Immune response and energy metabolism of Chlamys farreri under Vibrio anguillarum challenge and high temperature exposure

Single-cell transcriptomic dynamics of scallop heart reveals the heterogeneous response to heat stress

BACKGROUND

Animals with open circulatory systems are highly vulnerable to environmental temperature fluctuations, making them particularly threatened by global warming. However, research on the cellular heterogeneity of heart responses to elevated temperatures in animals with open circulatory systems remains limited.

RESULTS

Here, we conducted a comprehensive investigation of the morphology, metabolism and scRNA-seq of the heart in a molluscan model, Argopecten irradians, under heat stress. Our results unraveled that the severity of cardiac structure damage increased progressively with rising temperature, accompanied by widespread mitochondrial dysfunction and neurohumoral response. We identified two subpopulations within cardiomyocytes (CMs), including ventricular myocytes (VMs) and atrial myocytes (AMs), which exhibited specialized functional roles in response to thermal stress. Specifically, AMs enhanced cell-cell communications with the immune-like cells and fibroblasts to contribute to maintaining cardiac homeostasis under heat stress. Whereas, VMs displayed enhanced energy supply and differentiation potential to withstand thermal challenges. Furthermore, RNA interference targeting the most heat-responsive gene, PLRP2-like, resulted in a significant reduction in heat tolerance and triglyceride accumulation in scallops.

CONCLUSIONS

Our study investigated the heterogeneous response of the scallop heart to high temperatures, revealing distinct response patterns between VMs and AMs. We further identified a key gene, AiPLRP2-like, which exhibits unique cellular localization patterns compared to its mammalian counterpart and may play a pivotal role in regulating cardiac thermotolerance in organisms with open circulatory systems. These findings provide novel insights into the theoretical framework and evolutionary adaptations of marine invertebrate hearts in response to environmental temperature fluctuations.

Reproductive effort affects cellular response in the mantle of Nodipecten subnodosus scallops exposed to acute hyperthermia

In marine ecosystems, temperature regulates the energy metabolism of animals. In the last decades, the temperature increase was related to mass mortality events of marine ectotherms, particularly during high-energy investment for reproduction. In scallops, the mantle has been poorly investigated while this tissue covers more than 40 % of the body mass, contributing to the perception of surrounding environmental stimuli. Our aim was to assess the cellular and molecular responses linked to energy metabolism in the mantle of adult N. subnodosus facing acute hyperthermia during reproductive effort. Scallops collected in spring (late gametogenesis) and summer (ripe gonads) were exposed to a control temperature (22 °C) or acute hyperthermia (30 °C) for 24 h. In spring, increased arginine kinase (AK) activity together with increased pyruvate kinase/citrate synthase ratio (PK/CS) suggested an enhanced carbohydrate, pyruvate, and arginine metabolism to maintain the adenylate energy charge (AEC) in the mantle of scallops coping with acute thermal increase. In summer, animals decreased their AEC (5 %) and arginine phosphate pool (40 %) and increased their anaerobic metabolism as shown by enhanced activities of lactate dehydrogenase (LDH) and octopine dehydrogenase (ODH), respectively. The abundance of twenty proteins involved in energy metabolism (isocitrate dehydrogenase, ATP synthase subunit β), protein protection (cognate heat shock protein 70), and cytoskeleton (actins and tubulins) were affected only by season. These results underlie the role of the mantle of N. subnodosus in the seasonal responses of this tissue to thermal fluctuations during reproductive effort with possible implications for the physiological performance of scallops under heat waves in wild or harvest conditions.

CgmiR307 involved in the regulation of Nrf2-dependent oxidative response in the Pacific oyster Crassostrea gigas under high-temperature stress

miRNA, a type of endogenous small non-coding RNA, is involved in the response to various environmental stresses through post-transcriptional regulation. In the present study, the role of CgmiR307 in the regulation of oxidative response under high-temperature stress by targeting CgNrf2 was investigated in the Pacific oyster Crassostrea gigas. The binding site of CgmiR307 were predicted at 1799-1818 bp in the 3'-UTR of CgNrf2, and the binding activity of CgmiR307 with the mRNA of CgNrf2 was further proved by the dual-luciferase reporter assay. The expression levels of CgmiR307 and CgNrf2 in gill were significantly higher than in other tissues, and exhibited significant fluctuations and variations after exposure to 28 °C. There was a significant reduction in the expression levels of CgSOD, and CgCAT in gill, as well as the activities of SOD, CAT, and T-AOC, while ROS and MDA contents significantly increased in CgNrf2-RNAi oysters. After CgmiR307 agomir injection and high-temperature stress, the expression levels of CgNrf2, CgSOD and CgCAT in gill, the activities of SOD and CAT and T-AOC decreased significantly, while ROS and MDA content significantly increased. After CgmiR307 antagomir injection and high-temperature stress, the changes in the parameters of oxidative response shown exactly the opposite trend. These results demonstrated that CgmiR307 was involved in the regulation of oxidative response by inhibiting the mRNA expression of CgNrf2 under high-temperature stress.

TORC1 Regulates Thermotolerance via Modulating Metabolic Rate and Antioxidant Capacity in Scallop Argopecten irradians irradians

Target of rapamycin complex 1 (TORC1) is a key regulator of metabolism in eukaryotes across multiple pathways. Although TORC1 has been extensively studied in vertebrates and some invertebrates, research on this complex in scallops is limited. In this study, we identified the genes encoding TORC1 complex subunits in the scallop Argopecten irradians irradians through genome-wide in silico scanning. Five genes, including TOR, RAPTOR, LST8, DEPTOR, and PRAS40, that encode the subunits of TORC1 complex were identified in the bay scallop. We then conducted structural characterization and phylogenetic analysis of the A. i. irradians TORC1 (AiTORC1) subunits to determine their structural features and evolutionary relationships. Next, we analyzed the spatiotemporal expressions of AiTORC1-coding genes during various embryo/larvae developmental stages and across different tissues in healthy adult scallops. The results revealed stage- and tissue-specific expression patterns, suggesting diverse roles in development and growth. Furthermore, the regulation of AiTORC1-coding genes was examined in temperature-sensitive tissues (the mantle, gill, hemocyte, and heart) of bay scallops exposed to high-temperature (32 °C) stress over different durations (0 h, 6 h, 12 h, 24 h, 3 d, 6 d, and 10 d). The expression of AiTORC1-coding genes was predominantly suppressed in the hemocyte but was generally activated in the mantle, gill, and heart, indicating a tissue-specific response to heat stress. Finally, functional validation was performed using the TOR inhibitor rapamycin to suppress AiTORC1, leading to an enhanced catabolism, a decreased antioxidant capacity, and a significant reduction in thermotolerance in bay scallops. Collectively, this study elucidates the presence, structural features, evolutional relationships, expression profiles, and roles in antioxidant capacity and metabolism regulation of AiTORC1 in the bay scallop, providing a preliminary understanding of its versatile functions in response to high-temperature challenges in marine mollusks.

Comparative study of integrated bio-responses in deep-sea and nearshore mussels upon abiotic condition changes: Insight into distinct regulation and adaptation

Deep-sea mussels, one of the dominant species in most deep-sea ecosystems, have long been used as model organisms to investigate the adaptations and symbiotic relationships of deep-sea macrofauna under laboratory conditions due to their ability to survive under atmospheric pressure. However, the impact of additional abiotic conditions beyond pressure, such as temperature and light, on their physiological characteristics remains unknown. In this study, deep-sea mussels (Gigantidas platifrons) from cold seep of the South China Sea, along with nearshore mussels (Mytilus coruscus) from the East China Sea, were reared in unfavorable abiotic conditions for up to 8 days. Integrated biochemical indexes including antioxidant defense, immune ability and energy metabolism were investigated in the gill and digestive gland, while cytotoxicity was determined in hemocytes of both types of mussels. The results revealed mild bio-responses in two types of mussels in the laboratory, represented by the effective antioxidant defense with constant total antioxidant capability level and malondialdehyde content. There were also disparate adaptations in deep-sea and nearshore mussels. In deep-sea mussels, significantly increased immune response and energy reservation were observed in gills, together with the elevated cytotoxicity in hemocytes, implying the more severe biological adaptation was required, mainly due to the symbiotic bacteria loss under laboratory conditions. On the contrary, insignificant biological responses were exhibited in nearshore mussels except for the increased energy consumption, indicating the trade-off strategy to use more energy to deal with potential stress. Overall, this comparative study highlights the basal bio-responses of deep-sea and nearshore mussels out of their native environments, providing evidence that short-term culture of both mussels under easily achievable laboratory conditions would not dramatically alter their biological status. This finding will assist in broadening the application of deep-sea mussels as model organism in future research regardless of the specialized research equipment.

Potential threats of microplastics and pathogenic bacteria to the immune system of the mussels Mytilus galloprovincialis

As one of the main components of marine pollution, microplastics (MPs) inevitably enter the mussel aquaculture environment. At the same time, pathogenic bacteria, especially pathogens such as Vibrio, can cause illness outbreaks, leading to large-scale death of mussels. The potential harm of MPs and pathogenic bacteria to bivalve remains unclear. This study designed two experiments (1) mussels (Mytilus galloprovincialis) were exposed to 100 particles/L or 1,000 particles/L polymethyl methacrylate (PMMA, 17.01 ± 6.74 μm) MPs and 1 × 107 CFU/mL Vibrio parahaemolyticus at the same time (14 days), and (2) mussels were exposed to 100 particles/L or 1,000 particles/L MPs for a long time (30 days) and then exposed to 1 × 107 CFU/mL V. parahaemolyticus to explore the effects of these two stresses on the mussel immune system. The results showed that after the combined exposure of V. parahaemolyticus and MPs, the lysosomal membrane stability of hemocytes decreased, lysozyme activity was inhibited, and hemocytes were induced to produce more lectins and defensins to fight pathogenic invasion. Long-term exposure to MPs caused a large amount of energy consumption in mussels, inhibited most of the functions of humoral immunity, increased the risk of mussel infection with pathogenic bacteria, and negatively affected mussel condition factor, the number of hemocytes, and the number of byssuses. Mussels may allocate more energy to deal with MPs and pathogenic bacterial infections rather than for growth. Above all, MPs exposure can affect mussel immune function or reduce its stress resistance, which in turn has an impact on mollusk farming.

