Transcriptomic profiling revealed the signatures of intestinal barrier alteration and pathogen entry in turbot (Scophthalmus maximus) following Vibrio anguillarum challenge

LncRNA (BCO1-AS) regulate inflammatory responses in bacterial infection through caspase-1 in turbot (Scophthalmus maximus)

LncRNA plays key role in several biological processes, including transcriptional regulation, post transcriptional control and epigenetic regulation. However, research on the functional roles of lncRNAs in teleost species remains limited. Here, we discovered a lncRNA (BCO1-AS) with a critical role in antibacterial responses. Briefly, the full length of BCO1-AS was 2005 bp. Subsequently, BCO1-AS was distributed throughout the nucleus, where it may either trans- or cis-regulate the nearby genes. In addition, BCO1-AS was widely expressed in all the examined tissues with the highest expression level in intestine, while the lowest expression level was detected in muscle. Moreover, following Vibrio anguillarum challenge, BCO1-AS was significantly down-regulated in intestine, and up-regulated in gill and skin. In CHIRP experiment, BCO1-AS could effectively enrich RNA and might interact with several immune-related genes. Furthermore, we found that LPS could induce the expression of BCO1-AS. Finally, BCO1-AS could positively regulate caspase-1 at the mRNA and protein level. The BCO1-AS was speculated to inhibit the synthesis of inflammatory components. In summary, these results showed the roles of BCO1-AS in the regulation of inflammatory in turbot, which provided valuable information for further understanding the immune regulation network of lncRNA in teleost fish.

Effect of time series on the degradation of lignin by Trametes gibbosa: Products and pathways

Lignin is the third most abundant organic resource in nature. The utilization of white-rot fungi for wood degradation effectively circumvents environmental pollution associated with chemical treatments, facilitating the benign decomposition of lignin. Trametes gibbosa is a typical white-rot fungus with rapid growth and strong wood decomposition ability. The lignin content decreased from 23.62 mg/mL to 17.05 mg/mL, which decreased by 27 % in 30 days. The activity of manganese peroxidase increased steadily by 9.44 times. The activities of laccase and lignin peroxidase had the same trend of change and reached peaks of 49.88 U/L and 10.43 U/L on the 25th day, respectively. The change in H2O2 content in vivo was opposite to its trend. For FTIR and GC-MS analysis, the fungi attacked the side chain structure of lignin phenyl propane polymer and benzene ring to crack into low molecular weight aromatic compounds. The side chains of low molecular weight aromatic compounds are oxidized, and long-chain carboxylic acids are formed. Additionally, the absorption peak in the vibration region of the benzene ring skeleton became complex, and the structure of the benzene rings changed. In the beginning, fungal growth was inhibited. Fungal autophagy was aggravated. The metal cation binding proteins of fungi were active, and the genes related to detoxification metabolism were upregulated. The newly produced compounds are related to xenobiotic metabolism. The degradation peak focused on the redox process, and the biological function was enriched in the regulation of macromolecular metabolism, lignin metabolism, and oxidoreductase activity acting on diphenols and related substances as donors. Notably, genes encoding key degradation enzymes, including lcc3, lcc4, phenol-2-monooxygenase, 3-hydroxybenzoate-6-hydroxylase, oxalate decarboxylase, and acetyl-CoA oxidase were significantly upregulated. On the 30th day, the N-glycan biosynthesis pathway was significantly enriched in glycan biosynthesis and metabolism. Weighted correlation network analysis was performed. A total of 1452 genes were clustered in the coral1 module, which were most related to lignin degradation. The genes were significantly enriched in oxidoreductase activity, peptidase activity, cell response to stimulation, signal transduction, lignin metabolism, and phenylpropane metabolism, while the rest were concentrated in glucose metabolism. In this study, the lignin degradation process and products were revealed by T. gibbosa. The molecular mechanism of lignin degradation in different stages was explored. The selection of an efficient utilization time of lignin will help to increase the degradation rate of lignin. This study provides a theoretical basis for the biofuel and biochemical production of lignin. SYNOPSIS: Trametes gibbosa degrades lignin in a pollution-free way, improving the utilization of carbon resources in an environmentally friendly spontaneous cycle. The products are the new way towards sustainable development and low-carbon technology.

A comprehensive study on the multifunctional properties of galectin-4 in red-lip mullet (Planiliza haematocheilus): Insights into molecular interactions, antimicrobial defense, and cell proliferation

Galectin-4 belongs to the galactoside-binding protein family and is a type of tandem repeat galectin. Despite previous studies indicating its importance in fish immunology, a comprehensive investigation is necessary to fully understand its role in immunomodulatory functions and cellular dynamics. Therefore, this study aimed to explore the immunomodulatory functions of galectin-4 with a particular focus on its antimicrobial and cellular proliferative properties. The open reading frame of PhGal4 spans 1092 base pairs and encodes a soluble protein of 363 amino acids with a theoretical isoelectric point (IEP) of 6.39 and a molecular weight of 39.411 kDa. Spatial expression analysis under normal physiological conditions revealed ubiquitous expression of PhGal4 across all examined tissues, with the highest level observed in intestinal tissue. Upon stimulation with poly I:C, LPS, and L. garvieae, a significant increase (p < 0.05) in PhGal4 expression was observed in both blood and spleen tissues. Subsequent subcellular localization assay demonstrated that PhGal4 was predominantly localized in the cytoplasm. The recombinant PhGal4 (rPhGal4) exhibited specific binding capabilities to pathogen-associated molecular patterns (PAMPs), including LPS and peptidoglycan, but not poly I:C. The rPhGal4 negatively affected the bacterial growth kinetics. Additionally, rPhGal4 demonstrated complete hemagglutination of fish erythrocytes, which could be inhibited by the presence of D-galactose and α-lactose. The overexpression of PhGal4 in FHM epithelial cells demonstrated a significant suppression of viral replication during VHSV infection. Furthermore, the in vitro scratch assay and WST-1 assay demonstrated a wound healing effect of PhGal4 overexpression in FHM cells, potentially achieved through the promotion of cell proliferation by activating genes involved in cell cycle regulation. In conclusion, the responsive expression to immune stimuli, antimicrobial properties, and cell proliferation promotion of PhGal4 suggest that it plays a crucial role in immunomodulation and cellular dynamics of red-lip mullet. The findings in this study shed light on the multifunctional nature of galectin-4 in teleost fish.

Dietary cholesterol intervention could alleviate the intestinal injury of Oreochromis niloticus induced by plant-based diet via the intestinal barriers

This study aims to explore the effects of supplementing cholesterol in plant-based feed on intestinal barriers (including physical barrier, chemical barrier, immune barrier, biological barrier) of GIFT strain tilapia (Oreochromis niloticus). Four isonitrogenous and isolipidic diets were prepared as follows: plant-based protein diet (Con group) containing corn protein powder, soybean meal, cottonseed meal, and rapeseed meal, with the addition of cholesterol at a level of 0.6 % (C0.6 % group), 1.2 % (C1.2 % group), and 1.8 % (C1.8 % group), respectively. A total of 360 fish (mean initial weight of (6.08 ± 0.12) g) were divided into 12 tanks with 30 fish per tank, each treatment was set with three tanks and the feeding period lasted 9 weeks. Histological analysis revealed that both the C0.6 % and C1.2 % groups exhibited a more organized intestinal structure, with significantly increased muscle layer thickness compared to the Con group (P < 0.05). Furthermore, in the C1.2 % group, there was a significant up-regulation of tight junction-related genes (claudin-14, occludin, zo-1) compared to the Con group (P < 0.05). 5-ethynyl-2'-deoxyuridine staining results also demonstrated a notable enhancement in intestinal cell proliferation within the C1.2 % group (P < 0.05). Regarding the intestinal chemical barrier, trypsin and lipase activities were significantly elevated in the C1.2 % group (P < 0.05), while hepcidin gene expression was considerably down-regulated in this group but up-regulated in the C1.8 % group (P < 0.05). In terms of the intestinal immune barrier, inflammation-related gene expression levels (tnf-α, il-1β, caspase 9, ire1, perk, atf6) were markedly reduced in the C1.2 % group (P < 0.05). Regarding the intestinal biological barrier, the composition of the intestinal microbiota indicated that compared to the Con group, both the 0.6 % and 1.2 % groups showed a significant increase in Shannon index (P < 0.05). Additionally, there was a significant increase in the abundance of Firmicutes and Clostridium in the C1.2 % group (P < 0.05). In summary, supplementation of 1.2 % cholesterol in the plant-based diet exhibits the potential to enhance intestinal tight junction function and improve the composition of intestinal microbiota, thereby significantly promoting tilapia's intestinal health.

Fermented bile acids improved growth performance and intestinal health by altering metabolic profiles and intestinal microbiome in Micropterus salmoides

A type of fermented bile acids (FBAs) has been produced through a biological method, and its effects on growth performance, metabolism, and intestinal microbiota in largemouth bass were investigated. The results demonstrated that incorporating 0.03 %-0.05 % FBAs diet could improve the final weight, weight gain and specific growth rate, and decrease the feed conversion ratio. Dietary FBAs did not significantly affect the levels of high-density lipoprotein, low-density lipoprotein, and triglycerides, but decreased the activities of α-amylase in most groups. Adding FBAs to the diet significantly increased the integrity of the microscopic structure of the intestine, thickened the muscular layer of the intestine, and notably enhanced its intestinal barrier function. The addition of FBAs to the diet increased the diversity of the gut microbiota in largemouth bass. At the phylum level, there was an increase in the abundance of Proteobacteria, Firmicutes, Tenericutes and Cyanobacteria and a significant decrease in Actinobacteria and Bacteroidetes. At the genus level, the relative abundance of beneficial bacteria Mycoplasma in the GN6 group and Coprococcus in the GN4 group significantly increased, while the pathogenic Enhydrobacter was inhibited. Meanwhile, the highest levels of AKP and ACP were observed in the groups treated with 0.03 % FBAs, while the highest levels of TNF-α and IL-10 were detected in the group treated with 0.04 % FBAs. Additionally, the highest levels of IL-1β, IL-8T, GF-β, IGF-1, and IFN-γ were noted in the group treated with 0.06 % FBAs. These results suggested that dietary FBAs improved growth performance and intestinal wall health by altering lipid metabolic profiles and intestinal microbiota in largemouth bass.

