Differentially Expressed Genes in Hepatopancreas of Acute Hepatopancreatic Necrosis Disease Tolerant and Susceptible Shrimp (Penaeus vannamei)

Passive immunoprophylaxis with Ccombodies against Vibrio parahaemolyticus in Pacific white shrimp (Penaeus vannamei)

The Vibrio parahaemolyticus strain causing acute hepatopancreatic necrosis disease (AHPND) in shrimp secretes toxins A and B (PirAVp/PirBVp). These toxins have been implicated in pathogenesis and are targets for developing anti-AHPND therapeutics or prophylactics that include passive immunization. We have previously reported that Ccombodies (recombinant hagfish variable lymphocyte receptor B antibodies; VLRB) targeting PirBVp conferred protection against V. parahaemolyticus in shrimp when administered as a feed supplement. In this study, we screened a phage-displayed library of engineered VLRBs for PirAVp-targeting Ccombodies that were mass-produced in a bacterial expression system. We then introduced these Ccombodies into the diet of Pacific white shrimp (Penaeus vannamei) over a seven-day period. Subsequently, the shrimp were exposed to a challenge with V. parahaemolyticus. Mortality rates were then observed and recorded over the following seven days. Administering shrimp feed supplemented with Ccombodies at a high dose (100 mg per 100 g feed) reduced mortality in recipient animals (2.96-5.19 %) statistically similar to mock-challenged control (1.48 %), but significantly different from the Ccombody-deficient control (74.81 %). This suggests that the Ccombodies provided strong protection against the bacterium. Feeding shrimp with a median dose (10 mg/100 g feed) gave statistically comparable low mortality (5.93-6.67 %) as the high dose. Reducing the Ccombody dose to 1 mg/100 g feed showed variable effects. Ccombody A2 showed mortality (11.85 %) significantly lower than that of the Ccombody-deficient group (74.81 %), suggesting that it can effectively protect against the bacterial challenge at a low dose. Our results demonstrate the ability of the phage-displayed VLRB library to generate antigen-specific Ccombodies rapidly and simply, with the expression of high protein levels in bacteria. The protective effect provided by these Ccombodies aligns with our earlier results, strongly supporting the use of VLRB antibodies as a substitute for IgY in passive immunoprophylaxis against AHPND in shrimp.

Cellular and transcriptomic response to pathogenic and non-pathogenic Vibrio parahaemolyticus strains causing acute hepatopancreatic necrosis disease (AHPND) in Litopenaeus vannamei

The shrimp industry has historically been affected by viral and bacterial diseases. One of the most recent emerging diseases is Acute Hepatopancreatic Necrosis Disease (AHPND), which causes severe mortality. Despite its significance to sanitation and economics, little is known about the molecular response of shrimp to this disease. Here, we present the cellular and transcriptomic responses of Litopenaeus vannamei exposed to two Vibrio parahaemolyticus strains for 98 h, wherein one is non-pathogenic (VpN) and the other causes AHPND (VpP). Exposure to the VpN strain resulted in minor alterations in hepatopancreas morphology, including reductions in the size of R and B cells and detachments of small epithelial cells from 72 h onwards. On the other hand, exposure to the VpP strain is characterized by acute detachment of epithelial cells from the hepatopancreatic tubules and infiltration of hemocytes in the inter-tubular spaces. At the end of exposure, RNA-Seq analysis revealed functional enrichment in biological processes, such as the toll3 receptor signaling pathway, apoptotic processes, and production of molecular mediators involved in the inflammatory response of shrimp exposed to VpN treatment. The biological processes identified in the VpP treatment include superoxide anion metabolism, innate immune response, antimicrobial humoral response, and toll3 receptor signaling pathway. Furthermore, KEGG enrichment analysis revealed metabolic pathways associated with survival, cell adhesion, and reactive oxygen species, among others, for shrimp exposed to VpP. Our study proves the differential immune responses to two strains of V. parahaemolyticus, one pathogenic and the other nonpathogenic, enlarges our knowledge on the evolution of AHPND in L. vannamei, and uncovers unique perspectives on establishing genomic resources that may function as a groundwork for detecting probable molecular markers linked to the immune system in shrimp.

