Isolation and identification of antimicrobial components from the epidermal mucus of Atlantic cod (Gadus morhua)

Sea anemone-anemonefish symbiosis: Behavior and mucous protein profiling

Fish species of the genus Amphiprion (Perciformes: Pomacentridae) seek protection from predators among the tentacles of sea anemones as their natural habitat, where they live essentially unharmed from stinging by the host's nematocysts. The skin mucus of these anemonefish has been suggested as a protective mechanism that prevents the discharge of the nematocysts upon contact. Whereas some anemonefish species seem to produce their own protective mucous coating, others may acquire mucus (or biomolecules within) from the sea anemone during an acclimation period. In controlled experiments, we show that Amphiprion ocellaris acclimated successfully to their natural host anemone species Stichodactyla gigantea, and also to Stichodactyla haddoni, and in some cases Heteractis crispa, neither of which are natural host species. No symbiosis was observed for three other anemone species tested, Entacmaea quadricolor, Macrodactyla doreensis, and Heteractis malu. We explored the skin mucous protein profile from naive and experienced A. ocellaris during their acclimation to natural and unnatural host anemones. We confidently report the presence of metabolic and structural proteins in the skin mucus of all samples, likely involved in immunological defense, molecular transport, stress response, and signal transduction. For those anemonefish that established symbiosis, there was a clear increase in ribosomal-type proteins. We additionally provide evidence for the presence of anemone proteins only in the skin mucus of individuals that established symbiosis. Our results support previous speculation of the role of skin mucous-associated proteins in anemonefish-anemone symbiosis. Further exploration of these mucosal proteins could reveal the mechanism of anemonefish acclimation to host anemones.

Identification, Synthesis, and In Vitro Activities of Antimicrobial Peptide from African Catfish against the Extended-Spectrum Beta-Lactamase (ESBL)-Producing Escherichia coli

The global surge in multi-drug resistant bacteria, including extended-spectrum β-lactamase (ESBL)-producing Escherichia coli has led to a growing need for new antibacterial compounds. Despite being promising, the potential of fish-derived antimicrobial peptides (AMPs) in combating ESBL-producing E. coli is largely unexplored. In this study, native African catfish antimicrobial peptides (NACAPs) were extracted from the skin mucus of farmed African catfish, Clarias gariepinus, using a combination of 10% acetic acid solvent hydrolysis, 5 kDa ultrafiltration, and C18 hydrophobic interaction chromatography. Peptides were then sequenced using Orbitrap Fusion Lumos Tribrid Mass Spectrometry. The identified peptides were screened for potential antibacterial activity using Random Forest and AdaBoost machine learning algorithms. The most promising peptide was chemically synthesized and evaluated in vitro for safety on rabbit red blood cells and activity against ESBL-producing E. coli (ATCC 35218) utilizing spot-on-lawn and broth dilution methods. Eight peptides ranging from 13 to 22 amino acids with molecular weights between 968.42 and 2434.11 Da were identified. Peptide NACAP-II was non-hemolytic to rabbit erythrocytes (p > 0.05) with a zone of inhibition (ZOI) of 22.7 ± 0.9 mm and a minimum inhibitory concentration (MIC) of 91.3 ± 1.2 μg/mL. The peptide is thus a candidate antibacterial compound with enormous potential applications in the pharmaceutical industry. However, further studies are still required to establish an upscale production strategy and optimize its activity and safety in vivo.

Fractionation of the Caspian sand goby epidermal exudates using membrane ultrafiltration and reversed-phase chromatography: an investigation on bioactivities

Bioactive peptide-based drugs have gained exceeding attention as promising treatments for infectious and oxidative-stress-related diseases, are exacerbated by the advent and spread of various multidrug-resistant bacteria and industrial lifestyles. Fish skin mucus has been recognized as a potential source of bioactive peptides, providing the first line of fish defense against invading pathogens which are targeted here to be explored as a new source of biopharmaceutics. Peptide fractions were isolated from the epidermal exudates of Caspian sand goby, Neogobius fluviatilis pallasi, by solid-phase extraction (SPE), ultrafiltration, and reversed-phase chromatography. The resulting fractions were characterized for their antibacterial and antioxidant properties, and results showed that the molecular weight fraction < 5 kDa represented the highest (p < 0.05) bacterial inhibition activity against Staphylococcus aureus and Bacillus subtilis as well as scavenging activity against DPPH and ABTS radicals. Overall, these results introduce the epidermal mucus of Caspian sand goby as a valuable source of bioactive compounds that can be considered new and efficient biopharmaceutics.

Proteomic profile of epidermal mucus from Labeo rohita reveals differentially abundant proteins after Aeromonas hydrophila infection

We report the proteomic profile of Epidermal Mucus (EM) from Labeo rohita and identified the differentially abundant proteins (DAPs) against Aeromonas hydrophila infection through label-free liquid chromatography-mass spectrometry (LC-MS/MS). Using discovery-based proteomics, a total of 2039 proteins were quantified in nontreated group and 1,328 proteins in the treated group, of which 114 were identified as DAPs in both the groups. Of the 114 DAPs, 68 proteins were upregulated and 46 proteins were downregulated in the treated group compared to nontreated group. Functional annotations of these DAPs shows their association with metabolism, cellular process, molecular process, cytoskeletal, stress, and particularly immune system. Kyoto Encyclopedia of Genes and Genomes (KEGG) enrichment analysis and Fisher's exact test between the two groups shows that most of the proteins were immune-related, which were significantly associated with the proteasome, phagosome, and Salmonella infection pathways. Overall, this study shows a basic and primary way for further functional research of the involvement of vitellogenin 2, alpha-2-macroglobulin-like protein, toll-like receptors (TLR-13), calpain, keratin-like proteins, and heat shock proteins against bacterial infection. Nonetheless, this first-ever comprehensive report of a proteomic sketch of EM from L. rohita after A. hydrophila infection provides systematic protein information to broadly understand the biological role of fish EM against bacterial infection.

Mass Spectrometry Analysis of Shark Skin Proteins

The mucus layer covering the skin of fish has several roles, including protection against pathogens and mechanical damage in which proteins play a key role. While proteins in the skin mucus layer of various common bony fish species have been explored, the proteins of shark skin mucus remain unexplored. In this pilot study, we examine the protein composition of the skin mucus in spiny dogfish sharks and chain catsharks through mass spectrometry (NanoLC-MS/MS). Overall, we identified 206 and 72 proteins in spiny dogfish (Squalus acanthias) and chain catsharks (Scyliorhinus retifer), respectively. Categorization showed that the proteins belonged to diverse biological processes and that most proteins were cellular albeit a significant minority were secreted, indicative of mucosal immune roles. The secreted proteins are reviewed in detail with emphasis on their immune potentials. Moreover, STRING protein-protein association network analysis showed that proteins of closely related shark species were more similar as compared to a more distantly related shark and a bony fish, although there were also significant overlaps. This study contributes to the growing field of molecular shark studies and provides a foundation for further research into the functional roles and potential human biomedical implications of shark skin mucus proteins.

Genome-Wide Identification of Trachinotus ovatus Antimicrobial Peptides and Their Immune Response against Two Pathogen Challenges

Golden pompano, Trachinotus ovatus, as a highly nutritious commercially valuable marine fish, has become one of the preferred species for many fish farmers due to its rapid growth, wide adaptability, and ease of feeding and management. However, with the expansion of aquaculture scale, bacterial and parasitic diseases have also become major threats to the golden pompano industry. This study, based on comparative genomics, shows the possibility of preferential evolution of freshwater fish over marine fish by analyzing the phylogenetic relationships and divergence times of 14 marine fish and freshwater fish. Furthermore, we identified antimicrobial peptide genes from 14 species at the genomic level and found that the number of putative antimicrobial peptides may be related to species evolution. Subsequently, we classified the 341 identified AMPs from golden pompano into 38 categories based on the classification provided by the APD3. Among them, TCP represented the highest proportion, accounting for 23.2% of the total, followed by scolopendin, lectin, chemokine, BPTI, and histone-derived peptides. At the same time, the distribution of AMPs in chromosomes varied with type, and covariance analysis showed the frequency of its repeat events. Enrichment analysis and PPI indicated that AMP was mainly concentrated in pathways associated with disease immunity. In addition, our transcriptomic data measured the expression of putative AMPs of golden pompano in 12 normal tissues, as well as in the liver, spleen, and kidney infected with Streptococcus agalactiae and skin infected with Cryptocaryon irritans. As the infection with S. agalactiae and C. irritans progressed, we observed tissue specificity in the number and types of responsive AMPs. Positive selection of AMP genes may participate in the immune response through the MAPK signaling pathway. The genome-wide identification of antimicrobial peptides in the golden pompano provided a complete database of potential AMPs that can contribute to further understanding the immune mechanisms in pathogens. AMPs were expected to replace traditional antibiotics and be developed into targeted drugs against specific bacterial and parasitic pathogens for more precise and effective treatment to improve aquaculture production.

