Dietary seaweed (Enteromorpha) polysaccharides improves growth performance involved in regulation of immune responses, intestinal morphology and microbial community in banana shrimp Fenneropenaeus merguiensis

The present study was conducted to evaluate the effects of marine polysaccharides from seaweed Enteromorpha on growth performance, immune responses, intestinal morphology and microbial community in the banana shrimp Fenneropenaeus merguiensis. Two thousand and four hundred juvenile shrimps with an average body weight of 2.18 ± 0.06 g were fed for 42 d with diets containing different levels of Enteromorpha polysaccharides (EPS): 0 (control), 1, 2 and 3 g/kg as treatment groups, each of group was replicated three times with two hundred shrimps per replicate. Dietary supplementation of 1 g/kg EPS showed a consistent improvement in the final weight, weight gain, average daily gain rate (ADGR) and specific growth rate (SGR) (P < 0.05), while showed a decrease in the feed conversion ratio (FCR) of shrimp (P < 0.05). Besides, the total anti-oxidative capacity (T-AOC), superoxide dismutase (SOD), glutathione peroxidase (GPx), glutathione S-transferase (GST), lysozyme (Lyz), alkaline phosphatase (ALP), and phenoloxidase (PO) activities in hemolymph were enhanced by dietary supplementation of 1 g/kg EPS (P < 0.05), while it reduced the hemolymph MDA content (P < 0.05). Shrimp fed 1 g/kg EPS supplemented diets up-regulated FmLyz, FmSOD5 and FmCLAP gene expression level of hepatopancreas and gill (P < 0.05), and also improved the intestinal FmLC2, FmLyz, FmSOD5 and FmCLAP gene expression levels (P < 0.05). In addition, shrimp fed diets containing 1 g/kg EPS increased the villus width (P < 0.05) and resulted in a higher villus surface area (P < 0.05). According to 16S rRNA sequencing results, dietary supplementation of 1 g/kg EPS tended to increase the relative abundance of Firmicutes at phylum level (P = 0.07) and decrease the relative abundance of Vibrio at genus level (P = 0.08). There was a significant positive correlation between the relative abundance of Firmicutes and mRNA expression of intestinal immune-related genes (P < 0.05). These findings revealed that dietary 1 g/kg EPS could improve growth performance, enhance nonspecific immunity and modulate intestinal function of banana shrimp F. merguiensis.

Gill transcriptomes reveal involvement of cytoskeleton remodeling and immune defense in ammonia stress response in the banana shrimp Fenneropenaeus merguiensis

The banana shrimp, Fenneropenaeus merguiensis, is an important fishery species in the Indo-West Pacific region. As the shrimp is very sensitive to stressors such as ammonia stress in water, understanding the molecular mechanisms of stress tolerance in F. merguiensis is of pivotal importance for improving its farming performance. In the current study, by using the RNA sequencing platform and comparative transcriptomic analysis, we conducted a comprehensive study on the transcriptomic changes of F. merguiensis in response to ammonia stress. A total of 106,996 unique transcripts (or unigenes) with an average length of 672 bp and a N50 value of 1164 bp were recovered, and a large number of potential SSR loci in the transcriptome were identified. Totally, 55,529 transcripts can find significant hits when compared to known sequences in major databases including the nr, nt, SWISSPROT, GO, COG, and KEGG databases. Analysis of differential gene expression between the ammonia-challenged group and the control group revealed that 9190 annotated transcripts were differentially expressed upon ammonia exposure. Among them, 3712 were significantly induced while 5478 of them were repressed. Functional enrichment analysis of these differentially expressed genes further showed that 22 Gene Ontology terms and 62 KEGG pathways were significantly over-represented. Remarkably, many of the genes showing the largest magnitude of expression changes were related to cytoskeleton remodeling and immune response, highlighting the involvement of these biological processes in the ammonia stress response of F. merguiensis. Our study is the first comprehensive investigation on the transcriptomic response to ammonia stress in F. merguiensis. The genes and pathways identified here not only represent valuable genetic resources for development of molecular markers and genetic breeding studies, but open new avenues for studies on the molecular mechanisms of ammonia stress tolerance in penaeid shrimp.

De-novo transcriptome analysis of the banana shrimp (Fenneropenaeus merguiensis) and identification of genes associated with reproduction and development

The banana shrimp Fenneropenaeus merguiensis is a commercially important marine crustacean for world aquaculture and fisheries. Despite this, limited genetic information is available for it and many other penaeid shrimp species. Here we present the first in-depth analysis of the transcriptional content of 8 different tissues from the banana shrimp using RNA-Seq technologies. A total of over 1 million single-end and over 49 million paired-end reads were obtained from Roche 454FLX and illumina sequencing platforms, respectively, resulting in an assembly of 124,631 transcripts with an N50 of 1,332 and mean length of 514 nt. A total of 59,179 putative protein sequences obtained from the assembled transcripts were annotated using public protein sequence databases and assigned 20,430 BLAST hits, 16,866 GO terms and 13,304 KOG categories. Further analysis revealed a rich set of transcript sequences exhibiting homology with genes associated with reproduction, sex determination and development and distinguished the tissues responsible for this expression. This report adds a substantial contribution to the sequence data currently available for F. merguiensis, providing valuable resources for further research.