Gelsenicine disrupted the intestinal barrier of Caenorhabditis elegans

Gelsemium elegans Benth. (G. elegans) is a traditional medicinal herb that has anti-inflammatory, analgesic, sedative, and detumescence effects. However, it can also cause intestinal side effects such as abdominal pain and diarrhea. The toxicological mechanisms of gelsenicine are still unclear. The objective of this study was to assess enterotoxicity induced by gelsenicine in the nematodes Caenorhabditis elegans (C. elegans). The nematodes were treated with gelsenicine, and subsequently their growth, development, and locomotion behavior were evaluated. The targets of gelsenicine were predicted using PharmMapper. mRNA-seq was performed to verify the predicted targets. Intestinal permeability, ROS generation, and lipofuscin accumulation were measured. Additionally, the fluorescence intensities of GFP-labeled proteins involved in oxidative stress and unfolded protein response in endoplasmic reticulum (UPRER) were quantified. As a result, the treatment of gelsenicine resulted in the inhibition of nematode lifespan, as well as reductions in body length, width, and locomotion behavior. A total of 221 targets were predicted by PharmMapper, and 731 differentially expressed genes were screened out by mRNA-seq. GO and KEGG enrichment analysis revealed involvement in redox process and transmembrane transport. The permeability assay showed leakage of blue dye from the intestinal lumen into the body cavity. Abnormal mRNAs expression of gem-4, hmp-1, fil-2, and pho-1, which regulated intestinal development, absorption and catabolism, transmembrane transport, and apical junctions, was observed. Intestinal lipofuscin and ROS were increased, while sod-2 and isp-1 expressions were decreased. Multiple proteins in SKN-1/DAF-16 pathway were found to bind stably with gelsenicine in a predictive model. There was an up-regulation in the expression of SKN-1:GFP, while the nuclear translocation of DAF-16:GFP exhibited abnormality. The UPRER biomarker HSP-4:GFP was down-regulated. In conclusion, the treatment of gelsenicine resulted in the increase of nematode intestinal permeability. The toxicological mechanisms underlying this effect involved the disruption of intestinal barrier integrity, an imbalance between oxidative and antioxidant processes mediated by the SKN-1/DAF-16 pathway, and abnormal unfolded protein reaction.

Differentially expressed proteins and microbial communities of the skin regulate disease resistance to Chinese tongue sole (Cynoglossus semilaevis)

Vibriosis, caused by Vibrio, seriously affects the health of fish, shellfish, and shrimps, causing large economic losses. Teleosts are represent the first bony vertebrates with both innate and adaptive immune responses against pathogens. Aquatic animals encounter hydraulic pressure and more pathogens, compared to terrestrial animals. The skin is the first line of defense in fish, constituting the skin-associated lymphoid tissue (SALT), which belongs to the main mucosa-associated lymphoid tissues (MALT). However, little is known about the function of immunity related proteins in fish. Therefore, this study used iTRAQ (isobaric tags for relative and absolute quantitation) to compare the skin proteome between the resistant and susceptible families of Cynoglossus semilaevis. The protein integrin beta-2, the alpha-enolase isoform X1, subunit B of V-type proton ATPase, eukaryotic translation initiation factor 6, and ubiquitin-like protein ISG15, were highly expressed in the resistant family. The 16S sequencing of the skin tissues of the resistant and susceptible families showed significant differences in the microbial communities of the two families. The protein-microbial interaction identified ten proteins associated with skin microbes, including immunoglobulin heavy chain gene (IGH), B-cell lymphoma/leukemia 10 (BCL10) and pre-B-cell leukemia transcription factor 1 isoform X2 (PBX2). This study highlights the interaction between skin proteins and the microbial compositions of C. semilaevis and provides new insights into understanding aquaculture breeding research.

Nonspecific immune, histology and accumulation of marine worm, Urechis unicinctus in response to bisphenol A (BPA)

Bisphenol A (BPA) is one of the environmental endocrine disruptors, due to its chemical stability it exists in abundant concentrations in water and soil consequently accumulating in the food chain and causing many endocrine-related health problems. So far, studies on the effects of BPA on marine invertebrates have focused on acute toxicity, endocrine regulation, reproduction, and development. However, fewer studies have been conducted on marine benthos. The current study aimed to detect the accumulation of BPA and its impact on tissue structure, antioxidant capacity, and immune indexes in marine worm, Urechis unicinctus. U. unicinctus, as a common marine benthic animal, were exposed to different concentrations of BPA. Blood cells and intestinal tract were taken for tissue structure inspection, and supernatant of the coelomic fluid was collected for oxidative and antioxidant biomarkers. Results showed that the accumulation of BPA in muscles of U. unicinctus tended to increase with exposure time. BPA induced a rise in H2O2 and MDA content, and altered the activities of CAT, T-SOD, GST, LSZ and ACP, weaken the immune system functions. Moreover, pathological observation showed that BPA caused severe histopathology in the respiratory intestine, stomach, and midgut. These results will be helpful to understand the response mechanism of U. unicinctus under BPA exposure and provide a reference for controlling the aquaculture conditions and marine water quality of U. unicinctus.

Genome-wide DNA methylation mediates the resistance to vibriosis in Cynoglossus semilaevis

Chinese tongue sole (Cynoglossus semilaevis) is an economically important marine fish in China. However, vibriosis has caused huge mortality and economic losses in its culturing industry. To reveal the effect of DNA methylation on the resistance to vibriosis in tongue sole, we conducted RNA sequencing and whole genome bisulfite sequencing (WGBS), and compared the gene expressions and DNA methylation patterns between the resistant and susceptible families. We identified a total of 741 significantly differentially expressed genes (DEGs) in kidney and 17460 differentially methylated genes (DMGs), which were both enriched in immune-related pathways, such as "cAMP signaling pathway" and "NOD-like receptor signaling pathway". Through the correlation analysis of DEGs and DMGs, we identified two important immune pathways, including "complement and coagulation cascades", and "cytokine-cytokine receptor interaction", which played important roles in regulating the inflammation level and immune homeostasis. For example, the expression of proinflammatory cytokine il17c was down-regulated under the regulation of DNA methylation; in addition, the expression of protease-activated receptor 3 (par3) was up-regulated, which could induce the up-expressionof il8. These results demonstrated that the regulation of DNA methylation on the genes involved in immune responses might contribute to the resistance to vibriosis in tongue sole, and provided a basis for the control of diseases in fish aquaculture.

The Distribution of IgT mRNA+ Cells in the Gut of the Atlantic Salmon (Salmo salar L.)

The newly discovered IgT+ B cell is thought to play a dominant role in mucosal immunity, but limited studies have examined its distribution in fish species, hindering our understanding of its function. This study investigated IgT and poly Ig receptor (pIgR) mRNA+ cell distribution in Atlantic salmon (Salmo salar) gut using RNAscope in situ hybridization (ISH) and assessed the effects of vaccination. The pyloric caeca, mid-intestine (first and second parts), and posterior segment in two weight stages (Group 1: avg. 153 g, Group 2: avg. 1717 g) were examined in both vaccinated and unvaccinated fish. ISH revealed more IgT mRNA+ cells in the second part of the midgut compared to other intestinal segments, as well as a higher number of positive cells in Group 2 (older fish). In line with previous findings, intraperitoneal vaccination had no significant impact on the number of IgT+ transcripts. IgT mRNA+ cells were found mostly in the lamina propria and near capillaries, while pIgR was registered in both the lamina propria and mucosa. Interestingly, vaccinated fish presented adhesions and granulomatous tissue in the peritoneum, with both IgT and pIgR mRNA+ cells. Taken together, these results suggest that the distribution of IgT mRNA+ cells in the intestine of Atlantic salmon is region-specific and is not affected by intraperitoneal vaccination but varies with fish age.

The direct and gut microbiota-mediated effects of dietary bile acids on the improvement of gut barriers in largemouth bass (Micropterus salmoides)

Fish gut barrier damage under intensive culture model is a significant concern for aquaculture industry. This study aimed to investigate the effects of bile acids (BAs) on gut barriers in Micropterus salmoides. A germ-free (GF) zebrafish model was employed to elucidate the effects of the direct stimulation of BAs and the indirect regulations mediated by the gut microbiota on gut barrier functions. Four diets were formulated with BAs supplemented at 0, 150, 300 and 450 mg/kg, and these 4 diets were defined as control, BA150, BA300 and BA450, respectively. After 5 weeks of feeding experiment, the survival rate of fish fed with BA300 diet was increased (P < 0.05). Histological analysis revealed an improvement of gut structural integrity in the BA150 and BA300 groups. Compared with the control group, the expression of genes related to chemical barrier (mucin, lysozyme and complement 1) and physical barrier (occludin and claudin-4) was increased in the BA150 and BA300 groups (P < 0.05), and the expression of genes related to immunological barrier (interleukin [IL]-6, tumor growth factor β, IL-10, macrophage galactose-type lectin and immunoglobulin M [IgM]) was significantly increased in the BA300 group (P < 0.05), but the expression of genes related to chemical barrier (hepcidin) and immunological barrier (IL-1β, tumor necrosis factor-α, IL-6 and arginase) was significantly decreased in the BA450 group (P < 0.05). Gut microbiota composition analysis revealed that the abundance of Firmicutes was augmented prominently in the BA150 and BA300 groups (P < 0.05), while that of Actinobacteriota and Proteobacteria showed a downward trend in the BA150 and BA300 groups (P > 0.05). The results of the gut microbiota transferring experiment demonstrated an upregulation of gut barrier-related genes, including immunoglobulin Z/T (IgZ/T), IL-6, IL-1β and IL-10, by the gut microbiota transferred from the BA300 group compared with the control (P < 0.05). Feeding the BA300 diet directly to GF zebrafish resulted in enhanced expression of IgM, IgZ/T, lysozyme, occludin-2, IL-6 and IL-10 (P < 0.05). In conclusion, BAs can improve the gut barriers of fish through both direct and indirect effects mediated by the gut microbiota.

