Effect of infection with Aeromonas hydrophila on antioxidant capacity, inflammation response, and apoptosis proteins in Chinese mitten crab (Eriocheir sinensis)

Effects of air exposure time on tissue morphology, energy metabolism, and non-specific immunity of the juvenile Chinese mitten crab, Eriocheir sinensis

This study investigated the effect of aerial exposure duration (0, 24, 48, and 72 h) on the juvenile Chinese mitten crab, Eriocheir sinensis. The effects on histological structure, energy metabolism, non-specific immunity, and expression of cytochrome P450 (CYP2) and protein kinase B (AKT) genes in the anterior gill and hepatopancreas were analyzed. Longer durations of air exposure led to loss of anterior gill filament shape, and enlargement and deformation of the hepatopancreatic tubules with vacuolization. Pyruvate kinase activity in the hemolymph peaked, and was the lowest in the anterior gill, at 72 h. Lactate dehydrogenase activity and lactic acid content in the hemolymph and anterior gills peaked at 72 h of air exposure. Triglyceride content in hemolymph and anterior gill first increased, then decreased. Superoxide dismutase activity and total antioxidant capacity increased in the hemolymph but initially increased and then decreased in the hepatopancreas, peaking at 24 h. Hemolymph and hepatopancreas acid phosphatase activity peaked at 48 h and in these same tissues lysozyme activity declined with prolonged air exposure. The relative expression of CYP2 and AKT increased during exposure to air in both gill and hepatopancreas. Air exposure exceeding 48 h may affect tissue morphology, energy metabolism, oxidative stress, and immunity of juvenile E. sinensis. Juvenile crabs alter their energy utilization, antioxidant, and metabolic capacities to acclimate to air exposure stress. Therefore, the air exposure time for juvenile E. sinensis should be limited to 48 h during transportation.

The involvement of Rab5 in regulating haematopoiesis in the Chinese mitten crab Eriocheir sinensis

Rab5 functions as a pivotal regulator in the intricate processes of membrane trafficking, orchestrating a multitude of cellular activities. In the present study, a Rab5 homolog with conserved structure features was identified from Chinese mitten crab Eriocheir sinensis (designated EsRab5). The mRNA transcripts of EsRab5 were detected in all the tested tissues, with particularly high expression levels observed in brain and haematopoietic tissue (HPT). Notably, its mRNA expression in HPT was significantly up-regulated at 6 and 12 h following stimulation with Aeromonas hydrophila. Immunocytochemical assay showed that EsRab5 protein was diffusely distributed throughout the HPT, with a particularly prominent concentration in the cytoplasm. After A. hydrophila stimulation, the immunoreactive signals for EsRab5 in HPT were markedly more intense compared to those in the control group. Upon injection of EsRab5-specific siRNA to inhibit its expression, a significant increase in the percentage of EdU-positive cells within HPT was observed following A. hydrophila stimulation, which was 2.62-fold (p < 0.0001) of that in the EGFP-RNAi group. Meanwhile, the expression levels of proliferation related factors (EsRunx, EsGLP and EsAstakine), cell cycle-related proteins (EsCyclin E, EsCDK2, EsCDK4, and EsCyclin D) as well as the MAPK signal pathway were increased significantly in EsRab5-RNAi crabs after A. hydrophila stimulation. These results suggested that EsRab5 serves as a critical regulator in homeostasis maintenance of haematopoiesis in E. sinensis by modulating multiple factors.

Development of Duplex Loop-Mediated Isothermal Amplification with Hydroxynaphthol Blue for Detection of Infectious Spleen and Kidney Necrosis Virus and Aeromonas hydrophila in Chinese Perch (Siniperca chuatsi)

Bacterial sepsis caused by Aeromonas hydrophila (A. hydrophila) and infectious spleen and kidney necrosis virus disease (ISKNVD) caused by infectious spleen and kidney necrosis virus (ISKNV) frequently result in significant mortality among Chinese perch (Siniperca chuatsi). Co-infection of mandarin fish with A. hydrophila and ISKNV occurs from time to time. In this study, a visual detection method for ISKNV and A. hydrophila was developed, using loop-mediated isothermal amplification (LAMP) and pre-addition of hydroxynaphthol blue. Primers for amplifying LAMP in the same system were designed based on the conserved regions of the MCP gene of infectious spleen and kidney necrosis virus, as well as the hlyA gene of A. hydrophila. The results showed that this method amplified bright trapezoidal bands in the presence of only A. hydrophila or ISKNV and both, with sky blue for positive amplification and violet for negative amplification. There was no cross-reactivity with other pathogens, and fragments of 182 bp, 171 bp and 163 bp appeared after digestion of the A. hydrophila LAMP product and 136 bp, 117 bp and 96 bp appeared after digestion of the ISKNV LAMP product. This holds true even when both positive products are present simultaneously. The minimum detection limit of this method was 100 fg for A. hydrophila and 100 fg for ISKNV, and the minimum detection limit for the mixed template was 1 pg. Overall, this method has high sensitivity and specificity to rapidly detect and distinguish between the two pathogens.

