Sinonovacula Constricta Research Articles

Polymorphisms of LAP3 gene and their association with the growth traits in the razor clam Sinonovacula constricta.

Leucine aminopeptidase 3 (LAP3) is an important proteolytic enzyme that catalyzes the hydrolysis of leucine residues from the amino termini of protein or peptide substrates and plays a critical role in protein metabolism and growth. In the present study, we investigated the full-length cDNA sequence of the LAP3 gene in Sinonovacula constricta (ScLAP3) using expressed sequence tags and rapid amplification of cDNA ends. The full-length ScLAP3 cDNA was 2885bp, with a 1560bp open reading frame encoding 519 amino acids. Sequence analysis revealed that ScLAP3 shared 70.9% identity with LAP3 from the blood clam Tegillarca granosa and 62.0-68.0% with other species. ScLAP3 was expressed in all six tested tissues, with significantly higher expression levels in the foot compared with mantle, adductor muscle, liver, gills, and siphon tissues in adults (P < 0.01). In the eight developmental stages, ScLAP3 expression gradually increased, with significantly higher levels in D-shaped larvae compared with other developmental stages (P < 0.01), suggesting that it may be involved in the formation of certain organs during early development. Association analysis identified three shared single nucleotide polymorphisms (SNPs), c.1073A > G, c.1139C > T and c.1154A > G in exons of ScLAP3 gene from 177 individuals of two groups, one selective strain and one wild population, which had significant effects on growth traits of S. constricta. The results provided candidate genetic markers to assist selective breeding of razor clams toward improved growth.

Survival, growth and physiology of the juvenile razor clam ( Sinonovacula constricta ) under Na + /K + ratio stress

In this study, we investigated the response of the Chinese razor clam (Sinonovacula constricta) under the Na+/K+ ratio in inland saline water. Acute and long-term (30 days) stresses were studied to better delineate the process of the effect. At the end of the test, only the groups of Na+/K+ ratio from 21.28 to 159.95 contained surviving Juvenile S. constricta, and the Na+/K+ ratio 31.91 and 47.27 groups showed significantly higher survival rates (p < .001). In test groups of Na+/K+ ratio, the growth rate (shell length growth rate and weight gain rate) was significantly lower under than that the control group (p < .05 and p < .001 for length and weight). The Na+/K+-ATPase activities in the test Na+/K+ ratio groups (R3, R5, R6, R7 and R8) were significantly higher than that in the control group during 30 days (p < .05). The superoxide dismutase activity in the higher Na+/K+ ratio groups (R7 and R8) was significantly higher than that in the control group during 30 days. However, in the test groups, the aspartate aminotransferase (R3, R6, R7 and R8), acetylcholinesterase (R3, R7 and R8) and lysozyme (R7 and R8) activities were lower than that control group during 30 days. Under ultrahigh and ultralow Na+/K+ ratio acute stress, the oxygen consumption rate, phagocytosis rate and metabolic activity fluctuated significantly. Unbalances of Na+/K+ ratio may affect ion regulation, metabolism, immunity and neuromodulation. Juvenile S. constricta adapted to a range of Na+/K+ ratios and keep to growth. This suggested the possibility of breeding S. constricta to resist inland saline water.

A four-CRD C-type lectin from razor clam Sinonovacula constricta mediates agglutination and phagocytosis

C-type lectins are a superfamily of Ca2+-dependent carbohydrate-binding proteins that play crucial roles in invertebrate immunity. In this study, a novel C-type lectin gene (ScCTL-1) was identified in razor clam Sinonovacula constricta. The ScCTL-1 gene, consisting of four C-type carbohydrate recognition domains (CRDs) with an N-terminal signal peptide and a C-terminal transmembrane region. The gene is widely expressed in almost all tissues, with the highest expression in the hepatopancreas. To explore the functional characteristics of this structurally novel gene, tests of binding specificity, agglutinating activity, and phagocytic promoting activity were included in this study. Bacterial stimulation up-regulated ScCTL-1 expression in hemocytes. The binding activity of rScCTL-1 to bacteria was tested in vitro, and bacterial agglutination was observed under the same conditions. Ca2+ was essential for carbohydrate binding. Additionally, rScCTL-1 promoted the phagocytic activity of hemocytes to varying degrees against different bacteria, unlike the classical opsonin. These results suggest ScCTL-1 is a classical immune-related C-type lectin possessing unique immune-related properties.

