Etude des interactions hôte/parasite chez l'huître plate Ostrea edulis et son parasite Bonamia ostreae

The history of the French oyster production highlights the fragility of this production against overexploitation and disease outbreaks. In particular, the production of flot oyster, Ostrea edulis, has decreased following the emergence of two parasitic diseases including bonamiosis. The means to fight against bonamiosis are relatively limited. They are mainly based on oyster health surveillance to limit the spread of the disease. However, the use of predictive models of disease progression in infected area would help to improve stock management and minimize the impact pathogens. Moreover the development of resistant animais could help to revive this production. These different approaches require appropriate diagnostic tools, a good knowledge of the life cycle of the pathogen, and the interactions between the parasite and its host. In this context, the main objective of the phD work is to understand the interactions between the fiat oyster Ostrea edulis and the parasite Bonamia ostreae, and particularly the molecular basis of the resistance to the parasite. In a first step, a subtractive cDNA bank allowed the identification of ESTs differentially expressed in haemocytes in response to the parasite. Expression of some genes, among which a galectin, was measured by Real lime PCR in the context of in vitro infections. In addition, the cellular response was investigated by flow cytometry and the infection was checked by microscopy. These experiments showed a multiplication of the parasite inside haemocytes assoclated with a decreased of esterases and of the production of ROS. In a second step, a comparative approach was carried out between a population of oysters resistant to bonamiosis and a natural population. Results suggest that modulation of apopotosis and decrease of phagocytosis could be involved in mechanisms related to resistance to bonamiosis. This work is the first study on the response of haemocytes of fiat oysters to an infection with the parasite Bonamia ostreae at the cellular and molecular levels.