Essential function of transglutaminase and clotting protein in shrimp immunity

Unveiling a new hemocyte subpopulation in white shrimp (Penaeus vannamei) and the characterization of immune response in hemocyte subpopulation

Hemocytes are the primary cellular components of the shrimp immune system, playing a crucial role in host defense. However, a comprehensive understanding of their subpopulations and specific functions remains incomplete. In this study, four hemocyte subpopulations, designated as H1, H2, H3, and H4, were identified in Penaeus vannamei using transmission electron microscopy (TEM) and flow cytometry. The H1 subpopulation was the most abundant cells, the smallest in size, lacked granules, and had the highest nucleus-to-cytoplasm (N:C) ratio, identifying it as prohemocytes (immature cells). The H2 subpopulation fits the criteria of hyaline hemocytes. They are relatively small, have a large nucleus, and contain no or very few cytoplasmic granules. The H3 subpopulation was the least abundant cell. These cells are larger than HCs, have a moderate N:C ratio, and contain a few granules, identifying them as semi-granulocytes. The H4 subpopulation, representing granulocytes, had the largest cell size and the lowest N:C ratio and was characterized by the presence of large granules in the cytoplasm. Non-specific immune responses were investigated through various parameters and gene expression profiling. Each hemocyte subpopulation exhibited distinct immune functions. Prohemocytes strongly expressed notch-1, suggesting a role in hemocyte proliferation. Hyalinocytes exhibited strong phagocytic activity and produced superoxide anions. Semigranulocytes exhibited high expression of lysozyme and anti-lipopolysaccharide factor. Granulocytes showed high expression of propo-1, propo-2, and antimicrobial peptide genes. Following Vibrio parahaemolyticus injection, the H1 subpopulation significantly increased at 6 h post-infection before returning to baseline levels, whereas the H4 subpopulation followed an opposite trend. These findings suggest that both H1 and H4 hemocytes play critical roles in the immune response against V. parahaemolyticus.

Effects of two transglutaminases on innate immune responses in the oriental armyworm, Mythimna separata

Transglutaminase (TGase) is a key enzyme that mediates hemolymph coagulation and is thought to contribute to the elimination of pathogenic microorganisms in invertebrates. The objective of this study was to elucidate the involvement of TGase in insect immune responses via functional analysis of this enzyme in the oriental armyworm, Mythimna separata, using recombinant proteins and RNA interference technique. We identified two TGase genes, mystgase1 and mystgase2, in Mythimna separata and found that both genes are expressed in all surveyed tissues in M. separata larvae. Significant changes were induced in hemocytes following Escherichia coli injection. Injection of Gram-positive bacteria (Micrococcus luteus) and Gram-negative bacteria (Escherichia coli and Serratia marcescens) into larvae triggered a time-specific induction of both mystgase1 and mystgase2 in hemocytes. Recombinant MysTGase1 and MysTGase2 proteins bound to both E. coli and M. luteus, localizing within bacterial clusters and resulting in agglutination in a Ca2+-dependent manner. The hemocytes of larvae injected with recombinant MysTGase1 or MysTGase2 exhibited enhanced phagocytic ability against E. coli, improved in vivo bacterial clearance, and increased resistance to S. marcescens, decreasing larval mortality rate. Conversely, RNA interference targeting mystgase1 or mystgase2 significantly reduced hemocyte phagocytic capability, decreased bacterial clearance, and increased susceptibility to S. marcescens infection, thereby increasing larval mortality rate. The findings of this study are anticipated to expand our understanding of the function of TGases within insect immune responses and may contribute to developing new pest control strategies.

Potential mechanisms implied in tick infection by arboviruses and their transmission to vertebrate hosts

Ticks can transmit many pathogens, including arboviruses, to their vertebrate hosts. Arboviruses must overcome or evade defense mechanisms during their passage from the tick gut to the hemolymph, salivary glands, and the feeding site in the host skin. This review summarizes current knowledge of defense mechanisms in specific tick tissues and at the feeding site in the host skin. We discuss the possible roles of these defense mechanisms in viral infection and transmission. The responses of tick salivary proteins to arbovirus infection are also discussed. This review provides information that may help accelerate research on virus-tick interactions.

MicroRNA sequencing analysis reveals injury-induced immune responses of Scylla paramamosain against cheliped autotomy

During pond culture or intensive culture system of crabs (mainly Eriocheir sinensis, Portunus trituberculatus and Scylla paramamosain), high-density farming has typically contributed to a higher limb autotomy level in juvenile animals, especially in S. paramamosain which has a high level of cannibalism. Due to the high limb autotomy level, the survival and growth rates in S. paramamosain farming are restricted, which limit the growth of the mud crab farming industry. MicroRNAs (miRNAs) are small noncoding RNAs that regulate a series of biological processes including innate immune responses by post-transcriptional suppression of their target genes. MiRNAs are believed to be crucial for innate immune process of host wound healing. Many miRNAs have been verified to be required in host immune responses to repair wound and to defense pathogen after tissue damage. However, to our best knowledge, the miRNAs functions of crustacean innate immune reactions against injury induced by limb autotomy have not been studied yet. Here in this study, for the first time, miRNAs involved in the S. paramamosain immune reactions against injury induced by cheliped autotomy were obtained by high-throughput sequencing. A total of 575 miRNAs (518 known miRNAs and 57 novel predicted miRNAs) were obtained, of which 141 differentially expressed microRNAs (93 up-regulated microRNAs and 48 down-regulated microRNAs) were revealed to be modified against cheliped autotomy, and the qPCR results of randomly selected miRNAs confirmed the expression patterns in the miRNAs sequencing data. Numerous immune-related target genes associated with innate immune system were mediated by miRNAs to induce host humoral immune and cellular immune defense to minimize acute physical damage. Furthermore, the genes expression in hemolymph coagulation and melanization pathways, as well as Toll and Imd signaling pathways were mediated by miRNAs to activate host immune responses including melanization and antimicrobial peptides for rapid wound healing and killing invaded pathogens. These results will help to understand injury-induced immune responses in crabs and to develop an effective control strategy of autotomy rate in crabs farming.

Involvement of Nrf2 in the immune regulation of Litopenaeus vannamei against Vibrio harveyi infection

NF-E2-related factor-like-2 (Nrf2) is a transcription factor that belongs to the Cap'n'Collar transcription factor family and plays a role in regulating inflammation, autophagy, metabolism, proteostasis, and cancer prevention. However, its influence on Vibrio spp infection in L. vannamei remains uncertain. In this study, the effects of Nrf2 on the immune response in Vibrio spp infection was determined by RT-PCR and histopathological analysis. The results showed that RNAi of Nrf2 significantly decreased the expression of antioxidant-related genes (CAT, SOD and GST; p < 0.05), and significantly up-regulated inflammation-related genes (IMD, pro-PO, P38, Toll, Hsp70, NFκB and RAB6A; p < 0.05) and the apoptosis gene (caspase3). Under the infection of V. harveyi, histopathological analysis showed that after RNAi of Nrf2, the hepatopancreas of shrimp has an abnormal arrangement of hepatic tubules and vacuolization of hepatocyte; The basement membrane is peeled off and the epithelial cells are massively necrotic. Compared with the RNAi of Nrf2 group, the tissue damage in the SFN group was much lessened, and there were fewer apoptosis signals in the TUNEL assay. In conclusion, this experiment indicated that Nrf2 is involved in the regulation of inflammatory response, oxidative stress,and apoptosis induced by V. harveyi in L. vannamei.

Effects of environmental factors on the cellular and molecular parameters of the immune system in decapods

Crustaceans and in particular decapods (i.e. shrimp, crabs and lobsters) are a diverse, commercially and ecologically important group of organisms. They are exposed to a range of environmental factors whose abiotic and biotic components are prone to fluctuate beyond their optimum ranges and, in doing so, affect crustaceans' immune system and health. Changes in key environmental factors such as temperature, pH, salinity, dissolved oxygen, ammonia concentrations and pathogens can provoke stress and immune responses due to alterations in immune parameters. The mechanisms through which stressors mediate effects on immune parameters are not fully understood in decapods. Improved knowledge of the environmental factors - above all, their abiotic components - that influence the immune parameters of decapods could help mitigate or constrain their harmful effects that adversely affect the production of decapod crustaceans. The first part of this overview examines current knowledge and information gaps regarding the basic components and functions of the innate immune system of decapods. In the second part, we discuss various mechanisms provoked by environmental factors and categorize cellular and molecular immune responses to each environmental factor with special reference to decapods.

