How Oysters' Immune Systems Interact With Their Microbes

Jim Crocker
20th March, 2024

Image Source: Natural Science News, 2024

Key Findings

In coastal waters, Pacific oysters' immune systems are boosted for life by early exposure to diverse microbes
Oysters produce special proteins to maintain a healthy balance of these microbes
Disruption of this balance by diseases like POMS can lead to fatal infections in oysters

In the coastal waters where Pacific oysters (Crassostrea gigas) thrive, a microscopic world bustles with life. These oysters, studied by researchers at the University of Montpellier^[1], are not just passive inhabitants of their environment; they are active participants in a complex microbial ecosystem. The study sheds light on how the oysters' immune systems interact with this ecosystem, and how this relationship can determine their health and survival. The researchers found that the oysters' immune systems are educated early in life, right after fertilization, by exposure to the diverse microbial community in their environment. This early exposure is crucial because it leads to an increase in the oysters' immune competence that lasts their entire life. This enhanced immunity provides better protection against diseases, such as the Pacific Oyster Mortality Syndrome (POMS), later on. POMS is a significant threat to oyster populations and has been linked to a polymicrobial disease involving a virus known as ostreid herpesvirus 1 (OsHV-1) and several strains of bacteria, including Vibrio species^[2]. The disease has been causing mass die-offs of oysters across the globe, and understanding the interactions between oysters and their microbial environment is key to combating it. The study from the University of Montpellier indicates that the oysters' microbiota, the community of microorganisms living in or on the oysters, is essential for educating their immune system. This process involves epigenetic remodelling, which means that the oysters' experiences with microbes can cause changes in how their genes are expressed without altering the DNA sequence itself. These changes can then be passed on to the next generation, conferring benefits even to oysters that have not yet encountered the same microbial challenges. As oysters grow, their immune systems, which express a diverse array of immune genes, continue to interact with the microbiota. The balance of this relationship is maintained in part by antimicrobial peptides, molecules that the oysters produce to defend against harmful microbes. These peptides have specific and synergistic effects, fine-tuning the composition of the microbiota to maintain a healthy state, known as homeostasis^[3]. However, this balance can be disrupted by POMS. The study^[2] revealed that certain Vibrio bacteria, such as Vibrio harveyi, can exploit a weakened oyster immune system, caused by the OsHV-1 virus, to grow rapidly and cause disease. These bacteria can suppress the oyster's immune responses and even promote the growth of other bacteria, leading to a condition known as dysbiosis, where the normal microbial balance is disturbed. This can result in fatal sepsis, an overwhelming body-wide response to infection. Interestingly, rapid adaptation to diseases like POMS is possible through both genetic and epigenetic mechanisms. A study^[4] demonstrated that oysters exposed to POMS show signs of selection at the genetic and epigenetic levels, with changes in immune-related genes and DNA methylation patterns, which are a form of epigenetic modification. This suggests that oysters can quickly adapt to new threats, potentially offering a glimmer of hope for oyster conservation and aquaculture. In summary, the study from the University of Montpellier illustrates the delicate interplay between the Pacific oyster's immune system and its microbiota. This relationship is vital for the oyster's health and resilience against diseases. The findings underscore the importance of microbial exposure during early development and the role of antimicrobial peptides in maintaining a healthy balance of microbes. Understanding these interactions is crucial for managing the health of oyster populations and may inform strategies to protect them from threats like POMS.

Biotech Marine Biology

References

Main Study

1) Cross-talk and mutual shaping between the immune system and the microbiota during an oyster's life.

Published 18th March, 2024

https://doi.org/10.1098/rstb.2023.0065

Related Studies

2) Cooperation and cheating orchestrate Vibrio assemblages and polymicrobial synergy in oysters infected with OsHV-1 virus.

https://doi.org/10.1073/pnas.2305195120

3) Ecology-relevant bacteria drive the evolution of host antimicrobial peptides in Drosophila.

https://doi.org/10.1126/science.adg5725

4) Epigenetic variations are more substantial than genetic variations in rapid adaptation of oyster to Pacific oyster mortality syndrome.

https://doi.org/10.1126/sciadv.adh8990

Key Findings

References

Main Study

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