Fish Skin Mucus Extracts: An Underexplored Source of Antimicrobial Agents

The slow discovery of new antibiotics combined with the alarming emergence of antibiotic-resistant bacteria underscores the need for alternative treatments. In this regard, fish skin mucus has been demonstrated to contain a diverse array of bioactive molecules with antimicrobial properties, including peptides, proteins, and other metabolites. This review aims to provide an overview of the antimicrobial molecules found in fish skin mucus and its reported in vitro antimicrobial capacity against bacteria, fungi, and viruses. Additionally, the different methods of mucus extraction, which can be grouped as aqueous, organic, and acidic extractions, are presented. Finally, omic techniques (genomics, transcriptomics, proteomics, metabolomics, and multiomics) are described as key tools for the identification and isolation of new antimicrobial compounds. Overall, this study provides valuable insight into the potential of fish skin mucus as a promising source for the discovery of new antimicrobial agents.

Differences in fish mucus proteomes identify potential antimicrobial peptide biomarkers

We compared the secretion of antimicrobial peptides (AMPs) in the epidermal mucus of three healthy fish species: two aquacultured teleost species, Dicentrarchus labrax and Sparus aurata, and one wild-caught species, Pagrus pagrus. The AMPs detected in all mucus by LC-MS/MS-QTOF are: Chrysophsin-1, -2 and -3, Piscidins -1, -2, -3 and -4, terminal Histone parts and Hepcidin-like peptides. Secretion analysis of the mucus from aquacultured fish using ProGenesis IQ software distinguished the bactericidal activities of histone peptides and probiotic flora from those of other AMPs. Chrysophsin-1 was statistically the most abundant peptide in both mucus samples (p < 0.0035). A lower detection of Piscidins was also observed. Interestingly, the presence of Oncorhyncin I was most pronounced in Sparus aurata mucus. Altogether, these results suggest that Chrysophsin-1 and Oncorhyncin I are potential biomarkers for immunodetection-based studies of changes in secretion patterns which will be further investigated during bacterial challenge.

Revealing Natural Intracellular Peptides in Gills of Seahorse Hippocampus reidi

The seahorse is a marine teleost fish member of the Syngnathidae family that displays a complex variety of morphological and reproductive behavior innovations and has been recognized for its medicinal importance. In the Brazilian ichthyofauna, the seahorse Hippocampus reidi is among the three fish species most used by the population in traditional medicine. In this study, a protocol was performed based on fast heat inactivation of proteases plus liquid chromatography coupled to mass spectrometry to identify native peptides in gills of seahorse H. reidi. The MS/MS spectra obtained from gills allowed the identification of 1080 peptides, of which 1013 peptides were present in all samples and 67 peptide sequences were identified in an additional LC-MS/MS run from an alkylated and reduced pool of samples. The majority of peptides were fragments of the internal region of the amino acid sequence of the precursor proteins (67%), and N- and C-terminal represented 18% and 15%, respectively. Many peptide sequences presented ribosomal proteins, histones and hemoglobin as precursor proteins. In addition, peptide fragments from moronecidin-like protein, described with antimicrobial activity, were found in all gill samples of H. reidi. The identified sequences may reveal new bioactive peptides.

Applications of antimicrobial peptides (AMPs) as an alternative to antibiotic use in aquaculture: a mini-review

The use of antibiotics for the control of infections has not only been banned by FDA for use in food-producing animals, but also several countries have prohibited their use in aquaculture because of several reasons such as the occurrence of antibiotic-tolerant microorganisms, accumulation of antibiotic residues in fish and shrimp flesh, and aquatic environmental effluence concerns. These issues have led researchers and aquaculture scientists to conduct several studies to find antibiotic alternatives. Numerous substitutes have been evaluated, such as probiotics, synbiotics, prebiotics, postbiotics, phytogenics, essential oils, and several others. Results show that these supplements demonstrate proven efficacy in enhancing immune responses, reducing mortalities resulting from experimental infections, and reducing antibiotic usage in medicated aquafeed. Nonetheless, using antimicrobial peptides (AMPs) to control fish diseases and be used as antibiotic alternatives is a promising and interesting research topic. AMPs are a vital class of small peptides that could stimulate the innate immune system against challenging pathogens and also possess significant potent defensive responses against a variety of infectious and non-infectious pathogenic agents, including bacteria, parasites, fungi, and viruses. Regarding their source origin, AMPs can be classified into six main types: mammalian-, amphibian-, insect-, aquatic-, plant-, and microorganism-derived AMPs. On account of their unique structure, they can display an essential function in therapeutic strategies against infectious diseases affecting fish and shrimp. Reports showed several kinds of AMPs had a wide spectrum of antimicrobial properties. These effects are besides their prominent immunostimulatory functions. Thus, they may be considered a functional alternative to antibiotics in aquaculture. This article provides information on the current knowledge about the modes of action, sources, classification, functions, and potential applications for the development of aquatic animal health. The information included in this context will be valuable to enhance the sustainability of aquaculture.

Histones: The critical players in innate immunity

The highly conserved histones in different species seem to represent a very ancient and universal innate host defense system against microorganisms in the biological world. Histones are the essential part of nuclear matter and act as a control switch for DNA transcription. However, histones are also found in the cytoplasm, cell membranes, and extracellular fluid, where they function as host defenses and promote inflammatory responses. In some cases, extracellular histones can act as damage-associated molecular patterns (DAMPs) and bind to pattern recognition receptors (PRRs), thereby triggering innate immune responses and causing initial organ damage. Histones and their fragments serve as antimicrobial peptides (AMPs) to directly eliminate bacteria, viruses, fungi, and parasites in vitro and in vivo. Histones are also involved in phagocytes-related innate immune response as components of neutrophil extracellular traps (NETs), neutrophil activators, and plasminogen receptors. In addition, as a considerable part of epigenetic regulation, histone modifications play a vital role in regulating the innate immune response and expression of corresponding defense genes. Here, we review the regulatory role of histones in innate immune response, which provides a new strategy for the development of antibiotics and the use of histones as therapeutic targets for inflammatory diseases, sepsis, autoimmune diseases, and COVID-19.

