Characterization and diversity of mechanisms of mortality syndrome affecting juvenile Crassostrea gigas

• Main Author: Lucasson, Aude
• Other Authors: Interactions Hôtes-Pathogènes-Environnements (IHPE), Université de Perpignan Via Domitia (UPVD)-Institut Français de Recherche pour l'Exploitation de la Mer (IFREMER)-Centre National de la Recherche Scientifique (CNRS)-Université de Montpellier (UM), Université Montpellier, Guillaume Mitta
• Format: Doctoral or Postdoctoral Thesis
• Language: French
• Published: HAL CCSD 2018
• Subjects: Multifactorial diseases; Pathosystem; Oysters; Transcriptome; Microbiota structure; Ngs; Maladie multifactorielle; Pathosystème; Huîtres; Structure du microbiote; Séquençage haut débit; [SDV.MP]Life Sciences [q-bio]/Microbiology and Parasitology; Pacific; Crassostrea gigas; Pacific oyster
• Online Access: https://theses.hal.science/tel-02063435; https://theses.hal.science/tel-02063435/document; https://theses.hal.science/tel-02063435/file/2018_LUCASSON_archivage.pdf

Infectious diseases are very often explored using reductionist approaches, despite repeated evidence showing them to be strongly influenced by numerous interacting host and environmental factors. Many diseases with complex etiology therefore remain misunderstood. In this thesis, by developing a holistic approach to tackle the complexity of the interaction, (i) we deciphered the complex intra-host interactions underlying the Pacific oyster mortality syndrome affecting juveniles of Crassostrea gigas, the main oyster species exploited worldwide and (ii) we validated this mechanism in different infectious environments and oyster genotypes. Using ecologically realistic experimental infections combined with thorough molecular (metabarcoding, transcriptomics, pathogen monitoring) and histological analyses on oyster families with contrasting susceptibilities, we demonstrated that the disease is caused by a multiple infection whose initial and necessary step is the infection of oyster haemocytes by a herpesvirus. Viral replication leads to an immune-compromised state of the host, evolving toward subsequent bacteremia by opportunistic bacteria. By identifying critical intra-host interactions between microorganisms and host immunity, this study cracks the code of the Pacific oyster mortality syndrome and provides important molecular data for the design of prophylactic measures and breeding programs dedicated to the production of oysters resistant to the mortality syndrome. We believe that such a systems biology approach could be applied to decipher other multi-factorial diseases that affect non-model invertebrate species worldwide. Les maladies infectieuses sont souvent étudiées à l'aide d'approches réductionnistes alors qu'elles sont fortement influencées par de nombreux facteurs hôtes et environnementaux en interaction. Ainsi, de nombreuses maladies d’étiologie complexe restent difficiles à caractériser. En développant une approche holistique pour aborder la complexité de l'interaction, (i) nous avons déchiffré les ...