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Molecular basis of activity and resistance of bacteriocins in Streptococcus salivarius by Julien DAMOCZI -
Vendredi 30 janvier 2026 à 16h00 - Salle Jean-Baptiste Carnoy (B.059) - Bâtiment Carnoy - Croix du Sud - 1348 Louvain-la-Neuve -
The alarming rise of antimicrobial resistance represents one of the most critical global health threats, urgently calling for alternatives to conventional antibiotics. Among the most promising candidates are bacteriocins, antimicrobial peptides ribosomally synthesized by bacteria and active against both Gram-positive and Gram-negative bacteria. Their activity range, bioengineering potential, diversity, and other advantageous properties make them attractive for applications across multiple domains.
The commensal bacterium Streptococcus salivarius, one of the first colonizers of the human oral cavity, plays a key role in maintaining microbial homeostasis, partly through the production of multiple bacteriocins. Yet, the molecular basis underlying their activity and resistance mechanisms remains poorly understood.
In this thesis, the arsenal of class II bacteriocins produced by S. salivarius was systematically explored through genome mining, biochemical characterization, and structural modeling. Twenty-one distinct bacteriocins were identified, revealing an exceptional diversity of antimicrobial repertoires within this species. Structural and mutagenic analyses of two representative peptides, BlpK and PsnL, uncovered a conserved two-helix hairpin structure stabilized by a disulfide bridge and highlighted key residues essential for target recognition and membrane interaction. Furthermore, investigation of resistant mutants led to the discovery of an extruder-repressor module that mediates multi-bacteriocin resistance in response to bacteriocin exposure.
Together, these findings deepen our understanding of bacteriocin-mediated microbial competition and resistance, offering new perspectives for the rational design of probiotic and antimicrobial strategies.
Jury members :
Prof. Pascal Hols (UCLouvain) (Supervisor)
Dr. Johann Mignolet (UNIL, Switz.) (Co-supervisor)
Prof. Bernard Hallet (UCLouvain) (Chairperson)
Prof. Patrice Soumillion (UCLouvain) (Secretary)
Prof. Jacques Mahillon (UCLouvain)
Prof. Laurence Van Melderen (ULB)
Prof. Sébastien Rigali (ULiège)
Pay attention : the public defense of Julien DAMOCZI will also take place in the form of a videoconference (Numéro de réunion : 323 266 396 592 77 -
Code secret : Mp9XA2Hm)
