Structural characterization of glutaraldehyde crosslinked starch-based nanofibrous film and adsorption improvement for oyster peptide flavor.

The inferior hydrophobicity and mechanical properties of starch-based nanofibrous films significantly restrict their practical application. In view of this, this study prepared octenylsuccinylated starch-pullulan nanofibrous films using electrospinning and glutaraldehyde (GTA) gas-phase crosslinking. After GTA crosslinking, the starch-based nanofibrous films remained white, randomly oriented, smooth, and droplet-free. Meanwhile, as the crosslinking time increased from 0 to 24 h, the mean fibrous diameter augmented from 157.34 nm to 238.66 nm, and the water contact angle rose from 24.30° to 52.49°. Meanwhile, their tensile strength and thermal stability grow, and the mean pore area and elongation at break abate with changes in function groups. The crosslinked starch-based nanofibrous films exhibit an enhanced adsorption capacity for alcohols, ethers, esters, hydrocarbons, and N-compounds of oyster peptides. Correlation analysis shows that the adsorption capacity of the starch-based nanofibrous films was positively correlated with mean fibrous diameter and water contact angle and negatively correlated with mean pore area. These results provide a theoretical basis for the practical application of crosslinked starch-based nanofibrous film materials in deodorization.

The Potential Substitution of Oyster Shell Powder for Phosphate in Pork Patties Cured with Chinese Cabbage and Radish Powder.

The use of natural ingredients in meat processing has recently gained considerable interest, as consumers are increasingly attracted to clean-label meat products. However, limited research has been conducted on the use of natural substitutes for synthetic phosphates in the production of clean-label meat products. Therefore, this study aimed to explore the potential of oyster shell powder as a substitute for synthetic phosphates in pork patties cured with Chinese cabbage or radish powders. Four different groups of patties were prepared using a combination of 0.3% or 0.6% oyster shell powder and 0.4% Chinese cabbage or radish powder, respectively. These were compared with a positive control group that contained added nitrite, phosphate, and ascorbate and a negative control group without these synthetic ingredients. The results showed that patties treated with oyster shell powder had lower (p<0.05) cooking loss, thickness and diameter shrinkage, and lipid oxidation than the negative control but had lower (p<0.05) residual nitrite content and curing efficiency than the positive control. However, the use of 0.6% oyster shell powder adversely affected the curing process, resulting in a decreased curing efficiency. The impact of the vegetable powder types tested in this study on the quality attributes of the cured pork patties was negligible. Consequently, this study suggests that 0.3% oyster shell powder could serve as a suitable replacement for synthetic phosphate in pork patties cured with Chinese cabbage or radish powders. Further research on the microbiological safety and sensory evaluation of clean-label patties during storage is required for practical applications.

Climate change impacts on oyster aquaculture - Part II: Impact assessment and adaptation measures.

The oyster aquaculture sector plays a major role in food security, providing a sustainable way to obtain food and livelihood for coastal and Island nations. Oysters are one of the preferred choices by aquaculturists because of their resilience to harsh climatic conditions. Nonetheless, climate change will continue to pose threats to its culture. Climate-induced hazards such as floods, storms, disease, and invasive species are some of the key factors limiting oyster production globally. A thriving aquaculture industry needs optimal conditions to maximize exploitation. Here, we continue with the review of the impacts of climate change on oyster aquaculture at the global scale, highlighting climate vulnerability assessment. We also propose a framework for modeling oyster responses to future climate scenarios. Furthermore, we explore the health implications of infected oysters on consumer's health. We also identify knowledge gaps and challenges for sustainable oyster production. Additionally, we document mitigation and adaptation measures and future research directions.

Biogenic silica in sediment core indicates the historical development of off-bottom oyster farming.

