Characterization and ion channel activities of novel antibacterial proteins from the skin mucosa of carp (Cyprinus carpio)

Uncovering the antimicrobial activity of G-type lysozyme 2 derived from Cyprinus carpio mucus against bacterial and fungal pathogens

This study aimed to explore the antimicrobic potential of mucus samples collected from Cyprinus carpio and identify the specific antimicrobial peptides responsible for its activity. The crude extract was tested against various bacterial and fungal pathogens, and its protein content and profile were analyzed. Purification steps, including gel filtration chromatography, were employed to isolate the most active fraction (peak IV), which was further identified via liquid chromatography and mass spectroscopy. The results revealed varying degrees of antimicrobial activity of the crude extract against different bacterial and fungal strains, with Leclercia adecarboxylata, Candida glabrata, and Candida parapsilosis showing the highest susceptibility. SDS-PAGE analysis demonstrated the existence of multiple low molecular weight protein bands in the crude extract, while fraction IV obtained from gel filtration chromatography exhibited the strongest antimicrobial activity. Peak IV displayed a range of minimum inhibitory concentration (MIC), minimum bactericidal concentration (MBC), and minimum fungicidal concentration (MFC) values against the tested pathogens, spanning from 0.038 to 4.960 mg/mL. Further investigation identified the purified peptide derived from peak IV as G-type lysozyme 2, characterized by a molecular weight of 21 kDa. These findings shed light on the existence of a highly effective antimicrobial peptide, G-type lysozyme 2, within the mucus of Cyprinus carpio. This peptide demonstrates notable activity against diverse bacterial and fungal pathogens. The insights from this study enhance our understanding of the fish's antimicrobial defense mechanisms and hold promise for developing novel antimicrobial agents.

Health assessment of wild speckled dwarf tortoises, CHERSOBIUS SIGNATUS

BACKGROUND

In free-ranging reptile populations, bacterial, fungal, viral and parasitic pathogens may affect hosts through impairment in movements, thermoregulation, reproduction, survival, and population dynamics. The speckled dwarf tortoise (Chersobius [Homopus] signatus) is a threatened species that is mostly restricted to the Succulent Karoo biome in South Africa, and little information on pathogens of this species is available yet. We derived baseline parameters for five males and five females that were captured to genetically enhance a conservation breeding program in Europe. Upon collection of the tortoises, ticks were removed and identified. Immediately upon arrival in Europe, ocular, nasal, oral and cloacal swabs were taken for viral, bacteriological and mycological examinations. Fecal samples were collected before and 1 month after fenbendazole treatment, and analyzed for parasites. A panel of PCR, aiming to detect herpesviruses, adenoviruses and iridoviruses, was carried out.

RESULTS

Samples were negative for viruses, while bacteriological examination yielded detectable growth in 82.5% of the swabs with a mean load of 16 × 107 ± 61 × 108 colony forming units (CFU) per swab, representing 34 bacterial species. Cloacal and oral swabs yielded higher detectable growth loads than nasal and ocular swabs, but no differences between sexes were observed. Fungi and yeasts (mean load 5 × 103 ± 13 × 103 CFU/swab) were detected in 25% of the swabs. All pre-treatment fecal samples were positive for oxyurid eggs, ranging from 200 to 2400 eggs per gram of feces, whereas after the treatment a significantly reduced egg count (90-100% reduction) was found in seven out of 10 individuals. One remaining individual showed 29% reduction, and two others had increased egg counts. In five tortoises, Nycthocterus spp. and coccidian oocysts were also identified. Soft ticks were identified as Ornithodoros savignyi.

CONCLUSIONS

Our baseline data from clinically healthy individuals will help future studies to interpret prevalences of microorganisms in speckled dwarf tortoise populations. The study population did not appear immediately threatened by current parasite presence.

A Comparison of the Innate and Adaptive Immune Systems in Cartilaginous Fish, Ray-Finned Fish, and Lobe-Finned Fish

The immune system is composed of two subsystems-the innate immune system and the adaptive immune system. The innate immune system is the first to respond to pathogens and does not retain memory of previous responses. Innate immune responses are evolutionarily older than adaptive responses and elements of innate immunity can be found in all multicellular organisms. If a pathogen persists, the adaptive immune system will engage the pathogen with specificity and memory. Several components of the adaptive system including immunoglobulins (Igs), T cell receptors (TCR), and major histocompatibility complex (MHC), are assumed to have arisen in the first jawed vertebrates-the Gnathostomata. This review will discuss and compare components of both the innate and adaptive immune systems in Gnathostomes, particularly in Chondrichthyes (cartilaginous fish) and in Osteichthyes [bony fish: the Actinopterygii (ray-finned fish) and the Sarcopterygii (lobe-finned fish)]. While many elements of both the innate and adaptive immune systems are conserved within these species and with higher level vertebrates, some elements have marked differences. Components of the innate immune system covered here include physical barriers, such as the skin and gastrointestinal tract, cellular components, such as pattern recognition receptors and immune cells including macrophages and neutrophils, and humoral components, such as the complement system. Components of the adaptive system covered include the fundamental cells and molecules of adaptive immunity: B lymphocytes (B cells), T lymphocytes (T cells), immunoglobulins (Igs), and major histocompatibility complex (MHC). Comparative studies in fish such as those discussed here are essential for developing a comprehensive understanding of the evolution of the immune system.

Comparison of several non-specific skin mucus immune defences in three piscine species of aquaculture interest

Fish skin mucus is a viscous and semipermeable barrier made mainly of water, glycoproteins and soluble proteins. It represents an important defence against the environment and previous studies have reported the presence of different substances involved in immune defence responses in it. The aim of the present work was to characterize skin mucus protease activity by zymography and esterase activity of the subfamily of carboxylesterases in three species of interest for aquaculture: gilthead sea bream, sea bass and meagre. Mucus antioxidant power was also determined by adapting ferric reducing antioxidant power (FRAP) analysis. As a result of these non-specific immune defence parameters, we compared the antibacterial capacity of skin mucus in these species via in vitro dual bacteria strains-skin mucus co-culture growths. We used Pseudomonas anguilliseptica and Vibrio anguillarum as marine pathogenic bacteria and Escherichia coli as non-pathogenic. For each fish species, in the respective zymograms, we determined a pattern of proteolytic digestion bands. A high-molecular-weight band (around 200 kDa; H-band) was evident in sea bream and sea bass, and showed chymotrypsin activity. One or two intermediate-molecular-weight bands (around 75 kDa; I-bands) with non-trypsin and non-chymotrypsin activity, and putatively with metalloprotease activity, were evident in all species. Finally, low-molecular-weight bands (between 14 and 30 kDa; L-bands) showed distinct patterns for each species and matched trypsin activity. Despite the conservative pattern of digestion bands, the levels of total proteolytic activity (TPA) were 5 and 10 times higher in meagre than in sea bass and sea bream, respectively. In parallel, three carboxylesterase activities were detected in the mucus of the three fish species, using myristate (pNPM-CE activity), butyrate (pNPB-CE activity) and acetate (pNPA-CE activity) as substrates. Both pNPB-CE and pNPA-CE were the most abundant in fish mucus, and meagre was again the species with the highest levels. In contrast, the antioxidant power of meagre skin mucus was the lowest. We established the capacity of skin mucus to block or limit bacterial growth (lytic activity) using 24 h growth curves. The log-growth phase of V. anguillarum was strongly blocked by sea bream and meagre mucus for a few hours; but not by sea bass mucus. However, if mucus was not renewed, log-growth was at the end of 24 h studied period. For its part, P. anguilliseptica growth curve was delayed by the three mucus types during the entire growth period. Only meagre achieved lytic activity against E. coli growth. All parameters studied here will be of a great interest as non-invasive bioindicators of non-specific immune defences in fish skin mucus.