Survival, serum biochemical parameters, hepatic antioxidant status, and gene expression of three Nile tilapia strains under pathogenic Streptococcus agalactiae challenge

Streptococcosis is the leading bacterial disease impacting Nile tilapia (Oreochromis niloticus) and causes substantial economic losses in China. This study assessed the resistance and tolerance of three Nile tilapia (88, 99, and NG) to Streptococcus agalactiae infection. Survival rates were monitored, and samples were collected from blood, liver, and spleen at 0, 1, 2, 5, 7, and 14 days post-infection. Serum biochemical parameters, hepatic antioxidant enzymes, and the expression of related antioxidant and immune genes were measured. Results showed that strain 88 had superior resistance, with the highest survival rate, reduced liver damage, and lower alanine aminotransferase and alkaline phosphatase levels at 1 and 5 days post-infection. This strain also had higher serum cholesterol and triglyceride levels between days 5 and 14. Antioxidant activities increased in all strains post-infection, with strain 88 showing significantly higher superoxide dismutase (SOD) activity and elevated catalase (CAT) and SOD gene expressions; this indicated enhanced control of reactive oxygen species and reduced tissue damage. Additionally, strain 88 exhibited lower levels of inflammatory markers (TNF-α, IL-1β, IL-10) with higher IgM levels and superior MHC-II expression during early infection, which demonstrated a strong immune response. These results indicate that strain 88 is a promising candidate for selective breeding to improve streptococcosis resistance in tilapia.

Protective effect of fructooligosaccharide against oxidative stress and apoptosis induced by Aeromonas hydrophila in Megalobrama amblycephala

This research aimed to investigate the effects of dietary fructooligosaccharides (FOS) on attenuating the Aeromonas hydrophila (A. hydrophila)-induced oxidative stress and apoptosis in blunt snout bream Megalobrama amblycephala. Fish were divided into three groups as follows: C1 (Control), T1 (A. hydrophila), and T2 (A. hydrophila + 4 g/kg FOS). The results showed that the activities of antioxidant enzymes increased, the liver morphology had disorderly arrangement, and extensive cell necrosis occurred because of A. hydrophila-infection. While the dietary FOS improved the above-mentioned liver damage. Additionaly, FOS elevated mRNA levels of pro-apoptotic molecules, including caspase-8 and 9, and down-regulated mRNA levels of the anti-apoptotic molecule Bcl-2, which is triggered by A. hydrophila-infection. The transcriptome analysis showed that the oxidative stress-related DEGs pathways were activated in intestine of blunt snout bream by A. hydrophila-infection. The FOS-added group led to the enrichment of more pathways to health. Further WGCNA co-expression network analysis showed that the screened single genes were clustered into 49 modules. The two modules with the highest association to the five traits (10 hub genes) were chosen to build the network by combining the physiological and biochemical characteristic. In summary, this research offers a foundation for the exploring of A. hydrophila-restoration genes in dietary FOS, and also lays a theoretical foundation for aquaculture in the future.

Immune response to Aeromonas hydrophila and molecular characterization of polymeric immunoglobulin receptor in juvenile Megalobrama amblycephala