A Novel Hemocyte-Specific Small Protein Participates in White Spot Syndrome Virus Infection via Binding to Viral Envelope Protein

Hemocytes are essential components of the immune system against invading pathogens in shrimp. Many uncharacterized transcripts exist in hemocytes but the knowledge of them is very limited. In the present study, we identified a novel small protein from the uncharacterized transcripts in hemocytes of Litopenaeus vannamei. This transcript was specifically expressed in hemocytes and encoded a novel secretory protein, which was designated as hemocyte-specific small protein (LvHSSP). The expression level of LvHSSP was significantly up-regulated in the hemocytes of shrimp infected with white spot syndrome virus (WSSV). After knockdown of LvHSSP by RNA interference, the WSSV copy number in shrimp decreased significantly. Conversely, WSSV copy number increased in shrimp when they were infected by WSSV after incubation with recombinant LvHSSP protein. These results suggested that LvHSSP might promote viral infection in shrimp. Immunocytochemical assay showed that the recombinant LvHSSP protein was located on the membrane of hemocytes. Co-IP results showed that LvHSSP could interact with VP26, the main envelope protein of WSSV, suggesting that LvHSSP might mediate WSSV adhesion and entry into host cells by binding to viral envelope protein. Meanwhile, the total hemocyte counts were significantly decreased after LvHSSP knockdown while increased after supplementing with recombinant LvHSSP protein, supporting the idea of hemocytes as the carrier for systemic dissemination of WSSV. This study reported a novel small protein in hemocytes, which modulated the viral infection in shrimp. Our results will enrich the knowledge of invertebrate innate immunity and provide a new field in the study of hemocyte function.

Heat Shock Proteins (Hsps) in Cellular Homeostasis: A Promising Tool for Health Management in Crustacean Aquaculture

Heat shock proteins (Hsps) are a family of ubiquitously expressed stress proteins and extrinsic chaperones that are required for viability and cell growth in all living organisms. These proteins are highly conserved and produced in all cellular organisms when exposed to stress. Hsps play a significant role in protein synthesis and homeostasis, as well as in the maintenance of overall health in crustaceans against various internal and external environmental stresses. Recent reports have suggested that enhancing in vivo Hsp levels via non-lethal heat shock, exogenous Hsps, or plant-based compounds, could be a promising strategy used to develop protective immunity in crustaceans against both abiotic and biotic stresses. Hence, Hsps as the agent of being an immune booster and increasing disease resistance will present a significant advancement in reducing stressful conditions in the aquaculture system.

Immunological and biochemical changes in Pacific white shrimp, Litopenaeus vannamei, challenged with Vibrioparahaemolyticus

Vibrio parahaemolyticus (Vpara) is the causative agent of Acute Hepatopancreatic Necrosis Disease (AHPND), or Early Mortality Syndrome (EMS) in shrimp. Shrimp, like other invertebrates, lack an adaptive immune system and depend solely on innate immunity against invading pathogens. To better understand the defense mechanisms of shrimp to this problematic pathogen, we evaluated the changes in hematology, immunology and biochemical values of the hemolymph from shrimp challenged with V. parahaemolyticus up to 8 days post-challenge. Thirty-six shrimp (12 g) were distributed in 9 tanks (75 L), divided into three groups (non-challenged, challenged with 5 × 10² cfu/shrimp and challenged with 1 × 10³ cfu/shrimp) in triplicate. Pacific white shrimp, Litopenaeus vannamei, were administered an inoculum of V. parahaemolyticus under the shell between the 5th and 6th abdominal segment to assess cellular and humoral immune responses. Total hemocyte count (THC) significantly decreased in shrimp challenged with Vpara at 6 h, 12 h and 24 h-post infection. Hemocyte lysate phenoloxidase (PO) activity in Vpara-challenged shrimp at 48 h post challenge was significantly increased compared to that of control shrimp. No significant differences were observed in total plasma protein between plasma from control and Vpara-challenged shrimp. However, shrimp challenged with 5 × 10^2, and 1 × 10³ cfu/shrimp had significantly lower hemocyanin at 6 h and 48 h sampling point, respectively. At 24 h post-challenge, the ≥140 kDa and 70 kDa bands from SDS-PAGE of hemocyanin-concentrated hemolymph lysate samples showed a higher and lower intensity, respectively, in Vpara-challenged group than those of the control group. Plasma from Vpara-challenged shrimp at 6 h and 12 h-post infection significantly suppressed V. parahaemolyticus growth. However, significantly less bacterial growth suppression was observed in plasma of shrimp challenged with higher dose compared to control shrimp at the 192 h post-challenge point. Plasma chemistry parameters did not significantly differ among treatments. The changes observed in hemolymph parameters may be useful indicators of the health status of shrimp.

Dietary of Lactobacillus paracasei and Bifidobacterium longum improve nonspecific immune responses, growth performance, and resistance against Vibrio parahaemolyticus in Penaeus vannamei

This study investigated the effects of two probiotics, namely Lactobacillus paracasei and Bifidobacterium longum, as feed additives on growth performance, nonspecific immunity, immune-related gene expression, and disease resistance against Vibrio parahaemolyticus in Penaeus vannamei. The experimental diets were prepared using L. paracasei and B. longum at concentrations of 10⁵ and 10⁷ CFU/g; these diets were referred to as P5, P7, B5, and B7. After 8 weeks of the diets, regarding growth performance, the B7 group showed the highest weight gain rate (890.34 ± 103.65%), special growth rate (4.08 ± 0.19%), and feed conversion rate (1.52 ± 0.19%) compared with the other groups. Moreover, the total hemocyte counts were significantly increased (p < 0.05) in the P7 groups on day 14 during the 28-day feeding trial. The phagocytosis rate in all experimental groups was increased on day 14 and was persistently significantly activated to day 21, especially in the P7 and B5 group. The phagocytic index of the P7 group showed a significant increase on day 14 and persistent activation to day 21. In the analysis of respiratory burst activity and phenoloxidase activity, the P7 and B5 groups showed a significant increase on day 7 and persistent activation to day 21. The expression level of the immune-related genes of superoxide dismutase, clotting protein, Penaeidin2, Penaeidin3, Penaeidin4, anti-LPS factor, crustin, and lysozyme was significantly increased in the experimental groups, especially in the P7 group. Furthermore, the optimum conditions of feed additives were determined in challenge trials conducted using P7 and B5. Shrimps fed P7 and B5 showed an increased survival rate (72.73% and 66.67%) after the V. parahaemolyticus challenge. In sum, the results revealed that B. longum, as a feed additive at 10⁷ CFU/g, enhanced growth performance. L. paracasei at 10⁷ CFU/g and B. longum at 10⁵ CFU/g can enhance nonspecific immune responses and immune-related gene expression, and 10⁷ CFU/g L. paracasei has the highest resistance ability for V. parahaemolyticus. Thus, dietary supplementation with L. paracasei and B. longum may be a valuable approach in white shrimp aquaculture.

Combined dynamic transcriptomics and metabolomics analyses revealed the effects of trans-vp28 gene Synechocystis sp. PCC6803 on the hepatopancreas of Litopenaeus vannamei

Litopenaeus vannamei is the most important shrimp species throughout the world. However, diseases are increasing with the development of the industry, so enhancing the immunity of shrimp is of great significance. In this study, 1800 shrimp were divided into two groups randomly: the control group (N, feed with brine shrimp flake) and the experimental group (M, feed with mutant of Synechocystis sp. cells) (300 shrimp/group/replication) and each trial was conducted in triplicates. After immunization, sixty shrimp (with three replicates of twenty) were collected at 0 h in group N and 24, 72, and 144 h in group M, respectively, and the hepatopancreas were isolated for transcriptomic and metabolomic analysis. Transcriptome data revealed that compared with group N, genes related to antimicrobial peptides, cytoskeleton remodeling, detoxification, apoptosis, blood coagulation, immune defense, and antioxidant systems were differentially expressed in group M. In addition, combined transcriptomic and metabolomic analysis revealed that some immune-related differential genes or differential metabolites were consistently expressed in both omics. All the above results indicated that trans-vp28 gene Synechocystis sp. PCC6803 could improve the immunity of L. vannamei. This is the first report of the integration of dynamic transcriptomics combined with metabolomics to study the effect of trans-vp28 gene Synechocystis sp. PCC6803 in the hepatopancreas of L. vannamei and provided important information about the defense and immune mechanisms used by invertebrates against pathogens.