Seasonal variation of microflora in Sinonovacula constricta and its aquacultural pond based on high-throughput sequencing

In order to explore the seasonal changes of the bacterial community structure and the interaction of environmental factors in Sinonovacula constricta ponds, we used high throughput sequencing technology to examine the bacteria of water, sediment, and viscera. The results showed that microflora structure of water samples in winter was significantly different from that in spring, summer and autumn, while there was no significant difference in bacterial community structure of sediment and viscera in different seasons. There was no significant difference of Shannon diversity index in water across different seasons. The Shannon diversity index of sediment and viscera was the lowest in summer and the highest in winter. At the phylum level, Cyanobacteria, Proteobacteria and Tenericutes were the most predominant bacteria in water, sediment, and viscera, respectively. At the genus level, NS3a_marine_group was predominant in winter water, and Synechococcus in the other three seasons. By contrast, dominant bacteria in sediments were norank_f_Anaerolineacea and Nitrospira, and Mycoplasma and Arcobacter were the most abundant bacterial genera in viscera. Synechococcus had a positive correlation with water temperature, COD, PO4--P, NH4+-N, pH, and transparency. The norank_f_Anaerolineacea was positively correlated with water temperature, COD, and TP. Mycoplasma was positively correlated with water temperature, PO4--P, NH4+-N, pH, and transparency. Our results suggest that there were significant differences in the composition and diversity of microflora of S. constricta and ponds in different seasons. Bacteria in water was obviously affected by various environmental factors, especially water temperature and the concentrations of nitrogen and phosphorus.

A mild and efficient extraction method for polysaccharides from Sinonovacula constricta and study of their structural characteristic and antioxidant activities

The aim of this paper is to develop a mild and efficient extraction method for polysaccharides from Sinonovacula constricta (SCP) using enzyme extraction, and analyze the structural characteristics and antioxidant activities of the two purified polysaccharide fractions (SCP-1 and SCP-2). Firstly, enzyme extraction conditions were optimized, and the conditions were found to be, as follows: enzymolysis time 173.0 min, pH 8.2, enzymolysis temperature 50.0 ℃ and enzyme content 4.0%. Comparison between enzymatic extraction and water extraction was obtained from visual, UV–visible and IR spectrum images. The results clearly indicate that there is no significant difference between them with regard to the composition of the SCP fraction, but the polysaccharide content produced by enzymatic extraction is higher. Then, the physicochemical properties and structural characteristics of SCP-1 and SCP-2 were investigated using FT-TR, UV, GC and HPGPC. The carbohydrate content, sulfuric radicals and uronic acids of the two fractions were detected. Both SCP-1 and SCP-2 were mainly consisted of glucose, but their molecular weights were different. In addition, compared the Fe2+ chelating activity, ABTS+ radical and superoxide radical scavenging activity, and lipid peroxidation inhibition activity of SCP-1 and SCP-2, it turned out that SCP-2 had stronger antioxidant activity than SCP-1.

Chromosome-level genome assembly of the razor clam Sinonovacula constricta (Lamarck, 1818).

Bivalves, a highly diverse and the most evolutionarily successful class of invertebrates native to aquatic habitats, provide valuable molecular resources for understanding the evolutionary adaptation and aquatic ecology. Here, we reported a high-quality chromosome-level genome assembly of the razor clam Sinonovacula constricta using Pacific Bioscience single-molecule real-time sequencing, Illumina paired-end sequencing, 10X Genomics linked-reads and Hi-C reads. The genome size was 1,220.85Mb, containing scaffold N50 of 65.93Mb and contig N50 of 976.94Kb. A total of 899 complete (91.92%) and seven partial (0.72%) matches of the 978 metazoa Benchmarking Universal Single-Copy Orthologs were determined in this genome assembly. And Hi-C scaffolding of the genome resulted in 19 pseudochromosomes. A total of 28,594 protein-coding genes were predicted in the S.constricta genome, of which 25,413 genes (88.88%) were functionally annotated. In addition, 39.79% of the assembled genome was composed of repetitive sequences, and 4,372 noncoding RNAs were identified. The enrichment analyses of the significantly expanded and contracted genes suggested an evolutionary adaptation of S.constricta to highly stressful living environments. In summary, the genomic resources generated in this work not only provide a valuable reference genome for investigating the molecular mechanisms of S.constricta biological functions and evolutionary adaptation, but also facilitate its genetic improvement and disease treatment. Meanwhile, the obtained genome greatly improves our understanding of the genetics of molluscs and their comparative evolution.