An alternative function of C-type lectin comprising low-density lipoprotein receptor domain from Fenneropenaeus merguiensis to act as a binding receptor for viral protein and vitellogenin

A diversity of C-type lectins (CTLs) was coming reported and they are known to participate in invertebrate innate immunity by act as pattern recognition receptor (PRR). In the present study, a unique CTL containing low-density lipoprotein receptor (LDLR) domain from Fenneropenaeus merguiensis (designated as FmLdlr) was cloned. Its sequence contained a single LDLR domain and one carbohydrate recognition domain (CRD) with a QAP motif putative for galactose-specific binding. The expression of FmLdlr was detected only in hemocytes of healthy shrimp. Its expression was significantly up-regulated by Vibrio parahaemolyticus or white spot syndrome virus (WSSV) challenge. The knockdown by FmLdlr dsRNA resulted in severe gene down-regulation. The gene silencing with pathogenic co-inoculation led to reduction of the median lethal time and increasing in the cumulative mortality including the remained WSSV in WSSV co-challenge group. Recombinant proteins of FmLdlr and two domains could agglutinate various bacterial strains which LDLR domain revealed the lowest activity. Only FmLdlr and CRD could enhance phagocytosis and encapsulation by hemocytes. Both FmLdlr and CRD except LDLR domain exhibited the antibacterial activity by inhibiting the growth of pathogenic V. parahaemolyticus in cultured medium and disk diffusion assay. Only FmLdlr and CRD could bind to WSSV proteins, envelope VP28, tegument VP39A and also capsid VP15, which FmLdlr had the higher binding affinity than that of CRD. Altogether, we concluded that FmLdlr contributed in shrimp immune defense through the main action of CRD in capable of bacterial agglutination, enhancing the phagocytosis and encapsulation, antimicrobial activity and binding to viral proteins. Interestingly, ELISA approach revealed that LDLR domain displayed the highest binding affinity to vitellogenin than whole molecule and CRD. We signified a new function of FmLdlr that it might presumably act as a receptor for vitellogenin transportation in hemolymph during vitellogenesis of shrimp.

FmLC6: An ultimate dual-CRD C-type lectin from Fenneropenaeus merguiensis mediated its roles in shrimp defense immunity towards bacteria and virus

C-type lectins are a member of pattern recognition receptors (PRRs) that can interact with pathogen-associated molecular patterns of invading microorganisms by using their conserved motifs in carbohydrate recognition domain (CRD). The binding can trigger various immune responses in both direct and indirect mechanisms. Hereby, an ultimate C-type lectin with dual CRDs each of which containing a different motif was identified from hepatopancreas of Fenneropenaeus merguiensis (mentioned as FmLC6). The full-length cDNA of FmLC6 consisted of 1148 bp comprising one 1005 bp open reading frame (ORF) encoding a signal peptide and a mature protein of 317 residues. FmLC6 was composed of two CRDs with a highly conserved QPD (Gln-Pro-Asp) motif and one variant EPQ (Glu-Pro-Gln) motif for illustrating the carbohydrate binding affinity. The transcription of FmLC6 was detected only in hepatopancreas of normal shrimp. After injection with pathogens or immunostimulants, the expression of FmLC6 was significantly up-regulated and reached the highest level at 12 h post-injection except with lipoteichoic acid challenge. The FmLC6 expression was severely suppressed by knockdown based-silencing. This gene silencing with co-injection by Vibrio parahaemolyticus caused increasing in cumulative mortality and reduction of the median lethal time. Purified recombinant proteins of an entire ORF and two individual CRDs of FmLC6 produced in Escherichia coli could induce a broad spectrum of microbial agglutination with calcium dependence. The agglutination induced by rFmLC6, rCRD1 and rCRD2 was suppressed by galactose plus mannose, galactose and mannose, respectively which this event was confirmed by the inhibition of hemagglutination. All three recombinant proteins possessed ability to inhibit the bacterial growth with a dose-response. Purified rFmLC6 could bind directly to white spot syndrome virus particles and also its recombinant proteins including VP15, VP39A and VP28 with different affinity. Altogether, these results indicate that FmLC6 acts as a PRR to recognize invading microorganisms and leads to mediating the immune response to cooperation in pathogenic elimination via the binding, agglutination and antimicrobial activity.

