Expression of nitric oxide synthase (NOS) genes in channel catfish is highly regulated and time dependent after bacterial challenges

A review of soluble factors and receptors involved in fish skin immunity: The tip of the iceberg

The immune system of fish possesses soluble factors, receptors, pathways and cells very similar to those of the other vertebrates' immune system. Throughout evolutionary history, the exocrine secretions of organisms have accumulated a large reservoir of soluble factors that serve to protect organisms from microbial pathogens that could disrupt mucosal barrier homeostasis. In parallel, a diverse set of recognition molecules have been discovered that alert the organism to the presence of pathogens. The known functions of both the soluble factors and receptors mentioned above encompass critical aspects of host defense, such as pathogen binding and neutralization, opsonization, or modulation of inflammation if present. The molecules and receptors cooperate and are able to initiate the most appropriate immune response in an attempt to eliminate pathogens before host infection can begin. Furthermore, these recognition molecules, working in coordination with soluble defence factors, collaboratively erect a robust and perfectly coordinated defence system with complementary specificity, activity and tissue distribution. This intricate network constitutes an immensely effective defence mechanism for fish. In this context, the present review focuses on some of the main soluble factors and recognition molecules studied in the last decade in the skin mucosa of teleost fish. However, knowledge of these molecules is still very limited in all teleosts. Therefore, further studies are suggested throughout the review that would help to better understand the functions in which the proteins studied are involved.

Effects of dietary supplementation of Pseudomonas aeruginosa FARP72 on the immunomodulation and resistance to Edwardsiella tarda in Pangasius pangasius

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Pseudomonas aeruginosa FARP72 (PA) supplemented diet impacts the innate immunity.

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Innate immune responses of P. pangasius are differentially stimulated by PA diet.

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It improved the resistance of P. pangasius against E. tarda infection significantly.

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IL-1β & C3 genes upregulated significantly in kidney of PA diet-fed challenged fish.

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Highest upregulation of transferrin seen in liver of PA diet-fed challenged fish.

Edwardsiella tarda is one of the serious bacterial pathogens infecting both cultured and wild catfish urging an immediate need for effective protection strategies. This study assessed the effects of dietary supplementation of Pseudomonas aeruginosa FARP72 at 10⁸ cells/g feed (PA diet) for 30 days on the innate immunity parameters, viz., respiratory oxidative burst (ROB) activity, lysozyme, ceruloplasmin, myeloperoxidase, in-vitro nitric oxide (NO) production in addition to the expression of immune genes encoding interleukin-1β, C3 and transferrin in yellowtail catfish Pangasius pangasius and their resistance to Edwardsiella tarda challenge at a sub-lethal dose of 1.50 × 10⁷ cells/fish. A significant increase in the innate immunity parameters was noted in PA diet-fed catfish on 30 dpf compared to the control. Post E. tarda challenge, the levels of immune parameters increased significantly and peaked at 5 dpi irrespective of feeding to confer protection against E. tarda. Their levels, however, decreased on and from 10 dpi. The results on the expression of immune genes encoding interleukin-1β, C3 and transferrin in the kidney and liver tissue samples of PA diet-fed P. pangasius upon challenge with E. tarda further confirmed the ability of P. aeruginosa to stimulate primary immune organs at the gene level. The effects of feeding P. aeruginosa FARP72 on the immune functions of catfish as examined by the functional immune assays, thus, demonstrating the innate immune responses of catfish that are differentially stimulated by the PA diet. The findings of our study would help evolve management strategies to confer protection against E. tarda infection in commercial catfish aquaculture.

Inducible Nitric Oxide Synthase/Nitric Oxide System as a Biomarker for Stress and Ease Response in Fish: Implication on Na+ Homeostasis During Hypoxia

The cellular and organismal response to stressor-driven stimuli evokes stress response in vertebrates including fishes. Fishes have evolved varied patterns of stress response, including ionosmotic stress response, due to their sensitivity to both intrinsic and extrinsic stimuli. Fishes that experience hypoxia, a detrimental stressor that imposes systemic and cellular stress response, can evoke disturbed ion homeostasis. In addition, like other vertebrates, fishes have also developed mechanisms to recover from the impact of stress by way of shifting stress response into ease response that could reduce the magnitude of stress response with the aid of certain neuroendocrine signals. Nitric oxide (NO) has been identified as a potent molecule that attenuates the impact of ionosmotic stress response in fish, particularly during hypoxia stress. Limited information is, however, available on this important aspect of ion transport physiology that contributes to the mechanistic understanding of survival during environmental challenges. The present review, thus, discusses the role of NO in Na⁺ homeostasis in fish particularly in stressed conditions. Isoforms of nitric oxide synthase (NOS) are essential for the synthesis and availability of NO at the cellular level. The NOS/NO system, thus, appears as a unique molecular drive that performs both regulatory and integrative mechanisms of control within and across varied fish ionocytes. The activation of the inducible NOS (iNOS)/NO system during hypoxia stress and its action on the dynamics of Na⁺/K⁺-ATPase, an active Na⁺ transporter in fish ionocytes, reveal that the iNOS/NO system controls cellular and systemic Na⁺ transport in stressed fish. In addition, the higher sensitivity of iNOS to varied physical stressors in fishes and the ability of NO to lower the magnitude of ionosmotic stress in hypoxemic fish clearly put forth NO as an ease-promoting signal molecule in fishes. This further points to the signature role of the iNOS/NO system as a biomarker for stress and ease response in the cycle of adaptive response in fish.

