusionsThe expression of the tyrS gene present in the TDC cluster of E. durans is transcriptionally regulated by tyrosine concentration and extracelular pH. The regulation is mediated by both an antitermination system and the promoter itself.
Highlights
The tyramine producer Enterococcus durans IPLA655 contains all the necessary genes for tyramine biosynthesis, grouped in the TDC cluster
We have found an open reading frame coding for a protein of 418 amino acids with a molar mass of 47.38 kDa located next to the tyrosine decarboxylase and the tyrosine-tyramine antiporter genes of Enterococcus durans IPLA655
Results tyrS expression depends on the tyrosine concentration and extracellular pH RNA from E. durans IPLA655 cultures grown in presence (10 mM) or absence of tyrosine at two different pH conditions (4.9 and 7.5), was analyzed by Northern blot hybridization with a tyrS specific probe (Figure 1A)
Summary
The tyramine producer Enterococcus durans IPLA655 contains all the necessary genes for tyramine biosynthesis, grouped in the TDC cluster. This cluster includes tyrS, an aminoacyl-tRNA synthetase like gene. Fermented foods are likely to contain high levels of BA, mainly due to the decarboxylase activity of some lactic acid bacteria (LAB). BA are produced by the decarboxylation of a precursor amino acid by the enzymatic action of an amino acid decarboxylase [6,7]. In these foods, the main BA are tyramine, histamine, cadaverine
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