The expression patterns of exosomal miRNAs in the Pacific oyster after high-temperature stress or Vibrio stimulation

The exosomal miRNA plays a crucial role in the intercellular communication response to environmental stress and pathogenic stimulation. In the present study, the expression of exosomal miRNAs in the Pacific oyster Crassostrea gigas after high-temperature stress or Vibrio splendidus stimulation was investigated through high-throughput sequencing. The exosomes were identified to be teardrop-like vesicles with the average size of 81.7 nm by transmission electron microscopy. There were 66 known miRNAs and 33 novel miRNAs identified, of which 10 miRNAs were differentially expressed after both high-temperature stress and Vibrio stimulation compared to the control group. A total of 1868 genes were predicted as the putative targets of miRNAs, of which threonine aspartase 1-like was targeted by the highest number of related miRNAs. The robustness and reliability of miRNA expression from the sRNA sequencing data were verified by employing eight miRNAs for qPCR. GO and KEGG clustering analyses revealed that apoptosis was significantly enriched by the target genes of differentially expressed exosomal miRNAs after high-temperature stress, and autophagy and cytokine activity were significantly enriched after Vibrio stimulation. Energy metabolism was found to be significantly shared in the target gene enrichments after both high-temperature stress and Vibrio stimulation. These findings would improve our understanding of the regulatory mechanisms of exosomal miRNAs in C. gigas after high-temperature stress or Vibrio stimulation.

The combination of high temperature and Vibrio infection worsens summer mortality in the clam Meretrix petechialis by increasing apoptosis and oxidative stress

The interaction between environmental factors and Vibrio in bivalves is not well understood, despite the widely held belief that pathogen infection and seawater temperature significantly impact summer mortality. In the present study, we conducted simulated experiments to explore the effects of high temperature and Vibrio infection on the clam Meretrix petechialis. The survival curve analysis revealed that the combined challenge of high temperature and Vibrio infection (31°C-vibrio) led to significantly higher clam mortality compared to the groups exposed solely to Vibrio (27°C-vibrio), high temperature (31°C-control), and the control condition (27°C-control). Furthermore, PCoA analysis of 11 immune genes indicated that Vibrio infection predominated during the incubation period, with a gradual equilibrium between these factors emerging during the course of the infection. Additionally, our investigations into apoptosis and autophagy processes exhibited significant induction of mTOR and Bcl2 of the 31°C-vibrio group in the early challenge stage, followed by inhibition in the later stage. Oxidative stress analysis demonstrated a substantial additive effect on malondialdehyde (MDA) and glutathione (GSH) content in the combined challenge group compared to the control group. Comparative transcriptome analysis revealed a significant increase in differentially expressed genes related to immunity, such as complement C1q-like protein, C-type lectin, big defensin, and lysozyme, in the 31°C-vibrio group, suggesting that the synergistic effect of high temperature and Vibrio infection triggers more robust antibacterial immune responses. These findings provide critical insights for understanding the infection process and uncovering the causes of summer mortality.

Response of the terrestrial isopod Porcellio scaber to lipopolysaccharide challenge after microplastic and insecticide exposure

The exposure of organisms to microplastics could compromise their ability to cope with other environmental stressors, such as infections. In this context, we investigated the effects of a 14-day exposure of the terrestrial isopod Porcellio scaber to tire particles in soil (1.5 % w w-1 dry weight) on the organisms' response to a secondary exposure, i.e., injection of the bacterial endotoxin lipopolysaccharide. In addition, the insecticide chlorpyrifos (2 mg kg-1 dry weight) was tested as a positive control. The survival and immune response of P. scaber was assessed at the end of the 7- and 14-day primary exposure and two days after the secondary exposure, by analyzing selected haemolymph immune parameters (total haemocyte count, differential haemocyte count, and haemocyte viability). No change in survival was observed after primary exposure of P. scaber to tire particles or chlorpyrifos. However, primary exposure to chlorpyrifos triggered a strong activation of the immune response, which was not the case following exposure to the tire particles. Further injection of lipopolysaccharide into the body did not affect the survival of animals exposed to tire particles or chlorpyrifos, while a strong immunomodulatory change was observed, particularly with chlorpyrifos, and to some extent, tire particles. Based on these results, we conclude that exposure of P. scaber to tire particles or chlorpyrifos has no significant effect on the susceptibility of the organism to lipopolysaccharide in terms of their mortality, but primary exposure to an insecticide significantly modulates the immune response of the organisms to a second stressor. We discuss the "stress on stress" approach for testing low-toxic substances, such as microplastics, where an environmentally realistic exposure is followed by a secondary exposure.

PyLKB1 regulates glucose transport via activating PyAMPKα in Yesso Scallop Patinopecten yessoensis under high temperature stress

Liver kinase B1 (LKB1) is a classical serine/threonine protein kinase and plays an important role in maintaining energy homeostasis through phosphorylate AMP-activated protein kinase α subunit (AMPKα). In this study, a homologous molecule of LKB1 with a typical serine/threonine kinase domain and two nuclear localization sequences (NLSs) was identified in Yesso Scallop Patinopecten yessoensis (PyLKB1). The mRNA transcripts of PyLKB1 were found to be expressed in haemocytes and all the examined tissues, including gill, mantle, gonad, adductor muscle and hepatopancreas, with the highest expression level in hepatopancreas. PyLKB1 was mainly located in cytoplasm and nucleus of scallop haemocytes. At 3 h after high temperature stress treatment (25 °C), the mRNA transcripts of PyLKB1, PyAMPKα, and PyGLUT1 in hepatopancreas, the phosphorylation level of PyAMPKα at Thr170 in hepatopancreas, the positive fluorescence signals of PyLKB1 in haemocytes, glucose analogue 2-NBDG content in haemocytes, and glucose content in hepatopancreas, haemocytes and serum all increased significantly (p < 0.05) compared to blank group (15 °C). However, there was no significant difference at the protein level of PyLKB1 and PyAMPKα. After PyLKB1 was knockdown by siRNA, the mRNA expression level of PyGLUT1, and the glucose content in hepatopancreas and serum were significantly down-regulated (p < 0.05) compared with the negative control group receiving an injection of siRNA-NC. However, there were no significant difference in PyGLUT1 expression, glucose content and glucose analogue 2-NBDG content in haemocytes. These results collectively suggested that PyLKB1-PyAMPKα pathway was activated to promote glucose transport by regulating PyGLUT1 in response to high temperature stress. These results would be helpful for understanding the function of PyLKB1-PyAMPKα pathway in regulating glucose metabolism and maintaining energy homeostasis under high temperature stress in scallops.

Effectiveness of dietary heat-killed Bacillus subtilis harboring plasmid containing 60 copies of CpG-ODN 1668 against Vibrio harveyi in Penaeus vannamei

The cost of the purification process hinders the extensive use of cytosine phosphate guanosine-oligodeoxynucleotides (CpG-ODNs) for shrimp culture. Therefore, this study used a shuttle vector plasmid to carry 60 copies of CpG-ODN 1668 (pAD43-25_60CpG), which can replicate in Escherichia coli and Bacillus subtilis strain RIK1285. The first experiment used a reverse gavage procedure to deliver a substance (PBS [CK], pAD43-25 [P0], and pAD43-25_60CpG [P60], respectively) directly into the anterior midgut of Penaeus vannamei and transcriptome sequence analysis with a reference genome was performed to examine the expression of well-known immune-related genes. The results showed that the expression levels of immune-related genes in P60 group were significantly increased, particularly those associated with AMPs. In addition, using RT‒qPCR, the expression levels of AMP genes (LvALF, LvPEN-2, and LvPEN-3) in the P60 group may vary depending on the tissue and time point. The second experiment used dietary supplementation with three kinds of heat-killed B. subtilis (HKBS, HKBS-P0, and HKBS-P60) in 28 days of feeding experiments. The results showed that dietary supplementation with HKBS-P60 did not significantly improve shrimp growth performance and survival. However, on days 14 and 28 of the feeding regimens, alkaline phosphatase (AKP) and acid phosphatase (ACP) activity were considerably higher than in other treatments. In addition, following infection with Vibrio harveyi, AKP and ACP activity in the HKBS-P60 group was significantly higher than in other treatments, particularly at the early stage of bacterial infection. Moreover, HKBS-P60 was found to be better protected against V. harveyi infection with lower cumulative mortality (60%) compared to HKBS (90%) and HKBS-P0 (100%) at 7 days after infection. Overall, these findings confirmed that P60 could increase immunological responses in the shrimp midgut, and HKBS-P60 could be used as an effective tool to enhance the immune response and disease resistance in shrimp.

Collapse of scallop Nodipecten nodosus production in the tropical Southeast Brazil as a possible consequence of global warming and water pollution

Mollusc rearing is a relevant global socioeconomic activity. However, this activity has faced severe problems in the last years in southeast Brazil. The mariculture scallop production dropped from 51,2 tons in 2016 to 10,2 tons in 2022 in the Baia da Ilha Grande (BIG; Rio de Janeiro). However, the possible causes of this collapse are unknown. This study aimed to analyze decadal trends of water quality in Nodipecten nodosus spat and adult production in BIG. We also performed physical-chemical and biological water quality analyses of three scallop farms and two nearby locations at BIG in 2022 to evaluate possible environmental stressors and risks. Scallop spat production dropped drastically in the last five years (2018-2022: mean ± stdev: 0.47 ± 0.45 million). Spat production was higher in colder waters and during peaks of Chlorophyll a in the last 13 years. Reduction of Chlorophyll a coincided with decreasing spat production in the last five years. Warmer periods (>27 °C) of the year may hamper scallop development. Counts of potentially pathogenic bacteria (Vibrios) and Escherichia coli were significantly higher in warmer periods which may further reduce scallop productivity. Shotgun metagenomics of seawater samples from the five studied corroborated these culture-based counts. Vibrios and fecal indicator bacteria metagenomic sequences were abundant across the entire study area throughout 2022. The results of this study suggest the collapse of scallop mariculture is the result of a synergistic negative effect of global warming and poor seawater quality.

