Oyster Crassostrea Gigas Research Articles

Gene biomarkers in estuarine oysters indicate pollution profiles of metals, brominated flame retardants, and poly- and perfluoroalkyl substances in and near the Laizhou Bay

The Laizhou Bay (LZB) is of ecological and fishery importance. The discharge of effluents containing numerous pollutants into the LZB via rivers poses significant risks to ecosystem and human health. Estuarine biomonitoring is therefore crucial for assessing the contribution of rivers to coastal pollution and their impacts on species. Estuarine oyster Crassostrea gigas is a preferable bioindicator to pollution conditions. This study measured accumulation of contaminants and expression levels of gene biomarkers in the LZB and Northern Shandong Peninsula (NSP) oysters. The LZB oysters accumulated higher levels of brominated flame retardants (BFRs) and poly- and perfluoroalkyl substances (PFAS), while NSP oysters exhibited greater accumulation of heavy metals. Decabromodiphenyl ethane was the dominant BFR, while perfluorooctanoic acid and perfluoro-2-methoxyacetic acid were the dominant PFASs in oysters. The expression of gene biomarkers effectively distinguished the LZB and NSP oysters, with CYP2 subfamilies expression correlating with BFRs and PFASs and metallothionein expression indicating heavy metals. The reproductive endocrine and neuroendocrine-immune systems in oysters might be the targets of BFRs and heavy metal pollution, respectively. The negative correlation between contaminant accumulation and gene expression might be explained by adaptive evolution, emphasizing the need to consider genetic diversity in ecological risk assessments.

Comparative analysis of growth and metabolism in diploid and triploid Pacific oysters Crassostrea gigas under different temperature and salinity

Comparative analysis of growth and metabolism in diploid and triploid Pacific oysters Crassostrea gigas under different temperature and salinity

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. This study explores the concept of microbial education using controlled and pathogen-free bacterial communities and assesses its protective effects against POMS and Vibrio aestuarianus infections, highlighting potential applications in oyster production. We demonstrate that it is possible to educate the oyster immune system by adding microorganisms during the larval stage. Adding culture based bacterial mixes to larvae protects only against the POMS disease while adding whole microbial communities from oyster donors protects against both POMS and vibriosis. The efficiency of immune protection depends both on oyster origin and on the composition of the bacterial mixes used for exposure. No preferential protection was observed when the oysters were stimulated with their sympatric strains. Furthermore, the added bacteria were not maintained into the oyster microbiota, but this bacterial addition induced long term changes in the microbiota composition and oyster immune gene expression. Our study reveals successful immune system education of oysters by introducing beneficial microorganisms during the larval stage. We improved the long-term resistance of oysters against critical diseases (POMS disease and Vibrio aestuarianus infections) highlighting the potential of microbial education in aquaculture.

QTL mapping reveals predominantly nonadditive genetic architecture of heterotic growth traits in yearling Pacific oysters Crassostrea gigas

QTL mapping reveals predominantly nonadditive genetic architecture of heterotic growth traits in yearling Pacific oysters Crassostrea gigas

Genetic diversity and genetic structure in successive mass selected generations of tetraploid Pacific oysters (Crassostrea gigas), diploid Portuguese oysters (C. angulata) and their allotriploid oysters

In bivalve aquaculture, tetraploids are commonly used to generate sterile triploids for commercial aquaculture. We obtained the allotriploid population (tetraploid C. gigas ♂ × diploid C. angulata ♀) through the hybridization of tetraploid male C. gigas with diploid female C. angulata for the first time. However, the genetic diversity and genetic structure in successive mass selected generations of tetraploid C. gigas, diploid C. angulata and their allotriploid offspring are currently unknown. In this study, nine polymorphic microsatellite markers were used to evaluate their genetic diversity and genetic structure. The trend of reduced genetic diversity was recorded in successive generations of mass selected tetraploid C. gigas and diploid C. angulata. However, the diversity of the allotriploid population was significantly higher than that of the male parent population and the female parent population. This indicates that the hybridization technique of tetraploid C. gigas + diploid C. angulata to produce triploids is beneficial for increasing the genetic diversity of the hybrid triploid. Little genetic differentiation was found within tetraploid C. gigas and diploid C. angulata (except A3, the third generation of C. angulata), which is most likely caused by the insignificant genetic structure of the selected lines. The large genetic differences between tetraploid C. gigas and diploid C. angulata are caused by subspecies differences and ploidy difference. In addition, allotriploids were found to be more closely related to the female population, suggesting that this genetic relationship is more consistent with phenotypic traits. The findings of this study offer useful information for further genetic improvement of oyster polyploidy breeding.

