Study of the apoptotic effects induced by the neurotoxins of the dinoflagellate Alexandrium pacificum (catenella) on the oyster Crassostrea gigas: Consequences on the susceptibility of oysters to pathogens


Ec2CO microbien (2013-2014)
Project leader: Jean-Luc Rolland
This project aims to deepen our knowledge of the effects of the toxic alga Alexandrium pacificum (catenella) on the mechanisms of programmed cell death (apoptosis) in Crassostrea gigas. Indeed, although various pathogens (Vibrio splendidus, Vibrio aestuarianus and OHSV1) could have been shown to be associated with the massive mortalities of exploited molluscs that occur throughout the French littoral, under experimental conditions in the laboratory, the infection of oyster V. splendidus is quite weak and infection with V. aestuarianus does not induce mortality. In recent years there has also been a worrying expansion of toxin-producing microalgae (HAB, Harmful Algae Bloom) blooms on all French coasts. If these toxic blooms, in shellfish areas, result in the prohibition and delay of oyster marketing, only punctual, localized and reversible effects on molluscs have been described to date. Among the toxin algae encountered, A. pacificum responsible for the PSP (Paralytic Shellfish Poisoning) syndrome produces saxitoxins that are known to disrupt the functioning of human cells by binding to the ion channels (sodium, potassium and calcium) located in cell membranes and mitochondria leading sometimes to apoptotic cell death. Apoptosis is an active, controlled mechanism of self-destruction that occurs when cells are damaged or in response to infections. It plays a key role in development and homeostasis. The hypothesis of this project is that a dysfunction of this defense mechanism of the immune cells could affect the oyster’s resistance capacities to bacterial and viral infections and contribute to the massive and recurrent oyster mortalities observed in France and all over the World.
The Apotox project allowed us, for the first time, to experimentally demonstrate apoptosis-induced death of hemocytes (immune cells) in oysters after they were brought into contact with the toxic alga Alexandrium pacificum (Medhioub et al, 2013, Rolland et al, 2014). In the framework of Celina Abi-Khalil’s thesis (2015-2016) we have also shown that the PST toxins produced by A. pacificum were able, experimentally, to accumulate in the oyster’s immune cells and induce there death by apoptosis (Abi-Khalil et al, 2017). Moreover, A. pacificum was shown to experimentally affect oyster resistance to microbial infections (Abi-Khalil et al, 2016). This is a significant advance in the understanding of the phenomena of massive mortality of oysters which we know is of multifactorial origin.
Team 1 – Interactions Hôtes-Pathogènes-Environnements (IHPE, Université de Montpellier, CNRS, Ifremer, UPVD, Montpellier, France). Rolland Jean-Luc, Walid Medhioub, Destoumieux-Garzon Delphine, Celina Abi-Khalil, Vanhove Audrey, Vergne Agnes, Leroy Marc
Team 2 – MARine Biodiversity, Exploitation and Conservation (MARBEC, Université de Montpellier, CNRS, Ifremer, IRD, Montpellier, France). Laabir Mohamed, Masseret Estelle, , Evelyse Grousset, Rieuvilleneuve Fabien
Team 3 – Laboratoire phycotoxine (PHYC, Ifremer, Nantes). Amzil Zouher, Savar Véronique