Antiviral defense in shrimp: from innate immunity to viral infection

MicroRNA sequencing analysis reveals immune responses in hepatopancreas of Fenneropenaeus penicillatus under white spot syndrome virus infection

White Spot Disease is one of the most harmful diseases of the red tail shrimp, which can cause devastating economic losses due to the highest mortality up to 100% within a few days. MicroRNAs (miRNAs) are large class of small noncoding RNAs with the ability to post-transcriptionally repress the translation of target mRNAs. MiRNAs are considered to have a significant role in the innate immune response of crustaceans, particularly in relation to antiviral defense mechanisms. Numerous crustacean miRNAs have been verified to be required in host immune defense against viral infection, however, till present, the miRNAs functions of F. penicillatus defense WSSV infection have not been studied yet. Here in this study, for the first time, miRNAs involved in the F. penicillatus immune defense against WSSV infection were identified using high-throughput sequencing platform. A total of 432 miRNAs were obtained including 402 conserved miRNAs and 30 novel predicted miRNAs. Comparative analysis between the WSSV-challenged group and the control group revealed differential expression of 159 microRNAs in response to WSSV infection. Among these, 48 were up-regulated and 111 were down-regulated. Ten candidate MicroRNAs associated with immune activities were randomly selected for qRT-PCR analysis, which confirming the expression profiling observed in the MicroRNA sequencing data. As a result, most differentially expressed miRNAs were down-regulated lead to increase the expression of various target genes that mediated immune reaction defense WSSV infection, including genes related to signal transduction, Complement and coagulation cascade, Phagocytosis, and Apoptosis. Furthermore, the genes expression of the key members in Toll and Imd signaling pathways and apoptotic signaling were mediated by microRNAs to activate host immune responses including apoptosis against WSSV infection. These results will help to understand molecular defense mechanism against WSSV infection in F. penicillatus and to develop an effective WSSV defensive strategy in shrimp farming.

Identification of immune-responsive circular RNAs in shrimp (Litopenaeus vannamei) upon yellow head virus infection

Circular RNAs (circRNAs) are a subclass of non-coding RNAs (ncRNAs) formed through a process known as back-splicing. They play a crucial role in the genetic regulation of various biological processes. Currently, circRNAs have been identified as participants in the antiviral response within mammalian cells. However, circRNAs in shrimp infected with the yellow head virus (YHV) remain largely unexplored. Therefore, this study aims to identify circRNAs in the hemocytes of Litopenaeus vannamei during YHV infection. We discovered 358 differentially expressed circRNAs (DECs), with 177 of them being up-regulated and 181 down-regulated. Subsequently, eight DECs, including circ_alpha-1-inhibitor 3, circ_CDC42 small effector protein 2, circ_hemicentin 2, circ_integrin alpha V, circ_kazal-type proteinase inhibitor, circ_phenoloxidase 3, circ_related protein rab-8B, and circ_protein toll-like, were randomly selected for analysis of their expression patterns during YHV infection using qRT-PCR. Furthermore, the circRNAs' characteristics were confirmed through PCR, RNase R treatment, and Sanger sequencing, all of which were consistent with the features of circRNAs. These findings contribute to a better understanding of circRNAs' involvement in the antiviral response in shrimp.

Efficacy of White Spot Syndrome Virus Protein VP28-Expressing Chlorella vulgaris as an Oral Vaccine for Shrimp

The white spot syndrome virus (WSSV) is the causative agent of white spot disease, which kills shrimp within a few days of infection. Although WSSV has a mortality rate of almost 100% and poses a serious threat to the shrimp farming industry, strategies for its prevention and treatment are extremely limited. In this study, we examined the efficacy of VP28, a recombinant WSSV protein expressed in Chlorella vulgaris (C. vulgaris), as an oral shrimp vaccine. When compared with the control group, in which WSSV had a cumulative mortality of 100%, shrimp treated with 5% VP28-expressing C. vulgaris in their feed only had a 20% cumulative mortality rate 12 days after the WSSV challenge. When compared with the nonvaccinated group, the transcription of anti-lipopolysaccharide factor, C-type lectin, and prophenoloxidase genes, which are involved in shrimp defense against WSSV infection, was upregulated 29.6 fold, 15.4 fold, and 11.5 fold, respectively. These findings highlight C. vulgaris as a potential host for industrial shrimp vaccine production.

Scavenger receptor B2, a type III membrane pattern recognition receptor, senses LPS and activates the IMD pathway in crustaceans

The immune deficiency (IMD) pathway is critical for elevating host immunity in both insects and crustaceans. The IMD pathway activation in insects is mediated by peptidoglycan recognition proteins, which do not exist in crustaceans, suggesting a previously unidentified mechanism involved in crustacean IMD pathway activation. In this study, we identified a Marsupenaeus japonicus B class type III scavenger receptor, SRB2, as a receptor for activation of the IMD pathway. SRB2 is up-regulated upon bacterial challenge, while its depletion exacerbates bacterial proliferation and shrimp mortality via abolishing the expression of antimicrobial peptides. The extracellular domain of SRB2 recognizes bacterial lipopolysaccharide (LPS), while its C-terminal intracellular region containing a cryptic RHIM-like motif interacts with IMD, and activates the pathway by promoting nuclear translocation of RELISH. Overexpressing shrimp SRB2 in Drosophila melanogaster S2 cells potentiates LPS-induced IMD pathway activation and diptericin expression. These results unveil a previously unrecognized SRB2-IMD axis responsible for antimicrobial peptide induction and restriction of bacterial infection in crustaceans and provide evidence of biological diversity of IMD signaling in animals. A better understanding of the innate immunity of crustaceans will permit the optimization of prevention and treatment strategies against the arising shrimp diseases.

White feces syndrome in Penaeus vannamei is potentially an Enterocytozoon hepatopenaei (EHP) associated pathobiome origin of Vibrio spp

White feces syndrome (WFS) is a commercially important disease in Penaeus vannamei (whiteleg shrimp) farming. The aetiology beyond the white or golden white midgut with mediocre growth performance producing a floating mass of white fecal strings in WFS-affected shrimp farms remains uncharted. To give WFS a perception of pathobiome, healthy P. vannamei shrimps were subjected to an enteric microsporidian Enterocytozoon hepatopenaei (EHP) infection along with Vibrio harveyi and V. alginolyticus in different combinations. Immune responses in haemolymph (total haemocyte count (THC), prophenoloxidase activity (proPO), respiratory burst activity (RBA), superoxide dismutase activity (SOD) and catalase activity (CAT)), plasma biochemical changes (aspartate aminotransferase (AST), alanine aminotransferase (ALT) and alkaline phosphatase (ALP)) and digestive enzymes activity (alpha-amylase (AMY), lipase (LIP) and protease (PRO)) were assessed in the challenged shrimps at 5, 10 and 15 days post-infection (dpi). The microbial interactions between the EHP and Vibrio spp. have led to the formation of WFS in the challenged shrimps. The histological sections of the hepatopancreas revealed the presence of EHP along with colonized bacterial masses, leading to the formation of aggregated transformed microvilli (ATM) structures and increased sloughing of lipid vacuoles into the tubule lumen. A significantly decreased THC and increased proPO levels, dysregulated antioxidant system, prominent hepatic damage, reduced energy metabolism and higher lipid production were the key records supporting that EHP-associated WFS in P. vannamei is due to the pathobiome.

Single von Willebrand factor C-domain protein confers host defense against white spot syndrome virus by functioning as a pattern recognition receptor in Macrobrachium nipponense

The single von Willebrand factor C-domain proteins (SVWCs), also known as Vago, are primarily found in arthropods. Their expression was induced by nutritional status, bacterial and viral infections. Despite the prominence of SVWCs in antiviral immunity, the detailed molecular mechanisms remain poorly explained. SVWC has been proposed to elicit antiviral activities through its function as an interferon analog. In contrast, herein, we illustrate that an SVWC homolog from Macrobrachium nipponense (MnSVWC) confers host defense against white spot syndrome virus (WSSV) and covert mortality nodavirus (CMNV) as a pattern recognition receptor (PRR). qRT-PCR analyses demonstrated that the expression of MnSVWC was enhanced upon WSSV infection in all detected tissues, including gills, nerve cords, and hemocytes. Coating WSSV with recombinant MnSVWC (rMnSVWC) promoted the phagocytic activity of hemocytes and subsequent clearance of invasive WSSV from the prawn. On the other hand, the knockdown of MnSVWC with RNAi improved the proliferation ability of WSSV and CMNV in the prawn. Analysis of ELISA and Co-immunoprecipitation (Co-IP) showed that rMnSVWC could bind WSSV by interacting with the vesicle proteins VP26 and VP28. Co-IP analysis verified the interaction between MnSVWC and calmodulin, which implies a vesicle protein-SVWC-calmodulin-clathrin-dependent mechanism underlying the hemocyte-mediated phagocytosis against WSSV. Subsequently, MnSVWC was recognized to activate the expression of transcription factor STAT and an interferon-stimulating gene Viperin, illustrating its involvement in modulating humoral immunity via activation of the JAK/STAT pathway after WSSV infection. These findings indicate that MnSVWC could bind to WSSV as a PRR and participate in the promotion of hemocyte-mediated phagocytosis and the activation of the JAK/STAT pathway in prawns.