Polymeric immunoglobulin receptor (pIgR) is an important immune factor in the mucosal immune system of fish, which plays a key role in mediating the secretion and transport of immunoglobulin into mucus. In this study, the full-length cDNA sequence of Megalobrama amblycephala pIgR gene was firstly cloned and the immune response to Aeromonas hydrophila was detected. After being challenged by Aeromonas hydrophila at 3 d, significantly pathological features were observed in intestine, head kidney, spleen, liver and gill of Megalobrama amblycephala. The content of lysozyme (Lys) and the activities of acid phosphatase (ACP) and alkaline phosphatase (AKP) increased significantly at 1 d and reached the peak at 3 d, and the activities of total superoxide dismutase (T-SOD), glutathione peroxidase (GSH-PX) and catalase (CAT) in serum reached the peak at 5 d and 7 d after infection, respectively. The expression level of IL-1β gene reached the peak at 3 d in intestine, 5 d in gill and spleen, 7 d in head kidney and liver of Megalobrama amblycephala after infected by Aeromonas hydrophila, respectively. The TNF-α gene expression reached the peak at 3 d in intestine and gill, 5 d in head kidney and spleen, 7 d in liver after infection, respectively. The experimental results showed that the infection of Aeromonas hydrophila caused the pathological changes of immune-related tissues and triggered the inflammation responses. The full-length cDNA sequence of Megalobrama amblycephala pIgR was 1828 bp, and its open reading frame (ORF) was 1023 bp, encoding 340 amino acids. The pIgR of Megalobrama amblycephala has a signal peptide sequence, followed by extracellular region, transmembrane region and intracellular region. The extracellular region includes two Ig-like domains (ILDs), and its tertiary structure is twisted "L". The phylogenetic tree was constructed using the adjacency method, and the pIgR genes of Megalobrama amblycephala and cyprinidae fish were clustered into a single branch. Quantitative real-time PCR (qRT-PCR) was used to detect the expression of pIgR gene in different tissues of Megalobrama amblycephala. The expression level of pIgR gene was the highest in liver, followed by intestine, head kidney, skin, middle kidney and spleen, lower in heart, gill and brain, and the lowest in muscle. After being infected by Aeromonas hydrophila, the expression level of Megalobrama amblycephala pIgR gene in intestine, head kidney, spleen, liver and gill showed a trend of increasing first and then decreasing within 28 d. The pIgR gene expression reached the peak in mucosal immune-related tissues (gill and intestine) was earlier than that in systemic immune-related tissues (head kidney and spleen), and the relative expression level of pIgR gene at peak in intestine (12.3 fold) was higher than that in head kidney (3.73 fold) and spleen (7.84 fold). These results suggested that Megalobrama amblycephala pIgR might play an important role in the mucosal immune system to against Aeromonas hydrophila infection.

Changes of intestinal barrier in the process of intestinal inflammation induced by Aeromonas hydrophila in snakehead (Channa argus)

Bacterial intestinal inflammation frequently occurs in cultured fish. Nevertheless, research on intestinal barrier dysfunction in the process of intestinal inflammation is deficient. In this study, we explored the changes of intestinal inflammation induced by Aeromonas hydrophila (A. hydrophila) in snakehead and the relationship between intestinal barrier and inflammation. Snakehead [(13.05 ± 2.39) g] were infected via anus with A. hydrophila. Specimens were collected for analysis at 0, 1, 3, 7 and 21 d post-injection. The results showed that with the increase of exposure time, the hindgut underwent stages of normal function, damage, damage deterioration, repair and recovery. Relative to 0 d, the levels of IL-1β and TNF-α in serum, and the expression of nod1, tlr1, tlr5, nf-κb, tnf-α and il-1β in intestine were significantly increased, and showed an upward then downward pattern over time. However, the expression of tlr2 and il-10 were markedly decreased, and showed the opposite trend. In addition, with the development of intestinal inflammation, the diversity and richness of species, and the levels of phylum and genus in intestine were obviously altered. The levels of trypsin, LPS, AMS, T-SOD, CAT, GPx, AKP, LZM and C3 in intestine were markedly reduced, and displayed a trend of first decreasing and then rebounding. The ultrastructure observation showed that the microvilli and tight junction structure of intestinal epithelial cells experienced normal function initially, then damage, and finally recovery over time. The expression of claudin-3 and zo-1 in intestine were significantly decreased, and showed a trend of first decreasing and then rebounding. Conversely, the expression of mhc-i, igm, igt and pigr in intestine were markedly increased, and displayed a trend of increasing first and then decreasing. The above results revealed the changes in intestinal barrier during the occurrence and development of intestinal inflammation, which provided a theoretical basis for explaining the relationship between the two.

Effects of Citrobacter freundii on sturgeon: Insights from skin mucosal immunology and microbiota

