To diversify their genetic material, allowing adaptation to environmental disturbances and colonization of new ecological niches, bacteria use various evolutionary processes, including the acquisition of new genetic material by horizontal transfer mechanisms such as conjugation, transduction and transformation. Electrotransformation mediated by lightningrelated electrical phenomena may constitute an additional gene transfer mechanism occurring in nature. The presence in clouds of bacteria capable of forming ice nuclei that lead to precipitations and are involved in the triggering of lightning, such as the global phytopathogen Pseudomonas syringae, led us to postulate that natural electrotransformation in clouds may affect bacteria, by contributing to increase their adaptive potential. We first determined if the ice nucleator bacterium P. syringae could survive when in clouds and acquire exogenous genetic material through lightning shock-simulating in vitro electroporation. In comparison to two other bacteria, P. syringae appears to be best adapted for survival and for genetic electrotransformation under these conditions, which suggests that this bacterium would be able to survive and evolve whilst being transported in clouds. Secondly, we evaluated the impact of lightning shock-simulating in vitro electroporation on the survival, the electrotransformation potential and the diversity of bacteria collected from rain samples. These isolates better resisted lightning than the laboratory strains and some were able to electrotransform exogenous DNA. The rain bacteria we isolated were of different origins and were representative of life modes of the various sources of bacterial emissions on Earth. Our study suggests that bacteria aerosolized from diverse terrestrial ecosystems can spread to new habitats through clouds whilst also being able to acquire new genetic material via lightning-based electrotransformation, thereby potentially enhancing their genetic diversity. The final part of our work consisted of evaluating whether electrotransformation could be applied to the engineering of indigenous soil bacteria in order to develop a tool for the bioremediation of lindane, a once widely used pesticide. Optimized experiments revealed that both natural and electrotransformation contributed to the incorporation of a plasmid harboring a gene encoding the first lindane dechlorination steps by indigenous soil bacteria. In conclusion, we showed that natural electrotransformation mediated by electrical discharges such as those occurring in clouds or reaching soils can be involved in the horizontal gene transfer process among bacteria and, considering the importance of lightning worldwide, may play a role in the adaptation and evolution of these organisms.

Pour diversifier leur matériel génétique, s’adapter aux perturbations environnementales et coloniser de nouvelles niches, les bactéries utilisent plusieurs processus évolutifs dont l’acquisition de matériel génétique par transfert horizontal de gènes comme la conjugaison, la transduction et la transformation. À ces trois mécanismes naturels s’ajoute l’électrotransformation due aux phénomènes électriques liés à la décharge de foudre. La présence dans les nuages de bactéries aérosolisées capables de former des noyaux de glace à l’origine des précipitations et impliquées dans le déclenchement de la foudre, telles que la bactérie phytopathogène à répartition mondiale Pseudomonas syringae, nous a conduit à proposer que l’électrotransformation naturelle dans les nuages pouvait affecter les bactéries, contribuant ainsi à augmenter leur potentiel adaptatif. Dans un premier temps, nous avons déterminé si la bactérie glaçogène P. syringae pouvait survivre à des électroporations simulant des décharges de foudre et acquérir du matériel génétique exogène dans les nuages. Comparée à deux autres bactéries, P. syringae se révèle être mieux adaptée pour la survie et l’électrotransformation génétique, ce qui suggère qu’elle serait capable de survivre et d’évoluer durant son transport dans les nuages. Nous avons ensuite évalué l’impact d’électroporations simulant les décharges de foudre sur la survie, le potentiel d’électrotransformation et la diversité de bactéries présentes dans des échantillons de pluie comme substitut des communautés bactériennes des nuages. Ces dernières étaient plus résistantes que les souches de laboratoire et certaines étaient capables d’acquérir de l’ADN exogène par électrotransformation. Les bactéries de la pluie isolées provenaient de différentes origines et présentaient différents modes de vie, représentatifs des sources probables d’émissions de bactéries terrestres. Cette étude montre que les bactéries aérosolisées de divers écosystèmes terrestres sont susceptibles de se disséminer dans de nouveaux habitats grâce aux nuages tout en étant capable d’acquérir de nouveaux gènes par éléctrotransformation, et d’augmenter ainsi potentiellement leur diversité génétique. La dernière partie de mon travail a évalué si l’électrotransformation appliquée aux bactéries indigènes du sol pouvait être employée pour dépolluer les sols contaminés par un pesticide largement utilisé autrefois, le lindane. L’optimisation des expériences met en évidence l’incorporation par les bactéries indigènes d’un plasmide contenant le gène codant les premières déchlorinations du lindane au travers d’une combinaison de transformation naturelle et d’électrotransformation. En conclusion, nous avons montré que l’électrotransformation naturelle liée aux décharges électriques, comme celles se produisant dans les nuages ou atteignant le sol, peut être impliquée dans le transfert horizontal de gènes chez les bactéries et, considérant l’importance de la foudre à travers le monde, pourrait jouer un rôle dans l’adaptation et l’évolution de ces organismes. / To diversify their genetic material, allowing adaptation to environmental disturbances and colonization of new ecological niches, bacteria use various evolutionary processes, including the acquisition of new genetic material by horizontal transfer mechanisms such as conjugation, transduction and transformation. Electrotransformation mediated by lightningrelated electrical phenomena may constitute an additional gene transfer mechanism occurring in nature. The presence in clouds of bacteria capable of forming ice nuclei that lead to precipitations and are involved in the triggering of lightning, such as the global phytopathogen Pseudomonas syringae, led us to postulate that natural electrotransformation in clouds may affect bacteria, by contributing to increase their adaptive potential. We first determined if the ice nucleator bacterium P. syringae could survive when in clouds and acquire exogenous genetic material through lightning shock-simulating in vitro electroporation. In comparison to two other bacteria, P. syringae appears to be best adapted for survival and for genetic electrotransformation under these conditions, which suggests that this bacterium would be able to survive and evolve whilst being transported in clouds. Secondly, we evaluated the impact of lightning shock-simulating in vitro electroporation on the survival, the electrotransformation potential and the diversity of bacteria collected from rain samples. These isolates better resisted lightning than the laboratory strains and some were able to electrotransform exogenous DNA. The rain bacteria we isolated were of different origins and were representative of life modes of the various sources of bacterial emissions on Earth. Our study suggests that bacteria aerosolized from diverse terrestrial ecosystems can spread to new habitats through clouds whilst also being able to acquire new genetic material via lightning-based electrotransformation, thereby potentially enhancing their genetic diversity. The final part of our work consisted of evaluating whether electrotransformation could be applied to the engineering of indigenous soil bacteria in order to develop a tool for the bioremediation of lindane, a once widely used pesticide. Optimized experiments revealed that both natural and electrotransformation contributed to the incorporation of a plasmid harboring a gene encoding the first lindane dechlorination steps by indigenous soil bacteria. In conclusion, we showed that natural electrotransformation mediated by electrical discharges such as those occurring in clouds or reaching soils can be involved in the horizontal gene transfer process among bacteria and, considering the importance of lightning worldwide, may play a role in the adaptation and evolution of these organisms.