Nitric Oxide Production and Regulation in the Teleost Cardiovascular System

Nitric Oxide (NO) is a free radical with numerous critical signaling roles in vertebrate physiology. Similar to mammals, in the teleost system the generation of sufficient amounts of NO is critical for the physiological function of the cardiovascular system. At the same time, NO amounts are strictly controlled and kept within basal levels to protect cells from NO toxicity. Changes in oxygen tension highly influence NO bioavailability and can modulate the mechanisms involved in maintaining the NO balance. While NO production and signaling appears to have general similarities with mammalian systems, the wide range of environmental adaptations made by fish, particularly with regards to differing oxygen availabilities in aquatic habitats, creates a foundation for a variety of in vivo models characterized by different implications of NO production and signaling. In this review, we present the biology of NO in the teleost cardiovascular system and summarize the mechanisms of NO production and signaling with a special emphasis on the role of globin proteins in NO metabolism.

Hemolysin Co-regulated Family Proteins Hcp1 and Hcp2 Contribute to Edwardsiella ictaluri Pathogenesis

Edwardsiella ictaluri is a Gram-negative facultative intracellular pathogen causing enteric septicemia of catfish (ESC), a devastating disease resulting in significant economic losses in the U.S. catfish industry. Bacterial secretion systems are involved in many bacteria's virulence, and Type VI Secretion System (T6SS) is a critical apparatus utilized by several pathogenic Gram-negative bacteria. E. ictaluri strain 93-146 genome has a complete T6SS operon with 16 genes, but the roles of these genes are still not explored. In this research, we aimed to understand the roles of two hemolysin co-regulated family proteins, Hcp1 (EvpC) and Hcp2. To achieve this goal, single and double E. ictaluri mutants (EiΔevpC, EiΔhcp2, and EiΔevpCΔhcp2) were generated and characterized. Catfish peritoneal macrophages were able to kill EiΔhcp2 better than EiΔevpC, EiΔevpCΔhcp2, and E. ictaluri wild-type (EiWT). The attachment of EiΔhcp2 and EiΔevpCΔhcp2 to ovary cells significantly decreased compared to EiWT whereas the cell invasion rates of these mutants were the same as that of EiWT. Mutants exposed to normal catfish serum in vitro showed serum resistance. The fish challenges demonstrated that EiΔevpC and EiΔevpCΔhcp2 were attenuated completely and provided excellent protection against EiWT infection in catfish fingerlings. Interestingly, EiΔhcp2 caused higher mortality than that of EiWT in catfish fingerlings, and severe clinical signs were observed. Although fry were more susceptible to vaccination with EiΔevpC and EiΔevpCΔhcp2, their attenuation and protection were significantly higher compared to EiWT and sham groups, respectively. Taken together, our data indicated that evpC (hcp1) is involved in E. ictaluri virulence in catfish while hcp2 is involved in adhesion to epithelial cells and survival inside catfish macrophages.

Virulence of Vibrio alginolyticus Accentuates Apoptosis and Immune Rigor in the Oyster Crassostrea hongkongensis

Vibrio species are ubiquitously distributed in marine environments, with important implications for emerging infectious diseases. However, relatively little is known about defensive strategies deployed by hosts against Vibrio pathogens of distinct virulence traits. Being an ecologically relevant host, the oyster Crassostrea hongkongensis can serve as an excellent model for elucidating mechanisms underlying host-Vibrio interactions. We generated a Vibrio alginolyticus mutant strain (V. alginolyticus^△vscC ) with attenuated virulence by knocking out the vscC encoding gene, a core component of type III secretion system (T3SS), which led to starkly reduced apoptotic rates in hemocyte hosts compared to the V. alginolyticus^WT control. In comparative proteomics, it was revealed that distinct immune responses arose upon encounter with V. alginolyticus strains of different virulence. Quite strikingly, the peroxisomal and apoptotic pathways are activated by V. alginolyticus^WT infection, whereas phagocytosis and cell adhesion were enhanced in V. alginolyticus^△vscC infection. Results for functional studies further show that V. alginolyticus^WT strain stimulated respiratory bursts to produce excess superoxide (O2^•-) and hydrogen peroxide (H₂O₂) in oysters, which induced apoptosis regulated by p53 target protein (p53tp). Simultaneously, a drop in sGC content balanced off cGMP accumulation in hemocytes and repressed the occurrence of apoptosis to a certain extent during V. alginolyticus^△vscC infection. We have thus provided the first direct evidence for a mechanistic link between virulence of Vibrio spp. and its immunomodulation effects on apoptosis in the oyster. Collectively, we conclude that adaptive responses in host defenses are partially determined by pathogen virulence, in order to safeguard efficiency and timeliness in bacterial clearance.

