Molecular cloning, recombinant expression, and antimicrobial activity of EC-hepcidin3, a new four-cysteine hepcidin isoform from Epinephelus coioides

Revolutionizing orthopedic healthcare: a systematic review unveiling recombinant antimicrobial peptides

The increasing demand for orthopedic surgeries, including joint replacements, is driven by an aging population and improved diagnosis of joint conditions. Orthopedic surgeries carry a risk of infection, especially in patients with comorbidities. The rise of antibiotic resistance exacerbates this issue, necessitating alternatives like in vitro bioengineered antimicrobial peptides (AMPs), offering broad-spectrum activity and multiple action mechanisms. This review aimed to assess the prevalence of antimicrobial potential and the yield after purification among recombinant AMP families. The antimicrobial potential was evaluated using the Minimum Inhibitory Concentration (MIC) values against the most common bacteria involved in clinical infections. This systematic review adhered to PRISMA guidelines, focusing on in vitro studies of recombinant AMPs. The search strategy was run on PubMed, Scopus and Embase up to 30th March 2023. The Population, Exposure and Outcome model was used to extract the data from studies and ToxRTool for the risk of bias analysis. This review included studies providing peptide production yield data and MIC values against pathogenic bacteria. Non-English texts, reviews, conference abstracts, books, studies focusing solely on chemical synthesis, those reporting incomplete data sets, using non-standard MIC assessment methods, or presenting MIC values as ranges rather than precise concentrations, were excluded. From 370 publications, 34 studies on AMPs were analyzed. These covered 46 AMPs across 18 families, with Defensins and Hepcidins being most common. Yields varied from 0.5 to 2,700 mg/L. AMPs were tested against 23 bacterial genera, with MIC values ranging from 0.125 to >1,152 μg/mL. Arenicins showed the highest antimicrobial activity, particularly against common orthopedic infection pathogens. However, AMP production yields varied and some AMPs demonstrated limited effectiveness against certain bacterial strains. This systematic review emphasizes the critical role of bioengineered AMPs to cope infections and antibiotic resistance. It meticulously evaluates recombinant AMPs, focusing on their antimicrobial efficacy and production yields. The review highlights that, despite the variability in AMP yields and effectiveness, Arenicins and Defensins are promising candidates for future research and clinical applications in treating antibiotic-resistant orthopedic infections. This study contributes significantly to the understanding of AMPs in healthcare, underscoring their potential in addressing the growing challenge of antibiotic resistance. Systematic review registration:https://osf.io/2uq4c/.

Bacterial diseases in marine fish species: current trends and future prospects in disease management

The fisheries sub-sector of aquaculture-i.e., the pisciculture industry, contributes significantly to a country's economy, employing a sizable proportion of the population. It also makes important contributions to household food security because the current demand for animal protein cannot be fulfilled by harvesting wild fish from riverines, lakes, dams, and oceans. For good pond management techniques and sustaining fish health, the fisherfolk, and the industry require well-established regulatory structures, efficient disease management strategies, and other extended services. In rearing marine fish, infections resulting from disease outbreaks are a weighty concern because they can cause considerable economic loss due to morbidity and mortality. Consequently, to find effective solutions for the prevention and control of the major diseases limiting fish production in aquaculture, multidisciplinary studies on the traits of potential fish pathogens, the biology of the fish as hosts, and an adequate understanding of the global environmental factors are fundamental. This review highlights the various bacterial diseases and their causative pathogens prevalent in the pisciculture industry and the current solutions while emphasising marine fish species. Given that preexisting methods are known to have several disadvantages, other sustainable alternatives like antimicrobial peptides, synthetic peptides, probiotics, and medicinal treatments have emerged to be an enormous potential solution to these challenges.

Prokaryotic Expression, Purification, and Antibacterial Activity of the Hepcidin Peptide of Crescent Sweetlips (Plectorhinchus cinctus)

The hepcidin peptide of crescent sweetlips (Plectorhinchus cinctus) is a cysteine-rich, cationic antimicrobial peptide that plays a crucial role in the innate immune system's defense against invading microbes. The aim of this study was to identify the optimal parameters for prokaryotic expression and purification of this hepcidin peptide and characterize its antibacterial activity. The recombinant hepcidin peptides were expressed in Escherichia coli strain Arctic Express (DE3), with culture and induction conditions optimized using response surface methodology (RSM). The obtained hepcidin peptides were then purified before tag cleavage, and their antibacterial activity was determined. The obtained results revealed that induction temperature had the most significant impact on the production of soluble recombinant peptides. The optimum induction conditions were determined to be an isopropylthio-β-galactoside (IPTG) concentration of 0.21 mmol/L, induction temperature of 18.81 °C, and an induction time of 16.01 h. Subsequently, the recombinant hepcidin peptide was successfully purified using Ni-IDA affinity chromatography followed by SUMO protease cleavage. The obtained hepcidin peptide (without His-SUMO tag) demonstrated strong antimicrobial activity in vitro against V. parahaemolyticus, E. coli, and S. aureus. The results showed prokaryotic (E. coli) expression is a feasible way to produce the hepcidin peptide of crescent sweetlips in a cost-effective way, which has great potential to be used as an antimicrobial agent in aquaculture.

