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Séminaires Micalis


Andrew Camilli
By developing a transposon deep sequencing approach, we were able to accurately measure the contribution of all nonessential genes of the pathogen Streptococcus pneumoniae to fitness in 22 different environments, including in the mammalian nasopharynx and lung. Among the many genes found to contribute to virulence are two (murMN) involved in determining peptidoglycan stem peptide composition. We show that their effect is mediated in part through affecting the extent of Pneumolysin (Ply) export. Ply is a cholesterol-dependent pore-forming cytolysin that is the major exported virulence factor of S. pneumoniae. Ply, which lacks a recognizable secretion motif, somehow gets exported where it initially localizes to the cell wall compartment. Using hemolysis assays we show that Ply export beyond the cell wall into the extracellular environment is inhibited by the peptidoglycan layer. By manipulating the peptidoglycan stem peptide composition, we showed that an increase in the ratio of branched to unbranched stem peptides impedes Ply release. Naturally occurring hyperactive alleles of murMN associated with penicillin resistance also impeded Ply release. Finally, we found that an increased Ply release is detrimental to virulence. These results highlight the importance of peptidoglycan composition in pathogenesis.
Vendredi 09 octobre 14h
Auditorium - Bât. 442
INRA, Jouy en Josas


Leyla Slamti


Patrick Veiga


The emergence of molecular tools brought about a revolution in the understanding of the immense diversity and functioning of the gut microbiota in health and disease. Building on these new tools and knowledge, we are dedicated to deciphering the molecular mechanisms underlying the beneficial effects of live bacteria contained in fermented milk products. As an illustration of our research effort, we recently demonstrated that host lysozyme-mediated lysis of Lactococcus lactis CNCM I-1631 facilitates the delivery of colitis-attenuating superoxide dismutase to inflamed colons.

(Ballal, Veiga, Fenn et al., 2015, PNAS)
Vendredi 11 septembre 11h
Amphithéâtre J. Poly Bât. 440
INRA, Jouy en Josas


Saulius Kaulakauskas 

01 34 65 23 82

Andrew Camilli

Rédaction : Tristan
Date de création : 02 Avril 2011
Mise à jour : 28 Septembre 2015