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Effets de nanoparticules de silice sur la physicochimie de surface de bactéries planctoniques et sur l’architecture des biofilms : analyse par électrophorèse et holotomographie

Abstract : The release of manufactured nanoparticles (NPs) into the environment has profound repercussions on the physico-chemical equilibria operating in natural aquatic media. In order to appreciate these repercussions, it is critical to address, among other things, the interaction mechanisms between NPs and the biotic compartment of ecosystems, in particular bacteria in planktonic state or organized in a biofilm. In this context, this thesis work was devoted to the understanding of the physico-chemical interactions between silica nanoparticles with -NH2 or -COOH functionalized surface, and several mutants of a bacterial model system (Escherichia coli) selectively displaying different types of surface appendages at their periphery (YeeJ adhesive proteins or pili-F protein filaments). The use of electrophoresis applied to bacteria-NPs binary suspensions made it possible to detect (i) the electrostatic signatures of the first stages of interactions, (ii) the changes in the electro-hydrodynamic characteristics of both bacteria and NPs due to membrane damage and acquisition of bio-corona by NPs following the release of cellular compounds, and (iii) the strong dependence of the electrokinetic properties of both cells and nanoparticles on the nature of the parietal biostructure, on NPs concentration and on solution pH. The use of atomic force microscopy further allowed the evaluation of cells morphology depending on cells exposure conditions, as well as their surface roughness, these results corroborating the conclusions derived from electrokinetic study. The second part of this thesis, exploratory in nature, concerns the analysis by a 3D imaging technique (holotomography, no sample labelling required) of the structure of bacterial biofilms generated in the presence of NPs. A method for exploiting holotomographic data is proposed and leads to the determination of different proxies characterizing the structure of the biofilm, in particular its thickness, its density profile, or the identification of ‘chimneys’ at the biofilm/solution interface. The capabilities of the method to evaluate these physicochemical fingerprints are tested on a biofilm generated from bacteria decorated with YeeJ proteins. The impacts of silica nanoparticles on the structure of this biofilm are then discussed according to the nature of their functional surface groups (-NH2 or -COOH).
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Elise Vouriot. Effets de nanoparticules de silice sur la physicochimie de surface de bactéries planctoniques et sur l’architecture des biofilms : analyse par électrophorèse et holotomographie. Sciences de l'environnement. Université de Lorraine, 2019. Français. ⟨NNT : 2019LORR0278⟩. ⟨tel-02558994⟩

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