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Antibacterial activities. Each isolated peptide exhibited potent activity on a variety ofGram-positive bacteria. L50A was in most cases twice more active than L50B. A weaksynergy effect of EntL50A/EntL50B combination was observed on the Lactobacillus sakeisp. sakei strain, exclusively.Conformational studiesThe CD spectra revealed a helical conformation for L50A and L50B peptides in phosphatebuffer at pH 7.0, both in the absence and in the presence of SDS micelles. The helix contentincreased in the presence of micelles only in the case of L50B.Fig. 1. Circular dichroism spectra of L50A and L50B, 100 µM in 10 mM phosphate buffer,pH 7.ConclusionEnterococcus durans A5-11 produces the two leaderless peptides - enterocins L50A andL50B, what confers to this strain interest as a biopreservative or a probiotic. EnterocinsL50A and L50B are well structured in aqueous media and exhibit individual and weaksynergistic activities, two characteristics that differ from those shared by two-peptidebacteriocins from class IIb.The different properties observed for L50A and L50B in spite of high sequencesimilarities paves the way for studies of structure/activity relationships.AcknowledgmentsWe acknowledge the mass spectrometry facility of the MNHN for access to the ESI-Qq-TOFspectrometer.References1. Oppegård, C., Rogne, P., Emanuelsen, L., Kristiansen, P.E., Fimland, G., Nissen-Meyer, J. J. Mol.Microbiol. Biotechnol. 13, 210-219 (2007).2. Nissen-Meyer, J., Oppegård, C., Rogne, P., Haugen, H.S., Kristiansen, P.E. Probiotics Antimicrob.Proteins 2, 52-60 (2010).3. Franz, C.M.A., Belkum, M.J., Holzapfel, W.H., Abriouel, H., Gálvez, A. FEMS Microbiol. Rev. 31,293-310 (2007).4. Batdorj, B., Dalgalarrondo, M., Choiset, Y., Pedroche, J., Métro, F., Prévost, H., Chobert, J.-M.,Haertlé, T. J. Appl. Microbiol. 101, 837-848 (2006).5. Cintas, L,M., Casaus, P., Holo, H., Hernandez, P.E., Nes, I.F., Havarstein, L.S. J. Bacteriol. 180,1988-1994 (1998).399