Integrated application of transcriptomics and metabolomics provides insights into acute hepatopancreatic necrosis disease resistance of Pacific white shrimp Litopenaeus vannamei

Acute hepatopancreatic necrosis disease (AHPND) has caused a huge economic loss to shrimp aquaculture. Vibrio parahaemolyticus (VpAHPND) is regarded as a major causative agent of AHPND in the Pacific white shrimp Litopenaeus vannamei. However, knowledge about how shrimp resist to AHPND is very limited. In order to learn the molecular mechanisms underlying AHPND resistance of shrimp, comparison between disease-resistant family and susceptible family of L. vannamei were performed at transcriptional and metabolic levels. Integrated analysis of transcriptomics and metabolomics on hepatopancreas of shrimp, the target tissue of VpAHPND, showed that significant differences existed between resistant family and susceptible family of shrimp. The susceptible family showed higher level of glycolysis, serine-glycine metabolism, purine and pyrimidine metabolism, but lower level of betaine-homocysteine metabolism in the hepatopancreas in comparison with the resistant family without VpAHPND infection. Curiously, VpAHPND infection induced up-regulation of glycolysis, serine-glycine metabolism, purine metabolism, pyrimidine metabolism, and pentose phosphate pathway, and down-regulation of betaine-homocysteine metabolism in resistant family. In addition, arachidonic acid metabolism and some immune pathways, like NF-κB and cAMP pathways, were up-regulated in the resistant family after VpAHPND infection. In contrast, amino acid catabolism boosted via PEPCK-mediated TCA cycle flux was activated in the susceptible family after VpAHPND infection. These differences in transcriptome and metabolome between resistant family and susceptible family might contribute to the resistance of shrimp to bacteria. IMPORTANCE Vibrio parahaemolyticus (VpAHPND) is a major aquatic pathogen causing acute hepatopancreatic necrosis disease (AHPND) and leads to a huge economic loss to shrimp aquaculture. Despite the recent development of controlling culture environment, disease resistant broodstock breeding is still a sustainable approach for aquatic disease control. Metabolic changes occurred during VpAHPND infection, but knowledge about the metabolism in resistance to AHPND is very limited. Integrated analysis of transcriptome and metabolome revealed the basal metabolic differences exhibited between disease-resistant and susceptible shrimp. Amino acid catabolism might contribute to the pathogenesis of VpAHPND and arachidonic acid metabolism might be responsible for the resistance phenotype. This study will help to enlighten the metabolic and molecular mechanisms underlying shrimp resistance to AHPND. Also, the key genes and metabolites of amino acid and arachidonic acid pathway identified in this study will be applied for disease resistance improvement in the shrimp culture industry.

Two Independently Comparative Transcriptome Analyses of Hemocytes Provide New Insights into Understanding the Disease-Resistant Characteristics of Shrimp against Vibrio Infection

Vibrio parahaemolyticus carrying plasmid encoding toxins PirA and PirB is one of the causative agents leading to the severe disease of AHPND in shrimp aquaculture. However, there is a lack of deep understanding of the host-resistant characteristics against V. parahaemolyticus infection. Here, we established a method to obtain hemocytes from shrimp with different V. parahaemolyticus-resistant abilities and performed comparative transcriptome analysis on the expression profiles at the background level of hemocytes from shrimp in two independent populations. Principal component analysis and sample clustering results showed that samples from the same population had a closer relationship than that from shrimp with similar disease-resistant abilities. DEGs analysis revealed that the number of DEGs between two populations was much more than that between V. parahaemolyticus-resistant and susceptible shrimp. A total of 31 DEGs and 5 DEGs were identified from the comparison between V. parahaemolyticus-resistant and susceptible shrimp from populations 1 and 2, respectively. DEGs from population 1 were mainly cytoskeleton-related genes, metabolic related genes, and immune related genes. Although there was no DEGs overlap between two comparisons, DEGs from population 2 also included genes related to cytoskeleton and metabolism. The data suggest that these biological processes play important roles in disease resistance, and they could be focused by comprehensive analysis of multiple omics data. A new strategy for screening key biological processes and genes related to disease resistance was proposed based on the present study.

