Effect of photo-oxidative processes on interactions between microbial communities and the oyster Crassostrea gigas

In recent years, environmental changes have had a significant impact on the health of marine organisms, resulting in considerable economic losses, particularly for molluscs. A striking example of this problem is the Pacific Oyster Mortality Syndrome (POMS), a disease causing production losses of Crassostrea gigas oysters of up to 80%. The disease is complex, involving both a viral infection by Ostreid Herpes Virus 1 (OsHV-1 μVar) and several bacterial infections, mainly by bacteria of the Vibrio genus. To improve water quality, aquaculture facilities use disinfection methods such as UVC irradiation or filtration. However, none of these processes can treat both pathogens and abiotic pollutants that can affect oyster health. My thesis focuses on the study of a process called heterogeneous photocatalysis that uses the solar resource. This process has the potential to effectively treat seawater by eliminating both biotic (viruses, bacteria) and abiotic contaminants (organic compounds). It is based on the use of titanium dioxide (TiO₂) as a catalyst. This research work was divided into several stages. Firstly, the ability of photocatalysis to inactivate target pathogens was investigated, using OsHV-1 μVar virus and Vibrio harveyi bacteria as study models. The impact of the process on oyster health and water microbial communities was characterized. Next, bacterial inactivation was modeled to understand how weather conditions and geographic location could influence its efficiency. Finally, the feasibility of photocatalysis in seawater for the disinfection of oyster pathogens was demonstrated. This works offers new avenues for developing an innovative and eco-responsible solution for securing aquaculture facilities. (author)