Long-term hypoxia stress-induced oxidative stress, cell apoptosis, and immune response in the intestine of Pelteobagrus vachelli

Hypoxia is a common phenomenon in aquaculture. With the dissolved oxygen (DO) 3.75 ± 0.25 mg O2 /L for hypoxia group and 7.25 ± 0.25 mg O2 /L for control group for 30, 60, and 90 days, long-term hypoxia stress was used to investigate the oxidative stress, apoptosis, and immunity in the intestine of Pelteobagrus vachelli. According to the results of measurement of total superoxide dismutase (T-SOD), glutathione peroxidase (GSH-PX), and catalase (CAT) activities and malondialdehyde (MDA) content, the oxidative stress ability of the intestine was activated at 30 days and impaired at 60 and 90 days. The upregulation of Bcl-2-associated x (Bax); downregulation of B cell lymphoma-2 (Bcl-2); increased activities of caspase-3, caspase-9, and Na+-K+-ATPase; decreased activities of succinate dehydrogenase (SDH); and the release of cytochrome c (Cyt-c) in mitochondria revealed that hypoxia induced the apoptosis. Moreover, heat shock protein 70 (HSP 70), heat shock protein 90 (HSP 90), immunoglobulin M (IgM), and C-lysozyme (C-LZM) were activated to inhibit apoptosis, but the immunoregulatory function might be damaged at 60 and 90 days. This study provides a theoretical foundation for understanding the mechanisms of hypoxia stress and aquaculture management of P. vachelli.

Genome-wide identification, evolution and expression analysis of tight junction gene family and the immune roles of claudin5 gene in turbot (Scophthalmus maximus L.)

Tight junction proteins (TJs) are important component proteins that maintaining the structure and function of TJs, connecting to each other to form a TJ complex between cells, maintaining the biological homeostasis of the internal environment. In this study, a total of 103 TJ genes were identified in turbot according to our whole-transcriptome database. Transmembrane TJs were divided into seven subfamilies, including claudin (CLDN), occludin (OCLD), tricellulin (MARVELD2), MARVEL domain containing 3 (MARVELD3), junctional adhesion molecules (JAM), immunoglobulin superfamily member 5 (IGSF5/JAM4), blood vessel epicardial substance (BVEs). Moreover, the majority of homologous pairs of TJ genes showed highly conserved alongside length, exon/intron number and motifs. As for phylogenetic analysis for 103 TJ genes, eight of them have undergone a positive selection and JAMB-like has undergone the most neutral evolution. The expression patterns of several TJ genes showed the lowest expression levels in blood, while the highest expression levels were detected in intestine, gill and skin, which all belong to mucosal tissues. Meanwhile, most examined TJ genes showed down-regulated expression patterns during bacterial infection, while several TJ genes exhibited up-regulated expression patterns at a later stage (24 h). At the same time, several potential candidate genes (such as CLDN-15, CLDN-3, CLDN-12, CLDN-5 and OCLD) were significantly down-regulated, which may indicate their important functions that involved in the regulation of bacterial infection. Currently, there is little research on CLDN5 in the intestine, but it is highly expressed in the intestine and has significant changes in intestinal expression after bacterial infection. Thus, we knocked down CLDN5 by the method of lentiviral infection. The result showed CLDN5 was related to cell migration (wound healing) and apoptosis, and the method of dualluciferasereporterassay showed that the functions of CLDN5 could be regulated by miR-24. The study of TJs may lead to a better understanding of the function of TJs in teleost.

Transcriptomics in Rare Minnow (Gobiocypris rarus) towards Attenuated and Virulent Grass Carp Reovirus Genotype II Infection

Grass carp reovirus genotype Ⅱ (GCRV Ⅱ) causes a variety of fish hemorrhagic disease, which seriously affects the sustainable development of grass carp aquaculture in China. Rare minnow (Gobiocypris rarus) is an ideal model fish to study the pathogenesis of GCRV Ⅱ. To investigate the involved molecular responses against the GCRV Ⅱ infection, we performed comparative transcriptomic analysis in the spleen and liver of rare minnow injected with virulent strain DY197 and attenuated strain QJ205. Results showed that the virulent DY197 strain induced more differently expressed genes (DEGs) than the attenuated QJ205 strain, and tissue-specific responses were induced. In the spleen, the attenuated and virulent strains induced different DEGs; the attenuated QJ205 infection activated steroid synthesis pathway that involved in membrane formation; however, virulent DY197 infection activated innate immunity and apoptosis related pathways while suppressing cell proliferation and migration related pathways that are important for damage tissue repair, as well as hemorrhage related pathways. In the liver, the attenuated and virulent strains infection induced similar DEGs; both strains infection activated immunity and apoptosis related pathways but suppressed metabolism-related pathways; virulent DY197 infection especially activated protein digestion and absorption-related pathways and suppressed steroid synthesis pathway. To conclude, virulent strain infection especially induced tissue-specific alterations and caused severe suppression of hemorrhage-related pathways in spleen. Our findings will contribute to better understanding of the interactions between host and GCRV II.

Genome-wide identification and functional characterization of inhibitor of nuclear factor-κB (IκB) kinase (IKK) in turbot (Scophthalmus maximus)

The inhibitor of nuclear factor-κB (IκB) kinase (IKK) is involved in a variety of intracellular cell signaling pathways and is an important component of the NF-κB signaling pathway. IKK genes have been suggested to play important roles in the innate immune response to pathogen infection in both vertebrates and invertebrates. However, little information is available about IKK genes in turbot (Scophthalmus maximus). In this study, six IKK genes were identified including SmIKKα, SmIKKα2, SmIKKβ, SmIKKε, SmIKKγ, and SmTBK1. The IKK genes of turbot showed the highest identity and similarity with Cynoglossus semilaevis. Then, phylogenetic analysis showed that the IKK genes of turbot were most closely related to C. semilaevis. In addition, IKK genes were widely expressed in all the examined tissues. Meanwhile, the expression patterns of IKK genes were investigated by QRT-PCR after Vibrio anguillarum and Aeromonas salmonicida infection. The results showed that IKK genes had varying expression patterns in mucosal tissues after bacteria infection, indicating that they may play key roles in maintaining the integrity of the mucosal barrier. Subsequently, protein and protein interaction (PPI) network analysis showed that most proteins interacting with IKK genes were located in the NF-κB signaling pathway. Finally, the double luciferase report and overexpression experiments showed that SmIKKα/SmIKKα2/SmIKKβ involved in the activation of NF-κB in turbot. In summary, our results suggested that IKK genes of turbot played important roles in the innate immune response of teleost, and provide valuable information for further study of the function of IKK genes.

Integrative time series of cellular, humoral and molecular response revealed immunotoxicity of bifenthrin to Chinese rare minnow (Gobiocypris rarus) following Pseudomonas fluorescens challenge

Bifenthrin is a common pesticide that is widespread in aquatic environments. Although it has been shown to be toxic to aquatic organisms, its immunotoxicity and mechanism are unclear. Herein, we reported the immunotoxicity of bifenthrin on adult Chinese rare minnow (Gobiocypris rarus) after 28 days of exposure to different concentrations of bifenthrin (0.1, 0.3, and 1.0 μg/L) and 36-h Pseudomonas fluorescens challenge. Bifenthrin inhibited the fish humoral immune response to bacteria by altering the lymphocyte and neutrophil ratios and decreasing the production of lysozyme, complement component 3, immunoglobulin M, and C-reactive protein, particularly were 1.0 μg/L. Bifenthrin caused intestinal damage and significantly reduced the volume of intestinal mucus at 12 and 36 hours postinjection (hpi) (p < 0.05). Moreover, 1.0 μg/L bifenthrin significantly increased the fish mortality and bacterial loads at 12 and 36 hpi (p < 0.05). RNA-seq analysis revealed several enriched genes involved in pathogen attachment and recognition, inflammatory responses, and complement system at the early-to-mid stage of infection (4-12 hpi). Overall, our results corroborated that bifenthrin induced immunotoxicity in Gobiocypris rarus, resulting in immune dysfunction of fish and increasing their sensitivity to bacterial infection and accelerating mortality. Moreover, 4-12 hpi was better than 36 hpi for analyzing immune responses against pathogen infection in fish exposed to bifenthrin.

Applying genetic technologies to combat infectious diseases in aquaculture

Disease and parasitism cause major welfare, environmental and economic concerns for global aquaculture. In this review, we examine the status and potential of technologies that exploit genetic variation in host resistance to tackle this problem. We argue that there is an urgent need to improve understanding of the genetic mechanisms involved, leading to the development of tools that can be applied to boost host resistance and reduce the disease burden. We draw on two pressing global disease problems as case studies-sea lice infestations in salmonids and white spot syndrome in shrimp. We review how the latest genetic technologies can be capitalised upon to determine the mechanisms underlying inter- and intra-species variation in pathogen/parasite resistance, and how the derived knowledge could be applied to boost disease resistance using selective breeding, gene editing and/or with targeted feed treatments and vaccines. Gene editing brings novel opportunities, but also implementation and dissemination challenges, and necessitates new protocols to integrate the technology into aquaculture breeding programmes. There is also an ongoing need to minimise risks of disease agents evolving to overcome genetic improvements to host resistance, and insights from epidemiological and evolutionary models of pathogen infestation in wild and cultured host populations are explored. Ethical issues around the different approaches for achieving genetic resistance are discussed. Application of genetic technologies and approaches has potential to improve fundamental knowledge of mechanisms affecting genetic resistance and provide effective pathways for implementation that could lead to more resistant aquaculture stocks, transforming global aquaculture.

Transcriptomics and co-expression network analysis revealing candidate genes for the laccase activity of Trametes gibbosa

BACKGROUND

Trametes gibbosa, which is a white-rot fungus of the Polyporaceae family found in the cold temperate zone, causes spongy white rot on wood. Laccase can oxidize benzene homologs and is one of the important oxidases for white rot fungi to degrade wood. However, the pathway of laccase synthesis in white rot fungi is unknown.

RESULTS

The peak value of laccase activity reached 135.75 U/min/L on the 9th day. For laccase activity and RNA-seq data, gene expression was segmented into 24 modules. Turquoise and blue modules had greater associations with laccase activity (positively 0.94 and negatively -0.86, respectively). For biology function, these genes were concentrated on the cell cycle, citrate cycle, nicotinate, and nicotinamide metabolism, succinate dehydrogenase activity, flavin adenine dinucleotide binding, and oxidoreductase activity which are highly related to the laccase synthetic pathway. Among them, gene_8826 (MW199767), gene_7458 (MW199766), gene_61 (MW199765), gene_1741 (MH257605), and gene_11087 (MK805159) were identified as central genes.