Sediment cores are commonly used for reconstructing historical events by determining the biogenic elements in sediment vertical profiles. The vertical flux of biogenic silica (BSi) can be enhanced by bivalve mollusks through biodeposition and can be subsequently recorded in the sediment core. However, whether BSi in sediment core can indicate the interactions between aquaculture farms and the ecosystem is unclear. In this study, sediment cores were collected from a typical off-bottom oyster farm in Sanggou Bay, China. Based on 210Pb chronology analysis of the sediment vertical profile, BSi content was determined to reflect the BSi burial flux during the farming history. The BSi biodeposition fluxes were estimated based on the biodeposition model, to identify the correspondence among BSi burial flux, BSi biodeposition flux, and annual oyster production during the historical development of the farm. The results show that the BSi density in the sediment increased obviously after 1980 when intensive oyster farming began, and reduced after 2000 when farming began to decline. Moreover, BSi burial flux had a corresponding relationship with oyster production and the simulated biodeposition rate, except for 1997-2001 when oyster production peaked. Our finding supported that the variation of BSi from biodeposition can be preserved and then recorded in the sediment, suggesting that BSi could be considered as an indicator to reconstruct the historical development of the oyster farm.

Bank erosion drastically reduces oyster reef filtration services in estuarine environments.

Oyster reefs near estuarine channels have experienced substantial mortality over the last decades, primarily due to bank erosion, potentially exacerbated by boat activity. Using aerial imagery, we measured bank erosion along the Intracoastal Waterway and its main tributaries in the Guana-Tolomato-Matanzas estuary, finding that erosion outweighs progradation. This notably threatens oyster reefs and their filtration capabilities. By modeling the impact of bank erosion on oyster habitats and filtration using hydrodynamic, water quality, and particle tracking models, we observed a 12% filtration reduction due to reef mortality. Erosion results in an exponential decrease in reef area and filtration services, due to the removal of channel-adjacent reefs, which play a critical role in water filtration. If current erosion rates continue, simulations suggest a potential 20% filtration reduction over 100 years, potentially worsening water quality. Our findings highlight the urgency to protect and restore reefs near banks to mitigate erosion and maintain filtration services.

Characterization of Vibrio parahaemolyticus isolated from clinical specimens and oysters in Thailand.

INTRODUCTION: Vibrio parahaemolyticus is a common pathogen that can cause seafood-borne gastroenteritis in humans. We determined the prevalence and characteristics of V. parahaemolyticus isolated from clinical specimens and oysters in Thailand. METHODOLOGY: Isolates of V. parahaemolyticus from clinical specimens (n = 77) and oysters (n = 224) were identified by biochemical testing, polymerase chain reaction (PCR) assays, and serotyping. The toxin genes, antimicrobial resistance, and ß-lactamase production were determined. RESULTS: A total of 301 isolates were confirmed as V. parahaemolyticus by PCR using specific primers for the toxR gene. The majority of clinical isolates carried the tdh+/trh- genotype (82.1%), and one of each isolate was tdh-/trh+ and tdh+/trh+ genotypes. One isolate from oyster contained the tdh gene and another had the trh gene. Twenty-six serotypes were characterized among these isolates, and O3:K6 was the most common (37.7%), followed by OUT:KUT, and O4:K9. In 2010, most clinical and oyster isolates were susceptible to antibiotics, with the exception of ampicillin. In 2012, clinical isolates were not susceptible to cephalothin (52.4%), streptomycin (95.2%), amikacin (66.6%), kanamycin (61.9%), and erythromycin (95.2%), significantly more frequently than in 2010. More than 95% of isolates that were not susceptible to ampicillin produced ß-lactamase enzymes. CONCLUSIONS: We found toxin genes in two oyster isolates, and the clinical isolates that were initially determined to be resistant to several antibiotics. Toxin genes and antimicrobial susceptibility profiles of V. parahaemolyticus from seafood and environment should be continually monitored to determine the spread of toxin and antimicrobial resistance genes.

Contrasting effects of NADPH oxidases on the fungal hyphae growth and immune responses in Pleurotus ostreatus.