Comparative genomics of the fish pathogens Edwardsiella ictaluri 93-146 and Edwardsiella piscicida C07-087

Edwardsiella ictaluri and Edwardsiella piscicida are important fish pathogens affecting cultured and wild fish worldwide. To investigate the genome-level differences and similarities between catfish-adapted strains in these two species, the complete E. ictaluri 93-146 and E. piscicida C07-087 genomes were evaluated by applying comparative genomics analysis. All available complete (10) and non-complete (19) genomes from five Edwardsiella species were also included in a systematic analysis. Average nucleotide identity and core-genome phylogenetic tree analyses indicated that the five Edwardsiella species were separated from each other. Pan-/core-genome analyses for the 29 strains from the five species showed that genus Edwardsiella members have 9474 genes in their pan genome, while the core genome consists of 1421 genes. Orthology cluster analysis showed that E. ictaluri and E. piscicida genomes have the greatest number of shared clusters. However, E. ictaluri and E. piscicida also have unique features; for example, the E. ictaluri genome encodes urease enzymes and cytochrome o ubiquinol oxidase subunits, whereas E. piscicida genomes encode tetrathionate reductase operons, capsular polysaccharide synthesis enzymes and vibrioferrin-related genes. Additionally, we report for what is believed to be the first time that E. ictaluri 93-146 and three other E. ictaluri genomes encode a type IV secretion system (T4SS), whereas none of the E. piscicida genomes encode this system. Additionally, the E. piscicida C07-087 genome encodes two different type VI secretion systems. E. ictaluri genomes tend to encode more insertion elements, phage regions and genomic islands than E. piscicida. We speculate that the T4SS could contribute to the increased number of mobilome elements in E. ictaluri compared to E. piscicida. Two of the E. piscicida genomes encode full CRISPR-Cas regions, whereas none of the E. ictaluri genomes encode Cas proteins. Overall, comparison of the E. ictaluri and E. piscicida genomes reveals unique features and provides new insights on pathogenicity that may reflect the host adaptation of the two species.

Effects of inflammation and/or infection on the neuroendocrine control of fish intestinal motility: A review

Food is the largest expense in fish farms. On the other hand, the fish health and wellbeing are determining factors in aquaculture production where nutrition is a vital process for growing animals. In fact, it is important to remember that digestion and nutrition are crucial for animals' physiology. However, digestion is a very complex process in which food is processed to obtain necessary nutrients and central mechanisms of this process require both endocrine and neuronal regulation. In this context, intestinal motility is essential for the absorption of the nutrients (digestive process determining nutrition). An imbalance in the intestinal motility due to an inadequate diet or an infectious process could result in a lower use of the food and inefficiency in obtaining nutrients from food. Very frequently, farmed fish are infected with different pathogenic microorganism and this situation could alter gastrointestinal physiology and, indirectly reduce fish growth. For these reasons, the present review focuses on analysing how different inflammatory molecules or infections can alter conventional modulators of fish intestinal motility.

Expression of immune genes in Indian major carp, Catla catla challenged with Flavobacterium columnare

Columnaris disease, caused by Flavobacterium columnare, is one of the important bacterial diseases responsible for large-scale mortalities in numerous freshwater fishes globally. This disease can cause up to 100% mortality within 24 h of infection and is considered to be a cause of concern for aquaculture industry. Despite being a serious disease, scarce information is available regarding host-pathogen interaction, particularly the modulation of different immune genes in response to F. columnare infection. Therefore, in the present study, an attempt has been made to study expression of important immune regulatory genes, namely IL-1β, iNOS, INF-γ, IL-10, TGF-β, C3, MHC-I and MHC-II in gills and kidney of Catla catla following experimental infection with F. columnare. The expression analysis of immune genes revealed that transcript levels of IL-1β, iNOS, IL-10, TGF-β, C3 and MHC-I were significantly up-regulated (p < 0.05) in both the organs of the infected catla. IFN-γ and MHC-II were up-regulated in gills of infected catla whereas, both the genes showed down-regulation in kidney. The results indicate that important immune genes of C. catla are modulated following infection with F. columnare. The knowledge thus generated will strengthen the understanding of molecular pathogenesis of F. columnare in Indian major carp C. catla.

Expression of nitric oxide synthase (NOS) in Anabas testudineus ovary and participation of nitric oxide-cyclic GMP cascade in maintenance of meiotic arrest

Participation of cyclic nucleotide-mediated signaling in nitric oxide/soluble guanylate cyclase (NO/sGC) regulation of oocyte maturation (OM) in perch (Anabas testudineus) follicle-enclosed oocytes has been investigated. Congruent with sharp decline in follicular cyclic GMP (cGMP) level, nitric oxide synthase (NOS)-inhibitor (L-NAME) attenuates protein kinase A (PKA) phosphorylation but promotes p-ERK1/2 and p-p34Cdc2 (Thr-161) in maturing oocytes. Conversely, NO donor (SNP) prevents OM, potentially through elevated cGMP synthesis. Expression and localization of Nos2 and Nos3 immunoreactivity in perch ovary varied considerably at progressively higher stages of folliculogenesis. While sGC inhibitor (ODQ) alone could induce OM, 8-bromo-cGMP attenuates 17,20β-P-induced OM indicating functional significance of NO/sGC/cGMP in perch ovary. Interestingly, high NO/cGMP inhibition of OM shows positive relation with elevated cAMP level. MIS induced OM is more susceptible to the oocyte-specific phosphodiesterase (PDE) 3 than PDE4 inhibition. Collectively, high NO/cGMP attenuation of OM potentially involves PDE3 inhibition, cAMP accumulation and PKA activation.

