Vibrio parahaemolyticus Infection Influenced Trace Element Homeostasis, Impaired Antioxidant Function, and Induced Inflammation Response in Litopenaeus vannamei

Evaluation of the combined impact of aflatoxin B1 and deoxynivalenol fed to Penaeus vannamei and mitigation properties provided by a yeast cell wall extract

The purpose of this study was to examine how white shrimp (Penaeus vannamei) responded to varying concentrations of combined mycotoxins (aflatoxin B1 (AFB1) and deoxynivalenol (DON)) as well as the mitigating effects of an adsorbent (yeast cell wall extract, YCWE). The experiment comprised of five groups receiving isonitrogenous and isolipidic diets: CON (control group), LDA (CON with 20 μg/kg AFB1 and 1500 μg/kg DON), HDA (CON with 100 μg/kg AFB1 and 3000 μg/kg DON), LDAM (LDA with 0.2 % YCWE), and HDAM (HDA with 0.2 % YCWE). Results showed that the contents of total protein, total cholesterol, hemocyanin, and enzyme activities (e.g., catalase, phenoloxidase) in plasma were lower in HDA group, while the alanine aminotransferase activity and malondialdehyde content were higher. The HDA group showed up-regulated expression of apoptotic genes in the hepatopancreas but down-regulated expression of immune-related and antioxidant genes. In the LDA and HDA groups, the higher expression of inflammatory genes in hepatopancreas, the lowest chewiness of muscle and the higher abundance of potential pathogens (e.g., Escherichia-Shigella) in the intestine were observed. However, LDAM and HDAM diets were able to enhance the immune response, antioxidant capacity, and hepatopancreatic and intestinal health of shrimp, especially increased the abundance of intestinal bacteria for detoxification (e.g., Pseudomonas). Moreover, dietary YCWE also led to significantly greater mycotoxin content in the feces. In conclusion, the combined mycotoxins AFB1 and DON can negatively affect the health of shrimp, even at lower doses. But adding YCWE to the diets can effectively mitigate these negative effects.

Unravelling the pathogenesis of Vibrio parahaemolyticus infection: impacts on antioxidant and innate immunity gene responses in Scyllaparamamosain

This study investigated the etiology of Vibrio parahaemolyticus in mud crabs (Scylla paramamosain), a pivotal species in China's aquaculture industry. The results demonstrate that the V. parahaemolyticus strain LG2206 poses a significant threat to mud crabs by inducing oxidative stress and impairing their non-specific immune response. A 7-day immersion contagion test was conducted to determine the lethal dose 50 (LD50) of LG2206 for the mud crabs, which was established at 3.16 × 105 CFU/mL. The findings indicate that LG2206 can infiltrate multiple tissues of the mud crab, with the gills being the initial and primary site of invasion, followed by the hepatopancreas, midgut, and muscle. Throughout the infection period, an increasing LG2206 count across sampled tissues led to tissue damage and cell death, with the gills, hepatopancreas, midgut, and muscle affected in sequence. The modulation of various enzymatic and genetic responses to LG2206 incubation was also investigated. Notably, superoxide dismutase (SOD) and glucocorticoid reductase (GR) were upregulated in the gill tissue. Phenoloxidase (PO) and lysozyme (LZM) exhibited a transient surge on the first day post-infection, followed by a decline. Enzymatic activity in other tissues followed a pattern of initially increasing, peaking, and then gradually declining, with the gills, hepatopancreas, midgut, and muscle following this trend sequentially. Additionally, the expression patterns of heat shock protein 70 (HSP70) and CASP-3 genes mirrored this trend, with their peaks occurring at different times across the various tissue types. In summary, this study sheds light on the pathogenic process of LG2206 in mud crabs, revealing that V. parahaemolyticus initially adheres to and compromises gill tissue before spreading through the circulatory system to other organs, with a preference for the hepatopancreas. This work enhances our understanding of the effects of V. parahaemolyticus on mud crab farming and proposes potential intervention strategies to mitigate its harmful impacts.

