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Crassostrea rivularis are the main edible economic shellfish rich in bioactive substances. Therefore, Crassostrea rivularis resources have high development prospects. This study aimed to analyze the biological activity of neutral oyster polysaccharide powder (OPS-1) to enhance the comprehensive utilization value of oysters. OPS-1 was purified from Crassostrea rivularis by hot water agglutination using DEAE-cellulose column chromatography. Experimental results showed that OPS-1 was predominantly composed of 97.41 g/100g glucose, linked by a β-glycosidic bond, and exhibited a triple-helical conformation with a molecular weight of 954.32 kDa. OPS-1 solution is relatively stable with 15.87 ± 0.66 mV of zeta potential. In addition, OPS-1 has good thermal properties and a high antioxidant capacity. The median inhibitory concentrations (IC 50 values) of OPS-1 on DPPH radicals, ABTS+ radicals, OH radicals, and Fe2+ chelating ability were 0.23, 2.96, 2.68 and 2.33 mg/mL, respectively. Meanwhile, OPS-1 could inhibit the growth of common food-borne pathogenic bacteria (Escherichia coli , Salmonella Typhimurium, and Staphylococcus aureus). The inhibition zone sizes were not significantly different from penicillin (p > 0.05). These findings indicate that OPS-1 may be a novel natural antioxidant and antimicrobial agent derived from animal sources, providing a rationale for further investigating oyster polysaccharides. [Display omitted] • OPS-1 is mainly composed of glucose linked by β-glycosidic bonds. • OPS-1 has good thermal properties and antioxidant properties. • OPS-1 is bacteriostatic against major food-borne bacteria. • OPS-1 is an excellent candidate for antimicrobial and antioxidant products. [ABSTRACT FROM AUTHOR]

To understand the environmental adaptations among sessile bivalves lacking adaptive immunity, a series of analyses were conducted, with special emphasis on the widely distributed C. ariakensis. Employing Pacbio sequencing and Hi-C technologies, whole genome for each of a C. ariakensis (southern China) and C. hongkongensis individual was generated, with the contig N50 reaching 6.2 and 13.0 Mb, respectively. Each genome harbored over 30,000 protein-coding genes, with approximately half of each genome consisting of repeats. Genome alignment suggested possible introgression between C. gigas and C. ariakensis (northern China), and re-sequencing data corroborated this result and indicated significant gene flow between C. gigas and C. ariakensis. These introgressed candidates, well-represented by genes related to immunity and osmotic pressure, may be associated with environmental stresses. Gene family dynamics modeling suggested immune-related genes were well represented among the expanded genes in C. ariakensis. These outcomes could be attributed to the spread of C. ariakensis. [ABSTRACT FROM AUTHOR]

Regulatory variants in gene expression serve as bridges linking genetic variation and phenotypic plasticity. Environmental conditions typically influence the effects of regulatory variants on phenotypic plasticity; however, such genotype-by-environment interactions (G × E) are poorly understood. This study aimed to investigate the genetic basis of G × E in estuarine oyster (Crassostrea ariakensis), which is an important model animal for studying environmental adaption owing to its high plasticity and large intraspecific divergence. Genome-wide mapping of expression quantitative trait loci (eQTLs) for 23 environmental adaptive genes was performed for 256 estuarine oysters. We identified 1194 eQTL single nucleotide polymorphisms (eSNPs), including 433 cis -eSNPs in four genes and 722 trans -eSNPs in eight genes. The expression variation explanation of cis -eSNPs (9.95%) was significantly higher than that of trans -eSNPs (9.15%). We specifically showed cis- and trans-eSNPs with high linkage disequilibrium (LD) for Traf7 , Slc6a5 , Ggt , and Dap3. For example, we identified a cis -regulatory LD block containing 68 cis -eSNP and a trans -regulatory LD block, including 20 trans -eSNPs in Traf7. A high proportion (85%) of 40 vital eSNPs exhibited significant G × E effects. We identified crossing and nonparallel interactions of G × E, with the tag cis -eSNPs of Baat and Slc6a5 as representatives. Our results indicated that cis -eQTLs are highly conserved. This study provides insights into the understanding of adaptive evolutionary mechanisms and phenotypic response prediction to variable environments, as well as the genetic improvement for superior adaptive traits for genetic resource conservation and aquaculture. • We identified trans and cis regulatory variants and built potential regulatory networks. • Cis -eSNPs had larger contributions to gene expression plasticity and are conserved in different environments. • Trans -eSNPs are more abundant than cis -eSNPs and usually environment-specific. • A large proportion of eSNPs exhibited significant G × E effects. • Crossing and nonparallel G × E patterns were identified. [ABSTRACT FROM AUTHOR]