CONCLUSION

Laccase activity steadily increased in wood degradation. Laccase oxidation consumes oxygen to produce hydrogen ions and water during the degradation of wood. Some of the hydrogen ions produced can be combined by Flavin adenine dinucleotide (FAD) to form reduced Flavin dinucleotide (FADH2), which can be transmitted. Also, the fungus was starved of oxygen throughout fermentation, and the NADH and FADH2 are unable to transfer hydrogen under hypoxia, resulting in the inability of NAD and FAD to regenerate and inhibit the tricarboxylic acid cycle of cells. These key hub genes related to laccase activity play important roles in the molecular mechanisms of laccase synthesis for exploring industrial excellent strains.

The immune-related circRNA-miRNA-mRNA ceRNA regulatory network in the liver of turbot (Scophthalmus maximus L.) induced by Vibrio anguillarum

Recently, Vibrio anguillarum, a Gram-negative pathogenic bacterium, has been becoming a major constraint on the development of the turbot aquaculture industry because of its characteristics of worldwide distribution, broad host range and potentially devastating impacts. Although the functions of protein-coding mRNAs in the immune response against bacterial infection have been reported, as well as several non-coding RNAs (ncRNAs), such as circular RNAs (circRNAs) and microRNAs (miRNAs), the relationships between mRNAs and ncRNAs in the immune system of turbot liver are still limited during bacterial infection. In present study, the comprehensive analyses of whole-transcriptome sequencing were conducted in turbot liver infected by V. anguillarum. The differential expression was analyzed in the data of circRNAs, miRNAs, and mRNAs. The interactions of miRNA-circRNA pairs and miRNA-mRNA pairs were predicted basing on the negative regulatory relationships between miRNAs and their target circRNAs\mRNAs. The circRNA-related ceRNA regulatory networks were constructed for the analyses of regulated mechanism in turbot immune system. Subsequently, the RT-qPCR was carried out to verify the results of sequencing. Finally, we identified 31 circRNAs, 53 miRNAs and 948 mRNAs with differential expression. Gene set enrichment analyses using Gene ontology (GO) and Kyoto Encyclopedia of Genes and Genomes (KEGG) pathways showed that innate immunity was principally activated at the early stages of infection, while adaptive immunity was activated after 24 h. Finally, 65 circRNA-miRNA-mRNA pathways were constructed, based on the hypothesis of ceRNA regulatory networks. In conclusion, our findings provide new insights on the underlying immune response to bacterial infection and identify novel target genes for the prevention and control of disease in turbot.

Metabolite features of serum and intestinal microbiota response of largemouth bass (Micropterus salmoides) after Aeromonas hydrophila challenge

The enteric morphology, enteric microbiota structure and serum metabolomics of M. salmoides before and after infected by A. hydrophila were analysed to explore the pathogenic mechanism of A. hydrophila infection in M. salmoides. The results revealed that, after the infection of A. hydrophila, the villus boundary of largemouth bass became less obvious; the relative abundance of Proteobacteria and decreasing relative abundance of Tenericutes were increasing; genera relative abundance of putatively beneficial bacteria (Mycoplasma) were decreasing, whereas the genus Aeromonas increased after infection; serum metabolomic analysis showed that infection with A. hydrophila caused disorder to the metabolic processes of largemouth bass, particularly amino acid metabolism, and caused inflammation; several potential pathogen infection-related and significantly differential intestinal microbiota-related metabolite markers were identified, such as 6-hydroxy-5-methoxyindole glucuronide, zalcitabine, bilirubin, aciclovir. This study may provide new insights into the potential association between enteric microbiota and serum metabolism and the pathogenic mechanism of M. salmoides infected by A. hydrophila, providing a scientific basis for disease control in largemouth bass breeding.

Systematic identification and characterization of lncRNAs and lncRNA-miRNA-mRNA networks in the liver of turbot (Scophthalmus maximus L.) induced with Vibrio anguillarum

Long noncoding RNAs (lncRNAs), can regulate mRNA by targeting miRNA in a competing endogenous RNA network, have become a hot topic in the research of fish immune mechanism recent years. While in turbot (Scophthalmus maximus L.), an economically important marine fish, there are limited researches about the role of lncRNAs in its immune response to bacterial infection. In this study, a total of 184 differentially expressed lncRNAs (DElncRNAs) were systematically identified and characterized using whole-transcriptome sequencing of the liver of turbot challenged with Vibrioanguillarum at 0 h (control) and three different time points post infection (2 h, 12 h and 24 h, respectively). Subsequently, GO and KEGG signaling pathways of differentially expressed lncRNAs were analyzed to predict their function. We found that lncRNAs in our results were significantly enriched in several immune-related signaling pathways, including the NOD-like receptor signaling pathway, Toll-like receptor signaling pathway, Cytokine-cytokine receptor, MAPK signaling pathway, phagosome, PPAR signaling pathway and the regulation of autophagy. In addition, a total of 492 DE lncRNA - DE miRNA -DE mRNA networks were identified at three different time points post infection, which were consisted of 102 networks at 2 h, 122 networks at 12 h and 81 networks at 24 h post infection, respectively. Noticeably, 92 of these regulated networks were immune-related. These observations suggested that lncRNAs can regulate the expression of immune-related genes in the response to bacterial infection in turbot. Moreover, our findings would provide a new insight into the immune response of turbot to pathogen infection and lay a foundation for future study.

Comprehensive identification and expression profiling of immune-related lncRNAs and their target genes in the intestine of turbot (Scophthalmus maximus L.) in response to Vibrio anguillarum infection

Long non-coding RNA (lncRNA) play vital regulatory roles in various biological processes. Intestine is one of the most sensitive organs to environmental and homeostatic disruptions for fish. However, systematic profiles of lncRNAs in the intestine of teleost in responses to pathogen infections is still limited. Turbot (Scophthalmus maximus L.), an important commercial fish species in China, has been suffering with Vibrio anguillarum infection, resulted in dramatic economic loss. Hereinto, the intestinal tissues of turbot were sampled at 0 h, 2 h, 12 h, and 48 h following V. anguillarum infection. The histopathological analysis revealed that the pathological trauma was mainly present in intestinal tunica mucosal epithelium. After high-throughput sequencing and bioinformatic analysis, a total of 9722 lncRNAs and 21,194 mRNAs were obtained, and the average length and exon number of lncRNAs were both less than those of mRNAs. Among which, a set of 158 lncRNAs and 226 mRNAs were differentially expressed (DE-lncRNAs and DEGs) in turbot intestine at three time points, related to many immune-related genes such as complement, interleukin, chemokine, lysosome, and macrophage, indicating their potential critical roles in immune responses. In addition, 2803 and 1803 GO terms were enriched for DEGs and co-expressed target genes of DE-lncRNAs, respectively. Moreover, 127 and 50 KEGG pathways including cell adhesion molecules (CAMs), phagosome, JAK-STAT signaling pathway, cytokine-cytokine receptor interaction, and intestinal immune network for IgA production, were enriched for DEGs and co-expressed target genes of DE-lncRNAs, respectively. Finally, qRT-PCR was conducted to confirm the reliability of sequencing data. The present study will set the foundation for the future exploration of lncRNA functions in teleost in response to bacterial infection.

Physiological and Biochemical Characteristics of Rainbow Trout with Severe, Moderate and Asymptomatic Course of Vibrio anguillarum Infection

Simple Summary

During the past decades, bacterial infections have been a serious problem in aquaculture that causes very large economic losses. Currently, antibiotics are the most common method of disease prevention and control. A combination of water quality monitoring, early detection of fish infections, and other preventive biosecurity measures in fish farms can help prevent the spread of infection. We investigated the natural bacterial infection in fish farms and characterized the parameters of the health status of rainbow trout Oncorhynchus mykiss (Walbaum, 1792) during disease. Depending on the course of the disease (severity of the pathology, leukocyte profile, and expression of immune-related genes), three subpopulations of fish with severe damage, a moderate course of the infectious process, and asymptomatic fish were characterized. An unexpected result was a small metabolic difference between fish with moderate symptoms and fish with weak signs of pathology. Thus, we have described the characteristics of a trout subpopulation with a mild course of infection which has potential for recovery after infection.

Abstract

This article describes the clinical manifestation of natural Vibrio anguillarum infection in rainbow trout (Oncorhynchus mykiss) during an outbreak on a fish farm. (i) Using an integrated approach, we characterized the pathogenesis of vibriosis from the morphological, hematological, and biochemical points of view. The molecular mechanisms associated with the host immune response were investigated using mass spectrometric analysis of trout plasma proteins. (ii) According to the severity of infection (the extent of tissue damage, the level of expression of pro-inflammatory genes, and changes in the leukocyte profile) three fish populations were identified among infected trout: fish with severe lesions (SL), fish with the moderate infectious process (IP) and asymptomatic fish (AS). (iii) Lymphopenia, granulocytosis, and splenomegaly were strong trends during the progression of infection and informative indicators of severe manifestation of disease, associated with hemorrhagic shock, metabolic acidosis, and massive tissue damage. (iv) As expected, pro-inflammatory interleukins, complement components, acute phase proteins, and antimicrobial peptides were implicated in the acute pathogenesis. Systemic coagulopathy was accompanied by increased antithrombotic reactions. (v) Reconstruction of metabolic pathways also revealed a high energy requirement for the immune response in severely affected fish. (vi) An unexpected result was a small difference between fish with moderate symptoms and fish with no or minor external signs of pathology (putatively resistant to infection). Increased production of antiproteases and enhanced blood coagulation cascade were observed in healthier fish, which may underlie the mechanisms of a controlled, non-self-damaging immune response to infection. (vii) Depending on the progression of the disease and the presence of the pathogen, a stepwise or linear change in the abundance of some plasma proteins was revealed. These proteins could be proposed as molecular markers for diagnosing the health and immune status of trout when cultured in fish farms.