H2O2-Induced Oxidative Stress Responses in Eriocheir sinensis: Antioxidant Defense and Immune Gene Expression Dynamics

Eriocheir sinensis, a key species in China's freshwater aquaculture, is threatened by various diseases, which were verified to be closely associated with oxidative stress. This study aimed to investigate the response of E. sinensis to hydrogen peroxide (H2O2)-induced oxidative stress to understand the biological processes behind these diseases. Crabs were exposed to different concentrations of H2O2 and their antioxidant enzyme activities and gene expressions for defense and immunity were measured. Results showed that activities of antioxidant enzymes-specificallysuperoxide dismutase (SOD), catalase (CAT), total antioxidant capacity(T-AOC), glutathione (GSH), and glutathione peroxidase (GSH-Px)-varied with exposure concentration and duration, initially increasing then decreasing. Notably, SOD, GSH-Px, and T-AOC activities dropped below control levels at 96 h. Concurrently, oxidative damage markers, including malondialdehyde (MDA), H2O2, and 8-hydroxy-2'-deoxyguanosine (8-OHdG) levels, increased with exposure duration. The mRNA expression of SOD, CAT, and GSH-Px also showed an initial increase followed by a decrease, peaking at 72 h. The upregulation of phenoloxidaseloxidase (proPO) and peroxinectin (PX) was also detected, but proPO was suppressed under high levels of H2O2. Heat shock protein 70 (HSP70) expression gradually increased with higher H2O2 concentrations, whereas induced nitrogen monoxide synthase (iNOS) was upregulated but decreased at 96 h. These findings emphasize H2O2's significant impact on the crab's oxidative and immune responses, highlighting the importance of understanding cellular stress responses for disease prevention and therapy development.

ZntA maintains zinc and cadmium homeostasis and promotes oxidative stress resistance and virulence in Vibrio parahaemolyticus

Although metals are essential for life, they are toxic to bacteria in excessive amounts. Therefore, the maintenance of metal homeostasis is critical for bacterial physiology and pathogenesis. Vibrio parahaemolyticus is a significant food-borne pathogen that mainly causes acute gastroenteritis in humans and acute hepatopancreatic necrosis disease in shrimp. Herein, we report that ZntA functions as a zinc (Zn) and cadmium (Cd) homeostasis mechanism and contributes to oxidative stress resistance and virulence in V. parahaemolyticus. zntA is remarkably induced by Zn, copper, cobalt, nickel (Ni), and Cd, while ZntA promotes V. parahaemolyticus growth under excess Zn/Ni and Cd conditions via maintaining Zn and Cd homeostasis, respectively. The growth of ΔzntA was inhibited under iron (Fe)-restricted conditions, and the inhibition was associated with Zn homeostasis disturbance. Ferrous iron supplementation improved the growth of ΔzntA under excess Zn, Ni or Cd conditions. The resistance of ΔzntA to H2O2-induced oxidative stress also decreased, and its virulence was attenuated in zebrafish models. Quantitative real-time PCR, mutagenesis, and β-galactosidase activity assays revealed that ZntR positively regulates zntA expression by binding to its promoter. Collectively, the ZntR-regulated ZntA is crucial for Zn and Cd homeostasis and contributes to oxidative stress resistance and virulence in V. parahaemolyticus.

Characterization and antivibrio activity of chitosan-citral Schiff base calcium complex for a calcium citrate sustained release antibacterial agent

Vibrio parahemolyticus is the "Number one killer" of seafood products. Anti-vibrio agents having low cost and high-safety are urgently needed to supplement the application needs. This work attempted to prepare CS-CT-CCa complex with citral (CT), chitosan (CS) and calcium citrate (CCa) as raw material by microwave-assisted high-pressure homogenization. Additionally the coordination structure and morphology of Bridge-CS-CT-Schiff base/OH-CCa were verified. The prepared CS-CT-CCa had a well-dispersed property (the size: 3.55~9.33 μm and the zeta potential: +38.7~+67.5 mV) and an excellent sustained released ability (sustained release up to 180 min). MIC, Glucose assay, MDA assay, biofilm formation inhibition assay, SEM, swimming and swarming motility assay demonstrated that CS-CT-CCa had strong (MIC of 128 μg/ml) and sustained (more than 12 h) inhibitory effects against V. parahaemolyticus. Meanwhile, CS-CT-CCa could increase the membrane permeability of V. parahaemolyticus and inhibit their biofilm-forming ability in a dose-dependent manner. It could be inferred that the antibacterial activities against V. parahaemolyticus caused inhibition of biofilm formation, swimming and swarming motilities. This study provided necessary data for the further design and development of chitosan antibacterial agents, food and feed additives.