This study investigates the nutritional properties of edible oysters cultivated in Hong Kong (i.e. Deep Bay) to determine their nutritional values compared with other foodstuffs (e.g. land and aquatic-based foods). A total of ∼300 edible oysters were harvested and studied from aquaculture areas in Hong Kong. The Hong Kong oyster (Crassostrea hongkongensis) contained the highest concentrations (up to 32%) of polyunsaturated fatty acids (PUFAs), when compared to the Portuguese (Crassostrea angulata) and the Suminoe (Crassostrea ariakensis) oyster species. The C. hongkongensis also exhibited the best meat yield (∼28%) compared to oyster species from other regions (e.g., Crassostrea gigas). The C. ariakensis showed the highest concentrations (µg/g dwt.) of macro-and micro nutrients, e.g. Mg (∼3600), Na (∼22000), Zn (∼5000); compared to C. hongkongensis and C. angulata. Essential amino acids (EEA; mg/100 g wwt.) were highest in C. angulata (3439), followed by C. ariakensis (3330) and leaving C. hongkongensis (2619) as the poorest species in EAA. The comparison of the nutritional profile of oyster species cultivated in Hong Kong with different seafood species and other foodstuffs showed that oysters are nutrient-rich (or superfoods) shellfish species, which contribute with beneficial compounds (e.g. PUFAs, EAAs) and elements (e.g. Cu, Zn) for a human healthy diet. • The C. hongkongensis contained the highest concentration of PUFAs among oysters. • The C. hongkongensis has the best meat yield compared to oysters from other regions. • The C. ariakensis showed the highest concentrations of macro-and micro nutrients. • EEA were highest in C. angulata , following by C. ariakensis and C. hongkongensis. • Consumption of Hong Kong edible oysters can contribute positively for human health. [ABSTRACT FROM AUTHOR]

Cyclophilins (CyPs) are a family of proteins that bind the immunosuppressive agent cyclosporin A (CsA) with high-affinity and belong to one of the three superfamilies of peptidyl-prolyl cis-trans isomerases (PPIase). In this report, three cyclophilin genes (Ca-CyPs), including Ca-CyPA, Ca-CyPB and Ca-PPIL3, were identified from oyster, Crassostrea ariakensis Gould in which Ca-CyPA encodes a protein with 165 amino acid sequences, Ca-CyPB encodes a protein with 217 amino acid sequences and Ca-PPIL3 encodes a protein with 162 amino acid sequences. All of the three Ca-CyPs genes contain a typical CyP-PPIase domain with its signature sequences and Ca-CyPB contains an N-signal peptide sequences. Tissue distribution study revealed that Ca-CyPs were ubiquitously expressed in all examined tissues and the highest levels were observed in hemocytes. RLO incubation upregulated the mRNA expression levels of Ca-CyPs, indicating that three Ca-CyPs might be involved in oyster immune response against RLO infection. [ABSTRACT FROM AUTHOR]

Highlights: [•] We surveyed Marteilioides infection in marine bivalves using histology and PCR. [•] Marteilioides infection was also confirmed in the male oysters and clams. [•] The nested PCR was much more sensitive than histology in the detection of Marteilioides. [•] Marteilioides found in Manila clam is a considered to be a new Marteilioides sp. [Copyright &y& Elsevier]

Abstract: We identified a tetraspanin family member gene, named Ca-TSP, in the oyster Crassostrea ariakensis and found that the transcription profiles of Ca-TSP were variable in the oyster hemocytes. Three distinct patterns of variation of Ca-TSP were observed. Using immunofluorescence and immunoelectron microscopy, we show that Ca-TSP was present in granules and in vesicular structures of the oyster hemocyte. Sequence analysis, structural features and immunogold electron microscopy showed that Ca-TSP is an integral membrane glycoprotein of granules of hemocyte and may be a novel CD63-like gene of the tetraspanin family of molluscs. The gene expression analysis of Ca-TSP using isolated oyster hemocytes, was done following challenge of the oysters with LPS and Poly I:C. The Ca-TSP mRNA levels increased in hemocytes in the first 12 h after LPS and Poly I:C stimulation, and decreased after the addition of H2O2. Western blot analysis using anti-Ca-TSP antibody indicated that gene expression and protein levels were similar. The recombinant Ca-TSP was found to significantly inhibit hemocytes aggregation. Our results suggested that Ca-TSP participates in the innate immunity of the oyster. [Copyright &y& Elsevier]