The Role of Antimicrobial Peptides (AMPs) in Aquaculture Farming

&nbsp;Antimicrobial peptides (AMPs) are the vital constituents that stimulate the innate immune defense system against pathogens and perform several biological activities, which provide the first defensive line against infectious diseases. Owing to their unique structure, they can be utilized as a therapeutic strategy for infectious diseases in fishes. Several kinds of AMPs are reported in fishes with broad-spectrum antimicrobial properties. Besides, the bacterial cells cannot develop resistance strains against these cationic compounds with low molecular weight. Thus, AMPs may be considered an alternative to antibiotics to prevent or control infectious diseases in aquaculture. It is essential to provide sufficient knowledge about the mode of action of AMPs against fish pathogenic agents and their future applications.&nbsp;

Molecular cloning, expression analysis of the IgT gene and detection of IgT+ B cells in the half-smooth tongue sole (Cynoglossus semilaevis)

IgT is a specific Ig isotype in teleosts, which plays extremely important roles in the mucosal immunity of fish. In the present study, the membrane-bound and secretory IgT of the half-smooth tongue sole (Cynoglossus semilaevis) were identified for the first time. The V-D-J-C structure of two forms of csIgT are translated by the same Cτ gene, and the secretory tail and transmembrane domain were encoded through alternative splicing at the 3' end of the Cτ4. The CH regions of csIgT had high similarity with that of other flatfish (P. olivaceus and S. maximus). In healthy C. semilaevis, sIgT and mIgT were mainly expressed in mucus related tissues such as skin, intestine and gill. The transcript levels of sIgT and mIgT mRNA showed a significant induction in the immune-related tissues upon Vibrio Harveyi infection. A polyclonal rabbit anti-csIgT was successfully prepared using the csIgT heavy chain recombinant protein. Using this antibody, we detected the native IgT with the molecular mass at 220 kDa in skin total protein under non-reducing SDS-PAGE condition. Immunofluorescence analysis indicated that IgT⁺ B lymphocytes were intensively located in the skin, gill, intestine, and head kidney of C. semilaevis. These results suggest that IgT may participate in the immune response of C. semilaevis, which will facilitate the investigations of the immunoglobulins of marine fish.

Identification of Antimicrobial Peptides Isolated From the Skin Mucus of African Catfish, Clarias gariepinus (Burchell, 1822)

Antimicrobial peptides (AMPs) constitute a broad range of bioactive compounds in diverse organisms, including fish. They are effector molecules for the innate immune response, against pathogens, tissue damage and infections. Still, AMPs from African Catfish, Clarias gariepinus, skin mucus are largely unexplored despite their possible therapeutic role in combating antimicrobial resistance. In this study, African Catfish Antimicrobial peptides (ACAPs) were identified from the skin mucus of African Catfish, C. gariepinus. Native peptides were extracted from fish mucus scrapings in 10% acetic acid (v/v) and ultra-filtered using 5 kDa molecular weight cut-off membrane. The extract was purified using C18 Solid-Phase Extraction. The antibacterial activity was determined using the Agar Well Diffusion method and broth-dilution method utilizing Staphylococcus aureus (ATCC 25923) and Escherichia coli (ATCC 25922). Thereafter, Sephadex G-25 gel filtration was further utilized in bio-guided isolation of the most active fractions prior to peptide identification using Orbitrap Fusion Lumos Tribrid Mass Spectrometry. The skin mucus extracted from African Catfish from all the three major lakes of Uganda exhibited antimicrobial activity on E. coli and S. aureus. Lake Albert's C. gariepinus demonstrated the best activity with the lowest MIC of 2.84 and 0.71 μg/ml on S. aureus and E. coli, respectively. Sephadex G-25 peak I mass spectrometry analysis (Data are available via ProteomeXchange with identifier PXD029193) alongside in silico analysis revealed seven short peptides (11-16 amino acid residues) of high antimicrobial scores (0.561-0.905 units). In addition, these peptides had a low molecular weight (1005.57-1622.05 Da) and had percentage hydrophobicity above 54%. Up to four of these AMPs demonstrated α-helix structure conformation, rendering them amphipathic. The findings of this study indicate that novel AMPs can be sourced from the skin mucus of C. gariepinus. Such AMPs are potential alternatives to the traditional antibiotics and can be of great application to food and pharmaceutical industries; however, further studies are still needed to establish their drug-likeness and safety profiles.

Activity profile of innate immune-related enzymes and bactericidal of freshwater fish epidermal mucus extract at different pH

The epidermal mucus of fish performs diverse functions from prevention of mechanical abrasion to limit pathogen invasions. The current experiment was designed to extract skin mucus proteins of three freshwater fish, i.e. common carp (Cyprinus carpio), mrigal (Cirrhinus mrigala) and rohu (Labeo rohita) with organic solvent (methanol) and dissolve in different pH of Tris-HCl buffers to examine the significance of pH in the solubilisation of skin mucus proteins. The protein profiles of different pH solubilised methanol fish skin mucus extracts were determined by SDS-PAGE. The non-specific immune enzymes, alkaline phosphatase, lysozyme and protease of fish skin mucus were compared and this present study demonstrated that these enzymes differed in their activity depending on pH buffers. The higher lysozyme and protease activity were observed at the pH of 8.0 and higher alkaline phosphatase activity in the pH 9.0 of C. mrigala fish skin mucus methanol extract. In addition, the bactericidal activity was evaluated against the pathogens Proteus vulgaris and Pseudomonas aeruginosa. The pH 8.0 of C. mrigala skin mucus extract revealed better bactericidal activity than other fish species mucus pH buffers against both P. vulgaris and P. aeruginosa. In the case of protein profile from SDS-PAGE, based on pH buffers and the solubilisation of proteins, differences in the resolution of bands were observed. The higher alkaline pH of 9.0 showed smeared gel bands in all the three fish skin mucus methanol extract. The present study suggests that methanol extracted C. mrigala fish skin mucus at pH 8.0 showed better innate immune enzymes and bactericidal activity. The additional examinations of C. mrigala skin mucus methanol extract in this pH aids in identifying novel bioactive molecules. This is the study of proteome of three fish species skin mucus in the effect of pH. Further analyses are required to evaluate proteins present in fish skin mucus extracted with methanol and the influence of pH on protein solubility. These findings could be helpful in exploring natural alternatives to antibiotics in aquaculture industry against infectious pathogens.

Proteomic profile and protease activity in the skin mucus of greater amberjack (Seriola dumerili) infected with the ectoparasite Neobenedenia girellae - An immunological approach

Skin mucus is considered the first barrier against diseases in fish. The skin mucus protein profile of the greater amberjack (Seriola dumerili) and its changes due to experimental infection with Neobenedenia girellae were studied by combining 2-DE-MS/MS and gel-free LC-MS/MS proteomic approaches. The 2-DE results led to the identification of 69 and 55 proteins in noninfected and infected fish, respectively, and revealed that keratins were specifically cleaved in parasitized fish. Therefore, the skin mucus of the infected fish showed a higher protease activity due to, at least in part, an increase of metal-dependent protease and serine-type protease activities. Additionally, through a gel-free LC-MS/MS analysis, 1377 and 1251 different proteins were identified in the skin mucus of healthy and parasitized fish, respectively. The functional analysis of these proteins demonstrated a statistical overrepresentation of ribosomal proteins (a well-known source of antimicrobial peptides) in N. girellae-infected fish. In contrast, the components of membranes and protein transport GO categories were underrepresented after infection. Immune system process-related proteins constituted 2.5% of the total skin mucosal proteins. Among these skin mucosal proteins, 14 and 15 proteins exclusive to non-parasitized and parasitized fish were found, respectively, including specific serine-type proteases and metalloproteases in the parasitized fish. Moreover, the finding of tryptic peptides exclusive to some bacterial genera, obtained by gel-free LC-MS/MS, allowed us to construct a preliminary map of the microbiota living in the mucus of S. dumerili, with Pseudomonas and Paracoccus the most represented genera in both noninfected and infected fish.

Structural, ultrastructural, and functional aspects of the skin of the upper lip of silver carp (Hypophthalmichthys molitrix)

This study was carried out to analyze the architecture of the skin of the upper lip region in silver carp fishes using light, scanning, and transmission electron microscopies. The skin was composed of epidermis, dermis, and hypodermis. The epidermis of the upper lip was characterized by the presence of large number of metachromatic mucous goblet cells, which showed positive reaction with Periodic Acid-Schiff (PAS), Alcian blue (AB), and toluidine blue. The electroreceptive lateral line system was organized into ampullary and tuberous organs. The scanning electron microscopy showed that the surface of the skin of upper lip was covered by microridges and characterized by the presence of taste buds and openings of lateral line system. As observed by transmission electron microscopy, the cytoplasm of the epidermal layers appeared electron-dense except for the superficial layer, where the cytoplasm was electron-lucent and contained many vacuoles and few profiles of rER. Moreover, the epidermis contained rodlet cells and stem cells. Few organelles were found within the cytoplasm of club cells. Neutrophils and eosinophilic granular cells were also demonstrated as important immune cells in the epidermis of the upper lip. Furthermore, lymphocytes and basophils could be identified with macrophage in the epidermal layer of the upper lip. Numerous telocytes were demonstrated between the collagen fibers of the dermis and bundles of myelinated nerve fibers. In conclusion, the skin of the upper lip region of silver carp displayed many sensory and immunological characteristic features.