The involvement of AMP-activated protein kinase α in regulating glycolysis in Yesso scallop Patinopecten yessoensis under high temperature stress

AMP-activated protein kinase α subunit (AMPKα), the central regulatory molecule of energy metabolism, plays an important role in maintaining energy homeostasis and helping cells to resist the influence of various adverse factors. In the present study, an AMPKα was identified from Yesso scallop Patinopecten yessoensis (PyAMPKα). The open reading frame (ORF) of PyAMPKα was of 1599 bp encoding a putative polypeptide of 533 amino acid residues with a typical KD domain, a α-AID domain and a α-CTD domain. The deduced amino acid sequence of PyAMPKα shared 59.89-74.78% identities with AMPKαs from other species. The mRNA transcripts of PyAMPKα were found to be expressed in haemocytes and all the examined tissues, including gill, mantle, gonad, adductor muscle and hepatopancreas, with the highest expression level in adductor muscle. PyAMPKα was mainly located in cytoplasm of scallop haemocytes. At 3 h after high temperature stress treatment (25 °C), the mRNA transcripts of PyAMPKα, the phosphorylation level of PyAMPKα at Thr170 and the lactic acid (LD) content in adductor muscle all increased significantly, while the glycogen content decreased significantly. The activity of pyruvate kinase (PyPK) and the relative mRNA expression level of phosphofructokinase (PyPFK) were significantly up-regulated at 3 h after high temperature stress treatment (25 °C). Furthermore, the PyAMPKα activator AICAR could effectively upregulate the phosphorylation level of PyAMPKα, and increase activities of PyPFK and pyruvate kinase (PyPK). Meanwhile the glycogen content also declined under AICAR treatment. These results collectively suggested that PyAMPKα was involved in the high temperature stress response of scallops by enhancing glycolysis pathway of glycogen. These results would be helpful for understanding the functions of PyAMPKα in maintaining energy homeostasis under high temperature stress in scallops.

Effect of high temperature stress on glycogen metabolism in gills of Yesso scallop Patinopecten yessoensis

Glycogen was the main energy storage material in mollusc, and the regulation of its metabolism is essential for the response against high temperature stress. In the present study, the alternation of lactic acid (LD) content, glycogen reserves, mRNA expression level of genes encoding glycogen metabolism enzymes and activities of glycogen metabolism enzymes in gills of Yesso scallop Patinopecten yessoensis after an acute high temperature treatment at 25 °C were examined to understand the effect of high temperature on glycogen metabolism. The activity of T-ATPase in gills of scallops presented a gradual increase trend especially at 6 h after an acute high temperature treatment (p < 0.05). The glycogen reserves did not change significantly even there was a downward trend at 24 h after the acute high temperature treatment (p > 0.05). The mRNA transcripts of glycogen synthase (PyGCS) in gills of scallops decreased significantly at 1, 3, 6 and 12 h (p < 0.05), and recovered to normal level at 24 h (p > 0.05) after the acute high temperature treatment, while that of glycogen phosphorylase a (PyGPa) and phosphoenol pyruvate carboxy kinase (PyPEPCK) were both significantly down-regulated from 1 h to 24 h (p < 0.05) after the acute high temperature treatment. The activity of PyGPa at 1, 12 and 24 h and the content of LD at 3 and 24 h in gills of scallops after the acute high temperature treatment both increased significantly (p < 0.05). Furthermore, the mRNA transcripts of hexokinase (PyHK) and pyruvate kinase (PyPK) in gills of scallops increased significantly (p < 0.05) after the acute high temperature treatment, and the response of PyHK was stronger. However, there was no significant difference on the activity of PyPK in gills of scallops between the experimental samples and the blank samples (p > 0.05). In addition, the mRNA transcripts of citrate synthase (PyCS) in gills of scallops were significantly down-regulated at 6 h and 12 h (p < 0.05), and finally returned to normal level at 24 h (p > 0.05) after the acute high temperature treatment. These results collectively indicated acute high temperature stress leaded the alternation of glycogen metabolism in the gills of Yesso scallop, glycogenesis, gluconeogenesis and TCA cycle were inhibited, and the glycolysis pathway of glycogen was enhanced to produce more energy for coping with environmental pressure.

The first use of LC-MS/MS proteomic approach in the brown mussel Perna perna after bacterial challenge: Searching for key proteins on immune response

The brown mussel Perna perna is a valuable fishing resource, primarily in tropical and subtropical coastal regions. Because of their filter-feeding habits, mussels are directly exposed to bacteria in the water column. Escherichia coli (EC) and Salmonella enterica (SE) inhabit human guts and reach the marine environment through anthropogenic sources, such as sewage. Vibrio parahaemolyticus (VP) is indigenous to coastal ecosystems but can be harmful to shellfish. In this study, we aimed to assess the protein profile of the hepatopancreas of P. perna mussel challenged by introduced - E. coli and S. enterica - and indigenous marine bacteria - V. parahaemolyticus. Bacterial-challenge groups were compared with non-injected (NC) and injected control (IC) - that consisted in mussels not challenged and mussels injected with sterile PBS-NaCl, respectively. Through LC-MS/MS proteomic analysis, 3805 proteins were found in the hepatopancreas of P. perna. From the total, 597 were significantly different among conditions. Mussels injected with VP presented 343 proteins downregulated compared with all the other conditions, suggesting that VP suppresses their immune response. Particularly, 31 altered proteins - upregulated or downregulated - for one or more challenge groups (EC, SE, and VP) compared with controls (NC and IC) are discussed in detail in the paper. For the three tested bacteria, significantly different proteins were found to perform critical roles in immune response at all levels, namely: recognition and signal transduction; transcription; RNA processing; translation and protein processing; secretion; and humoral effectors. This is the first shotgun proteomic study in P. perna mussel, therefore providing an overview of the protein profile of the mussel hepatopancreas, focused on the immune response against bacteria. Hence, it is possible to understand the immune-bacteria relationship at molecular levels better. This knowledge can support the development of strategies and tools to be applied to coastal marine resource management and contribute to the sustainability of coastal systems.

Effects of titanium dioxide (TiO2)/activated carbon (AC) nanoparticle on the growth and immunity of the giant freshwater prawn, Macrobrachium rosenbergii: potential toxicological risks to the aquatic crustaceans

Due to their unique physicochemical characteristics, nanomaterials exhibit many excellent properties and functions, leading to their applications in numerous fields. The large-scale production and widespread application of nanomaterials have inevitably resulted in their release into the environment, especially the water environment. Several studies have confirmed that exposure to nanomaterials can be toxic to aquatic organisms. However, few studies have focused on the effects of nanomaterial exposure on growth and immunity in crustaceans. In the present study, juvenile Macrobrachium rosenbergii were exposed to different concentrations of titanium dioxide (TiO₂)/activated carbon (AC) composite nanomaterial (0.1 and 0.5 mg/L) for 45 days. The effects of nanoparticle exposure on digestion and antioxidant-related enzyme activities, as well as the expression of growth and immunity-related genes and signaling pathway, were evaluated. Our results show that in response to low concentration of TiO₂/AC nanoparticle (0.1 mg/L), most of the enzyme activities related to digestion and antioxidation (TPS, LPS, AMS, SOD, and CAT) were diminished. On the contrary, the GSH-Px activity increased under the 0.1 mg/L group of TiO₂/AC nanoparticle concentration. Additionally, the level of digestive and antioxidant enzyme activities we detected was increased when exposed to 0.5 mg/L TiO₂/AC nanoparticle. By comparison to the expression level of growth-related genes in the control group, MSTN, CaBP, E75, Raptor, EcR, and EGF were significantly inhibited at 0.1 and 0.5 mg/L concentrations of TiO₂/AC nanoparticle, whereas the expression level of genes (TLR, JAK, STAT, PPAF, ACP, and AKP) related to immunity was increased when exposed to different concentrations of TiO₂/AC nanoparticle. Compared with the control group (0 mg/L concentration), 5166 DEGs were identified in the TiO₂/AC nanoparticle group, and a large number of DEGs were involved in molting, energy metabolism, stress tolerance, and germ cell development. Moreover, KEGG analysis revealed that many DEGs were assigned into signaling pathways related to metabolic growth and immune stress. These results showed that exposure to TiO₂/AC nanoparticle will result in the changes of enzyme activity and routine mRNA expression, suggesting that TiO₂/AC nanoparticle which existed in aquatic environment might affect the physiology of M. rosenbergii. This study will provide significant information for the evaluation of nanomaterial toxicity on aquatic crustaceans.

A preliminary report of exploration of the exosomal shuttle protein in marine invertebrate Chlamys farreri

Exosomes are extracellular vesicles secreted by diverse cell under normal or abnormal physiological conditions, which could carry a range of bioactive molecules and play significant roles in biological processes, such as intercellular communication and immune response. In the current study, a preliminary study was performed to investigate the exosomal shuttle protein in Chlamys farreri (designated as CfesPro) and to predict the potential function of exosomes in scallop innate immunity. The serum derived exosomes (designated as CfEVs) were obtained from lipopolysaccharide (LPS)-stimulated C. farreri and untreated ones. After confirmation and characterization by transmission electron microscopy (TEM), nano-HPLC-MS/MS spectrometry was performed on CfEVs using a label-free quantitative method. Totally 2481 exosomal shuttle proteins were identified in CfEVs proteomic data, which included many innate immune related proteins. GO and KOG functional annotation showed that CfesPro participated in cellular processes, metabolism reactions, signaling transductions, immune responses and so on. Moreover, 1421 proteins in CfesPro were enriched to 324 pathways by KEGG analysis, including several immune-related pathways, such as autophagy, apoptosis and lysosome pathway. Meanwhile, eight autophagy-related proteins were initially identified in CfesPro, indicating that CfEVs had a potential role with autophagy. All these findings showed that CfEVs were involved in C. farreri innate immune defenses. This research would enrich the protein database of marine exosomes and provide a basis for the exploration of immune defense systems in marine invertebrates.