Molecular characterization of a novel sulfide:quinone oxidoreductase from the razor clam Sinonovacula constricta and its expression response to sulfide stress.

The razor clam Sinonovacula constricta is a commercial benthic bivalve, and burrows the deeper cave than the other buried benthic bivalves. Due to the little exchange of seawater and to anoxic conditions, S. constricta is exposed to considerable amounts of sulfide during low tide, but exhibits strong sulfide tolerance. Mitochondrial sulfide oxidation is a particular defense strategy against sulfide toxicity of sulfide-tolerant organisms, for which sulfide:quinone oxidoreductase (SQR) is the first key enzyme. In order to investigate the mechanism of sulfide tolerance in S. constricta, its SQR (designated as ScSQR), was cloned and characterized. The full-length cDNA of ScSQR was 3698 bp and encoded 443 amino acids. The deduced ScSQR protein contained conserved FAD-binding domains, two cysteine residues, two histidines, and one glutamic acid, which are the essential elements for the catalytic mechanism of SQR. Subcellular localization analysis by the TargetP 1.1 prediction and the Western blot confirmed that ScSQR was only located in the mitochondria. The response of ScSQR in the gill and liver of S. constricta were investigated during sulfide exposure (50, 150, and 300 μM sulfide) for 0, 3, 6, 12, 24, 48, 72, and 96 h by qRT-PCR. Moreover, the time-course expressions of ScSQR protein in the S. constricta gill were detected when exposed to 150 μM sulfide by Western blot. The expression level of ScSQR increased significantly and showed a time-dependent pattern. In addition, under sulfide stress, the expression level of the gill was higher than that of liver. Together, our results suggest that ScSQR may perform important roles in protecting cells from sulfide stress by participating in mitochondrial sulfide detoxification and providing high sulfide tolerance to S. constricta.

Identification of a dopamine receptor in Sinonovacula constricta and its antioxidant responses

The dopamine (DA) D2 receptor is a member of the G protein-coupled receptors of organisms and plays an important role in immune system regulation. The presence of DA receptors has been widely reported in vertebrates, but few studies have been conducted in shellfish. Here, we identified a novel DA-D2 receptor gene, ScDopR2-1, in the razor clam Sinonovacula constricta. ScDopR2-1 belongs to the family of G protein-coupled receptors, containing seven hydrophobic transmembrane domains, along with 16 predicted N-glycosylation sites and 69 phosphorylation sites. A longer third intracellular loop and a shorter C-terminus in ScDopR2-1 are characteristic features of D2 receptors. ScDopR2-1 is widely expressed in tissues from adult clams, showing high expression in siphon and foot tissues. Furthermore, in response to Vibrio anguillarum challenge, ScDopR2-1 expression levels are significantly increased in liver tissue. Moreover, changes in the activities of catalase (CAT) and superoxide dismutase (SOD) also indicate that the organism causes an immune response. In summary, the results indicate that ScDopR2-1 plays a pivotal role in antioxidant responses in S. constricta.

Complement factor B/C2 in molluscs regulates agglutination and illuminates evolution of the Bf/C2 family.