Specific Evolution and Gene Family Expansion of Complement 3 and Regulatory Factor H in Fish

The complement system comprises a large family of plasma proteins that play a central role in innate and adaptive immunity. To better understand the evolution of the complement system in vertebrates and the contribution of complement to fish immunity comprehensive in silico and expression analysis of the gene repertoire was made. Particular attention was given to C3 and the evolutionary related proteins C4 and C5 and to one of the main regulatory factors of C3b, factor H (Cfh). Phylogenetic and gene linkage analysis confirmed the standing hypothesis that the ancestral c3/c4/c5 gene duplicated early. The duplication of C3 (C3.1 and C3.2) and C4 (C4.1 and C4.2) was likely a consequence of the (1R and 2R) genome tetraploidization events at the origin of the vertebrates. In fish, gene number was not conserved and multiple c3 and cfh sequence related genes were encountered, and phylogenetic analysis of each gene generated two main clusters. Duplication of c3 and cfh genes occurred across the teleosts in a species-specific manner. In common, with other immune gene families the c3 gene expansion in fish emerged through a process of tandem gene duplication. Gilthead sea bream (Sparus aurata), had nine c3 gene transcripts highly expressed in liver although as reported in other fish, extra-hepatic expression also occurs. Differences in the sequence and protein domains of the nine deduced C3 proteins in the gilthead sea bream and the presence of specific cysteine and N-glycosylation residues within each isoform was indicative of functional diversity associated with structure. The diversity of C3 and other complement proteins as well as Cfh in teleosts suggests they may have an enhanced capacity to activate complement through direct interaction of C3 isoforms with pathogenic agents.

Selective induced apoptosis and cell cycle arrest in MCF7 and LNCap cell lines by skin mucus from round goby (Neogobius melanostomus) and common carp (Cyprinus carpio) through P53 expression

The skin mucus in lower vertebrates such as fish with strong innate immune system has many unique and valuable bioactive compounds that can be used for inducing apoptosis in cancer cells. This study was looking for the cytotoxic potential of mucus from the two fish species, including round goby (Neogobius melanostomus) and common carp (Cyprinus carpio), and inducing apoptosis in MCF7 and LNCaP cancer cell lines via influencing P53 gene expression and cell cycle arrest. Results showed that the both mucus types have cytotoxic effects on the both cancer cell lines whereas they have no severe effect on normal primary fibroblast cells. In addition, round goby mucus and common carp mucus selectively induced apoptosis in the LNCaP and MCF7 cells, respectively, through up-regulating P53 gene and arresting cell cycle at the G1 phase. Taken together, this study suggested that the both mucus types can selectively influence P53 pathway and induce apoptosis in especial cancer cells. The skin mucus derived from round Goby and common Carp can be a promising candidate for investigation about apoptosis and molecular targeting therapy in cancer.

Extraction, Identification, Modification, and Antibacterial Activity of Histone from Immature Testis of Atlantic salmon

In the present study, histone from immature testis of Atlantic salmon was extracted and identified, and its antibacterial activity after enzymolysis was investigated. Histone extracted from Atlantic salmon (Salmo salar) testis using the acid extraction method was successfully identified by LC-MS/MS, and revealed significant inhibitory activity on both the Gram-negative and Gram-positive bacteria. With a low concentration of 10 mg/mL, the observed inhibitory zone diameter (IZD) could significantly reach up to 15.23 mm. After modification of enzymatic hydrolysis by pepsin, histone could be digested to three fragments, while the antibacterial activity increased up to 57.7%. All the results suggested the leftovers from commercial fishing could be utilized for the extraction of antimicrobial peptides.

Fish and fish side streams are valuable sources of high-value components

The current practice of fish processing generates increasing quantities of side streams and waste, such as skin, heads, frames, viscera, and fillet cut offs. These may account for up to 70% of the fish used in industrial processing. Low-value fish catches, and under-utilized fish species comprise another source of side streams. These side streams have been discarded in the environment leading to environmental problems or they have ended up as low commercial value products, such as feed for fur animals and aquaculture. However, several studies have shown that fish side streams contain valuable bioactive ingredients and fractions, such as fish oils, proteins and peptides, collagen, gelatin, enzymes, chitin, and minerals. These compounds and fractions may provide the opportunity to develop novel applications in health promoting foods, special feeds, nutraceuticals, pharmaceuticals, and cosmetic products. Better utilization of side streams and low-value fish would simultaneously improve both the environmental and ecological sustainability of production. This review summarizes the current knowledge on fish and fish side streams as sources of high-value components such as peptides with antimicrobial, antioxidative, antihypertensive, and antihyperglycemic properties, proteins such as fish collagen and gelatin, fish enzymes, fish oils and fatty acids, polysaccharides like glucosaminoglycans, chitin and chitosan, vitamin D, and minerals. Production technologies for recovering the high-value fractions and potential product applications are discussed. Furthermore, safety aspects related to the raw material, technologies, and fractions are considered.

Biochemical and molecular identification of a novel hepcidin type 2-like antimicrobial peptide in the skin mucus of the pufferfish Takifugu pardalis

Fish skin mucus is considered to act as the first line of defense against waterborne pathogens and to be potential source of novel antimicrobial components. Here we report the purification and characterization of a novel hepcidin type 2-like antimicrobial peptide (TpHAMP2) from the skin mucus of the pufferfish Takifugu pardalis. The purified TpHAMP2 comprised of 23 amino acids (AAs) with eight Cys residues that form four intramolecular disulfide bonds. The TpHAMP2 gene shared overall structural characteristics with all known hepcidins, which have a tripartite exon-intron gene organization and three structural signatures in the precursor protein. Phylogenetically, TpHAMP2 was classified as HAMP2 class in acanthopterygian fish. Interestingly, the AA sequence of TpHAMP2 did not contain a proprotein cleavage site (RXXR motif) that conserved in most hepcidins and showed a highly positive charged (RKR-) short N-terminus and Val¹⁸ and Gly²² residues, which are distinctive structures compared to other known active hepcidins. Recombinant TpHAMP2 identical to the native form exhibited a broad spectrum and potent antimicrobial activity against tested gram-positive and -negative bacteria. Expression of TpHAMP2 mRNA was predominant in the liver and was upregulated in the liver, the spleen, the intestine, and the skin of T. pardalis post immune challenge. Thus, our findings suggests that TpHAMP2 might be of importance in the framework of discovering the fish hepcidins, especially type 2s, and provide noteworthy insight into its gene structure and expression and in the innate immunity as well as the mucosal immunity in regard to hepcidins' evolutionary history in fish species.

A histone H2A derived antimicrobial peptide, Fi-Histin from the Indian White shrimp, Fenneropenaeus indicus: Molecular and functional characterization

Antimicrobial peptides (AMPs) derived from histone proteins form an important category of peptide antibiotics. Present study deals with the molecular and functional characterization of a 27-amino acid histone H2A derived AMP from the Indian White shrimp, Fenneropenaeus indicus designated as Fi-Histin. This peptide displayed distinctive features of AMPs such as amphiphilic alpha helical structure and a net charge of +6. The synthetic peptide exhibited significant antimicrobial activity against Gram-negative and Gram-positive bacteria especially against V. vulnificus, P. aeruginosa, V. parahaemolyticus, V. cholera and S. aureus. Disruption of cell membrane and cell content leakage were observed in peptide treated V. vulnificus using scanning electron microscopy. The synthetic peptide Fi-His_1-21 exhibited DNA binding activity and found to be non-haemolytic at the tested concentrations. Peptide was also found to possess anticancer activity against NCI-H460 and HEp-2 cell lines with an IC₅₀ of 22.670 ± 13.939 μM and 31.274 ± 24.531 μM respectively. This is the first report of a histone H2A derived peptide from F. indicus with a specific antimicrobial activity and anticancer activity, which could be a new candidate for future applications in aquaculture and medicine.