Intestinal changes associated with nitrite exposure in Bufo gargarizans larvae: Histological damage, immune response, and microbiota dysbiosis

Nitrite is a ubiquitous toxic compound in aquatic ecosystems and has negative effects on aquatic organisms. The intestine and the trillions of microbes that inhabit it, play an integral role in maintaining digestive and immune functions. However, the effects of nitrite on intestinal health and microflora have been poorly investigated. Therefore, the present study evaluated the response of intestinal histology, immunity, digestive enzyme activities and microbiota to nitrite exposure in Bufo gargarizans tadpoles. The results showed that nitrite caused damage to the intestine and impaired digestive performance. Significant changes in the transcriptional profiles of genes involved in oxidative stress (sod, gpx and hsp), inflammation, and immunity (socs3, il-27, il-1β and il-17d) were observed in the NO₂-N treatment groups. In addition, exposure to nitrite induced alterations of intestinal microbial diversity, structure and composition, suggesting that nitrite may lead to intestinal microbiota dysbiosis. It is noteworthy that probiotics (e.g., Bacteroidetes and Fusobacteria) were decreased after exposure to nitrite, whereas potentially opportunistic pathogens such as Proteobacteria and Enterobacteriaceae were elevated. Functional prediction and correlation analysis suggested that the above changes may interfere with metabolic function and trigger various diseases. Taken together, we concluded that nitrite exposure induced intestinal microbial dysbiosis, which may lead to immune dysfunction and metabolic disorder, and ultimately to histological damages in B. gargarizans. Further, this study will provide a scientific basis for further understanding the risk of nitrite pollution on the intestinal health of amphibians.

CRISPR-Cas9 Approach Constructed Engineered Saccharomyces cerevisiae with the Deletion of GPD2, FPS1, and ADH2 to Enhance the Production of Ethanol

Bioethanol plays an important value in renewable liquid fuel. The excessive accumulation of glycerol and organic acids caused the decrease of ethanol content in the process of industrial ethanol production. In this study, the CRISPR-Cas9 approach was used to construct S. cerevisiae engineering strains by the deletion of GPD2, FPS1, and ADH2 for the improvement of ethanol production. RNA sequencing and transcriptome analysis were used to investigate the effect of gene deletion on gene expression. The results indicated that engineered S. cerevisiae SCGFA by the simultaneous deletion of GPD2, FPS1, and ADH2 produced 23.1 g/L ethanol, which increased by 0.18% in comparison with the wild-type strain with 50 g/L of glucose as substrate. SCGFA strain exhibited the ethanol conversion rate of 0.462 g per g of glucose. In addition, the contents of glycerol, lactic acid, acetic acid, and succinic acid in SCGFA decreased by 22.7, 12.7, 8.1, 19.9, and 20.7% compared with the wild-type strain, respectively. The up-regulated gene enrichment showed glycolysis, fatty acid, and carbon metabolism could affect the ethanol production of SCGFA according to the Kyoto Encyclopedia of Genes and Genomes (KEGG) analysis. Therefore, the engineering strain SCGFA had great potential in the production of bioethanol.

Characterization, evolution and expression analysis of Toll-like receptor 7 (TLR7) in turbot (Scophthalmus maximus L.)

The pattern recognition receptors (PRRs) can recognize the conserved molecular structures of pathogens to active the innate immune responses, and subsequently induce the antigen-specific adaptive immune responses for the clearance of infected pathogen. Among the PRRs, Toll-like receptors (TLRs) are the first and best characterized PRRs across all the species. Among the TLR members, TLR7 showed significant conservation across the vertebrates, with the lowest rate of evolution for its LRR domains from primates to fishes. In the current study, one TLR7 (SmTLR7) gene was captured in turbot, with a 3144 bp open reading frame (ORF), that encoding 1047 amino acid residues. Following multiple sequence comparison, SmTLR7 was found to have the highest similarity and identity both to Paralichthys olivaceus with 91.9% and 85.9%, respectively. In phylogenetic analysis, SmTLR7 was firstly clustered with Japanese flounder, and then clustered with fugu, rainbow trout, and zebrafish. In addition, SmTLR7 was widely expressed in all the examined tissues with the highest expression level in spleen, followed by skin, while the lowest expression level was detected in blood. Following both Edwardsiella tarda and Vibrio anguillarum challenge, SmTLR7 was significantly down-regulated in gill and intestine, and up-regulated in skin. Moreover, SmTLR7 was significantly up-regulated in head kidney macrophages following LPS, LTA, PGN and polyI:C stimulation, as well as showed the strongest binding ability to LPS, followed by PGN, LTA, and polyI:C in a dose-dependent manner. Finally, following RNAi of SmTLR7, MyD88 and IL-1β were slightly up-regulated, while TRAF6 and IL-8 were significantly down-regulated. The characterization of TLR7 can expand our understanding of the PRRs in teleost fishes, and eventually aid the exploration of interactions between host and pathogen.

Characterization and the potential immune role of class A scavenger receptor member 4 (SCARA4) in bacterial infection in turbot (Scophthalmus maximus L.)

The class A scavenger receptors play important roles in innate immunity and are distributed on plasma membrane of macrophages and other cell types. Notably, the class A scavenger receptor 4 (SCARA4) contains a typical C-type (calcium-dependent) lectin domain, which belongs to the collectin family of pattern recognition receptors and is involved in the immune response against infection. Here, one turbot SCARA4 gene was identified with a 2,292 bp open reading frame (ORF) encoding 763 amino acid residues. Multiple sequence analysis and phylogenetic analysis confirmed that SmSCARA4 gene was more close to that of P. olivaceus. Gene structure and syntenic analysis showed conserved exon/intron organization pattern and syntenic pattern across selected vertebrate species. Tissue distribution analysis showed SmSCARA4 was expressed in all the tested healthy tissues with the relative high expression levels in skin, gill and spleen. Following both E. tarda and V. anguillarum challenge in vivo, SmSCARA4 was significantly repressed in gill and intestine. Remarkably, SmSCARA4 showed the strongest binding ability to LPS and strongest upregulation in turbot head kidney macrophages in response to LPS. Knockdown and overexpression of SmSCARA4 revealed its interactions with the two pro-inflammatory cytokines, TNF-α and IL-1β. Finally, repression of SmSCARA4 via combined treatment of LPS and overexpression of SmSCARA4 construct in turbot head kidney macrophages further indicated an inhibitory role of SmSCARA4 in LPS-stimulated inflammation. Taken together, turbot SmSCARA4 plays an important role in turbot immunity, especially in the mucosa-related systems; SmSCARA4 possesses strong binding specificity to LPS, and exerts protective roles in response to LPS infection by reducing the release of pro-inflammatory cytokines. The mechanisms of inhibitory role of SmSCARA4 in LPS-elicited inflammation await further investigation.

Oxidative stress, intestinal damage, and cell apoptosis: Toxicity induced by fluopyram in Caenorhabditis elegans

Fluopyram, a succinate dehydrogenase inhibitor fungicide and nematicide, has been used extensively for agricultural pest control and toxicologically affects non-target organisms. In the present study, Caenorhabditis elegans, a well-established model organism, was used to evaluate the toxic effect of fluopyram and the possible molecular mechanisms. C. elegans was exposed to fluopyram for 24 h at three sublethal concentrations (0.01, 0.05 and 0.25 mg/L) and the physiological, biochemical, and molecular indicators were examined. The results showed that sublethal exposure to fluopyram could cause damage to growth, locomotion behavior, feeding, lifespan and reproduction of the nematodes. Fluopyram exposure induced oxidative stress as indicated by increase of ROS production, lipofuscin and lipid accumulation, and MDA level in the nematodes. In contrast, exposure to fluopyram significantly decreased the activities of target enzyme SDH and antioxidant enzymes including SOD, CAT and GST. Moreover, the expression of genes associated with oxidative stress (e.g., gst-4, sod-3, fat-7, mev-1 and daf-16), intestinal damage (e.g., mtm-6, nhx-2, opt-2, pkc-3, par-6, act-5 and egl-8), and cell apoptosis (e.g., ced-13, ced-3, egl-38, efl-2, cep-1 and lgg-1) was significantly influenced after exposure to fluopyram. According to Pearson correlation analyses, significant correlation existed between 190 pairs of parameters, which indicated that fluopyram induced multiple toxic related effects in C. elegans. These findings suggest that oxidative stress, intestinal damage, and cell apoptosis may play major roles in toxicity of fluopyram in the nematodes.

Immune correlates of NF-κB and TNFα promoter DNA methylation in Japanese flounder (Paralichthys olivaceus) muscle and immune parameters change response to vibrio anguillarum infection

Vibrio anguillarum infection can activate NF-κB/TNFα pathway in the immune organs of fish. Fish muscle is also an important immune organ, but the research on its immune function is few. Our aim was to study regulating mechanism of NF-κB and TNFα gene expressions in the muscle of Japanese flounder (Paralichthys olivaceus) which was under Vibrio anguillarum infection (0, 24, 48, 72 and 96 h). The results showed that the expressions of NF-κB and TNFα increased significantly at 48 h, and there was a significant positive correlation between them. In situ hybridization confirmed the co-existence of NF-κB and TNFα genes in Japanese flounder muscle. Interestingly, the expression of the TNFα gene was regulated by the DNA methylation and its methylation level was negatively correlated with the expression. The lowest methylation level of TNFα occurred at 48 h under Vibrio anguillarum infection (P < 0.05). And more, when the fragment (-2122 ∼ -730) was deleted on TNFα gene promoter, double luciferase activity was the highest, indicating that fragment (-730-0) was the transcription factor binding region. The site (-78 ~ -69) on the fragment (-730-0) binding NF-κB was mutated, and double luciferase activity decreased significantly. The results confirmed that the site (-78 ~ -69) was indeed an important binding site for NF-κB. In addition, the activity of TNFα in the serum of Japanese flounder changed with the prolongation of vibrio anguillarum infection, and the concentration of other immune factors such as ALP, ALT, AST and LDH also changed in the muscle under vibrio anguillarum infection. They all showed a trend of first increasing and then decreasing. Above studies implied that Japanese flounder responded to Vibrio anguillarum infection at the immune level with the change of its methylation status and the activation of transcription factor. By studying the mechanism of immune pathways, understanding the response to immune stress is great significant to the research of fish breeding for disease resistance.