Physiological relevance of nitric oxide in ovarian functions: An overview

Nitric oxide (NO, nitrogen monoxide), a short-lived, free radical carrying an unpaired electron, is one of the smallest molecules synthesized in the biological system. In addition to its role in angiogenesis, neuronal function and inflammatory response, NO has wide-spread significance in regulation of ovarian function in vertebrates. Based on tissue-specific expression, three different nitric oxide synthase (NOS) isoforms, neuronal (nNOS) or NOS1, inducible (iNOS) or NOS2 and endothelial (eNOS) or NOS3 have been identified. While expression of both inducible (iNOS) and constitutive NOS (eNOS) isoforms varies considerably in the ovary at various stages of follicular growth and development, selective binding of NO with proteins containing heme moieties have significant influence on ovarian steroidogenesis. Besides, NO modulation of ovulatory response suggests physiological significance of NO/NOS system in mammalian ovary. Compared to the duality of NO action on follicular development, steroidogenesis and meiotic maturation in mammalian models, participation of NO/NOS system in teleost ovary is less investigated. Genes encoding nos1 and nos2 have been identified in fish; however, presence of nos3 is still ambiguous. Interestingly, two distinct nos2 genes, nos2a and nos2b in zebrafish, possibly arose through whole genome duplication. Differential expression of major NOS isoforms in catfish ovary, NO inhibition of meiosis resumption in Anabas testudineus follicle-enclosed oocytes and NO/sGC/cGMP modulation of oocyte maturation in zebrafish are some of the recent advancements. The present overview is an update on the advancements made and shortfalls still remaining in NO/NOS modulation of intercellular communication in teleost vis-à-vis mammalian ovary.

Nitric Oxide and the Neuroendocrine Control of the Osmotic Stress Response in Teleosts

The involvement of nitric oxide (NO) in the modulation of teleost osmoresponsive circuits is suggested by the facts that NO synthase enzymes are expressed in the neurosecretory systems and may be regulated by osmotic stimuli. The present paper is an overview on the research suggesting a role for NO in the central modulation of hormone release in the hypothalamo-neurohypophysial and the caudal neurosecretory systems of teleosts during the osmotic stress response. Active NOS enzymes are constitutively expressed by the magnocellular and parvocellular hypophysiotropic neurons and the caudal neurosecretory neurons of teleosts. Moreover, their expression may be regulated in response to the osmotic challenge. Available data suggests that the regulatory role of NO appeared early during vertebrate phylogeny and the neuroendocrine modulation by NO is conservative. Nonetheless, NO seems to have opposite effects in fish compared to mammals. Indeed, NO exerts excitatory effects on the electrical activity of the caudal neurosecretory neurons, influencing the amount of peptides released from the urophysis, while it inhibits hormone release from the magnocellular neurons in mammals.

Characterization, expression signatures and microbial binding analysis of cathepsin A in turbot, Scophthalmus maximus L.(SmCTSA)

Mucosal immune system is one of the most vital components in the innate immunity and constitutes the first line of host defense against bacterial infections, especially for the teleost, which live in the pathogen-rich aquatic environment. Cathepsins, a superfamily of hydrolytic enzymes produced and enclosed within lysosomes, play multiple roles at physiological and pathological states. In this regard, we sought here to identify Cathepsin A in turbot (SmCTSA), characterize its mucosal expression patterns following Vibrio anguillarum and Streptococcus iniae infections in mucosal tissues, and explore its binding ability with three microbial ligands for the first time. The SmCTSA was 2631 bp long containing a 1422 bp open reading frame (ORF) that encoded 473 amino acids. Phylogenetic analysis revealed that SmCTSA showed the closest relationship to half-smooth tongue sole (Cynoglossus semilaevis). In addition, SmCTSA was ubiquitously expressed in all examined healthy tissues, with high expression levels in head kidney (HK) and intestine, while the lowest expression level in blood. Moreover, SmCTSA was significantly differentially expressed at least two timepoints in each mucosal tissue, suggesting its potential important roles in innate immune responses of turbot. Finally, in vitro assays showed that recombinant SmCTSA bound Lipopolysaccharide (LPS) with high affinity, and lipoteichoic acid (LTA) and peptidoglycan (PGN) with relatively low affinity. This study provides valuable data for understanding the roles of ctsa in the host defense against bacterial infections.

A Review of Molecular Responses of Catfish to Bacterial Diseases and Abiotic Stresses

Catfish is one of the major aquaculture species in the United States. However, the catfish industry is threatened by several bacterial diseases such as enteric septicemia of catfish (ESC), columnaris disease and Aeromonas disease, as well as by abiotic stresses such as high temperature and low oxygen. Research has been conducted for several decades to understand the host responses to these diseases and abiotic stresses. With the development of sequencing technologies, and the application of genome-wide association studies in aquaculture species, significant progress has been made. This review article summarizes recent progress in understanding the molecular responses of catfish after bacterial infection and stress challenges, and in understanding of genomic and genetic basis for disease resistance and stress tolerance.

JAK and STAT members in channel catfish: Identification, phylogenetic analysis and expression profiling after Edwardsiella ictaluri infection

The Janus kinase/signal transducers and activators of transcription (JAK/STAT) signaling pathway is one of the main pleiotropic cascades used to transmit information from extracellular receptors to the nucleus, which results in DNA transcription and expression of genes involved in immunity, proliferation, differentiation, migration, apoptosis, and cell survival. Members of JAK family and STAT family have been extensively studied in different mammalian species because of their important roles in innate and adaptive immune responses. However, they have not been systematically studied among teleost fish species. In this study, five JAK family members and eight STAT family members were identified and characterized from channel catfish. Phylogenetic analysis was conducted to properly annotate these genes. Syntenic analysis was also conducted to establish orthology, and confirm the results from phylogenetic analysis. Compared to mammals, more members of the JAK and STAT family were identified in channel catfish genome. Expression of JAK and STAT family members was detected in healthy catfish tissues, but was induced in gill, liver, and intestine after bacterial challenge. Notably, the significant upregulation of STAT1b gene in catfish liver, gill and intestine after Edwardsiella ictaluri infection supported the notion that high STAT1 expression are involved in defense against pathogens. Collectively, the increased expression of JAK and STAT members in tested tissues suggested their crucial function in defending the host against pathogen invasion.