Microplastic-Contaminated Feed Interferes with Antioxidant Enzyme and Lysozyme Gene Expression of Pacific White Shrimp (Litopenaeus vannamei) Leading to Hepatopancreas Damage and Increased Mortality

Microplastic pollution can interfere with aquatic animal health and nonspecific immunity, increasing the potential for pathogen infection in crustaceans. However, the long-term effects of microplastics on crustacean immunity are less understood, especially regarding their toxicity in Pacific white shrimp (Litopenaeus vannamei). Effects of high-density polyethylene microplastics (HDPE-MPs) in feed on the mortality rate, hepatopancreas, and nonspecific immune system gene expression of Pacific white shrimp are presented. The LC₅₀ at day 28 of HDPE-MP exposure was determined as 3.074% HDPE-MP in feed. A significant upregulation of the superoxide dismutase (SOD) and glutathione peroxidase (GPx) genes was observed in shrimp that were fed with 0.1 and 0.5% of HDPE-MP; then, they were downregulated significantly, except for the SOD gene expression of shrimp fed with 0.1% of HDPE-MP. The lysozyme (LYZ) gene was upregulated significantly in shrimp that were fed with 0.5, 1, and 3% HDPE-MP for 7 days and downregulated significantly in HDPE-receiving groups for at least 14 days. Significant histopathological changes in the hepatopancreas were observed in the treatment groups. The histopathological score of each lesion was correlated with the increase in HDPE-MP concentration. This study shows that the ingestion of HDPE microplastics can alter the expression of nonspecific immune system genes and damage the hepatopancreas in Pacific white shrimp.

Gut Microbiota Mediates Skin Ulceration Syndrome Outbreak by Readjusting Lipid Metabolism in Apostichopus japonicus

The intestinal tract is the most important location for symbiotes and pathogens, and the microbiota plays a crucial role in affecting the health of the gut and other host organs. Dysbacteriosis in the intestinal system has been proven to be significant in skin ulceration syndrome (SUS) in sea cucumbers. This study investigates whether the gut microbiota and lipid metabolites are relevant to the initiation and progression of SUS in a Vibrio-splendidus-infected sea cucumber model. The tight junction genes were downregulated and the inflammatory factor gene transcriptions were upregulated after V. splendidus infection in the intestinal tissue of the sea cucumber. V. splendidus infection modulated the gut microbiota by interacting with Psychromonas macrocephali, Propionigenium maris, Bacillus cereus, Lutibacter flavus, and Hoeflea halophila. Meanwhile, the metabolites of the long-chain fatty acids in the intestinal tissue, including triglycerides (TG), phosphatidylethanolamines (PE), and phosphatidylglycerols (PG), were altered after V. splendidus infection. V. splendidus engaged in positive interactions with PG and PE and negative interactions with specific TG. These results related to gut microbiota and metabolites can offer practical assistance in the identification of the inflammatory mechanisms related to SUS, and this study may serve as a reference for predicting the disease.

Cadmium and copper mixture effects on immunological response and susceptibility to Vibrio harveyi in white shrimp Litopenaeus vannamei

Cadmium (Cd2+) and copper (Cu2+) are considered immunotoxic metals and their presence in combination in the aquatic environment may cause effects on shrimp species as Litopenaeus vannamei. Thus, this research evaluates the combined effects of Cd2+ and Cu2+ on shrimp inoculated with Vibrio harveyi bacteria. The experiments were performed at 96-h of exposure to sublethal concentrations of both metals. No mortality was observed in organisms exposed to the sum of Criterion of Continuous Concentration (ΣCCC) in Cd + Cu mixture and those inoculated with V. harveyi. Higher clotting times were recorded in Cd + Cu + V. harveyi treatment at higher metal concentrations. No significant differences (P > 0.05) were recorded in hemocyanin content between shrimp exposed to metals and those experimentally infected. Significantly higher (P < 0.05) total hemocyte count (THC) was recorded at 96 h exposure in the ΣCCC and 10% treatments of Cd + Cu + V. harveyi experiment. Regarding Cd + Cu + V. harveyi bioassay, the highest phenoloxidase (PO) activity was recorded in shrimp inoculated with V. harveyi (0.326 ± 0.031 PO units/mg protein) at 96-h exposure. The lowest PO activity was observed in organisms exposed to Cd + Cu + V. harveyi. Regarding superoxide dismutase (SOD) activity, shrimp exposed to higher metal concentrations at 96 h showed the lowest hemolymph activity (6.03 ± 0.62 SOD units/mL). Protein decrease was observed in organisms exposed to metal mixture. The results showed that L. vannamei could be more susceptible to V. harveyi when exposed to Cd + Cu.