Pleurotus ostreatus is one of the most consumed mushroom species, as it serves as a high-quality food, favors a rich secondary metabolism, and has remarkable adaptability to the environment and predators. In this study, we investigated the function of two key reactive oxygen species producing enzyme NADPH oxidase (PoNoxA and PoNoxB) in P. ostreatus hyphae growth, metabolite production, signaling pathway activation, and immune responses to different stresses. Characterization of the Nox mutants showed that PoNoxB played an important role in the hyphal formation of the multicellular structure, while PoNoxA regulated apical dominance. The ability of P. ostreatus to tolerate a series of abiotic stress conditions (e.g., osmotic, oxidative, membrane, and cell-wall stresses) and mechanical damage repair was enhanced with PoNoxA over-expression. PoNoxB had a greater responsibility in regulating the polysaccharide composition of the cell wall and methyl jasmonate and gibberellin GA1 biosynthesis, and improved mushroom resistance against Tyrophagus putrescentiae. Moreover, mutants were involved in the jasmonate and GA signaling pathway, and toxic protein defense metabolite production. Our findings shed light on how the oyster mushroom senses stress signals and responds to adverse environments by the complex regulators of Noxs.

Hurricanes temporarily weaken human-ecosystem linkages in estuaries.

Intense disturbances such as hurricanes may drastically affect ecosystems, producing both acute and long-term changes along coastlines. By disrupting human activities (e.g., fishing), hurricanes can provide an opportunity to quantify the effects of these activities on coastal ecosystems. We performed predator-exclusion experiments on oyster reefs in 2016, one-year before a category-4 hurricane ("Harvey") and again in 2018 one-year post-hurricane where the storm made landfall. Additionally, we examined 8 years (2011-2018) of fisheries-independent data to gauge how fishing pressure and fish populations were affected by the storm in three locations that varied in storm impacts. In the month following Hurricane Harvey, fishing effort dropped by 90% in the area with wind and flooding damage, and predatory fish species commonly targeted by anglers were 300% more abundant than the year prior to the hurricane. The locations without damage to fishing infrastructure did not experience declines in fishing pressure or changes in fish abundance, regardless of flooding disturbance. Reef fish and invertebrate communities directly affected by the storm were significantly different after the hurricane and were ~ 30% more diverse. With low fishing pressure, sportfish CPUE were 1.7-6.9 × higher immediately after the hurricane. Intermediate consumers, such as crabs that prey on oysters, were 45% less abundant and 10% smaller. These results indicate that hurricanes can temporarily disrupt human-ecosystem linkages and reconstitute top-down control by sportfish in estuarine food webs. Disturbance events that interrupt or weaken those interactions may yield indirect ecological benefits and provide insights into the effects of human activities on food webs.

What Are the Sensory Attributes Associated with Consumer Acceptance of Yellow Oyster Mushrooms (Pleurotus citrinopileatus)?

The oyster mushroom is cultivated globally, renowned for its unique texture and umami flavor, as well as its rich content of nutrients and functional ingredients. This study aims to identify the descriptive sensory characteristics, assess the consumer acceptability of new superior lines and cultivars of yellow oyster mushrooms, in addition to exploring the relationship between these descriptive characteristics and consumer acceptability. Statistical analyses were performed using one-way analysis of variance (ANOVA), principal component analysis (PCA), and partial least squares regression (PLSR). Twenty attributes were delineated, including three related to appearance/color (gray, yellow, and white), four associated with the smell/odor of fresh mushroom (oyster mushroom, woody, fishy, and seafood smells), three pertaining to the smell/odor of cooked mushrooms (mushroom, umami, and savory smells), four describing flavor/taste (sweet, salty, umami, and savory tastes), and five for texture/mouthfeel (chewy, smooth, hard, squishy, and slippery textures). Consumer acceptability tests involved 100 consumers who evaluated overall liking, appearance, overall taste, sweetness, texture, savory taste, MSG taste, smell, color, purchase intention, and recommendation. The general oyster mushroom (548 samples) scored highest in acceptability. Seven attributes, namely fresh mushroom smell, seafood smell (fresh), fishy smell (fresh), umami smell (cooked), nutty smell (cooked), salty taste, and MSG taste with the exception of appearance showed significant differences among samples (p < 0.001). The three yellow oyster mushroom samples were strongly associated with attributes like hardness, softness (texture), sweet taste (745 samples), MSG taste, salty taste, squishy texture, and fishy smell (483 and 629 samples). The development of sensory lexicons and increasing consumer acceptance of new superior lines and cultivars of yellow oyster mushroom will likely enhance sensory quality and expand the consumer market, aligning with consumer needs and preferences.