Immunotoxicity of pentachlorophenol to a marine bivalve species and potential toxification mechanisms underpinning

The ubiquitous presence of pentachlorophenol (PCP) in ocean environments threatens marine organisms. However, its effects on immunity of marine invertebrates at environmentally realistic levels are still largely unknown. In this study, the immunotoxicity of PCP to a representative bivalve species was evaluated. In addition, its impacts on metabolism, energy supply, detoxification, and oxidative stress status were also analysed by physiological examination as well as comparative transcriptomic and metabolomic analyses to reveal potential mechanisms underpinning. Results illustrated that the immunity of blood clams was evidently hampered upon PCP exposure. Additionally, significant alterations in energy metabolism were detected in PCP-exposed clams. Meanwhile, the expressions of key detoxification genes and the in vivo contents (or activity) of key detoxification enzymes were markedly altered. Exposure to PCP also triggered significant elevations in intracellular ROS and MDA whereas evident suppression of haemocyte viability. The abovementioned findings were further supported by transcriptomic and metabolomic analyses. Our results suggest that PCP may hamper the immunity of the blood clam by (i) constraining the cellular energy supply through disrupting metabolism; and (ii) damaging haemocytes through inducing oxidative stress. Considering the high similarity of immunity among species, many marine invertebrates may be threatened by PCP, which deserves more attention.

Atmospheric wet deposition serves as an important nutrient supply for coastal ecosystems and fishery resources: Insights from a mariculture area in North China

To determine the ecological effects of atmospheric wet deposition of dissolved nutrients on the coastal waters around the Yangma Island, rain and snow samples were collected and analyzed at a shore-based site for one year. The wet deposition fluxes of dissolved inorganic nitrogen and phosphorus (DIN and DIP) and dissolved organic nitrogen and phosphorus were 69.2, 0.136, 13.3 and 0.143 mmol m^-2 a^-1, respectively. In summer, the new production fueled by wet deposition accounted for 19.3 % of that in seawater and 16.4 % of the amount of particulate organic carbon ingested by the scallops cultivated in the study area, indicating the potential contribution of wet deposition to fishery resources. Meanwhile, precipitation increased the seasonal average DIN/DIP ratios in surface seawater by 17.7 %, 16.3 %, 23.4 % and 6.5 % in spring, summer, autumn and winter, respectively, which could change the composition of ecological community and cause obvious negative impact on the ecosystem and mariculture.

A Novel Disease (Water Bubble Disease) of the Giant Freshwater Prawn Macrobrachium rosenbergii Caused by Citrobacter freundii: Antibiotic Treatment and Effects on the Antioxidant Enzyme Activity and Immune Responses

The giant freshwater prawn, Macrobrachium rosenbergii, is an important and economical aquaculture species widely farmed in tropical and subtropical areas of the world. A new disease, "water bubble disease (WBD)", has emerged and resulted in a large loss of M. rosenbergii cultured in China. A water bubble with a diameter of about 7 mm under the carapace represents the main clinical sign of diseased prawns. In the present study, Citrobacter freundii was isolated and identified from the water bubble. The optimum temperature, pH, and salinity of the C. freundii were 32 °C, 6, and 1%, respectively. A challenging experiment showed that C. freundii caused the same typical signs of WBD in prawns. Median lethal dose of the C. freundii to prawn was 104.94 CFU/g. According to the antibiogram tests of C. freundii, florfenicol and ofloxacin were selected to evaluate their therapeutic effects against C. freundii in prawn. After the challenge with C. freundii, 86.67% and 72.22% survival of protective effects against C. freundii were evaluated in the oral florfenicol pellets and oral ofloxacin pellets feding prawns, respectively, whereas the mortality of prawns without fed antibiotics was 93%. After antibiotic treatment and C. freundii infection, the activities of superoxide dismutase (SOD), catalase (CAT), glutathione peroxidase (GPx), glutathione S-transferase (GST), malondialdehyde (MDA), acid phosphatase (ACP), alkaline phosphatase (ALP), and lysozyme (LZM) in the hemolymph and hepatopancreas of the prawns and the immune-related gene expression levels of Cu/Zn-SOD, CAT, GPx, GST, LZM, ACP, anti-lipopolysaccharide factor, crustin, cyclophilin A, and C-type lectin in hepatopancreas were all significantly changed, indicating that innate immune responses were induced by C. freundii. These results can be beneficial for the prevention and control of C. freundii in prawns.

Cortisol modulates glucose metabolism and oxidative response after acute high temperature stress in Pacific oyster Crassostrea gigas

Cortisol is the main stress hormone that plays crucial roles in energy metabolism and immune response in vertebrates. In the present study, the homologues of 11β-hydroxysteroid dehydrogenase type 1 (designated Cg11β-HSD1) and 5α-reductase 1 (designated Cg5αR1), the key enzymes related to cortisol metabolism, were identified from Pacific oyster Crassostrea gigas. The Cg11β-HSD1 harbored a conserved SDR domain, and Cg5αR1 contained a Steroid_dh domain and three transmembrane domains. The mRNA transcripts of Cg11β-HSD1 and Cg5αR1 were constitutively expressed in all the examined tissues of oysters, with the highest expression level in haemocytes and labial palp, respectively. After acute high temperature stress (28 °C), the mRNA expression level of Cg11β-HSD1 in hepatopancreas significantly up-regulated at 6 h and 12 h, and that of Cg5αR1 significantly up-regulated at 6 h, compared with the Blank group (11 °C). The concentration of cortisol and glucose, as well as the activities of superoxide dismutase (SOD) and catalase (CAT) in hepatopancreas all significantly up-regulated after acute high temperature stress, while the glycogen concentration in adductor muscle decreased significantly at 6 h and 12 h. After the blockage of Cg11β-HSD1 with metyrapone, the cortisol concentration and the activities of SOD and CAT significantly decreased after acute high temperature stress, the glucose concentration in hepatopancreas significantly increased at 24 h, and the glycogen concentration in adductor muscle significantly increased at 6 h. These results collectively suggested that cortisol played a crucial role in regulating glucose metabolism and oxidative response in oysters upon acute high temperature stress.

Tissue-Specific and Time-Dependent Expressions of PC4s in Bay Scallop (Argopecten irradians irradians) Reveal Function Allocation in Thermal Response

Transcriptional coactivator p15 (PC4) encodes a structurally conserved but functionally diverse protein that plays crucial roles in RNAP-II-mediated transcription, DNA replication and damage repair. Although structures and functions of PC4 have been reported in most vertebrates and some invertebrates, the PC4 genes were less systematically identified and characterized in the bay scallop Argopecten irradians irradians. In this study, five PC4 genes (AiPC4s) were successfully identified in bay scallops via whole-genome scanning through in silico analysis. Protein structure and phylogenetic analyses of AiPC4s were conducted to determine the identities and evolutionary relationships of these genes. Expression levels of AiPC4s were assessed in embryos/larvae at all developmental stages, in healthy adult tissues and in different tissues (mantles, gills, hemocytes and hearts) being processed under 32 °C stress with different time durations (0 h, 6 h, 12 h, 24 h, 3 d, 6 d and 10 d). Spatiotemporal expression profiles of AiPC4s suggested the functional roles of the genes in embryos/larvae at all developmental stages and in healthy adult tissues in bay scallop. Expression regulations (up- and down-) of AiPC4s under high-temperature stress displayed both tissue-specific and time-dependent patterns with function allocations, revealing that AiPC4s performed differentiated functions in response to thermal stress. This work provides clues of molecular function allocation of PC4 in scallops in response to thermal stress and helps in illustrating how marine bivalves resist elevated seawater temperature.

The thermal regime modifies the response of aquatic keystone species Daphnia to microplastics: Evidence from population fitness, accumulation, histopathological analysis and candidate gene expression

The water bodies are greatly influenced by chemical contamination and global increasing temperature. As an emerging pollutant, microplastics are widely distributed in the freshwater environment, raising concerns regarding their potential toxicity to organisms. Especially for zooplankton filter feeders, many of microplastics are in similar size as their food. Individually, both microplastics and temperature have profound effects on zooplankton populations and their function in ecosystems. However, the strength and direction of their interactive effects are still not clear. Here, we performed a comprehensive biotoxicity assessment providing empirical evidence that the temperature played a key role in shaping the sensitivity of the zooplankter, Daphnia magna, against microplastic toxicity. We found that exposure to microplastics generally caused negative effects on Daphnia individual fitness, such as increased lethality, declined fecundity and reduced population growth rate. This microplastic toxicity was more prominent at 30 °C than at 20 °C, and was rather minor at 15 °C. Moreover, the warming accelerated the ingestion of microplastics, and triggered abnormal ultrastructure of intestinal epithelial cells. In addition, the expression profiling of candidate genes revealed oxidative damage, fecundity impairment and energy retardation by microplastics were amplified with increasing temperature, which may contribute to the enhancement of microplastic toxicity under warming. Given that high temperature fluctuations are becoming more common and difficult to predict, the interactive effects of microplastics and climate warming on Daphnia population dynamics and biomass production may become increasingly aggravated in nature. Collectively, extrapolation for environmental risk assessment studies conducted under different temperature contexts may broaden our knowledge microplastic toxicity on aquatic organism fitness.