Effect of Clostridium butyricum on intestinal microbiota and resistance to Vibrio alginolyticus of Penaeus vannamei

In order to evaluate the effect of Clostridium butyricum (C. butyricum) feeding on intestinal microorganisms and protection against infection by Vibrio alginolyticus (V. alginolyticus) in Penaeus vannamei (P. vannamei). We set up two groups, CG30 (fed normal feed) and CB30 (fed feed supplemented with C. butyricum), for the 30d C. butyricum feeding test, and four groups, CG (CG30 group injected with PBS), CB (CB30 group injected with PBS), VACG (CG30 group injected with V. alginolyticus), and VACB (CB30 group injected with V. alginolyticus), for the 24h infection test. The protective effect of C. butyricum against acute V. alginolyticus infection in P. vannamei was explained in terms of survival, histopathology, changes in enzyme activity, transcriptome analysis, and immune-related genes. We found that feeding C. butyricum significantly altered intestinal microbial populations' abundance and significantly reduced Vibrio spp. In the V. alginolyticus stress test, C. butyricum improved the survival rate and alleviated pathological changes in hepatopancreatic tissues, alleviated the reduction of superoxide dismutase (SOD) and phenoloxidase (PO) activity caused by infection, and increased the lysozyme content in P. vannamei. VACB group compared with the VACG group, 1730 up-regulated differentially expressed genes (DEGs) and 2029 down-regulated DEGs were screened. Quantitative real-time PCR (qRT-PCR) showed that dietary supplementation with C. butyricum suppressed the upregulation of alkaline phosphatase (AKP) transcription factors and the downregulation of prophenoloxidase (proPO), alpha-2-macroglobulin (A2M), and anti-lipopolysaccharide factor (ALF) induced by V. alginolyticus infection. In conclusion, feed supplementation with C. butyricum changed P. vannamei's population ratio of intestinal microorganisms. Moreover, C. butyricum has the potential to act as an inhibitor of V. alginolyticus infection and enhance the resistance of P. vannamei to V. alginolyticus infection.

Comprehensive Characterization of a Novel Bacteriophage, vB_VhaS_MAG7 against a Fish Pathogenic Strain of Vibrio harveyi and Its In Vivo Efficacy in Phage Therapy Trials

Vibrio harveyi, a significant opportunistic marine pathogen, has been a challenge to the aquaculture industry, leading to severe economical and production losses. Phage therapy has been an auspicious approach in controlling such bacterial infections in the era of antimicrobial resistance. In this study, we isolated and fully characterized a novel strain-specific phage, vB_VhaS_MAG7, which infects V. harveyi MM46, and tested its efficacy as a therapeutic agent in challenged gilthead seabream larvae. vB_VhaS_MAG7 is a tailed bacteriophage with a double-stranded DNA of 49,315 bp. No genes linked with virulence or antibiotic resistance were harbored in the genome. The phage had a remarkably large burst size of 1393 PFU cell^-1 and showed strong lytic ability in in vitro assays. When applied in phage therapy trials in challenged gilthead seabream larvae, vB_VhaS_MAG7 was capable of improving the survival of the larvae up to 20%. Due to its distinct features and safety, vB_VhaS_MAG7 is considered a suitable candidate for applied phage therapy.

Residue behavior of cyantraniliprole and its ecological effects on Procambarus clarkii associated with the rice-crayfish integrated system

BACKGROUND

Cyantraniliprole, a second-generation diamide insecticide, was recently introduced in China, where the rice-crayfish integrated system (RCIS) is practiced to control rice pest infestations. The aim of this study was to investigate the residue behavior of cyantraniliprole in RCIS and its potential ecological effects on nontarget Procambarus clarkii in order to recommend safe pesticide application strategies.

