I am pleased to invite you to my PhD defense, November 4th at 2:30pm in amphithéatre Charpak. My PhD project is entitled "Experimental study of a multi-species bacterial biofilm model in video-microscopy: Kinetics of formation and interactions between species". We are also invited to take a drink after in the seminar room of the laboratory at the 5th floor, tower 32-33 around 17h.

Abstract :

During my PhD work, I characterized the development of a multi-species biofilm in milli-fluidic channels under constant flow of nutrient medium. I first developed the use of a new fluorescent reporter on a single-species Escherichia coli biofilm. I have shown the limitations of classical GFP type reporters on the system and introduced the inducible fluorescence protein FAST to overcome these limitations. With this new tool, I studied the formation of a multi-species biofilm, resulting from a natural biofilm adapted to the laboratory, consisting of Bacillus thuringiensis (Bt), Pseudomonas fluorescens (Pf), Kocuria salsicia (Ks) and Rhodocyclus sp. (R). I characterized the development of this adherent community by video-microscopy of transmitted light and fluorescence, by measuring in real time the kinetics of development of global biomass and fluorescent species within the community. I thus highlighted a succession of phases of growth and recession of the biofilm, then the establishment of stationary state after 30h of growth. I also found that Pf, numerically the dominant species of this community, operates after a few hours a change of niche probably giving him an important advantage. These results led me to formulate the hypothesis that the formation mechanism of this adherent community is largely governed by the equilibrium of O₂ in the system. Finally, I have studied the different combinations that can be formed by members of the community in search of existing interactions between bacteria. I was able to show the existence of competitive interactions between Pf and Bt, the parasitism relation of Bt on Ks, as well as that of amensalism of Pf on Ks. We also determined that R develops in a neutral way towards the other species. Our results suggest that these interactions are mainly based on physical interactions and physicochemical regulation.