NK-lysin from skin-secreted mucus of Atlantic salmon and its potential role in bacteriostatic activity

NK-lysin, despite being a direct effector of cytotoxic T and natural killer cells, is an antimicrobial peptide (AMP) with known antibacterial function in vertebrates and so in fish. Its presence has been described in different tissues of teleost fish. One of the strongest antimicrobial barriers in fish is skin-secreted mucus; however, this mucus has been found to contain only a small number of AMPs. The present study describes for the first time the constitutive expression of NK-lysin in Atlantic salmon (Salmo salar) mucus produced by the skin, recording the AMP at a higher concentration than in serum with greater bacteriostatic activity. Hepcidin may be involved to a greater extent in systemic responses since it was expressed to a higher degree in serum which was more potent for alternative complement and peroxidase activities.

Mucosal and systemic immune responses in Senegalese sole (Solea senegalensis Kaup) bath challenged with Tenacibaculum maritimum: A time-course study

Tenacibaculosis, caused by Tenacibaculum maritimum, continues to inflict substantial losses among cultured marine species, particularly in the Senegalese sole. However, the immune mechanisms in fish involved in fighting against this disease are still poorly understood. Thus, the present study aimed to investigate the skin mucus's terminal carbohydrate composition, several immune-related enzymes (i.e. lysozyme, peroxidase, proteases and antiproteases), the haemolytic activity of complement and the bactericidal activity in the skin mucus and plasma of the Senegalese sole in a time-course study following a bath challenge with T. maritimum. The haematological profile and the kinetics of cell migration post-infection were also considered. The bath challenge induced slight variations in the terminal carbohydrate composition of Senegalese sole skin mucus. In general, results from this study showed a delay in the mucosal immune response compared to that found at the systemic level (i.e. blood and plasma). For instance, a significant increase in the skin mucus's lysozyme, complement, protease and antiprotease activities were observed at the end of the experiment (14 d post-challenge). Interestingly, the higher activity of these enzymes could be related to the skin mucus's bactericidal capacity and haemolytic complement activity, suggesting that these enzymes play an important role in the defence against Gram-negative bacteria. The haematological profile revealed a significant increase in circulating neutrophils in challenged fish after 48 and 72 h, which was positively correlated to the increments observed in peroxidase and lysozyme activities, respectively, in the plasma of challenged fish at the same time. Although the route of entry and the survival strategy of T. maritimum are still not fully elucidated, results from the present study will contribute to this endeavour through the study of the mucosal immune responses of fish against this particular pathogen.

Angiotensins processing activities in the venom and epidermic mucus of Scorpaena plumieri

The venom of marine animals is a rich source of compounds with remarkable selectivity and functional diversity. Scorpaena plumieri is the most venomous fish in the Brazilian fauna and is responsible for relatively frequent accidents involving anglers and bathers. In humans, its venom causes edema, erythema, ecchymoses, anxiety, nausea, vomiting, and syncope. The venom is chemically characterized by Sp-CTx, a enzyme able to generate an initial endothelium-dependent relaxation response, followed by a contraction response. This study sought to investigate the proteolytic activities regarding vasopeptides angiotensin I and II. Both the venom and the epidermal mucus presented angiotensin conversion activity for angiotensin I, as well as a capacity to form Ang 1-7 directly via Ang I and II. Captopril (10 μM) and EDTA (1 mM) were able to abolish the converting activity of the venom and the epidermal mucus, representing the first description of a converting activity in S. plumieri venom and epidermal mucus.

Alterations in the intestine of Patagonian silverside (Odontesthes hatcheri) exposed to microcystin-LR: Changes in the glycosylation pattern of the intestinal wall and inhibition of multidrug resistance proteins efflux activity

Accumulation and toxicity of cyanobacterial toxins, particularly microcystin-LR (MCLR) have been extensively studied in fish and aquatic invertebrates. However, MCLR excretion mechanisms, which could reduce this toxin's effects, have received little attention. The Patagonian silverside, Odontesthes hatcheri, is an omnivorous-planktivorous edible fish, which has been shown to digest cyanobacterial cells absorbing MCLR and eliminating the toxin within 48h without suffering significant toxic effects. We studied the effects of MCLR on glycoconjugate composition and the possible role of multidrug resistance associated proteins (Abcc) in MCLR export from the cells in O. hatcheri intestine. We treated O. hatcheri with 5μg MCLRg(-1) body mass administered with the food. Twenty four hours later, the intestines of treated and control fish were processed for lectin-histochemistry using concanavalin A (ConA), Triticum vulgaris agglutinin (WGA), and Dolichos biflorus agglutinin (DBA). MCLR affected the distribution of glycoconjugates by augmenting the proportion of ConA-positive at the expense of WGA-positive cells. We studied MCLR effects on the transport of the Abcc-like substrates 2,4-dinitrophenyl-S-glutathione (DNP-SG) and calcein in ex vivo intestine preparations (everted and no-everted sacs and strips). In treated preparations, CDNB together with MCLR (113μg MCLRg(-1) intestine, equivalent to 1.14μmolL(-1) when applied in the bath) or the Abcc inhibitor, MK571 was applied for one hour, during which DNP-SG was measured in the bath every 10min in order to calculate mass-specific DNP-SG transport rate. MCLR significantly inhibited DNP-SG transport (p<0.05), especially in middle intestine (47 and 24%, for luminal and serosal transport, respectively). In middle intestine strips, MCLR and MK571inhibited DNP-SG transport in a concentration dependent fashion (IC50 3.3 and 0.6μmolL(-1), respectively). In middle intestine strips incubated with calcein-AM (0.25μmolL(-1)), calcein efflux was inhibited by MCLR (2.3μmolL(-1)) and MK571 (3μmolL(-1)) by 38 and 27%, respectively (p<0.05). Finally, middle intestine segments were incubated with different concentrations of MCLR applied alone or together with 3μM MK571. After one hour, protein phosphatase 1 (PP1) activity, the main target of MCLR, was measured. 2.5μM MCLR did not produce any significant effect, while the same amount plus MK571 inhibited PP1 activity (p<0.05). This effect was similar to that of 5μM MCLR. Our results suggest that in O. hatcheri enterocytes MCLR is conjugated with GSH via GST and then exported to the intestinal lumen through Abcc-like transporters. This mechanism would protect the cell from MCLR toxicity, limiting toxin transport into the blood, which is probably mediated by basolateral Abccs. From an ecotoxicological point of view, elimination of MCLR through this mechanism would reduce the amount of toxin available for trophic transference.

