THESE Maryse Bonnin Jusserand - Université de Bourgogne

Résultats
Figure 1: Growth of Lactobacillus plantarum IR BL0076 in medium with free tyrosine or in
medium containing synthetic peptides. The tyramine measured by HPLC is produced by L.
plantarum IR BL0076 at different stages of the growth (OD600nm = 1.0; 1.6; 1.8), in both
culture media: free tyrosine versus tyrosine containing peptides.
tyrP transcription
In order to compare and correlate tdc and tyrP expression, transcripts of both genes were first
analyzed. RT-PCR experiments on cDNA obtained from RNA extracted from both culture
conditions, gave an amplicon of approximately 1700 bp, with primers located inside tdc and
tyrP genes. The length of the RT-PCR product means that tyrP is part of a polycistronic
mRNA together with tdc. Tyramine-producing bacteria carry the tdc cluster composed of four
genes: a tyrosil-tRNA synthetase tyrS, the decarboxylase tyrDC, the transporter tyrP and
finally a gene nhaC encoding an antiporter Na + /H + . This genetic organization exists in
Enterococcus faecalis (Connil et al, 2002), Lactococcus lactis (Fernandez et al, 2004) and
Lactobacillus brevis (Lucas et al, 2003). Moreover the co-transcription of tdc and tyrP was
always shown for E. faecalis (Connil et al, 2002), L. brevis (Lucas et al, 2003) and recently
for Sporolactobacillus sp. (Coton et al, 2011). However other transcripts have been detected.
In L. brevis, the four genes can be co-transcribed or tyrS together with tyrDC, or tyrP and
nhaC. Actually the four genes of the tyrosine decarboxylase pathway operon are disseminated
through lactic acid bacteria via a horizontal gene transfer. Therefore it is expected that they
are regulated by the same way among lactobacilli including L. plantarum. The tdc trait is
strain-specific, and the L. plantarum genomes sequenced, like WCFS1 and ATCC 14917
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