Crayfish (Procambarus clarkii) TRPA1 is required for the defense against Aeromonas hydrophila infection under high temperature conditions and contributes to heat sensing

Temperature is an important environmental factor influencing immune responses of crayfish. However, the mechanism underlying how temperature affects immune responses remains unclear. Here, we identified an ortholog of the transient receptor potential ankyrin subtype 1 (TRPA1), a temperature sensor of Drosophila, from Procambarus clarkii (PcTRPA1-1). Its expression was induced by high temperature and challenge with heat-killed A. hydrophila at high temperature, but not at lower temperature. PcTRPA1-1 silencing led to increased mortality of crayfish challenged with live A. hydrophila at high temperature (32 °C), but had no statistically significant effect on crayfish mortality at 24 °C. This suggests that PcTRPA1-1 is involved in the immune responses of crayfish at high temperature as a potential temperature sensor. Further assay exhibited that PcTRPA1-1 silencing affected immune responses of crayfish, including increase of lipid peroxidation, reduction of total antioxidant capacity, decreased phenoloxidase activity and disruption of circadian rhythm of total hemocyte count entrained by temperature cycles. PcTRPA1-1 silencing also decreased the expression of PcHSP70 and PcHSP90 which are responsive to heat stimuli and bacterial challenge. The results collectively indicate that TRPA1 contributes to heat sensing of crayfish and is required for crayfish defense against bacterial infection.

Integrated transcriptomics and metabolomics analyses reveal benzo[a]pyrene enhances the toxicity of mercury to the Manila clam, Ruditapes philippinarum

Mercury (Hg²⁺) and benzo[a]pyrene (BaP) are ubiquitous and persistent pollutants with multiple toxicities in bivalve molluscs. Here, the toxicological responses in the gills of Manila clams, Ruditapes philippinarum, to Hg²⁺ (10 μg L^-1), BaP (3 μg L^-1), and their mixture were analysed using transcriptomics and metabolomics approaches. Comparisons of the transcriptomes and metabolomes of Hg²⁺-and/or BaP-treated clams with control animals revealed the involvement of the detoxification metabolism, immune defence, energy-related pathways, and osmotic regulation in the stress response of R. philippinarum. Exposure to Hg²⁺ alone primarily enhanced the detoxification and energy metabolic pathways by significantly increasing the expression of genes associated with heat-shock proteins and oxidative phosphorylation. However, co-exposure to Hg²⁺ and BaP caused greater immunotoxicity and disrupted detoxification metabolism, the TCA cycle, glycolysis, and ATP generation. The expression levels of cytochrome P450 1A1 (CYP1A1), multidrug resistance-associated protein 1 (MRP1), and myosin (MYO), and the activity of electron transport system (ETS) in gills were detected, supporting the underlying toxic mechanisms of Hg²⁺ and BaP. We suggest that the presence of BaP enhances the toxicity of Hg²⁺ by 1) hampering the detoxification of Hg²⁺, 2) increasing the immunotoxicity of Hg²⁺, and 3) constraining energy availability for clams.

Construction of a Vibrio anguillarum flagellin B mutant and analysis of its immuno-stimulation effects on Macrobrachium rosenbergii

Vibrio anguillarum is a globally distributed aquatic pathogen, and its flagellin B (FlaB) protein can evoke innate immune responses in hosts. In order to explore the role of FlaB in V. anguillarum infection, we constructed a FlaB-deficient mutant using overlapping PCR and two-step homologous recombination, and gene sequencing confirmed successful knockout of the FlaB gene. Scanning electron microscopy showed no significant differences in the morphological structure of the flagellum between wild-type and FlaB-deficient strains. The mutant was subsequently injected into the freshwater prawn (Macrobrachium rosenbergii) to explore its pathogenicity in the host, and expression of myeloid differentiation factor 88, prophenoloxidase, catalase, superoxide dismutase and glutathione peroxidase was investigated by real-time PCR. The results showed that deletion of FlaB had little effect on V. anguillarum-induced expression of these immune-related genes (p > 0.05). In general, the FlaB mutant displayed similar flagella morphology and immune characteristics to the wild-type strain, hence we speculated that knockout of FlaB might promote the expression and function of other flagellin proteins. Furthermore, this study provides a rapid and simple method for obtaining stable mutants of V. anguillarum free from foreign plasmid DNA.

Antioxidant responses of the mussel Mytilus coruscus co-exposed to ocean acidification, hypoxia and warming

In the present study, the combined effects of pH, dissolved oxygen (DO) and temperature levels on the antioxidant responses of the mussel Mytilus coruscus were evaluated. Mussels were exposed to two pH (8.1, 7.7-acidification), two DO (6 mg L^-1, 2 mg L^-1-hypoxia) and two temperature levels (20 °C, 30 °C-warming) for 30 days. SOD, CAT, MDA, GPx, GSH, GST, TAOC, AKP, ACP, GPT, AST levels were measured in the gills of mussels. All tested biochemical parameters were altered by these three environmental stressors. Values for all the test parameters except GSH first increased and then decreased at various experimental treatments during days 15 and 30 as a result of acidification, hypoxia and warming. GSH content always increased with decreased pH, decreased DO and increased temperature. PCA showed a positive correlation among all the measured biochemical indexes. IBR results showed that M. coruscus were adversely affected by reduced pH, low DO and elevated temperature.

Effects of dietary asafoetida (Ferula sinkiangensis K. M. Shen) levels on feeding attraction activity, growth performance, healthiness, and digestive enzyme activity in juvenile Lateolabrax japonicus

The study was to investigate effects of asafoetida (Ferula sinkiangensis K. M. Shen) powder on feeding attraction activity (FAA), growth performance, healthiness, and digestive enzyme activity of juvenile Lateolabrax japonicus. Six concentration levels (0, 5, 10, 15, 20, and 25 g/kg diets) were formulated for luring and feeding experiment. Results showed that asafoetida could stimulate the appetite of L. japonicus at the dietary levels from 10 to 25 g/kg; reduce the feed conversion ratio (FCR) and feed intake (FI) at 10-20 g/kg; increase the weight gain (WG) and specific growth rate (SGR) at 5-10 g/kg; increase the hepatosomatic index (HSI), body crude lipid content, serum total protein (TP) content, and lysozyme activity at 10-15 g/kg; decrease the moisture at 10-15 g/kg; and increase the serum total superoxide dismutase (T-SOD) activity at 5-15 g/kg, when compared with the control group (p < 0.05). Digestive enzyme activities including amylase (AMS) and trypsin in the intestine were significantly affected by the asafoetida powder (p < 0.05). Regression analyses between the FAA, FCR, WG, SGR, HSI, LZM, T-SOD, AMS, trypsin, and the dietary asafoetida powder levels showed that the optimal additional amount was 16.95, 13.65, 8.36, 8.15, 15.45, 9.94, 8.75, 11.77, and 7.07 g/kg, respectively, indicating that the optimal amount of asafoetida powder was located in 7.07-16.95 g/kg diet. However, combined with the significant difference analyses obtained from the current study, we would suggest the additive suitable dosage was 10 g/kg.

Transcriptomic analysis of Manila clam Ruditapes philippinarum under lipopolysaccharide challenge provides molecular insights into immune response

The Manila clam, Ruditapes philippinarum, is an economically important shellfish in marine aquaculture. A better understanding of the immune system in R. philippinarum will provide the basis for the development of strategies to mitigate the impact of infectious diseases affecting this species but can also be of relevance for other bivalves of commercial interest. In this study, the transcriptional response of the Manila clam under lipopolysaccharide (LPS) challenge was characterized using RNA sequencing. The transcriptomes of LPS challenged group of clams (LH1, LH2 and LH3), and the PBS control group (CH1, CH2 and CH3), were sequenced with the Illumina HiSeq platform. Compared with the unigene expression profile of the control group, 223 unigenes were up-regulated and 389 unigenes were down-regulated in the LPS challenged group. Gene Ontology (GO) and Kyoto Encyclopedia of Genes and Genomes (KEGG) analyses revealed that signal transduction, defense response, and immune-related pathways such as Chemokine signaling pathway, Complement and coagulation cascades, NOD-like receptor signaling pathway, and Inflammatory mediator regulation of TRP channels in sensory system were the most highly enriched pathways among the genes that were differentially expressed under LPS challenge. This study present understanding of the molecular basis underpinning response to LPS challenge and provides useful information for future work on the molecular mechanism of pathogen resistance and immunity in Manila clam.

Characterization of Free Fatty Acid Receptor 4 and Its Involvement in Nutritional Control and Immune Response in Pacific Oysters (Crassostrea gigas)

Free fatty acid receptor 4 (FFAR4) has various physiological functions, including energy regulation and immunological homeostasis. We examined the only FFAR4 homologue in the Pacific oyster Crassostrea gigas (CgFFAR4), which functions as a sensor of long-chain fatty acids. CgFFAR4 is 1098 bp long and contains a seven-transmembrane G protein-coupled receptor domain. CgFFAR4 expression was high in the hepatopancreas, but it was downregulated after fasting, indicating that it plays an essential role in food digestion. Lipopolysaccharide stimulation downregulated CgFFAR4 level, probably as an immune response of the animal. Reduced glycogen level alongside decreased insulin receptor, insulin receptor substrate, and C. gigas glycogen synthase transcription levels after CgFFAR4 knockdown revealed that CgFFAR4 was involved in the regulation of fatty acid and glycogen levels via the insulin pathway. Accordingly, this is the first study on an invertebrate FFAR and provides new insights into the role of this receptor in immune response and nutritional control.

The correlated expression of immune and energy metabolism related genes in the response to Salmonella enterica serovar Enteritidis inoculation in chicken

Background

Salmonella enterica serovar Enteritidis (SE) is one of the food-borne pathogenic bacteria, which affects poultry production and poses severe threat to human health. The correlation of immune system and metabolism in chicken after SE inoculation is important but not clear. In the current study, we identified the expression of immune and energy metabolism related genes using quantitative PCR to evaluate the correlation between immune system and energy metabolism against SE inoculation in Jining Bairi chicken.