Characterization and functional study of nuclear factor erythroid 2-related factor 2 (Nrf2) in black tiger shrimp (Penaeus monodon)

Nuclear factor erythroid 2-related factor 2 (Nrf2) is a member of the Cap'n'collar basic region leucine zipper (CNC-bZIP) transcription factor family, and is activated by diverse oxidants, pro-oxidants, antioxidants and chemopreventive agents. The full-length cDNA of Nrf2 from Penaeus monodon (PmNrf2; 2024 bp long with 729 bp coding region, GenBank accession no. MW390830) was cloned. The 242-amino-acid polypeptide encoded by this gene had a predicted molecular mass of 27.80 kDa. Sequence homology and phylogenetic analysis showed that PmNrf2 was similar to the insect Cap'n'Collar (CNC) transcription factor and mammalian Nrf2. Tissue expression profile analyzed by quantitative real-time RT-PCR (qRT-PCR) demonstrated that PmNrf2 was constitutively expressed in all examined tissues, with the highest expression observed in the intestines and the weakest expression observed in the hemocyte. PmNrf2 expression profiles were detected in the hepatopancreas of shrimp after bacterial challenge. The results suggested that PmNrf2 was involved in the responses to bacterial challenge, but the temporal expression pattern trend of PmNrf2 differed between the gram-negative and gram-positive bacterial challenges in the shrimp hepatopancreas. The recombinant PmNrf2 protein was expressed and purified through affinity chromatography. Furthermore, an anti-PmNrf2 polyclonal antibody was obtained, which was able to clearly detect PmNrf2 protein expression in the hepatopancreas of shrimp. Knockdown of PmNrf2 by RNA interference (RNAi) resulted in a reduction in the expression of PmGPx gene. Taken together, the results of our study indicated that PmNrf2 played a role in regulation the transcription of PmGPx antioxidant enzyme genes.

Immune defence mechanisms presented in liver homogenates and bile of gilthead seabream (Sparus aurata)

Because the role of the liver of fishes in providing possible immunity remains largely unknown, the aim of this work was to identify and characterize different humoral defence mechanisms in the liver homogenates and bile of gilthead seabream (Sparus aurata) for the first time. Total protein levels and several immune parameters (complement activity, lysozyme and immunoglobulin M level) were studied. Furthermore, the activity of some lytic (proteases, antiproteases, esterase, alkaline phosphatase) and antioxidant (superoxide dismutase, catalase and peroxidase) enzymes was determined. Finally, bacteriostatic activity on three opportunist fish pathogens (Vibrio harveyi, Vibrio angillarum and Photobacterium damselae) was measured. Lysozyme and antiprotease activity were undetected in liver and bile, while natural haemolytic complement activity was only detected in bile, and immunoglobulin M was detected in both samples. The levels of proteases, esterase and antioxidant enzymes were greater in bile than in liver homogenates, while the level of alkaline phosphatase was very low in both samples. In addition, while no bacteriostatic activity was detected on liver homogenates, the bile revealed a very potent bacteriostatic activity against all the tested pathogenic bacteria. These results corroborate that fish liver - especially fish bile - contains many factors involved in innate immunity that could be useful for better understanding the role of the liver as an organ involved in fish immune functions as well as the possible contribution of bile to gut mucosal immunity.

Comparative analysis of the miRNA-mRNA regulation networks in turbot (Scophthalmus maximus L.) following Vibrio anguillarum infection

MicroRNAs could not only regulate posttranscriptional silencing of target genes in eukaryotic organisms, but also have positive effect on their target genes as well. These microRNAs have been reported to be involved in mucosal immune responses to pathogen infection in teleost. Therefore, we constructed the immune-related miRNA-mRNA networks in turbot intestine following Vibrio anguillarum infection. In our results, 1550 differentially expressed (DE) genes and 167 DE miRNAs were identified. 113 DE miRNAs targeting 89 DE mRNAs related to immune response were used to construct miRNA-mRNA interaction networks. Functional analysis showed that target genes were associated with synthesis and degradation of ketone bodies, mucin type O-Glycan biosynthesis, homologous recombination, biotin metabolism, and intestinal immune network for IgA production that were equivalent to the function of IgT and IgM in fish intestine. Finally, 10 DE miRNAs and 7 DE mRNAs were selected for validating the accuracy of high-throughput sequencing results by qRT-PCR. The results of this study will provide valuable information for the elucidation of the regulation mechanisms of miRNA-mRNA interactions involved in disease resistance in teleost mucosal immune system.

Ammonia stress influences intestinal histomorphology, immune status and microbiota of Chinese striped-neck turtle (Mauremys sinensis)

Ammonia is one of major pollutants in aquatic environment that induces severe stress and toxicity to organisms in aquatic system. The intestine acts a major defense line that protects living organisms from biotic and abiotic stresses. In the current study, we examined the effects of ammonia on intestinal histomorphology, transcriptional levels of intestinal barrier functioning genes and intestinal microbiota of Chinese striped-neck turtle (Mauremys sinensis). Thus, the turtles were placed in water with addition of ammonia at 0 (control), 100, 200 mg L^-1 for 30 days. Our findings showed that ammonia reduced the villus length and induced the inflammatory cells appearance. In addition, the epithelial tight junction genes, claudin and zonola occludin significantly downregulated in ammonia exposed groups as compared to control group (P < 0.05). Similarly, the mRNA expression levels of MUC-2 gene also significantly decreased in ammonia treated groups (P < 0.05). However, the expression levels of intestinal immune related genes such as IL-10, IL-12, TGF-β1, TNF-α and IFN-γ significantly increased (P < 0.05). Furthermore, ammonia changed gut microbial diversity variedly. At the phylum levels, Firmicutes increased, whereas Bacteroidota, Desulfobacterota and Synergistota decreased significantly. Likewise, Lachnospiraceae, Bacteroides, Eubacteriaceae, Desulfovibrio, Muribaculaceae, Bilophila, Cloacibacillus, Christensenellaceae, Ruminococcus and Parabacteroides decreased while, Romboutsia and Turicibacter increased in ammonia exposed groups. In conclusion, ammonia at 100 and 200 mg L^-1 could alter the intestinal barrier function and change the composition of intestinal microbiota, leading to bad health status in M. sinensis.

The CC and CXC chemokine receptors in turbot (Scophthalmus maximus L.) and their response to Aeromonas salmonicida infection

Chemokines are crucial regulators of cell mobilization for development, homeostasis, and immunity. Chemokines signal through binding to chemokine receptors, a superfamily of seven-transmembrane domain G-coupled receptors. In the present study, eleven CC chemokine receptors (CCRs) and seven CXC chemokine receptors (CXCRs) were identified from turbot genome. Phylogenetic and syntenic analyses were performed to annotate these genes, indicating the closest relationship between the turbot chemokine receptors and their counterparts of Japanese flounders (Paralichthys olivaceus). Evolutionary analyses revealed that the tandem duplications of CCR8 and CXCR3, the whole genome duplications of CCR6, CCR9, CCR12, and CXCR4, and the teleost-specific CCR12 led to the expansion of turbot chemokine receptors. In addition, turbot chemokine receptors were ubiquitously expressed in nine examined healthy tissues, with high expression levels observed in spleen, gill, and head kidney. Moreover, most turbot chemokine receptors were significantly differentially expressed in spleen and gill after Aeromonas salmonicida infection, and exhibited general down-regulations at early time points and then gradually up-regulated. Finally, protein-protein interaction network (PPI) analyses indicated that chemokine receptors interacted with a few immune-related genes such as interleukins, Grk genes, CD genes, etc. These results should be valuable for comparative immunological studies and provide insights for further functional characterization of chemokine receptors in turbots.

Identification and characterization of a C-type lectin in turbot (Scophthalmus maximus) which functioning as a pattern recognition receptor that binds and agglutinates various bacteria

C-type lectins (CTLs) are important pathogen pattern recognition receptors that recognize carbohydrate structures. In present study, a C-type lectin domain family 4 member E-like gene from turbot, which tentatively named SmCLEC4E-like (SmCLEC4EL), was identified, and the expressional and functional analyses were performed. In our results, SmCLEC4EL showed conserved synteny with CLEC4E-like genes from several fish species in genome, and possessed a typical type II transmembrane CTL architecture: an N-terminal intracellular region, a transmembrane domain and a C-terminal extracellular region which contained a predicted carbohydrate recognition domain (CRD). In addition, SmCLEC4EL exhibited the highest expression level in spleen in healthy fish, and showed significantly induced expression in mucosal tissues, intestine and skin, under bacteria challenge. Finally, the recombinant SmCLEC4EL protein combined with LPS, PGN, LTA and five different kinds of bacteria in a dose-dependent manner, and agglutinated these bacteria strains in the presence of calcium. These findings collectively demonstrated that SmCLEC4EL, a calcium-dependent CTL, could function as a pattern recognition receptor in pathogen recognition and participate in host anti-bacteria immunity.

Characterization of toll-like receptor 1 (TLR1) in turbot (Scophthalmus maximus L.)

TLRs are the first and best-characterized pattern recognition receptors conserved across all the species. Different from mammals, the TLRs in teleost fishes are very diversified due to various evolutionary mechanisms. Here, we characterized one TLR1 gene in turbot, with a 2,415 bp open reading frame (ORF), that encoding 804 amino acid residues, and have the highest similarity and identity both to Paralichthys olivaceus with 88.9% and 79.9%. In phylogenetic analysis, it was firstly clustered with P. olivaceus, and then clustered with Takifugu rubripes. TLR1 was widely expressed in all the examined healthy tissues with the highest expression level in spleen, followed by head-kidney. In addition, it was significantly regulated in gill, skin and intestine following Edwardsiella tarda and Vibrio anguillarum challenge with different expression patterns. In in vitro stimulation with pathogen-associated molecular patterns, TLR1 showed significantly strong and elevated responses to LPS, but only responded to LTA and Poly(I:C) at the highest evaluated concentration, while no response was detected using PGN stimulation. Moreover, in subcellular localization analysis, TLR1 was distributed in the cytoplasm, membrane and nucleus. Taken together, TLR1 played vital roles for host immune response to bacterial infection, only with strong binding ability to LPS and involved in the production of inflammatory cytokines. However, the specific ligand for TLR1 and its functional association with other TLRs should be further characterized in fish species.