Aloe vera bathing improved physical and humoral protection in breeding stock after induced spawning in matrinxã (Brycon amazonicus)

In this study, we show that induced spawning causes stress, an intense loss of epithelia and immunosuppression, decreasing physical and humoral protection in fish, effects that were prevented or improved in fish bathed with Aloe vera. A. vera has several medicinal properties, including wound healing and immunostimulatory effects, which we observed in this study. Fish bathed with A. vera had a higher number of epidermal goblet cells and, in general, an improved wound healing rate compared with the control after induced spawning. These effects might be related to (1) the stimulation of leukocyte activity, represented here by the increased leukocyte respiratory activity triggered by A. vera (leukocytes are recognized as playing an important role in wound repair); (2) the antimicrobial properties of A. vera, which decrease wound infection and accelerate the healing process; and (3) several mechanisms that explain the healing effect of A. vera (increased collagen synthesis, rate of epithelialization, and anti-inflammatory and moisturizing effects). Our results also suggest that caution is necessary during the induced spawning process, especially during stripping, and A. vera bathing is recommended after intensive aquaculture operations.

Comparative analysis of the humoral immunity of skin mucus from several marine teleost fish

Fish skin mucus contains several immune substances that provide the first line of defence against a broad spectrum of pathogens although they are poorly studied to date. Terminal carbohydrate composition and levels of total IgM antibodies, several immune-related enzymes (lysozyme, peroxidase, alkaline phosphatase, esterases, proteases and antiproteases) as well as the bactericidal activity (against fish pathogenic Vibrio harveyi, Vibrio angillarum, Photobacterium damselae and non-pathogenic bacteria Escherichia coli, Bacillus subtilis, Shewanella putrefaciens) were identified and measured in the skin mucus of five marine teleosts: gilthead seabream (Sparus aurata), European sea bass (Dicentrarchus labrax), shi drum (Umbrina cirrosa), common dentex (Dentex dentex) and dusky grouper (Epinephelus marginatus). First, lectin binding results suggests that skin mucus contain, in order of abundance, N-acetylneuraminic acid, glucose, N-acetyl-glucosamine, N-acetyl-galactosamine, galactose and fucose residues. Second, results showed that while some immune activities were very similar in the studied fish (e.g. IgM and lysozyme activity) other such as protease, antiprotease, alkaline phosphatase, esterase and peroxidase activities varied depending on the fish species. High levels of peroxidase and protease activity were found in U. cirrosa respect to the values obtained in the other species while E. marginatus and S. aurata showed the highest levels of alkaline phosphatase and esterase activities, respectively. Moreover, skin mucus of S. aurata revealed higher bactericidal activity against pathogenic bacteria, contrarily, to what happened with non-pathogenic bacteria (E. coli, B. subtilis). Thus, study of the variations in the carbohydrate profile and immune-related components of the fish skin mucus could help to understand the fish resistance as well as the presence and distribution of pathogens and magnitude of infections, aspects that are of major importance for the aquaculture industry.

Molecular characterization of LEAP-2 cDNA in common carp (Cyprinus carpio L.) and the differential expression upon a Vibrio anguillarum stimulus; indications for a significant immune role in skin

LEAP-2 is a cysteine-rich cationic antimicrobial peptide (AMP) playing an important role in host innate immune system. LEAP-2 genes have been identified from higher vertebrates and several fish species. Here we report the cloning and identification of two LEAP-2 cDNA sequences from the liver of common carp (Cyprinus carpio L.). The LEAP-2A cDNA was 1325 bp long and contained an ORF of 279 bp encoding a protein of 92 amino acids. The LEAP-2B cDNA was 608 bp long and contained an ORF of 276 bp encoding a protein of 91 amino acids. Both LEAP-2 proteins consisted of 41 amino acid residues and shared four cysteines at the conserved positions in the predicted mature peptides, highly similar to LEAP-2 of other species. Sequence alignment showed that LEAP-2 amino acid sequences were well conserved in different species, and the phylogenetic relation of LEAP-2 was coincident with evolution of biological species. Expression analysis data revealed that LEAP-2A and LEAP-2B mRNAs were expressed in a wide range of common carp tissues including liver, spleen, head kidney, skin, gills, hindgut and foregut. When injected intraperitoneally with Vibrio anguillarum, the expression level of common carp LEAP-2A was quickly up-regulated in liver, spleen, head kidney, skin, gills, foregut and hindgut, however, the expression level of LEAP-2B was similarly up-regulated in spleen, skin, gills and hindgut but not in liver, head kidney and foregut. Our results showed that the LEAP-2A had a markedly high constitutive expression in skin, and the LEAP-2A and the LEAP-2B had a significantly high up-regulated expression after stimulus in skin. This differential expression of LEAP-2 in common carp suggests that it may play a key role in immune responses against invading pathogens and both LEAP-2 molecules may be involved in mucosal immunity.

Comparative skin mucus and serum humoral defence mechanisms in the teleost gilthead seabream (Sparus aurata)

Mucosal surfaces of fish, including skin, gill and gut, contain numerous immune substances poorly studied that act as the first line of defence against a broad spectrum of pathogens. This study aimed to identify and characterize for the first time different constitutive humoral defence mechanisms of the skin mucus of gilthead seabream (Sparus aurata). To do this, the levels of total immunoglobulin M, several enzymes and proteins (peroxidase, lysozyme, alkaline phosphatase, esterases, proteases and antiproteases), as well as the bactericidal activity against opportunist fish pathogens (Vibrio harveyi, Vibrio angillarum, Photobacterium damselae) and non-pathogenic bacteria (Escherichia coli, Bacillus subtilis) were measured in the skin mucus and compared with those found in the serum. This study demonstrates that gilthead seabream skin mucus contains lower levels of IgM, similar levels of lysozyme, alkaline phosphatase and proteases, and higher esterase, peroxidase and antiprotease activities than serum. In addition, skin mucus revealed stronger bactericidal activity against tested fish pathogen bacteria compared to the serum activity, while human bacteria can even grow more in the presence of mucus. The results could be useful for better understanding the role of the skin mucus as a key component of the innate immune system with potential application for the aquaculture.