Recent progress in the use of purple non-sulfur bacteria as probiotics in aquaculture

The use of probiotics in aquaculture is widely recognized as an ecological and cost-effective approach to raising healthy, pathogen-tolerant aquatic animals, including fish and shrimp. In particular for shrimp, probiotics are viewed as a promising countermeasure to the recent severe damage to the shrimp industry by bacterial and viral pathogens. Purple non-sulfur bacteria (PNSB) are Gram-negative, non-pathogenic bacteria with wide application potential in agriculture, wastewater treatment, and bioenergy/biomaterials production. In aquaculture, lactic bacteria and Bacillus are the major probiotic bacteria used, but PNSB, like Rhodopseudomonas and Rhodobacter, are also used. In this review, we summarize the previous work on the use of PNSB in aquaculture, overview the previous studies on the stimulation of innate immunity of shrimp by various probiotic microorganisms, and also share our results in the probiotic performance of Rhodovulum sulfidophilum KKMI01, a marine PNSB, which showed a superior effect in promotion of growth and stimulation of immunity in shrimp at a quite low concentration of 1 × 10³ cfu (colony forming unit)/ml in rearing water.

WSSV exploits AMPK to activate mTORC2 signaling for proliferation by enhancing aerobic glycolysis

AMPK plays significant roles in the modulation of metabolic reprogramming and viral infection. However, the detailed mechanism by which AMPK affects viral infection is unclear. The present study aims to determine how AMPK influences white spot syndrome virus (WSSV) infection in shrimp (Marsupenaeus japonicus). Here, we find that AMPK expression and phosphorylation are significantly upregulated in WSSV-infected shrimp. WSSV replication decreases remarkably after knockdown of Ampkα and the shrimp survival rate of AMPK-inhibitor injection shrimp increases significantly, suggesting that AMPK is beneficial for WSSV proliferation. Mechanistically, WSSV infection increases intracellular Ca2+ level, and activates CaMKK, which result in AMPK phosphorylation and partial nuclear translocation. AMPK directly activates mTORC2-AKT signaling pathway to phosphorylate key enzymes of glycolysis in the cytosol and promotes expression of Hif1α to mediate transcription of key glycolytic enzyme genes, both of which lead to increased glycolysis to provide energy for WSSV proliferation. Our findings reveal a novel mechanism by which WSSV exploits the host CaMKK-AMPK-mTORC2 pathway for its proliferation, and suggest that AMPK might be a target for WSSV control in shrimp aquaculture.

Transcriptome-wide identification and characterization of the Macrobrachium rosenbergii microRNAs potentially related to immunity against non-O1 Vibrio cholerae infection

Non-O1 Vibrio cholerae, a member of the Vibrio family, could cause gastrointestinal infection of Macrobrachium rosenbergii and result in significant economic losses. However, few studies on microRNA immunity related to non-O1 V. cholerae infection of M. rosenbergii. The aim of this study was to elucidate the mechanism of miRNA in the potential immune response of M. rosenbergii. to non-O1 V. cholerae MSVC-GY01 infection by transcriptome sequencing. Following quality screening, the control group received 10, 616, 712 clean reads, whereas the infected group received 9,727,616. The miRNA sequences in the two samples are extremely consistent and have a length of roughly 23 nt. In all, 871 known miRNAs were discovered, with 279 differentially expressed miRNAs (DEMs). Meanwhile, 62 novel miRNAs were predicted, including 43 DEMs. In order to understand the immune-related biological functions of DEMs, target genes were predicted. Pathway function annotation analysis showed that non-O1 V. cholerae affected the NOD-like receptor signaling pathway, RIG-I-like receptor signaling pathway, and Toll-like receptor signaling pathway, suggesting that miRNAs in the hepatopancreas play a key role in immune responses to pattern recognition receptors. Twelve DEMs were randomly selected for Quantitative Real-time PCR (qRT-PCR). Overall, the expression trends of qRT-PCR were consistent with the sequencing results. These findings corroborate the immunomodulatory function of miRNA in M. rosenbergii against non-O1 V. cholerae infection and provide guidance for the prevention and treatment of related illnesses.

The immunostimulatory effects of Theobroma cacao L. pod husk extract via injection and dietary administrations on Macrobrachium rosenbergii and its resistance against Lactococcus garvieae

The extract from Theobroma cacao L, pod husk served as the immunostimulant to enhance the immunity and resistance against Lactococcus garvieae of Macrobrachium rosenbergii. In this study, we employed the injection method and dietary administration method to determine the effect of cocoa pod husk (CPH) on M. rosenbergii. The non-specific immune parameters and disease resistance were evaluated after the prawn injected with 1 μg prawn^-1 CPH extract (C1), 3 μg prawn^-1 CPH extract (C3), and 5 μg prawn^-1 CPH extract (C5) for 1, 3, and 7 days. The results showed a significant increase of total haemocyte count (THC), differential haemocyte count (DHC), phenoloxidase (PO) activity, respiratory bursts (RBs), and phagocytic activity and clearance efficiency to L. garvieae. The non-specific immune parameters, physiological parameters, and disease resistance and growth performance were evaluated after the prawn fed with 1 g kg^-1 CPH extract diet (CD1), 3 g kg^-1 CPH extract diet (CD3) and 5 g kg^-1 CPH extract diet (CD5). The results showed a significant increase in all immune parameters and showed a significant decrease in physiological parameters. No significant difference was observed in growth performance of prawn fed with the CPH containing diet. Both injection and dietary method showed a significant increase in disease resistance against to L. garvieae. We therefore recommend that CPH extract can be used as a immunostimulant for prawn by dietary administration to regulate immune responses, and carbohydrate metabolism lead to enhance resistance against pathogen.

PvML1 suppresses bacterial infection by recognizing LPS and regulating AMP expression in shrimp

Toll and Toll-like receptors (TLRs) play essential roles in the innate immunity of Drosophila and mammals. Recent studies have revealed the presence of Toll-mediated immune signaling pathways in shrimp. However, the recognition and activation mechanism of Toll signaling pathways in crustaceans remain poorly understood due to the absence of key recognition molecules, such as peptidoglycan recognition proteins. Here, a novel MD2-related lipid-recognition (ML) member named PvML1 was characterized in Penaeus vannamei. We found that PvML1 shared a similar 3D structure with human MD2 that could specifically recognize lipopolysaccharides (LPS) participating in LPS-mediated TLR4 signaling. PvML1 was highly expressed in hemocytes and remarkably upregulated after Vibrio parahemolyticus challenge. Furthermore, the binding and agglutinating assays showed that PvML1 possessed strong binding activities to LPS and its key portion lipid A as well as Vibrio cells, and the binding of PvML1 with bacterial cells led to the agglutination of bacteria, suggesting PvML1 may act as a potential pathogen recognition protein upon interaction with LPS. Besides, coating V. parahemolyticus with recombinant PvML1 promoted bacterial clearance in vivo and increased the survival rate of bacterium-challenged shrimp. This result was further confirmed by RNAi experiments. The knockdown of PvML1 remarkably suppressed the clearance of bacteria in hemolymph and decreased the survival rate of infected shrimp. Meanwhile, the silencing of PvML1 severely impaired the expression of a few antimicrobial peptides (AMPs). These results demonstrated the significant correlation of bacterial clearance mediated by PvML1 with the AMP expression. Interestingly, we found that PvML1 interacted with the extracellular region of PvToll2, which had been previously shown to participate in bacterial clearance by regulating AMP expression. Taken together, the proposed antibacterial model mediated by PvML1 might be described as follows. PvML1 acted as a potential recognition receptor for Gram-negative bacteria by binding to LPS, and then it activated PvToll2-mediated signaling pathway by interacting with PvToll2 to eliminate invading bacteria through producing specific AMPs. This study provided new insights into the recognition and activation mechanism of Toll signaling pathways of invertebrates and the defense functions of ML members.

RNA-seq analysis revealing the immune response of Neocaridina denticulata sinensis gill to Vibrio parahaemolyticus infection

Vibrio parahaemolyticus causes serious economic losses to the shrimp farming industry. There is still a lack of adequate understanding of the changes in the overall response of N. denticulata sinensis caused by V. parahaemolyticus, particularly with respect to gill tissue, which is severely damaged by the pathogen. In this study, a total of 1358 differentially expressed genes were identified between the PBS control and Vibrio stimulation groups using transcriptome sequencing techniques. After further screening and analysis, many immune-related genes were obtained, involving lysosome pathway, metabolic process, chitin-binding protein, and serine protease family members. In addition, we randomly selected six DEGs in the lysosome pathway for qRT-PCR verification, and the results showed that their expression patterns were consistent with the RNA-seq. The results demonstrate the molecular regulation of the gill tissue response to V. parahaemolyticus infection in N. denticulata sinensis, contributing to the understand of the complex and efficient innate immune system and defense mechanisms in crustaceans.