Assessment of Performance, Microbial Community, Bacterial Food Quality, and Gene Expression of Whiteleg Shrimp (Litopenaeus vannamei) Reared under Different Density Biofloc Systems

Biofloc shrimp culture, as a way of improving shrimp production, gains worldwide consideration. However, the effects of the biofloc system on shrimp culture at high densities could be a challenge. Here, this study is aimed at identifying a better stocking density of whiteleg shrimp (Litopenaeus vannamei) between two intensive biofloc systems of 100 and 300 org./m2. Achieving that was done by comparing growth performance, water quality, feed utilization, microbial loads from water and shrimps, and gene expression of growth, stress, and immune-related genes. Shrimp postlarvae with a mean weight of 35.4 ± 3.7 mg were reared in six indoor cement tanks (36 m3 total capacity each) at two stocking densities (3 replicates each) for a rearing period of 135 days. Better final weight, weight gain, average daily weight gain, specific growth rate, biomass increase percentage, and survival rate were associated with lower density (100/m2), whereas high-density showed significantly higher total biomass. Better feed utilization was found in the lower density treatment. Lower density treatment enhanced water quality parameters, including higher dissolved oxygen and lower nitrogenous wastes. Heterotrophic bacterial count in water samples was recorded as 5.28 ± 0.15 and 5.11 ± 0.28 log CFU/ml from the high- and low-density systems, respectively, with no significant difference. Beneficial bacteria such as Bacillus spp. were identified in water samples from both systems, still, the Vibrio-like count was developed in the higher density system. Regarding shrimp food bacterial quality, the total bacterial count in the shrimp was recorded as 5.09 ± 0.1 log CFU/g in the 300 org./m2 treatment compared to 4.75 ± 0.24 log CFU/g in the lower density. Escherichia coli was isolated from the shrimps in a lower density group while Aeromonas hydrophila and Citrobacter freundii were associated with shrimps from a higher density system. Immune-related genes including prophenoloxidase, superoxide dismutase (SOD), and lysozyme (LYZ) expressions were all significantly higher expressed in the shrimp from the lower density treatment. Toll receptor (LvToll), penaiedin4 (PEN4), and stress-related gene (HSP 70) showed a decreased gene expression in the shrimp raised in the lower density. Significant upregulation of growth-related gene (Ras-related protein-RAP) expression was associated with the lower stocking density system. In conclusion, the current study found that applying high stocking density (300 org./m2) contributes negatively to performance, water quality, microbial community, bacterial food quality, and gene expression of immune, stress, and growth-related genes when compared with the lower stocking density system (100 org./m2) under biofloc system.

Therapeutic effect and immune mechanism of chitosan-gentamicin conjugate on Pacific white shrimp (Litopenaeus vannamei) infected with Vibrio parahaemolyticus

To explore the disease resistance mechanism of chitosan conjugates, chitosan-gentamicin conjugate (CS-GT) was synthesized and systematically characterized, the immune mechanism of CS-GT on Litopenaeus vannamei infected with Vibrio parahaemolyticus was further explored. The results showed that imine groups in CS-GT were effectively reduced. Dietary supplementation of CS-GT can significantly increase the survival rate, total hemocyte counts, the antioxidant and immune related enzyme activity levels of shrimps (P < 0.05), which are all dose-dependent under the experimental conditions. In addition, CS-GT can protect the hepatopancreas from invading bacteria and alleviate inflammation. Particularly, CS-GT promotes the expressions of legumain (LGMN), lysosomal acid lipase (LIPA) and Niemann-Pick type C2 (NPC2) up-regulated. It is speculated that CS-GT may stimulate the lysosome to phagocytose pathogens more effectively. In conclusions, shrimps fed with CS-GT can produce immune response via lysosome and greatly improve the disease resistance to Vibrio parahaemolyticus.

The Molecular Mechanism of Hemocyte Immune Response in Marsupenaeus japonicus Infected With Decapod Iridescent Virus 1