Molecular characterization of hepcidin gene in common carp (Cyprinus carpio L.) and its expression pattern responding to bacterial challenge

Hepcidin is a cysteine-rich cationic antimicrobial peptide (AMP), which plays an important role in host innate immune system and iron regulation. A great many of hepcidin genes have been identified from vertebrates, including various fish species. Here we report the cloning and identification of a hepcidin cDNA from the liver of common carp (Cyprinus carpio L.). The full-length cDNA of the common carp hepcidin was 647 bp, which contained an ORF of 276 bp encoding a prepropeptide of 91 amino acid residues. The predicted preprohepcidin consisted of three domains: a signal peptide of 24 amino acids, a prodomain of 42 amino acids and a mature peptide of 25 amino acids, which containd eight cysteine residues at the identical conserved position. The genomic organization of common carp hepcidin was identified, which contained three exons and two introns, similarly to corresponding genes in mammals and other fish species. Sequence alignment and phylogenetic analysis showed that hepcidins were conserved in different species, and common carp hepcidin was type 1 hepcidin according to the phylogenetic tree, which had the highest identity with mud loach and zebrafish. Real-time PCR assay showed that the hepcidin gene was mostly expressed in liver, and expressed in all the other tested tissues of common carp in different levels. When challenged with pathogenic bacterium, Vibrio anguillarum, the expression level of common carp hepcidin was quickly up-regulated in liver, spleen, head kidney and hindgut, implying that hepcidin may be an important component of the innate immune system of common carp and involved in mucosal immune response against invading pathogens.

Antimicrobial peptides (AMPs) from fish epidermis: perspectives for investigative dermatology

Mammalian and fish skin share protective activities against environments that are rich in infectious agents. Fish epidermis is endowed with an extrinsic barrier consisting of a mucus layer and antimicrobial peptides (AMPs). These operate together as a protective chemical shield. As these AMPs are evolutionarily well preserved and also found in higher vertebrate skin (including human epidermis), fish skin offers a unique opportunity to study the origins of innate antimicrobial defense systems. Furthermore, the broad spectrum of fish mucus antimicrobial activities renders piscine AMPs interesting to investigative dermatology, as these may become exploitable for various indications in clinical dermatology. Therefore, this article aims at casting light on fish mucus, the evolutionary relationship between human and fish AMPs, and the latter's antibacterial, antifungal, and even antiviral activities. Moreover, we develop dermatological lessons from, and sketch potential future clinical applications of, fish mucus and piscine AMPs.

Immune system and immune responses in fish and their role in comparative immunity study: a model for higher organisms

The basal position of fish in vertebrate phylogeny makes them very attractive for genomic and functional comparative immunity studies. Adaptive immunity arose early in vertebrate evolution, 450 million years ago between the divergence of cyclostomes and cartilaginous fish. The fundamental immune molecules, which include Ag-recognizing lymphocytes, immunoglobulins (Abs and Ig-family TCR), MHC products, and recombination-activating (RAG) 1 and 2 genes and the recombination mechanisms (cause of diversity in TCRs and Igs) are similar in fish and mammals. These molecules and their immune response mechanisms unravelled the primordial vertebrate immune system repertoire and adaptive radiations. Moreover, screening of animal models like zebrafish has a great importance to discover genes involved in T cell development, thymic organogenesis, and in immunity to infections. The zebrafish model may also be useful for cancer research due to its various features like rapid development, tractable genetics, ease in in vivo imaging and chemical screening.

Effects of dietary Ergosan on cutaneous mucosal immune response in rainbow trout (Oncorhynchus mykiss)

The effects of dietary Ergosan on the growth performance and mucosal immunity in rainbow trout skin were investigated. 60 rainbow trout (100-110 g) were randomly assigned to 2 groups in triplicates and fed one of the experimental diet formulated with 5 g kg⁻¹ Ergosan or control diet for 50 days. Results showed that on the 45th day of feeding trial, Ergosan supplementation significantly enhanced the growth performance compared to control group. Various enzyme activities, namely lysozyme, protease, alkaline phosphatase and esterase in treatment group were also enhanced on the 45th and 50th day. Skin mucus in Ergosan-fed fish showed the agglutination of erythrocytes while in control group, no visible agglutination was shown. In addition, skin mucus in treatment group showed strong antibacterial activity against Yersinia ruckeri. In conclusion, the major immune components of rainbow trout mucus that are involved in the non-specific immunity were enhanced by administration of Ergosan in 5 g kg⁻¹.

Isolation and identification of a novel inducible antibacterial peptide from the skin mucus of Japanese eel, Anguilla japonica

In this study, acetone extracts and acidic extracts were prepared from skin mucus, gill, kidney, liver and spleen of the Japanese eel, Anguilla japonica, and they exhibited different levels of antibacterial activities against three strains of Gram-negative bacteria, Edwardsiella tarda, Aeromonas hydrophila, Aeromonas sp. and one Gram-positive bacterium Micrococcus leteus. The mucus was chosen as the source of antibacterial peptide for further purification of antibacterial peptides. Following the intraperitoneal injection of A. hydrophila, one of the main pathogenic bacteria of Japanese eel and many other fish, a peptide was purified from acetic acid extraction of the skin mucus, by using cationic exchange liquid chromatography and reverse-phase high-performance liquid chromatography (RP-HPLC). The isolated antibacterial peptide, named as AJN-10, exhibited antibacterial activity against A. hydrophila. The AJN-10 is a heat-tolerant and hydrophilic peptide. The molecular weight of this peptide is 6,044.28 Da, as determined by matrix-assisted laser desorption ionisation time of flight mass spectrometry. The 20 N-terminal amino acid sequences were clarified by Edman degradation, and based on results of homology search by BLAST analysis of the 20 N-terminal sequences, the AJN-10 showed little similarity to other proteins in databases.

Distribution of mucous cells on the body surface of Japanese flounder Paralichthys olivaceus

The distribution of mucous cells was examined in the skin on the ocular and blind sides of Japanese flounder Paralichthys olivaceus. Observations were performed on both body sides at the following regions: cheek, lower jaw (blind side), gill cover (ocular side), dorsal side, lateral line, belly and caudal peduncle. The mucous cells observed were elliptic and positively stained for periodic acid Schiff reaction and Mayer's mucicarmine and showed a higher density and larger size on the ocular side compared to the blind side. Low densities of mucous cells were observed on the lower jaw compared with other regions of the body. The depth of the crack located between scales was deeper on the ocular side than the blind side, which might reflect total epidermis area and total number of mucous cells. Bacterial infection elucidated some information on the effect on the density and size of mucous cells, where the density and size decreased slightly after infection. Only the lower jaw, however, showed an increased number of mucous cells. The results show that the potential of skin to secrete mucus is higher on the ocular than on the blind side and bacterial infection decreases mucous secretion.