Antibacterial Activity and Mechanisms of TroHepc2-22, a Derived Peptide of Hepcidin2 from Golden Pompano (Trachinotus ovatus)

Hepcidin, a cysteine-rich antimicrobial peptide, has a highly conserved gene structure in teleosts, and it plays an essential role in host immune response against various pathogenic bacteria. Nonetheless, few studies on the antibacterial mechanism of hepcidin in golden pompano (Trachinotus ovatus) have been reported. In this study, we synthesized a derived peptide, TroHepc2-22, from the mature peptide of T. ovatus hepcidin2. Our results showed that TroHepc2-22 has superior antibacterial abilities against both Gram-negative (Vibrio harveyi and Edwardsiella piscicida) and Gram-positive (Staphylococcus aureus and Streptococcus agalactiae) bacteria. Based on the results of a bacterial membrane depolarization assay and propidium iodide (PI) staining assay in vitro, TroHepc2-22 displayed antimicrobial activity by inducing the bacterial membrane depolarization and changing the bacterial membrane permeability. Scanning electron microscopy (SEM) visualization illustrated that TroHepc2-22 brought about membrane rupturing and the leakage of the cytoplasm for the bacteria. In addition, TroHepc2-22 was verified to have hydrolytic activity on bacterial genomic DNA in view of the results of the gel retardation assay. In terms of the in vivo assay, the bacterial loads of V. harveyi in the tested immune tissues (liver, spleen, and head kidney) were significantly reduced in T. ovatus, revealing that TroHepc2-22 significantly enhanced the resistance against V. harveyi infection. Furthermore, the expressions of immune-related genes, including tumor necrosis factor-α (TNF-α), interferon-γ (IFN-γ), interleukin 1-β (IL-1β), IL-6, Toll-like receptor 1 (TLR1), and myeloid differentiation factor 88 (MyD88) were significantly increased, indicating that TroHepc2-22 might regulate inflammatory cytokines and activate immune-related signaling pathways. To summarize, TroHepc2-22 possesses appreciable antimicrobial activity and plays a vital role in resisting bacterial infection. The observation of our present study unveils the excellent application prospect of hepcidin as a substitute for antibiotics to resist pathogenic microorganisms in teleosts.

Antibacterial and immunoregulatory activity of an antimicrobial peptide hepcidin in loach (Misgurnus anguillicaudatus)

Antimicrobial peptides (AMPs) are members of humoral immunity and particpate in resisting microbial invasion. In this study, an AMP gene hepcidin was obtained from the oriental loach Misgurnus anguillicaudatus and named Ma-Hep. This Ma-Hep encodes a peptide of 90 amino acids, with a predicted active peptide segment (Ma-sHep) of 25 amino acids at C terminus. Stimulation by a bacterial pathogen Aeromonas hydrophila resulted in significant up-regulation of Ma-Hep transcripts in loach midgut, head kidney, and gill. Ma-Hep and Ma-sHep proteins were expressed in Pichia pastoris and their antibacterial activity was examined. Results showed that Ma-sHep possessed stronger antibacterial activity against various Gram-positive and Gram-negative bacteria, compared to Ma-Hep. Scanning electron microscopy showed that Ma-sHep might kill bacteria by destroying bacterial cell membranes. Moreover, we found that Ma-sHep had an inhibitory effect on blood cell apoptosis induced by A. hydrophila and facilitated the bacterial phagocytosis and clearance in loach. Histopathological analysis indicated Ma-sHep could protect liver and gut of loach from bacterial infection. Ma-sHep has high thermal stability and PH stability, which is conducive to further feed addition. Feed supplemented with Ma-sHep expressing yeast improved the intestinal flora of loach by increasing the dominant bacteria and decreasing the harmful bacteria. Feed supplemented with Ma-sHep expressing yeast also regulated the expression of inflammatory related factors in various tissues of loach and reduced the mortality of loach upon bacterial infection. These findings show that the antibacterial peptide Ma-sHep is involved in the antibacterial defense of loach and can be used as a candidate for new antimicrobial agents in aquaculture.

Integrative analyses of mRNA and microRNA expression profiles reveal the innate immune mechanism for the resistance to Vibrio parahaemolyticus infection in Epinephelus coioides

Vibrio parahaemolyticus, as one of the main pathogens of marine vibriosis, has brought huge losses to aquaculture. However, the interaction mechanism between V. parahaemolyticus and Epinephelus coioides remains unclear. Moreover, there is a lack of comprehensive multi-omics analysis of the immune response of grouper spleen to V. parahaemolyticus. Herein, E. coioides was artificially injected with V. parahaemolyticus, and it was found that the mortality was 16.7% in the early stage of infection, and accompanied by obvious histopathological lesions in the spleen. Furthermore, 1586 differentially expressed genes were screened by mRNA-seq. KEGG analysis showed that genes were significantly enriched in immune-related pathways, Acute-phase immune response, Apoptosis, Complement system and Cytokine-cytokine receptor interaction. As for miRNA-seq analysis, a total of 55 significantly different miRNAs were identified. Further functional annotation analysis indicated that the target genes of differentially expressed miRNAs were enriched in three important pathways (Phosphatidylinositol signaling system, Lysosome and Focal adhesions). Through mRNA-miRNA integrated analysis, 1427 significant miRNA–mRNA pairs were obtained and “p53 signaling pathway”, “Intestinal immune network for IgA production” were considered as two crucial pathways. Finally, miR-144-y, miR-497-x, novel-m0459-5p, miR-7133-y, miR-378-y, novel-m0440-5p and novel-m0084-3p may be as key miRNAs to regulate immune signaling pathways via the miRNA-mRNA interaction network. The above results suggest that the mRNA-miRNA integrated analysis not only sheds new light on the molecular mechanisms underlying the interaction between host and V. parahaemolyticus but also provides valuable and new insights into resistance to vibrio infection.

