Microbial education plays a crucial role in harnessing the beneficial properties of microbiota for infectious disease protection in Crassostrea gigas.

The increase in marine diseases, particularly in economically important mollusks, is a growing concern. Among them, the Pacific oyster (Crassostrea gigas) production faces challenges from several diseases, such as the Pacific Oyster Mortality Syndrome (POMS) or vibriosis. The microbial education, which consists of exposing the host immune system to beneficial microorganisms during early life stages is a promising approach against diseases.

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

Disease emergence is accelerating with global changes. Understanding by which mechanisms host populations can rapidly adapt will be crucial for management practices. Pacific oyster mortality syndrome (POMS) imposes a substantial and recurrent selective pressure on oyster populations, and rapid adaptation may arise through genetics and epigenetics.

A core of functional complementary bacteria infects oysters in Pacific Oyster Mortality Syndrome.

Background: The Pacific oyster Crassostrea gigas is one of the main cultivated invertebrate species worldwide. Since 2008, oyster juveniles have been confronted with a lethal syndrome known as the Pacific Oyster Mortality Syndrome (POMS). POMS is a polymicrobial disease initiated by a primary infection with the herpesvirus OsHV-1 µVar that creates an oyster immunocompromised state and evolves towards a secondary fatal bacteremia.

Functional Diversification of Oyster Big Defensins Generates Antimicrobial Specificity and Synergy against Members of the Microbiota.

Big defensins are two-domain antimicrobial peptides (AMPs) that have highly diversified in mollusks. -BigDefs are expressed by immune cells in the oyster , and their expression is dampened during the Pacific Oyster Mortality Syndrome (POMS), which evolves toward fatal bacteremia. We evaluated whether -BigDefs contribute to the control of oyster-associated microbial communities.

mA Profile Dynamics Indicates Regulation of Oyster Development by mA-RNA Epitranscriptomes.

The N-methylation of RNA adenosines (N-methyladenosine, mA) is an important regulator of gene expression with critical implications in vertebrate and insect development. However, the developmental significance of epitranscriptomes in lophotrochozoan organisms remains unknown. Using methylated RNA immunoprecipitation sequencing (MeRIP-seq), we generated transcriptome-wide mA-RNA methylomes covering the entire development of the oyster from oocytes to juveniles.

Time-series incubations in a coastal environment illuminates the importance of early colonizers and the complexity of bacterial biofilm dynamics on marine plastics.

The problematic of microplastics pollution in the marine environment is tightly linked to their colonization by a wide diversity of microorganisms, the so-called plastisphere. The composition of the plastisphere relies on a complex combination of multiple factors including the surrounding environment, the time of incubation along with the polymer type, making it difficult to understand how the biofilm evolves during the microplastic lifetime over the oceans. To better define bacterial community assembly processes on plastics, we performed a 5 months spatio-temporal survey of the plastisphere in an oyster farming area in the Bay of Brest (France).

Phage-host coevolution in natural populations.

Coevolution between bacteriophages (phages) and their bacterial hosts occurs through changes in resistance and counter-resistance mechanisms. To assess phage-host evolution in wild populations, we isolated 195 Vibrio crassostreae strains and 243 vibriophages during a 5-month time series from an oyster farm and combined these isolates with existing V. crassostreae and phage isolates.

Early life microbial exposures shape the Crassostrea gigas immune system for lifelong and intergenerational disease protection.

Background: The interaction of organisms with their surrounding microbial communities influences many biological processes, a notable example of which is the shaping of the immune system in early life. In the Pacific oyster, Crassostrea gigas, the role of the environmental microbial community on immune system maturation - and, importantly, protection from infectious disease - is still an open question.

Results: Here, we demonstrate that early life microbial exposure durably improves oyster survival when challenged with the pathogen causing Pacific oyster mortality syndrome (POMS), both in the exposed generation and in the subsequent one.

Life history of oysters influences Vibrio parahaemolyticus accumulation in Pacific oysters (Crassostrea gigas).

Vibrio parahaemolyticus infection in humans is associated with raw oyster consumption. Evaluation of V. parahaemolyticus presence in oysters is of most interest because of the economic and public health issues that it represents.

Seaweeds influence oyster microbiota and disease susceptibility.

A growing awareness of role that microbiota can play in mediating the effects of pathogens on hosts has given rise to the concept of the pathobiome. Recently, we demonstrated that the Pacific oyster mortality syndrome affecting Crassostrea gigas oysters is caused by infection with the Ostreid herpesvirus type 1 (OsHV-1) followed by infection with multiple bacterial taxa. Here we extend the concept of this pathobiome beyond the host species and its bacterial microbiota by investigating how seaweed living in association with oysters influences their response to the disease.

Microbiota of the Digestive Glands and Extrapallial Fluids of Clams Evolve Differently Over Time Depending on the Intertidal Position.

The Manila clam (Ruditapes philippinarum) is the second most exploited bivalve in the world but remains threatened by diseases and global changes. Their associated microbiota play a key role in their fitness and acclimation capacities. This study aimed at better understanding the behavior of clam digestive glands and extrapallial fluids microbiota at small, but contrasting spatial and temporal scales.

