The Pacific oyster Magallana gigas is the main farmed oyster species in France and worldwide, representing a major economic resource. However, intensive aquaculture practices and the introduction of exotic species have increased the risk of infectious diseases. Over recent decades, mass mortality events in juveniles have been associated with Ostreid herpesvirus 1 (OsHV-1) and have caused severe economic losses. Currently, no effective treatment exists, making disease prevention and health management critical for industry sustainability.
In bivalves, mucosal surfaces represent the first and most critical interface between the host and its environment, constituting a primary barrier against pathogen entry. Beyond its physical role, mucus is now recognized as a highly dynamic immunological compartment composed of a complex mixture of immune effector molecules and a diverse resident microbiota, considered as an integral component of host homeostasis. Despite this growing body of evidence, the role of mucus-associated immunity and microbiota in the context of OsHV-1 infection remains largely unexplored
In this context, we investigate the interactions between OsHV-1 and M. gigas at the mucosal interface, with the goal of identifying factors driving virulence and resistance. With this goal in mind, earliest host–pathogen interactions at the mucosal interface have been investigated through experimental OsHV-1 infections. Six different oyster lineages, produced in Ifremer facilities and expressing contrasted susceptibility to OsHV-1, have been used in order to understand whether mucosal immunity plays a role in this contrasted phenotypic response to viral infection.
Following pallial mucus collection according to time post infection, particular attention has been given to immune-related components, mucus-associated microbiota, and viral load dynamics at early stages of infection. Mucus samples have been analyzed using holistic approach, including: (i) proteomic characterization of immune-related proteins secreted in pallial mucus using liquid chromatography coupled with tandem mass spectrometry (LC-MS/MS); (ii) bacterial community profiling through 16S metabarcoding using Oxford Nanopore Technology sequencing; and (iii) viral load dynamics in pallial mucus over time post-infection.
survival rates confirmed the contrasting susceptibility between groups: low-susceptibility oysters (L) showed approximately 90% survival after one week, whereas highly susceptible oysters (H) exhibited less than 10% survival at 48 hours post-infection (hpi). Quantitative PCR analyses further revealed that viral load in pallial mucus increased significantly over time (two-way ANOVA, p < 0.001). Importantly, a significant interaction between time and oyster group was observed (p = 0.0024), indicating that viral load dynamics differed between L and H oyster families.
Moreover, preliminary analyses of the bacterial microbiota associated with pallial mucus revealed significant differences in both richness and diversity between L and H oyster families. In parallel, proteomic analyses identified more than 4,500 master proteins across all samples, including proteins involved in antiviral responses. Preliminary data visualization also suggested clear differences between oyster families.
Ongoing analyses will provide further insight into the earliest mechanisms and interactions occurring at the mucosal interface between OsHV-1, host immune proteins secreted in mucus, and the associated bacterial microbiota. Furthermore, the generated datasets—including bioinformatic resources on mucus composition, microbiota, and responses to pathogen pressure—will be made accessible to the scientific community, fostering further research in marine biology, disease ecology, and environmental health.