A mannose-specific C-type lectin from Fenneropenaeus merguiensis exhibited antimicrobial activity to mediate shrimp innate immunity

Being one type of pattern recognition receptors (PRRs), lectins exhibit a crucial role in the defense mechanism of invertebrates which are deficient in an adaptive immune system. A new C-type lectin called FmLC3 was isolated from hepatopancreas of Fenneropenaeus merguiensis by cloning approaches, RT-PCR and 5' and 3' RACE (rapid amplification of cDNA ends). A full-length cDNA of FmLC3 contains 607 bp with one open reading frame of 480bp, encoding a 159-amino acids peptide. The predicted primary structure of FmLC3 is composed of a signal peptide, a carbohydrate recognition domain with an EPN motif and one Ca²⁺ binding site-2, including a double-loop region assisted by two conserved disulfide linkages. FmLC3 had a molecular mass of 17.96kDa and pI of 4.92. In normal or unchallenged shrimp, the mRNA expression of FmLC3 was detected only in hepatopancreas whilst its native proteins were found in hemolymph, heart, stomach and intestine but not in the expressed tissue, indicating that after being synthesized in hepatopancreas, FmLC3 would be secreted to other tissues. The significant up-regulation of FmLC3 was manifested in shrimp challenged with Vibrio harveyi or white spot syndrome virus. After knockdown with gene-specific double-stranded RNA and following by co-pathogenic inoculation, the FmLC3 expression was severely suppressed with coherence of increasing in cumulative mortality and reduction of the median lethal time. Recombinant FmLC3 (rFmLC3) had agglutinating activity towards diverse bacterial strains in a Ca²⁺-dependent manner. Its activity was inhibited by lipopolysaccharide and mannose, implying that FmLC3 was mannose-binding C-type lectin. Moreover, rFmLC3 could bind directly to various microbial strains with Ca²⁺-requirement. Otherwise, rFmLC3 exhibited the antimicrobial activity by inhibiting effectively the microbial growth in vitro. All these results signified that FmLC3 might act as PRR to recognize with a broad specificity for diverse pathogens, and contribute in shrimp immune response via the agglutination, binding and antimicrobial activity.

Identification and function of penaeidin 3 and penaeidin 5 in Fenneropenaeus merguiensis

Antimicrobial peptides (AMPs) participate in immune defenses of invertebrate, vertebrate and plant species. As a kind of AMPs, penaeidins play important roles in innate immunity of shrimp. In this study, two penaeidin homologues termed FmPEN3 and FmPEN5 were cloned and identified from Fenneropenaeus merguiensis for the first time. The complete open reading frames (ORFs) of FmPEN3 and FmPEN5 were 216 bp and 240 bp, encoding 71 and 79 amino acids, respectively. Both FmPEN3 and FmPEN5 contain an N-terminal proline-rich domain (PRD) and a C-terminal cysteine-rich domain (CRD). The genome structure of FmPEN3 and FmPEN5 genes both consist of 2 exons and 1 intron. qPCR analysis showed that FmPEN3 was constitutively expressed but FmPEN5 transcripts were found only in hemocytes, gills, epidermis, nerve and pyloric cecum. The FmPEN3 and FmPEN5 expression were responsive to Vibrio parahaemolyticus and Micrococcus lysodeikticus infection and their transcription levels were downregulated by RNAi silencing of the transcription factors FmDorsal and FmRelish. In addition, recombinant proteins of FmPEN3 (rFmPEN3) and FmPEN5 (rFmPEN5) were successfully expressed in E. coli. The antibacterial assays revealed that rFmPEN3 and rFmPEN5 could inhibit the growth of M. lysodeikticus but only rFmPEN5 could inhibit the growth of V. parahaemolyticus in vitro. In summary, the results presented in this study indicated the functions of FmPEN3 and FmPEN5 played in anti-bacterial immunity of F. merguiensis, providing some insights into the function of AMPs in shrimp.

A unique lectin composing of fibrinogen-like domain from Fenneropenaeus merguiensis contributed in shrimp immune defense and firstly found to mediate encapsulation