RESULTS

Cyantraniliprole dissipated in rice plants according to first-order kinetics, with an average half-life of 5.25 days and a dissipation rate of >95% over 28 days. The terminal cyantraniliprole residue levels in rice straw, paddy hull and brown rice were all within 0.2 mg kg^-1 , which is the China-recommended maximum residue limit. The tissues of P. clarkii accumulated and distributed cyantraniliprole in the descending order gill > hepatopancreas > intestine > muscles. Procambarus clarkii exposed to cyantraniliprole exhibited a moderate decrease in weight gain, specific growth rate and condition factor compared to the control group. Exposure of P. clarkii to cyantraniliprole caused histopathological alterations to the hepatopancreas, but the alterations were not statistically significant in the 60 g ai ha^-1 cyantraniliprole group when compared with the control group.

CONCLUSION

We suggest that 10% cyantraniliprole oil dispersion be sprayed twice at an interval of 14 days and dosage of 60 g ai ha^-1 during the growth stage of rice in RCIS. © 2023 Society of Chemical Industry.

Transcriptome Analysis on Hepatopancreas Reveals the Metabolic Dysregulation Caused by Vibrio parahaemolyticus Infection in Litopenaeus vannamei

Acute hepatopancreas necrosis disease (AHPND) has caused massive deaths of shrimp and has led to huge economic losses in aquaculture. Vibrio parahaemolyticus (VPAHPND) carrying a plasmid encoding binary toxins homologous to the photorhabdus insect-related (Pir) toxins is one of the main pathogens causing this disease. Previous studies have reported many immune-related genes of shrimp in response to this pathogenic bacteria. However, few studies have so far focused on the metabolic changes in Litopenaeus vannamei upon VPAHPND infection. In the present study, comparative transcriptomic analysis was performed on the hepatopancreas of shrimp at different times during VPAHPND infection. Functional analyses on the differentially expressed genes (DEGs) during infection showed that pathways related to glucose, energy and amino acid metabolism, as well as nucleic acid synthesis, were obviously changed in the hepatopancreas after VPAHPND infection. Additionally, three signaling pathways, which could regulate metabolic processes, including HIF-1 signaling pathway, PI3K-Akt signaling pathway and NF-KappaB signaling pathway, also changed significantly. Collectively, these data reveal a close relationship between host metabolism processes and Vibrio infection. The information will enrich our understanding of the interaction mechanism between the shrimp and Vibrio.

Fucosyltransferase 2 is involved in immune-related functions in Penaeus vannamei by modulating antimicrobial peptides' expression

In mammals fucosyltransferase 2 (FUT2) plays an important regulatory role in inflammation, bacterial or viral infection, and tumor metastasis. However, the specific role of FUT2 in invertebrate immunity has not been reported. Here, the FUT2 homolog of Penaeus vannamei (designated as PvFUT2) was cloned and found to have a full-length cDNA of 1104 bp with an open reading frame (ORF) encoding 316 amino acids. PvFUT2 is constitutively expressed in all shrimp tissues tested with the highest found in intestines. Moreover, PvFUT2 was induced in the main immune organs (hemocytes and hepatopancreas) of shrimp by Gram-positive (Vibrio parahaemolyticus), Gram-negative (Streptococcus iniae) bacteria and virus (White Spot Syndrome Virus), indicating the involvement of PvFUT2 in shrimp antimicrobial response. Intriguingly, PvFUT2 knockdown with or without pathogen challenge reduced the expression of Pvβ-catenin and antimicrobial peptides genes, particularly anti lipopolysaccharide factor and lysozyme. Further analysis revealed that the knockdown of PvFUT2 increased Vibrio abundance in hemolymph and resulted in an increase in shrimp cumulative mortality rate. Thus, during pathogen challenge, the expression of PvFUT2 is induced to regulate β-catenin and subsequently antimicrobial peptides expression to augment shrimp antimicrobial immune response.

