Increasing oyster immunity: educating larvae with friendly bacteria

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By Milthon Lujan


Pacific oysters Crassostrea gigas (also known as Magallana gigas) are particularly susceptible to Pacific Oyster Mortality Syndrome (POMS) and vibriosis. Traditional methods such as selective breeding have limitations. But a new frontier in oyster health is emerging: microbial education.

Scientists from the University of Perpignan (France), the University of Montpellier (France), the University of Brest (France), and Sorbonne University are exploring a new approach called microbial education. This involves exposing young oysters (during their larval stage) to controlled communities of beneficial bacteria. These friendly microbes act as trainers, helping the oyster’s immune system learn to recognize and combat harmful pathogens in the future. The study adds to other research on the importance of “teaching” oysters to defend themselves against viruses such as OsHV-1.

Deadly duos: POMS and vibriosis

POMS, caused by the Ostreid herpesvirus, particularly attacks young oysters, sometimes wiping out entire batches in French farms. Vibriosis, caused by the bacterium Vibrio aestuarianus, primarily attacks market-sized oysters, causing significant economic losses.

Combating the threat: new approaches emerge

The fight against these diseases has multiple fronts. The genetic selection of farmed oysters aims to produce resistant oysters, but this approach can have unintended consequences. Immune priming with viral mimics is promising against POMS, but it does not offer protection against vibriosis.

The power of microbes: Can friendly bacteria help?

Previous research explored the use of wild microbiota from healthy adult oysters to educate the immune system. While this showed promise, there is a risk of transferring harmful pathogens along with beneficial bacteria.

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Research suggests a fascinating solution: microbial education. This involves exposing young oysters to beneficial bacteria during their larval stage. Studies show that a healthy gut microbiome in the early stages of life plays a crucial role in the long-term immune response of various marine organisms.

The power of early exposure

The recent study investigated the effectiveness of microbial education in four distinct populations of oysters from different geographic regions. This allows us to understand how geographic factors might influence the response to bacterial exposure. Researchers exposed the larvae to different types of bacteria:

  • Cultured bacterial mixes: These mixes were designed to combat a specific disease, Pacific Oyster Mortality Syndrome (POMS).
  • Complete microbial communities: These came from healthy adult oysters and offered broader protection against POMS and another bacterial infection, Vibrio aestuarianus.

The study’s findings demonstrate that exposing oyster larvae to specific microbial communities can “educate” their immune system. By introducing these beneficial bacteria early on, scientists observed a protective effect against POMS and vibriosis. However, the effectiveness varied depending on:

  • Origin of the oysters: Different oyster populations responded better to specific bacterial mixes.
  • Composition of the bacterial mix: The type of bacteria used for exposure played a crucial role. Interestingly, exposing oysters to bacteria from their own environment (sympatric strains) did not offer any specific advantage.

Long-term benefits, transient hosts

The study also revealed some fascinating details about the impact of microbial education. While the introduced bacteria did not permanently colonize the oyster’s gut, the exposure caused long-term changes in the overall microbial composition. This suggests a form of “immune memory” developed by the oyster’s own microbiome. Additionally, the study found that microbial education triggered changes in the expression of immune genes within the oyster itself, further strengthening its defenses.

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The research opens up interesting possibilities for the future of oyster aquaculture. By implementing microbial education techniques, aquaculturists could potentially raise oysters with greater resistance to a variety of diseases. This could lead to healthier oyster populations, reduced economic losses, and a more sustainable fishing industry.

  • Exposing oyster larvae to beneficial bacteria can “educate” their immune system.
  • This education offers protection against diseases like POMS and vibriosis.
  • Effectiveness depends on the origin of the oysters and the type of bacteria used.
  • The benefits are long-lasting despite the transient presence of introduced bacteria.
  • Microbial education holds great promise for the future of oyster aquaculture.

This study was supported by the Ifremer GT-huitre project and the European Maritime and Fisheries Fund, the “Microval” project of the Bonus Qualité Recherche program of the University of Perpignan, the “gigantimic 1” project of the research federation of the University of Perpignan, the “gigantimic 2” project of the Kim Nutrition and Health Foundation of MUSE, and the ANR DECICOMP project.

Luc Dantan
IHPE, Univ. Montpellier, CNRS, IFREMER, Univ. Perpignan Via Domitia, Perpignan, France
Email: luc.dantan@gmail.com

Reference (open access)
Luc Dantan, Prunelle Carcassonne, Lionel Dégremont, Benjamin Morga, Marie-Agnès Travers, Bruno Petton, Mickael Mege, Elise Maurouard, Jean-François Allienne, Gaëlle Courtay, Océane Romatif, Juliette Pouzadoux, Raphaël Lami, Laurent Intertaglia, Yannick Gueguen, Jeremie Vidal-Dupiol, Eve Toulza, Céline Cosseau. 2024. Microbial education plays a crucial role in harnessing the beneficial properties of microbiota for infectious disease protection in Crassostrea gigas. bioRxiv 2024.05.17.594303; doi: https://doi.org/10.1101/2024.05.17.594303