Complement factor B/C2 family (Bf/C2F) proteins are core complement system components in vertebrates that are absent in invertebrates and have been lost by numerous species, raising evolutionary questions. At least 3 duplication events have occurred from Cnidaria (ancestor) to mammals. Type II Bf/C2 genes appeared during separation of Proterostomia and Deuterostomes. The second event occurred during separation of vertebrates and invertebrates, yielding type II-2 Bf/C2. The third event occurred when jawed and jawless fish were separated, eventually producing Bf and C2 genes. Herein, we report the second mollusc Sinonovacula constricta Bf/C2-type gene (ScBf). ScBf is similar to Ruditapes decussatus Bf-like because both lack the first complement control protein module at the N terminus present in mammalian Bf/C2 proteins. Uniquely, the Ser protease (SP) module at the C terminus of ScBf is ∼50 aa longer than in other complement factor B/C2-type (Bf/C2T) proteins, and is Glu-rich. Bf/C2T proteins in molluscs lack the catalytic Ser in the SP module. Surprisingly, ScBf regulates rabbit erythrocyte agglutination, during which it is localized on the erythrocyte surface. Thus, ScBf may mediate the agglutination cascade and may be an upstream regulator of this process. Our findings provide new insight into the origin of the Bf/C2F.-Peng, M., Li, Z., Niu, D., Liu, X., Dong, Z., Li, J. Complement factor B/C2 in molluscs regulates agglutination and illuminates evolution of the Bf/C2 family.

Ecological quality dynamics around marine reserves in the Bohai Sea coastal zone and their relationship with landscape artificialization

Numerous marine reserves worldwide are losing their ability to protect wild endemic species due to surrounding ecological deterioration caused by coastal landscape artificialization. Such risk of becoming invalid nature reserves is particularly high in China's Bohai Sea coastal zone, a region with rapid urbanization and industrialization. In this study, the ecological quality (EQ) status around Laizhou Bay Ostrea rivularis germplasm reserve (R1), Yellow River Estuary Meretrix meretrix germplasm reserve (R2), and Taoer Estuary Sinonovacula constricta germplasm reserve (R3) was dynamically diagnosed using seven indicators characterizing ecological support and threat from peripheral environments. A series of thresholds indicating EQ and corresponding landscape artificialization intensity (LAI) were determined based on multi-factor clustering analysis and relational regression simulation. The results show that the surroundings of these three reserves were favorable in 1984, insufficient in 2000, and unfavorable in 2015. With an average 7.5 times increase in LAI over the past three decades, the EQ levels around R1-R3 declined significantly and have deviated greatly from their optimal reference status by 2015, which stemmed mainly from intertidal landscape artificialization, such as establishing salt pans, industrial areas and ports after reclaiming wetlands. It was found that R3 > R1 > R2 in terms of overall peripheral ecological degradation, implying that the closer the marine reserve is to the land, the more likely it is to lose its effectiveness. The changes in EQ status and LAI were well indicated by the proportion of natural ecosystems, the distance between seawalls and protected boundaries, and the reserves' enclosed degree by artificial systems, which, as a quick and simple diagnostic approach, can facilitate spatial planning and management practices around marine reserves in the Bohai Sea coastal zone and elsewhere.

Tolerance, Growth, and Physiological Responses of the Juvenile Razor Clam (Sinonovacula constricta) to Environmental Ca2+ and Mg2+ Concentrations.

To facilitate transplanting razor clam (Sinonovacula constricta) populations to inland saline-alkaline waters (ISWs), we evaluated the tolerance of juvenile S. constricta (JSC) to Ca2+ and Mg2+ concentrations, and determined the effects of these ions on JSC growth and physiological parameters. After 30 days stress, the tolerable ranges of JSC to Ca2+ and Mg2+ were determined to be 0.19 mmol⋅L-1–19.46 mmol⋅L-1 and 0 mmol⋅L-1–29.54 mmol⋅L-1, respectively. The concentrations of Ca2+ (less than 0.65 mmol⋅L-1 or more than 3.24 mmol⋅L-1) and Mg2+ (less than 0.37 mmol⋅L-1 or more than 14.17 mmol⋅L-1) significantly inhibit JSC growth. Physiological enzyme activity no significant response when the concentrations range of Ca2+ and Mg2+ are 0.93 mmol⋅L-1–6.49 mmol⋅L-1 and 0.37 mmol⋅L-1–14.77 mmol⋅L-1, respectively. For transplantation practice, these data indicate that only high concentrations of Ca2+ (3.24–6.825 mmol⋅L-1) and Mg2+ (14.77–33.69 mmol⋅L-1) in target inland saline-alkaline water had significantly impact on growth and physiological response. In addition, present study suggests that the increase in Ca2+ and Mg2+ ion concentrations caused by ocean acidification will not affect the survival, growth and physiology of S. constricta. Current research suggests that S. constricta can adapt to extreme changes in the marine environment (Ca2+ and Mg2+) and may be an excellent candidate for inland saline-alkaline water transplantation practice.