In-depth proteomic analysis of Boleophthalmus pectinirostris skin mucus

Fish skin mucus serves as the first line of defence against pathogens and external stressors. The mudskipper Boleophthalmus pectinirostris inhabits intertidal mudflats containing abundant and diverse microbial populations; thus, the skin and mucus of B. pectinirostris are very important for immune defence. However, the molecules involved in the immune response and mucus secretion in the skin of this fish are poorly understood. To explore the proteomic profile of the skin mucus and understand the molecular mechanisms underlying B. pectinirostris adaption to amphibious environments, the microstructure of B. pectinirostris skin was analysed, and a series of histochemical procedures were employed for mucous glycoprotein localization and characterization. In addition, the antibacterial activity of B. pectinirostris skin mucus was studied, and the transcriptome of the skin and in-depth proteome of the mucus were determined. These studies revealed the hierarchical structure of B. pectinirostris skin and different types of glycoproteins (GPs) in the dermal bulge (DB) of the B. pectinirostris skin epidermis. The mucus has a broad antimicrobial spectrum and significant effects on the bacterial morphology. Furthermore, 93,914 unigenes were sequenced from B. pectinirostris skin tissue, and a total of 559 proteins were identified from B. pectinirostris skin mucus. SIGNIFICANCE.

Smell of Infection: A Novel, Noninvasive Method for Detection of Fish Excretory-Secretory Proteins

Chemical signals are produced by aquatic organisms following predatory attacks or perturbations such as parasitic infection. Ectoparasites feeding on fish hosts are likely to cause release of similar alarm cues into the environment due to the stress, wounding, and immune response stimulated upon infection. Alarm cues are often released in the form of proteins, antimicrobial peptides, and immunoglobulins that provide important insights into bodily function and infection status. Here we outline a noninvasive method to identify potential chemical cues associated with infection in fish by extracting, purifying, and characterizing proteins from water samples from cultured fish. Gel free proteomic methods were deemed the most suitable for protein detection in saline water samples. It was confirmed that teleost proteins can be characterized from water and that variation in protein profiles could be detected between infected and uninfected individuals and fish and parasite only water samples. Our novel assay provides a noninvasive method for assessing the health condition of both wild and farmed aquatic organisms. Similar to environmental DNA monitoring methods, these proteomic techniques could provide an important tool in applied ecology and aquatic biology.

Biological and Ecological Roles of External Fish Mucus: A Review

Fish mucus layers are the main surface of exchange between fish and the environment, and they possess important biological and ecological functions. Fish mucus research is increasing rapidly, along with the development of high-throughput techniques, which allow the simultaneous study of numerous genes and molecules, enabling a deeper understanding of the fish mucus composition and its functions. Fish mucus plays a major role against fish infections, and research has mostly focused on the study of fish mucus bioactive molecules (e.g., antimicrobial peptides and immune-related molecules) and associated microbiota due to their potential in aquaculture and human medicine. However, external fish mucus surfaces also play important roles in social relationships between conspecifics (fish shoaling, spawning synchronisation, suitable habitat finding, or alarm signals) and in interspecific interactions such as prey-predator relationships, parasite–host interactions, and symbiosis. This article reviews the biological and ecological roles of external (gills and skin) fish mucus, discussing its importance in fish protection against pathogens and in intra and interspecific interactions. We also discuss the advances that “omics” sciences are bringing into the fish mucus research and their importance in studying the fish mucus composition and functions.

Post-translational protein deimination in cod (Gadus morhua L.) ontogeny novel roles in tissue remodelling and mucosal immune defences?

Peptidylarginine deiminases (PADs) are calcium dependent enzymes with physiological and pathophysiological roles conserved throughout phylogeny. PADs promote post-translational deimination of protein arginine to citrulline, altering the structure and function of target proteins. Deiminated proteins were detected in the early developmental stages of cod from 11 days post fertilisation to 70 days post hatching. Deiminated proteins were present in mucosal surfaces and in liver, pancreas, spleen, gut, muscle, brain and eye during early cod larval development. Deiminated protein targets identified in skin mucosa included nuclear histones; cytoskeletal proteins such as tubulin and beta-actin; metabolic and immune related proteins such as galectin, mannan-binding lectin, toll-like receptor, kininogen, Beta2-microglobulin, aldehyde dehydrogenase, bloodthirsty and preproapolipoprotein A-I. Deiminated histone H3, a marker for anti-pathogenic neutrophil extracellular traps, was particularly elevated in mucosal tissues in immunostimulated cod larvae. PAD-mediated protein deimination may facilitate protein moonlighting, allowing the same protein to exhibit a range of biological functions, in tissue remodelling and mucosal immune defences in teleost ontogeny.

Combined proteomic and functional analysis reveals rich sources of protein diversity in skin mucus and venom from the Scorpaena plumieri fish

The biological activities observed upon envenomation by Scorpaena plumieri could be linked to both the venom and the skin mucus. Through a proteomic/functional approach we analyzed protein composition and biological activities of the venom and skin mucus. We identified 885 proteins: 722 in the Venomous Apparatus extracts (Sp-VAe) and 391 in the Skin Mucus extract (Sp-SMe), with 494 found exclusively in Sp-VAe, being named S. plumieri Venom Proteins (Sp-VP), while 228 were found in both extracts. The majority of the many proteins identified were not directly related to the biological activities reported here. Nevertheless, some were classified as toxins/potentially interesting molecules: lectins, proteases and protease inhibitors were detected in both extracts, while the pore-forming toxin and hyaluronidase were associated with Sp-VP. Proteolytic and anti-microbial activities were linked to both extracts, while the main toxic activities - cardiovascular, inflammatory, hemolytic and nociceptive - were elicited only by Sp-VAe. Our study provided a clear picture on the composition of the skin mucus and the venom. We also show that the classic effects observed upon envenomation are produced by molecules from the venomous gland. Our results add to the growing catalogue of scorpaeniform fish venoms and their skin mucus proteins.

SIGNIFICANCE

In this study a large number of proteins - including classical and non-classical toxins - were identified in the venomous apparatus and the skin mucus extracts of the Scorpaena plumieri fish through shotgun proteomic approach. It was shown that the toxic effects observed upon envenomation are elicited by molecules originated from the venomous gland. These results add to the growing catalogue of scorpaeniform fish venoms and their skin mucus proteins - so scarcely explored when compared to the venoms and bioactive components of terrestrial animals. Data are available via ProteomeXchange with identifier PXD009983.

Chronic wounds alter the proteome profile in skin mucus of farmed gilthead seabream

Background

Skin and its mucus are known to be the first barrier of defence against any external stressors. In fish, skin wounds frequently appear as a result of intensive culture and also some diseases have skin ulcers as external clinical signs. However, there is no information about the changes produced by the wounds in the mucosae. In the present paper, we have studied the alterations in the proteome map of skin mucus of gilthead seabream during healing of experimentally produced chronic wounds by 2-DE followed by LC-MS/MS. The corresponding gene expression changes of some identified skin proteins were also investigated through qPCR.

Results

Our study has successfully identified 21 differentially expressed proteins involved in immunity and stress processes as well as other metabolic and structural proteins and revealed, for the first time, that all are downregulated in the skin mucus of wounded seabream specimens. At transcript level, we found that four of nine markers (ighm, gst3, actb and krt1) were downregulated after causing the wounds while the rest of them remained unaltered in the wounded fish. Finally, ELISA analysis revealed that IgM levels were significantly lower in wounded fish compared to the control fish.

Conclusions

Our study revealed a decreased-expression at protein and for some transcripts at mRNA levels in wounded fish, which could affect the functionality of these molecules, and therefore, delay the wound healing process and increase the susceptibility to any infection after wounds in the skin of gilthead seabream.