In invertebrates, both fibrinogen-related proteins (FREPs) and C-type lectins are acknowledged to act as pattern recognition receptors (PRRs) to participate particularly in an innate immunity. Hereby, a unique C-type lectin designated as FmLFd was isolated from the hemocytes of Fenneropenaeus merguiensis. FmLFd contained one open reading frame which encoding a peptide of 312 amino acid residues and a signal peptide of 18 amino acids. The primary sequence of FmLFd was composed of a fibrinogen-like domain (Fd) with a Ca²⁺-binding site and possessing specificity to bind N-acetyl glucosamine (GlcNAc). The FmLFd transcripts were detected mainly in hemocytes of healthy shrimp. The expression of FmLFd was significantly up-regulated upon challenge shrimp with Vibrio parahaemolyticus and Vibrio harveyi which more potent than by white spot syndrome virus (WSSV). The knocking down shrimp with FmLFd double-stranded RNA caused dramatical gene down-regulation. The gene silencing with co-injection of pathogens resulted in reduction of the shrimp survival rate. Recombinant protein of FmLFd (rFmLFd) could agglutinate and bind directly to both Gram-negative and Gram-positive bacteria in a Ca²⁺-dependent manner and showed the sugar specificity to GlcNAc and bacterial saccharides; peptidoglycan (PGN), lipopolysaccharide (LPS) and lipoteichoic acid (LTA). Recombinant protein of Fd domain (rFd) displayed the lower activity and specificity only to PGN. The binding between recombinant proteins of FmLFd and its domain confirming by ELISA demonstrated that both rFmLFd and rFd could bind to PGN, LPS and LTA with the highest affinity respected to PGN including a less extent of rFd. Besides, rFmLFd but not rFd could bind to WSSV proteins with the highest binding affinity to capsid VP15 and decreasing in order to envelope VP28 and tegument VP39A, respectively. It was presumed that entire molecule of FmLFd exhibited the antimicrobial ability by inhibiting the growth of pathogenic V. parahaemolyticus and this action was not affected by GlcNAc. Otherwise, FmLFd, a lectin containing fibrinogen-like domain, was firstly reported to be capable of promoting encapsulation by hemocytes. Altogether, we concluded that FmLFd belonged to a FREP family indentified by the existence of a conserved fibrinogen-like domain with possessing an ability to bind GlcNAc. It was a new C-type lectin existed in F. merguiensis and might presumably act as a kind of PRRs to participate in the shrimp immune defense towards bacterial and viral pathogens.

Lipopolysaccharide- and β-1,3-glucan-binding protein from Fenneropenaeus merguiensis functions as a pattern recognition receptor with a broad specificity for diverse pathogens in the defense against microorganisms

In crustaceans, lipopolysaccharide- and β-1,3-glucan-binding protein (LGBP) plays an important role in innate immunity by mediating the recognition of pathogens to host cells. Hereby, LGBP was cloned from Fenneropenaeus merguiensis hepatopancreas. Its full-length cDNA (1280 bp) had an open reading frame of 1101 bp, encoding a peptide of 366 amino acids. The LGBP primary structure comprises a recognition motif for β-1,3-linkage of polysaccharides, two integrin binding motifs, a kinase C phosphorylation site and a bacterial glucanase motif. The LGBP mRNA was strongly expressed in hepatopancreas and significantly up-regulated to get the maximum at 12 h upon Vibrio harveyi challenge. Recombinant LGBP (rLGBP) could agglutinate Gram-negative and Gram-positive bacteria including yeast with Ca²⁺-dependence. V. harveyi agglutination induced by rLGBP was intensively inhibited by lipoteichoic acid, less in order were lipopolysaccharide, β-1,3-glucan and N-acetyl neuraminic acid. Western blotting revealed that rLGBP bound widely to Gram-negative and Gram-positive bacteria and also yeast. By ELISA quantification, rLGBP could bind to β-1,3-glucan better than to lipopolysaccharide and lipoteichoic acid. These findings suggest that LGBP may function as a receptor which recognizes invading diverse pathogens and contribute in F. merguiensis immune response.

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.

Research into the hemocyte immune response of Fenneropenaeus merguiensis under decapod iridescent virus 1 (DIV1) challenge using transcriptome analysis

The banana shrimp (Fenneropenaeus merguiensis) is a common cultural species worldwide. With the development of the shrimp farming industry, increasing number of diseases have emerged and cause huge impacts. Decapod iridescent virus 1 (DIV1) is a new virus of the family Iridoviridae isolated in China that causes very high mortality in shrimp. In this study, DIV1 and PBS were injected into two groups of shrimp, and hemocytes were collected for comparative transcriptomic analysis. We confirmed that F. merguiensis was the new host of DIV1 by nested PCR. A total of 100,759 unigenes were assembled from the control group and the DIV1 infected group, with an average length of 733.06 bp and N50 of 1136 bp. Significant hits were found in 21,465 unigenes compared to known sequences in major databases including COG (33.30%), GO (42.17%), KEGG (46.76%), KOG (61.37%), Pfam (66.90%), Swissprot (54.21%) and Nr (93.86%). A total of 1003 differentially expressed genes (DEGs) were identified, including 929 up-regulated genes and 74 down-regulated genes. Several known immune-related genes, including caspase, C-type lectin, Wnt5 and integrin, were among the differentially expressed transcripts. A total of 14,459 simple sequence repeats, including 8128 monomers, 3276 dimers, 1693 trimers, 150 quadmers, 4 pentamers and 16 hexamers, were found in the transcriptomic dataset. Our study is the first comprehensive investigation of the transcriptomic response to DIV1 infection in F. merguiensis. Collectively, these results not only provide valuable information for characterizing the immune mechanisms of the shrimp responses to DIV1 infection, they open new ways for the study of the molecular mechanisms of DIV1 infection in F. merguiensis.

