Dr Christine Paillard - The Brown Ring disease in clams, a double-edged defense mechanism for shell disease recovery!

Réalisation : 24 mars 2021 Mise en ligne : 24 mars 2021
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Brown Ring disease is caused by Vibrio tapetis, which, by adhering tonewly secreted shell matrices, interferes with the biomineralization process. Colonizationand alteration of the matrices induce the deposit of conchiolin on the innersurface of the valves, forming a characteristic brown deposit instead ofcontributing to shell growth. This defense mechanism consists firstly incoating the bacteria within the organic layers of melanized matrices, andsecondly in covering the brown deposit with shell layers to achieve completehealing of the shell. This defense phenotype varies greatly depending on, (1)the host physiology, its immune response and its microbiota, (2) the pathogenvirulence and its capacity to modulate shell fluid pH, and (3) theenvironmental conditions. The first barriers V. tapetis faces, the mantle epithelium and the extrapallialfluids, react rapidly and hemocytosis and the activation of enzymes. This earlyimmune response does not induce a decrease of host physiological parameters,suggesting a commensal relationship. On the other hand, in advanced stages ofdisease or incomplete recovery, the microparasite induces immunodepression and interruptedshell growth, clearly showing trade-offs between immune defense and biomineralizationprocesses. Thus, in the context of Brown Ring Disease, immunity and shellrepair processes interact closely either in synergy or as trade-offs dependingon their position along the mutualism-parasitism interaction gradient.



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