Lysyl Oxidase-like Protein Recognizes Viral Envelope Proteins and Bacterial Polysaccharides against Pathogen Infection via Induction of Expression of Antimicrobial Peptides

Lysyl oxidases (LOXs) are copper-dependent monoamine oxidases, and they play critical roles in extracellular matrix (ECM) remodeling. The LOX and LOX-like (LOXL) proteins also have a variety of biological functions, such as development and growth regulation, tumor suppression, and cellular senescence. However, the functions of LOXLs containing repeated scavenger receptor cysteine-rich (SRCR) domains in immunity are rarely reported. In this study, we characterized the antiviral and antibacterial functions of a lysyl oxidase-like (LOXL) protein containing tandem SRCR domains in Marsupenaeus japonicus. The mRNA level of LoxL was significantly upregulated in the hemocytes and intestines of shrimp challenged using white spot syndrome virus (WSSV) or bacteria. After the knockdown of LoxL via RNA interference, WSSV replication and bacterial loads were apparently increased, and the survival rate of the shrimp decreased significantly, suggesting that LOXL functions against pathogen infection in shrimp. Mechanistically, LOXL interacted with the envelope proteins of WSSV or with lipopolysaccharide and peptidoglycan from bacteria in shrimp challenged using WSSV or bacteria, and it promoted the expression of a battery of antimicrobial peptides (AMPs) via the induction of Dorsal nuclear translocation against viral and bacterial infection. Moreover, LOXL expression was also positively regulated by Dorsal in the shrimp challenged by pathogens. These results indicate that, by acting as a pattern recognition receptor, LOXL plays vital roles in antiviral and antibacterial innate immunity by enhancing the expression of AMPs in shrimp.

Infection with white spot syndrome virus affects the microbiota in the stomachs and intestines of kuruma shrimp

Maintaining eubiosis of the gastrointestinal (GI) microbiota is essential for animal health. White spot syndrome virus (WSSV) is the most lethal viral pathogen because it causes extremely high mortality in shrimp farming. However, it remains poorly understood how WSSV infection affects the microbiota in different regions of the GI tract of shrimp. In the present study, we established an experimental model of kuruma shrimp (Marsupenaeus japonicus) infection with WSSV and then investigated the effects of WSSV infection on the microbiota in the cardiac stomach, pyloric stomach, and intestines using metataxonomics. We identified 34 phyla and 576 genera of bacteria collectively. At the phylum level, Proteobacteria and Firmicutes were the most abundant in all the three GI segments. The WSSV infection decreased microbial diversity to a different extent in the stomachs and in a time-dependent manner. The infection with WSSV affected the microbiota composition in the two stomachs, but not the intestines. Firmicutes increased significantly, while Actinobacteria, Bacteroidetes, and Cyanobacteria decreased in the two stomachs of the WSSV-infected shrimp. At the genus level, Trichococcus and Vibrio increased, but Bradyrhizobium and Roseburia decreased in the cardiac stomach of the WSSV-infected shrimp. Trichococcus and Photobacterium increased in the pyloric stomach. Although Vibrio showed a slight downward trend, Aliivibrio (formerly Vibrio) increased in the pyloric stomach. Thiothrix, Fusibacter, and Shewanella decreased in the pyloric stomach, but no significant differences in these genera were detected in the cardiac stomach. Analysis of the predicted functions of the GI microbiota indicated that the WSSV infection resulted in losses of some microbiota functions. The new information from this study may help better understand the bacteria-virus interaction in the GI tract of shrimp and other crustacean species, and inform pathogen prevention/control and sustainable aquaculture production.

Immunostimulation of shrimp through oral administration of silkworm pupae expressing VP15 against WSSV

White spot syndrome virus (WSSV) is one of the most concerning pathogens in penaeid shrimp and can cause severe loss in shrimp aquaculture worldwide. Among the WSSV structural proteins, VP15, a DNA-binding protein located in the WSSV nucleocapsid, is an antiviral protein candidate to protect kuruma shrimp (Marsupenaeus japonicus) from WSSV infection. We identified that the truncated VP15, VP15_(26-57), is responsible for the protective effect against the WSSV. This study attempts to develop an immunizing agent against WSSV using silkworm pupa as a delivery vector through oral administration. The VP15, VP15_(26-57), and SR11 peptide derived from VP15_(26-57) were expressed in silkworm pupae. Oral administration of feed mixed with the powdered pupae that expressed VP15-derived constructs enhanced the survivability of kuruma shrimp with an overall relative percent survival (RPS) higher than 70%. There is no death for the group receiving pupa/VP15_(26-57), and the RPS is 100%. In addition, we also investigated the relative mRNA expression levels of immune-related genes by qPCR at different time points. Our results indicate that the oral administration of pupa/VP15-derived products could provide a high protective effect against WSSV and be a practical approach for controlling WSSV in aquaculture.

Early responses in Penaeus vannamei during experimental infection with Enterocytozoon hepatopenaei (EHP) spores by injection and oral routes

Hepatopancreatic microsporidiosis caused by Enterocytozoon hepatopenaei (EHP) is associated with severe production losses in Penaeus vannamei farming. Early responses in P. vannamei experimentally infected with EHP was assessed in this study by feeding infected hepatopancreatic tissue and by injecting purified EHP spores (∼1 × 10⁵ Spores/shrimp). Immune responses to EHP infection were assessed in the haemolymph by analysing the total haemocyte count (THC), superoxide dismutase (SOD) activity, prophenoloxidase activity (proPO), respiratory burst activity (RBA), catalase activity (CAT), lysozyme activity (LYS) and Toll gene expression in hepatopancreas at 0, 6, 12, 24, 36, 48, 60 and 72 h post-infection (hpi). Experimental infection with EHP resulted in a significant (p < 0.05) reduction in the immune parameters such THC, CAT and LYS at 6, 24 and 24 hpi respectively while there was a significant increase (p < 0.05) in the levels of SOD, proPO and RBA at 6 hpi. The expression of the Toll gene was significantly upregulated (p < 0.05) after experimental infection with EHP from 6 hpi. These findings on immune responses in P. vannamei during EHP infection will assist in the development of suitable management measures to reduce the negative impacts of EHP in P. vannamei farming. This is the first report on early responses in P. vannamei during EHP infection.

Combined administration routes of marine yeasts enhanced immune-related genes and protection of white shrimp (Penaeus vannamei) against Vibrio parahaemolyticus

Antibiotic usage to control infectious diseases in shrimp aquaculture has led to serious problems on antimicrobial resistance. An alternative to mitigate this issue is the use of probiotics, which can be easily administered by feed and water. This study examines immunomodulatory and protective effects of the marine yeasts Debaryomyces hansenii CBS8339 (Dh) and Yarrowia lipolytica Yl-N6 (Yl) -alone and mixed-in white shrimp Penaeus vannamei post-larvae. Administration routes (fed and water alone or in combination), supplementation frequency and time elapsed after the last dietary supplement were tested on growth and gene expression of penaeidin, lectin, lysozyme, superoxide dismutase, catalase, and peroxidase, as well as survival upon Vibrio parahaemolyticus IPNGS16 challenge. Penaeidin and lectin genes were upregulated in post-larvae fed orally with Yl or combined Dh + Yl. Higher growth and survival for yeast supplementation treatments were observed compared to the control group, mainly when yeasts (Dh + Yl) and administration routes (feed and water) were combined. In conclusion, mixed yeast and combined administration routes improved growth and immunity against V. parahaemolyticus.

Double‐edged sword role of shrimp miRNA explains an evolutionary language between shrimp‐pathogen interactions that unties the knot of shrimp infection

Shrimp production, using a small‐scale enclosed pond system, is a rapidly growing aquaculture sector, which is valued around USD 18.30 billion in 2020. Intensified shrimp culture leads to the outbreak of transmissible diseases to eventually cause a huge loss in the production process and thus the economy. Studies on microRNA (miRNA) reveal that miRNA has an influential role in the host‐pathogen interaction during an infection. Recently, shrimp miRNA has been shown to help pathogen‐like viruses for their replication and infection. Several shrimp miRNAs were reported to be involved in enhancing host immunity against viral infection, especially white spot syndrome virus (WSSV) infection and Vibrio infection caused by bacterial species, whereas some shrimp miRNAs were reported to be hijacked by WSSV and to enhance the viral replication and establish the infection in shrimp. This gives an insight into the double‐edged sword role played by shrimp miRNA during host‐pathogen interaction. In future, this role could be employed against the virus to strengthen the shrimp culture. In this review, we discuss the role of shrimp miRNA and their mechanism(s) associated with the establishment of host‐pathogen interaction during infection, which will reveal the complexity associated with shrimp infection.

Characterization of the Gene Repertoire and Environmentally Driven Expression Patterns in Tanner Crab (Chionoecetes bairdi)

Tanner crab (Chionoecetes bairdi) is an economically important species that is threatened by ocean warming and bitter crab disease, which is caused by an endoparasitic dinoflagellate, Hematodinium. Little is known about disease transmission or its link to host mortality, or how ocean warming will affect pathogenicity or host susceptibility. To provide a transcriptomic resource for the Tanner crab, we generated a suite of RNA-seq libraries encompassing pooled hemolymph samples from crab displaying differing infection statuses and maintained at different temperatures (ambient (7.5˚C), elevated (10˚C), or decreased (4˚C)). After assembling a transcriptome and performing a multifactor differential gene expression analysis, we found genes influenced by temperature in relation to infection and detected some of those genes over time at the individual level using RNA-seq data from one crab. Biological processes associated with those genes include lipid storage, transcription, response to oxidative stress, cell adhesion, and morphogenesis. Alteration in lipid storage and transcription provide insight into how temperature impacts energy allocation in Hematodinium infected crabs. Alteration in expression patterns in genes associated with morphogenesis could suggest that hemocytes were changing morphology and/or type in response to temperature. This project provides insight into how Hematodinium infection could influence crab physiology as oceans warm.