Skin mucus analysis has recently been used as a non-invasive method to evaluate for fish welfare. The present research study was conducted to examine the skin mucosal immunity and skin microbiota profiles of sturgeons infected with Citrobacter freundii. Our histology results showed that the thickness of the epidermal layer of skin remained thinner, and the number of mucous cells was significantly decreased in sturgeons after infection (p < 0.05). Total protein, alanine aminotransferase, aspartate aminotransferase, superoxide dismutase, and creatine kinase levels in the mucus showed biphasic pattern (decrease and then increase). Lactate dehydrogenase, lysozyme, and acid phosphatase activities in the mucus showed an increasing trend after infection. Furthermore, 16S rRNA sequencing also revealed that C. freundii infection also affected the diversity and community structure of the skin mucus microbiota. An increase in microbial diversity (p > 0.05) and a decrease in microbial abundance (p < 0.05) after infection were noted. The predominant bacterial phyla in the skin mucus were Proteobacteria, Fusobacteria, Bacteroidetes, Firmicutes, and Actinobacteria. Specifically, the relative abundance of Fusobacteria increased after infection. The predominant bacterial genera in the skin mucus were Cetobacterium, Pelomonas, Bradyrhizobium, Flavobacterium, and Pseudomonas. The relative abundance of Cetobacterium, Pseudomonas, and Flavobacterium increased after infection. Our current research findings will provide new insights into the theoretical basis for future research studies exploring the mechanism of sturgeon infection with C. freundii.

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.

Aquafeed fermentation improves dietary nutritional quality and benefits feeding behavior, meat flavor, and intestinal microbiota of Chinese mitten crab (Eriocheir sinensis)

Normally, proper fermentation can be an efficient and widely used method to improve feed quality in animal rearing; however, the studies on crustaceans, especially Eriocheir sinensis, remain limited. This study aimed to investigate whether feed fermentation could meliorate dietary nutritional value and benefit E. sinensis rearing. First, non-fermented feed (NFD) and fermented feed (FD) were produced and assessed, respectively. Then, the "Y" maze feed choice behavior test (180 times; 30 times, 6 rounds) was conducted to assess the attractiveness of these 2 feeds for crabs. Finally, a total of 80 crabs (44.10 ± 0.80 g) were randomly assigned into 2 groups with 4 replicates, and fed the experimental diets for 8 weeks to evaluate the effects of each feed on growth, antioxidant capacity, meat flavor, and intestinal microbiota. In this study, FD showed higher levels of crude protein (P < 0.01), soluble protein (P < 0.01), amino acids (P < 0.05), lactic acid (P < 0.001), and lower levels of crude fiber (P < 0.05) and antinutritional factors (agglutinin, trypsin inhibitor, glycinin, and β-conglycinin) (P < 0.001) than NFD. Additionally, FD was more attractive to crabs than NFD (P < 0.01) and it stimulated the appetite of crabs more than NFD (P < 0.05). The growth performance, feed efficiency, and digestive enzyme activity of FD-fed crabs were significantly higher than those of NFD-fed crabs (P < 0.05). The electronic sensory measurements and free amino acid profiles revealed that the FD diet had positive impacts on the meat flavor of crabs, particularly in "sweet" and "umami" tastes. Moreover, the antioxidant capacity of FD-fed crabs was significantly higher than that of NFD-fed crabs (P < 0.05). Fermented feed also affected the diversity and composition of intestinal microflora. The functional prediction of microbial communities showed that crabs fed FD had a better microecological environment in the intestine. In conclusion, the fermentation of aquafeed could be an effective approach to enhance feed quality and therefore benefit E. sinensis rearing.

Effect of kelp powder on the resistance of Aeromonas hydrophila in the gut of hybrid snakeheads (Channa maculata ♀ × Channa argus ♂)

To assess the level of oxidative stress, expression of immune-related genes, histomorphology, and changes in the intestinal tract of hybrid snakeheads(Channa maculata ♀ × Channa argus ♂) under stress from kelp powder in place of flour against Aeromonas hydrophila. We set up experimental diets: a control (C) diet of 20% flour, an experimental (MR) diet of 10% kelp powder and 10% flour, and an experimental (FR) diet of 0% starch and 15% kelp powder. The experimental fish in each group were infected with Aeromonas hydrophila after 60 days of feeding. For this experiment, some of the experimental fish in group C were injected with PBS as a negative control group (PBS). The results showed that the C group had significantly higher SOD, CAT, and T-AOC activity and expression of TAK1, IKKβ, IL-1β, and TNF-α genes in the MyD88 pathway than the PBS group. CAT activity and the expression of TAK1, IL-1β and TNF-α genes in the MyD88 pathway were significantly lower in the MR group than in the C group. Furthermore, the number of goblet cells in the MR group was significantly higher than in the C group. Furthermore, microorganisms such as Bacteroidota and Actinobacteriota were significantly lower in the C group than in the PBS and FR groups, as were beneficial bacteria such as Clostridium_sensu_stricto_1 and Sphingomonas. Replacing flour with kelp powder increases hybrid snakehead gut resistance to Aeromonas hydrophila.