Novel L-amino acid oxidase with antibacterial activity against methicillin-resistant Staphylococcus aureus isolated from epidermal mucus of the flounder Platichthys stellatus

Fish produce mucus substances as a defensive outer barrier against environmental xenobiotics and predators. Recently, we found a bioactive protein in the mucus layer of the flounder Platichthys stellatus, which showed antibacterial activity against Staphylococcus epidermidis, Staphylococcus aureus and methicillin-resistant S. aureus. In this study, we isolated and identified the antibacterial protein from the mucus components of P. stellatus using a series of column chromatography steps. We then performed gel electrophoresis and cDNA cloning to characterize the protein. The antibacterial protein in the mucus had a molecular mass of approximately 52 kDa with an isoelectric point of 5.3, and cDNA sequencing showed that it corresponded completely with the peptide sequence of antibacterial protein from the gill. A BLAST search suggested that the cDNA encoded an antibacterial protein sharing identity with a number of L-amino acid oxidases (LAAOs) and possessing several conserved motifs found in flavoproteins. RT-PCR using a specific primer, and immunohistochemical analysis with anti-LAAO IgG, demonstrated tissue-specific expression and localization in the gill. Moreover, the anti-LAAO IgG was able to neutralize the antibacterial activity of the protein against methicillin-resistant S. aureus. Thus, we demonstrated that this antibacterial protein, identified from P. stellatus-derived epidermal mucus, is a novel LAAO-like protein with antibacterial activity, similar to snake LAAOs.

Myxinidin, a novel antimicrobial peptide from the epidermal mucus of hagfish, Myxine glutinosa L

Fish epidermal mucus contains innate immune components that provide a first line of defense against various infectious pathogens. This study reports the bioassay-guided fractionation and characterization of a novel antimicrobial peptide, myxinidin, from the acidic epidermal mucus extract of hagfish (Myxine glutinosa L.). Edman sequencing and mass spectrometry revealed that myxinidin consists of 12 amino acids and has a molecular mass of 1,327.68 Da. Myxinidin showed activity against a broad range of bacteria and yeast pathogens at minimum bactericidal concentration (MBC) ranging from 1.0 to 10.0 microg/mL. Screened pathogens, Salmonella enterica serovar Typhimurium C610, Escherichia coli D31, Aeromonas salmonicida A449, Yersinia ruckeri 96-4, and Listonella anguillarum 02-11 were found to be highly sensitive to myxinidin at the MBC of 1.0-2.5 microg/mL; Staphylococcus epidermis C621 and yeast (Candida albicans C627) had an MBC of 10.0 microg/mL. The antimicrobial activity of myxinidin was found to be two to 16 times more active than a potent fish-derived antimicrobial peptide, pleurocidin (NRC-17), against most of the screened pathogens. The microbicidal activity of myxinidin was retained in the presence of sodium chloride (NaCl) at concentrations up to 0.3 M and had no hemolytic activity against mammalian red blood cells. These results suggest that myxinidin may have potential applications in fish and human therapeutics.

A histochemical study on the snout tentacles and snout skin of bristlenose catfish Ancistrus triradiatus

Histological sections of the tentacles of Ancistrus triradiatus revealed that they contain many goblet cells with granule-like sections distributed along the edge of the tentacles (mean 302 cells mm(-1)). Various histochemical methods were used to characterize the contents of the goblet cells. The results indicated that the contents were periodic acid-Schiff (PAS) positive, glycogen negative and no sulphated mucins could be found. The contents of the goblet cells were acid mucins and O-acetylated sialomucins which had high energy content. The snout skin of the male also contained goblet cells with higher density (mean 755 cells mm(-1)) than that of the tentacles. Snout skin of female A. triradiatus, on the contrary, did not contain any goblet cells. Instead, many minute spines could be found. Based on the acid mucins and O-acetylated sialomucins secretions of goblet cells which are of high nutritional values, it is hypothesized that snout tentacle secretions are used to provide nutrients to fish larvae when they are under paternal care.

Purification and characterization of a 630 kDa bacterial killing metalloprotease (KilC) isolated from plaice Pleuronectes platessa (L.), epidermal mucus

Antibacterial chemicals in the mucus of fish such as lysozyme, lectins, peptides and proteases provide an efficient first line of defence against pathogens. This study shows that there are at least three antibacterial proteins in plaice skin mucus in addition to lysozyme. One of these proteins is responsible for approximately 74% of the antibacterial activity and is a 630 kDa protease complex designated KilC (bacterial killing metalloprotease C). Purified KilC kills the bacteria Staphylococcus aureus, Escherichia coli, Bacillus subtilis and Pseudomonas aeruginosa efficiently. The protease activity of KilC is dependent upon the divalent cation Mg(2+) and shows pH dual optima of 5.0 and 8.0. The enzyme has a temperature optimum of 25 degrees C and is made up of at least five different sized peptides. Studies with protease inhibitors show that the catalytic site of KilC may be cysteine- or serine protease-like. KilC may kill bacterial cells by acting directly upon the bacteria or by producing low molecular weight bioactive compounds such as peptides.

Ultrastructure and Histochemical Study of Glycoconjugates in the Gills of the White Croaker (Micropogonias furnieri)

The ultrastructure of the primary and secondary lamellae of gills was investigated in a marine teleost, the white croaker. The following cells were identified and briefly described: pavement cells, mucous cells, mitochondria-rich cells and rodlet cells. These cell types are present throughout the length of the lamellae. They are studied by means of a series of carbohydrate histochemical methods, including lectin procedures. Neutral sugars and substituted sialic acid were detected by means of periodic acid-borohydride reduction-saponification-periodic acid Schiff reaction (PA/Bh/KOH/PAS), saponification-selective periodic acid Schiff reaction (KOH/PA*S) and saponification-selective periodic acid-borohydride reduction-periodic acid Schiff reaction (KOH/PA*/Bh/PAS) histochemical techniques. A battery of seven lectins was used to study binding on tissue sections at the light microscopic level to characterize glycoconjugates in gills. The reaction to Canavalia ensiformis agglutinin (Con-A), Triticum vulgaris agglutinin (WGA), and Ricinus cummunis agglutinin-1 (RCA-1) was weak in pavement cells; unlike Con-A, the reaction to WGA and RCA-1 was more intense in mucous cells. Arachis hypogaea agglutinin (PNA) lectin showed a strong reaction in mucous cells. Ulex europaens agglutinin-1 (UEA-1) lectin was negative in all cell types. The lectin pattern was similar for both primary and secondary lamellae, except for PNA reaction, which was weak in the pavement cells of the secondary lamella and negative in the pavement cells of the primary lamella.