Novel approaches for the treatment of infections due to multidrug-resistant bacterial pathogens

Antimicrobial resistance (AMR), which is a major challenge for global healthcare, emerging because of several reasons including overpopulation, increased global migration and selection pressure due to enhanced use of antibiotics. Antibiotics are the widely used therapeutic options to combat infectious diseases; however, unfortunately, inadequate and irregular antibiotic courses are also major contributing factors in the emergence of AMR. Additionally, persistent failure to develop and commercialize new antibiotics has created the scarcity of effective anti-infective drugs. Thus, there is an urgent need for a new class of antimicrobials and other novel approaches to curb the menace of AMR. Besides the conventional approaches, some novel approaches such as the use of antimicrobial peptides, bacteriophages, immunomodulation, host-directed therapy and antibodies have shown really promising potentials.

The Long-Term Effect of a Nine Amino-Acid Antimicrobial Peptide AS-hepc3(48-56) Against Pseudomonas aeruginosa With No Detectable Resistance

The emergence of multidrug-resistant (MDR) pathogens has become a global public health crisis. Among them, MDR Pseudomonas aeruginosa is the main cause of nosocomial infections and deaths. Antimicrobial peptides (AMPs) are considered as competitive drug candidates to address this threat. In the study, we characterized two AMPs (AS-hepc3_(41-71) and AS-hepc3_(48-56)) that had potent activity against 5 new clinical isolates of MDR P. aeruginosa. Both AMPs destroyed the integrity of the cell membrane, induced leakage of intracellular components, and ultimately led to cell death. A long-term comparative study on the bacterial resistance treated with AS-hepc3_(41-71), AS-hepc3_(48-56) and 12 commonly used antibiotics showed that P. aeruginosa quickly developed resistance to the nine antibiotics tested (including aztreonam, ceftazidime, cefepime, imipenem, meropenem, ciprofloxacin, levofloxacin, gentamicin, and piperacillin) as early as 12 days after 150 days of successive culture generations. The initial effective concentration of 9 antibiotics against P. aeruginosa was greatly increased to a different high level at 150 days, however, both AS-hepc3_(41-71) and AS-hepc3_(48-56) maintained their initial MIC unchangeable through 150 days, indicating that P. aeruginosa did not produce any significant resistance to both AMPs. Furthermore, AS-hepc3_(48-56) did not show any toxic effect on mammalian cells in vitro and mice in vivo. AS-hepc3_(48-56) had a therapeutic effect on MDR P. aeruginosa infection using a mouse lung infection model and could effectively increase the survival rate of mice by inhibiting bacterial proliferation and attenuating lung inflammation. Taken together, the short peptide AS-hepc3_(48-56) would be a promising agent for clinical treatment of MDR P. aeruginosa infections.

The Era of Antimicrobial Peptides: Use of Hepcidins to Prevent or Treat Bacterial Infections and Iron Disorders

The current treatments applied in aquaculture to limit disease dissemination are mostly based on the use of antibiotics, either as prophylactic or therapeutic agents, with vaccines being available for a limited number of fish species and pathogens. Antimicrobial peptides are considered as promising novel substances to be used in aquaculture, due to their antimicrobial and immunomodulatory activities. Hepcidin, the major iron metabolism regulator, is found as a single gene in most mammals, but in certain fish species, including the European sea bass (Dicentrarchus labrax), two different hepcidin types are found, with specialized roles: the single type 1 hepcidin is involved in iron homeostasis trough the regulation of ferroportin, the only known iron exporter; and the various type 2 hepcidins present antimicrobial activity against a number of different pathogens. In this study, we tested the administration of sea bass derived hepcidins in models of infection and iron overload. Administration with hamp2 substantially reduced fish mortalities and bacterial loads, presenting itself as a viable alternative to the use of antibiotics. On the other hand, hamp1 seems to attenuate the effects of iron overload. Further studies are necessary to test the potential protective effects of hamp2 against other pathogens, as well as to understand how hamp2 stimulate the inflammatory responses, leading to an increased fish survival upon infection.

Immunomodulatory function of antimicrobial peptide EC-Hepcidin1 modulates the induction of inflammatory gene expression in primary cells of Caspian Trout (Salmo trutta caspius Kessler, 1877)

Hepcidins, a group of antimicrobial peptides (AMPs), play a key role in the innate immune system of fishes and act against different pathogens. In this study, antimicrobial and immune-inflammatory activity of a synthetic EC-hepcidin1, previously identified from orange-spotted grouper, were evaluated. EC-hepcidin1 showed weak activity against the zoonotic fish pathogen Streptococcus iniae (MIC 100 μg mL^-1 and MBC 150 μg mL^-1). To study the effect of AMPs in general, and EC-hepcidin1 in particular, a primary cell culture (SC) from the fin tissue of the Caspian Trout (Salmo trutta caspius) was established. The neutral Red method on SC cells revealed that EC-hepcidin1 has no or very low cytotoxic properties. Treatment of cells with either EC-hepcidin1 (150 μg mL^-1) or fish pathogen Streptococcus iniae (MOI = 10) and a mixture of both resulted in the up-regulation of gene expression of MHC-UBA, IL-6, and TNFα indicating the modulatory function on inflammatory processes. These findings indicate that EC-hepcidin1 might act as a candidate for modulation of the innate immune system in S. iniae-based infection.