Comparative performance of selected triploid oysters Crassostrea (Magallana) gigas, produced by chemical induction and mated triploid techniques, to their diploid counterparts

Comparative performance of selected triploid oysters Crassostrea (Magallana) gigas, produced by chemical induction and mated triploid techniques, to their diploid counterparts

KiNext: a portable and scalable workflow for the identification and classification of protein kinases

BackgroundProtein kinases are a diverse superfamily of proteins common to organisms across the tree of life that are typically involved in signal transduction, allowing organisms to sense and respond to biotic or abiotic environmental factors. They have important roles in organismal physiology, including development, reproduction, acclimation to environmental stress, while their dysregulation can lead to disease, including several forms of cancer. Identifying the complement of protein kinases (the kinome) of any organism is useful for understanding its physiological capabilities, limitations and adaptations to environmental stress. The increasing availability of genomes makes it now possible to examine and compare the kinomes across a broad diversity of organisms. Here we present a pipeline respecting the FAIR principles (findable, accessible, interoperable and reusable) that facilitates the search and identification of protein kinases from a predicted proteome, and classifies them according to group of serine/threonine/tyrosine protein kinases present in eukaryotes.ResultsKiNext is a Nextflow pipeline that regroups a number of existing bioinformatic tools to search for and classify the protein kinases of an organism in a reproducible manner, starting from a set of amino acid sequences. Conventional eukaryotic protein kinases (ePKs) and atypical protein kinases (aPKs) are identified by using Hidden Markov Models (HMMs) generated from the catalytic domains of kinases. Furthermore, KiNext categorizes ePKs into the eight kinase groups by employing dedicated Hidden Markov Models (HMMs) tailored for each group. The performance of the KiNext pipeline was validated against previously identified kinomes obtained with other tools that were already published for two marine species, the Pacific oyster Crassostrea gigas and the unicellular green alga Ostreoccocus tauri. KiNext outperformed previous results by finding previously unidentified kinases and by attributing a large proportion of previously unclassified kinases to a group in both species. These results demonstrate improvements in kinase identification and classification, all while providing traceability and reproducibility of results in a FAIR pipeline. The default HMM models provided with KiNext are most suitable for eukaryotes, but the pipeline can be easily modified to include HMM models for other taxa of interest.ConclusionThe KiNext pipeline enables efficient and reproducible identification of kinomes based on predicted amino acid sequences (i.e. proteomes). KiNext was designed to be easy to use, automated, portable and scalable.

Environmental Conditions Associated with Four Index Cases of Pacific Oyster Mortality Syndrome (POMS) in Crassostrea gigas in Australia Between 2010 and 2024: Emergence or Introduction of Ostreid herpesvirus-1?

Warm water temperature is a risk factor for recurrent mass mortality in farmed Pacific oysters Crassostrea gigas caused by Ostreid herpesvirus-1, but there is little information on environmental conditions when the disease first appears in a region-the index case. Environmental conditions between four index cases in Australia (2010, 2013, 2016 and 2024) were compared to provide insight into possible origins of the virus. Each index case was preceded by unusually low rainfall and higher rates of temperature change that could increase oyster susceptibility through thermal flux stress. Water temperature alone did not explain the index cases, there being no consistency in sea surface, estuary or air temperatures between them. Tidal cycles and chlorophyll-a levels were unremarkable, harmful algae were present in all index cases and anthropogenic environmental contamination was unlikely. The lack of an interpretable change in the estuarine environment suggests the recent introduction of OsHV-1; however, viral emergence from a local reservoir cannot be excluded. Future events will be difficult to predict. Temperature flux and rainfall are likely important, but they are proxies for a range of undetermined factors and to identify these, it will be necessary to develop comprehensive protocols for data acquisition during future index cases.