Digestive pathology of sea turtles stranded in the Canary Islands between 1993 and 2001

Digestive lesions were observed in 84 of 136 sea turtles (128 Caretta caretta, four Chelonia mydas and four Dermochelys coriacea) stranded in the Canary Islands between January 1993 and December 2001. In the oral cavity ulcerative and necropurulent stomatitis were the most frequently observed lesions, and in the oesophagus ulcerative and fibrinous oesophagitis, and traumatic oesophageal perforation were most frequently observed; all these lesions were mainly associated with the ingestion of fishing hooks. Different histological types of gastritis were observed in 35 of the turtles; necropurulent and fibrinous gastritis were associated with bacterial infections caused mainly by Proteus species, Vibrio alginolyticus, and Staphylococcus species, and larval nematodes of the genus Anisakis were responsible for a form of parasitic gastritis observed in 16 of the turtles. Different histological types of enteritis, including catarrhal, fibrinous, necropurulent and necrotising enteritis, affected 36 turtles; a wide range of gram-negative and gram-positive bacteria, including Bacillus species, Escherichia coli, Pasteurella species, Proteus species, Staphylococcus species, Streptococcus species and V. alginolyticus, were isolated from these lesions. All the cases of necrotising enteritis were associated with intestinal intussusception caused by the ingestion of monofilament fishing lines. Necrotising and/or multifocal granulomatous hepatitis were the lesions most commonly observed in the liver; they affected 29 of the turtles and were associated with Aeromonas hydrophila, Citrobacter species, E. coli, Proteus species, Staphylococcus species and V. alginolyticus infections. According to the stranding reports and the gross and histological lesions observed, 33 of the turtles had digestive lesions associated with the ingestion of hooks and monofilament lines, and two had lesions associated with the ingestion of crude oil.

Anti-microbial peptides: from invertebrates to vertebrates

Gene-encoded anti-microbial peptides (AMPs) are widespread in nature, as they are synthesized by microorganisms as well as by multicellular organisms from both the vegetal and the animal kingdoms. These naturally occurring AMPs form a first line of host defense against pathogens and are involved in innate immunity. Depending on their tissue distribution, AMPs ensure either a systemic or a local protection of the organism against environmental pathogens. They are classified into three major groups: (i) peptides with an alpha-helical conformation (insect cecropins, magainins, etc.), (ii) cyclic and open-ended cyclic peptides with pairs of cysteine residues (defensins, protegrin, etc.), and (iii) peptides with an over-representation of some amino acids (proline rich, histidine rich, etc.). Most AMPs display hydrophobic and cationic properties, have a molecular mass below 25-30 kDa, and adopt an amphipathic structure (alpha-helix, beta-hairpin-like beta-sheet, beta-sheet, or alpha-helix/beta-sheet mixed structures) that is believed to be essential to their anti-microbial action. Interestingly, in recent years, a series of novel AMPs have been discovered as processed forms of large proteins. Despite the extreme diversity in their primary and secondary structures, all natural AMPs have the in vitro particularity to affect a large number of microorganisms (bacteria, fungi, yeast, virus, etc.) with identical or complementary activity spectra. This review focuses on AMPs forming alpha-helices, beta-hairpin-like beta-sheets, beta-sheets, or alpha-helix/beta-sheet mixed structures from invertebrate and vertebrate origins. These molecules show some promise for therapeutic use.

Antimicrobial egg cleaning by the fringed darter (Perciformes: Percidae: Etheostoma crossopterum): implications of a novel component of parental care in fishes

Broad-spectrum antimicrobial compounds have recently been identified in the epidermal mucus of fishes and probably serve as a first line of defence against microbial pathogens. Because of the ubiquitous nature of fungi and bacteria in aquatic systems, defence against these pathogens should be required throughout the lifespan of fishes, including the egg stage. We conducted experiments on Etheostoma crossopterum (Percidae: Catonotus), the fringed darter, to determine if the presence of a guarding male inhibits microbial colonization of eggs. Based on results from a combination of in-stream experiments, in vitro microbial assays, and morphological characteristics and behaviour of breeding males, we propose that antimicrobial egg cleaning by the guarding male is an effective component of parental care in these fish. Although innate antimicrobial compounds have been identified in a variety of organisms ranging from insects to vertebrates, integration of these compounds into a species's reproductive life history has been identified only in a small number of insect species. The results from this study not only indicate that E. crossopterum males provide a novel form of vertebrate parental care, but also have implications regarding the evolution of parental care in fishes and transitional evolutionary stages from no parental care to male parental care.

Identification, structure and differential expression of novel pleurocidins clustered on the genome of the winter flounder, Pseudopleuronectes americanus (Walbaum)

Antimicrobial peptides form one of the first lines of defense against invading pathogens by killing the microorganisms and/or mobilizing the host innate immune system. Although over 800 antimicrobial peptides have been isolated from many different species, especially insects, few have been reported from marine fish. Sequence analysis of two genomic clones (15.6 and 12.5 kb) from the winter flounder, Pseudopleuronectes americanus (Walbaum) resulted in the identification of multiple clustered genes for novel pleurocidin-like antimicrobial peptides. Four genes and three pseudogenes (Psi) are encoded in these clusters, all of which have similar intron/exon boundaries but specify putative antimicrobial peptides differing in sequence. Pseudogenes are easily detectable but have incorrect initiator codons (ACG) and often contain a frameshift(s). Potential promoters and binding sites for transcription factors implicated in regulation of expression of immune-related genes have been identified in upstream regions by comparative genomics. Using reverse transcription-PCR assays, we have shown for the first time that each gene is expressed in a tissue-specific and developmental stage-specific manner. In addition, synthetic peptides based on the sequences of both genes and pseudogenes have been produced and tested for antimicrobial activity. These data can be used as a basis for prediction of antimicrobial peptide candidates for both human and nonhuman therapeutants from genomic sequences and will aid in understanding the evolution and transcriptional regulation of expression of these peptides.

Purification and characterization of an antibacterial protein in the skin secretion of rockfish Sebastes schlegeli

An antibacterial protein in the skin secretion of rockfish (Sebastes schlegeli) was purified by lectin affinity chromatography on Con A-Sepharose and gel filtration on TSKgel G3000SW. The antibacterial protein featured the high molecular mass and selective action against Gram-negative bacteria. The molecular mass of the protein was estimated to be approximately 150 kDa in gel filtration and approximately 75 kDa by SDS-PAGE, suggesting that it is dimeric. The antibacterial principle was an acidic glycoprotein with pI 4.5, 3.4% reducing sugar and 2.8% amino sugar. Its sugar chains had N-type (high mannose-type) oligosaccharide and sialic acid components. It inhibited strongly the growth of Aeromonas salmonicida, Photobacterium damselae and Shewanella putrefaciens with a minimum inhibitory concentration (MIC) of approximately 3 microg/ml, and moderately the growth of Vibrio parahaemolyticus and A. hydrophila with a MIC of 12.5 microg/ml and 25 microg/ml, respectively. The values of the minimum bactericidal concentration were almost equivalent to those of MIC. The potent sensitivity against virulent pathogens such as A. hydrophila, A. salmonicida and P. damselae may contribute considerably to the innate host defense mechanism to combat microbes on the mucosal surfaces of the rockfish.

