The culture of Manila clams in Brittany has faded from the 80 years after the onset of the disease called vibriosis of the Brown Ring (MAB). This disease is caused by the presence of the bacterium Vibrio tapetis causes a characteristic conchiolin deposit on the inner edge of the valves of the clams. The animals are able to repair the shell at the conchiolin deposits by a phenomenon of recalcification. Broodstock was selected according to their stage of disease development after inoculation of bacteria into the pallial cavity or following their physiological response in the hemolymph. Families of clams were produced and comparisons of the response to the disease were made between families in order to differentiate with the least susceptible individuals to this disease. Thus, these studies have to distinguish two families showing different characteristics of the immune level and hemocyte parameters in the development of the MAB. A relationship between families and ornamentation/color of the shell has been detected and enabled, in the thesis, to differentiate families in addition to the microsatellite tool. Moreover, it was shown that the V. tapetis induces production of nitric oxide in vitro in hemocytes of Manila clams. Moreover, when NO production is inhibited, the number of adherent cells decreases. Finally, molecular approaches have helped to highlight the specific expression of two gene transcripts (carbonic anhydrase like and serpin) in the mantle related to the development of the MAB.