The Bacteroid Periplasm in Soybean Nodules Is an Interkingdom Symbiotic Space

The functional role of the periplasm of nitrogen-fixing bacteroids has not been determined. Proteins were isolated from the periplasm and cytoplasm of Bradyrhizobium diazoefficiens bacteroids and were analyzed using liquid chromatography tandem mass spectrometry proteomics. Identification of bacteroid periplasmic proteins was aided by periplasm prediction programs. Approximately 40% of all the proteins identified as periplasmic in the B. diazoefficiens genome were found expressed in the bacteroid form of the bacteria, indicating the periplasm is a metabolically active symbiotic space. The bacteroid periplasm possesses many fatty acid metabolic enzymes, which was in contrast to the bacteroid cytoplasm. Amino acid analysis of the periplasm revealed an abundance of phosphoserine, phosphoethanolamine, and glycine, which are metabolites of phospholipid metabolism. These results suggest the periplasm is a unique space and not a continuum with the peribacteroid space. A number of plant proteins were found in the periplasm fraction, which suggested contamination. However, antibodies to two of the identified plant proteins, histone H2A and lipoxygenase, yielded immunogold labeling that demonstrated the plant proteins were specifically targeted to the bacteroids. This suggests that the periplasm is an interkingdom symbiotic space containing proteins from both the bacteroid and the plant.

Immune relevant molecules identified in the skin mucus of fish using -omics technologies

This review will give an overview of immune relevant molecules in fish skin mucus. The skin of fish is continuously exposed to a water environment, and unlike that of terrestrial vertebrates, it is a mucosal surface with a thin epidermis of live cells covered by a mucus layer. The mucosa plays an important role in maintaining the homeostasis of the fish and preventing the entry of invading pathogens. This review provides an overview of proteins, RNA, DNA, lipids and carbohydrates found in the skin mucus of studied species. Proteins such as actin, histones, lectins, lysozyme, mucin, and transferrin have extracellular immune relevant functions. Complement complement molecules, heat shock molecules and superoxide dismutase present in mucus show differential expression during pathogen challenge in some species, but their functions in mucus, if any, need to be shown. RNA, DNA, lipids, carbohydrates and metabolites in mucus have been studied to a limited extent in fish, the current knowledge is summarized and knowledge gaps are pointed out.

Survey of Antibiotic-producing Bacteria Associated with the Epidermal Mucus Layers of Rays and Skates

Elasmobranchs represent a distinct group of cartilaginous fishes that harbor a remarkable ability to heal wounds rapidly and without infection. To date very little work has addressed this phenomenon although it is suggested that antibiotic capabilities associated with epidermal surfaces may be a factor. The study of benefits derived from mutualistic interactions between unicellular and multicellular organisms is a rapidly growing area of research. Here we survey and identify bacterial associates of three ray and one skate species in order to assess the potential for antibiotic production from elasmobranch associated bacteria as a novel source for new antibiotics.

De novo assembly of the sea trout (Salmo trutta m. trutta) skin transcriptome to identify putative genes involved in the immune response and epidermal mucus secretion

In fish, the skin is a multifunctional organ and the first barrier against pathogens. Salmonids differ in their susceptibility to microorganisms due to varied skin morphology and gene expression patterns. The brown trout is a salmonid species with important commercial and ecological value in Europe. However, there is a lack of knowledge regarding the genes involved in the immune response and mucus secretion in the skin of this fish. Thus, we characterized the skin transcriptome of anadromous brown trout using next-generation sequencing (NGS). A total of 1,348,306 filtered reads were obtained and assembled into 75,970 contigs. Of these contigs 48.57% were identified using BLAST tool searches against four public databases. KEGG pathway and Gene Ontology analyses revealed that 13.40% and 34.57% of the annotated transcripts, respectively, represent a variety of biological processes and functions. Among the identified KEGG Orthology categories, the best represented were signal transduction (23.28%) and immune system (8.82%), with a variety of genes involved in immune pathways, implying the differentiation of immune responses in the trout skin. We also identified and transcriptionally characterized 8 types of mucin proteins–the main structural components of the mucosal layer. Moreover, 140 genes involved in mucin synthesis were identified, and 1,119 potential simple sequence repeats (SSRs) were detected in 3,134 transcripts.

Skin mucus proteins of lumpsucker (Cyclopterus lumpus)

Fish skin mucus serves as a first line of defense against pathogens and external stressors. In this study the proteomic profile of lumpsucker skin mucus was characterized using 2D gels coupled with tandem mass spectrometry. Mucosal proteins were identified by homology searches across the databases SwissProt, NCBInr and vertebrate EST. The identified proteins were clustered into ten groups based on their gene ontology biological process in PANTHER (www.patherdb.org). Calmodulin, cystatin-B, histone H2B, peroxiredoxin1, apolipoprotein A1, natterin-2, 14-3-3 protein, alfa enolase, pentraxin, warm temperature acclimation 65 kDa (WAP65kDa) and heat shock proteins were identified. Several of the proteins are known to be involved in immune and/or stress responses. Proteomic profile established in this study could be a benchmark for differential proteomics studies.

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A proteome reference map of lumpsucker skin mucus was established.

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Proteins involved in immune and stress responses were identified in skin mucus of Cyclopterus lumpus.

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Mucosal proteins identified could be potential biomarkers.

Changes in the levels of humoral immune activities after storage of gilthead seabream (Sparus aurata) skin mucus

Skin mucus is increasingly used as a source for determining immunity-related proteins and enzymes. However, the ability to accurately measure some activities may be modified by inadequate handling and storage of the samples. This study aims to measure the effect of freezing and lyophilization at the time of collection on such activities. Fresh, frozen (immediately after collection at -20 °C and -80 °C) and lyophilized skin mucus samples obtained from the same groups of fish specimens of gilthead seabream (Sparus aurata L.) were analysed in the assays. The amount of total proteins and sugar residues (determined by lectin binding) present in skin mucus samples fell after both freezing and lyophilization of the samples. While no significant differences were exhibited in the levels of some proteins or enzymes (immunoglobulin M, antiprotease, peroxidase, esterase and alkaline phosphatase) determined in fresh or frozen mucus samples, protease and lysozyme activities were lower in frozen mucus samples than in fresh samples. Lyophilization of the mucus samples drastically decreased the total level of proteins obtained, as well as of protease, peroxidase, lysozyme and alkaline phosphatase activities. The results suggest that freezing skin mucus samples is more suitable than lyophilization if samples are stored before determining enzymatic activities.

Effects of Fish-Derived Biological Preservatives on Cold Storage of Grass Carp ( Ctenopharyngodon idellus ) Fillets

Two kinds of fish-derived natural antimicrobial substances, protamine and catfish ( Clarias fuscus ) epidermal mucus extract (CEME), were evaluated for their effect on the quality of grass carp fillets. Fillets were atmosphere packaged in cast polypropylene bags and were stored at 4°C in a low-temperature incubator without light. Solutions (0.5%, wt/vol) of CEME and protamine were used for dip pretreatment, respectively. Bacteriological (aerobic plate count, Shewanella putrefaciens , Pseudomonas fluorescens ) and physicochemical (pH, total volatile basic nitrogen, K value, surface color, texture profiles, water distribution) parameters and volatile odor compounds were measured on days 0, 3, 6, 9, 12, and 15. The results indicated that CEME and protamine could improve all bacteriological and physicochemical indexes, except water distribution within muscle. In comparison, CEME had a more inhibitory effect, as determined by the aerobic plate count, and was more effective in inhibiting the growth of P. fluorescens ; however, protamine was more effective in preventing the production of sulfur-organic (H₂S) group substances. Protamine was more effective in inhibiting the growth of S. putrefaciens . This research suggests that protamine and CEME have the potential to improve the quality and extend the shelf life of grass carp fillets.