Comparative transcriptomic analysis of gill reveals genes belonging to mTORC1 signaling pathway associated with the resistance trait of shrimp to VPAHPND

Selective breeding for acute hepatopancreatic necrosis disease (AHPND) resistant shrimp is an effective way to deal with heavy losses to shrimp aquaculture caused by AHPND. However, knowledge about the molecular mechanism of susceptibility or resistance to AHPND is very limited. We herein performed a comparative transcriptomic analysis of gill tissue between AHPND susceptible and resistant families of the white Pacific shrimp Litopenaeus vannamei during Vibrio parahaemolyticus (VP_AHPND) infection. A total of 5,013 genes that were differentially expressed between the two families at 0 and 6 h post-infection, and 1,124 DEGs were shared for both two time points. Both GO and KEGG analyses in each or two time point's comparisons showed DEGs involved in endocytosis, protein synthesis and cell inflammation were significantly enriched. Several immune DEGs including PRRs, antioxidants and AMPs were also identified. The susceptible shrimp showed enhanced endocytosis, higher aminoacyl-tRNA ligase activity and occurrence of inflammatory response, while the resistant shrimp had much more strong ability in ribosome biogenesis, antioxidant activity and pathogen recognition and clearance. These genes and processes were mostly associated with mTORC1 signaling pathway, which could reflect differences in cell growth, metabolism and immune response between the two families. Our findings indicate a close link between mTORC1 signaling-related genes and Vibrio-resistance phenotype of shrimp, and provide new clues for further research on resistance strategy of shrimp to AHPND.

A novel type I Crustin from Exopalaemon carinicauda: Antimicrobial ability related to conserved cysteine

Crustins are a kind of antibacterial peptides (AMP) existing in crustaceans, and their antibacterial abilities are considered to be related to the conserved WAP domain. In this study, a novel type I Crustin gene was identified in Exopalaemon carinicauda, named EcCru. The deduced amino acid sequence revealed that the conserved cysteine at position 7 in the WAP domain was replaced by aspartic acid. The gene is 405 bp in length, encoding 134 amino acids, and is mainly distributed in gills and hepatopancreas. After Vibrio parahaemolyticus and Aeromonas hydrophila stimulation, the expression of EcCru was significantly up-regulated within 12 h, and then returned to normal levels. The recombinant protein was obtained using the Pichia pastoris expression system, and the recombinant protein had neither antibacterial activity against gram-positive or gram-negative bacteria. But the antibacterial ability emerged when Asp¹⁰¹ was mutated to Cys. Notably, we also obtained a mutant that had a deletion at the 6 th conserved Cys in the WAP domain, and this mutant had antibacterial ability against gram-positive bacteria Bacillus subtilis and B. cereus. This indicates that the conserved cysteine with different positions in WAP domain can have different effects on the antibacterial ability of Crustins.

Comparison of Gene Expression Between Resistant and Susceptible Families Against VPAHPND and Identification of Biomarkers Used for Resistance Evaluation in Litopenaeus vannamei

Acute hepatopancreatic necrosis disease (AHPND) has caused a heavy loss to shrimp aquaculture since its outbreak. Vibrio parahaemolyticus (VP_AHPND) is regarded as one of the main pathogens that caused AHPND in the Pacific white shrimp Litopenaeus vannamei. In order to learn more about the mechanism of resistance to AHPND, the resistant and susceptible shrimp families were obtained through genetic breeding, and comparative transcriptome approach was used to analyze the gene expression patterns between resistant and susceptible families. A total of 95 families were subjected to VP_AHPND challenge test, and significant variations in the resistance of these families were observed. Three pairs of resistant and susceptible families were selected for transcriptome sequencing. A total of 489 differentially expressed genes (DEGs) that presented in at least two pairwise comparisons were screened, including 196 DEGs highly expressed in the susceptible families and 293 DEGs in the resistant families. Among these DEGs, 16 genes demonstrated significant difference in all three pairwise comparisons. Gene set enrichment analysis (GSEA) of all 27,331 expressed genes indicated that some energy metabolism processes were enriched in the resistant families, while signal transduction and immune system were enriched in the susceptible families. A total of 32 DEGs were further confirmed in the offspring of the detected families, among which 19 genes were successfully verified. The identified genes in this study will be useful for clarifying the genetic mechanism of shrimp resistance against Vibrio and will further provide molecular markers for evaluating the disease resistance of shrimp in the breeding program.