Sausage Quality during Storage under the Partial Substitution of Meat with Fermented Oyster Mushrooms.

The increasing global demand for meat production, driven by a rapidly expanding population and changing dietary preferences has prompted the search for protein-rich, sustainable, and healthier meat alternatives. In this context, edible mushrooms are viewed as advantageous substitutes for meat, offering a viable solution. This study aimed to investigate the effects of partially replacing (25% and 50%) pork meat in sausage samples with fermented oyster mushrooms (Pleurotus ostreatus), which were subjected to various pretreatments. Six different pretreatments were applied to fresh oyster mushrooms as follows: blanching in water, steaming, oven-cooking, microwave treatment, high hydrostatic pressure treatment, and ultraviolet light treatment. The effects of mushroom replacement on the moisture, pH, lipid oxidation, color, and textural properties of sausages during the 4-week refrigerated storage period were evaluated. The results revealed that replacing pork meat with fermented oyster mushrooms resulted in an increase in moisture content and b* values and a decrease in pH, L*, a*, and shear force values, proportional to the mushroom percentage. The lipid oxidation findings suggest that the antioxidant capabilities of fermented oyster mushrooms were influenced by the pretreatment methods applied to the mushrooms, exhibiting varying levels of effectiveness.

Elevated temperature and decreased salinity impacts on exogenous Vibrio parahaemolyticus infection of eastern oyster, Crassostrea virginica.

Anthropogenic carbon emissions have resulted in drastic oceanic changes, including increased acidity, increased temperature, and decreased salinity. Anthropogenic carbon emissions have resulted in drastic oceanic changes, including increased acidity, increased temperature, and decreased salinity. Few studies have directly assessed the compounded impact of alterations to oceanic conditions on oyster physiology and the relation to the presence of V. parahaemolyticus. This project investigated the relationship between projected climate scenarios and their influence on both eastern oyster, Crassostrea virginica, and the aquatic bacteria, Vibrio parahaemolyticus. Specifically, we examined whether an increase in water temperature and/or decrease in salinity would impair oyster resistance to V. parahaemolyticus, a human food and waterborne pathogen. Using a culture-dependent approach, our data revealed that the alterations in environmental conditions did not significantly impact the numbers of V. parahaemolyticus numbers within oyster hemolymph or tissues. However, we did observe a dramatic increase in the total amount of bacteria and pathogenic native Vibrio species, Vibrio aestuarianus and Vibrio harveyi. Despite detecting V. parahaemolyticus in most tissues at 7 days post-challenge, oysters were able to reduce bacterial levels below our limit of detection by 28 days of exposure. Furthermore, in our second experimental trial exploring single vs. multiple inoculation of bacteria, we observed that oysters were either able to reduce total bacterial levels to pre-treatment burdens (i.e., below our limit of detection) or die. This study demonstrates that the synergistic effects of elevated temperature and decreased salinity do not inhibit oysters from preventing the long-term colonization of exogenous V. parahaemolyticus. However, our data do show these environmental stressors impact oyster physiology and the native microbiota. This can lead to the proliferation of opportunistic pathogens, which could have impacts on oyster population numbers and ecosystem and human health.

A concise review of the nutritional profiles, microbial dynamics, and health impacts of fermented mushrooms.