Characterization and gene expression analysis of pacu (Piaractus mesopotamicus) inducible nitric oxide synthase (iNOS) following Aeromonas dhakensis infection

Nitric oxide (NO) is an important effector molecule which is involved in a myriad of biological processes, including immune responses against pathogens such as parasites, virus and bacteria. During the inflammatory processes in vertebrates, NO is produced by the inducible nitric oxide synthase (iNOS) enzyme in practically all nucleated cells to suppress or kill intracellular pathogens. The aim of the present study was to characterize the full coding region of the iNOS gene of pacu (Piaractus mesopotamicus), an economically and ecologically important South American fish species, and to analyze mRNA expression levels following intraperitoneal infection with the pathogenic bacterium Aeromonas dhakensis by means of quantitative real time PCR (qPCR). The results showed that the pacu iNOS transcript is 3237 bp in length, encoding a putative protein composed of 1078 amino acid residues. The amino acid sequence showed similarities ranging from 69.03% to 94.34% with other teleost fish and 57.70% with the human iNOS, with all characteristic domains and cofactor binding sites of the enzyme detected. Phylogenetic analysis showed that the iNOS from the red-bellied piranha, another South American characiform, was the closest related sequence to the pacu iNOS. iNOS transcripts were constitutively detected in the liver, spleen and head kidney, and there was a significant upregulation in the liver and spleen at 12, 24 and 48 h after infection with A. dhakensis. No significant variations were observed in the head kidney during the periods analyzed. These results show that iNOS expression was induced by A. dhakensis infection and suggest that this enzyme may be involved in the response to this bacterium in pacu.

TO17: A teleost antimicrobial peptide that induces degradation of bacterial nucleic acids and inhibits bacterial infection in red drum, Sciaenops ocellatus

Tissue factor pathway inhibitor (TFPI)-1 is well known for its role as an inhibitor of blood coagulation. Several studies have demonstrated that the C-terminal peptides of TFPI-1 are active against a broad spectrum of microorganisms. In a previous study, we found that TO17 (with 17 amino acids), a TFPI-1 C-terminal peptide from red drum (Sciaenops ocellatus), was active against Edwardsiella tarda. In the present study, we investigated further the antimicrobial spectrum, action mode, as well as the immunostimulatory property of TO17. Our results showed that TO17 displayed antimicrobial activity against Staphylococcus aureus, Micrococcus luteus, Vibrio vulnificus, and infectious spleen and kidney necrosis virus, independent of host serum. Furthermore, the activity of TO17 was influenced by the length or type of amino acids at the N and C termini. During its interaction with V. vulnificus, TO17 exerted its antibacterial activity by destroying cell membrane integrity, penetrating the cytoplasm and inducing degradation of genomic DNA and total RNA. In addition, TO17 had no hemolytic activity against red drum blood cells. In vitro, TO17 enhanced production of nitric oxide and bactericidal activity of red drum macrophages. In vivo, administration of red drum with TO17 before bacterial infection significantly reduced pathogen dissemination and replication in tissues. These results indicate that TO17 is a broad-spectrum antimicrobial peptide with immunostimulatory properties and it has the potential to be used as an antimicrobial agent in aquaculture.

Effect of dietary Clostridium butyricum on growth, intestine health status and resistance to ammonia stress in Pacific white shrimp Litopenaeus vannamei

The present study evaluated the effect of dietary Clostridium butyricum (CB) on growth, intestine microstructure, intestine digestive and immune function, intestine short-chain fatty acids (SCFA) content and body composition of Pacific white shrimp Litopenaeus vannamei. The shrimp was fed for 56 d with diets containing different levels of C. butyricum (1 × 10⁹ cfu/g): 0% (Control), 0.25% (CB1), 0.5% (CB2) and 1.0% (CB3) as treatment groups, followed by an acute ammonia stress test for 72 h. The results indicated that dietary supplementation of C. butyricum decreased the feed conversion rate (FCR) and increased the growth performance of shrimp. Compared with the control group, after shrimp fed with C. butyricum 56 d, intestine amylase and protease activity in the three C. butyricum group increased, while lipase activity was only affected in the CB1 and CB2 group. Total antioxidant capacity (T-AOC) content, lysozyme (LSZ) activity, and the relative expression level of Toll and immune deficiency (Imd) gene all increased in three C. butyricum groups. Inducible nitric oxide synthase (iNOS) activity increased in the CB2 and CB3 group, heat shock protein 70 (HSP70) gene expression level increased in the CB3 group, while nitric oxide (NO) content was not affected by C. butyricum. After shrimp exposed to ammonia stress, intestine immune biochemical parameters (T-AOC, LSZ, iNOS and NO) and genes (HSP70, Toll and Imd) expression level of C. butyricum group was higher than that of the control. HE stain showed that C. butyricum increased the intestine epithelium height of L. vannamei. These results revealed that C. butyricum could improve the growth performance, increased intestine SCFA content and body crude protein content, modulated intestine digestive capacity, and enhanced intestine immune function of L. vannamei against ammonia stress.