Results

ATP5G1, ATP5G3 and ND2 were significantly up-regulated at 1 dpi (day post inoculation), and ATP5E, ATP5G1, ATP5G3 were significantly down-regulated at 7 dpi (P < 0.05). IL-8 and IL-1β were significantly down-regulated at 1 dpi, IL-8 and IL-18 were significantly down-regulated at 3 dpi, IL-8 and BCL10 were significantly up-regulated at 7 dpi (P < 0.05).

Conclusions

These findings indicate that the correlation between immune and energy metabolism related genes gradually change with time points post SE inoculation, from one homeostasis to an opposite homeostasis with 3 dpi as a turning point. These results will pave the foundation for the relationship between immune system and energy metabolism in the response to SE inoculation in chicken.

Enzymes and non-enzymatic antioxidants responses to sequential cold stress in polymorphic noble scallop Chlamys nobilis with different total carotenoids content

Noble scallop, an economically important edible marine bivalve displays polymorphism in shells (golden and brown) and flesh colors (orange and white). Mass mortality of noble scallops usually occurs during the winter months. Interestingly, carotenoid-rich golden scallops demonstrated much higher survival rates than brown scallops in winter. In order to understand the response of polymorphic noble scallops to sequential cold stress, the present study aimed to investigate the enzyme and non-enzymatic antioxidant responses of golden and brown scallops under sequential cold stress. Parameters evaluated included total carotenoid content (TCC), fatty acid composition, total antioxidant capacity (TAC), methylenedioxyamphetamine (MDA) content, catalase (CAT) activity, and superoxide dismutase (SOD) enzyme activity. The results of the present study revealed that golden scallops have higher cold tolerance than brown scallops. Golden and brown scallops are well adapted to low water temperature of above 12 °C, but in areas where winter water temperatures are below 12 °C, golden scallops are more suitable for aquaculture than brown scallops. The findings of this study are crucial to understanding the physiological responses of polymorphic scallops to cold stress and identify suitable candidates for winter aquaculture.

Oxidative stress responses of golden and brown noble scallops Chlamys nobilis to acute cold stress

The noble scallop Chlamys nobilis is an important edible marine bivalve that is widely cultivated in the sea of southern China. Unfortunately, the mass mortality of noble scallops frequently occurs during the winter months. The present study investigated the effects of acute cold stress (8 °C) to the physiological responses of polymorphic noble scallops, by assessing the HSP70 gene expression, total carotenoid content (TCC), total antioxidant capacity (TAC), malondialdehyde (MDA) content, catalase (CAT) activity and superoxide dismutase (SOD) enzymatic activity in different tissues of golden and brown scallops. The results of the present study revealed that MDA, TCC and CAT increased drastically in most tissues in the early stage of acute cold stress (0-3 h), but TCC, SOD and CAT generally showed a downward trend. Within 3-6 h of acute cold stress, MDA content decreased in most tissues and the SOD content increased significantly in most tissues, while TCC and CAT remained at peak. After 6 h of acute cold stress, MDA content continued to increase in most tissues, while TCC, CAT, SOD and TAC decreased or remained at a lower level. For HSP70 expression, up-regulation of the HSP70 gene was observed only in mantle of brown scallops and hemolymph of golden scallops at 3 h and 24 h, respectively. The findings of the present study can better understand the physiological response of noble scallops to acute cold stress.

Temperature elevation and Vibrio cyclitrophicus infection reduce the diversity of haemolymph microbiome of the mussel Mytilus coruscus

Haemolymph microbiome was considered to be unique to healthy invertebrates and beneficial to the host against external pathogens, including disease resistance and maintenance of homeostasis. Here, we investigated the effects of elevated water temperature on infection of haemolymph microbiome of the hard-shelled mussel (Mytilus coruscus). Exposure to Vibrio. cyclitrophicus resulted in high mortality of mussels on day nine at 27 °C. The haemolymph was collected to determine the microbiota by 16 S rRNA gene sequencing. Exposure to waterborne V. cyclitrophicus increased the mortality of mussels that was associated with a reduction in the diversity of their microbial community. Principal coordinate analysis (PCoA) revealed that temperature was an essential factor in shaping microbial communities in mussel haemolymph. Vibrio exposure promoted the proliferation of opportunistic pathogens (e.g., Arcobacter and Francisella) at a lower temperature. A high abundance of Vibrio present in live and dead mussels, at 27 °C might contribute greatly to mortality, as indicated by linear discriminant analysis effect size (LEfSe). These data suggested that the dynamics of microbial community have unique biomarker species in mussel haemolymph that could be used as health indicators. An elevated temperature may reduce the ability of bacterial elimination function against infection in mussel haemolymph.

Dynamic immune and metabolism response of clam Meretrix petechialis to Vibrio challenge revealed by a time series of transcriptome analysis

Meretrix petechialis is an important commercial aquaculture species in China. During the clam culture period, mass mortality events often occurred due to the Vibrio infection. In this paper, M. petechialis were challenged with Vibrio parahaemolyticus immersion to simulate a natural infection, and the infection process were divided into four phases including latency, prodrome, onset and recovery phases based on the clam mortality data. Then, the dynamic response of clams to Vibrio infection at different infection phases were investigated by transcriptome analysis. A total of 38,067 differentially expressed genes (DEGs) were identified at different infection phases. DEG annotations showed that immune-related and metabolism-related signaling pathways were enriched, indicating that immune defense and metabolism process play key roles during bacterial infection. Three kinds of expression pattern were classified by cluster analysis, including U-shape, L-shape and inverted V-shape. Anabolism and cellular growth proliferation related signaling pathways were repressed (long-lasting or transient) during bacterial infection. However, the immune related signaling pathways with different immune functions showed induction expression or repression expression against bacterial infection, which indicated that immune system take different strategies against bacterial infection. Furthermore, some signaling pathways such as PI3K-Akt signaling pathway both involved in immune defense and cell metabolism. This study provides a sight that the dynamic immunity and metabolic responses may be integrated to improve the host survival and shift more energy for immune defense.

The differences of bacterial communities in the tissues between healthy and diseased Yesso scallop (Patinopecten yessoensis)

The tissues of marine invertebrates are colonized by species-rich microbial communities. The dysbiosis of host's microbiota is tightly associated with the invertebrate diseases. Yesso scallop (Patinopecten yessoensis), one of the most important maricultured scallops in northern China, has recently suffered massive summer mortalities, which causes huge production losses. The knowledge about the interactions between the Yesso scallop and its microbiota is important to develop the strategy for the disease prevention and control. In the present study, the bacterial communities in hemolymph, intestine, mantle and adductor muscle were compared between the healthy and diseased Yesso scallop based on the high-throughput sequencing of 16S rRNA gene. The results indicated obvious difference of the composition rather than the diversity of the bacterial communities between the healthy and diseased Yesso scallop. Vibrio, Francisella and Photobacterium were found to overgrow and dominate in the mantle, adductor muscle and intestine of the diseased scallops, respectively. The prediction of bacterial community metagenomes and the variations of KEGG pathways revealed that the proportions of the pathways related with neurodegenerative diseases and carbohydrate metabolism both increased significantly in the mantle and hemolymph of the diseased scallops. The abundance of the metabolism pathways including carbohydrate metabolism, lipid metabolism and amino acid metabolism decreased significantly in the intestine of diseased scallops. The results suggested that the changes of bacterial communities might be closely associated with the Yesso scallop's disease, which was helpful for further investigation of the pathogenesis as well as prevention and control of the disease in Yesso scallop.

Survival and immune response of white shrimp Litopenaeus vannamei following single and concurrent infections with WSSV and Vibrio parahaemolyticus

The survival and immune responses of Litopenaeus vannamei were evaluated during white spot syndrome virus (WSSV) or Vibrio parahaemolyticus single and concurrent infections. The mortality, WSSV load, activities of 4 immune enzymes: acid phosphatase (ACP), alkaline phosphatase (AKP), peroxidase (POD) and superoxide dismutase (SOD), and the transcription of Evolutionarily Conserved Signaling Intermediate in Toll pathways of L.vannamei (LvECSIT) were quantified at 0, 3, 6, 12, 24, 48, 72 and 96 h post-infection (pi). The results showed: (i) the cumulative mortality of the co-infection group (WSSV and V. Parahaemolyticus 83%) was significantly lower than the WSSV infection group (97%) (P < 0.05) at 96 hpi; (ii) copies of WSSV in the co-infection group were significantly lower than that of the single infection group from 24 to 96 hpi (P < 0.05); (iii) ACP, AKP,POD and SOD activity in the gills of the co-infection group was higher than that of the WSSV group at12, 48 and 96 hpi (P < 0.05).The expression of LvECSIT mRNA in the co-infection group was significantly higher than in the WSSV infection group from 12 to 72 hpi (P < 0.05).The results indicate that proliferation of WSSV is inhibited by V.parahaemolyticus infection. In addition, infection with WSSV alone causes a significant reduction in some immune responses of shrimp than co-infection with WSSV and V.parahaemolyticus occurs at 26 °C. Third, LvECSIT, an essential member of TLR signaling pathway might play a crucial role in shrimp defense against WSSV - Vibrio co-infection.