Control of vibriosis in shrimp through the management of the microbiota and the immune system

Shrimp aquaculture is constantly threatened by recurrent outbreaks of diseases caused by pathogenic bacteria of the genus Vibrio. Acute hepatopancreatic necrosis disease (AHPND) is one of the most aggressive vibriosis reported to date in the shrimp industry. AHPND provokes massive mortalities, causing economic losses with strong social impacts. Control of vibriosis requires the application of multifactorial strategies. This includes vibrio exclusion, shrimp microbiota, particularly in the digestive tract, and shrimp health management through immune stimulation. This paper reviews these two strategies for the prophylactic control of vibriosis. First, we describe the devastating effects of AHPND and the cellular and humoral effectors of the shrimp immune system to cope with this pathology. Secondly, the mechanisms of action of probiotics and their positive impacts are highlighted, including their immunostimulant effects and their role in the balance of the shrimp microbiota. Finally, we reviewed immunostimulants and prebiotics polysaccharides that together with probiotics act benefiting growth, feed efficiency and the microbiota of the digestive tract of farmed shrimp.

Transglutaminase 3 negatively regulates immune responses on the heart of the mosquito, Anopheles gambiae

The immune and circulatory systems of insects are functionally integrated. Following infection, immune cells called hemocytes aggregate around the ostia (valves) of the heart. An earlier RNA sequencing project in the African malaria mosquito, Anopheles gambiae, revealed that the heart-associated hemocytes, called periostial hemocytes, express transglutaminases more highly than hemocytes elsewhere in the body. Here, we further queried the expression of these transglutaminase genes and examined whether they play a role in heart-associated immune responses. We found that, in the whole body, injury upregulates the expression of TGase2, whereas infection upregulates TGase1, TGase2 and TGase3. RNAi-based knockdown of TGase1 and TGase2 did not alter periostial hemocyte aggregation, but knockdown of TGase3 increased the number of periostial hemocytes during the early stages of infection and the sequestration of melanin by periostial hemocytes during the later stages of infection. In uninfected mosquitoes, knockdown of TGase3 also slightly reduced the number of sessile hemocytes outside of the periostial regions. Taken altogether, these data show that TGase3 negatively regulates periostial hemocyte aggregation, and we hypothesize that this occurs by negatively regulating the immune deficiency pathway and by altering hemocyte adhesion. In conclusion, TGase3 is involved in the functional integration between the immune and circulatory systems of mosquitoes.

Natural ingredient paeoniflorin could be a lead compound against white spot syndrome virus infection in Litopenaeus vannamei

White spot syndrome virus (WSSV) is an important pathogen causing high mortality in the shrimp industry in aquaculture, yet there is no treatment available to date. In order to find a treatment against WSSV infection, this study examined the anti-WSSV activity of eight natural compounds using shrimp larvae as a model. Among the eight compounds, paeoniflorin showed the most obvious anti-WSSV effect, with a maximum protection efficiency of WSSV-infected shrimp >60% at 100 μM. Furthermore, pretreatment and post-treatment experiments revealed that paeoniflorin could prevent and treat WSSV infection in shrimp. The antiviral activity of paeoniflorin in aquaculture water decreased rapidly with time, and the results showed that the stable anti-WSSV activity of paeoniflorin could only remain in water for 1 day. Thus, the dosing pattern of continuous medication changes was evaluated. Obviously, in the model of continuous change of paeoniflorin, WSSV copy numbers in the virus-treated shrimp group still progressively increased, while the virus content in WSSV_paeoniflorin -treated group continued to decrease. Interestingly, paeoniflorin inhibited horizontal transmission of WSSV to a certain extent. Notably, paeoniflorin significantly increased the expression of antimicrobial peptides of shrimp to resist WSSV. In conclusion, paeoniflorin has the potential to protect shrimp against WSSV.

Antiviral activity of esculin against white spot syndrome virus: A new starting point for prevention and control of white spot disease outbreaks in shrimp seedling culture

White spot syndrome virus (WSSV) is a pathogenic and threatening virus in shrimp culture for which there is no effective control strategy. Finding antiviral lead compounds for the development of anti-WSSV drugs is urgent and necessary; in this study, esculin from 12 monomeric compounds exhibited an excellent anti-WSSV activity. The results showed that esculin increased the survival rate of WSSV-infected shrimps by 59% and reduced the virus copy number in vivo over 90% at 100 μM. In the pre-treatment and post-treatment experiments, esculin could prevent and treat WSSV infection. Compared with the control group, the virus copy number decreased by 30% after 6 h of esculin pre-incubation with WSSV particles and inhibited horizontal transmission of WSSV to a certain extent. Considering that the antiviral activity of esculin was stable in the aquacultural water for 2 days, we evaluated the dosing pattern of continuous medication changes. Obviously, the survival rate of WSSV-infected shrimps was 0% at 108 h when no esculin exchange was made, while at 120 h the survival rate was over 40% at continuous medicine changes. In addition, esculin significantly increased the expression of antimicrobial peptides and thus improved the ability of shrimp to resist WSSV. Overall, our findings suggest that esculin has the potential to be developed into an anti-WSSV medicine.

Moringa oleifera Leaves' Extract Enhances Nonspecific Immune Responses, Resistance against Vibrio alginolyticus, and Growth in Whiteleg Shrimp (Penaeus vannamei)

Simple Summary

This study found that moringa (Moringa oleifera) leaves’ water extract triggered phenoloxidase activity, phagocytic rate, and superoxide anion production in whiteleg shrimp (Penaeus vannamei) hemocytes by an in vitro assay. By an in vivo assay, a dietary moringa extract enhanced the total hemocyte count, phenoloxidase activity, phagocytic rate, immune-related gene expressions, and growth performance of the whiteleg shrimp. The administration of dietary moringa extract increased the survival rate after challenging the whiteleg shrimp with Vibrio alginolyticus.

Abstract

Moringa is widely known as a plant with high medicinal properties. Therefore, moringa has a high potential for use as an immunostimulant in shrimp. This study investigated the effect of a moringa water extract on the immune response, resistance against V. alginolyticus, and growth performance of whiteleg shrimp. To perform the in vitro assay, hemocytes were incubated with different concentrations of the moringa extract. Furthermore, the moringa extract was incorporated at 0 (control), 1.25 g (ME1.25), 2.5 g (ME2.5), and 5.0 g (ME5.0) per kg of diet for the in vivo assay. During the rearing period, immune responses, namely the total hemocyte count (THC), phenoloxidase (PO) activity, phagocytosis activity, superoxide anion production, and immune-related gene expression were examined on days 0, 1, 2, 4, 7, 14, 21, and 28. Growth performance was measured 60 days after the feeding period. Furthermore, the shrimp were challenged with V. alginolyticus after being fed for different feeding durations. The results of the in vitro assay revealed that 100–250 ppm of the moringa extract enhanced the PO activity, phagocytic rate (PR), and superoxide anion production. The findings of the in vivo assay demonstrated that the THC, PO activity, PR, and immune-related gene expression, including alpha-2-macroglobulin, prophenoloxidase II, penaeidin2, penaeidin3, anti-lipopolysaccharide factor, crustin, lysozyme, superoxide dismutase, and clotting protein, were higher in the group of ME.25 and ME5.0 than in the control and ME1.25 at several time points. Growth performance was significantly increased (p < 0.05) in the ME2.5 group compared to the control group. Furthermore, the dietary ME2.5 resulted in a higher survival rate compared to that of the control group after challenging with V. alginolyticus, especially at ME2.5 administered for 4 and 7 days. This study indicated that the incorporation of the moringa extract at 2.5 g per kg of diet enhanced the immune response, the growth performance of the whiteleg shrimp, and the resistance against V. alginolyticus infection.