Toxic effects of cadmium and lead exposure on intestinal histology, oxidative stress response, and microbial community of Pacific white shrimp Litopenaeus vannamei

Cadmium (Cd) and lead (Pb) are two hazardous pollutants that threaten shrimp farming. The intestine is an important organ for digestion and immunity. We separately exposed Pacific white shrimp Litopenaeus vannamei to 500 μg/L Cd or 500 μg/L Pb seawater for 7 days, and 45 shrimp from each group were used to evaluate the changes of intestinal histopathological, oxidative stress, and microbiota composition. After Cd and Pb exposure, shrimp intestine appeared significant mucosal damage and oxidative stress, and the microbiota variation were induced. Specifically, the abundance of the phyla Bacteroidetes and Actinobacteria were induced, that of Proteobacteria and Firmicutes were deduced. The abundances of putative beneficial bacteria (Lactobacillus, Weissella, Demequina, Formosa and Ruegeria) and potentially pathogenic bacteria (Vibrio and Photobacterium) were fluctuated. Furthermore, the nutrient metabolic function of intestinal microbes was significantly altered. We concluded that Cd and Pb exposure had negative effects on the intestinal health of shrimp.

Fishing for the right probiotic: Host-microbe interactions at the interface of effective aquaculture strategies

Effective aquaculture management strategies are paramount to global food security. Growing demands stimulate the intensification of production and create the need for practices that are both economically viable and environmentally sustainable. Importantly, pathogenic microbes continue to be detrimental to fish growth and survival. In terms of host health, the intestinal mucosa and its associated consortium of microbes have a critical role in modulating fitness and present an attractive opportunity to promote health at this interface. In light of this, the administration of probiotic microorganisms is being considered as a means to restore and sustain health in fish. Current evidence suggests that certain probiotic strains might be able to augment immunity, enhance growth rate, and protect against infection in salmonids, the most economically important family of farmed finfish. This review affirms the relevance of host-microbe interactions in salmonids in light of emerging evidence, with an emphasis on intestinal health. In addition, the current understanding of the mode of action of probiotics in salmonid fish is discussed, along with delivery systems that can effectively carry the living microbes.

Transcriptome Analysis and Autophagy Investigation of LoVo Cells Stimulated with Exosomes Derived from T. asiatica Adult Worms

Taenia asiatica is a zoonotic parasite found in the human intestine and pig liver that evolved various strategies to survive the host’s defenses. Exosomes are membranous vesicles released by cells and are an important vehicle in parasite-host interactions. However, no literature exists on the specific infection mechanisms of T. asiatica against the host defense response, and further research is required to understand the parasite-host interaction. In this study, we investigated the host’s differentially expressed genes (DEGs) while stimulating them with exosomes derived from the T. asiatica adult worm (Tas-exo) on LoVo by RNA-seq analysis. Our results identified 348 genes as being significantly differentially expressed for the Tas-exo group when comparing with that of the NC group. Some of these genes are related to modulation of cell proliferation and cell autophagy. Surprisingly, autophagy and cell proliferation have crucial roles in the defense against parasites; accordingly, we detected cell proliferation and autophagy in LoVo cells by CCK8, immunofluorescence, and Western blotting, demonstrating that Tas-exo could inhibit LoVo cell proliferation and autophagy via AMPK pathway. When P62 and p-mTOR/mTOR expression were significantly increased, BeclinI and pAMPK/AMPK were significantly decreased. These results expand our understanding of parasite-host interactions mediated by exosomes.

Genome-wide identification of NOD-like receptors and their expression profiling in mucosal tissues of turbot (Scophthalmus maximus L.) upon bacteria challenge

The innate immune system plays an important role in host defense against pathogenic infections. In the innate immune system, several families of innate pattern recognition receptors, including Toll-like receptors, RIG-I-like receptors, NOD-like receptors (NLRs), and DNA receptors (cytosolic sensors for DNA), are known to play vital roles in detecting and responding to various pathogens. In this study, we identified 29 NLRs in turbot including 4 NLRs from subfamily A: NOD1, NOD2, CIITA, NLRC5, 1 NLR from subfamily B: NLRB1, 21 NLRs from subfamily C: NLR-C3.1∼NLRC3.21, 1 from NLRX subfamily, and two that do not fall within these subfamilies: APAF1, NWD1. Phylogenetic analysis showed that these NLR genes were clearly divided into five subfamilies. Protein-protein interaction network analysis showed that some of these NLR genes shared same interacting genes and might participate in signal transductions associated with immunity. The evolutionary pressure selection analysis showed that the Ka/Ks ratios for all detected NLR genes were much less than one, implying more synonymous changes than non-synonymous changes. In addition, tissue expression analysis showed that the relative higher expression levels were observed in gill, skin and intestine. Meanwhile, NLR genes expression after bacterial infection results showed that most NLR genes participated in the process of defense of V. anguillarum and A. salmonicida infections in mucosal tissues. Taken together, identification and expression profiling analysis of NLR genes can provide valuable information for further functional characterization of these genes in turbot.

Characterization and expression analysis of mitochondrial localization molecule: NOD-like receptor X1 (Nlrx1) in mucosal tissues of turbot (Scophthalmus maximus) following bacterial challenge

The NOD-like receptor X1 (NLRX1) is a member of highly conserved nucleotide-binding domain (NBD)- and leucine-rich-repeat (LRR)-containing family (known as NLR), that localizes to the mitochondrial outer membrane and regulate the innate immunity by interacting with mitochondrial antiviral-signaling protein (MAVS). As one of cytoplasmic PRRs, NLRX1 plays key roles for pathogen recognition, autophagy and regulating of subsequent immune signaling pathways. In this study, we identified the nlrx1 in turbot as well as its expression profiles in mucosal surfaces following bacterial infection. In our results, the full-length nlrx1 transcript consists of an open reading frame (ORF) of 4,886 bp encoding the putative peptide of 966 amino acids. The phylogenetic analysis revealed the SmNlrx1 showed the closest relationship to Cynoglossus semilaevis. In addition, the Nlrx1 mRNA expression could be detected in all the examined tissues, with the most abundant expression level in head kidney, and the lowest expression level in liver. Moreover, Nlrx1 showed similar expression patterns following Vibrio anguillarum and Streptococcus iniae infection, that were both significantly up-regulated following challenge, especially post S. iniae challenge. Finally, fluorescence microscopy unveiled that the SmNlrx1 localized to mitochondria in HEK293T by N-terminal mitochondrial targeting sequence. Characterization of Nlrx1 might have an important implication in bioenergetic adaptation during metabolic stress, oncogenic transformation and innate immunity and will probably contribute to the development of novel intervention strategies for farming turbot.

The Dynamic Immune Response of Yellow Catfish (Pelteobagrus fulvidraco) Infected With Edwardsiella ictaluri Presenting the Inflammation Process

Edwardsiella ictaluri is a highly destructive pathogen in cultured yellow catfish, thus it was very necessary to study the immune response of yellow catfish against bacterial infection. In this study, RNA-Seq technology was used to study the immune response in two distinct tissues of yellow catfish at eight different time points (h) after E. ictaluri infection. The number of differentially expressed genes (DEGs) in the spleen and liver was low at 3 h and 6 h post-infection, respectively. Afterwards, the most number of DEGs in the spleen was detected at 72 h, while the number of DEGs in the liver maintained a high level from 24 h to 120 h. The GO and KEGG enrichment analyses of DEGs at different time points uncovered that cytokines were continuously transcribed at 6 h to 120 h; whereas the liver is the main organ that secretes the components of the complement system, and metabolic regulation was activated from 12 h to 120 h. Moreover, an overview of the inflammation response of yellow catfish was exhibited including pattern-recognition receptors, inflammatory cytokines, chemokines, complements, and inflammation-related signal pathways. The similar expression tendency of nine genes by qRT-PCR validated the accuracy of transcriptome analyses. The different transcriptomic profiles obtained from the spleen and liver will help to better understand the dynamic immune response of fish against bacterial infection, and will provide basic information for establishing effective measures to prevent and control diseases in fish.

Toxic effects of ammonia and thermal stress on the intestinal microbiota and transcriptomic and metabolomic responses of Litopenaeus vannamei

Ammonia and thermal stress frequently have harmful effects on aquatic animals. The intestine is an important barrier allowing the body to defend against stress. In this study, we investigated the intestinal microbiota and transcriptomic and metabolomic responses of Litopenaeus vannamei subjected to individual and combined ammonia and thermal stress. The results showed that obvious variation in the intestinal microbiota was observed after stress exposure, with increased levels of Firmicutes and decreased levels of Bacteroidetes and Planctomycetes. Several genera of putatively beneficial bacteria (Demequina, Weissella and Bacteroides) were abundant, while Formosa, Kriegella, Ruegeria, Rhodopirellula and Lutimonas were decreased; pathogenic bacteria of the genus Vibrio were increased under individual stress but decreased under combined stress. The intestinal transcriptome revealed several immune-related differentially expressed genes associated with the peritrophic membrane and antimicrobial processes in contrasting accessions. Haemolymph metabolomic analysis showed that stress exposure disturbed the metabolic processes of the shrimp, especially amino acid metabolism. This study provides insight into the underlying mechanisms associated with the intestinal microbiota, immunity and metabolism of L.vannamei in response to ammonia and thermal stress; ten stress-related metabolite markers were identified, including L-lactic acid, gulonic acid, docosahexaenoic acid, l-lysine, gamma-aminobutyric acid, methylmalonic acid, trans-cinnamate, N-acetylserotonin, adenine, and dihydrouracil.