Anti-lipopolysaccharide factor D from kuruma shrimp exhibits antiviral activity

Anti-lipopolysaccharide factors (ALFs) exhibit a potent antimicrobial activity against a broad range of bacteria, filamentous fungi, and viruses. In previous reports, seven groups of ALFs (groups A-G) were identified in penaeid shrimp. Among them, group D showed negative net charges and weak antimicrobial activity. Whether this group has antiviral function is not clear. In this study, the ALF sequences of penaeid shrimp were analyzed, and eight groups of ALF family (groups A-H) were identified. The four ALFs including MjALF-C2, MjALF-D1, MjALF-D2, and MjALF-E2 from kuruma shrimp Marsupenaeus japonicus were expressed recombinantly in Escherichia coli, and the antiviral activity was screened via injection of purified recombinant ALFs into shrimp following white spot syndrome virus (WSSV) infection. Results showed that the expression of Vp28 (WSSV envelope protein) decreased significantly in the MjALF-D2-injected shrimp only. Therefore, MjALF-D2 was chosen for further study. Expression pattern analysis showed that MjAlf-D2 was upregulated in shrimp challenged by WSSV. The WSSV replication was detected in RNA, genomic DNA, and protein levels using VP28 and Ie1 (immediate-early gene of WSSV) as indicators in MjALF-D2-injected shrimp following WSSV infection. Results showed that WSSV replication was significantly inhibited compared with that in the rTRX- or PBS-injected control groups. After knockdown of MjAlf-D2 in shrimp by RNA interference, the WSSV replication increased significantly in the shrimp. All these results suggested that MjALF-D2 has an antiviral function in shrimp immunity, and the recombinant ALF-D2 has a potential application for viral disease control in shrimp aquaculture.

Probiotic Effects of a Marine Purple Non-Sulfur Bacterium, Rhodovulum sulfidophilum KKMI01, on Kuruma Shrimp (Marsupenaeus japonicus)

Purple non-sulfur bacteria (PNSB) are used as probiotics in shrimp aquaculture; however, no studies have examined the probiotic effects of PNSB in shrimp at the gene expression level. In this study, we examined the effects of a marine PNSB, Rhodovulum sulfidophilum KKMI01, on the gene expression of kuruma shrimp (Marsupenaeus japonicus). Short-term (3 days) effects of R. sulfidophilum KKMI01 on the gene expression in shrimp were examined using small-scale laboratory aquaria experiments, while long-term (145 days) effects of R. sulfidophilum KKMI01 on the growth performance and gene expression were examined using 200-ton outdoor aquaria experiments. Gene expression levels were examined using qRT-PCR. Results of the short-term experiments showed the upregulation of several molting-related genes, including cuticle proteins, calcification proteins, and cuticle pigment protein, suggesting that PNSB stimulated the growth of shrimp. The upregulation of several immune genes, such as prophenoloxidase, antimicrobial peptides, and superoxide dismutase, was also observed. In the 145-day outdoor experiments, the average body weight at harvest time, survival rate, and feed conversion ratio were significantly improved in PNSB-treated shrimp, and upregulation of molting and immune-related genes were also observed. When PNSB cells were added to the rearing water, the effective dosage of PNSB was as low as 10³ cfu/mL, which was more than a million times dilution of the original PNSB culture (2–3 × 10⁹ cfu/mL), indicating that R. sulfidophilum KKMI01 provides a feasible and cost-effective application as a probiotic candidate in shrimp aquaculture.

Effects of Lactobacillus pentosus combined with Arthrospira platensis on the growth performance, immune response, and intestinal microbiota of Litopenaeus vannamei

Litopenaeus vannamei is one of the most productive shrimp species in the world. However, shrimp farming is suffering from adverse environmental conditions and disease outbreaks. Typically, Lactobacillus pentosus and Arthrospira platensis are used as substitutes for some antibiotics. In the present study, we assessed the effects of dietary supplements along with living bacteria or cell-free extracts of L. pentosus combined with A. platensis on the growth performance, immune response, intestinal microbiota, and disease resistance of L. vannamei against Vibrio alginolyticus. Shrimp fed L. pentosus live bacteria combined with A. platensis showed the best growth performance and lowest feed conversion rate. The supplementation diet with L. pentosus live bacteria and A. platensis could significantly enhance the trypsin activity in shrimp after the feeding trial. Given the lowest feed conversion rate in shrimp fed L. pentosus live bacteria combined with A. platensis, we reasonably speculated that the decrease in feed conversion rate may be related to the increase in trypsin activity. In addition, dietary cell-free extracts of L. pentosus combined with A. platensis enhanced the expression of immune-related genes after the feeding trial or challenge test. Moreover, results of the bacterial challenge test indicated that the shrimp fed cell-free extracts of L. pentosus combined with A. platensis diet resulted in the highest survival rate, which suggested that cell-free extracts of L. pentosus and A. platensis could improve the disease resistance against V. alginolyticus by up-regulating the expressions of immune-related genes. Dietary L.pentosus or A. platensis, or their combination, reduced the abundance of harmful bacteria, including Proteobacteria in shrimp intestine, which suggested that L. pentosus and A. platensis could improve the growth performance and health of shrimp by regulating the structure of the intestinal microbiota. The findings of this study demonstrated that L. pentosus live bacteria and A. platensis exerted synergistic effects on the growth performance and digestion in shrimp, while cell-free extracts of L. pentosus and A. platensis showed synergistic effects on the immune response and disease resistance of shrimp against V. alginolyticus.

Transcriptome profiling reveals the novel immunometabolism-related genes against WSSV infection from Fenneropenaeus merguiensis

The white spot syndrome virus (WSSV) has been considered a serious threat to shrimp aquaculture. Besides, the activation of cell metabolism as an immune reaction to the virus is now recognized as a piece of the pivotal puzzle of the antiviral responses. Hence, this study explores the relationship between metabolic gene expression and antiviral responses in shrimp using transcriptome analysis. The RNA-seq libraries of Fenneropenaeus merguensis hemocytes after WSSV challenge at early (6 hpi) and late (24 hpi) stages of infection were analyzed to identify differentially expressed genes (DEGs) that the WSSV subverted the expression. One-hundred-thirty-three DEGs that were expressed in response to WSSV infection at both stages were identified. Based on the GO annotation, they were related to innate immunity and metabolic pathway. The expression correlation between "full term" (NGS) and qRT-PCR of 16 representative DEGs is shown. Noticeably, the expression profiles of all the selected metabolic genes involved in glucose metabolism, lipid metabolism, amino acid metabolism, and nucleotide metabolism showed a specific correlation between NGS and qRT-PCR upon WSSV infection. Of these, we further characterized the function related to the WSSV response of glutamine: fructose-6-phosphate aminotransferase (FmGFAT), the rate-limiting enzyme of the hexosamine biosynthesis pathway, which was found to be up-regulated at the late stage of WSSV infection. Suppression of FmGFAT by RNA interference resulted in postponing the death of WSSV-infected shrimp and reduction of viral copy number. These results suggested that the FmGFAT is linked between metabolic change and WSSV responses in shrimp, where the virus-induced metabolic rewiring hijack biological compounds and/or energy sources to benefit the viral replication process.

Process optimization for fermented siwu decoction by multi-index-response surface method and exploration of the effects of fermented siwu decoction on the growth, immune response and resistance to Vibrio harveyi of Pacific white shrimp (Litopenaeus vannamei)

The purpose of this study was to explore the optimal fermentation technology of Chinese herbal medicine formula-Siwu Decoction and the effects of fermented Siwu Decoction (FSW) on the growth performance, immune response, intestinal microflora and anti microbial ability of Litopenaeus vannamei. Response to surface methodology (RSM) was used to optimize the fermentation process of Siwu Decoction. The optimal fermentation conditions were obtained as follows: inoculation amount of mixed strains was 4.5%, fermentation time was 36 h, and the ratio of material to liquid was 20%. A total of 1260 shrimps were selected and divided into seven groups, three in parallel in each group. The dietary level of each group was as follows: Control （No additions）, USW1 (0.2% unfermented herbal medicine), USW2 (0.5% unfermented herbal medicine), USW3 (0.8% unfermented herbal medicine), FSW1 (0.2% fermented herbal medicine), FSW2 (0.5% fermented herbal medicine), FSW3 (0.8% fermented herbal medicine). The immune response and antioxidant defense ability of hemocytes and intestine were measured at 21 and 42 days of feeding and the intestinal flora and growth performance were measured at 42 days of feeding, after that, a 7-day challenge test against Vibrio harveyi was conducted. The results showed that fermented Siwu Decoction significantly improved the growth performance and body composition of Litopenaeus vannamei; significantly increased the total number of hemocytes, phagocytic activity, antibacterial activity and bacteriolytic activity of Litopenaeus vannamei, and improved the antioxidant activity of Litopenaeus vannamei; the addition of fermented Siwu Decoction significantly increased the gene expression level of hemocytes and intestinal tract of Litopenaeus vannamei, and improved the antioxidant activity of Litopenaeus vannamei. The abundance of Bacillus increased, while the abundance of Vibrio decreased. After Vibrio harveyi challenge, the cumulative mortality of FSW group was significantly lower than that of control group. Fermented Siwu Decoction may be a potential physiological enhancer in aquaculture, and can be widely used in aquaculture.