Galectin, another lectin from Fenneropenaeus merguiensis contributed in shrimp immune defense

Numerous lectins act as pattern recognition receptors (PRRs) in the innate immune system of invertebrates. Here, a galectin (FmGal) was isolated from hemocytes of Fenneropenaeus merguiensis. FmGal contained one open reading frame encoding a peptide of 338 amino acids. The primary sequence of FmGal comprised a carbohydrate recognition domain with a specific galactose binding site. The FmGal transcripts were found mostly in hemocytes of healthy shrimp. The expression of FmGal was up-regulated upon challenge with Vibrio parahaemolyticus and white spot syndrome virus (WSSV). Gene-silencing with FmGal double-stranded RNA resulted in extreme down-regulation of FmGal. Knockdown with a co-injection of pathogens reduced the survival rate of shrimp. Recombinant protein of FmGal (rFmGal) required Ca²⁺ to agglutinate pathogenic bacteria and exhibited sugar-specificity to galactose, lactose, lipopolysaccharide (LPS) and lipoteichoic acid (LTA). The ELISA-validated binding of rFmGal revealed higher affinity to LTA than LPS. rFmGal did not exhibit antibacterial activity but could enhance the phagocytosis and encapsulation of pathogenic invaders by hemocytes. Encapsulation was suppressed by galactose and lactose. Moreover, rFmGal also promoted the in vivo clearance of V. parahaemolyticus. FmGal, a galectin in F. merguiensis, participated in shrimp immunity, functioning as a PRR which might be involved in certain cellular responses.

Lipopolysaccharide-specific binding C-type lectin with one CRD domain from Fenneropenaeus merguiensis (FmLC4) functions as a pattern recognition receptor in shrimp innate immunity

In crustaceans, an innate immune system is solely required because they lack an adaptive immunity. One kind of pattern recognition receptors (PRRs) that plays a particular role in the innate immunity of aquatic shrimp is lectin. A new diverse C-type lectin (FmLC4) was cloned from the hepatopancreas of Fenneropenaeus merguiensis by using RT-PCR and 5' and 3' rapid amplification of cDNA ends approaches. A full-length FmLC4 cDNA comprises 706 bp with an open reading frame of 552 bp, encoding a peptide of 184 amino acids. The predicted primary sequence of FmLC4 consists of a signal peptide of 19 amino acids, a molecular mass of 20.4 kDa, an isoelectric point of 5.13, one carbohydrate recognition domain with a QPD motif and a Ca²⁺ binding site as well as a double-loop characteristic supported by two conserved disulfide bonds. The FmLC4 mRNA expression was found only in the hepatopancreas of normal shrimp and significantly up-regulated upon challenge the shrimp with Vibrio harveyi or white spot syndrome virus (WSSV). Recombinant FmLC4 (rFmLC4) could agglutinate various bacterial strains with Ca²⁺-dependence. Lipopolysaccharide (LPS) could specifically inhibit the agglutinating activity and potently bind to rFmLC4, indicating that FmLC4 was LPS-specific binding C-type lectin. Moreover, rFmLC4 itself displayed the in vivo effective clearance of the pathogenic bacterium V. harveyi. Altogether, FmLC4 may serve as LPS-specific PRR to recognize opportunistic bacterial and viral pathogens, and thus to play a role in the immune defense of aquatic shrimp via the binding and agglutination.

Long non-coding RNA profile in banana shrimp, Fenneropenaeus merguiensis and the potential role of lncPV13 in vitellogenesis