As a new type of shrimp lethal virus, decapod iridescent virus 1 (DIV1) has caused huge economic losses to shrimp farmers in China. Up to now, DIV1 has been detected in a variety of shrimps, but there is no report in Marsupenaeus japonicus. In the current study, we calculated the LC₅₀ to evaluate the toxicity of DIV1 to M. japonicus and determined through nested PCR that M. japonicus can be the host of DIV1. Through enzyme activity study, it was found that DIV1 can inhibit the activities of superoxide dismutase, catalase, lysozyme, and phenoloxidase, which could be a way for DIV1 to achieve immune evasion. In a comprehensive study on the transcriptomic changes of M. japonicus in response to DIV1 infection, a total of 52,287 unigenes were de novo assembled, and 20,342 SSR markers associated with these unigenes were obtained. Through a comparative transcriptomic analysis, 6,900 differentially expressed genes were identified, including 3,882 upregulated genes and 3,018 downregulated genes. The Gene Ontology (GO) and Kyoto Encyclopedia of Genes and Genomes (KEGG) enrichment analysis showed that some GO terms related to virus invasion, replication, and host antiviral infection were promoted under DIV1 infection, such as carbohydrate binding, chitin binding, chitin metabolic process, and DNA replication initiation, and some KEGG pathways related to immune response were significantly influenced by DIV1 infection, including Toll and IMD signaling pathway, JAK-STAT signaling pathway, IL-17 signaling pathway, C-type lectin receptor signaling pathway, complement and coagulation cascades, antigen processing and presentation, necroptosis, apoptosis, NOD-like receptor signaling pathway, apoptosis-multiple species, and TNF signaling pathway. Further analysis showed that STAT, Dorsal, Relish, heat shock protein 70 (HSP70), C-type lectins, and caspase play an important role in DIV1 infection. This is the first detailed study of DIV1 infection in M. japonicus, which initially reveals the molecular mechanism of DIV1 infection in M. japonicus by using the transcriptome analysis of hemocytes combined with enzyme activity study.

Transcriptome Analysis of the Hepatopancreas in the Litopenaeus vannamei Responding to the Lead Stress

Lead (Pb) is one of the most hazardous pollutants and toxic heavy metal in marine environment. The molecular mechanisms of Pb toxicity in aquatic organism are not well understood. In this study, hepatopancreas transcriptome of Litopenaeus vannamei (L. vannamei) was characterized by a comparison between control and Pb exposure samples using RNA-Seq approach. Hepatopancreas morphology of L. vannamei was also assessed. The result reveals that compared with the control group, an increase in the number of B cells was observed following Pb exposure in L. vannamei. Transcriptome data showed that a total of 1593 genes were recognized to be differentially expressed including 1278 up-regulated and 315 down-regulated genes. These genes were mainly associated with energy metabolism, cell apoptosis, exogenous microbial infection, cell junction, and cell adhesion. Fifteen ribosomal protein genes (RPS3, RPS13, RPSA, RPL11, RPS2, RPL8, RPS23, RPL3, RPL5, RPS6, RPS4X, RPS18, RPL19, RPL9, RPL6) were identified as the common hubs of protein-protein interaction (PPI) networks, as well as part of modules of the PPI network. Besides ribosomal protein, we identified differential expression genes (DEGs) including GAPDH, EEF1A1, HSPA8, UBC, and EEF1G as the common hubs of PPI networks. These findings may have important implications for understanding the adverse biological effects of Pb and its toxic mechanisms, as yet not clearly defined, and provide potential biomarkers of Pb exposure in hepatopancreas of L. vannamei, which might be useful for monitoring aquatic environments and assessing the health of the marine ecosystem.

Effects of Chitosan-Gentamicin Conjugate Supplement on Non-Specific Immunity, Aquaculture Water, Intestinal Histology and Microbiota of Pacific White Shrimp (Litopenaeus vannamei)

When the aquaculture water environment deteriorates or the temperature rises, shrimp are susceptible to viral or bacterial infections, causing a large number of deaths. This study comprehensively evaluated the effects of the oral administration of a chitosan-gentamicin conjugate (CS-GT) after Litopenaeus vannamei were infected with Vibrio parahaemolyticus, through nonspecific immunity parameter detection, intestinal morphology observation, and the assessment of microbial flora diversification by 16S rRNA gene sequencing. The results showed that the oral administration of CS-GT significantly increased total hemocyte counts and reduced hemocyte apoptosis in shrimp (p < 0.05). The parameters (including superoxide dismutase, glutathione peroxidase, glutathione, lysozyme, acid phosphatase, alkaline phosphatase, and phenoloxidase) were significantly increased (p < 0.05). The integrity of the intestinal epithelial cells and basement membrane were enhanced, which correspondingly alleviated intestinal injury. In terms of the microbiome, the abundances of Vibrio (Gram-negative bacteria and food-borne pathogens) in the water and gut were significantly reduced. The canonical correspondence analysis (CCA) showed that the abundances of Vibrio both in the water and gut were negatively correlated with CS-GT dosage. In conclusion, the oral administration of CS-GT can improve the immunity of shrimp against pathogenic bacteria and significantly reduce the relative abundances of Vibrio in aquaculture water and the gut of Litopenaeus vannamei.