The transcriptional response of the Pacific oyster Crassostrea gigas under simultaneous bacterial and heat stresses

Bacterial infection and heat stress are considered as two major environmental threats for the aquaculture industry of oyster Crassostrea gigas. In the present study, the expression profiles of mRNA transcripts in the hemocytes of oysters under bacterial challenge and heat stress were examined by next-generation sequencing. There were 21,095, 21,957 and 21,141 transcripts identified in the hemocytes of oysters from three groups, respectively, including control group (designated as Con group), Vibrio splendidus challenge group (Bac group), and bacterial and heat stress combined treatment group (BacHeat group). There were 4610, 5093 and 5149 differentially expressed transcripts (DTs) in the three pairwise comparisons Con/Bac, Con/BacHeat and Bac/BacHeat, respectively. The main enriched GO terms in biological process category of the DTs included the metabolic processes, cellular process, response to stimulus and immune system process. The expression patterns of DTs involved in pattern recognition, immune signal transduction and energy metabolic indicated that the immune response to bacterial challenge was disturbed under acute heat stress, which was also confirmed by quantitative real-time PCR. The neuroendocrine immunomodulation, especially the catecholaminergic regulation, played indispensable roles in stress response. The total energy reserves as well as cellular energy allocation (CEA) in hepatopancreas of oysters decreased remarkably especially in BacHeat group, while the energy consumption generally increased, suggesting that the immune defense against the simultaneous stimulation of pathogen and heat stress imposed greater costs on oyster's energy expenditure than a single stressor. These results above indicated that, the heat stress disturbed the normal expression of genes involved in immune response and energy metabolism, accelerated energy consumption and broke the metabolic balance, leading to a decline in resilience to infection and mass mortality of oyster in summer.

A crayfish Ras gene is involved in the defense against bacterial infection under high temperature

Temperature is an important environmental factor influencing crustacean resistance to pathogen infection. However, the mechanism underlying immune regulation by temperature remains unclear in crustacean. Here, we report a Ras gene of crayfish (designated as PcRAS1) which is involved in immune regulation of crayfish under high temperature. PcRAS1 is induced by both high temperature and bacterial infection and the induction by bacterial infection is associated with temperature. Significant changes of PcRAS1 expression was observed at 32 °C and 24 °C after infection with Aeromonas hydrophila, but relative moderate alternation was found at 16 °C after challenged with A. hydrophila. PcRAS1 silencing significantly reduced crayfish survival from high temperature (32 °C and 24 °C) or bacterial infection at 32 °C, but there was no significant effect on survival from bacterial infection at 24 °C or 16 °C. Further analysis reveals that PO activity is reduced by high temperature or enhanced by bacterial infection. Moreover, both the decreased PO activity and the enhanced PO activity are affected by PcRAS1 expression. PcRAS1 silencing further reduces PO activity under high temperature and compromises the enhanced PO activity by bacterial infection. Lipid peroxidation (LPO) and total antioxidant capacity (TAC) are also involved in the responses to high temperature. LPO is enhanced by lower temperature. TAC is reduced by high temperature and TAC change resulting from high temperature is amplified by PcRAS1 silencing. These results collectively indicate that PcRAS1 is involved in immune regulation against bacterial infection mediated by temperature.

Physiological and immunological responses to mass mortality in noble scallop Chlamys nobilis cultured in Nan'ao waters of Shantou, China

The noble scallop Chlamys nobilis has been a commercially important marine cultured bivalve in the Southern Sea of China for decades. Mass mortality events, however, often occur during scallops' cultivation. Mortality of up to 67%-90% was recorded at the beginning of March in 2017 in some culture areas of Nan'ao (Shantou, China), spreading to all scallops within a week. In the present study, in order to investigate the response of the noble scallop at the physiological and molecular level during mass mortality, scallops with different mortalities of 90%, 67%, and 6% were sampled from three sites at Hunter bay, Baisha bay, and Longhai, respectively. Total carotenoids content (TCC), total antioxidant capacity (TAC), malondialdehyde (MDA) content and the expression levels of three immune-related genes (toll-like receptor, C-type lectin receptor and big defensing) in different scallop tissues were determined. The scallops were divided into three groups of sub-health, lesion, and health. TAC, TCC, as well as transcript levels of CnTLR-1, Cnlec-1 and CnBD in sub-health and lesion scallops were all significantly lower (P < 0.05) than those in health scallops, while MDA in sub-health and lesion scallops were significantly higher than those in health scallops (P < 0.05). Similarly, TCC and TAC in lesion scallops were both higher than sub-health scallops. Moreover, significantly positive correlations were found between TCC and TAC (P < 0.05) and between CnTLR-1 and Cnlec-1 (P < 0.05), while significantly negative correlations were found between TCC and CnTLR-1 (P < 0.05), TCC and Cnlec-1 (P < 0.05), TAC and CnBD (P < 0.05), as well as between MDA and Cnlec-1 (P < 0.001). All the results indicate that noble scallops significantly change their physiological and molecular levels when suffering from stress, and that their antioxidant and immune response systems play important defense functions.

Transcriptome analysis of the Yesso scallop, Patinopecten yessoensis gills in response to water temperature fluctuations

Water temperature fluctuations are considered to be a major factor affecting the immune functions and metabolic processes of scallops. To better understand the immune defense mechanisms of Yesso scallop, Patinopecten yessoensis following exposure to water temperature fluctuations, transcriptomic profiles in the gills from high-frequency fluctuations (HF_G), low-frequency fluctuations (LF_G), and no fluctuations (NF_G) groups were obtained using HiSeq™ 2500 (Illumina). For HF_G, scallops were transferred directly between 18 and 8 °C every 4 h and for 10 fluctuations, while scallops in LF_G were transferred between 18 and 13 °C every 12 h, for a total of 4 fluctuations. A total of 442,922,590 clean reads were generated in 9 libraries and then assembled into 210,780 unigenes with an average length of 705 bp and an N50 of 1253 bp. Based on sequence similarity, 54,529 unigenes (25.87%) were annotated in at least one database. Comparative analysis revealed that 696 unigenes differentially expressed in temperature stressed groups compared with the control, including 229 unigenes between HF_G and NF_G, and 548 unigenes between LF_G and NF_G, respectively. Additionally, among these differentially expressed genes (DEGs), there were 41 immune-related unigenes and 16 protein metabolism-related unigenes. These results provide fundamental information on the molecular defense mechanisms in the Yesso scallop gills after exposure to water temperature fluctuations.

Responses of an oyster host (Crassostrea virginica) and its protozoan parasite (Perkinsus marinus) to increasing air temperature

Background

Changes in climate are predicted to influence parasite and pathogen infection patterns in terrestrial and marine environments. Increases in temperature in particular may greatly alter biological processes, such as host-parasite interactions. For example, parasites could differentially benefit from increased reproduction and transmission or hosts could benefit from elevated immune responses that may mediate or even eliminate infections. In the southeastern United States, the Eastern oyster, Crassostrea virginica, is infected by the lethal protozoan parasite, Perkinsus marinus. Under field conditions, intertidal (air-exposed) oysters have been found to have significantly higher P. marinus infection intensity and marginally higher infection prevalence than subtidal (submerged) oysters. During summer, air temperatures are much warmer than water and this exposure of intertidal oysters to higher temperatures is a suggested mechanism for increased infection intensity.

Methods

We simulated intertidal exposure using controlled laboratory experiments to determine how host traits (survival and immune response) and parasite infection intensity will respond to elevated air temperature ranging from 27 °C to 53 °C during emersion at low tide. In Georgia, where our work was conducted, the average summer water temperature is 29 °C and the average maximum high air temperature in July is 33 °C (though oysters have been shown to survive at much higher air temperatures).

Results

Host survival declined as temperature increased, with a definitive drop-off between 39–43 °C. Negative effects of air temperature on host immune response (phagocytic activity) were detectable only at extremely high temperatures (47–50 °C) when hosts were suffering acute mortality. Parasite infection intensity peaked at 35 °C.

Discussion

Our results suggest that an increase in average summer air temperature to 35 °C or higher could affect oyster survival directly through temperature-related impacts in the short-term and indirectly through increased P. marinus infection intensity over the long-term.

CO2-induced ocean acidification impairs the immune function of the Pacific oyster against Vibrio splendidus challenge: An integrated study from a cellular and proteomic perspective

Ocean acidification (OA) and pathogenic diseases pose a considerable threat to key species of marine ecosystem. However, few studies have investigated the combined impact of reduced seawater pH and pathogen challenge on the immune responses of marine invertebrates. In this study, Pacific oysters, Crassostrea gigas, were exposed to OA (~2000 ppm) for 28 days and then challenged with Vibrio splendidus for another 72 h. Hemocyte parameters showed that V. splendidus infection exacerbated the impaired oyster immune responses under OA exposure. An iTRAQ-based quantitative proteomic analysis revealed that C. gigas responded differently to OA stress and V. splendidus challenge, alone or in combination. Generally, OA appears to act via a generalized stress response by causing oxidative stress, which could lead to cellular injury and cause disruption to the cytoskeleton, protein turnover, immune responses and energy metabolism. V. splendidus challenge in oysters could suppress the immune system directly and lead to a disturbed cytoskeleton structure, increased protein turnover and energy metabolism suppression, without causing oxidative stress. The combined OA- and V. splendidus-treated oysters ultimately presented a similar, but stronger proteomic response pattern compared with OA treatment alone. Overall, the impaired oyster immune functions caused by OA exposure may have increased the risk of V. splendidus infection. These results have important implications for the impact of OA on disease outbreaks in marine invertebrates, which would have significant economic and ecological repercussions.

A mitochondrial manganese superoxide dismutase involved in innate immunity is essential for the survival of Chlamys farreri

Superoxide dismutase (SOD) ubiquitously found in both prokaryotes and eukaryotes functions as the first and essential enzyme in the antioxidant system. In the present study, a manganese SOD (designated as CfmtMnSOD) was cloned from Zhikong scallop Chlamys farreri. The complete cDNA sequence of CfmtMnSOD contained a 681 bp open reading frame (ORF), encoding a peptide of 226 amino acids. A SOD_Fe_N domain and a SOD_Fe_C domain were found in the deduced amino acid sequence of CfmtMnSOD. The mRNA transcripts of CfmtMnSOD were constitutively expressed in all the tested tissues, including gill, gonad, hepatopancreas, hemocytes, mantle and muscle, with the highest expression level in hemocytes. After the stimulation of Vibrio splendidus, Staphylococcus aureus and Yarrowia lipolytica, the mRNA transcripts of CfmtMnSOD in hemocytes all significantly increased. The purified rCfmtMnSOD protein exhibited Mn²⁺ dependent specific and low stable enzymatic activities. After Vibrio challenge, the cumulative mortality of CfmtMnSOD-suppressed scallops was significantly higher than those of control groups and the semi-lethal time for CfmtMnSOD-suppressed scallops was rather shorter than those of control groups either. Moreover, the final mortality rate of CfmtMnSOD-suppressed group was significant higher than those of control groups, even without Vibrio challenge. All these results indicated that CfmtMnSOD was efficient antioxidant enzyme involved in the innate immunity, and also essential for the survival of C. farreri.