Regulation Mechanisms of the Glutamate Transporter in the Response of Pacific Oyster upon High-Temperature Stress.

Glutamate transporters (GLTs) are integral to the glutamatergic system, modulating glutamate homeostasis to enhance resilience and resistance against environmental stress. There are six GLTs identified in the Pacific oyster (Crassostrea gigas), which were categorized into two subfamilies: excitatory amino acid transporters (CgEAATs) and vesicular glutamate transporters (CgVGLUTs). The CgEAATs harbor a GltP domain, while CgVGLUTs feature an MFS domain, both with conserved sequence and structural characteristics. The expression of CgGLTs is elevated during the planktonic larval stage compared to the fertilized egg stage and is constitutively expressed in various tissues of adult oysters, suggesting its critical role in both larval development and the physiological processes of adult oysters. Transcriptomic analysis revealed diverse expression patterns of GLTs in oyster gills after 7 days of high-temperature stress, with CgEAAT3 showing a significant upregulation. A KEGG pathway enrichment analysis identified glutathione metabolism and ferroptosis as prominently enriched pathways. At 48 h after high-temperature stress, the expression levels of Glutathione Peroxidase 4 (CgGPX4) and CgEAAT3, along with elevated Fe content in the gills, significantly increased. Moreover, the RNAi-mediated the inhibition of CgEAAT3 expression under high-temperature stress, resulting in a significant reduction in CgGPX4 expression and a further increase in Fe accumulation in oyster gills. These results indicate that CgEAAT3 contributes to the regulation of ferroptosis and redox homeostasis by modulating CgGPX4 expression. This study provides new insights into the adaptive mechanisms of bivalves to environmental stress.

Insights into PFAS contaminants before and after sewage discharges into a marine protected harbour

Per and polyfluoroalkyl substances (PFAS) and their degradation products are a concern to human and ecosystem health. Wastewater treatment plants are not efficient at removing PFAS compounds and are thought to be a major source of these compounds to marine environments. The sewerage infrastructure in the UK, has over 20,000 combined stormwater overflows (CSOs). These CSOs are relief values whereby untreated wastewater can discharge under permit from the Environment Agency with exceptional rain/snowfall conditions. CSOs discharged 3.6 million monitored hours of untreated wastewater into English rivers and coasts in 2023. Concerns have been raised about the proximity of these CSO discharges to highly protected marine habitats. This study is the first to determine that PFAS concentrations are elevated in a highly protected marine bay (Langstone Harbour, England) following recent sewage releases compared to an extended period without discharge. Analysis was carried out into a suite of 54 PFAS compounds of which only one (PFHpA) was detectable above LOD prior to discharges but 8 afterwards. These included banned PFOS (Linear and Branched 8.6 ng/L ∓ 0.90) and PFOA (2.9 ng/L ∓ 0.29) which were above annual average EQS for inland and ‘other’ surface waters. Most of the PFAS compounds detected doubled in concentration above LODs. These two-fold increases we discuss are likely conservative estimates based on the use of LODs and tidal conditions. Additional Oysters (Crassostrea gigas) and Seaweed (Fucus vesiculosus) were taken revealing high concentrations of the shorter chain PFBA (6.99μg/kg ∓ 2.42 ww) in seaweed samples. These seaweeds were calculated to have conservative bioaccumulation factors (BAF) > 6000 for PFBA indicating these algae might be an important reservoir of some PFAS contamination. We discuss these results in the context of the largescale discharges of untreated wastewater nationally and globally, and call upon a need for a better understanding of the transfer of PFAS contaminants into marine food chains.

DHMBA, a molecule from Pacific oyster (Crassostrea gigas) alleviates AD pathology by inhibiting ubiquination of Nrf2

