ED Sciences Physiques et de l'Ingénieur
In situ study of radiation-induced fragmentation of DNA molecules in aqueous solution.
by Rémy LIENARD (Laboratoire de Physique des 2 Infinis de Bordeaux)
The defense will take place at 10h00 - Marie Curie Site du Haut Vigneau · 19 chemin du Solarium · 33170 GRADIGNAN.
in front of the jury composed of
- Franck GOBET - Professeur - Université de Bordeaux - Directeur de these
- Bernadette FARIZON - Directeur de recherche - Université Claude Bernard Lyon 1 - Rapporteur
- Marie-Anne HERVé DU PENHOAT - Maître de conférences - Sorbonne Université - Rapporteur
- Christine GRAUBY-HEYWANG - Professeur - Université de Bordeaux - Examinateur
- Jean-Christophe POULLY - Maître de conférences - Université de Caen Normandie - Examinateur
- Philippe BARBERET - Professeur - Université de Bordeaux - CoDirecteur de these
- Thomas SALEZ - Directeur de recherche - LOMA - Université de Bordeaux - Examinateur
- Judith PETERS - Professeure - Université Grenoble Alpes - Examinateur
Radiation-induced fragmentation of DNA molecules in aqueous solution represents a central issue in both radiobiology and radiotherapy, where a precise understanding of DNA double-strand break mechanisms remains crucial. In this work, particular attention was given to the influence of the solvent on DNA double-strand breaks (DSBs) induced by a 3 MeV proton beam, through a pump-probe experimental approach. An original in situ methodology using localized irradiation (pump) and fluorescence microscopy (probe) has been developed on the microbeam line of the AIFIRA platform (Applications Interdisciplinaires de Faisceaux d'Ions en Région Aquitaine). The DNA studied is that of bacteriophage T4, labeled with a fluorescent dye, and monitored in real time before and after irradiation in a solution where both ionic strength and radical lifetime are controlled. To support this study, an innovative numerical tool using machine learning and single particle tracking was designed. This tool enables event-by-event, molecule-by-molecule analysis and quantification of DNA fragmentation in solution under various solvent conditions. In association with models from statistical physics and soft matter physics, this approach allows the extraction of cross sections associated with double-strand breaks caused by the direct ionization effects of protons on DNA molecules in aqueous environments. This manuscript presents the methodology implemented and the first experimental results obtained, in particular those highlighting the protective effect of water during DNA irradiation and the stabilizing influence of ionic strength on DNA fragmentation.