Identification of NF-κB related genes in channel catfish and their expression profiles in mucosal tissues after columnaris bacterial infection

Interactions of NF-κB family, IκB family and IKK complex are the key components of NF-κB pathway that is essential for many biological processes including innate and adaptive immunity, inflammation and stress responses. In spite of their importance, systematic analysis of these genes in fish has been lacking. Here we report a systematic study of the NF-κB related genes in channel catfish. Five NF-κB family genes, five IκB family genes and three IKK complex genes were identified in the channel catfish genome. Annotation of these 13 NF-κB related genes was further confirmed by phylogenetic and syntenic analysis. Negative selection was found to play a crucial role in the adaptive evolution of these genes. Expression profiles of NF-κB related genes after Flavobacterium columnare (columnaris) infection were determined by analysis of the existing RNA-Seq dataset. The majority of NF-κB related genes were significantly regulated in mucosal tissues of gill, skin and intestine after columnaris infection, indicating their potential involvement in host defense responses. Distinct expression patterns of NF-κB related genes were observed in susceptible and resistant catfish in response to columnaris infection, suggesting that expression of these genes may contribute to the variations in disease resistance/susceptibility of catfish.

Intestine oxidative stress and immune response to sulfide stress in Pacific white shrimp Litopenaeus vannamei

The effects of sulfide stress on oxidative stress and immune response in intestine of Pacific white shrimp Litopenaeus vannamei were evaluated in the present study. Oxidative stress parameters, immune enzymes activity and immune gene mRNA expression level were detected in intestine of L. vannamei after the exposure of 5.0 mg/L sulfide stress 72 h. The duration of sulfide stress influenced the shrimp survival, and the cumulative mortality rate was 30.0% and 33.3% at 48 h and 72 h respectively. HE staining showed that sulfide stress caused the intestine tissue damage symptoms. Compared with the control group, after exposed to sulfide stress, the content of lipid peroxidation (LPO), malondialdehyde (MDA) and ROS production (·O₂^- generation capacity) increased. Total antioxidant capacity (T-AOC) activity increased at 6 h and decreased at 48 h. Superoxide dismutase (SOD) activity increased in the entire experiment. Inducible nitric oxide synthase (iNOS) activity and nitric oxide (NO) content increased to the highest at 6 h and 12 h respectively, and both decreased at 48 h. The relative mRNA expression level of heat shock protein 70 (HSP70) gene decreased at 6 h and increased to the highest at 48 h. The relative mRNA expression level of hypoxia inducible factor 1α (HIF-1α) gene increased at 12 h and decreased to a lower level at 72 h. The relative mRNA expression level of Toll and immune deficiency (Imd) gene increased to the highest at 12 h and 24 h respectively, and both decreased at 48 h. These results revealed that sulfide stress could induce oxidative stress and immune response via confusion of immune enzymes activity and gene expression level in intestine of L. vannamei.

The chemokinome superfamily in channel catfish: I. CXC subfamily and their involvement in disease defense and hypoxia responses

Chemokines are a superfamily of structurally related chemotactic cytokines exerting significant roles in regulating cell migration and activation. They are defined by the presence of four conserved cysteine residues and are divided into four subfamilies depending on the arrangement of the first two conserved cysteines residues: CXC, CC, C and CX3C. In this study, a complete set of 17 CXC chemokine ligand (CXCL) genes was systematically identified and characterized from channel catfish genome through data mining of existing genomic resources. Phylogenetic analysis allowed annotation of the 17 CXC chemokines. Extensive comparative genomic analyses supported their annotations and orthologies, revealing the existence of fish-specific CXC chemokines and the expansion of CXC chemokines in the teleost genomes. The analysis of gene expression after bacterial infection indicated the CXC chemokines were expressed in a gene-specific manner. CXCL11.3 and CXCL20.3 were expressed significantly higher in resistant fish than in susceptible fish after ESC infection, while CXCL20.2 were expressed significantly higher in resistant fish than in susceptible fish after columnaris infection. The expression of those CXC chemokines, therefore can be a useful indicator of disease resistance. A similar pattern of expression was observed between resistant and susceptible fish with biotic and abiotic stresses, ESC, columnaris and hypoxia, suggesting that high levels of expression of the majority of CXC chemokines, with exception of CXC11 and CXC20, are detrimental to the host.

Effect of dietary poly-β-hydroxybutyrate (PHB) on growth performance, intestinal health status and body composition of Pacific white shrimp Litopenaeus vannamei (Boone, 1931)

In the present study, the effect of dietary supplementation of poly-β-hydroxybutyrate (PHB) on the growth performance, intestinal digestive and immune function, intestinal short-chain fatty acids (SCFA) content and body composition of Pacific white shrimp Litopenaeus vannamei (Boone, 1931) was evaluated. The shrimp was fed for 35 days with four different diets: 0%, 1%, 3% and 5% PHB supplemented feed. The results indicated that supplementation of PHB significantly increased the growth performance of the shrimp, and the feed conversion rate (FCR) in 3%PHB treatment group was significantly lower than the control (P < 0.05). The intestinal amylase, lipase and trypsin activity in the three PHB treatment groups were all significantly higher than that of the control (P < 0.05), but the pepsin activity were only significantly affected by 3%PHB treatment (P > 0.05). The activities of intestinal immune enzymes such as total antioxidant capacity (T-AOC) and inducible nitric oxide synthase (iNOS) was significantly induced by 3%PHB treatment (P < 0.05), while lysozyme (LSZ) activity was significantly affected by 5%PHB treatment and nitric oxide (NO) content was significantly induced in three PHB treatments. Meanwhile, PHB induced significantly the expression level of intestinal heat shock protein 70 (HSP70), Toll and immune deficiency (Imd) gene. HE staining showed that PHB induced the intestinal health status of L. vannamei. Intestinal SCFA content analysis revealed that the content of propionic and butyric acid of 3%PHB treatment were significantly higher than that of the control (P < 0.05). Body composition analysis showed that the crude protein in 3% and 5%PHB treatments, and the crude lipid in 1% and 5%PHB treatments were all significantly higher than the control (P < 0.05). These results revealed that PHB could improve the growth performance, modulated intestinal digestive and immune function, increased intestinal SCFA content and body composition in L. vannamei, and the optimum dietary PHB requirement by L. vannamei was estimated at 3% (w/w) diet.