Alzheimer's disease (AD) is an age-related, progressive neurodegenerative disorder with oxidative stress and infammation in brain. 3,5-dihydroxy-4-methoxybenzyl alcohol (DHMBA) is a newly identified molecule with antioxidant capacity in Pacific oyster (Crassostrea gigas), but its detailed mechanism of antioxidant activity remains unexplored. In this study, we identified that DHMBA inhibits Nrf2 degradation and alleviates AD Pathology in AD model mice. Treatment with DHMBA significantly reduced levels of β-amyloid (Aβ) and phosphorylated Tau protein in the hippocampus, while also improving anxiety-like behaviors, depressive-like behaviors, and working memory capabilities in AD model mice. Furthermore, DHMBA increased neuronal density within the brain. Additionally, both in the AD cell model and AD model mice, DHMBA was found to significantly upregulate nuclear factor erythroid 2-like 2 (Nrf2) protein levels along with its target genes. We revealed that DHMBA hinders the binding between Keap1 and Nrf2, thereby relieving Nrf2 ubiquitination and increasing Nrf2 protein levels to enhance cellular capacities for antioxidation and anti-inflammation. These findings demonstrate the mechanism by which DHMBA alleviates AD and provide a new insight into the treatment of AD.

Identification of a T-box transcription factor TBX2 and its negative regulatory role in melanin production in the Pacific oyster Crassostrea gigas

Oyster shells exhibit varying color patterns—black, white, or black and white striations—attributable to differences in melanin content and distribution. In this study, we identified a new homolog of TBX2, a member of the T-box transcription factor family, in the Pacific oyster (Crassostrea gigas) named CgTBX2. The mRNA expression of CgTBX2 was higher in tissues from white-shelled oysters than in those from black-shelled oysters. Knockdown of CgTBX2 in C. gigas significantly upregulated the expression of two key genes involved in melanin synthesis, CgTYR and CgTYR2. The tissue expression profile revealed that CgTBX2 is highly expressed in gill and mantle. CgTBX2 protein is mainly localized in the nucleus and can combine with TBX-binding elements (TBEs) present in the CgOCA2 promoter. CgTBX2 repressed the activity of the CgOCA2 promoter, with a strong transcriptional inhibition effect on the −2000 to −878 and −211 to −1 regions. Furthermore, the combination of CgTBX2 with GTTGACACCTT sequence is responsible for the transcriptional inhibition on the −211 to −1 region of the CgOCA2 promoter. Our findings reveal that CgTBX2, a novel regulator of melanin pigmentation in C. gigas, negatively regulates melanin deposition by inhibiting tyrosinase genes expression and repressing the transcriptional activity of the CgOCA2 promoter.

Overexpression of CDC42 causes accumulation of DNA damage leading to failure of oogenesis in triploid Pacific oyster Crassostrea gigas

Triploid Pacific oyster Crassostrea gigas exhibits notable differences in fecundity, with the majority being sterile individuals, referred to as female β, which produce few oocytes, while a minority are fertile individuals, referred to as female α, which produce abundant oocytes. However, the molecular mechanisms underlying these differences in triploid fecundity remain poorly understood. CDC42 has been implicated in processes related to increased DNA damage and genomic instability. Here, we investigate the crucial role of CDC42 in DNA damage repair during oogenesis in triploid C. gigas. Immunofluorescence analysis of γH2AX, a marker for DNA double-stranded breaks, showed significantly higher levels of DNA damage in gonadal cells of triploids compared to diploids, particularly in female β. Histological and ultrastructural analyses revealed abnormal germ cells, termed β gonia, characterized by giant nuclei condensed into irregular chromosome-like chromatin, present in triploid gonadal follicles. RNAseq and proteomic analyses revealed significantly elevated CDC42 expression in triploid gonads compared to the diploids. Inhibition of CDC42 activity in triploids using ZCL278, a CDC42-specific inhibitor, resulted in a significant reduction in DNA damage, increased oocyte numbers, and a decrease in β gonia count. Transcriptome profiling revealed that CDC42 inhibition upregulated the PI3K-AKT signaling pathway along with DNA repair activation. Overall, our findings suggest that overexpression of CDC42 during oogenesis in triploid C. gigas impedes DNA repair, leading to the accumulation of DNA damage, and consequently, oogenesis blockade and abnormal germ cell differentiation. Conversely, inhibition of CDC42 activity activates the PI3K-AKT signaling pathway and promotes DNA repair, thereby mitigating DNA damage and facilitating oogenesis in triploids. This study provides new insights into the molecular mechanisms of sterility in female triploid C. gigas.