Transcriptome analysis identifies immune-related genes and antimicrobial peptides in Siamese fighting fish (Betta splendens)

Siamese fighting fish (Betta splendens) is one of the most widely cultivated ornamental fish in global trade. However, transcriptomic data, which can reveal valuable genetic data for disease control and prevention, are extremely limited for this species. In this study, whole-body transcriptome sequencing of juvenile betta fish generated 4.457 GB of clean data and a total of 71,775 unigenes using the Illumina HiSeq4000 platform. These unigenes were functionally classified using 7 functional databases, yielding 45,316 NR (63.14%), 47,287 NT (65.88%), 39,105 Swiss-Prot (54.48%), 16,492 COG (22.98%), 37,694 KEGG (52.52%), 4,506 GO (6.28%), and 35,374 Interpro (49.28%) annotated unigenes. Furthermore, we also detected 13,834 SSRs distributed on 10,636 unigenes and 49,589 predicted CDSs. Based on KEGG analysis, five innate immune pathways (997 unigenes) were reported, including the NOD-like receptor signaling pathway, complement and coagulation cascades, toll-like receptor signaling pathway, RIG-I-like receptor signaling pathway and cytosolic DNA-sensing pathway. Moreover, four antimicrobial peptide (AMP) families (hepcidin, piscidin, LEAP-2, and defensins) from the betta fish transcriptome were also identified. Additionally, cDNA and genomic DNA of two β-defensins was successfully isolated from four betta fish species. RT-PCR analysis showed that BsBD1 transcripts were most abundant in the muscle and kidney and BsBD2 transcripts were most abundant in the gill. The genomic organization showed that the BD1 and BD2 genes consisted of three exons and two introns according to the GT-AG rule. Most importantly, this is the first report of the betta fish whole-body transcriptome obtained by high-throughput sequencing. Our transcriptomic data and the discovery of betta fish AMPs should promote a better understanding of molecular immunology for disease prevention for further ornamental fish aquaculture.

Antimicrobial peptides: new hope in the war against multidrug resistance

The discovery of antibiotics marked a golden age in the revolution of human medicine. However, decades later, bacterial infections remain a global healthcare threat, and a return to the pre-antibiotic era seems inevitable if stringent measures are not adopted to curb the rapid emergence and spread of multidrug resistance and the indiscriminate use of antibiotics. In hospital settings, multidrug resistant (MDR) pathogens, including carbapenem-resistant Pseudomonas aeruginosa, vancomycin-resistant enterococci (VRE), methicillin-resistant Staphylococcus aureus (MRSA), and extended-spectrum β-lactamases (ESBL) bearing Acinetobacter baumannii, Escherichia coli, and Klebsiella pneumoniae are amongst the most problematic due to the paucity of treatment options, increased hospital stay, and exorbitant medical costs. Antimicrobial peptides (AMPs) provide an excellent potential strategy for combating these threats. Compared to empirical antibiotics, they show low tendency to select for resistance, rapid killing action, broad-spectrum activity, and extraordinary clinical efficacy against several MDR strains. Therefore, this review highlights multidrug resistance among nosocomial bacterial pathogens and its implications and reiterates the importance of AMPs as next-generation antibiotics for combating MDR superbugs.

Antimicrobial activity and mechanisms of multiple antimicrobial peptides isolated from rockfish Sebastiscus marmoratus

Pathogenic disease is a major factor affecting the aquaculture of the rockfish Sebastiscus marmoratus, an important commercial species inhabiting the nearshore waters of the Western Pacific Ocean. Antimicrobial peptides (AMPs), as critical components of innate immunity, have been considered as promising antibiotic substitutes. The aims of this study were 1) to identify major AMPs in the rockfish, 2) to assess their antimicrobial activity and 3) to evaluate their potential therapeutic application. Six AMPs were identified, Hepcidin 1, liver-expressed antimicrobial peptide 2 (LEAP-2), Piscidin, Moronecidin, NK-lysin and β-defensin through analysis of the liver transcriptome of S. marmoratus. The transcriptional expression profiles of these AMPs were investigated by real-time quantitative PCR (RT-qPCR). These AMPs showed tissue-specific distribution patterns, and S. marmoratus displays a time-, dose- and tissue-dependent expression of AMPs in response to lipopolysaccharide (LPS) challenge. While the synthetic peptides of LEAP-2 and Moronecidin exerted broad-spectrum antimicrobial activity against important aquatic pathogens in vitro by directly disrupting microbial membrane, and no cytotoxicity against murine hepatic cells was observed at the effective concentrations from 5 μM to 40 μM. The existence of multiple AMPs and their distinct tissue distribution patterns and inducible expression patterns suggests a sophisticated, highly redundant, and multilevel network of antimicrobial defensive mechanisms of S. marmoratus. Therefore, S. marmoratus-derived AMPs appear to be potential therapeutic applications against pathogen infections in aquaculture.

