Communication Dans Un Congrès Année : 2025

Immune response of Mytilus edulis challenged with low-virulence and high-virulence isolates of F. halioticida

Résumé

Introduction In France and other European countries, several hypotheses are currently being explored to explain the recurrent mass mortality events observed in mussels since 2014. Two of these hypotheses involve bacterial species: Vibrio splendidus, known pathogen of aquatic species and Francisella halioticida, pathogen of abalone and Yesso scallop. Our previous studies led to the isolation of several F. halioticida strains. Virulence assessment revealed that some isolates were significantly more virulent than others under the same environmental conditions. In mussels, few pathogens are capable of inducing significant mortality at concentrations below 10⁵ CFU/mL—F. halioticida is one of them. The main objective of this study was to investigate the immune response of hemocytes and gill tissues in Mytilus edulis following infection with F. halioticida. Methodology Adult mussels were injected with either the low-virulence isolate FR21, the high-virulence isolate FR22c, or sterile broth (control) at a high concentration (10⁶ CFU/mL). Samples from the haemolymph and gills were collected before injection (T0 control), at 24 hours (T1), and at 72 hours (T2) post-injection for gill tissue only. RNA was extracted using the conventional TRIzol method and sequenced via Illumina technology. A de novo transcriptome was produced using all samples from gills, followed by a differential expression analysis. Proteins and peptides were extracted in parallel and analysed by mass spectrometry for identification. Results As expected, survival was significantly compromised in individuals infected with FR22c up to 72 hours post-injection, while mussels injected with FR21 exhibited fewer signs of distress (e.g., shell gaping) after 35–48 hours. Transcriptomic analyses revealed a broadly similar gene expression profile at 24 hours in mussels injected with either FR21 or FR22c. Although fewer transcripts were identified in gill samples, the same immune-related genes were regulated in both conditions. At 72 hours, only gill samples were analysed. Mussels infected with FR21 showed expression patterns trending back toward control levels, whereas individuals exposed to FR22c maintained a strong upregulation of immune-related genes. Conclusions This study provides new insights into the immune response of Mytilus edulis to the emerging pathogen F. halioticida. The combined use of transcriptomic and proteomic approaches validated the de novo transcriptome and shed light on the host’s immune response strategies. Further studies incorporating different environmental conditions and additional time points are necessary to deepen our understanding of host–pathogen interactions in this system.

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Dates et versions

hal-05240201 , version 1 (04-09-2025)

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  • HAL Id : hal-05240201 , version 1

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Hélène Bouras, Erwan Corre, Benoit Bernay, Jean Louis Blin, Manuel Savary, et al.. Immune response of Mytilus edulis challenged with low-virulence and high-virulence isolates of F. halioticida. 22nd International Conference on Disease of Fish and Shellfish, European Association of Fish Pathologist; Institute of Marine Biology, Biotechnology and Aquaculture (IMBBC) - Hellenic Center for Marine Research (HCMR), Sep 2025, Heraklion - Crète, Greece. ⟨hal-05240201⟩
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