Effects of nonylphenol exposure on histological changes, apoptosis and time-course transcriptome in gills of white shrimp Litopenaeus vannamei

Nonylphenol (NP) is considered as one of the persistent organic pollutants (POPs) in the environment. Pacific white shrimp Litopenaeus vannamei is the predominant species in China, which is frequently affected by environmental pollutants. However, potential toxicity mechanism of NP in shrimp has not been comprehensively studied. To explore the physiological changes and molecular mechanism involved in NP exposure of shrimp, we analyzed histological alterations, apoptosis and transcriptional responses of L.vannamei subjected to NP. Results indicated that significant changes in the histoarchitecture of the gills were observed after NP exposure for 3, 12 and 48 h. Apoptosis was also detected in a time-dependent manner. Numerous differentially expressed genes (DEGs) were obtained at 3 h, 12 h and 48 h after exposure. On the basis of the expression patterns over the time course, these DEGs were classified into 12 clusters. GO and KEGG enrichment analysis of these DEGs was carried out and a dynamic and global view was obtained in shrimp after NP exposure on a transcriptome level. In addition, 15 DEGs involved in immune response, apoptosis, DNA repair, osmoregulation etc. were selected for qRT-PCR validation. The expression patterns of these DEGs kept a well consistent with the high-throughput data at different timepoints, which confirmed the accuracy and reliability of the transcriptome data. All the results demonstrated that NP exposure might lead to impairments of biological functions in gills, alter immune and antioxidant response, compromise DNA repair and anti-apoptosis abilities of shrimp, cause severe histopathological changes and eventually trigger apoptosis. The present study enriched the information on the toxicity mechanism of crustaceans in response to NP exposure.

Effect of dietary Xiao-Chaihu-Decoction on growth performance, immune response, detoxification and intestinal microbiota of pacific white shrimp (Litopenaeus vannamei)

Xiao-Chaihu-Decoction (XCHD), a classical traditional Chinese medicine with diverse biological activities, is widely applied to prevent and treat many human diseases. Effects of dietary XCHD on growth performance, immune response, detoxification system, intestinal microbiota and resistance against aflatoxin B1(AFB₁) of Litopenaeus vannamei was studied. Four isonitrogenous and isolipidic diets were formulated to contain 0, 1, 2, and 5 g/kg (control, XCHD1, XCHD2 and XCHD3) of XCHD, respectively. Seven hundred and eighty shrimp (1.16 ± 0.09 g) were assigned randomly to 12 tanks (400 L, three tanks each group, 65 shrimp in each tank) for 6 weeks. After sampling, 25 shrimp from each tank were selected for a 2-week AFB₁ (2500 μg/kg) challenge experiment. The results indicated that the final weight, weight gain and specific growth rate in XCHD2 and XCHD3 groups were significantly increased compared to control. The protease, amylase, superoxide dismutase (SOD), glutathione s-transferase (GST), sulfotransferase (SULT) activities, total antioxidant capacity (T-AOC) and glutathione (GSH) contents in hepatopancreas were significantly increased in XCHD3 groups and the expressions of immune-related genes (Toll, Dorsal and Cru) in hepatopancreas were significantly up-regulated in XCHD2 and XCHD3 groups. High-throughput sequencing analysis revealed that the abundance of Proteobacteria decreased and the abundances of Bacteroidetes increased in XCHD2 and XCHD3 groups. Additionally, AFB₁ challenge experiments showed that AFB₁ caused histological damage to the hepatopancreas and significantly increased the levels of malondialdehyde (MDA) and protein carbonylation (PC) in hepatopancreas as well as the activities of alanine aminotransferase (ALT) and aspartate aminotransferase (AST). Nevertheless, XCHD could effectively alleviated the growth toxicity, immunosuppression and macromolecular damage caused by AFB₁ to shrimp by inhibiting the Phase I enzyme and enhancing Phase II enzyme and antioxidant system.

Ubiquitination as an Important Host-Immune Response Strategy in Penaeid Shrimp: Inferences From Other Species

Shrimp aquaculture is an essential economic venture globally, but the industry faces numerous challenges, especially pathogenic infections. As invertebrates, shrimp rely mainly on their innate immune system for protection. An increasing number of studies have shown that ubiquitination plays a vital role in the innate immune response to microbial pathogens. As an important form of posttranslational modification (PTM), both hosts and pathogens have exploited ubiquitination and the ubiquitin system as an immune response strategy to outwit the other. This short review brings together recent findings on ubiquitination and how this PTM plays a critical role in immune modulation in penaeid shrimps. Key findings inferred from other species would help guide further studies on ubiquitination as an immune response strategy in shrimp-pathogen interactions.

FOXO regulates the expression of antimicrobial peptides and promotes phagocytosis of hemocytes in shrimp antibacterial immunity

Invertebrates rely on innate immunity, including humoral and cellular immunity, to resist pathogenic infection. Previous studies showed that forkhead box transcription factor O (FOXO) participates in mucosal immune responses of mammals and the gut humoral immune regulation of invertebrates. However, whether FOXO is involved in systemic and cellular immunity regulation in invertebrates remains unknown. In the present study, we identified a FOXO from shrimp (Marsupenaeus japonicus) and found that it was expressed at relatively basal levels in normal shrimp, but was upregulated significantly in shrimp challenged by Vibrio anguillarum. FOXO played a critical role in maintaining hemolymph and intestinal microbiota homeostasis by promoting the expression of Relish, the transcription factor of the immune deficiency (IMD) pathway for expression of antimicrobial peptides (AMPs) in shrimp. We also found that pathogen infection activated FOXO and induced its nuclear translocation by reducing serine/threonine kinase AKT activity. In the nucleus, activated FOXO directly regulated the expression of its target Amp and Relish genes against bacterial infection. Furthermore, FOXO was identified as being involved in cellular immunity by promoting the phagocytosis of hemocytes through upregulating the expression of the phagocytotic receptor scavenger receptor C (Src), and two small GTPases, Rab5 and Rab7, which are related to phagosome trafficking to the lysosome in the cytoplasm. Taken together, our results indicated that FOXO exerts its effects on homeostasis of hemolymph and the enteric microbiota by activating the IMD pathway in normal shrimp, and directly or indirectly promoting AMP expression and enhancing phagocytosis of hemocytes against pathogens in bacteria-infected shrimp. This study revealed the different functions of FOXO in the mucosal (local) and systemic antibacterial immunity of invertebrates.

Identification and characterization of a Toll-like receptor gene from Macrobrachium nipponense

Outbreaks of infectious disease in shrimp pose a serious threat to shrimp agriculture worldwide. Shrimp lack adaptive immunity and depend only on innate immunity as a defense system against infectious disease. Toll-like receptors (TLR) are reported to play a critical role in the innate immune system. In this study, we identified a Toll-like receptor gene of a species of freshwater shrimp, Macrobrachium nipponense, designated MnToll, for the first time. The sequence of MnToll encoded 935 residues arranged as 10 leucine-rich repeat (LRR) domains, a leucine-rich repeat C-terminal (LRR CT) domain and a Toll/interleukin-1 receptor (TIR) domain and displayed 90% amino acid similarity to previously identified TLRs (Toll 1 and 2) of Macrobrachium rosenbergii. We additionally evaluated mRNA expression of MnToll in various tissues, including heart, gills, stomach, digestive gland, ventral nerve cord, antennal gland and muscle. Following infection with a viral pathogen, white spot syndrome virus (WSSV), MnToll expression was significantly upregulated between 12 and 72 h. Our data collectively suggest that the newly identified MnToll gene belongs to the TLR family in shrimp and is potentially involved in innate host defense, especially against WSSV.

Differential Apoptotic Responses of Hemocyte Subpopulations to White Spot Syndrome Virus Infection in Fenneropenaeus chinensis

The apoptosis of hemocytes plays an essential function in shrimp immune defense against pathogen invasions. In order to further elucidate the differential apoptotic responses of the granulocytes and the hyalinocytes in Fenneropenaeus chinensis post WSSV infection, the characteristics of apoptotic dynamics and viral proliferation in total hemocytes and hemocyte subpopulations were respectively investigated in the present work. The results showed that the apoptotic rate of hemocytes changed significantly, and the apoptosis-related genes also showed significantly differential expression responses during WSSV infection. Interestingly, we found that the apoptotic rate of virus-negative hemocytes was significantly higher than that of virus-positive hemocytes in the early stage of WSSV infection, while it was significantly lower than that of virus-positive cells in the middle and late infection stages. The difference of apoptosis between virus-positive and virus-negative hemocytes seems to be an important way for the WSSV to destroy the host’s immune system and facilitate the virus spread at different infection stages. It was further found that the apoptosis rate of granulocytes was always significantly higher than that of hyalinocytes during WSSV infection, indicating that granulocytes have a stronger apoptotic response to WSSV infection. Moreover, a higher viral load was detected in granulocytes, and the density of granulocytes decreased more rapidly post WSSV infection, indicating that the granulocytes are more susceptible and vulnerable to WSSV infection compared with the hyalinocytes. These results collectively demonstrated that the apoptotic response in shrimp hemocytes was significantly influenced by the WSSV infection, and the differential apoptotic response of granulocytes and hyalinocytes to WSSV indicated the differences of antiviral mechanisms between the two hemocyte subpopulations.