Gone gene fishing: how to catch novel marine antimicrobials

Medical or health-promoting products of marine origin are often regarded with skepticism--some, such as shark fins and cod liver oil, are frequently perceived as low-tech "alternative treatments" largely because they have not been exploited to their full potential. The marine environment is an enormous source of biodiversity--80% of all life is found under the oceans' surfaces--yet very little of this rich resource has been utilized. Furthermore, most marine organisms rely heavily on antimicrobial components of their innate immune defenses to combat pathogens. The past three years has seen a revolution in the methods used to identify novel antimicrobials from marine sources; among the most promising are marine cationic antimicrobial peptides (CAPs).

Identification and expression analysis of hepcidin-like antimicrobial peptides in bony fish

Antimicrobial peptides play a crucial role as the first line of defense against invading pathogens. Several types of antimicrobial peptides have been isolated from fish, mostly of the cationic alpha-helical variety. Here, we present the cDNA sequences of five highly disulphide-bonded hepcidin-like peptides from winter flounder, Pseudopleuronectes americanus (Walbaum) and two from Atlantic salmon, Salmo salar (L.). These hepcidin-like molecules consist of a 24 amino acid signal peptide and an acidic propiece of 38-40 amino acids in addition to the mature processed peptide of 19-27 amino acids. Exhaustive data mining of GenBank with these sequences revealed that similar peptides are encoded in the genomes of Japanese flounder, rainbow trout, hybrid striped bass and medaka, indicating that they are widespread among fish. Southern hybridization analysis suggests that closely related hepcidin-like genes are present in other flatfish species, and that they exist as a multigene family clustered on the winter flounder genome. Hepcidin variants are differentially expressed during bacterial challenge, during larval development of P. americanus and in different tissues of adult fish.

Cellular localization of pleurocidin gene expression and synthesis in winter flounder gill using immunohistochemistry and in situ hybridization

Pleurocidin is an antimicrobial peptide isolated from winter flounder and has been previously localized to mucous cells of the skin epidermis and the intestine. The present study was designed to determine the cell type involved in pleurocidin gene expression and protein synthesis in gills from the same species. Whole-mount in situ hybridization with a pleurocidin-specific RNA probe and whole-mount immunohistochemistry with an anti-pleurocidin antibody localized the expression of this gene and the synthesis of its corresponding protein in a population of cells primarily isolated to the non-lamellar portion of the gill filament. Histological techniques allowed the presumptive identification of these cells as eosinophilic granular cells. These observations suggest that pleurocidin is expressed in not one but two distinct populations of cells within the winter flounder, one being an important group of inflammatory cells, the eosinophilic granular cells.

Local expression of apolipoprotein A-I gene and a possible role for HDL in primary defence in the carp skin

Antimicrobial proteins and peptides play an important role in the primary defence of epithelial barriers in vertebrates and invertebrates. Here we report the detection of the apolipoproteins A-I and A-II in the epidermis and epidermal mucus of the carp (Cyprinus carpio L.) by immunohistochemistry and Western blot analysis. Both apolipoproteins are major constituents of high density lipoprotein and have been shown to display antiviral and antimicrobial activity in mammals. Therefore the aim of this study was to evaluate if they could be part of the innate immune system of teleost fish. A cDNA clone containing most of the coding region for carp apoA-I was isolated and used as a probe to demonstrate the expression of apoA-I gene in the skin. In addition, mucus apoA-I was shown to be associated to small particles that could correspond to nascent HDL. Finally, affinity purified plasma HDL displayed bactericidal activity in vitro against a non-pathogenic Escherichia coli strain, suggesting a defensive role for HDL and its associated proteins in the carp epidermis and mucus.

Purification and characterization of three isoforms of chrysophsin, a novel antimicrobial peptide in the gills of the red sea bream, Chrysophrys major

We report here the isolation of three isoforms of a novel C-terminally amidated peptide from the gills of red sea bream, Chrysophrys (Pagrus) major. Peptide sequences were determined by a combination of Edman degradation, MS and HPLC analysis of native and synthetic peptides. Three peptides, named chrysophsin-1, chrysophsin-2, and chrysophsin-3, consist of 25, 25, and 20 amino acids, respectively, and are highly cationic, containing an unusual C-terminal RRRH sequence. The alpha-helical structures of the three chrysophsin peptides were predicted from their secondary structures and were confirmed by CD spectroscopy. The synthetic peptides displayed broad-spectrum bactericidal activity against Gram-negative and Gram-positive bacteria including Escherichia coli, Bacillus subtilis, and fish and crustacean pathogens. The three peptides were also hemolytic. Immunohistochemical analysis showed that chrysophsins were localized in certain epithelial cells lining the surface of secondary lamellae and eosinophilic granule cell-like cells at the base of the secondary lamellae in red sea bream gills. Their broad ranging bactericidal activities, combined with their localization in certain cells and eosinophilic granule cell-like cells in the gills, suggest that chrysophsins play a significant role in the innate defense system of red sea bream gills.

Nonmammalian vertebrate antibiotic peptides

With the exception of cyclostomes, all vertebrates share the common immune strategy of adaptive, highly specific immunity, based on the products of recombination-activating genes and recombined noninherited receptors for antigens. In addition, they have retained ancient vectors of innate immunity, such as antimicrobial peptides, which are widespread in all eukaryotic organisms and show a high degree of structural homology across most animal taxa. Recently, these substances have become the objects of intensive study for their outstanding bioactive properties with the aim to be applied as very efficient antibiotics, antimicrobials, and even cancerostatics in clinical practice.

Antibacterial, antifungal and cytotoxic activities of extracts from fish epidermis and epidermal mucus

Annual discards from the world fisheries are estimated to be approximately 20 million metric tonnes (25%) per year. The main objective of this work is to increase the utilisation of by-products (notably skin) from fish species in order to isolate new biologically active compounds. This study presents the results of a screening program for antifungal, antibacterial and cytotoxic activities in epidermal mucus and epidermis extracts of thirteen fish species that are commonly caught in North Atlantic waters and generate an important amount of fish waste. Antimicrobial assays used five Gram-positive bacteria five Gram-negative bacteria and five fungi. Of the 78 extracts tested, 15 showed antibacterial and/or antifungal activities. None of the aqueous fractions were active. One third of the active extracts were ethanolic fractions and three fourth of extracts were dichloromethane fractions. One third of the active fractions were of epidermal origin and the remaining came from mucus fractions. The high levels of inhibitory activity and no apparent toxicity against mouse fibroblasts of extracts of Pollachius virens (CH(3)CH(2)OH/epidermis), Labrus bergylta (CH(2)Cl(2)/mucus), Platichthys flesus (CH(3)CH(2)OH/mucus), Solea solea (CH(2)Cl(2)/mucus) and Scophtalamus rhombus (CH(2)Cl(2)/mucus) suggest they may have potential as novel active therapeutic agents.

