THESE Maryse Bonnin Jusserand - Université de Bourgogne

Résultats
located at the N-terminus. Di- and tri-peptidases, such as PepV, isolated from Lactococcus.
lactis (Hwang et al, 1981) and several Lactobacilli, are able to breakdown dipeptides
containing a Gly redisue at the N-terminus. Also Gly-Leu-Tyr and Gly-Gly-Tyr-Arg contain
effectively a Gly amino acid at the N-terminus.
The growth was monitored by measuring the OD at 600 nm. L. plantarum IR BL0076 was
able to grow in the synthetic medium either with free amino acids or synthetic peptides
containing tyrosine. Moreover the growth curve was the same whatever the source of tyrosine
(Fig 1). L. plantarum is known to be auxotroph for the L-tyrosine (Teusink et al, 2005).
Indeed L. plantarum IR BL0076 could not grow in the synthetic medium used in this study
without tyrosine. Therefore the proteolysis of the synthetic peptides has to be done in the
early stages of the development to release tyrosine and to allow the growth. This has been
demonstrated for two Lactobacillus strains: Lactobacillus homohiochii and Lactobacillus
curvatus isolated from sausages, which were positive for tyrosine and ornithine decarboxylase
activities (Pereira et al, 2001). These both strains display a extracellular proteolytic activity
which reach a maximum in the early exponential growth. Furthermore this activity was higher
when cells were grown in a peptide-rich medium. However we could not exclude the
possibility of a peptides transport and a subsequent intracellular hydrolysis. Although LAB
proteinases have a broad specificity and release oligopeptides in the range of 4 to 8 AA,
intracellular peptidases are required for the complete degradation of peptides (Kunji et al,
1996).
Tyramine production by Lactobacillus plantarum IR BL0076
At different stages of the growth, the culture supernatant was analyzed by HPLC to determine
tyramine production (Fig 1). Tyramine was identified by HPLC-MS (Table 2). At OD600nm =
0.2, no tyramine is detected in any case. But tyramine is measured in both culture media from
OD600nm = 1.0; and no difference in production is observed between both media. Therefore L.
plantarum was able to synthesize tyramine in the same quantity with either 400 mg.L -1 of free
tyrosine or 300 mg.L -1 of peptides.
132