Penaeidins restrict white spot syndrome virus infection by antagonizing the envelope proteins to block viral entry

Emerging studies have indicated that some penaeidins restrict virus infection; however, the mechanism(s) involved are poorly understood. In the present study, we uncovered that penaeidins are a novel family of antiviral effectors against white spot syndrome virus (WSSV), which antagonize the envelope proteins to block viral entry. We found that the expression levels of four identified penaeidins from Litopenaeus vannamei, including BigPEN, PEN2, PEN3, and PEN4, were significantly induced in hemocytes during the early stage of WSSV infection. Knockdown of each penaeidin in vivo via RNA interference resulted in elevated viral loads and rendered shrimp more susceptible to WSSV, while the survival rate was rescued via the injection of recombinant penaeidins. All penaeidins, except PEN4, were shown to interact with several envelope proteins of WSSV, and all four penaeidins were observed to be located on the outer surface of the WSSV virion. Co-incubation of each recombinant penaeidin with WSSV inhibited virion internalization into hemocytes. More importantly, we found that PEN2 competitively bound to the envelope protein VP24 to release it from polymeric immunoglobulin receptor (pIgR), the cellular receptor required for WSSV infection. Moreover, we also demonstrated that BigPEN was able to bind to VP28 of WSSV, which disrupted the interaction between VP28 and Rab7 – the Rab GTPase that contributes to viral entry by binding with VP28. Taken together, our results demonstrated that penaeidins interact with the envelope proteins of WSSV to block multiple viral infection processes, thereby protecting the host against WSSV.

Transcriptomic analysis of Procambarus clarkii affected by "Black May" disease

Each year from April to May, high mortality rates are reported in red swamp crayfish (Procambarus clarkii) cultured in Jiangsu and other regions, in China, and this phenomenon has come to be known as “Black May” disease (BMD). Therefore, in order to investigate the possible causes of this disease, this study gathered BMD-affected P. clarkii samples and performed transcriptome analysis on hepatopancreas, gill, and muscle tissues. A total of 19,995,164, 149,212,804, and 222,053,848 clean reads were respectively obtained from the gills, muscle, and hepatopancreas of BMD-affected P. clarkii, and 114,024 unigenes were identified. The number of differentially expressed genes (DEGs) in gill, muscle, and hepatopancreas was 1703, 964, and 476, respectively. GO and KEGG enrichment analyses of the DEGs were then conducted. Based on KEGG pathway enrichment analysis, the most significantly differentially expressed pathways were mainly those involved with metabolism, human disease, and cellular processes. Further analysis of the significantly DEGs revealed that they were mainly related to the mitochondrial-mediated apoptosis pathway and that the expression of these DEGs was mostly down-regulated. Moreover, the expression of genes related to immune and metabolism-related pathways was also significantly down-regulated, and these significantly-inhibited pathways were the likely causes of P. clarkii death. Therefore, our results provide a basis for the identification of BMD causes.

Effects of Yu-Ping-Feng polysaccharides (YPS) on the immune response, intestinal microbiota, disease resistance and growth performance of Litopenaeus vannamei

A 28-day feeding trial was conducted to investigate the effects of Yu-Ping-Feng polysaccharides (YPS) containing Astragalus polysaccharides (APS), Atractylodes macrocephala polysaccharides (AMP) and Saposhnikoviae polysaccharides (SPS) on the immune response, intestinal microbiota, disease resistance and growth performance of Litopenaeus vannamei. Seven hundred and twenty shrimp (3.04 ± 0.33 g) were fed the following diets: Control, YPS1 (0.13% APS + 0.0325% AMP + 0.0325% SPS), YPS2 (0.13% APS + 0.0325% AMP + 0.065% SPS) and YPS3 (0.13% APS + 0.0325% AMP+0.0975% SPS). After 14 and 28 days of feeding, the immune responses of hemocytes and intestine were measured. Intestinal microbiota and growth performance were measured after 28 days of feeding, after that, a 7-day challenge test against Vibrio harveyi was conducted. A significant (P < 0.05) increase of the total haemocyte count (THC), phagocytic activity, antibacterial activity and phenoloxidase (PO) activity was observed in shrimp fed YPS diets compared to the control. Also, dietary YPS supplementation particularly YPS3 group significantly increased the expressions of immune-related genes in the hemocytes and intestine. Regarding the intestinal microbiota, the microbial diversity and richness decreased and functional genes associated with short-chain fatty acids metabolism increased in YPS groups. After Vibrio harveyi challenge, the cumulative mortality in YPS groups was significantly lower than that of the control. Besides, dietary YPS had no significant effect on growth performance of shrimp (P > 0.05). The present results suggested that YPS could be considered as potential prebiotics for aquaculture farmed shrimp.

Environmental rearing conditions are key determinants of changes in immune gene expression patterns in shrimp midgut

The super-intensive BioFloc Technology (BFT) system has been highlighted as a promising eco-friendly alternative to the traditional shrimp rearing systems. To gain insight into the impact of environmental rearing conditions on shrimp intestinal immunity, we assessed the expression profile of key immunological genes in the midgut of Litopenaeus vannamei shrimp reared in two contrasting culture systems: the indoor super-intensive BFT and the outdoor intensive Green-Water System (GWS). From the 30 analyzed genes, the expression levels of 25 genes were higher in the midgut of shrimp reared in BFT than in GWS. The main functional categories represented in BFT-shrimp were the prophenoloxidase-activating system, immune signaling, antimicrobial peptides, and RNA interference pathway. Comparatively, only the RNAi pathway gene Dicer-1 (LvDcr1) was more expressed in animals from the GWS group. However, despite the differences in gene expression, the total midgut bacterial abundance was similar between the experimental groups. Altogether, our results suggest that the microbial-rich environment offered by the BFT system can be acting as an immunostimulant by altering the immune expression profile of the midgut. The gene expression level found in GWS animals could be related to the chronic presence of the IMNV in the Brazilian Northeast. Knowing the effects of environmental stress factors on the intestinal immune defenses can provide an in-depth understanding of the relationship between cultivated shrimp and the major pathogens affecting the shrimp industry.

The krüppel-like factor of Penaeus vannamei negatively regulates transcription of the small subunit hemocyanin gene as part of shrimp immune response

Hemocyanin is a multifunctional respiratory glycoprotein, which has also been implicated in other biological functions in shrimp. Moreover, recent studies have revealed that hemocyanin is also involved in a broad range of immune-related activities in shrimp. However, in spite of the considerable interest in unraveling the reasons behind the multiple immune-related functions of hemocyanin, little is known about its transcriptional regulation. Here, DNA pull-down and Liquid Chromatography - Tandem Mass Spectrometry (LC-MS/MS) analyses were used to isolate and identify the putative transcription factor(s) that are involved in the transcriptional regulation of the small subunit hemocyanin gene of Penaeus vannamei (PvHMCs). Krüppel-like factor (designated PvKruppel), a zinc finger transcription factor homolog in P. vannamei, was identified among the putative transcription factors, while bioinformatics analysis revealed the presence of Krüppel-like factor binding site (KLF motif) on the core promoter region of PvHMCs. Mutational analysis and electrophoretic mobility shift assay (EMSA) confirmed that PvKruppel could bind to the KLF motif on the core promoter region of PvHMCs. Moreover, in response to lipopolysaccharide (LPS), Vibrio parahaemolyticus and white spot syndrome virus (WSSV) challenge, transcript levels of PvKruppel and PvHMCs were negatively correlated. Furthermore, overexpression of PvKruppel significantly reduced the promoter activity of PvHMCs, while PvKruppel knockdown by RNA interference or lipopolysaccharides (LPS) stimulation resulted in a significant increase in the transcript level of PvHMCs. Taken together, our present study provides mechanistic insights into the transcriptional regulation of PvHMCs by PvKruppel during shrimp immune response to pathogens.

The Complete Genome of an Endogenous Nimavirus (Nimav-1_LVa) From the Pacific Whiteleg Shrimp Penaeus (Litopenaeus) Vannamei

White spot syndrome virus (WSSV), the lone virus of the genus Whispovirus under the family Nimaviridae, is one of the most devastating viruses affecting the shrimp farming industry. Knowledge about this virus, in particular, its evolution history, has been limited, partly due to its large genome and the lack of other closely related free-living viruses for comparative studies. In this study, we reconstructed a full-length endogenous nimavirus consensus genome, Nimav-1_LVa (279,905 bp), in the genome sequence of Penaeus (Litopenaeus) vannamei breed Kehai No. 1 (ASM378908v1). This endogenous virus seemed to insert exclusively into the telomeric pentanucleotide microsatellite (TAACC/GGTTA)n. It encoded 117 putative genes, with some containing introns, such as g012 (inhibitor of apoptosis, IAP), g046 (crustacean hyperglycemic hormone, CHH), g155 (innexin), g158 (Bax inhibitor 1 like). More than a dozen Nimav-1_LVa genes are involved in the pathogen-host interactions. We hypothesized that g046, g155, g158, and g227 (semaphorin 1A like) were recruited host genes for their roles in immune regulation. Sequence analysis indicated that a total of 43 WSSV genes belonged to the ancestral/core nimavirus gene set, including four genes reported in this study: wsv112 (dUTPase), wsv206, wsv226, and wsv308 (nucleocapsid protein). The availability of the Nimav-1_LVa sequence would help understand the genetic diversity, epidemiology, evolution, and virulence of WSSV.