Dietary supplementation of probiotics fermented Chinese herbal medicine Sanguisorba officinalis cultures enhanced immune response and disease resistance of crucian carp (Carassius auratus) against Aeromonas hydrophila

Aeromonas hydrophila, a Gram-negative bacterium, is one of the major pathogens causing bacterial sepsis in aquatic animals due to drug resistance and pathogenicity, which could cause high mortality and serious economic losses to the aquaculture. Sanguisorba officinalis (called DiYu in Chinese, DY) is well known as herbal medicine, which could inhibit the growth of pathogenic bacteria, hemostasis and regulate the immune response. Moreover, the active ingredients in DY could remarkably reduce drug resistance. In this study, we investigated the effects of probiotic fermentation cultures on A. hydrophila through in vitro and in vivo experiments. Three lactic acid bacteria, including Lactobacillus rhamnosus (LGG), Lactobacillus casei (LC) and Lactobacillus plantarum (LP), were selected to ferment the Chinese herbal medicine DY. The assays of antagonism showed that all three fermented cultures could influence the ability of A. hydrophila growth, among which L. rhamnosus fermented DY cultures appeared to be the strongest inhibitory effect. In addition, the biofilm determination revealed that L. rhamnosus fermented DY cultures could significantly inhibit the biofilm formation of A. hydrophila compared to the other groups. Furthermore, protease, lecithinase and urease activities were found in the three fermentation cultures. Three probiotics fermented DY cultures were orally administration with crucian carp to evaluate the growth performance, immunological parameters and pathogen resistance. The results showed that the three fermentation cultures could promote the growth performance of crucian carp, and the immunoglobulins, antioxidant-related enzymes and immune-related genes were significantly enhanced. Besides, the results showed that crucian carp received L. rhamnosus (60.87%), L. casei (56.09%) and L. plantarum (41.46%) fermented DY cultures had higher survival rates compared with the control group after infection with A. hydrophila. Meanwhile, the pathological tissue results revealed that the probiotic fermented cultures could largely improve the tissues damage caused by the pathogenic bacteria. In conclusion, this study proved that the fermentation cultures of three probiotics could effectively inhibit the growth of A. hydrophila, regulate the level of immune response and improve the survival rate against A. hydrophila in crucian carp. The present data suggest that probiotic fermented Sanguisorba officinalis act as a potential gut-targeted therapy regimens to protecting fish from pathogenic bacteria infection.

A new potential risk: The impacts of Klebsiella pneumoniae infection on the histopathology, transcriptome and metagenome of Chinese mitten crab (Eriocheir sinensis)

Klebsiella pneumoniae is a common conditional pathogen found in natural soil water sources and vegetation and can infect invertebrates, vertebrates, and plants. In this study, we isolated K. pneumoniae from the hepatopancreas of the Chinese mitten crab (Eriocheir sinensis) for the first time and then we analysed its effects of on the histopathological changes, the transcriptome of the hepatopancreas, and the gut microbiota of this crab species. The findings of this study showed that K. pneumoniae infection has led to significant structural changes in the hepatopancreas, such as the production of vacuolated tissue structures, disorganized cell arrangement, and lysis of some hepatopancreatic cells. Also, the infection caused activation of the antioxidant-related enzymes such as SOD and CAT by inducing oxidative stress. The transcriptome of the hepatopancreas identified 10,940 differentially expressed genes (DEGs) in the susceptible (SG) groups and control (CG) groups, and 8495 DEGs in the SG groups and anti-infective (AI) groups. The KEGG pathway revealed upregulated DEGs caused by K. pneumoniae infection that involved in the immune response and apoptotic functional pathways, and also downregulated DEGs involved in the digestive absorption, metabolic, and biosynthetic signaling pathways. Meanwhile, metagenics sequencing revealed that at the phylum, class, order, family, and genus levels, K. pneumoniae infection altered the composition of the gut microbiota of E. sinensis, through increasing the abundance of Prolixibacteraceae, Enterobacterales, and Roseimarinus and decreasing the abundance of Alphaproteobacteria. The flora structure has also been changed between the SG and AI groups, with the abundance of Firmicutes, Erysipelotrichales, and Erysipelotrichaceae that were significantly decreased in the SG groups than in the AI groups. But, the abundance of Acinetobacter was considerably higher than in the AI group. In summary, K. pneumoniae infection induced oxidative stress in E. sinensis, triggered changes in immune-related gene expression, and caused structural changes in the gut microbiota. This study provides data to support the analysis of bacterial infection probes in several crustacean species.