Characterization and functional study of nuclear factor erythroid 2-related factor 2 (Nrf2) in black tiger shrimp (Penaeus monodon)

Nuclear factor erythroid 2-related factor 2 (Nrf2) is a member of the Cap'n'collar basic region leucine zipper (CNC-bZIP) transcription factor family, and is activated by diverse oxidants, pro-oxidants, antioxidants and chemopreventive agents. The full-length cDNA of Nrf2 from Penaeus monodon (PmNrf2; 2024 bp long with 729 bp coding region, GenBank accession no. MW390830) was cloned. The 242-amino-acid polypeptide encoded by this gene had a predicted molecular mass of 27.80 kDa. Sequence homology and phylogenetic analysis showed that PmNrf2 was similar to the insect Cap'n'Collar (CNC) transcription factor and mammalian Nrf2. Tissue expression profile analyzed by quantitative real-time RT-PCR (qRT-PCR) demonstrated that PmNrf2 was constitutively expressed in all examined tissues, with the highest expression observed in the intestines and the weakest expression observed in the hemocyte. PmNrf2 expression profiles were detected in the hepatopancreas of shrimp after bacterial challenge. The results suggested that PmNrf2 was involved in the responses to bacterial challenge, but the temporal expression pattern trend of PmNrf2 differed between the gram-negative and gram-positive bacterial challenges in the shrimp hepatopancreas. The recombinant PmNrf2 protein was expressed and purified through affinity chromatography. Furthermore, an anti-PmNrf2 polyclonal antibody was obtained, which was able to clearly detect PmNrf2 protein expression in the hepatopancreas of shrimp. Knockdown of PmNrf2 by RNA interference (RNAi) resulted in a reduction in the expression of PmGPx gene. Taken together, the results of our study indicated that PmNrf2 played a role in regulation the transcription of PmGPx antioxidant enzyme genes.

Characterization of a novel shrimp pathogen, Vibrio brasiliensis, isolated from Pacific white shrimp, Penaeus vannamei

A novel pathogenic strain Vibrio 20190611023 was isolated from the hepatopancreas of moribund cultured Penaeus vannamei suffering from black gill disease. This strain was identified as V. brasiliensis based on the phylogenetic analyses of 16S rDNA gene and five other housekeeping genes (i.e., gapA, ftsZ, mreB, topA and gyrB). Some biochemical features of this strain were determined with an API 20NE system, and its haemolytic activity was determined using a sheep blood agar plate. The pathogenicity of this isolate 20190611023 was confirmed by the experimental challenge tests and histopathological examinations. P. vannamei were challenged via reverse gavage with different doses of bacterial suspensions. The calculated median lethal dose (LD₅₀ ) was (3.16 ± 1.78) × 10⁵  CFU/g (body weight). Moreover, antibiotic susceptibility tests were performed, the results of which showed that the strain 20190611023 was sensitive to chloramphenicol, compound sulphamethoxazole, ciprofloxacin, doxycycline and oxacillin, but resistant to erythromycin, kanamycin, gentamicin, cefoperazone, ceftriaxone, cefamezin and piperacillin. To our knowledge, this is the first report for demonstrating V. brasiliensis as a shrimp pathogen, which expands the host range of V. brasiliensis infection. The present study highlights that more attention should be paid to this novel pathogen in intensive shrimp aquaculture.

Evaluation of probiotic characteristics and whole genome analysis of Pediococcus pentosaceus MR001 for use as probiotic bacteria in shrimp aquaculture

The development of non-antibiotic and environmentally friendly agents is a key consideration for health management in shrimp aquaculture. In this study, the probiotic potential in shrimp aquaculture of Pediococcus pentosaceus MR001, isolated from Macrobrachium rosenbergii, was investigated by means of feeding trial and genetic characterization. In the feeding trial, dietary supplementation with P. pentosaceus MR001 significantly increased weight gain and digestive enzyme activity (p < 0.05) in shrimp, Litopenaeus vannamei. The intestinal histology showed that shrimp given the probiotic diet had healthier guts than the control group. Also, the immune gene expression and the survival rate in the treatment group were significantly increased when compared with the control group. The genetic characteristics of P. pentosaceus strain MR001 were explored by performing whole-genome sequencing (WGS) using the HiSeq 2500 platform and PacBio system, revealing the complete circular genome of 1,804,896 bp. We also identified 1789 coding genes and subsequently characterized genes related to the biosynthesis of bacteriocins, stress resistance, and bile tolerance. Our findings suggest that insights in the functional and genetic characteristics of P. pentosaceus strain MR001 could provide opportunities for applications of such strain in shrimp diet supplementation.

Proteomic Analysis of the Hemolymph After Metschnikowia bicuspidata Infection in the Chinese Mitten Crab Eriocheir sinensis

The “milky disease” of the Chinese mitten crab, Eriocheir sinensis, is a highly lethal fungal disease caused by Metschnikowia bicuspidata infection. To elucidate the immune responses of the hemolymph of E. sinensis to M. bicuspidata infection, a comparative analysis of the hemolymph of E. sinensis infected with M. bicuspidata and that treated with phosphate buffered saline was performed using label-free quantitative proteomics. A total of 429 proteins were identified. Using a 1.5-fold change in expression as a physiologically significant benchmark, 62 differentially expressed proteins were identified, of which 38 were significantly upregulated and 24 were significantly downregulated. The upregulated proteins mainly included cytoskeleton-related proteins (myosin regulatory light chain 2, myosin light chain alkali, tubulin α-2 chain, and tubulin β-1 chain), serine protease and serine protease inhibitor (clip domain-containing serine protease, leukocyte elastase inhibitor, serine protein inhibitor 42Dd), catalase, transferrin, and heat shock protein 70. Upregulation of these proteins indicated that phenoloxidase system, phagocytosis and the ROS systems were induced by M. bicuspidata. The downregulated proteins were mainly organ and tissue regeneration proteins (PDGF/VEGF-related factor protein, integrin-linked protein kinase homing pat-4 gene) and hemagglutination-associated proteins (hemolymph clottable protein, hemocyte protein-glutamine gamma-glutamyltransferase). Downregulation of these proteins indicated that M. bicuspidata inhibited hemocyte regeneration and hemolymph agglutination. Fifteen differentially expressed proteins related to immunity were verified using a parallel reaction monitoring method. The expression trend of these proteins was similar to that of the proteome. To the best of our knowledge, this is the first report on the proteome of E. sinensis in response to M. bicuspidata infection. These results not only provide new and important information on the immune response of crustaceans to yeast infection but also provide a basis for further understanding the molecular mechanism of complex host pathogen interactions between crustaceans and fungi.

A novel research on isolation and characterization of Photobacterium damselae subsp. damselae from Pacific white shrimp, Penaeus vannamei, displaying black gill disease cultured in China

In June 2019, massive mortalities of cultured Penaeus vannamei occurred in a local farm in Hainan Province, China. The diseased shrimp displayed evident black gills. Three bacterial strains 20190611001, 20190611007 and 20190611022 were isolated from hepatopancreas and gills of the diseased shrimp and identified as Photobacterium damselae subsp. damselae based on the sequence analysis of 16S rRNA and toxR genes. These three isolates showed haemolytic activities. Of them, strain 20190611022 isolated from hepatopancreas was selected and processed for pathogenic analysis. The calculated median lethal dose (LD₅₀ ) was 9.75 ± 4.29 × 10⁵ CFU/g (body weight) by challenging P. vannameivia reverse gavage. The diseased shrimp displayed enlarged hepatopancreatic tubules and sloughing of epithelial cells in tubular lumens. The strain 20190611022 was also characterized by the testing of API 20NE systems and antibiotic susceptibility. The results of disc diffusion test showed that strain 20190611022 was sensitive to chloramphenicol, compound sulfamethoxazole, cefoperazone, ceftriaxone, ceftazidime and cefuroxime. To our knowledge, this is the first report of isolation and characterization of Photobacterium damselae subsp. damselae from natural diseased P. vannamei. Our findings can serve as a basis for further studies of its pathogenicity and provide technological support for disease controlling in shrimp aquaculture.

Synthesis and evaluation of polyamine carbon quantum dots (CQDs) in Litopenaeus vannamei as a therapeutic agent against WSSV

White spot syndrome virus (WSSV) is the causative agent of white spot syndrome (WSS), a disease that has led to severe mortality rates in cultured shrimp all over the world. The WSSV is a large, ellipsoid, enveloped double-stranded DNA virus with a wide host range among crustaceans. Currently, the main antiviral method is to block the receptor of the host cell membrane using recombinant viral proteins or virus antiserum. In addition to interference with the ligand-receptor binding, disrupting the structure of the virus envelope may also be a means to combat the viral infection. Carbon quantum dots (CQDs) are carbonaceous nanoparticles that have many advantageous characteristics, including small size, low cytotoxicity, cheap, and ease of production and modification. Polyamine-modified CQDs (polyamine CQDs) with strong antibacterial ability have been identified, previously. In this study, polyamine CQDs are shown to attach to the WSSV envelope and inhibit the virus infection, with a dose-dependent effect. The results also show that polyamine CQDs can upregulate several immune genes in shrimp and reduce the mortality upon WSSV infection. This is first study to identify that polyamine CQDs could against the virus. These results, indeed, provide a direction to develop effective antiviral strategies or therapeutic methods using polyamine CQDs in aquaculture.