The long non-coding RNAs (lncRNAs) have been known to play important roles in several biological processes as well as in reproduction. This study aimed to identify lncRNA in ovary female banana shrimp, Fenneropenaeus merguiensis, and investigate the potential role of lncPV13 in the vitellogenesis. After the in silico identification of the ovarian transcriptome, a total of 24,733 putative lncRNAs were obtained, and only 147 putative lncRNAs were significantly differentially expressed among the ovarian development stages. To validate the in silico identification of lncRNAs, the 16 lncRNAs with the highest differential expression in the transcriptome analysis were evaluated by RT-qPCR. The 6 lncRNAs showed higher expression levels in the mature stage than in the previtellogenic stage and were found in several tissues such as in eyestalks, brains, thoracic ganglia, gills, and muscle. Furthermore, most candidate lncRNAs were amplifiable in Litopenaeus vannamei's and Penaeus monodon's DNA but not in Macrobrachium rosenbergii's DNA, suggesting some lncRNAs are expressed in a species-specific manner among penaeid shrimp. In this study, the lncPV13 was investigated for its vitellogenin regulating function by RNA interference. The result indicates that the lncPV13 expression was suppressed in the ovary on day 7 after the injection of double-stranded RNA specific to lncPV13 (dslncPV13), while vitellogenin (Vg) expression was significantly decreased. In contrast, the gonad inhibiting hormone (GIH) expression was significantly increased in the lncPV13 knockdown shrimp. However, the oocyte proliferation was not significantly different between control and lncPV13 knockdown shrimp. This suggests that lncPV13 regulate Vg synthesis through GIH inhibition. Finally, our findings provide lncRNA information and potential lncRNAs involved in the vitellogenesis of female banana shrimp.

Effects of the interaction between a clip domain serine protease and a white spot syndrome virus protein on phenoloxidase activity

Clip domain serine proteinases participate in invertebrate innate immunity by acting as crucial enzymes in the signaling cascade involved in shrimp immunity. To functionally characterize its role in Fenneropenaeus merguiensis, FmclipSP cDNA was cloned and characterized. The FmclipSP gene comprised 1353 bp with an open reading frame of 1110 bp and encoded 369 amino acids. The protein contained clip and serine protease domains. FmClipSP mRNA is highly expressed in hemocytes, and its expression was significantly upregulated by bacterial or viral pathogen challenge. Furthermore, FmClipSP recombinant protein (rFmClipSP) was produced and possessed protease activity, stimulating prophenoloxidase activity. Additionally, rFmClipSP exhibited antibacterial activity against pathogens and nonpathogens. ELISA results demonstrated the binding ability of rFmClipSP to a recombinant protein of VP28 (rVP28). Interestingly, the binding significantly inhibited prophenoloxidase activity. Altogether, we partially characterized the function of FmclipSP and demonstrated its association with VP28. This study indicates the importance of clipSP as a component of F. merguiensis innate immunity. However, the role of clipSP in crustaceans remains unclear and requires further investigation.

The complete mitochondrial genome of banana shrimp Fenneropenaeus merguiensis with phylogenetic consideration

The complete mitochondrial genome sequence of Fenneropenaeus merguiensis was determined by shotgun assembly method. The complete mitochondrial DNA sequence is a circular molecule with 16,023 bp in length including 13 protein-coding genes, 22 transfer RNA genes, 2 rRNA genes and a control region. The gene arrangements are consistent with the pan crustacean ground pattern. The molecular analyses provided robust evidence for the monophyly of Fenneropenaeus, but Litopenaeus was not monophyletic. Phylogenetic analyses robustly supported the fact that genus Penaeus s.l. contains the two lineages: Marsupenaeus and Penaeus s.s+ Fenneropenaeus + Litopenaeus + Farfantepenaeus.

Pathogenicity and transcriptome analysis of a strain of Vibrio owensii in Fenneropenaeus merguiensis

Vibrio is an important conditional pathogen in shrimp aquaculture. This research reported a dominant bacteria strain E1 isolated from a shrimp tank with the method of biofloc culture, which was further identified as Vibrio owensii. To understand the interaction between V. owensii and the host shrimp, we studied the pathogenicity of the V. owensii and the molecular mechanisms of the Fenneropenaeus merguiensis immunity during the Vibrio invasion. Drug susceptibility tests showed that V. owensii was resistant to antibiotics streptomycin oxacillin, tetracycline, minocycline, and aztreonam, but highly sensitive to cefazolin, cefotaxime, and ciprofloxacin, and moderately sensitive to cefotaxime, ampicillin, and piperacillin. Lethal concentration 50 (LC₅₀) test was performed to evaluate the toxicity of V. owensii to F. merguiensis. The LC₅₀ of V. owensii infected F. merguiensis after 24, 48, 72, 96, 120, 144 and 168 h were 1.21 × 10⁷, 1.68 × 10⁶, 6.36 × 10⁵, 2.15 × 10⁵, 7.58 × 10⁴, 5.55 × 10⁴ and 4.33 × 10⁴ CFU/mL. In order to explore the molecular response mechanism of F. merguiensis infected with V. owensii, the hepatopancreas of F. merguiensis were sequenced at 24 hpi and 48 hpi, and a total 40,181 of unigenes were obtained. Through comparative transcriptomic analysis, 86 differentially expressed genes (DEGs) (including 38 up-regulated DEGs, and 48 down-regulated DEGs) and 305 DEGs (including 150 up-regulated DEGs, and 155 down-regulated DEGs) were identified at 24 hpi and 48 hpi, respectively. Annotation and classification analysis of these 391 DEGs showed that most of the DEGs were annotated to metableolic and immune pathways, which indicated that F. merguiensis responded to the invasion through the regulation of material metableolism and immune system genes during V. owensii infection. In the KEGG enrichment analysis, some pathways related to immune response were significantly influenced by V. owensii infection, including phagosome, MAPK signalling pathway and PI3K-Akt signalling pathway. In addition, some pathways related to the warburg effect were also significantly enriched after V. owensii infection, including pyruvate metableolism, glycolysis/gluconeogenesis, and citrate cycle (TAC cycle). Further analysis showed that C-type lectins and ficolin were also play important roles in the immune response of F. merguiensis against V. owensii infection. The current research preliminarily revealed the immune response of F. merguiensis to V. owensii infection at the molecular level, which provided valuable information to further understand the disease control and the interaction between shrimp and Vibrio.