Mushrooms have garnered significant attention for their nutritional composition and potential health benefits, including antioxidant, antihypertensive, and cholesterol-lowering properties. This review explores the nutritional composition of edible mushrooms, including their high protein content, essential amino acids, low fat, cholesterol levels, and bioactive compounds with medicinal value. Moreover, the study analyzes the microbiology of mushroom fermentation, focusing on the diverse microbial ecosystem involved in the transformation of raw mushrooms and the preservation methods employed to extend their shelf life. Special emphasis is placed on lactic acid fermentation as a cost-effective and efficient preservation technique. It involves controlling the growth of lactic acid bacteria to enhance the microbial stability and nutritional quality of mushrooms. Furthermore, the bioactivities of fermented mushrooms are elucidated, which are antioxidant, antimicrobial, anticancer, anti-glycemic, immune modulatory, and other biological activities. The mechanisms underlying these bioactivities are explored, emphasizing the role of fermented mushrooms in suppressing free radicals, enhancing antioxidant defenses, and modulating immune responses. Overall, this review provides comprehensive insights into the nutritional composition, microbiology, bioactivities, and underlying mechanisms of fermented mushrooms, highlighting their potential as functional foods with significant health-promoting properties.

Genome-wide analysis of the cytochrome P450 gene family in Pacific oyster Crassostrea gigas and their expression profiles during gonad development.

The cytochrome P450 (CYP) gene superfamily plays a significant role in various physiological processes, producing different compounds such as hormones, fatty acids, and biomolecules. However, little information is known their roles during gonad development in Pacific oyster (Crassostrea gigas). In this study, total of 116 CgCYP (Crassostrea gigas cytochrome P450) genes were identified and their expression pattern was analyzed for the first time. The relative molecular weights of these CgCYP genes ranged from 63.52 to 113.41 kDa, and the length of encoded amino acids ranged from 103 to 993. And total 26 cis-acting elements of these CgCYP genes were identified. GO and KEGG enrichment analysis showed some CgCYP genes are essential for the metabolism of male and female sex hormones. Additionally, expression anslysis showed 69 CgCYP genes were over-expressed in early gonad development and triploid infertile individuals. More importantly, expression levels of CgCYP1, CgCYP15, CgCYP34, CgCYP46, CgCYP69, CgCYP87, CgCYP88, and CgCYP103, were found to be significantly higher in female gonad, suggesting their important roles in female gonad development. The results of this study will provide a better understanding of the CgCYP genes in the gonad development of Pacific oyster.

Comparative transcriptome analysis reveals molecular damage associated with cryopreservation in Crassostrea angulata D-larvae rather than to cryoprotectant exposure.

BACKGROUND: The Portuguese oyster Crassostrea angulata, a bivalve of significant economic and ecological importance, has faced a decline in both production and natural populations due to pathologies, climate change, and anthropogenic factors. To safeguard its genetic diversity and improve reproductive management, cryopreservation emerges as a valuable strategy. However, the cryopreservation methodologies lead to some damage in structures and functions of the cells and tissues that can affect post-thaw quality. Transcriptomics may help to understand the molecular consequences related to cryopreservation steps and therefore to identify different freezability biomarkers. This study investigates the molecular damage induced by cryopreservation in C. angulata D-larvae, focusing on two critical steps: exposure to cryoprotectant solution and the freezing/thawing process. RESULTS: Expression analysis revealed 3 differentially expressed genes between larvae exposed to cryoprotectant solution and fresh larvae and 611 differentially expressed genes in cryopreserved larvae against fresh larvae. The most significantly enriched gene ontology terms were "carbohydrate metabolic process", "integral component of membrane" and "chitin binding" for biological processes, cellular components and molecular functions, respectively. Kyoto Encyclopedia of Genes and Genomes enrichment analysis identified the "neuroactive ligand receptor interaction", "endocytosis" and "spliceosome" as the most enriched pathways. RNA sequencing results were validate by quantitative RT-PCR, once both techniques presented the same gene expression tendency and a group of 11 genes were considered important molecular biomarkers to be used in further studies for the evaluation of cryodamage. CONCLUSIONS: The current work provided valuable insights into the molecular repercussions of cryopreservation on D-larvae of Crassostrea angulata, revealing that the freezing process had a more pronounced impact on larval quality compared to any potential cryoprotectant-induced toxicity. Additionally, was identify 11 genes serving as biomarkers of freezability for D-larvae quality assessment. This research contributes to the development of more effective cryopreservation protocols and detection methods for cryodamage in this species.