Crustacean Hemolymph Lipoproteins

Lipoproteins mediate the transport of apolar lipids in the hydrophilic environment of physiological fluids such as the vertebrate blood and the arthropod hemolymph. In this overview, we will focus on the hemolymph lipoproteins in Crustacea that have received most attention during the last years: the high density lipoprotein/β-glucan binding proteins (HDL-BGBPs), the vitellogenins (VGs), the clotting proteins (CPs) and the more recently discovered large discoidal lipoproteins (dLPs). VGs are female specific lipoproteins which supply both proteins and lipids as storage material for the oocyte for later use by the developing embryo. Unusual within the invertebrates, the crustacean yolk proteins-formerly designated VGs-are more related to the ApoB type lipoproteins of vertebrates and are now termed apolipocrustaceins. The CPs on the other hand, which are present in both sexes, are related to the (sex specific) VGs of insects and vertebrates. CPs serve in hemostasis and wound closure but also as storage proteins in the oocyte. The HDL-BGBPs are the main lipid transporters, but are also involved in immune defense. Most crustacean lipoproteins belong to the family of the large lipid transfer proteins (LLTPs) such as the intracellular microsomal triglyceride transfer protein, the VGs, CPs and the dLPs. In contrast, the HDL-BGBPs do not belong to the LLTPs and their relationship with other lipoproteins is unknown. However, they originate from a common precursor with the dLPs, whose functions are as yet unknown. The majority of lipoprotein studies have focused on decapod crustaceans, especially shrimps, due to their economic importance. However, we will present evidence that the HDL-BGBPs are restricted to the decapod crustaceans which raises the question as to the main lipid transporting proteins of the other crustacean groups. The diversity of crustaceans lipoproteins thus appears to be more complex than reflected by the present state of knowledge.

SpTGase plays an important role in the hemolymph clotting in mud crab (Scylla paramamosain)

Transglutaminase (TGase) is important in blood coagulation, a conserved immunological defense mechanism among invertebrates. This study is the first report of the TGase in mud crab (Scylla paramamosain) (SpTGase) with a 2304 bp ORF encoding 767 amino acids (molecular weight 85.88 kDa). SpTGase is acidic, hydrophilic, stable and thermostable, containing three transglutaminase domains, one TGase/protease-like homolog domain (TGc), one integrin-binding motif (Arg²⁷⁰, Gly²⁷¹, Asp²⁷²) and three catalytic sites (Cys³³³, His⁴⁰¹, Asp⁴²⁴) within the TGc. Neither a signal peptide nor a transmembrane domain was found, and the random coil is dominant in the secondary structure of SpTGase. Phylogenetic analysis revealed a close relation between SpTGase to its homolog EsTGase 1 from Chinese mitten crab (Eriocheir sinensis). Expression of SpTGase was investigated using qRT-PCR (1) in eight tissues from healthy mud crabs, with the highest expression in hemocytes, and (2) in response to various immune challenges (Vibrio parahaemolyticus, lipopolysaccharide (LPS) or Poly I:C infection), revealing a major up-regulation in hemocytes, skin, and hepatopancreas during the 96-h post injection. The recombinant SpTGase showed a capacity of agglutination activities on both Gram-negative bacteria and yeast. SpTGase was found to directly interact with another important blood coagulation component clip domain serine protease (SpcSP). Moreover, knockdown of SpTGase resulted in a decreased expression of both clotting protein precursor (SppreCP) and SpcSP and an increase of duration time in the blood coagulation. Taken together, the findings of this study suggest SpTGase play an important role in the hemolymph clotting in mud crab S. paramamosain.

Litopenaeus vannamei heat shock protein 70 (LvHSP70) enhances resistance to a strain of Vibrio parahaemolyticus, which can cause acute hepatopancreatic necrosis disease (AHPND), by activating shrimp immunity

Heat shock protein 70 (HSP70) acts as a molecular chaperone and a stress protein, but also plays important roles in innate and adaptive immune responses. Previous studies have reported that non-lethal heat shock (NLHS) could enhance the resistance of Pacific white shrimp Litopenaeus vannamei to a specific strain of Vibrio parahaemolyticus, which carried a toxin-producing plasmid (VP_AHPND), via the induction of LvHSP70 transcription. Here, we further investigated the specific function of LvHSP70 in shrimp immunity. The upregulation of LvHSP70 at the protein level was detected during recovery time after NLHS treatment, using both western blot analysis and immunofluorescence microscopy. We found that NLHS immediately activated the production of LvHSP70 in shrimp hemocytes and that such induction was observed in all three types of hemocytes: hyaline; granular and semi-granular cells. Furthermore, the role of LvHSP70 in bacterial defense was investigated using the heterologous expression of recombinant LvHSP70 (rLvHSP70) in Escherichia coli. Shrimp receiving rLvHSP70 by injection showed an increased survival rate (75%) to VP_AHPND infection compared to just 20% survival in the control group injected with bovine serum albumin (BSA). We also demonstrated that the injected rLvHSP70 accumulated in shrimp hemocytes and was detected in the intracellular space of hemocyte cells leading to the induced expression (P<0.05) of several immune-related genes (LvMyD88, LvIKKβ, LvIKKε, LvCrustin I, LvPEN2, LvPEN3, LvproPO1, LvproPO2 and LvTG1). Collectively, these results suggest that LvHSP70 plays a crucial role in bacterial defense by activating the shrimp immune system.

Differentially expressed genes in hemocytes of Litopenaeus vannamei challenged with Vibrio parahaemolyticus AHPND (VPAHPND) and VPAHPND toxin

While toxin-harboring Vibrio parahaemolyticus has been previously established as the causative agent of early mortality syndrome (EMS) or acute hepatopancreatic necrosis disease (AHPND) in shrimp, information on the mechanistic processes that happen in the host during infection is still lacking. Here, we examined the expression responses of the shrimp hemocyte transcriptome to V. parahaemolyticus AHPND (VP_AHPND) by RNA sequencing (RNA-seq). Using libraries (SRA accession number SRP137285) prepared from shrimp hemocytes under experimental conditions, a reference library was de novo assembled for gene expression analysis of VP_AHPND-challenged samples at 0, 3/6, and 48 h post infection (hpi). Using the library from 0-hpi as the control, 359 transcripts were found to be differentially expressed in the 3/6-hpi library, while 429 were differentially expressed in the 48-hpi library. The expression patterns reported in the RNA-seq of 9 representative genes such as anti-lipopolysaccharide factor (LvALF), crustin p (CRU), serpin 3 (SER), C-type lectin 3 (CTL), clottable protein 2 (CLO), mitogen-activated protein kinase kinase 4 (MKK4), P38 mitogen-activated protein kinase (P38), protein kinase A regulatory subunit 1 (PKA) and DNAJ homolog subfamily C member 1-like (DNJ) were validated by qRT-PCR. The expression of these genes was also analyzed in shrimp that were injected with the partially purified VP_AHPND toxin. A VP_AHPND toxin-responsive gene, LvALF was identified, and its function was characterized by RNA interference. LvALF knockdown resulted in significantly rapid increase of shrimp mortality caused by toxin injection. Protein-protein interaction analysis by molecular docking suggested that LvALF possibly neutralizes VP_AHPND toxin through its LPS-binding domain. The data generated in this study provide preliminary insights into the differences in the immune response of shrimp to the bacterial and toxic aspect of VP_AHPND as a disease.

Gills specific type 2 crustin isoforms: Its molecular cloning and characterization from kuruma shrimp Marsupenaeus japonicus

Crustins are diverse group of antimicrobial peptides (AMPs) that have numerous isoforms mainly identified from hemocytes in decapods crustacean. However, little is known about its presence solely in gills tissue. In this study, we found two new crustin isoforms MjCRS8 and MjCRS9 by using transcriptome analysis from gills. Open reading frame of MjCRS8 and MjCRS9 were 593 bp and 459 bp encoding 197aa and 152aa, respectively. Tissue distribution analysis indicated that both MjCRS8 and MjCRS9 are expressed only in gills tissue. Multiple sequence alignment and phylogenetic analysis with previously reported crustin suggested that both MjCRS8 and MjCRS9 belong to type 2 crustin family. Experimental infection was conducted against Vibrio parahaemolyticus and white spot syndrome virus (WSSV) by immersion test. However, no significant upregulation was observed.