Cryopreservation of Germ Cells of Banana Shrimp (Fenneropenaeus merguiensis) and Black Tiger Shrimp (Penaeus monodon)

Germ cell cryopreservation has been used to preserve many fish species. However, this method has not been established for crustaceans; thus, we attempted to do this herein. The efficiency of slow freezing was compared to vitrification methods for germ cell cryopreservation in two types of marine shrimp, Fenneropenaeus merguiensis and Penaeus monodon. In situ hybridization with a vasa probe was used to identify germ cells. The effects of three cryoprotectants, dimethyl sulfoxide (DMSO), glycerol (GLY), and magnesium chloride (MgCl₂), on germ cell viability and recovery rate were compared at three concentrations (5%, 10%, and 15%). The effects of thawing temperature, including 10 and 27 °C, were also investigated. We discovered that 10% DMSO with the vitrification is suitable for preserving the germ cells of F. merguiensis for a long time, whereas 10% GLY with vitrification is suitable for P. monodon. Moreover, the most suitable thawing temperature was 10 °C for both species. This is the first report of germ cell cryopreservation in crustaceans. Thus, we provide evidence that crustacean germ cells can be preserved long-term in liquid nitrogen; this is the first step in the sustainable preservation of crustaceans, especially shrimp.

Molecular Markers of Ovarian Germ Cells of Banana Prawn (Fenneropenaeus merguiensis)

The banana prawn (Fenneropenaeus merguiensis) is a valuable prawn in the worldwide market. However, cultivation of this species is limited owing to the difficulty in culture management and limited knowledge of reproduction. Therefore, we studied the gene expression and molecular mechanisms involved in oogenesis for elucidating ovarian germ cell development in banana prawns. The tissue-specific distribution of certain genes identified from previous transcriptome data showed that FmCyclinB, FmNanos, and nuclear autoantigenic sperm protein (FmNASP) were only expressed in gonads. The in situ hybridization (ISH) of these three genes showed different expression patterns throughout oogenesis. FmCyclinB was highly expressed in pre-vitellogenic oocytes. FmNanos was expressed at almost the same level during oogenesis but showed the most expression in late pre-vitellogenic stages. Based on the highest expression of FmCyclinB and FmNanos in mid pre-vitellogenic and late pre-vitellogenic oocytes, respectively, we suggested that FmNanos may suppress FmCyclinB expression before initiation of vitellogenesis. Meanwhile, FmNASP expression was detected only in pre-vitellogenesis. Moreover, quantitative real-time polymerase chain reaction (qRT-PCR) analysis of FmNASP expression was supported by FmNASP ISH analysis based on high expression of FmNASP in sub-adult ovaries, which contain most of pre-vitellogenic oocytes. In this study, we found three reliable ovarian markers for banana prawns and also found a dynamic change of molecular mechanism during the sub-stage of pre-vitellogenesis. We determined the expression levels of these genes involved in oogenesis. Our findings provide information for further studies on banana prawn reproduction which may assist in their cultivation.

Potential receptors in Fenneropenaeus merguiensis ovary and role of saxophone, the bone morphogenetic protein receptor, in ovarian development

