The Relationship among Tyrosine Decarboxylase and Agmatine Deiminase Pathways in Enterococcus faecalis

Abstract

Enterococci are considered mainly responsible for the undesirable accumulation of the biogenic amines tyramine and putrescine in cheeses. The biosynthesis of tyramine and putrescine has been described as a species trait in <i>Enterococcus faecalis.</i> Tyramine is formed by the decarboxylation of the amino acid tyrosine, by the tyrosine decarboxylase (TDC) route encoded in the <i>tdc</i> cluster. Putrescine is formed from agmatine by the agmatine deiminase (AGDI) pathway encoded in the <i>agdi</i> cluster. These biosynthesis routes have been independently studied, tyrosine and agmatine transcriptionally regulate the <i>tdc</i> and <i>agdi</i> clusters. The objective of the present work is to study the possible co-regulation among TDC and AGDI pathways in <i>E. faecalis</i>. In the presence of agmatine, a <i>positive</i> correlation between putrescine biosynthesis and the tyrosine concentration was found. Transcriptome studies showed that tyrosine induces the transcription of putrescine biosynthesis genes and up-regulates pathways involved in cell growth. The tyrosine modulation over AGDI route was not observed in the mutant Δ<i>tdc</i> strain. Fluorescence analyses using <i>gfp</i> as reporter protein revealed P<i>aguB</i> (the promoter of <i>agdi</i> catabolic genes) was induced by tyrosine in the wild-type but not in the mutant strain, confirming that <i>tdc</i> cluster was involved in the tyrosine induction of putrescine biosynthesis. This study also suggests that AguR (the transcriptional regulator of <i>agdi</i>) was implicated in interaction among the two clusters.