The expression signatures of neuronal nitric oxide synthase (NOS1) in turbot (Scophthalmus maximus L.) mucosal surfaces against bacterial challenge

The mucosal surfaces constitute the first immune barrier of host defense and also serve as the dynamic interfaces that simultaneously mediate a diverse array of critical physiological processes. It has been long hypothesized that observed difference of disease resistance among different fish strains and species are strongly correlated to the activities of the immune actors in mucosal surfaces. Particularly, neuronal NOS (nNOS or NOS1) is a constitutively expressed gene that catalyzes the oxidation of l-arginine and water to nitric oxide (NO), which is known as a potent host defence effector in immune system with antimicrobial activity. Moreover, NOS1 was detected to be expressed in fish mucosal surfaces, but its activities in mucosal immune responses were always overlooked. In this regard, we identified the NOS1 of turbot and characterized its expression patterns in mucosal tissues following Vibrio anguillarum and Streptococcus iniae challenge. The results showed that the NOS1 gene had a 4389 bp open reading frame (ORF) that encoded 1462 amino acids. Phylogenetic analysis showed the turbot NOS1 had the strongest relationship to Larimichthys crocea. And the syntenic analysis revealed the similar neighboring genes associated with turbot NOS1, compared with other teleost and mammals. In addition, NOS1 was widely expressed in all examined tissues with the highest expression level in brain, followed by intestine and gill. Finally, the NOS1 showed a general trend of up-regulation in mucosal tissues following both bacterial challenge, with the highest up-regulation in intestine. The significant quick induction of NOS1 in mucosal surfaces against infection indicated its key roles to prevent pathogen attachment and entry in mucosal immunity. More functional studies are needed to conduct in teleost to better understand the roles of NOS1 in maintaining the integrity of the mucosal barriers against infection.

The first description of complete invertebrate arginine metabolism pathways implies dose-dependent pathogen regulation in Apostichopus japonicus

In this study, three typical members representative of different arginine metabolic pathways were firstly identified from Apostichopus japonicus, including nitric oxide synthase (NOS), arginase, and agmatinase. Spatial expression analysis revealed that the AjNOS transcript presented negative expression patterns relative to those of Ajarginase or Ajagmatinase in most detected tissues. Furthermore, Vibrio splendidus-challenged coelomocytes and intestine, and LPS-exposed primary coelomocytes could significantly induce AjNOS expression, followed by obviously inhibited Arginase and AjAgmatinase transcripts at the most detected time points. Silencing the three members with two specific siRNAs in vivo and in vitro collectively indicated that AjNOS not only compete with Ajarginase but also with Ajagmatinase in arginine metabolism. Interestingly, Ajarginase and Ajagmatinase displayed cooperative expression profiles in arginine utilization. More importantly, live pathogens of V. splendidus and Vibrio parahaemolyticus co-incubated with primary cells also induced NO production and suppressed arginase activity in a time-dependent at an appropriate multiplicity of infection (MOI) of 10, without non-pathogen Escherichia coli. When increasing the pathogen dose (MOI = 100), arginase activity was significantly elevated, and NO production was depressed, with a larger magnitude in V. splendidus co-incubation. The present study expands our understanding of the connection between arginine's metabolic and immune responses in non-model invertebrates.

Induction of Inducible Nitric Oxide Synthase by Lipopolysaccharide and the Influences of Cell Volume Changes, Stress Hormones and Oxidative Stress on Nitric Oxide Efflux from the Perfused Liver of Air-Breathing Catfish, Heteropneustes fossilis

The air-breathing singhi catfish (Heteropneustes fossilis) is frequently being challenged by bacterial contaminants, and different environmental insults like osmotic, hyper-ammonia, dehydration and oxidative stresses in its natural habitats throughout the year. The main objectives of the present investigation were to determine (a) the possible induction of inducible nitric oxide synthase (iNOS) gene with enhanced production of nitric oxide (NO) by intra-peritoneal injection of lipopolysaccharide (LPS) (a bacterial endotoxin), and (b) to determine the effects of hepatic cell volume changes due to anisotonicity or by infusion of certain metabolites, stress hormones and by induction of oxidative stress on production of NO from the iNOS-induced perfused liver of singhi catfish. Intra-peritoneal injection of LPS led to induction of iNOS gene and localized tissue specific expression of iNOS enzyme with more production and accumulation of NO in different tissues of singhi catfish. Further, changes of hydration status/cell volume, caused either by anisotonicity or by infusion of certain metabolites such as glutamine plus glycine and adenosine, affected the NO production from the perfused liver of iNOS-induced singhi catfish. In general, increase of hydration status/cell swelling due to hypotonicity caused decrease, and decrease of hydration status/cell shrinkage due to hypertonicity caused increase of NO efflux from the perfused liver, thus suggesting that changes in hydration status/cell volume of hepatic cells serve as a potent modulator for regulating the NO production. Significant increase of NO efflux from the perfused liver was also observed while infusing the liver with stress hormones like epinephrine and norepinephrine, accompanied with decrease of hydration status/cell volume of hepatic cells. Further, oxidative stress, caused due to infusion of t-butyl hydroperoxide and hydrogen peroxide separately, in the perfused liver of singhi catfish, resulted in significant increase of NO efflux accompanied with decrease of hydration status/cell volume of hepatic cells. However, the reasons for these cell volume-sensitive changes of NO efflux from the liver of singhi catfish are not fully understood with the available data. Nonetheless, enhanced or decreased production of NO from the perfused liver under osmotic stress, in presence of stress hormones and oxidative stress reflected its potential role in cellular homeostasis and also for better adaptations under environmental challenges. This is the first report of osmosensitive and oxidative stress-induced changes of NO production and efflux from the liver of any teleosts. Further, the level of expression of iNOS in this singhi catfish could also serve as an important indicator to determine the pathological status of the external environment.