"Groundbreaking study: Combined effect of marine heatwaves and polyethylene microplastics on Pacific oysters, Crassostrea gigas"

Microplastics (MPs) and rising marine seawater temperatures are one of the major environmental problems threatening the survival of marine organisms and biodiversity. However, interactions between such multiple stressors are virtually unexplored. This study aimed to assess the combined effect of two temperatures and polyethylene MPs on the Pacific oyster Crassostrea gigas, one of the most globalized mollusc species for aquaculture. Our work highlights the potential ecological risk posed by these two factors on marine bivalve molluscs. The experimental design was carried out following a 14-day exposure of oysters to environmental concentrations of polyethylene MPs (0.01 mg.L-1), and to two temperatures (15 °C and 22 °C). Sampling was performed on days 0, 7, and 14. The μ-FTIR analysis was applied to quantify MPs of interest and to check a potential environmental contamination. Tissue samples of digestive glands were collected from the oysters to evaluate the activity of biomarkers including superoxide dismutase, glutathione-s-transferase, malondialdehyde and laccase through protein levels. We note that the combination of MPs and high water temperature (HWT, 22 °C) had a significant impact both on the survival of animals and on stress markers, by modifying lipid peroxidation and immune responses. This original study gave the first innovative results on this topic and provides us with knowledge of the combined effects of MPs pollution and HWT (simulating marine heatwaves situation) on C. gigas. There remains a lack of information on the toxicity and the potential environmental hazard of plastics in the marine environment.

Microfiber Content in Pacific Oysters (Crassostrea gigas) from Morro Bay, California

Microfiber Content in Pacific Oysters (Crassostrea gigas) from Morro Bay, California

Microbial profiling of oysters from a processing plant and retail products: Analysis based on culture-dependent methods and 16S rRNA gene sequencing

Oysters (Crassostrea gigas) are one of the most consumed shellfish globally. However, there is a lack of comprehensive microbiome studies that include the processing and distribution stages of oysters. The present study used both culture-based methods and 16S rRNA sequencing to produce comprehensive microbial profiles of oysters in two parts: (1) an oyster processing plant that processes raw and frozen oysters (n = 57) and (2) retail oyster products across two seasons (winter and spring) (n = 112). In the processing plant, shucking increased the aerobic plate count (APC) from 1.86 log CFU/g in freshly harvested oysters to 3.95 log CFU/g in shucked oysters. Controlling the washing process is important, as the APCs decreased after washing and remained level until the final products, raw and frozen oysters (2.54 and 2.34 log CFU/g, respectively). After desalting in the frozen oyster plant, the bacterial community shifted to be dominated by the family Spirochaetaceae, Mycoplasma, and Shigella taxa, indicating a need to control problematic bacteria in the desalting process. SourceTracker analysis revealed that raw materials contributed more to the microbiota of final products than environmental samples. In retail oyster products, APCs were marginally higher in spring (3.58 log CFU/g) than in winter (3.05 log CFU/g) samples. While bacterial count differences were not dramatic, the proportions of taxa in the microbial community differed by season. In winter retail products, Photobacterium (27.91 %) and Aliivibrio (20.42 %) dominated, while spring samples showed a diverse distribution of the family Vibrionaceae (19.90 %), Photobacterium (14.20 %), Psychromonas (11.84 %), and Aliivibrio (7.20 %). These findings contributed to our understanding of oyster microorganisms and identified food safety control points and cross-contamination sources. This in-depth understanding is expected to inform the development of fishery and seafood safety management measures.

Marine thermal fluctuation induced gluconeogenesis by the transcriptional regulation of CgCREBL2 in Pacific oysters

Marine thermal fluctuation profoundly influences energy metabolism, physiology, and survival of marine life. In the present study, short-term and long-term high-temperature stresses were found to affect gluconeogenesis by inhibiting PEPCK activity in the Pacific oyster (Crassostrea gigas), which is a globally distributed species that encounters significant marine thermal fluctuations in intertidal zones worldwide. CgCREBL2, a key molecule in the regulation of gluconeogenesis, plays a critical role in the transcriptional regulation of PEPCK in gluconeogenesis against high-temperature stress. CgCREBL2 was able to increase the transcription of CgPEPCK by either binding the promoter of CgPEPCK gene or activating CgPGC-1α and CgHNF-4α after short-term (6 h) high-temperature stress, while only by binding CgPEPCK after long-term (60 h) high-temperature stress. These findings will further our understanding of the effect of marine thermal fluctuation on energy metabolism on marine organisms.