Cloning, characterization and tissue-specific expression of the antimicrobial peptide hepcidin from caspian trout (Salmo caspius) and the antibacterial activity of the synthetic peptide

Antimicrobial peptides have a wide range of antimicrobial activity and widely occur in different organisms including mollusks, crustaceans and vertebrates. Hepcidins are a group of cysteine-rich antimicrobial peptides that are active against a variety of pathogens including gram-positive and gram-negative bacteria, as well as viruses. In this study, the hepcidin gene of Caspian trout (CtHep) was identified and characterized. Our results showed that CtHep cDNA has a 267-bp Open Reading Frame (ORF), which is translated to 88 amino acids. The CtHep was classified in the HAMP1 class of hepcidins. Comparison of DNA and cDNA sequences showed that CtHep has 3 exons and 2 introns. The signal, prodomain and mature part of CtHep have 24, 39 and 25 amino acids, respectively. The mature peptide has a molecular weight of 2881.43 Da and a theoretical isoelectric point of 8.53. The expression of CtHep mRNA was detected in different tissues of healthy and infected fish. CtHep expression in the liver, head kidney, spleen and skin was significantly enhanced after bacterial challenge. Expression of CtHep in different embryonic development stages was also substantial. Antibacterial activity of synthetic CtHep peptides was investigated against a number of Gram-positive and Gram-negative bacteria. CtHep inhibited some pathogenic bacteria such as Streptococcus iniae and Aeromonas hydrophila. In the in vivo experiment, CtHep upregulated the cytokines IL-6 and TNF-α in both kidney and spleen tissues after 24 h of the peptide injection. In conclusion, our study showed that CtHep plays an important role in the immune system of Caspian trout and also in the embryonic stages. Moreover, CtHep peptide has a potential to be used as an antimicrobial therapeutic agent as well as an immunostimulant in aquaculture.

Design, recombinant expression, and antibacterial activity of a novel hybrid magainin-thanatin antimicrobial peptide

Antimicrobial peptides are small molecule polypeptides with biological activity, which can avoid the drug resistance. Magainin and thanatin are antimicrobial peptides with a broad spectrum of inhibitory microbes, and the core sequence of magainin is linked to a core sequence of thanatin. Here, the hybrid magainin-thanatin (MT) antimicrobial peptide was designed through bioinformatics analysis. The recombinant MT antimicrobial peptide was successfully expressed and purified in Escherichia coli BL21 (DE3). The molecular weight of the hybrid MT antimicrobial peptide was about 3.35 kDa. Moreover, the target protein indeed has an inhibitory effect on Staphylococcus aureus, E. coli DH5α, and Bacillus subtilis, with the minimum inhibitory concentrations 16.5, 20, and 9 μM, respectively. The rational designed hybrid MT antimicrobial peptide will hopefully provide large-scale fermentable antimicrobial peptides in the industrial production in the future.

Mudskipper (Boleophthalmus pectinirostris) Hepcidin-1 and Hepcidin-2 Present Different Gene Expression Profile and Antibacterial Activity and Possess Distinct Protective Effect against Edwardsiella tarda Infection

Hepcidins are small cysteine-rich antimicrobial peptides that play an important role in fish immunity against pathogens. Most fish species have two or more hepcidin homologs that have distinct functions. This study investigated the immune functions of mudskipper (Boleophthalmus pectinirostris) hepcidin-1 (BpHep-1) and hepcidin-2 (BpHep-2) in vitro and in vivo. Upon infection with Edwardsiella tarda, the expression of BpHep-1 and BpHep-2 mRNA in immune tissues was significantly upregulated, but the expression profiles were different. Chemically synthesized BpHep-1 and BpHep-2 mature peptides exhibited selective antibacterial activity against various bacterial species, and BpHep-2 exhibited a stronger antibacterial activity and broader spectrum than BpHep-1. BpHep-1 and BpHep-2 both inhibited the growth of E. tarda in vitro, with the latter being more effective than the former. In addition, both peptides induced hydrolysis of purified bacterial genomic DNA (gDNA) or gDNA in live bacteria. In vivo, an intraperitoneal injection of 1.0 μg/g BpHep-2 significantly improved the survival rate of mudskippers against E. tarda infection compared with 0.1 μg/g BpHep-2 or 0.1 and 1.0 μg/g BpHep-1. Similarly, only BpHep-2 treatment effectively reduced the tissue bacterial load in E. tarda-infected mudskippers. Furthermore, treatment with 1.0 or 10.0 μg/ml BpHep-2 promoted the phagocytic and bactericidal activities of mudskipper monocytes/macrophages (MO/MФ). However, only the highest dose (10.0 μg/ml) of BpHep-1 enhanced phagocytosis, and BpHep-1 exerted no obvious effects on bactericidal activity. In conclusion, BpHep-2 is a stronger bactericide than BpHep-1 in mudskippers, and acts not only by directly killing bacteria but also through an immunomodulatory function on MO/MФ.

Molecular characterization of a hepcidin homologue in starry flounder (Platichthys stellatus) and its synergistic interaction with antibiotics

Hepcidins are small cysteine-rich antimicrobial peptides that play an important role in host immunity against pathogenic organisms. Most fish hepcidins exert bactericidal activities against a wide range of pathogens. In this study, we identified a cDNA sequence encoding a hepcidin homologue (PsHepcidin) in the starry flounder Platichthys stellatus. The predicted amino acid sequence of PsHepcidin comprises a signal peptide and a prodomain, which are followed by the mature peptide. Sequence analysis revealed that PsHepcidin belongs to the fish HAMP2 cluster and that it is closely related to mudskipper hepcidin-2. Expression of PsHepcidin mRNA was detected in all examined immune-related tissues, with the highest transcript levels being found in the liver. In response to lipopolysaccharide treatment, PsHepcidin was significantly up-regulated in the liver, kidney, and spleen in a time-dependent manner. Chemically synthesized mature peptides of PsHepcidin were found to exhibit broad antimicrobial activity in vitro. We also investigated the combined effect of PsHepcidin and conventional antibiotics and found that these combinations showed synergistic effects against most of the examined bacterial strains. Collectively, the results of this study indicate that PsHepcidin exhibits potent antibacterial activity both independently and when used in combination with conventional antibiotics.