Functional elucidation of LvToll 3 receptor from P. vannamei through RNA interference and its potential role in the shrimp antiviral response

There is a continuing debate on whether an antiviral immunity similar to vertebrate interferon response exists in invertebrates. Recent advances in penaeid immunology identified several new members of the Toll receptor family and one of these is LvToll3 (Litopenaeus vannamei Toll3). It is hypothesized in this study that LvToll3 responds to pathogen associated molecular patterns (PAMPs) such as dsRNA, which then activates certain antiviral pathways in penaeids. RNA interference (RNAi) was used to determine differences in the expression levels of specific genes putatively involved in the antiviral response through qPCR. Results showed that LvToll3 upregulation could be elicited through the introduction of double stranded RNA (dsRNA) regardless of sequence relative to initial levels in the 3rd hour. Furthermore, statistically intriguing trend in the overall expression of Vago 4/5 and Interferon regulatory factor (IRF) suggests that both these genes are affected by the expression of LvToll3. Dicer showed no statistical difference between the experimentally treated (LvToll3-dsRNA), positive control (GFP-dsRNA), and control (PBS) samples corroborating the assertion that dicer is part of another antiviral mechanism that acts in concert with Toll system. These findings suggests that LvToll3 plays a critical role in penaeid antiviral immunity when molecular patterns associated with viruses are detected.

White spot syndrome virus (WSSV) suppresses penaeidin expression in Marsupenaeus japonicus hemocytes

Penaeidins are a unique family of antimicrobial peptides specific to penaeid shrimp and have been reported mainly function as anti-bacterial and anti-fungal. In order to investigate whether penaeidins could also respond to virus or not, we examined the effect of WSSV on MjPen-II (penaeidin in kuruma shrimp, Marsupenaeus japonicus) expression. In the control group, MjPen-II transcript level can be detected in almost all test tissues but was expressed most strongly in hemocytes. After WSSV infection, MjPen-II transcript level was significantly downregulated in hemocytes. Moreover, the proportion of MjPen-II+ hemocytes was not significantly different between non-infected and WSSV-infected shrimp, but the number of MjPen-II+ highly expressing hemocytes decreased after infection. In addition, MjPen-II was observed in the cytoplasm of granule-containing hemocytes. These results suggest that WSSV suppresses MjPen-II expression in hemocytes.

Comparative sequence analysis of crustin isoform MjCRS7 and MjWFDC-like gene from kuruma shrimp Marsupenaeus japonicus shows variant of the WFDC domain

Crustins are well known cysteine-rich cationic antimicrobial peptides (AMPs) in crustaceans that have WFDC [WAP (whey acidic protein) four-disulfide core] domain at the carboxyl terminus. Proteins containing a WFDC domain have been discovered in many invertebrates and vertebrates. Although, there have been many WFDC domain containing nucleotide sequences found in NCBI GenBank database, their distinct sequential characteristics and their role in the innate immune system is not well understood. Here, we identified a new crustin isoform from Marsupenaeus japonicus by transcriptome analysis. The full-length cDNA of this isoform (MjCRS7) consists of 537 bp that include a 489 bp open reading frame (ORF) encoding 162 deduced amino acids (aa). The sequence contains the eight conserved cysteine residues characteristic of the WFDC domain. A phylogenetic analysis showed that MjCRS7 is a type II crustin. We also identified the full-length cDNA of a M. japonicus MjWFDC-like gene. MjWFDC-like has a 543 bp ORF encoding 180 aa. In an RT-PCR analysis, MjCRS7 and MjWFDC-like transcripts were mainly detected in gill tissue. An alignment of MjCRS7 and MjWFDC-like with previously reported M. japonicus crustin isoform 1-5 (MjCRS1-5) showed variation in the WFDC-like domain. Neither of the genes was responsive to Vibrio parahaemolyticus, Vibrio penaeicida or white spot syndrome virus (WSSV) either by immersion or injection challenge test. Although crustins are mainly antimicrobial peptides, the present results suggest that MjCRS7 may have other roles in M. japonicus.

A novel white spot syndrome virus-induced gene (MjVIG1) from Marsupenaeus japonicus hemocytes

cDNA of a newly recognized white spot syndrome virus (WSSV)-induced gene (MjVIG1) was characterized from Marsupenaeus japonicus hemocytes; this gene encodes a protein that lack similarity to any known characterized protein. To identify this novel gene, we mainly conducted transcript level analysis, immunostaining and flow cytometry after WSSV infection. MjV1G1 transcript levels were also measured after Yellow head virus (YHV) and Vibrio parahaemolyticus infection tests. In non-infected and WSSV-infected shrimp, MjVIG1 was observed in granule-containing hemocytes. In addition, the MjVIG1 transcript level and ratio of MjVIG1-positive hemocytes both significantly increased, and number of MjVIG1-positive hemocytes slightly increased after WSSV infection. In contrast, MjVIG1 transcript level did not change after YHV and V. parahaemolyticus infection. These results indicated that MjVIG1 might be a WSSV-specific induced gene in M. japonicus hemocytes.

Comparative proteomic analysis of hepatopancreas in Macrobrachium rosenbergii responded to Poly (I:C)

Gel-enhanced liquid chromatography coupled with tandem mass spectrometry (GeLC-MS/MS) was used to analyze the proteome of Macrobrachium rosenbergii hepatopancreas responded to Poly (I:C). GeLC-MS/MS analysis identified 515 differentially-expressed proteins with ≥1.5 and ≤ -0.5 log₂ fold change. Of these, 195 differentially-expressed proteins were significantly matched to known proteins in the database, of which 102 proteins were up-regulated and 93 proteins were down-regulated. These proteins were classified into 21 categories, i.e. metabolic process, oxidative stress response, signaling, transcription, translation, cell cycle, transport, etc. Several immune factors were up-regulated upon Poly (I:C) injection. Protein-protein interaction network analysis of these immune factors identified three major protein clusters including RNAi, stress responses, and Toll pathway-proPO system, implying that Poly (I:C) activates immune responses in prawn through several mechanisms.

A novel viral responsive protein (MjVRP) from Marsupenaeus japonicus haemocytes is involved in white spot syndrome virus infection

A viral responsive protein (MjVRP) was characterized from Marsupenaeus japonicus haemocytes. In amino acid homology and phylogenetic tree analyses, MjVRP clustered in the same group with the viral responsive protein of Penaeus monodon (PmVRP15), showing 34% identity. MjVRP transcripts were mainly expressed in haemocytes and the lymphoid organ. Western blotting likewise showed that MjVRP was strongly expressed in haemocytes and the lymphoid organ. Immunostaining detected MjVRP within the cytosol next to the perinuclear region in some haemocytes. Experimental challenge with white spot syndrome virus (WSSV) significantly up-regulated the mRNA level of MjVRP in the M. japonicus haemocytes at 6 and 48 h. Flow cytometry and indirect immunofluorescence assays revealed that the ratio of MjVRP⁺ haemocytes significantly increased 24 and 48 h post-WSSV infection. These results suggest that MjVRP⁺ haemocytes have a supporting role in the pathogenesis of WSSV.

A probiotic Bacillus strain containing amorphous poly-beta-hydroxybutyrate (PHB) stimulates the innate immune response of Penaeus monodon postlarvae

In this study, the PHB-accumulating Bacillus sp. JL47 strain (capable of accumulating 55% PHB on cell dry weight) was investigated for its effects on the immune response of giant tiger shrimp (Penaeus monodon) postlarvae (PL) before and after the Vibrio campbellii challenge. Briefly, shrimp PL were cultured and fed with Artemia nauplii enriched with Bacillus sp. JL47. Shrimp receiving the Artemia nauplii without JL47 enrichment were used as control. After 15 days of feeding, the shrimp were challenged with pathogenic V. campbellii LMG 21363 at 10⁶ cells mL^-1 by immersion. Relative expression of the immune related genes encoding for prophenoloxidase (proPO), transglutaminase (TGase) and heat shock protein 70 (Hsp70) in the shrimp were measured before (0 h) and after (3, 6, 9, 12, 24 h) the Vibrio challenge by quantitative real-time PCR using β-actin as the reference gene. The expressions of TGase and proPO were significantly up-regulated (p < 0.05) within 9 h and 12 h, respectively after challenge in shrimp receiving the Bacillus sp. JL47 as compared to the challenged and non-challenged controls. Hsp70 expression was significantly increased (p < 0.05) at 3 h post-challenge in all challenged shrimp. Interestingly, proPO and TGase genes were significantly up-regulated (p < 0.05) in Bacillus sp. JL47 treated shrimp even before the Vibrio challenge was applied. No up-regulation in the Hsp70 gene, however, was observed under these conditions. The data suggest that the protective effect of the PHB-accumulating Bacillus sp. JL47 in shrimp was due to its capacity to stimulate the innate immune related genes of the shrimp, specifically the proPO and TGase genes. The application of probiotic Bacillus species, capable of accumulating a significant amount of PHB, is suggested as potential immunostimulatory strategy for aquaculture.