Apoptosis of hemocytes is associated with the infection process of white spot syndrome virus in Litopenaeus vannamei

Previous studies have demonstrated that white spot syndrome virus (WSSV) could induce hemocytes apoptosis in shrimps, however the inter-relationship between apoptotic process and the WSSV infection status is still currently underexplored. In the present work, the apoptosis and the viral proliferation in hemocytes of Litopenaeus vannamei were simultaneously investigated post WSSV infection by two-color immunofluorescence flow cytometry and real-time quantitative PCR. The apoptotic hemocytes of WSSV-infected shrimp was significantly increased at 12 h post infection (hpi), whereas underwent a slight decline at 24 hpi subsequently. Since 24 hpi, the apoptotic rate of hemocytes in the WSSV-infected shrimp exhibited a rapid and significant increase, and reached the peak level at 48 hpi with the ratio of 18.1 ± 2.0%. Meanwhile, the percentage of WSSV-infected hemocytes and WSSV copies in hemocytes significantly increased at 24 hpi and maintained at a high level afterwards. With the rapid increase of hemocytes apoptosis, hemocyte density in hemolymph decreased dramatically to less than 20% of the mean value of control. Co-localization assay showed that the apoptotic WSSV-infected hemocytes occupied the dominant proportion of total apoptotic hemocytes, which reached the peak at 48 hpi with 12.6 ± 1.5%. The expression profiles of seven pro-apoptotic genes and two apoptosis-inhibiting genes showed significant differential responses at different stages of WSSV infection, reflecting the interplay between the virus and the host immune response. Our results demonstrated that the apoptotic response of shrimp hemocytes could be significantly influenced by the WSSV infection process, which might provide an insight into deeper relationships between viral infection and apoptosis.

Evolutionary adaptation analysis of immune defense and hypoxia tolerance in two closely related Marsupenaeus species based on comparative transcriptomics

Kuruma shrimp, a major farmed shrimp species in the world, includes two cryptic or sibling species, Form I (Marsupenaeus japonicus) and Form II (Marsupenaeus pulchricaudatus). Due to the lack of genomic resources, little is known about the molecular mechanisms associated with immune defense and hypoxia tolerance. Here, we sequenced the transcriptomes of two closely related Marsupenaeus species and compared genomic divergence. This study obtained 77049 and 84561 unigenes with N50 values of 1281bp and 1244bp for M. japonicus and M. pulchricaudatus, respectively, and 5036 pairs of putative orthologs were identified between two Marsupenaeus species. Estimation of Ka/Ks ratios indicated that 165 orthologous genes may be under positive selection (Ka/Ks > 0.5), including 49 pairs with a Ka/Ks ratio >1. According to the peak of synonymous rates, the divergence time between M. japonicus and M. pulchricaudatus was about 0.26-0.69 Mya. These positively selected orthologous genes related to the immune process mainly comprised single VWC domain protein, legumain, ras-related C3 botulinum, caspase, C-type lectin and were enriched in functions related to immune (Toll-like receptor and PI3K-Akt signaling) and hypoxia signaling (HIF-1 signaling and VEGF signaling). In this study, dozens of caspase-like unigenes were screened from two Marsupenaeus transcriptomes. Among these, the PjCaspase orthologous gene was subjected to positive selection (Ka/Ks = 1.22), which had different secondary and three-dimensional structure prediction. Based on the single copy caspase gene, eight populations of Marsupenaeus species were divided into two phylogeographic lineages from the East and South China. We characterized the transcriptomes of the two Marsupenaeus species and obtained several key orthologs associated with immune defense and hypoxia tolerance, which provides new insights into the immunity and genetic divergence of the two varieties. Moreover, this study will facilitate further comparative genomic studies of the two varieties.

Alginate from Sargassum siliquosum Simultaneously Stimulates Innate Immunity, Upregulates Immune Genes, and Enhances Resistance of Pacific White Shrimp (Litopenaeus vannamei) Against White Spot Syndrome Virus (WSSV)

Although alginate is known as an immunostimulant in shrimp, the comprehensive and simultaneous study on its activity to resolve the relationship of the hematological parameters, upregulation of immune-related gene expression, and resistance to pathogen has not been found in shrimp. We performed experiments to evaluate the effect and mechanism of alginate from S. siliquosum on Pacific white shrimp immune system. Hematological parameters were examined after oral administration of Na alginate in the shrimp. White spot syndrome virus (WSSV) was injected to the shrimp at 14 days, and its copy number was examined quantitatively (qRT-PCR). Immune-related gene expression was evaluated by qRT-PCR. Alginate increased some hematological immune parameters of shrimp. Before WSSV infection, expression levels of Toll and lectin genes were upregulated. The lectin gene were upregulated post infection, and the Toll gene in all the treatments were downregulated, except the shrimps fed with alginate at 6.0 g kg-1 at 48 h post infection (hpi). The shrimps fed with alginate at 6.0 g kg-1 were the most resistant and gave the least WSSV copy number at 48 hpi. Resistance of shrimps fed the alginate-supplemented diets against WSSV was significantly higher compared to that of the control treatment with 56% and 10% of survival rates, respectively. Oral administration of alginate did not affect the growth and total protein plasma. At 120 h post challenge, alginate treatment at 6.0 g kg-1 exhibited the highest survival rate. It is concluded that oral administration of alginate enhanced the innate immunity by upregulating immune-related gene expression. Consequently, the enhancement of the shrimp innate immunity improves the resistance against WSSV infection.

The Two NF-κB Pathways Regulating Bacterial and WSSV Infection of Shrimp

The outbreak of diseases ordinarily results from the disruption of the balance and harmony between hosts and pathogens. Devoid of adaptive immunity, shrimp rely largely on the innate immune system to protect themselves from pathogenic infection. Two nuclear factor-κB (NF-κB) pathways, the Toll and immune deficiency (IMD) pathways, are generally regarded as the major regulators of the immune response in shrimp, which have been extensively studied over the years. Bacterial infection can be recognized by Toll and IMD pathways, which activate two NF-κB transcription factors, Dorsal and Relish, respectively, to eventually lead to boosting the expression of various antimicrobial peptides (AMPs). In response to white-spot-syndrome-virus (WSSV) infection, these two pathways appear to be subverted and hijacked to favor viral survival. In this review, the recent progress in elucidating microbial recognition, signal transduction, and effector regulation within both shrimp Toll and IMD pathways will be discussed. We will also highlight and discuss the similarities and differences between shrimps and their Drosophila or mammalian counterparts. Understanding the interplay between pathogens and shrimp NF-κB pathways may provide new opportunities for disease-prevention strategies in the future.

Comparative transcriptomic analysis of Marsupenaeus japonicus hepatopancreas in response to Vibrio parahaemolyticus and white spot syndrome virus

Vibrio parahaemolyticus and white spot syndrome virus (WSSV) are pathogens that cause epidemics in kuruma shrimp (Marsupenaeus japonicus) during aquaculture, resulting in severe economic losses to local farmers. To characterise the mechanisms of the molecular responses to V. parahaemolyticus and WSSV infection in M. japonicus, the transcriptome of hepatopancreas was sequenced using next-generation sequencing after infection. A total of 29,180 unigenes were assembled, with an average length of 1,151 bp (N50 = 1,951 bp). After BLASTX searching against the Nr database (E-value cut-off = 10^-5), 15,176 assembled unigenes remained, with 3,039 and 1,803 differentially expressed transcripts identified in the V. parahaemolyticus- and WSSV-infected groups, respectively. Of these, 1466 transcripts were up-regulated and 1573 were down-regulated in V. parahaemolyticus-infected shrimps, and 970 transcripts were up-regulated and 833 were down-regulated in the WSSV-infected shrimps. Additionally, 761 transcripts were differentially expressed in both V. parahaemolyticus- and WSSV-infected shrimps. Several known immune-related genes including caspase 4, integrin, crustin, ubiquitin-conjugating enzyme E2, C-type lectin, and α₂-macroglobulin were among the differentially expressed transcripts. These results provide valuable information for characterising the immune mechanisms of the shrimp responses of to V. parahaemolyticus andWSSV infection.

The Penaeus stylirostris densovirus capsid interacts with Litopenaeus vannamei troponin I

The Penaeus stylirostris densovirus (PstDNV) (also known as infectious hypodermal and hematopoietic necrosis virus, IHHNV), a very small DNA virus, is a major shrimp pathogen. The PstDNV genome encodes only two nonstructural proteins and one capsid protein. This virus is thus an ideal, simple model for the investigation of virus-host interactions. To explore the role of the PstDNV capsid in viral infections, a yeast two-hybrid (Y2H) cDNA library was constructed based on Pacific white shrimp, Litopenaeus vannamei mRNA. The Y2H library was then screened, using the PstDNV capsid protein as bait. We identified a host protein that interacted strongly with the PstDNV capsid as L. vannamei troponin I (LvTnI). An in vitro co-immunoprecipitation experiment further supported this interaction. In addition, an in vivo neutralization experiment showed that the vaccination with anti-LvTnI significantly reduced PstDNV copies in PstDNV-challenged shrimp, indicating that the interaction between the PstDNV capsid and cellular LvTnI is essential for PstDNV infection. This result has important implications for our understanding of the mechanisms by which PstDNV infects shrimp.