Transmission of Oyster Mushroom Spherical Virus to Progeny via Basidiospores and Horizontally to a New Host Pleurotus floridanus.

Mycoviruses are usually transmitted horizontally via hyphal anastomosis and vertically through sporulation in natural settings. Oyster mushroom spherical virus (OMSV) is a mycovirus that infects Pleurotus ostreatus, with horizontal transmission via hyphal anastomosis. However, whether OMSV can be vertically transmitted is unclear. This study aimed to investigate the transmission characteristics of OMSV to progeny via basidiospores and horizontally to a new host. A total of 37 single-basidiospore offspring were obtained from OMSV-infected P. ostreatus and Pleurotus pulmonarius for Western blot detection of OMSV. The OMSV-carrying rate among monokaryotic isolates was 19% in P. ostreatus and 44% in P. pulmonarius. Then, OMSV-free and OMSV-infected monokaryotic isolates were selected for hybridization with harvested dikaryotic progeny strains. Western blot analyses of the offspring revealed that the OMSV transmission efficiency was 50% in P. ostreatus and 75% in P. pulmonarius, indicating vertical transmission via sexual basidiospores. Furthermore, we observed the horizontal transfer of OMSV from P. pulmonarius to Pleurotus floridanus. OMSV infection in P. floridanus resulted in significant inhibition of mycelial growth and yield loss. This study was novel in reporting the vertical transmission of OMSV through basidiospores, and its infection and pathogenicity in a new host P. floridanus.

A novel route of intercellular copper transport and detoxification in oyster hemocytes.

Bivalve hemocytes are oyster immune cells composed of several cellular subtypes with different functions. Hemocytes accumulate high concentrations of copper (Cu) and exert critical roles in metal sequestration and detoxification in oysters, however the specific biochemical mechanisms that govern this have yet to be fully uncovered. Herein, we demonstrate that Cu(I) is predominately sequestered in lysosomes via the Cu transporter ATP7A in hemocytes to reduce the toxic effects of intracellular Cu(I). We also found that Cu(I) is translocated along tunneling nanotubes (TNTs) relocating from high Cu(I) cells to low Cu(I) cells, effectively reducing the burden caused by overloaded Cu(I), and that ATP7A facilitates the efflux of intracellular Cu(I) in both TNTs and hemocyte subtypes. We identify that elevated glutathione (GSH) contents and heat-shock protein (Hsp) levels, as well as the activation of the cell cycle were critical in maintaining the cellular homeostasis and function of hemocytes exposed to Cu. Cu exposure also increased the expression of membrane proteins (MYOF, RalA, RalBP1, and cadherins) and lipid transporter activity which can induce TNT formation, and activated the lysosomal signaling pathway, promoting intercellular lysosomal trafficking dependent on increased hydrolase activity and ATP-dependent activity. This study explores the intracellular and intercellular transport and detoxification of Cu in oyster hemocytes, which may help in understanding the potential toxicity and fate of metals in marine animals.

Exploring Release, Isomerization, and Absorption of Cypermethrin in Pacific Oysters (Crassostrea gigas) with Different Processing Methods during In Vivo Digestion: Insights from a Gastrointestinal Tract Quantitative Tracing Method.

Cypermethrin (CP) is a neurotoxic insecticide found accumulated in oysters, one of the most commonly consumed seafoods, posing potential health risks to the human body. We designed a gastrointestinal tracing method allowing for accurate quantification of the propulsion of chyme and further established the mouse in vivo digestion model to explore the behavior of CP in the digestion of raw, steamed, and roasted oysters. The results showed that bioaccumulation of CP in oysters may be accompanied by the biotransformation of CP. Thermal processing decreased both the CP content in oysters and its bioaccessibility. The small intestine is the main site for CP digestion and absorption. The cis-isomers of CP might finally accumulate in the body at a higher ratio and further become the predominant configuration for toxic effects. Taken together, the study contributes to the risk assessment of the dietary exposure of CP from aquatic products.

Intergenerational toxicity of 17α-ethinylestradiol (EE2): Effects of parental exposure on early larval development and transcriptomic profiles in the Sydney rock oyster, Saccostrea glomerata.