Determining the biological zero for gonadal development razor clams Sinonovacula constricta (lamarck 1818) in Zhejiang, China

The biological zero of gonadal development and the effective accumulated temperature of one and two-year-old razor clams Sinonovacula constricta (Lamarck 1818) were studied in Sanmen County, Zhejiang Province, China between April 2016 to October 2017, using a new variety named “Shen-Zhe No. 1”. The biological zero was determined by using the rule of effective accumulated temperature and the linear regression method, which was confirmed using a histological analysis of the full gonadal development cycle. The results showed that the biological zero of gonadal reproduction of 1-year-old and 2-year-old S. constricta was the same: 20.8 °C. When the temperature reached 20–21 °C, analysis of the histological sections indicated that more than half of the S. constricta individuals initiated gonadal development. The average effective accumulated temperature over two years was 806 d °C. This study contributes to our understanding of the regulation and control of gonadal maturation, suggesting that changes in the spawning and breeding season during one-year of farming using the new variety of razor clam could provide an economic benefit to industrialized large-scale spat production. The results demonstrated that the razor clam S. constricta is a typical clam of the accumulative temperature mature oviposition type. In addition, although S. constricta does not display hypothermy, it requires a lower temperature for gonadal maturity and spawning.

Lipid Profile and Glycerophospholipid Molecular Species in Two Species of Edible Razor Clams Sinonovacula constricta and Solen gouldi.

Total lipids were extracted from razor clams Sinonovacula constricta and Solen gouldi, and the molecular species of glycerophospholipid (Gpl) including choline glycerophospholipid (ChoGpl), ethanolamine glycerophospholipid (EtnGpl), serine glycerophospholipid (SerGpl), inositol glycerophospholipid (InsGpl), lysoChoGpl, lysoEtnGpl, and lysoSerGpl were characterized using a direct-infusion tandem mass spectrometric method for the first time. Meanwhile, the lipid class composition and phospholipid (PL) class composition as well as the fatty acid (FA) composition of total lipids, triacylglycerol (TAG), and PL were also investigated. About 238 and 235 molecular species were characterized, respectively, in Sinonovacula constricta and Solen gouldi. The majority of the dominant Gpl molecular species contained n-3 long-chain polyunsaturated fatty acids (n-3 LC-PUFA), especially docosahexaenoic acid (DHA) and eicosapentaenoic acid (EPA). Also, razor clam lipids contained a high-proportioned PL (52.19-65.41% of total lipids) and PUFA (47.94-54.81 mol%). Furthermore, PL contained a higher proportion of PUFA (63.05-67.13 mol%), especially DHA (20.04-22.47 mol%) and EPA (16.27-21.46 mol%) than TAG (the corresponding values being 33.73-34.45, 11.95-12.27, and 8.13-0.8.99 mol%, respectively). Meanwhile, phosphatidylcholine (44.38-46.21 mol%) and phosphatidylethanolamine (38.84-39.95 mol%) were dominant among PL. In consideration of the high proportion of PUFA-enriched Gpl, razor clam plays a great role in promoting human health.