Septin genes in channel catfish (Ictalurus punctatus) and their involvement in disease defense responses

Septins are an evolutionarily conserved family of GTP-binding proteins. They are involved in diverse processes including cytokinesis, apoptosis, infection, neurodegeneration and neoplasia. In this study, through thorough data mining of existed channel catfish genomic resources, we identified a complete set of 15 septin genes. Septins were classified into four subgroups according to phylogenetic analysis. Extensive comparative genomic analysis, including domain and syntenic analysis, supported their annotation and orthologies. The expression patterns of septins in channel catfish were examined in healthy tissues and after infection with two major bacterial pathogens, Edwardsiella ictaluri and Flavobacterium columnare. In healthy channel catfish, most septin genes were ubiquitously expressed and presented diversity patterns in various tissues, especially mucosal tissues, proposing the significant roles septin genes may play in maintaining homeostasis and host immune response activities. After bacterial infections, most septin genes were regulated, but opposite direction in expression profiles were found with the two bacterial pathogens: the differentially expressed septin genes were down-regulated in the intestine after E. ictaluri infection while generally up-regulated in the gill after F. columnare infection, suggesting a pathogen-specific and tissue-specific pattern of regulation. Taken together, these results suggested that septin genes may play complex and important roles in the host immune responses to bacterial pathogens in channel catfish.

Complement regulatory protein genes in channel catfish and their involvement in disease defense response

Complement system is one of the most important defense systems of innate immunity, which plays a crucial role in disease defense responses in channel catfish. However, inappropriate and excessive complement activation could lead to potential damage to the host cells. Therefore the complement system is controlled by a set of complement regulatory proteins to allow normal defensive functions, but prevent hazardous complement activation to host tissues. In this study, we identified nine complement regulatory protein genes from the channel catfish genome. Phylogenetic and syntenic analyses were conducted to determine their orthology relationships, supporting their correct annotation and potential functional inferences. The expression profiles of the complement regulatory protein genes were determined in channel catfish healthy tissues and after infection with the two main bacterial pathogens, Edwardsiella ictaluri and Flavobacterium columnare. The vast majority of complement regulatory protein genes were significantly regulated after bacterial infections, but interestingly were generally up-regulated after E. ictaluri infection while mostly down-regulated after F. columnare infection, suggesting a pathogen-specific pattern of regulation. Collectively, these findings suggested that complement regulatory protein genes may play complex roles in the host immune responses to bacterial pathogens in channel catfish.

Quantitative proteomics and bioinformatic analysis provide new insight into the dynamic response of porcine intestine to Salmonella Typhimurium

The enteropathogen Salmonella Typhimurium (S. Typhimurium) is the most commonly non-typhoideal serotype isolated in pig worldwide. Currently, one of the main sources of human infection is by consumption of pork meat. Therefore, prevention and control of salmonellosis in pigs is crucial for minimizing risks to public health. The aim of the present study was to use isobaric tags for relative and absolute quantification (iTRAQ) to explore differences in the response to Salmonella in two segment of the porcine gut (ileum and colon) along a time course of 1, 2, and 6 days post infection (dpi) with S. Typhimurium. A total of 298 proteins were identified in the infected ileum samples of which, 112 displayed significant expression differences due to Salmonella infection. In colon, 184 proteins were detected in the infected samples of which 46 resulted differentially expressed with respect to the controls. The higher number of changes in protein expression was quantified in ileum at 2 dpi. Further biological interpretation of proteomics data using bioinformatics tools demonstrated that the expression changes in colon were found in proteins involved in cell death and survival, tissue morphology or molecular transport at the early stages and tissue regeneration at 6 dpi. In ileum, however, changes in protein expression were mainly related to immunological and infection diseases, inflammatory response or connective tissue disorders at 1 and 2 dpi. iTRAQ has proved to be a proteomic robust approach allowing us to identify ileum as the earliest response focus upon S. Typhimurium in the porcine gut. In addition, new functions involved in the response to bacteria such as eIF2 signaling, free radical scavengers or antimicrobial peptides (AMP) expression have been identified. Finally, the impairment at of the enterohepatic circulation of bile acids and lipid metabolism by means the under regulation of FABP6 protein and FXR/RXR and LXR/RXR signaling pathway in ileum has been established for the first time in pigs. Taken together, our results provide a better understanding of the porcine response to Salmonella infection and the molecular mechanisms underlying Salmonella-host interactions.