Receptors, which play an initial role in signaling pathways in several physiological processes, including reproduction, are among the several molecular factors that control ovarian development in organisms. This study aimed to identify and study receptors potentially involved in controlling the reproductive process of female banana shrimp, Fenneropenaeus merguiensis. Ovarian transcriptomes derived from 4 developmental stages were generated by RNA sequencing. A total of 53,763 transcripts were obtained from the de novo assembled transcriptome, and 663 genes were identified as receptors. Among them, 185 receptors were differentially expressed during ovarian development. Fifteen of these differentially expressed receptors showed distinct expression patterns that were validated by RT-qPCR. Bone morphogenetic protein receptors (BMPR) and their signaling genes were investigated for their roles in shrimp vitellogenesis. The expressions of F. merguiensis saxophone (FmSax), a BMP type I receptor, and BMP type II receptor (FmBMPRII) as well as FmMad, FmMed, and FmSMAD3 were significantly altered during ovarian development. RNA interference was used to investigate the role of FmSax in vitellogenesis. The result indicated that the expression of vitellogenin (Vg) was significantly reduced in both ovary and hepatopancreas of FmSax-knockdown shrimp compared to control shrimp. Furthermore, in FmSax-silencing shrimp, FmBMPRII, FmMad, and FmMed expressions were decreased as well as Vg expression. These findings suggest that FmSax positively regulates Vg synthesis via the BMP signaling pathway.

A Comprehensive Assessment of the Nutritional Value, Antioxidant Potential, and Genetic Diversity of Fenneropenaeus merguiensis from Three Different Regions in China

Fenneropenaeus merguiensis is one of the largest species of penaeid shrimp. It has a wide distribution of germplasm resources in the South China Sea and the southeastern coastal regions of China, yet its germplasm characteristics remain insufficiently understood. Therefore, we conducted analyses of basic nutritional components, amino acids, fatty acids, antioxidant indices, and genetic diversity in three F. merguiensis populations (FmRP, FmSZ, FmSY). The results showed a significant difference in ash content, with FmSZ having the highest ash content (1.77 g/100 g) (p < 0.05). A total of 17 amino acids were detected, and FmSZ exhibited higher concentrations of most amino acids, especially essential amino acids (p < 0.05). The analysis of fatty acid composition revealed significant differences between the populations, with FmSY potentially having a nutritional advantage overall (p < 0.05). In terms of antioxidant capacity and genetic diversity, there were no significant differences in total antioxidant capacity (T-AOC), catalase (CAT), or superoxide dismutase (SOD) among the populations (p > 0.05). However, genetic analysis indicated that FmSZ had the lowest inbreeding coefficient and relatively higher genetic diversity. In conclusion, among the three F. merguiensis populations, FmSZ has relatively higher nutritional quality and genetic diversity, and F. merguiensis is a high-quality aquatic product worth promoting. The analysis and characterization of various aspects of F. merguiensis from the three locations provide important information and data support for germplasm resources and genetic breeding efforts.

Identification of an essential role against shrimp pathogens of prophenoloxidase activating enzyme 1 (PPAE1) from Fenneropenaeus merguiensis hemocytes

Prophenoloxidase (proPO) activating enzymes, known as PPAEs, are pivotal in activating the proPO system within invertebrate immunity. A cDNA encoding a PPAE derived from the hemocytes of banana shrimp, Fenneropenaeus merguiensis have cloned and analyzed, referred to as FmPPAE1. The open reading frame of FmPPAE1 encompasses 1392 base pairs, encoding a 464-amino acid peptide featuring a presumed 19-amino acid signal peptide. The projected molecular mass and isoelectric point of this protein stand at 50.5 kDa and 7.82, respectively. Structure of FmPPAE1 consists of an N-terminal clip domain and a C-terminal serine proteinase domain, housing a catalytic triad (His272, Asp321, Ser414) and a substrate binding site (Asp408, Ser435, Gly437). Expression of the FmPPAE1 transcript is specific to hemocytes and is heightened upon encountering pathogens like Vibrio parahaemolyticus, Vibrio harveyi, and white spot syndrome virus (WSSV). Using RNA interference to silence the FmPPAE1 gene resulted in reduced hemolymph phenoloxidase (PO) activity and decreased survival rates in shrimp co-injected with pathogenic agents. These findings strongly indicate that FmPPAE1 plays a vital role in regulating the proPO system in shrimp. Furthermore, upon successful production of recombinant FmPPAE1 protein (rFmPPAE1), it became evident that this protein exhibited remarkable abilities in both agglutinating and binding to a wide range of bacterial strains. These interactions were primarily facilitated through the recognition of bacterial lipopolysaccharides (LPS) or peptidoglycans (PGN) found in the cell wall. This agglutination process subsequently triggered melanization, a critical immune response. Furthermore, rFmPPAE1 exhibited the ability to actively impede the growth of pathogenic bacteria harmful to shrimp, including V. harveyi and V. parahaemolyticus. These findings strongly suggest that FmPPAE1 not only plays a pivotal role in activating the proPO system but also possesses inherent antibacterial properties, actively contributing to the suppression of bacterial proliferation. In summary, these results underscore the substantial involvement of FmPPAE1 in activating the proPO system in F. merguiensis and emphasize its crucial role in the shrimp's immune defense against invading pathogens.