Biosynthesis of long-chain polyunsaturated fatty acids in the razor clam Sinonovacula constricta: Characterization of four fatty acyl elongases and a novel desaturase capacity

As an unusual economically important aquaculture species, Sinonovacula constricta possesses high levels of long-chain polyunsaturated fatty acids (LC-PUFA). Previously, our group identified fatty acyl desaturases (Fad) with Δ5 and Δ6 activities in S. constricta, which was the first report of Δ6 Fad in a marine mollusc. Here, we further successfully characterize elongases of very long-chain fatty acids (Elovl) in this important bivalve species, including one Elovl2/5, two Elovl4 isoforms (a and b) and a novel Elovl (c) with Elovl4 activity. In addition, we also determined the desaturation activity of S. constricta Δ6 Fad toward 24:5n-3 to give 24:6n-3, a key intermediate in docosahexaenoic acid (DHA) biosynthesis. Therefore, S. constricta is the first marine mollusc reported to possess all Fad and Elovl activities required for LC-PUFA biosynthesis via the ‘Sprecher pathway’. This finding greatly increases our understanding of LC-PUFA biosynthesis in marine molluscs. Phylogenetic analysis by interrogating six marine molluscan genomes, and previously functionally characterized Elovl and Fad from marine molluscs, suggested that DHA biosynthetic ability was limited to a few species, due to the general lack of Δ4 or Δ6 Fad in most molluscs.

Gene identification and antimicrobial activity analysis of a novel lysozyme from razor clam Sinonovacula constricta

Lysozymes are important immune effectors present in phylogenetically diverse organisms. They play vital roles in bacterial elimination during early immune responses. In the present study, a second invertebrate-type (i-type) lysozyme gene from razor clam Sinonovacula constricta (denoted as ScLYZ-2) was cloned by RACE and nested PCR methods. The full-length cDNA sequences of ScLYZ-2 were 1558 bp, including a 5′ untranslated region (UTR) of 375 bp, an open reading frame of 426 bp, and a 3′-UTR of 757 bp with polyadenylation signal sequence (AATAAA) located upstream of the poly(A) tail. SMART analysis showed that ScLYZ-2 contains a signal peptide in the first 16 amino acid (AA) sequences and a destabilase domain located from 24 to 134 AA sequences. The deduced AA sequences of ScLYZ-2 were highly similar (42%–58%) to other known lysozyme genes of bivalve species. Multiple alignments of AA sequences showed that ScLYZ-2 possesses the classical i-type lysozyme family signature of two motifs [“MDVGSLSCGP(Y/F)QIK” and “CL(E/L/R/H)C(I/M)C”] and two catalytic residues (Glu35 and Asp46). Moreover, phylogenetic analysis showed that ScLYZ-2 is a new member of the i-type lysozyme family. In healthy razor clams, ScLYZ-2 was highly expressed in the hepatopancreas, followed by the gills, water pipes, and abdominal foot. Lysozyme activity and ScLYZ-2 expression levels were significantly upregulated in the hepatopancreas and gills after being infected with V. splendidus, V. harveyi, V. parahaemolyticus and S. aureus and M. luteus. Moreover, the recombinant ScLYZ-2 had strong antimicrobial activities against V. splendidus, V. harveyi, and V. parahaemolyticus. Furthermore, the minimal inhibitory concentration of the recombinant ScLYZ-2 against V. parahaemolyticus was 7.2 μmol/mL. Taken together, our results show that ScLYZ-2 plays an important role in the immune defense of razor clam by eliminating pathogenic microorganisms.

Comparative transcriptome analyses provide insights into the adaptation mechanisms to acute salt stresses in juvenile Sinonovacula constricta.

Sinonovacula constricta is an economically important bivalve species in China, Korea and Japan that widely resides in estuarine and coastal areas where salinity fluctuates rapidly. However, little is known about its adaptation mechanisms to acute salt stresses. To reveal the underlying molecular mechanisms involved in acute salt stresses in juvenile S. constricta. Nine cDNA libraries (triplicate each trial) were established from juvenile S. constricta, which were subjected to low salinity (5psu), optimal salinity (15psu) and high salinity (25psu) for 6h, respectively. Illumina sequencing generated 478,587,310 clean reads totally, which were assembled into 427,057 transcripts of 246,672 unigenes. Compared with the control, 1259 and 2163 differentially expressed genes (DEGs) were identified under acute low and high salt stresses, respectively. GO and KEGG enrichment analyses of DEGs revealed that several key metabolic modulations were mainly responsible for the acute salt stresses. According to the significantly highlighted KEGG pathways, some key DEGs were identified and discussed in details. Notably, based on which, some potential osmolytes were further speculated. Here, we carried out a unique report of comparative transcriptome analyses in juvenile S. constricta in response to acute salt stresses. The identified DEGs and their significantly enriched GO terms and KEGG pathways were critical for understanding and further investigating the underlying the physical and biochemical performances, and ultimately facilitated S. constricta breeding. Besides, the transcriptome data greatly enriched the genetic information of S. constricta, which were valuable for promoting its molecular biology researches.