Fatty acid binding protein regulate antimicrobial function via Toll signaling in Chinese mitten crab

Fatty acid binding proteins (FABPs) are members of the lipid binding protein superfamily and play crucial role in fatty acid transport and lipid metabolism. In macrophages, Adipocyte-type FABP is an important mediator of inflammation. However, the immune functions of FABPs in invertebrates are not well understood; here, we obtained the gene structure of Eriocheir sinensis FABP 3 and FABP 9 (EsFABP 3 and EsFABP 9), and compared with EsFABP 10. The mRNA expression profiles show that all three FABPs were significantly up-regulated in hemocytes after being challenged with bacteria. Of the three, EsFABP 3 was the most stable and also the most highly up-regulated. Further studies showed that knockdown of EsFABP 3 led to higher bacterial counts in the hemocyte culture medium and a significant decrease in the mRNA expression of some antimicrobial peptides following bacterial stimulation. Moreover, a subcellular study demonstrated that EsFABP 3 can affect nuclear translocation of the dorsal after Gram-positive bacterial stimulation in hemocytes. These findings support the notion that EsFABP 3 could inhibit bacterial proliferation by regulating antimicrobial peptides expression via the Toll signaling pathway.

Effect of 4-nonylphenol on the immune response of the Pacific oyster Crassostrea gigas following bacterial infection with Vibrio campbellii

The xenoestrogen 4-nonylphenol (NP) is a ubiquitous aquatic pollutant and has been shown to impair reproduction, development, growth and, more recently, immune function in marine invertebrates. We investigated the effects of short-term (7 d) exposure to low (2 μg l^-1) and high (100 μg l^-1) levels of NP on cellular and humoral elements of the innate immune response of Crassostrea gigas to a bacterial challenge. To this end, we measured 1) total hemocyte counts (THC), 2) relative transcript abundance of ten immune-related genes (defh1, defh2, bigdef1, bigdef2, bpi, lysozyme-1, galectin, C-type lectin 2, timp, and transglutaminase) in the hemocytes, gill and mantle, and 3) hemolymph plasma lysozyme activity, following experimental Vibrio campbellii infection. Both low and high levels of NP were found to repress a bacteria-induced increase in THC observed in the control oysters. While several genes were differentially expressed following bacterial introduction (bigdef2, bpi, lysozyme-1, timp, transglutaminase), only two genes (bpi in the hemocytes, transglutaminase in the mantle) exhibited a different bacteria-induced expression profile following NP exposure, relative to the control oysters. Independently of infection-status, exposure to NP also altered mRNA transcript abundance of several genes (bpi, galectin, C-type lectin 2) in naïve, saline-injected oysters. Finally, plasma lysozyme activity levels were significantly higher in low dose NP-treated oysters (both naïve and bacteria challenged) relative to control oysters. Combined, these results suggest that exposure to ecologically-relevant (low) and extreme (high) levels of NP can alter both cellular and humoral elements of the innate immune response in C. gigas, an aquaculture species of global economic importance.

Characterization of a Kunitz-type protease inhibitor (MjKuPI) reveals the involvement of MjKuPI positive hemocytes in the immune responses of kuruma shrimp Marsupenaeus japonicus

Serine proteases and their inhibitors play vital roles in biological processes. Serine protease inhibitors, including Kunitz-type protease inhibitors play important roles not only in physiological process (i.e. blood clotting and fibrinolysis) but also in immune responses. In this study, we characterized a Kunitz-type protease inhibitor, designated MjKuPI, from kuruma shrimp Marsupenaeus japonicus. An expression profile showed that MjKuPI was mainly expressed in hemocytes. Immunostaining revealed that some hemocytes expressed MjKuPI (MjKuPI(+) hemocytes) and others did not (MjKuPI(-) hemocytes). Injection of shrimp with Vibrio penaeicida and white spot syndrome virus (WSSV) upregulated the mRNA level of MjKuPI, and a flow cytometry analysis revealed that the proportion of MjKuPI(+) hemocytes increased significantly 24 h after injection. Together, these results suggest that MjKuPI and MjKuPI(+) hemocytes have a role in the innate immune system of kuruma shrimp.

Antimicrobial functions of EsLecH, a C-type lectin, via JNK pathway in the Chinese mitten crab, Eriocheir sinensis

C-type lectins (CTLs) are pattern recognition proteins that play significant roles in the innate immune system by identifying and eliminating pathogens. Here, we have reported a CTL (EsLecH) from the Chinese mitten crab that can bind to microorganisms and regulate antimicrobial peptide (AMP) expression via the c-Jun N-terminal kinase (JNK) pathway. EsLecH was found to have an N-terminal signal peptide and a single carbohydrate recognition domain. The EsLecH transcript was detected abundantly in various tissues, and it was significantly upregulated in hemocytes after challenging with lipopolysaccharides and bacteria. Recombinant (r)EsLecH could bind to microorganisms, but at different levels. Ca(2+) significantly increased rEsLecH binding affinity to microorganisms. Furthermore, growth inhibition by rEsLecH increased with increasing rEsLecH levels. Knockdown of EsLecH was accompanied by a significant reduction in AMP expression and JNK phosphorylation; AMP expression was reduced with JNK silencing and can not rescued by rEsLecH when absence of JNK. These results indicate that EsLecH could regulate AMPs via JNK signaling.

The known two types of transglutaminases regulate immune and stress responses in white shrimp, Litopenaeus vannamei

Transglutaminases (TGs) play critical roles in blood coagulation, immune responses, and other biochemical functions, which undergo post-translational remodeling such as acetylation, phosphorylation and fatty acylation. Two types of TG have been identified in white shrimp, Litopenaeus vannamei, and further investigation on their potential function was conducted by gene silencing in the present study. Total haemocyte count (THC), differential haemocyte count (DHC), phenoloxidase activity, respiratory bursts (release of superoxide anion), superoxide dismutase activity, transglutaminase (TG) activity, haemolymph clotting time, and phagocytic activity and clearance efficiency to the pathogen Vibrio alginolyticus were measured when shrimps were individually injected with diethyl pyrocarbonate-water (DEPC-H2O) or TG dsRNAs. In addition, haemolymph glucose and lactate, and haemocytes crustin, lysozyme, crustacean hyperglycemic hormone (CHH), transglutaminaseI (TGI), transglutaminaseII (TGII) and clotting protein (CP) mRNA expression were determined in the dsRNA injected shrimp under hypothermal stress. Results showed that TG activity, phagocytic activity and clearance efficiency were significantly decreased, but THC, hyaline cells (HCs) and haemolymph clotting time were significantly increased in the shrimp which received LvTGI dsRNA and LvTGI + LvTGII dsRNA after 3 days. However, respiratory burst per haemocyte was significantly decreased in only LvTGI + LvTGII silenced shrimp. In hypothermal stress studies, elevation of haemolymph glucose and lactate was observed in all treated groups, and were advanced in LvTGI and LvTGI + LvTGII silenced shrimp following exposure to 22 °C. LvCHH mRNA expression was significantly up-regulated, but crustin and lysozyme mRNA expressions were significantly down-regulated in LvTGI and LvTGI + LvTGII silenced shrimp; moreover, LvTGII was significantly increased, but LvTGI was significantly decreased in LvTGI silenced shrimp following exposure to 28 and 22 °C. Knockdown of LvTGI and LvTGI + LvTGII also significantly increased the mortality of L. vannamei challenged with the pathogen V. alginolyticus. The same consequences have been confirmed in LvTGII silenced shrimp in our previous study. These results indicate that LvTGI and LvTGII not only reveal a complementary effect in gene expression levels but also play a key function in the immune defence mechanism of shrimp, by regulating the haemolymph coagulation, immune parameters and immune related gene expression, and in the regulation of carbohydrate metabolism.

