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Etude du rôle des pili de Lactococcus lactis dans la structuration d'un biofilm : approche biophysique multi-échelle

Dramé Ibrahima 1
1 LAAS-ELIA - Équipe Ingénierie pour les sciences du vivant
LAAS - Laboratoire d'analyse et d'architecture des systèmes
Abstract : Biofilms can be considered as more or less complex, highly structured microbial communities attached to a surface. In bacteria, biofilms are formed from clusters of cells of one or more species, producing their own exopolymeric, protective and adhesive matrix. This form of community life allows bacteria to protect themselves and resist physical, chemical and biological phenomena. However, in pathogenic and opportunistic bacteria, the formation of biofilm poses significant economic and health problems. In non-pathogenic bacteria, particularly probiotic or lactic acid bacteria (LAB), biofilm formation and its role in controlling other spoilage or pathogenic bacteria is increasingly being studied. From this perspective, the adhesion stage, intercellular interactions and biofilm formation mechanisms are crucial. In recent years, while most work has focused on the probiotic bacterium Lactobacillus rhamnosus GG, the model LAB Lactococcus lactis is also t! he subject of several studies aimed at understanding its ability to adhere to biotic and abiotic surfaces, the mechanisms of cell-cell interactions and biofilm formation, both under static and flowing conditions. In these thesis works, in order to understand the role of L. lactis pili in the organization and cohesion of cells in a biofilm, we first demonstrated, using cell-scale force spectroscopy (SCFS), the involvement of pili in homotypic interactions and their ability to interact with other surface proteins such as Mub proteins. The role of pili in the morphological characteristics of the biofilm (heterogeneous, aerial, rough), related to cell cohesion and its nanomechanical properties was analyzed. The use of a library of strains with different phenotypes has shown that other surface proteins, such as Mub proteins, participate in the structuring and characteristics of the biofilm. On the other hand, this difference in structure between the biofilms of the pili! ated strains does not appear to be correlated with their nanom! echanical properties. All piliated strains have similar mechanical properties: the biofilms are a thousand times softer or more elastic than those of control strains without pili. Finally, under flow conditions, different shear stresses (from 0.02 to 1 Pa) were applied to the biofilms in order to show their effects on both the detachment and the morphology of the biofilm as well as on its development during 24h. Thus, under these flow conditions, the crucial role of pili in the structuring and persistence of L. lactis biofilms was demonstrated.
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Submitted on : Wednesday, June 2, 2021 - 11:18:41 AM
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Dramé Ibrahima. Etude du rôle des pili de Lactococcus lactis dans la structuration d'un biofilm : approche biophysique multi-échelle. Génie des procédés. Institut National des Sciences Appliquées de Toulouse, 2021. Français. ⟨tel-03246140⟩

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