Cathepsin D produces antimicrobial peptide parasin I from histone H2A in the skin mucosa of fish

Parasin I is a potent 19-residue antimicrobial peptide isolated from the skin mucus of wounded catfish (Parasilurus asotus). Here we describe the mechanism of parasin I production from histone H2A in catfish skin mucosa on epidermal injury. Cathepsin D is found to exist in the mucus as an inactive proenzyme (procathepsin D), and a metalloprotease, induced on injury, cleaves procathepsin D to generate active cathepsin D. This activated form of cathepsin D then cleaves the Ser19-Arg20 bond of histone H2A to produce parasin I. Immunohistochemical analysis reveals that unacetylated histone H2A, a precursor of parasin I, and procathepsin D are present in the cytoplasm of epithelial mucous cells and that parasin I is produced on the mucosal surface on epidermal injury. Western blot analysis shows that parasin I is also present in the skin mucus of other fish species. Furthermore, parasin I shows good antimicrobial activity against fish-specific bacterial pathogens. Taken together, these results indicate that cathepsin D and a metalloprotease participate in the production of parasin I from histone H2A and that parasin I contributes to the innate host defense of the fish against invading microorganisms.

Histone H1: an antimicrobial protein of Atlantic salmon (Salmo salar)

Antimicrobial activity was detected in acid extracts of liver, intestine, and stomach of healthy Atlantic salmon (Salmo salar). An antimicrobial protein was isolated from salmon liver using acid extraction followed by ammonium sulfate precipitation, large-scale gel filtration chromatography, reverse-phase HPLC, and size exclusion HPLC. The salmon antimicrobial (SAM) protein was found to have a molecular mass of 20,734 Da by MALDI TOF mass spectrometry. Peptide mass fingerprinting and partial sequencing by tandem nanoelectrospray mass spectrometry identified the protein as histone H1. The protein had a minimal inhibitory concentration of 31 microg/mL against E. coli D31 in a plate clearing assay. The effect of the SAM protein on bacterial morphology was indistinguishable from that of (Ala-(8,13,18))-magainin II, as shown by scanning electron microscopy, which suggests that the protein disrupts E. coli membranes in a manner similar to that of most antimicrobial peptides. This protein may act as an antimicrobial in vivo through active secretion or by release from cells during infection-related apoptosis.

Synergy of histone-derived peptides of coho salmon with lysozyme and flounder pleurocidin

Recent research has identified endogenous cationic antimicrobial peptides as important factors in the innate immunity of many organisms, including fish. It is known that antimicrobial activity, as well as lysozyme activity, can be induced in coho salmon (Oncorhynchus kisutch) mucus after exposure of the fish to infectious agents. Since lysozyme alone does not have antimicrobial activity against Vibrio anguillarum and Aeromonas salmonicida, a four-step protein purification protocol was used to isolate and identify antibacterial fractions from bacterially challenged coho salmon mucus and blood. The purification consisted of extraction with hot acetic acid, extraction and concentration on a C(18) cartridge, gel filtration, and reverse-phase chromatography on a C(18) column. N-terminal amino acid sequence analyses revealed that both the blood and the mucus antimicrobial fractions demonstrated identity with the N terminus of trout H1 histone. Mass spectroscopic analysis indicated the presence of the entire histone, as well as fragments thereof, including a 26-amino-acid N-terminal segment. These fractions inhibited the growth of antibiotic-supersuscptible Salmonella enterica serovar Typhimurium, as well as A. salmonicida and V. anguillarum. Synthetic peptides identical to the N-terminally acetylated or C-terminally amidated 26-amino-acid fragment were inactive in antimicrobial assays, but they potentiated the antimicrobial activities of the flounder peptide pleurocidin, lysozyme, and crude lysozyme-containing extracts from coho salmon. The peptides bound specifically to anionic lipid monolayers. However, synergy with pleurocidin did not appear to occur at the cell membrane level. The synergistic activities of inducible histone peptides indicate that they play an important role in the first line of salmon defenses against infectious pathogens and that while some histone fragments may have direct antimicrobial effects, others improve existing defenses.

Cutaneous biology and diseases of fish

The normal structure and function of the piscine integument reflects the adaptation of the organism to the physical, chemical, and biological properties of the aquatic environment, and the natural history of the organism. Because of the intimate contact of fish with the environment, cutaneous disease is relatively more common in fish than in terrestrial vertebrates and is one of the primary disease conditions presented to the aquatic animal practitioner. However, cutaneous lesions are generally nonspecific and may be indicative of disease that is restricted to the integument or a manifestation of systemic disease. Regardless, a gross and microscopic examination of the integument is simple to perform, but is highly diagnostic and should always be included in the routine diagnostic effort of the aquatic animal practitioner, especially since various ancillary diagnostic procedures are either not practical or lack predictive value in fish. The purpose of this article is to provide an overview of normal cutaneous biology prior to consideration of specific cutaneous diseases in fish.

Isolation of antibacteriologically active compounds from species of the Cottidae family

Antibacteriologically active compounds were isolated from the skin of several species of the fish family Cottidae. Suitable samples were obtained from species living in the Pacific, lakes in North America and the Fenno-Scandinavian peninsula as well as the Baltic sea. The compounds isolated from the skin of Triglops quadricornis (fourhorn sculpin) from the Baltic sea were particularly studied. The activity was partially characterised by chemical and biochemical investigations and the susceptibility of several human and fish pathogens described. The substance or substance(s) are of a high molecular mass, resist proteolytic and glycolytic enzymes, are heat and pH sensitive and water soluble.

Cloning and developmental expression of a family of pleurocidin-like antimicrobial peptides from winter flounder, Pleuronectes americanus (Walbaum)

Low molecular weight antimicrobial peptides are an important component of the innate immune system in animals, yet they have not been examined widely in fish. Of particular interest is their expression during development and in response to environmental conditions and disease. Here, we report the isolation of four genomic sequences encoding putative antimicrobial peptides from the winter flounder, Pleuronectes americanus (Walbaum), as well as reverse transcription-PCR products from two tissues that form the first defensive barrier to microbes - skin and intestine. Alignment of the predicted polypeptide sequences shows a conserved hydrophobic signal peptide of 22 amino acids followed by 25 amino acids that are identical (WF2) or homologous to the amino acid sequence of pleurocidin, followed by a conserved acidic portion. Southern hybridisation analysis indicates that related peptides are encoded in the genomes of other flatfish species. Northern and RT-PCR analyses of RNA from multiple tissues show that two of the pleurocidin genes are expressed predominantly in the skin whereas two other genes are expressed mainly in the intestine. RT-PCR assays of total RNA from larvae of different ages provide the first evidence of developmental expression of antimicrobial peptides in fish and indicate that the pleurocidin gene is first expressed at 13 days post-hatch in winter flounder.