Transcription of histones H1 and H2B is regulated by several immune stimuli in gilthead seabream and European sea bass

Histones (H1 to H4) are the primary proteins which mediate the folding of DNA into chromatin; however, and in addition to this function, histones have been also related to antimicrobial peptides (AMPs) activity in vertebrates, in fact, mammalian H1 is mobilized as part as the anti-viral immune response. In fish, histones with AMP activity have been isolated and characterized mainly from skin and gonads. One of most threatening pathogens for wild and cultured fish species nowadays is nodavirus (NNV), which target tissues are the brain and retina, but it is also able to colonize the gonad and display vertical transmission. Taking all this into account we have identified the h1 and h2b coding sequences in European sea bass (Dicentrarchus labrax) and gilthead seabream (Sparus aurata) fish species and studied their pattern of expression under naïve conditions and NNV in vivo infection. The data obtained prompted us to study their role on the immune response of gonad and head-kidney leucocytes upon viral (NNV), bacteria (Vibrio anguillarum or Photobacterium damselae), pathogen-associated molecular patterns (PAMPs) or mitogens stimulation. The h1 and h2b genes are expressed in a wide range of tissues and their expression is modify by infection or other immune stimuli, but further studies will be needed to determine the significance of these changes. These results suggest that h1 expression is related to the immune response against NNV in the brain, while h2b transcription seems to be more important in the head-kidney. Moreover, the potential role of histones as anti-viral agents is suggested and further characterization is in progress.

Hydrolyzed fish proteins modulates both inflammatory and antioxidant gene expression as well as protein expression in a co culture model of liver and head kidney cells isolated from Atlantic salmon (Salmo salar)

Hydrolyzed fish proteins (H-pro) contain high concentrations of free amino acids and low molecular peptides that potentially may benefit fish health. The following study aimed to test whether the water-soluble phase of H-pro could attenuate lipopolysaccharide (LPS) provoked inflammation in liver cells and head kidney cells isolated from Atlantic salmon. Cells were grown as mono cultures or co cultures to assess possible crosstalk between immune cells and metabolic cells during treatments. Cells were added media with or without H-pro for 2 days before LPS exposure and harvested 24 h post LPS exposure. Respective cells without H-pro and LPS were used as controls. H-pro alone could affect expression of proteins directly as H-pro increased catalase protein expression in head kidney- and liver cells, regardless of culturing methods and LPS treatment. Leukotriene B4 (LTB4) production was also increased by H-pro in head kidney cells co cultured with liver cells. H-pro increased LPS induced interleukin 1β (IL-1β) transcription in liver cells co cultured with head kidney cells. All cultures of head kidney cells showed a significant increase in IL-1β transcription when treated with H-pro + LPS. H-pro decreased caspase-3 transcription in liver cells cultured co cultured with head kidney cells. Peroxisome proliferator activated receptor α (PPAR α) was upregulated, regardless of treatment, in liver cells co cultured with head kidney cells clearly showing that culturing method alone affected gene transcription. H-pro alone and together with LPS as an inflammation inducer, affect both antioxidant and inflammatory responses.

Mechanism study on a new antimicrobial peptide Sphistin derived from the N-terminus of crab histone H2A identified in haemolymphs of Scylla paramamosain

Histone H2A is known to participate in host immune defense through generating special antimicrobial peptides (AMPs), for which it has been an interesting research focus to characterize this kind of peptides in vertebrates and invertebrates. Although thousands of AMPs have been reported in variety of life species, only several AMPs are known in crabs and in particular no H2A-derived AMP has yet been reported. In the present study, a 38-amino acid peptide with antimicrobial activity was determined based on the sequence analysis of a histone H2A identified from the mud crab Scylla paramamosain. The histone H2A derived peptide was an AMP-like molecule and designated as Sphistin. Sphistin showed typical features of AMPs such as amphiphilic α-helical second structrue and positive charge net. The synthetic Sphistin exerted high antimicrobial activity against Gram-positive, Gram-negative bacteria and yeast, among which Aeromonas hydrophila, Pseudomonas fluorescens and Pseudomonas stutzeri are important aquatic pathogens. Leakage of the cell content and disruption of the cell surface were observed in bacterial cells treated with Sphistin using scanning electron microscopy. It was proved that the increasing cytoplasmic membrane permeability of Escherichia coli was caused by Sphistin. Further observation under confocal microscopy showed that Sphistin could combine onto the membrane of Staphylococcus aureus, E. coli MC1061 and Pichia pastoris but not translocate into the cytoplasm. Moreover, the affinity of Sphistin with either LPS or LTA was also testified that there was an interaction between Sphistin and cell membrane. Thus, the antimicrobial mechanism of this peptide likely exerted via adsorption and subsequently permeabilization of the bacterial cell membranes other than penetrating cell membrane. In addition, synthetic Sphistin exhibited no cytotoxicity to primary cultured crab haemolymphs and mammalian cells even at a high concentration of 100 μg/mL for 24 h. This is the first report of a histone-derived Sphistin identified from S. paramamosain with a specific antimicrobial activity and mechanism, which could be a new candidate for future application in aquaculture and veterinary medicine.

Physiology and immunology of mucosal barriers in catfish (Ictalurus spp.)

The mucosal barriers of catfish (Ictalurus spp) constitute the first line of defense against pathogen invasion while simultaneously carrying out a diverse array of other critical physiological processes, including nutrient adsorption, osmoregulation, waste excretion, and environmental sensing. Catfish depend more heavily on mucosal barriers than their terrestrial counterparts as they are continuously interacting with the aquatic microbiota. Our understanding of these barriers, while growing, is still limited relative to that of mammalian model systems. Nevertheless, a combination of molecular and cellular studies in catfish over the last few decades, and particularly within the last few years, has helped to elucidate many of the primary actors and pathways critical to their mucosal health. Here we describe aspects of innate and adaptive immune responses in the primary mucosal tissues (skin, gill, and intestine) of catfish, focusing on mucus-driven responses, pathogen recognition, soluble mediators, and immunoglobulin and T-cell derived immunity. Modulation of mucosal barriers will be critical moving forward for crafting better diets, improving vaccine delivery, enhancing water quality, and ensuring sustainable production practices in catfish.

Identification of the Atlantic cod L-amino acid oxidase and its alterations following bacterial exposure

Antibacterial factors that are present in epidermal mucus of fish have a potential role in the first line of host defence to bacterial pathogens. This study reports the identification of L-amino acid oxidase (LAO) in Atlantic cod (GmLao) and the changes in the molecule following bacterial exposure. The gmlao transcripts and LAO activity were present on both the body surface and in the internal organs of the fish. Relative mRNA level of gmlao increased significantly in the gills, the spleen and the head kidney (up to 8-fold) of fish that were challenged with the pathogen Vibrio anguillarum. The gmlao expression in skin was 4-fold higher in challenged fish. Our data indicate that LAO may be an important effector of antibacterial defence in Atlantic cod.

The impact of Aeromonas salmonicida infection on innate immune parameters of Atlantic salmon (Salmo salar L)

Enzyme activities and gene expression of a number of innate immune parameters in the serum, mucus and skin of Atlantic salmon (Salmo salar) were investigated after challenge with a pathogenic strain of Aeromonas salmonicida (A. salmonicida). Fish were injected in the dorsal muscle with either 100 μl bacterium solution, about 3.05 × 10(7) CFU/ml A. salmonicida, or 100 μl 0.9% NaCl (as control group) and tissue samples were collected at days 0, 2, 4 and 6 post-injection. Lysozyme (LSZ) and alkaline phosphatase (AKP) activities in serum, mucus and skin, and LSZ and AKP mRNA expression in skin of the challenged fish were higher than those of the control at most of the experimental time, with significant differences at several time points (P < 0.05), indicating the involvement of LSZ and AKP in the innate immunity of Atlantic salmon to A. salmonicida. Superoxide dismutase (SOD), peroxidase (POD) and catalase (CAT) activities in mucus and skin, along with the SOD, POD and CAT mRNA expression in skin significantly decreased at day 4 and 6, indicating the decreased antioxidant capacity of the challenged fish. Glutamate pyruvate transaminase (GPT) and glutamic oxalacetic transaminase (GOT) activities in serum, mucus and skin of the challenged group were all higher than those of the control after the injection, and at several time points significant differences were found between the two groups, suggesting organs of fish were impaired after the pathogen infection. The changes of the GPT and GOT activities could be used as potential biomarkers for the impairment of physiological functions caused by the pathogen infection. Identified biomarkers of the immune responses will contribute to the early-warning system of the disease. So this study will not only provide a theoretical basis for vaccine development, but also provide basic data for the establishment of early warning systems for diseases caused by A. salmonicida in Atlantic salmon rearing.