An improved genome assembly for Larimichthys crocea reveals hepcidin gene expansion with diversified regulation and function

Larimichthys crocea (large yellow croaker) is a type of perciform fish well known for its peculiar physiological properties and economic value. Here, we constructed an improved version of the L. crocea genome assembly, which contained 26,100 protein-coding genes. Twenty-four pseudo-chromosomes of L. crocea were also reconstructed, comprising 90% of the genome assembly. This improved assembly revealed several expansions in gene families associated with olfactory detection, detoxification, and innate immunity. Specifically, six hepcidin genes (LcHamps) were identified in L. crocea, possibly resulting from lineage-specific gene duplication. All LcHamps possessed similar genomic structures and functional domains, but varied substantially with respect to expression pattern, transcriptional regulation, and biological function. LcHamp1 was associated specifically with iron metabolism, while LcHamp2s were functionally diverse, involving in antibacterial activity, antiviral activity, and regulation of intracellular iron metabolism. This functional diversity among gene copies may have allowed L. crocea to adapt to diverse environmental conditions.

The transcriptional regulation of an antimicrobial peptide hepcidin1 in Oryzias melastigma upon EE2 exposure involved in a new pathway with a novel transcriptional regulatory element HepERE

17α-ethinylestradiol (EE2) exerts endocrine disrupting effect and immunotoxic effect on marine animals, including modulation of hepcidin expression. The antimicrobial peptide hepcidin displays a crucial role in innate immunity in fish against invading pathogens. It is known that the transcription of hepcidin in mammals is individually regulated by many stimuli, including inflammation, iron overload, anemia or hypoxia, through several distinct molecular pathways. The canonical mechanism for endocrine disrupting effects is mediated by an estrogen receptor (ER) and estrogen responsive element (ERE), whereas the underlying mechanism for immunotoxic effect is still unclear. In this study, a hepcidin from Oryzias melastigma (OM-hep1) was found to be down-regulated upon EE2 exposure and was associated with ERα. Unlike the revealed signaling pathways for hepcidin regulation in mammals, it was revealed by promoter activity analysis that the OM-hep1 transcription was not associated with canonical immune-associated and hormone-associated regulatory elements, known as the nuclear factor κB (NF-κB), signal transducer and activator of transcription 3 (STAT3), ERE and estrogen-related receptor responsive element (ERRE). Further analysis through a series of base mutations revealed a short fragment from -315 to -289 bp on the OM-hep1 promoter with high activity. This fragment was composed of a putative ERE-like element (23 bases) plus an adjacent down-streamed four bases motif GTGT. Replacement of either of the core bases (GGTCA) of ERE-like or GTGT motif showed non-activity and non-response to EE2 exposure, thus a new hepcidin-associated element named as HepERE was revealed. Evidences from electrophoretic mobility shift assay (EMSA) and surface plasmon resonance (SPR) assay demonstrated that the EE2-mediated down-regulation of OM-hep1 expression was associated with ERα binding to HepERE but not classical ERE. Taken together, a novel signaling pathway was revealed and the regulatory mechanism associated with the ERα and HepERE element on immunomodulation of OM-hep1 expression upon EE2 exposure was first reported here.

Antimicrobial peptides within the Yellowtail Kingfish (Seriola lalandi)

A number of Seriola species are currently farmed or being investigated as future aquaculture species in countries around the world. However they face a number of issues and limitations which will need to be overcome to ensure future stability and growth, one of which are disease outbreaks. Despite this, very little has been done to understand the immune system of Seriola species and very few immune genes have been characterised. Antimicrobial peptides (AMP) are naturally occurring low molecular weight polypeptides that play a major role in an organism's immune system and act effectively as a first line of defence. This investigation isolates the full length cDNA sequences of two AMP's, piscidin and hepcidin from the yellowtail kingfish (Seriola lalandi). The full-length cDNA of the piscidin gene encodes a 65 amino acid prepropeptide, containing a 25-residue peptide, predicted to form an amphipathic helix-loop-helix structure. Phylogenetic analysis using fish piscidin sequences, showed that this AMP is only found in bony fish within the Acanthomorpha clade and that a possible three groups within the piscidin family exists, with S. lalandi belonging to a particular group. The full-length cDNA of the hepcidin gene encodes a 90 amino acid preprohepcidin, which contains a typical RX(R/K)R motif for cleavage of the mature peptide which comprises of eight conserved cysteine residues. Phylogenetic analysis of known vertebrate hepcidin antimicrobial peptide (HAMP) sequences, shows sequences from the Neoteleostei clade of bony fish form two very separate groups, HAMP1 and HAMP2, with the S. lalandi hepcidin gene grouped with the HAMP1 sequences. HAMP2 sequences are found to have multiple copies within fish and genome analysis showed very clearly that these two groups of genes are located on separate regions on the genome, with the multiple HAMP2 copies formed from tandem gene duplications. Lastly, using qPCR the expression of the S. lalandi piscidin gene within healthy fish was highest within, spleen and gills and lowest in liver, whereas hepcidin was highest in the liver with little or no expression in the spleen and gills.