Next-Generation Sequencing and the Crustacean Immune System: The Need for Alternatives in Immune Gene Annotation

Next-generation sequencing has been a huge benefit to investigators studying non-model species. High-throughput gene expression studies, which were once restricted to animals with extensive genomic resources, can now be applied to any species. Transcriptomic studies using RNA-Seq can discover hundreds of thousands of transcripts from any species of interest. The power and limitation of these techniques is the sheer size of the dataset that is acquired. Parsing these large datasets is becoming easier as more bioinformatic tools are available for biologists without extensive computer programming expertise. Gene annotation and physiological pathway tools such as Gene Ontology and Kyoto Encyclopedia of Genes and Genomes (KEGG) Orthology enable the application of the vast amount of information acquired from model organisms to non-model species. While noble in nature, utilization of these tools can inadvertently misrepresent transcriptomic data from non-model species via annotation omission. Annotation followed by molecular pathway analysis highlights pathways that are disproportionately affected by disease, stress, or the physiological condition being examined. Problems occur when gene annotation procedures only recognizes a subset, often 50% or less, of the genes differently expressed from a non-model organisms. Annotated transcripts normally belong to highly conserved metabolic or regulatory genes that likely have a secondary or tertiary role, if any at all, in immunity. They appear to be disproportionately affected simply because conserved genes are most easily annotated. Evolutionarily induced specialization of physiological pathways is a driving force of adaptive evolution, but it results in genes that have diverged sufficiently to prevent their identification and annotation through conventional gene or protein databases. The purpose of this manuscript is to highlight some of the challenges faced when annotating crustacean immune genes by using an American lobster (Homarus americanus) transcriptome as an example. Immune genes have evolved rapidly over time, facilitating speciation and adaption to highly divergent ecological niches. Complete and proper annotation of immune genes from invertebrates has been challenging. Modulation of the crustacean immune system occurs in a variety of physiological responses including biotic and abiotic stressors, molting and reproduction. A simple method for the identification of a greater number of potential immune genes is proposed, along with a short introductory primer on crustacean immune response. The intended audience is not the advanced bioinformatic user, but those investigating physiological responses who require rudimentary understanding of crustacean immunological principles, but where immune gene regulation is not their primary interest.

Priming the immune system of Penaeid shrimp by bacterial HSP70 (DnaK)

This study was conducted to test the effect of DnaK on priming immune responses in Penaeid shrimp. Juvenile-specific pathogen-free (SPF) P. vannamei shrimp were injected with 0.05 μg recombinant DnaK. One hour post-DnaK priming, a non-lethal dose of Vibrio campbellii (10(5) CFU shrimp(-1)) was injected. Other treatments include only DnaK or V. campbellii injection or control with blank inocula. The haemolymph of three shrimp from each treatment was collected at 1.5, 6, 9 and 12 h post-DnaK priming (hpp). It was verified that injection with DnaK and V. campbellii challenge affected the transcription of 3 immune genes, transglutaminase-1 (TGase-1), prophenoloxidase-2 (proPO-2) and endogenous HSP70 (lvHSP70). In P. monodon, shrimp were first injected with DnaK at a dose of 10 μg shrimp(-1) and one hour later with 10(6) CFU of V. harveyi (BB120) shrimp(-1). Shrimp injected with DnaK showed a significant increase in proPO expression compared to the control (P < 0.05). Yet a double injection (DnaK and Vibrio) seemed to cause an antagonistic response at the level of expression, which was not equalled at the level of PO activity. Those results suggest that DnaK is able to modulate immune responses in P. vannamei and P. monodon.

Crustacean hematopoiesis

Crustacean hemocytes are important mediators of immune reactions, and the regulation of hemocyte homeostasis is of utmost importance for the health of these animals. This review discusses the current knowledge on the lineages, synthesis and differentiation of hemocytes in crustaceans. Hematopoietic tissues, their origins, and the regulation of hematopoiesis during molting, seasonal variation and infection are discussed. Furthermore, studies concerning the molecular regulation of hemocyte formation in crustaceans are also described, and the different lineages and their molecular markers are discussed and compared with several insect species. Signaling pathways and the regulation of hematopoiesis by transcription factors are typically conserved among these arthropods, whereas cytokines and growth factors are more variable and species specific. However, considering the great diversity among the crustaceans, one should be cautious in drawing general conclusions from studies of only a few species.

A transcriptome study on Macrobrachium rosenbergii hepatopancreas experimentally challenged with white spot syndrome virus (WSSV)

The world production of shrimp such as the Malaysian giant freshwater prawn, Macrobrachium rosenbergii is seriously affected by the white spot syndrome virus (WSSV). There is an urgent need to understand the host pathogen interaction between M. rosenbergii and WSSV which will be able to provide a solution in controlling the spread of this infectious disease and lastly save the aquaculture industry. Now, using Next Generation Sequencing (NGS), we will be able to capture the response of the M. rosenbergii to the pathogen and have a better understanding of the host defence mechanism. Two cDNA libraries, one of WSSV-challenged M. rosenbergii and a normal control one, were sequenced using the Illumina HiSeq™ 2000 platform. After de novo assembly and clustering of the unigenes from both libraries, 63,584 standard unigenes were generated with a mean size of 698bp and an N50 of 1137bp. We successfully annotated 35.31% of all unigenes by using BLASTX program (E-value <10-5) against NCBI non-redundant (Nr), Swiss-Prot, Kyoto Encyclopedia of Genes and Genome pathway (KEGG) and Orthologous Groups of proteins (COG) databases. Gene Ontology (GO) assessment was conducted using BLAST2GO software. Differentially expressed genes (DEGs) by using the FPKM method showed 8443 host genes were significantly up-regulated whereas 5973 genes were significantly down-regulated. The differentially expressed immune related genes were grouped into 15 animal immune functions. The present study showed that WSSV infection has a significant impact on the transcriptome profile of M. rosenbergii's hepatopancreas, and further enhanced the knowledge of this host-virus interaction. Furthermore, the high number of transcripts generated in this study will provide a platform for future genomic research on freshwater prawns.

Yellow head virus infection in black tiger shrimp reveals specific interaction with granule-containing hemocytes and crustinPm1 as a responsive protein

Yellow head virus (YHV) causes acute infections and mass mortality in black tiger shrimp culture. Our study aims to investigate molecular interaction between YHV and circulating hemocytes of Penaeus monodon at early infection. Total shrimp hemocytes were isolated by Percoll gradient centrifugation and identified by flow cytometric analysis. At least three types of hemocyte cells were identified as hyaline, semi-granular, and granular hemocytes. Experimental infection of YHV in shrimp culture demonstrated drastic changes in total and each hemocyte cell counts. Immunohistochemistry analysis demonstrated interaction and replication of YHV mainly with the granule-containing hemocytes and little to none in hyaline cell. These granule-containing hemocytes are proposed to be YHV targets providing the first line of defense to viral infection. Protein expression profiling of granule-containing hemocytes revealed several immune-responsive proteins including antimicrobial protein crustins (crustinPm1 and crustinPm4), alpha-2-macroglobulin, and kazal-type serine proteinase inhibitor. During an early phase of YHV infection at 6 hpi crustinPm1 illustrated a significant increase of mRNA and protein expression level in plasma. The results suggest that an antimicrobial crustinPm1 may participate in shrimp defense mechanism against YHV, especially on the granule-containing hemocytes.

Impact of ammonia exposure on coagulation in white shrimp, Litopenaeus vannamei

Ammonia (un-ionized plus ionized ammonia as nitrogen), the end product of protein catabolism, is produced by decomposing organic matter. In aquaculture, shrimp are commonly exposed to high concentrations of ammonia that induces immunological and histological changes. The purpose of this study was to evaluate the effects on hemolymph coagulation time, transglutaminase (TG) activity as well as TG and clottable protein (CP) genes expressions in Litopenaeus vannamei when exposed to ambient ammonia-nitrogen (N) at 0, 1, 5, and 10mg/L for 0, 2, and 7 days. The actual concentrations in control and tests solution were 0.001, 1.15, 5.11, and 11.68mg/L for ammonia-N, and 7×10(-5), 0.080, 0.357, and 0.815mg/L for NH3-N (unionized ammonia). Delayed coagulation time following exposure to 5 and 10mg/L of ambient ammonia-N for 7 days, and increased transglutaminase (TG) activity following exposure to 5 and 1mg/L of ambient ammonia-N for 2 and 7 days, respectively, were observed. Downregulated TG expression and upregulated clottable protein (CP) expression in the hemocytes of L. vannamei exposed to 10 and 5mg/L of ambient ammonia-N for 2 and 7 days, respectively, were shown. These results indicated that ambient ammonia-N (>5mg/L) and NH3-N (>0.357mg/L) interrupted coagulation and down-regulated TG gene expression in L. vannamei, which caused ecotoxicity on immune deficiencies and may contribute the increased susceptibility to infection by pathogens.