Effect of diet on larval settlement, growth, and spat survival of the oyster Crassostrea gigas (Thunberg, 1793)

This study aimed to assess the impact of microalgal concentrations in diets on the settlement and metamorphosis stages of pediveliger larvae and spat of Crassostrea gigas oysters. Diets containing microalgal concentrations of 8, 12, and 16×104 cells mL-1 were administered for seven days during the larval settlement phase of pediveliger larvae. In the metamorphosis and postlarval cultivation phases, diets with microalgal concentrations of 8, 16, 24, and 32×104 cells mL-1 and a control group without food were tested for 14 and 21 days, respectively. Growth, yield, and survival were assessed every seven days. The diet comprised 30% Isochrysis galbana and 70% Chaetoceros muelleri microalgae. In the metamorphosis phase, the results revealed no significant differences in larval metamorphosis rate and survival across the tested diets. The concentrations exhibited similar survival in the spat with an initial average shell height of 0.657 ± 0.05 mm, with a significant difference only in growth. In the spat with an initial average shell height of 0.830 ± 0.12 mm, no differences in survival were observed among the tested concentrations. We concluded that diets of 12 and 16×104 cells mL-1 provide high rates of larval metamorphosis and spat yield during the larval settlement and metamorphosis phases. During the spat cultivation phases, diets of 32 and 24×104 cells mL-1 could optimize the cultivation time and yield of C. gigas spat in the laboratory. However, when considering survival alone, no advantage was found in providing a diet with a microalgal concentration above 8×104 cells mL-1 across all C. gigas oyster cultivation phases.

Profiling of chromatin accessibility and regulatory elements toward understanding the mechanisms underlying growth regulation in the Pacific oyster (Crassostrea gigas)

Changes in phenotype are precisely controlled by transcriptional regulators, which depend on chromatin remodeling. Although artificial genetic breeding has significantly improved the growth performance of the Pacific oyster (Crassostrea gigas), the identification of gene regulatory elements and transcription factors related to growth is obscure. In this study, we performed a genome-wide characterization of chromatin accessibility using two strains of C. gigas that exhibit significant differences in growth. The results showed that accessible chromatin regions were mainly distributed in the noncoding regions of the genome, with a greater proportion of distal intergenic regions than that of promoters and introns. A total of 2044 differentially accessible regions and 2574 differentially expressed genes were identified through comparative analysis. Genes annotated from regions with differential chromatin accessibility were enriched in cell adhesion molecules, JAK-STAT, insulin resistance, HIF-1α, and platelet activation signaling pathways. Correlation analysis of ATAC-seq and RNA-seq data showed that differential gene expression was positively correlated with differential chromatin accessibility. Furthermore, motif screening and identification of accessible chromatin regions revealed a set of transcription factors, including LHX3, TCF7L2, and LEF1, that may play important roles in the growth of C. gigas. Integrated analysis with public Hi-C datasets allowed the identification of a differential peak located 47 kb upstream of angiopoietin-2, which may act as a potential enhancer that affects the growth of C. gigas. In summary, our work contributes to a better understanding of growth-related regulation in C. gigas and provides valuable information for deciphering the economic traits underlying growth, which is conducive to the development of the breeding industry of C. gigas in the future.

Metabolic profiles and protein expression responses of Pacific oyster (Crassostrea gigas) to polystyrene microplastic stress

The underlying toxicity mechanisms of microplastics on oysters have rarely been explored. To fill this gap, the present study investigated the metabolic profile and protein expression responses of oysters to microplastic stress through metabolomics and biochemical analyses. Oysters were exposed to microplastics for 21 days, and the results indicated that the microplastics induced oxidative stress, with a significant decrease in SOD activity in the 0.1 mg/L exposure group. Metabolomics revealed that exposure to microplastics disturbed many metabolic pathways, such as amino acid metabolism, lipid metabolism, biosynthesis of amino acids, aminoacyl-tRNA biosynthesis, and that different concentrations of microplastics induced diverse metabolomic profiles in oysters. Overall, the current study provides new reference data and insights for assessing food safety and consumer health risks caused by microplastic contamination.