Recent updates of marine antimicrobial peptides

Antimicrobial peptides are group of proteins showing broad-spectrum antimicrobial activity that have been known to be powerful agents against a variety of pathogens. This class of compounds contributed to solving the microbial resistance dilemma that limited the use of many potent antimicrobial agents. The marine environment is known to be one of the richest sources for antimicrobial peptides, yet this environment is not fully explored. Hence, the scientific research attention should be directed toward the marine ecosystem as enormous amount of useful discoveries could be brought to the forefront. In the current article, the marine antimicrobial peptides reported from mid 2012 to 2017 have been reviewed.

Molecular characterization and functional analysis of the hepcidin gene from roughskin sculpin (Trachidermus fasciatus)

Hepcidin is a kind of cysteine-rich antimicrobial peptide that plays a vital role in host innate immune activity and iron regulation. Here, we report the molecular characterization and functional analysis of a novel hamp1 hepcidin isoforms Tf-Hep from roughskin sculpin, Trachidermus fasciatus. A cDNA fragment of 988 bp with an ORF of 273 bp was obtained. The coding sequence encodes for a signal peptide of 24 amino acids coupled with a prodomain of 40 amino acids and a mature peptide of 26 amino acids. Tissue distribution analysis indicated that Tf-Hep was most abundant in the liver. It could be significantly induced post lipopolysaccharide (LPS) challenge and heavy metal exposure. The mature peptide was expressed as a 6.061 kDa fusion protein in Pichia pastoris GS115. The active purified recombinant protein (rTf-Hep) exhibited a wide spectrum of potent antimicrobial activity in vitro against 4 Gram-negative bacteria Escherichia coli, Vibrio Anguillarum, Klebsiella pneumoniae, and Pseudomonas aeruginosa and 4 Gram-positive bacteria Staphylococcus aureus, Bacillus subtilis, Bacillus thuringiensis, and Bacillus megaterium with minimum inhibitory concentrations (MICs) of 5-80 μg/ml (0.825-13.2 μM). It also displayed high affinity to polysaccharides on bacteria surface including LPS, lipoteichoic acid (LTA) and peptidoglycan (PGN). We further revealed that rTf-hep was capable of agglutinating 6 of the 8 bacteria. All these results suggest that rTf-hep may be both an antibacterial effector and a pattern recognition molecule in fish immune defense. The in vivo bacterial treatment results demonstrated that rTf-Hep could significantly improve the survival rate of fish infected with V. anguillarum. Taken together, these data indicate an important role for Tf-hep in the innate immunity of Trachidermus fasciatus and suggest its potential application in aquaculture for increasing fish resistance to disease.

Immune responses of channel catfish following the stimulation of three recombinant flagellins of Yersinia ruckeri in vitro and in vivo

Innate immunity is initiated depending on the recognition of certain protein receptors termed pattern recognition receptors (PRRs) of pathogen-associated molecular patterns (PAMPs) to protect the host from various invading pathogens. As one of the most powerful PAMPs, flagellin is the major structural component of the flagellum that provides the main force for bacterial motility in flagellated microorganisms. The genome of the Y. ruckeri strain SC09 contains three flagellin genes, which encode the flagellins FlaA, FlaB and FlaC, respectively. In this study, we produced the three full-length recombinant flagellins-i.e., rFlaA, rFlaB and rFlaC-from the Y. ruckeri strain SC09 for the first time and then compared the host cell responses to rFlaA, rFlaB and rFlaC using channel catfish cultured head kidney monocytes/macrophages in vitro. Moreover, the time-dependent modulation of the nine genes expression of primary kidneys injected with rFlaC was also detected by qPCR. We found that rFlaA, rFlaB and rFlaC all can stimulate the production of some pro-inflammatory cytokines, such as IL1-β1, TNFα, IL8, iNOS1 and Hepcidin. In addition, the expression of TLR5M, TLR5S, NF-κB and MHC II β was all increased after channel catfish cultured head kidney monocytes/macrophages were stimulated by the three recombinant flagellins. Importantly, rFlaC stimulated the highest expression of all the genes mentioned above compared with that of rFlaB and rFlaA and enhanced the expression of the nine above-mentioned genes in vivo. Our study lays the foundation for the effect of flagellin on immune responses, suggesting that flagellin may be a useful immune adjuvant or stimulant in the aquaculture field.

Antimicrobial Peptides as Mediators of Innate Immunity in Teleosts

Antimicrobial peptides (AMPs) have been identified throughout the metazoa suggesting their evolutionarily conserved nature and their presence in teleosts is no exception. AMPs are short (18–46 amino acids), usually cationic, amphipathic peptides. While AMPs are diverse in amino acid sequence, with no two AMPs being identical, they collectively appear to have conserved functions in the innate immunity of animals towards the pathogens they encounter in their environment. Fish AMPs are upregulated in response to pathogens and appear to have direct broad-spectrum antimicrobial activity towards both human and fish pathogens. However, an emerging role for AMPs as immunomodulatory molecules has become apparent—the ability of AMPs to activate the innate immune system sheds light onto the multifaceted capacity of these small peptides to combat pathogens through direct and indirect means. Herein, this review focuses on the role of teleost AMPs as modulators of the innate immune system and their regulation in response to pathogens or other exogenous molecules. The capacity to regulate AMP expression by exogenous factors may prove useful in modulating AMP expression in fish to prevent disease, particularly in aquaculture settings where crowded conditions and environmental stress pre-dispose these fish to infection.