Aquatic animal viruses mediated immune evasion in their host

Viruses are important and lethal pathogens that hamper aquatic animals. The result of the battle between host and virus would determine the occurrence of diseases. The host will fight against virus infection with various responses such as innate immunity, adaptive immunity, apoptosis, and so on. On the other hand, the virus also develops numerous strategies such as immune evasion to antagonize host antiviral responses. Here, We review the research advances on virus mediated immune evasions to host responses containing interferon response, NF-κB signaling, apoptosis, and adaptive response, which are executed by viral genes, proteins, and miRNAs from different aquatic animal viruses including Alloherpesviridae, Iridoviridae, Nimaviridae, Birnaviridae, Reoviridae, and Rhabdoviridae. Thus, it will facilitate the understanding of aquatic animal virus mediated immune evasion and potentially benefit the development of novel antiviral applications.

Litopenaeus vannamei attenuates white spot syndrome virus replication by specific antiviral peptides generated from hemocyanin

Recent studies have shown that hemocyanin plays immune-related functions apart from its canonical respiratory function. While shrimp hemocyanin is found to generate antimicrobial peptides, antiviral related peptides have not been reported. In the present study, the serum of white spot syndrome virus (WSSV) infected Litopenaeus vannamei analyzed by two-dimensional gel electrophoresis, revealed 45 consistently down-regulated protein spots and 10 up-regulated protein spots. Five of the significantly up-regulated spots were identified as hemocyanin derived peptides. One of the five peptides, designated LvHcL48, was further characterized by analyzing its primary sequence via Edman N-terminal sequencing, C-terminal sequencing and amino acid sequence alignment. LvHcL48 was found to be a 79 amino acid fragment (aa584-662) from the C-terminal domain of L. vannamei hemocyanin protein (ADZ15149). Both in vivo and in vitro functional studies revealed that LvHcL48 has immunological activities, as recombinant LvHcL48 protein (rLvHcL48) significantly inhibited the transcription of the WSSV genes wsv069 and wsv421 coupled with a significant reduction in WSSV copy numbers. Further analysis showed that LvHcL48 could interact with the WSSV envelope protein 28 (VP28). Our present data therefore reveals the generation of an antiviral hemocyanin derived peptide LvHcL48 from WSSV infected shrimp, which binds to the envelope protein VP28 of WSSV.

c-Jun regulates the promoter of small subunit hemocyanin gene of Litopenaeus vannamei

Hemocyanin (HMC) is a respiratory glycoprotein, which also plays multifunctional non-specific innate immune defense functions in shrimp. However, the transcriptional regulatory mechanisms of the hemocyanin gene expression have not been reported. In the present study, we cloned a 4324 bp fragment of small subunit hemocyanin (HMCs) gene of Litopenaeus vannamei including the 5'-flanking region, from upstream 2475 bp to downstream 1849 bp (exon 1-intron 1-exon 2) by genome walking method. Four deletion constructs were then generated and their promoter activity assessed using the luciferase reporter system. Interestingly, we identified an alternative promoter (+1516/+1849 bp) located in exon 2, which has stronger promoter activity than the full-length or the other constructs. Bioinformatics analyses revealed that the alternative promoter region contains two conserved binding sites of the transcription factor c-Jun. Mutational analysis and electrophoretic mobility shift assay showed that Litopenaeus vannamei c-Jun (Lvc-Jun) binds to the region +1582/+1589 bp and +1831/+1837 bp of the alternative promoter. Furthermore, overexpression of Lvc-Jun significantly increased the alternative promoter activity, while co-transfection with dsRNA-Lvc-Jun significantly reduced the alternative promoter activity of HMCs. Taken together, our present data indicate that the transcription factor Lvc-Jun is essential for the transcriptional regulation of the HMCs gene expression.

Thymosins participate in antibacterial immunity of kuruma shrimp, Marsupenaeus japonicus

Thymosins β are actin-binding proteins that play a variety of different functions in inflammatory responses, wound healing, cell migration, angiogenesis, and stem cell recruitment and differentiation. In crayfish, thymosins participate in antiviral immunology. However, the roles of thymosin during bacterial infection in shrimp remain unclear. In the present study, four thymosins were identified from kuruma shrimp, Marsupenaeus japonicus, and named as Mjthymosin2, Mjthymosin3, Mjthymosin4, and Mjthymosin5 according the number of their thymosin beta actin-binding motifs. Mjthymosin3 was selected for further study because its expression level was the highest in hemocytes. Expression analysis showed that Mjthymosin3 was upregulated in hemocytes after challenged by Vibrio anguillarum or Staphylococcus aureus. The recombinant Mjthymosin3 protein could inhibit the growth of certain bacteria in an in vitro antibacterial test. Mjthymosins could facilitate external bacterial clearance in shrimp, and were beneficial to shrimp survival post V. anguillarum or S. aureus infection. The results suggested that Mjthymosins played important roles in the antibacterial immune response of kuruma shrimp.

Transfection of crayfish hematopoietic tissue cells

Transfection is a powerful tool useful for studying gene function. Establishing transfection methods that enable highly efficient DNA uptake has become increasingly important. The crayfish hematopoietic tissue (Hpt) cell cultures have been proven to be suitable for studies on immunity and cell differentiation in crustaceans including shrimps, but no efficient gene transfer and expression method is available for these cells. Here we report a novel and highly efficient DNA transfection system based on electroporation. This method depends on a recombinant plasmid with the promoter from white spot syndrome virus immediate-early gene wsv249. This plasmid could be introduced into primary cells and efficiently express foreign genes by electroporation. By optimizing different electroporation parameters, more than 30% transfection efficiency could be achieved with the relative viability of cells around 50%. This is the first report of gene introduction to crayfish Hpt cells and will be useful for the expanding our research on crustacean immunity.

Comparative transcriptomic analysis of crab hemocytes in response to white spot syndrome virus or Vibrio alginolyticus infection

To assess the immune response of hemocytes to white spot syndrome virus (WSSV) or Vibrio alginolyticus infection in the mud crab Scylla paramamosain, a transcriptome analysis was performed. We report the analysis of 45131 transcripts from S. paramamosain hemocytes by de novo assembly. A comparison with GenBank protein and nucleotide sequences identified 33699 genes as previously known. The length distribution of the genes was 8147 genes ≥200 bp, 4714 genes ≥300 bp, and 3517 genes ≥2000 bp. A total of 21579 simple sequence repeats (SSRs) were found in the transcriptomic dataset, including 9% monomers, 53.34% dimers and 32.55% trimers. A total of 13172 and 5087 differentially expressed transcripts were found in the V. alginolyticus-infected group and WSSV-infected group, respectively. Of these, 5920 transcripts were up-regulated and 7252 were down-regulated in the V. alginolyticus-infected crabs and 2302 transcripts were up-regulated and 2785 were down-regulated in the WSSV-infected crabs. Additionally, 3096 transcripts were differentially expressed simultaneously in the V. alginolyticus-infected crabs and the WSSV-infected crabs. Several known immune-related genes such as heat shock protein, Janus kinase, STAT, relish, caspase, Ca²⁺-transporting ATPase and lysosomal alpha-mannosidase were found among the differentially expressed transcripts. Transcription and its regulation were significant biological processes, and ATP binding and zinc ion binding were significant molecular functions. This is the first report of comparative transcriptomic analysis of crab hemocytes in response to WSSV or V. alginolyticus infection. These findings will contribute to our understanding of the immune response to WSSV and V. alginolyticus infection in crustaceans.

Eriocheir sinensis microRNA-7 targets crab Myd88 to enhance white spot syndrome virus replication

MicroRNAs (miRNAs) are non-coding RNAs that regulate gene expression at the posttranscriptional level. In this study, the function of microRNA-7 (miR-7) in host-virus interaction was investigated. Replication of White spot syndrome virus (WSSV) was enhanced with the overexpression of miR-7 and inhibited with the downregulation of miR-7 by using anti-miRNA oligonucleotide AMO-miR-7. The target gene of miR-7 was predicted using bioinformatics methods. Results showed that crab myeloid differentiation factor 88 (Myd88) could be targeted by miR-7. When the expression of Myd88 was knocked down by sequence-specific siRNA, WSSV copies in crabs were significantly increased. Further findings revealed that knockdown of Myd88, Tube, or Pelle inhibited the expressions of interleukin enhancer-binding factor 2 homolog (ILF2) and interleukin-16-like gene (IL-16L). While ILF2 was silenced, IL-16L expression was inhibited. The overexpression of miR-7 inhibited the expressions of ILF2 and IL-16L. Moreover, when ILF2 or IL-16L was silenced, WSSV copies in crabs were increased. Thus, the upregulated expression of miR-7 during WSSV challenge suppressed the host Myd88-ILF2-(IL-16L) signaling pathway in crabs and enhanced WSSV replication. Our study indicated that WSSV utilized crab miR-7 to enhance virus replication during infection.