This study exposed adult Sydney rock oysters, of either sex or both, to the synthetic estrogen 17α-ethinylestradiol (EE2) at 50 ng/L for 21 days, followed by an examination of developmental endpoints and transcriptomic responses in unexposed larvae. Reduced survival was observed at 1 day post-fertilisation (dpf) in larvae from bi-parental exposure (FTMT). Motile larvae at 2 dpf were fewer from maternal (FTMC), paternal (FCMT), and FTMT exposures. Additionally, shell length at 7 dpf decreased in larvae from FTMC and FTMT parents. RNA sequencing (RNA-seq) revealed 1064 differentially expressed genes (DEGs) in 1-dpf larvae from FTMT parents, while fewer DEGs were detected in larvae from FTMC and FCMT parents, with 258 and 7, respectively. GO and KEGG analyses showed significant enrichment of DEGs in diverse terms and pathways, with limited overlap among treatment groups. IPA results indicated potential inhibition of pathways regulating energy production, larval development, transcription, and detoxification of reactive oxygen species in FTMT larvae. qRT-PCR validation confirmed significant downregulation of selected DEGs involved in these pathways and relevant biological processes, as identified in the RNA-seq dataset. Overall, our results suggest that the intergenerational toxicity of EE2 is primarily maternally transmitted, with bi-parental exposure amplifying these effects.

Evidence for immune priming specificity and cross-protection against sympatric and allopatric Vibrio splendidus strains in the oyster Magalana (Crassostrea) gigas.

Infections with pathogenic Vibrio strains are associated with high summer mortalities of Pacific oysters Magalana (Crassostrea) gigas, affecting production worldwide. This raises the question of how M. gigas cultures can be protected against deadly Vibro infection. There is increasing experimental evidence of immune priming in invertebrates, where previous exposure to a low pathogen load boosts the immune response upon secondary exposure. Priming responses, however, appear to vary in their specificity across host and parasite taxa. To test priming specificity in the Vibrio - M. gigas system, we used two closely related Vibrio splendidus strains with differing degrees of virulence towards M. gigas. These V. splendidus strains were either isolated in the same location as the oysters (sympatric, opening up the potential for co-evolution) or in a different location (allopatric). We extracted cell-free haemolymph plasma from infected and control oysters to test the influence of humoral immune effectors on bacterial growth in vitro. While addition of haemolypmph plasma in general promoted growth of both strains, priming by an exposure to a sublethal dose of bacterial cells lead to inhibitory effects against a subsequent challenge with a potentially lethal dose in vitro. Inhibitory effects and immune priming was strongest when oysters had been primed with the sympatric Vibrio strain, but inhibitory effects were seen both when challenged with the sympatric as well as against allopatric V. splendidus, suggesting some degree of cross protection. The stronger immune priming against the sympatric strain suggests that priming could be more efficient against matching local strains potentially adding a component of local adaptation or co-evolution to immune priming in oysters. These in vitro results, however, were not reflected in the in vivo infection data, where we saw increased bacterial loads following an initial challenge. This discrepancy might suggests that that it is the humoral part of the oyster immune system that produces the priming effects seen in our in vitro experiments.

Biomagnification of mercury in an estuarine food web.

Methylmercury is a toxin of local, regional, and global concern, with estuarine habitats possessing ecological characteristics that support conversion of inorganic mercury into this methylated form. We monitored Hg concentrations in species within the food web of the lower Cape Fear River (CFR) estuary in 2018-2020. Samples were analyzed for Hg concentrations and nitrogen isotopes (a measure of trophic level), and we found a positive relationship within this food web each year (p < 0.0001), indicating biomagnification is occurring. The highest Hg concentrations were among the upper trophic level species (Royal Terns, 4.300 ppm). While the Hg concentrations we documented are below assumed thresholds for toxic effects, we found spikes in Hg concentrations after Hurricane Florence in 2018 and with other disturbances to the CFR that resuspended bottom sediments. Continued monitoring is needed to understand the cause of annual variations, health implications, and conservation needs.