Primary culture of Zhikong scallop Chlamys farreri hemocytes as an in vitro model for studying host-pathogen interactions

Primary cultured cells can be a useful tool in studies on physiology, virology, and toxicology. Hemocytes play an important role in animal rapid response to pathogen invasion. In this study, an appropriate medium for primary culture of hemocytes of the bivalve Chlamys farreri was developed by adding 5% fetal bovine serum and 1% C. farreri serum to Leibovitz L-15 medium. These primary cultured hemocytes were maintained for more than 40 d in vitro and were classified into 3 types: (1) granulocytes containing numerous granules in the cytoplasm, (2) hyalinocytes with no or few granules, (3) a small percentage of macrophage-like cells. Furthermore, the primary cultured hemocytes were observed to be sensitive to bacterial and viral challenges. These hemocytes could phagocytose the bacterium Vibrio anguillarum, and presented cytopathic effects on the extracellular products (ECPs) of V. anguillarum; the mRNA level of QM, which plays an important role in immune response, also significantly increased 12 h after infection. When these hemocytes were challenged with ostreid herpesvirus 1 (OsHV-1), virus particles and empty capsids in the cells infected for 48 h were observed by transmission electron microscopy, and the QM mRNA level increased significantly at 12 h and 24 h following OsHV-1 challenge. This primary culture system is available for C. farreri hemocytes which can be used in the future to study host-pathogen interactions.

Crustacean hyperglycemic hormones directly modulate the immune response of hemocytes in shrimp Litopenaeus vannamei

A robust immune response against invading pathogens is crucial for host to survive, which depends greatly on the well balance of metabolism. Increasing evidence has indicated that some metabolic hormones, such as insulin, could modulate immune responses directly. Crustacean hyperglycemic hormone (CHH) family is a group of ecdysozoans-specific peptide hormone involved in glucose metabolism and other biological events. In the present study, two members of CHH family (designated as LvCHH I and LvCHH II) in shrimp Litopenaeus vannamei with one and two crustacean neurohormone domains respectively were chosen to investigate their putative modulatory roles in both glucose metabolism and immune response. LvCHH I and LvCHH II were both expressed in the sinus gland and lamina ganglionalis of eyestalks and were significantly induced after white spot syndrome virus (WSSV) infection. Meanwhile, significant increases of hemolymph glucose levels were observed in shrimp at 12 and 24 h after WSSV infection while the glucose inside the hemocytes decreased at 6 h and then increased at 12 h. Gain-of-function of rLvCHHs was subsequently conducted in vivo by injecting the recombinant proteins (rLvCHH I and rLvCHH II). The hemolymph glucose increased significantly from 0.5 h to 3 h after the shrimps received an injection of rLvCHH I, while it decreased at 0.5 h and increased afterward at 3 h post rLvCHH II injection. At the meantime, significant decreases of reactive oxygen species level in hemocytes were observed at 3 h and 6 h post rLvCHH I injection, while it remained unchanged in rLvCHH II injection group. rLvCHH I and rLvCHH II could bind to the cytomembrane of primary shrimp hemocytes in vitro, and the expressions of superoxide dismutase and LvRelish increased when the hemocytes were incubated with rLvCHH I for 3 h. Meanwhile, the expression of antimicrobial peptides, crustin and penaeidin-4, were also induced by rLvCHH I and rLvCHH II. These results demonstrated that host immune response, in addition to glucose metabolism, could be directly modulated by LvCHH family, and the present study provided new insights into the immunomodulation role of metabolic hormones in invertebrate.

High carotenoids content can enhance resistance of selected Pinctada fucata families to high temperature stress

Carotenoids are a class of natural antioxidants widely found in aquatic, and they have significant effects on the growth, survival, and immunity of these organisms. To investigate the mechanisms of carotenoids in high temperature resistance, we observed the immune response of selected pearl oyster Pinctada fucata (Akoya pearl oyster) families with different carotenoids contents to high temperature stress. The results indicated that the survival rate (SR) of P. fucata decreased significantly with increase in temperature from 26 °C to 34 °C and with the decrease of total carotenoids content (TCC); when the TCC was higher, the SR tended to be higher. TCC and total antioxidant capacity (TAC) decreased significantly at 30 °C with increasing stress time. Correlation analysis indicated that TAC was positively and linearly correlated with TCC, and SR was S-type correlated with TCC and TAC. Immune analysis indicated that levels of superoxide dismutase (SOD), catalase (CAT), and malondialdehyde (MDA) in selected families (with higher TCC) under temperature stress (at 30 °C) were generally significantly lower than in the control group (with lowest TCC) and from 0 to 96 h, the levels of each of these substances varied significantly. Levels of SOD, CAT, and MDA within each family first rose from 0 to 3 h, then decreased to their lowest point after 24 h, and then rose again to their highest levels at 96 h. When TCC was higher, the levels of SOD, CAT, and MDA tended to be lower. These findings indicated that carotenoids play an important role in improving survival rates of P. fucata under high temperature stress by enhancing animals' antioxidant system, and could serve as an index for breeding stress-resistant lines in selective breeding practices.

Metabolic product response profiles of Cherax quadricarinatus towards white spot syndrome virus infection

White spot syndrome virus (WSSV) is one of the most devastating viral pathogens in both shrimp and crayfish farms, which often causes disease outbreak and leads to massive moralities with significant economic losses of aquaculture. However, limited research has been carried out on the intrinsic mechanisms toward WSSV challenge at the metabolic level. To gain comprehensive insight into metabolic responses induced by WSSV, we applied an NMR approach to investigate metabolic changes of crayfish gill and hepatopancreas infected by WSSV for 1, 6 and 12 h. In gill, an enhanced energy metabolism was observed in WSSV-challenged crayfish samples at 1 h, as marked by increased glucose, alanine, methionine, glutamate and uracil. Afterwards, energy metabolism, lipid metabolism as well as osmoregulation were markedly increased at 6 hpi, as shown by elevated glucose, alanine, methionine, fumarate, tyrosine, tryptophan, histidine, phosphorylcholine, betaine and uracil, whereas no obvious metabolites change was detected at 12 hpi. As for hepatopancreas, disturbed lipid metabolism and induced osmotic regulation was found at 6 hpi based on the metabolic biomarkers such as branched chain amino acids, threonine, alanine, methionine, glutamate, glutamine, tyrosine, phenylalanine, lactate and lipid. However, no obvious metabolic change was shown in hepatopancreas at both 1 hpi and 12 hpi. Taken together, our present results provided essential metabolic information about host-pathogen interactions in crayfish, which shed new light on our understanding of WSSV infection at metabolic level.

Effects of artificial infection of Litopenaeus vannamei by Micrococcus lysodeikticus and WSSV on the activity of immunity related enzymes

In this study, the activities of 5 immunity related enzymes namely acid phosphatase (ACP), alkaline phosphatase (AKP), phenoloxidase (PO), peroxidase (POD) and lysozyme phosphatase (LZM)) of Litopenaeus vannamei after they have been injected with different concentrations of Micrococcus lysodeikticus and the white spot syndrome virus (WSSV) were examined. The cumulative mortality at 0, 24, 48, 72, 96 h was obtained. Copy numbers of WSSV in L. vannamei after a single infection, secondary infection and concurrent infection were measured. Hemolymph samples of M. lysodeikticus and WSSV injected shrimp were collected at 0, 6, 12 24, 48, 72, 78, 84, 96 and 120 h. The results were: (i) The cumulative mortality of L. vannamei increased as the shrimp were infected with higher concentration of the bacteria; (ii) The most sensitive changes of ACP, AKP and LZM were in the 6.2 × 10(5), 6.2 × 10(6), 6.2 × 10(7) cfu/mL M. lysodeikticus group; (iii) ACP but LZM were more sensitive to M. lysodeikticus than WSSV, and AKP, PO and POD is more sensitive to WSSV; (iv) The copies of WSSV in the co-injected group were higher than WSSV-single infection and WSSV-bacteria-secondary infection group at 48 h. The amount of WSSV in L. vannamei of concurrent infection and WSSV-bacteria-secondary infection groups were higher than that of the WSSV-single infection group.

The immune system and its modulation mechanism in scallop

Scallops are a cosmopolitan family of bivalves, and some of them are highly prized as dominant aquaculture species. In the past decades, there have been increasing studies on the basic biology and immunology of scallops, and this review summarizes the research progresses of immune system and its modulation mechanism in scallop. As invertebrate, scallops lack adaptive immunity and they have evolved an array of sophisticated strategies to recognize and eliminate various invaders by employing a set of molecules and cells. It is evident that basic immune reactions such as immune recognition, signal transduction, and effector synthesis involved in immune response are accomplished in a variety of ways. They rely upon an extensive repertoire of phagocytosis, apoptosis and encapsulation of the circulating hemocytes for eliminating invasive pathogens, as well as the production of immune effectors that are active against a large range of pathogens or sensitive for the environmental stress. Furthermore, the molecular constitutions, metabolic pathways and immunomodulation mechanisms of the primitive catecholaminergic, cholinergic, enkephalinergic system and NO system in scallop are also discussed, which can be taken as an entrance to better understand the origin and evolution of the neuroendocrine-immune regulatory network in lower invertebrates.