Abstract: A SMARTer™ cDNA library of hemocyte from Rickettsia-like organism (RLO) challenged oyster, Crassostrea ariakensis Gould was constructed. Random clones (400) were selected and single-pass sequenced, resulted in 200 unique sequences containing 96 known genes and 104 unknown genes. The 96 known genes were categorized into 11 groups based on their biological process. Furthermore, we identified and characterized three complement-related fragments (CaC1q1, CaC1q2 and CaC3). Tissue distribution analysis revealed that all of three fragments were ubiquitously expressed in all tissues studied including hemocyte, gills, mantle, digestive glands, gonads and adductor muscle, while the highest level was seen in the hemocyte. Temporal expression profile in the hemocyte monolayers reveled that the mRNA expression levels of three fragments presented huge increase after the RLO incubation at 3 h and 6 h in post-challenge, respectively. And the maximal expression levels at 3 h in post-challenge are about 256, 104 and 64 times higher than the values detected in the control of CaC1q1, CaC1q2 and CaC3, respectively. [Copyright &y& Elsevier]

Abstract: The Suminoe oyster Crassostrea ariakensis has been attempted to be introduced in the Chesapeake Bay, USA, as an alternative to the eastern oyster Crassostrea virginica. Commercial production of Suminoe oysters is currently restricted due to the incomplete understanding of their biological, physiological and immunological nature. Accordingly, understanding immune system of C. ariakensis is crucial to prevent disease associated mortality and subsequent management of the Suminoe oyster. We investigated immunological activities and morphology of hemocytes of the Suminoe oyster using flow cytometry and light microscopy. Three types of hemocytes were identified in the hemolymph including hyalinocyte, granulocyte and blast-like cells. Hyalinocytes were the largest cells and the most abundant, while granulocytes were intermediate-size cell containing numerous granules in the cytoplasm. Blast-like cells were the smallest and least numerous. Flow cytometry revealed that the granulocytes are most active in the cell phagocytosis and spontaneous reactive oxygen species (ROS) production. The hyalinocytes also showed a certain level of the phagocytosis and oxidative activity but in a lesser extent than the granulocytes. In contrast, the blast-like cells did not show any phagocytosis or oxidative activity. The flow cytometry used in this study confirmed that as observed from other marine bivalves, the granulocytes are the main hemocytes involved in the cellular defence in the Suminoe oyster. [Copyright &y& Elsevier]

Abstract: The BMP1/TLD-like proteinases are pleiotropic, astacin-like metalloproteinases. They play central roles in regulating the formation of the extracellular matrix (ECM) and signaling through various TGFβ-like proteins in morphogenetic and homeostatic events. Here we describe the cloning, structural characterization and expression of Tolloid-like gene in the oyster, Crassostrea ariakensis (CaTLL). The full-length cDNA of CaTLL spans 3492 nucleotides including an open reading frame of 2811 nucleotides which encodes a hypothetical protein of 936 amino acids, with a molecular mass of approximately 103 kDa. The CaTLL molecule possessed structural features of several motifs including an N-terminal signal peptide sequence, a prodomain with an RTRR motif, an astacin-like domain that contains a conserved zinc-binding motif HELGHVIGFWHEH, five CUBs and two EGF domains with the arrangement CUB-CUB-EGF-CUB-EGF-CUB-CUB. The proteolytic domain of Ca-Tolloid shares more than 30% identity with other astacins of various animals from squail to mammals, indicating its conserved catalytic ability. RT-PCR and quantitative real-time PCR analyses revealed that CaTLL showed the lowest expression level in hemocytes of normal groups, but was affected significantly by the challenge of an obligate intracellular Gram-negative bacterium, Rickettsia-like organisms, suggesting that Ca-Tolloid might be involved in the molluscan immune response, and its function is more diverse than previously assumed. [Copyright &y& Elsevier]