Effects of chronic nitrate exposure on the intestinal morphology, immune status, barrier function, and microbiota of juvenile turbot (Scophthalmus maximus)

Coming along with high water reuse in sustainable and intensive recirculating aquaculture systems (RASs), the waste products of fish in rearing water is continuously accumulated. Nitrate, the final product of biological nitrification processes, which may cause aquatic toxicity to fish in different degrees when exposed for a long time. Therefore, the present study was conducted to evaluate the impact of chronic nitrate exposure on intestinal morphology, immune status, barrier function, and microbiota of juvenile turbot. For that, groups of juvenile turbot were exposed to 0 (control check, CK), 50 (low nitrate, L), 200 (medium nitrate, M), and 400 (high nitrate, H) mg L^-1 nitrate-N in small-sized recirculating aquaculture systems. After the 60-day experiment period, we found that exposure to a high concentration of nitrate-N caused obvious pathological damages to the intestine; for instance, atrophy of intestinal microvilli and necrosis in the lamina propria. Quantitative real-time PCR analysis revealed a significant downregulation of the barrier forming tight junction genes like occludin, claudin-like etc. under H treatment (P < 0.05). Intestinal MUC-2 expression also decreased significantly in the nitrate treatment groups compared to that in the control (P < 0.05). Additionally, the expression of HSP70 and HSP90 heat-shock proteins, toll-like receptor-3 (TLR-3), interleukin-1β (IL-1β), and tumor necrosis factor-α (TNF-α) significantly increased (P < 0.05), whereas that of transforming growth factor-β (TGF-β), lysozyme (LYS), and insulin-like growth factor-I (IGF-I) significantly decreased with H treatment (P < 0.05). The results also revealed that intestinal microbial community was changed following nitrate exposure and could alter the α-diversity and β-diversity. Specifically, the proportion of intrinsic flora decreased, whereas that of the potential pathogens significantly increased with M and H treatments (P < 0.05). In conclusion, chronic nitrate exposure could weaken the barrier function and disturb the composition of intestinal microbiota in marine teleosts, thereby harming their health condition.

Characterization and expression analysis of Nod-like receptor 3 (NLRC3) against infection with Piscirickettsia salmonis in Atlantic salmon

The nucleotide binding oligomerization domain like receptors, or NOD like receptors (NLRs), are intracellular receptors responsible for recognizing pathogens in vertebrates. Several NLR mammalian models have been characterized and analyzed but few studies have been performed with teleost species. In this study, we analyzed the nucleotide sequence of six mRNA variants of NLRC3 in Atlantic salmon (SsNLRC3), and we deduced the amino acid sequence coding for two different isoforms with a total length of 1135 amino acids and 1093 amino acids. We analyzed the phylogeny of all variants, including a Piscirickettsia salmonis infection in Atlantic salmon. All variants and their expression pattern during infection were analyzed using real-time qPCR. One of the analyzed variants was over-expressed during the early stages of Piscirickettsia salmonis infection, and we were able to identify two different SsNLRC3 isoforms. Lastly, we observed that an alteration in the amino acid sequence of one of the isoforms can directly affect the pathogen recognition function.

Toxicity of lindane induced by oxidative stress and intestinal damage in Caenorhabditis elegans

Lindane, a lipophilic pollutant, may be toxic to organisms. To explore the toxic effects of lindane and the underlying mechanisms of this toxicity, the animal model Caenorhabditis elegans (C. elegans) was exposed to lindane for 3 d at environmentally relevant concentrations (0.01-100 ng/L) and the physiological, biochemical, and molecular indices were evaluated. Subacute exposure to 10-100 ng/L of lindane caused adverse physiological effects on the development, reproduction, and locomotion behaviors in C. elegans. Exposure to 1-100 ng/L of lindane increased the accumulation of Nile red and blue food dye, which suggested high permeability of the intestine in nematodes. Lindane exposure also significantly influenced the expression of genes related to intestinal development (e.g., mtm-6 and opt-2). Moreover, reactive oxygen species production, lipofuscin accumulation, and expression of oxidation resistance genes (e.g., sod-5 and isp-1) were significantly increased in C. elegans exposed to 10-100 ng/L of lindane, which indicated that lindane exposure induced oxidative stress. According to Pearson correlation analyses, oxidative stress and intestinal damage were significantly correlated with the adverse physiological effects of lindane. Therefore, the adverse effects of lindane may have been induced by intestinal damage and oxidative stress, and mtm-6, opt-2, sod-5, isp-1, and mev-1 might play important roles in the toxicity of lindane.

Genome-wide identification, expression signature and immune functional analysis of two cathepsin S (CTSS) genes in turbot (Scophthalmus maximus L.)

Cathepsins, a superfamily of hydrolytic enzymes produced and enclosed within lysosomes, play multiple roles at physiological and pathological states. Cathepsin S is a lysosomal cysteine endopeptidase of the papain family, and exerts critical roles in the regulation of MHC class II immune responses. In the present study, we captured two Cathepsin S genes in turbot (SmCTSS1 and SmCTSS2.1), characterized their expression patterns following V. anguillarum and S. iniae infections, and explored their binding ability and agglutination capability. Firstly, the SmCTSS1 contained a 990 bp ORF encoding 329 amino acids, while SmCTSS2.1 contained a 1,014 bp ORF encoding 337 amino acids. The phylogenetic analysis revealed that both genes showed the closest relationship to their counterparts of Japanese flounder (Paralichthys olivaceus). In addition, both genes were ubiquitously expressed in all examined healthy tissues, with the highest expression level observed in spleen and intestine, respectively, while the lowest expression level both observed in liver. Both SmCTSS1 and SmCTSS2.1 were significantly differentially expressed, and exhibited general down-regulations at most time points in skin and intestine after two bacterial infections. Finally, both rSmCTSS1 and rSmCTSS2.1 showed significant binding ability to three examined microbial ligands (LPS, PGN and LTA), and strong agglutination effect to different bacteria (E. tarda, S. agalactiae, S. aureus and V. anguillarum). Collectively, this study provided valuable data for understanding the roles of CTSS in the host defense against bacterial infections in turbot, and indicated the potential vital roles of CTSS in innate immune responses of teleost species.

Histopathological study and intestinal mucous cell responses against Aeromonas hydrophila in Nile tilapia administered with Lactobacillus rhamnosus GG

Aim

This study aimed to examine the intestinal histopathological lesions and mucous cell responses in the entire intestines of Nile tilapia administered with Lactobacillus rhamnosus GG (LGG)-mixed feed, after Aeromonas hydrophila challenge.

Materials and Methods

Intestinal samples from fish fed with control normal diet or LGG-mixed feed (10¹⁰ colony-forming unit [CFU]/g feed) with or without A. hydrophila in phosphate-buffered saline challenge (7.46 × 10⁸ CFU/mL/fish) were collected and processed for histopathological study. The mucous cell responses were evaluated using histochemistry, using Alcian blue (AB) at pH 2.5, AB at pH 1.0, and periodic acid-Schiff-AB at pH 2.5. The quantification of the intestinal mucous cell size and the staining character of each mucin type from the entire intestine were recorded and counted.

Results

Histopathological study showed remarkable lesions only in the proximal intestine in fish infected with A. hydrophila, while LGG-fed fish had less intestinal damage, perhaps resulting from heterophil infiltration. Furthermore, a significant (p<0.01) increase in mixed mucous cell numbers was observed mainly in the proximal intestine of all challenged fish, compared with normal diet-fed fish without challenge, and also in LGG-fed fish with A. hydrophila challenge compared with LGG-fed fish without challenge.

Conclusion

Dietary LGG-fed Nile tilapia showed improvements in host innate immunity. In addition, LGG was effective in decreasing intestinal lesions from A. hydrophila-induced intestinal damage. Moreover, increasing numbers of mixed mucous cells in the proximal intestine might be indicative of certain pathological conditions in Nile tilapia after A. hydrophila infection.

Growth and health status of Pacific white shrimp, Litopenaeus vannamei, exposed to chronic water born cobalt

Cobalt (Co) is an important component of vitamin B₁₂, but is toxic to aquatic animals at a high level. In this study, the Pacific white shrimp, Litopenaeus vannamei were exposed to three Co concentrations (0, 100, and 1000 μg/L) for 4 weeks. The survival and condition factor in shrimp exposed to the Co treatments were not different from the control, but the shrimp exposed to 100 μg Co/L gained more weight than in other two groups, and the shrimp exposed to 1000 μg Co/L gained less weight than in other groups. The SOD and GSH-PX activities were higher in shrimp exposed to 100 μg Co/L, but lower in the shrimp exposed to 100 μg Co/L compared with the control, respectively. The MDA contents in the hepatopancreas decreased in the 100 μg Co/L, but increased in the 1000 μg Co/L. The serum lysozyme decreased with ambient cobalt, was lower in the shrimp exposed to 1000 μg Co/L than in other two groups. The expression of C-type lectin 3 was down-regulated by Co concentrations. The Toll and immune deficiency in shrimp exposed to 100 μg Co/L was higher than in other two groups. The mucin-1 was lower in the 1000 μg Co/L group than in other two groups, but mucin-2 and mucin-5AC were higher in the 1000 μg Co/L group than in the control. With increasing Co concentration, Shannon and Simpson indexes of the intestinal microbial communities were decreased. The abundance of pathogenic bacteria (Ruegeria and Vibrio) increased in both Co groups. This study indicates that chronic exposure to waterborne cobalt could affect growth, cause oxidative stress, stimulate the immune response, damage intestinal histology, and reshape intestinal microbiota community L. vannamei.

Characterization of class B scavenger receptor type 1 (SRB1) in turbot (Scophthalmus maximus L.)

Class B scavenger receptor type 1 (SRB1) serves as a high-density lipoprotein (HDL) receptor essential for HDL metabolism, and plays vital roles in innate immunity. In this study, the turbot (Scophthalmus maximus) SRB1 was cloned and characterized. The gene structure consists of a coding region of 1,527 bp nucleotides dividing into 13 exons and 12 introns. Such genome structure is highly conserved among teleost fishes. The deduced SRB1 encodes 508 amino acids that mainly has a CD36 transmembrane domain. Tissue distribution of SRB1 showed the lowest expression in liver, while the highest expression was found in intestine. Significantly down-regulation pattern of SmSRB1 expression in intestine was shared after infection with Vibrio anguillarum and Streptococcus iniae. Brach and site models in CODEML program showed that SmSRB1 underwent a conservative evolutionary and three potential positive selected sites 470K, 496E, and 501Y were detected, which requires further investigation and confirmation using base-editing technologies. Subcellular localization demonstrated that turbot SRB1 was distributed in the membrane and cytoplasm. rSmSRB1 showed binding ability in vitro to bacteria, LPS, PGN, LTA and virus. Protein-protein interaction network agrees the function of SRB1 as lipoprotein receptor. Our results indicated SmSRB1 might act as co-receptors to TLRs and NLRs to modulate the immune response to pathogens. Further studies should pay attention to evaluate the specific co-receptor for SRB1 in recognition of different pathogens and selective mechanisms involved.