Bioturbation by the razor clam Sinonovacula constricta affects benthic nutrient fluxes in aquaculture wastewater treatment ecosystems

Bioturbation by the razor clam Sinonovacula constricta affects benthic nutrient fluxes in aquaculture wastewater treatment ecosystems

Survival, growth and physiology of marine bivalve (Sinonovacula constricta) in long-term low-salt culture

In this study, we investigated the possibility of rearing and breeding the razor clam (Sinonovacula constricta) in inland low salinity water or freshwater. Long-term low salinity (LS) rearing was performed for 3 months to determine the effects of LS on the survival rate, growth rate, and the activities of critical enzymes in juvenile S. constricta (JSC). The survival rate in the LS group was only 15.67% at the end of the LS rearing test. In the first month, the survival rate in the LS group was significantly lower than that in the control group (P < 0.001). The growth rate (shell length growth rate and weight gain rate) was significantly lower in the LS group than the control group in the first month (P < 0.001 for length and weight). However, the growth rates in the two groups differed little during the second and third months. The oxygen consumption and ammonia excretion rates by JSCs were significantly higher in the LS group than the control group during the first month, but they decreased gradually during the following 2 months. The Na+/K+ ATPase and superoxide dismutase activities were significantly higher in the LS group than the control group during the first month, but they then decreased gradually until there were no significant differences between the groups. However, the aspartate aminotransferase activity was higher in the LS group than the control group during all 3 months. Most of the JSCs died due to LS but the survival of some JSCs suggests the possibility of breeding LS resistant or freshwater S. constricta.

Characterization of the ScghC1q-1 gene in Sinonovacula constricta and its role in innate immune responses

C1q is an important immune gene that can mediate a variety of immune regulatory functions, and is involved in complement pathway activation. In the present study, a ghC1q gene from the razor clam Sinonovacula constricta was identified and named ScghC1q-1. The complete ScghC1q-1 gene is 692 bp in length, with an open reading frame (ORF) of 489 bp encoding a protein of 162 amino acids. ScghC1q-1 mRNA was widely expressed in various tissues, and transcript levels in the hemolymph were significantly up-regulated following Staphylococcus aureus or Vibrio anguillarum challenge. Recombinant ScghC1q-1 protein was found to agglutinate both Gram-positive and Gram-negative bacteria. These results indicate that ScghC1q-1 plays an essential role in the immune defense of S. constricta.

Identification of a novel C1q complement component in razor clam Sinonovacula constricta and its role in antibacterial activity

The serum complement component C1q mediates a variety of immune regulatory functions. Herein, we identified a globular head C1q (ghC1q) gene in razor clam Sinonovacula constricta. The complete Sc-ghC1q gene was 872 bp long included an 81 bp 5ʹ-untranslated region (UTR), a 95 bp 3′-UTR with a poly(A) tail, and an open reading frame (ORF) of 696 bp. The mRNA expression of Sc-ghC1q was upregulated in hepatopancreas and hemocytes. After Staphylococcus aureus or Vibrio anguillarum challenge, Sc-ghC1q mRNA transcript abundance was significantly upregulated in hemolymph. Recombinant Sc-ghC1q protein could bind lipopolysaccharide (LPS) and lipoteichoic acid (LTA), and it could agglutinate both Gram-positive and Gram-negative bacteria. Additionally, flow cytometry revealed that Sc-ghC1q strongly promoted phagocytosis in hemocytes. Together, these results demonstrated that Sc-ghC1q played an important role in innate immunity in S. constricta.