The Pacific Oyster Mortality Syndrome, a Polymicrobial and Multifactorial Disease: State of Knowledge and Future Directions.

The Pacific oyster () has been introduced from Asia to numerous countries around the world during the 20th century. is the main oyster species farmed worldwide and represents more than 98% of oyster production. The severity of disease outbreaks that affect , which primarily impact juvenile oysters, has increased dramatically since 2008.

Amino-nanopolystyrene exposures of oyster () embryos induced no apparent intergenerational effects.

Early life stages (ELS) of numerous marine invertebrates mustcope with man-made contaminants, including plastic debris, during their pelagic phase. Among the diversity of plastic particles, nano-sized debris, known as nanoplastics, can induce effects with severe outcomes in ELS of various biological models, including the Pacific oyster . Here, we investigated the effects of a sub-lethal dose (0.

Oyster hemolymph is a complex and dynamic ecosystem hosting bacteria, protists and viruses.

Background: The impact of the microbiota on host fitness has so far mainly been demonstrated for the bacterial microbiome. We know much less about host-associated protist and viral communities, largely due to technical issues. However, all microorganisms within a microbiome potentially interact with each other as well as with the host and the environment, therefore likely affecting the host health.

High temperature induces transcriptomic changes in that hinder progress of ostreid herpesvirus (OsHV-1) and promote survival.

Of all environmental factors, seawater temperature plays a decisive role in triggering marine diseases. Like fever in vertebrates, high seawater temperature could modulate the host response to pathogens in ectothermic animals. In France, massive mortality of Pacific oysters, , caused by the ostreid herpesvirus 1 (OsHV-1) is markedly reduced when temperatures exceed 24°C in the field.

Contribution of Viral Genomic Diversity to Oyster Susceptibility in the Pacific Oyster Mortality Syndrome.

Juvenile Pacific oysters () are subjected to recurrent episodes of mass mortalities that constitute a threat for the oyster industry. This mortality syndrome named "Pacific Oyster Mortality Syndrome" (POMS) is a polymicrobial disease whose pathogenesis is initiated by a primary infection by a variant of an Ostreid herpes virus named OsHV-1 μVar. The characterization of the OsHV-1 genome during different disease outbreaks occurring in different geographic areas has revealed the existence of a genomic diversity for OsHV-1 μVar.

A functional m A-RNA methylation pathway in the oyster Crassostrea gigas assumes epitranscriptomic regulation of lophotrochozoan development.

N -methyladenosine (m A) is a prevalent epitranscriptomic mark in eukaryotic RNA, with crucial roles for mammalian and ecdysozoan development. Indeed, m A-RNA and the related protein machinery are important for splicing, translation, maternal-to-zygotic transition and cell differentiation. However, to date, the presence of an m A-RNA pathway remains unknown in more distant animals, questioning the evolution and significance of the epitranscriptomic regulation.

The marine intertidal zone shapes oyster and clam digestive bacterial microbiota.

Digestive microbiota provide a wide range of beneficial effects on host physiology and are therefore likely to play a key role in marine intertidal bivalve ability to acclimatize to the intertidal zone. This study investigated the effect of intertidal levels on the digestive bacterial microbiota of oysters (Crassostrea gigas) and clams (Ruditapes philippinarum), two bivalves with different ecological niches. Based on 16S rRNA region sequencing, digestive glands, seawater and sediments harbored specific bacterial communities, dominated by operational taxonomic units assigned to the Mycoplasmatales,Desulfobacterales and Rhodobacterales orders, respectively.

Latitudinal drivers of oyster mortality: deciphering host, pathogen and environmental risk factors.

Diseases pose an ongoing threat to aquaculture, fisheries and conservation of marine species, and determination of risk factors of disease is crucial for management. Our objective was to decipher the effects of host, pathogen and environmental factors on disease-induced mortality of Pacific oysters (Crassostrea gigas) across a latitudinal gradient. We deployed young and adult oysters at 13 sites in France and we monitored survival, pathogens and environmental parameters.

Author Correction: Proteinaceous secretion of bioadhesive produced during crawling and settlement of Crassostrea gigas larvae.

An amendment to this paper has been published and can be accessed via a link at the top of the paper.

Microbiota Composition and Evenness Predict Survival Rate of Oysters Confronted to Pacific Oyster Mortality Syndrome.

Pacific Oyster Mortality Syndrome (POMS) affects oysters worldwide and causes important economic losses. Disease dynamic was recently deciphered and revealed a multiple and progressive infection caused by the OsHV-1 μVar, triggering an immunosuppression followed by microbiota destabilization and bacteraemia by opportunistic bacterial pathogens. However, it remains unknown if microbiota might participate to protect oysters against POMS, and if microbiota characteristics might be predictive of oyster mortalities.

A Sustained Immune Response Supports Long-Term Antiviral Immune Priming in the Pacific Oyster, Crassostrea gigas.

Over the last decade, innate immune priming has been evidenced in many invertebrate phyla. If mechanistic models have been proposed, molecular studies aiming to substantiate these models have remained scarce. We reveal here the transcriptional signature associated with immune priming in the oyster Oysters were fully protected against Ostreid herpesvirus 1 (OsHV-1), a major oyster pathogen, after priming with poly(I·C), which mimics viral double-stranded RNA.