Preliminary study on expression of antimicrobial peptides in European sea bass (Dicentrarchus labrax) following in vivo infection with Vibrio anguillarum. A time course experiment

Antimicrobial polypeptides (AMPPs) are humoral components of the vertebrates and invertebrates innate immune system. Their potent broad spectrum antimicrobial activities have drawn the attention of the scientific community to their potential use not only as an alternative to antibiotics but also as functional targets for immunostimulants in order to enhance the host immunity. Fish synthesize a great number of these peptides but in European sea bass, an important fish species in the Mediterranean aquaculture, only a few AMPPs have been studied and these surveys have highlighted their functional role as predictive markers of stressful conditions. Many aspects concerning AMPP mode of action in the host during bacterial infections are still unknown. In this work a 72 h time course experiment, performed on juvenile sea bass intraperitoneally (i.p.) injected with a sub-lethal dose of Vibrio anguillarum, was aimed to investigate the mRNA expression of four specific AMPP genes and interleukin-1β (IL-1β) in skin, gills, spleen, and head kidney. AMPP genes were: dicentracin (DIC), histone-like protein 1 (HLP-1), histone-like protein 2 (HLP-2) and hemoglobin-like protein (Hb-LP). The delta-delta C(T) method in real-time RT-PCR allowed to gain more knowledge about temporal dynamics, preferential sites of expression as well as immunological and physiological role of these molecular markers. DIC was significantly up-regulated mainly in head kidney at 1.5-3 h post-infection (p.i.). HLP-1 showed an extended-time overexpression in gills and a significant up-regulation in spleen. HLP-2 was interestingly overexpressed in gills at 24 h p.i., while Hb-LP showed a significant up-regulation in skin for all the 72 h trial as well as lower but always significant values either in gills or in spleen. Different was the response of IL-1β that showed a dramatic up-regulation in spleen and head kidney at 8 h p.i. whilst in gills it displayed a severe inhibition. During this survey the i.p. stimulus surely conditioned the AMPP expression in skin and gills, especially as regards the DIC that as piscidin-related gene has an important defensive role in the mucosal tissues. However, two unconventional AMPP genes such as HLP-2 and Hb-LP, strictly related to the physiological mechanisms of fish, were less affected in terms of expression by the route of infection, being more evident in peripheral loci. These findings might suggest them as potential markers to be analyzed within plans of health survey in fish farms.

Chemical aspects of the preservation and safety control of sea foods

The interest in biopreservation of food has prompted the quest for new natural antimicrobial compounds from different origins.

Antimicrobial peptides from fish

Antimicrobial peptides (AMPs) are found widely distributed through Nature, and participate in the innate host defense of each species. Fish are a great source of these peptides, as they express all of the major classes of AMPs, including defensins, cathelicidins, hepcidins, histone-derived peptides, and a fish-specific class of the cecropin family, called piscidins. As with other species, the fish peptides exhibit broad-spectrum antimicrobial activity, killing both fish and human pathogens. They are also immunomodulatory, and their genes are highly responsive to microbes and innate immuno-stimulatory molecules. Recent research has demonstrated that some of the unique properties of fish peptides, including their ability to act even in very high salt concentrations, make them good potential targets for development as therapeutic antimicrobials. Further, the stimulation of their gene expression by exogenous factors could be useful in preventing pathogenic microbes in aquaculture.

Changes in protein composition of epidermal mucus in turbot Scophthalmus maximus (L.) under high water temperature

To explore the skin mucous of juvenile turbot (Scophthalmus maximus) protein under thermo-treatment in different temperatures (20, 23, 25, and 27 °C), the corresponding proteome maps were constructed by two-dimensional gel electrophoresis (2-DE), from which the peptide mass map with MALDI-TOF-TOF was obtained, and a novel protein of polypeptide was identified by database retrieval. Results show that the proteome maps varied remarkably with temperature, indicating the increase or decrease in protein spot. Totally, 209 protein spots were matched in five maps in temperature using ImageMaster 2D Platinum 6.0. In addition, six unique protein spots were selected and identified with MALDI-TOF-TOF. By searching database for protein identification and function prediction, five proteins were confirmed, of which lectin and cytokeratin are highly potential as protein marker for further research. The information should be useful for better understanding the role of mucus as a component of innate immune system and for identifying genotypes that suit best to the aquiculture environment. These proteins could be used as potential biomarkers to environmental stressors in mucus for providing early warning when fish suffers in a dangerous situation.

The Aeromonas salmonicida subsp. salmonicida exoproteome: global analysis, moonlighting proteins and putative antigens for vaccination against furunculosis

BACKGROUND

Aeromonas salmonicida subsp. salmonicida, the etiologic agent of furunculosis, is a major pathogen of fisheries worldwide. Despite the identification of several virulence factors the pathogenesis is still poorly understood. We have used high-throughput proteomics to display the differences between in vitro secretome of A. salmonicida wild-type (wt, hypervirulent, JF5054) and T3SS-deficient (isogenic ΔascV, extremely low-virulent, JF2747) strains in exponential (GP) and stationary (SP) phases of growth.

RESULTS

Among the different experimental conditions we obtained semi-quantitative values for a total of 2136 A. salmonicida proteins. Proteins of specific A. salmonicida species were proportionally less detected than proteins common to the Aeromonas genus or those shared with other Aeromonas species, suggesting that in vitro growth did not induce the expression of these genes. Four detected proteins which are unidentified in the genome of reference strains of A. salmonicida were homologous to components of the conjugative T4SS of A. hydrophila pRA1 plasmid. Polypeptides of three proteins which are specific to the 01-B526 strain were also discovered. In supernatants (SNs), the number of detected proteins was higher in SP (326 for wt vs 329 for mutant) than in GP (275 for wt vs 263 for mutant). In pellets, the number of identified proteins (a total of 1536) was approximately the same between GP and SP. Numerous highly conserved cytoplasmic proteins were present in A. salmonicida SNs (mainly EF-Tu, EF-G, EF-P, EF-Ts, TypA, AlaS, ribosomal proteins, HtpG, DnaK, peptidyl-prolyl cis-trans isomerases, GAPDH, Enolase, FbaA, TpiA, Pgk, TktA, AckA, AcnB, Mdh, AhpC, Tpx, SodB and PNPase), and several evidences support the theory that their extracellular localization was not the result of cell lysis. According to the Cluster of Orthologous Groups classification, 29% of excreted proteins in A. salmonicida SNs were currently poorly characterized.

CONCLUSIONS

In this part of our work we elucidated the whole in vitro exoproteome of hypervirulent A. salmonicida subsp. salmonicida and showed the secretion of several highly conserved cytoplasmic proteins with putative moonlighting functions and roles in virulence. All together, our results offer new information about the pathogenesis of furunculosis and point out potential candidates for vaccine development.

Isolation and characterization of a novel antibacterial peptide derived from hemoglobin alpha in the liver of Japanese eel, Anguilla japonica

We isolated and characterized a novel antibacterial peptide, AJHbα, derived from hemoglobin alpha in the liver of Japanese eel, Anguilla japonica. It with concentration of 11.30 μM exhibited stronger antibacterial activity against pathogenic bacterium 1 × 10(6) cell ml(-1)Edwardsiella tarda than other two bacteria. The extraction procedure for AJHbα included extraction with acetate acid, ultrafiltration, cation-exchange chromatography on HiTrap™ CM FF, reverse-phase liquid chromatography on Source 5R RPC and C18 RP-HPLC. MALDI-TOF MS suggested that the peptide had an observed molecular weight of 2388.05 Da. Its amino acid sequence determined by Edman degradation was similar to those of hemoglobin alpha chain in other fish by BLAST analysis. A complete N-terminal amino acid sequence of the AJHbα was FAHWPDLGPGSPSVKKHGKVIM corresponding to the cDNA sequence by RACE amplification. Its synthetic peptide had strong antibacterial activities against ten Gram-positive or negative bacteria. To our knowledge, AJHbα was the first identified fragment of hemoglobin alpha chain with strong antibacterial activity in fish.