A New Membrane Lipid Raft Gene SpFLT-1 Facilitating the Endocytosis of Vibrio alginolyticus in the Crab Scylla paramamosain

Pathogens can enter their host cells by way of endocytosis in which the membrane lipid raft gene flotillins are probably involved in the invasion process and this is an important way to cause infection. In this study, a new gene SpFLT-1 was identified in Scylla paramamosain, which shared high identity with the flotillin-1 of other species. The SpFLT-1 gene was widely distributed in tissues and showed the highest level of mRNA transcripts in the hemocytes. This gene might be a maternal gene based on the evident results that it was highly expressed in maternal ovaries and in the early developmental stages of the zygote and early embryo stage whereas it gradually decreased in zoea 1. SpFLT-1 positively responded to the challenge of Vibrio alginolyticus with a significantly increased level of mRNA expression in the hemocytes and gills at 3 hours post infection (hpi). The SpFLT-1 protein was detected densely in the same fraction layer where the Vibrio protein was most present in the hemocytes and gills at 3 hpi. Furthermore, it was found that the expression of SpFLT-1 decreased to the base level following disappearance of the Vibrio protein at 6 hpi in the gills. Silencing SpFLT-1 inhibited the endocytosis rate of V. alginolyticus but overexpression of the gene could facilitate bacterial entry into the epithelioma papulosum cyprinid cells. Our study indicated that SpFLT-1 may act as a key protein involved in the process of bacterial infection and this sheds light on clarifying the pathogenesis of pathogens infecting S. paramamosain.

Antibacterial products of marine organisms

Marine organisms comprising microbes, plants, invertebrates, and vertebrates elaborate an impressive array of structurally diverse antimicrobial products ranging from small cyclic compounds to macromolecules such as proteins. Some of these biomolecules originate directly from marine animals while others arise from microbes associated with the animals. It is noteworthy that some of the biomolecules referred to above are structurally unique while others belong to known classes of compounds, peptides, and proteins. Some of the antibacterial agents are more active against Gram-positive bacteria while others have higher effectiveness on Gram-negative bacteria. Some are efficacious against both Gram-positive and Gram-negative bacteria and against drug-resistant strains as well. The mechanism of antibacterial action of a large number of the chemically identified antibacterial agents, possible synergism with currently used antibiotics, and the issue of possible toxicity on mammalian cells and tissues await elucidation. The structural characteristics pivotal to antibacterial activity have been ascertained in only a few studies. Demonstration of efficacy of the antibacterial agents in animal models of bacterial infection is highly desirable. Structural characterization of the active principles present in aqueous and organic extracts of marine organisms with reportedly antibacterial activity would be desirable.

On the Functional Overlap between Complement and Anti-Microbial Peptides

Intriguingly, activated complement and anti-microbial peptides share certain functionalities; lytic, phagocytic, and chemo-attractant activities and each may, in addition, exert cell instructive roles. Each has been shown to have distinct LPS detoxifying activity and may play a role in the development of endotoxin tolerance. In search of the origin of complement, a functional homolog of complement C3 involved in opsonization has been identified in horseshoe crabs. Horseshoe crabs possess anti-microbial peptides able to bind to acyl chains or phosphate groups/saccharides of endotoxin, LPS. Complement activity as a whole is detectable in marine invertebrates. These are also a source of anti-microbial peptides with potential pharmaceutical applicability. Investigating the locality for the production of complement pathway proteins and their role in modulating cellular immune responses are emerging fields. The significance of local synthesis of complement components is becoming clearer from in vivo studies of parenchymatous disease involving specifically generated, complement-deficient mouse lines. Complement C3 is a central component of complement activation. Its provision by cells of the myeloid lineage varies. Their effector functions in turn are increased in the presence of anti-microbial peptides. This may point to a potentiating range of activities, which should serve the maintenance of health but may also cause disease. Because of the therapeutic implications, this review will consider closely studies dealing with complement activation and anti-microbial peptide activity in acute inflammation (e.g., dialysis-related peritonitis, appendicitis, and ischemia).

Transcriptome analysis of the effect of Vibrio alginolyticus infection on the innate immunity-related complement pathway in Epinephelus coioides

Background

Orange-spotted grouper (Epinephelus coioides) with protogynous hermaphroditic features are one of the most economically important aquaculture species in Taiwan. However, larvae stage grouper are susceptible to infection by the bacterial pathogen Vibrio alginolyticus. To better understand the molecular mechanisms of the immune response to V. alginolyticus in Epinephelus coioides larvae, we used high-throughput deep sequencing technology to study the effect of infection on gene expression.

Results

A total of 114,851,002 reads were assembled, consisting of 9,687,355,560 nucleotides; these were further assembled into 209,082 contigs with a mean length of 372 bp. Gene ontology (GO) analysis of the transcriptome revealed 12 cellular component subcategories, 16 molecular function subcategories, and 42 biological process subcategories (P value <0.05). A total of 32664 Epinephelus coioides genes were mapped to the Kyoto Encyclopedia of Genes and Genomes (KEGG); 1504 differentially expressed genes (DEGs) were subsequently identified, in 12 categories (P value <0.05). Vibrio infection affected the expression of genes involved in complementation, coagulation cascades, pathogen (Staphylococcus aureus) infection, phagosome activity, antigen processing, and the antigen presentation pathway.

Conclusion

We conclude that the complement pathway of innate immunity and the hepicidin antimicrobial peptide may play important roles in the defense of Epinephelus coioides larvae against V. alginolyticus, and the immune response may activate at 4 h after bacterial infection. These results implicate the complement pathway signal pathway in immunity during V. alginolyticus infection at early developmental stages, enhancing our understanding of the mechanisms underlying the immune response to Vibrio infection in Epinephelus coioides.

Electronic supplementary material

The online version of this article (doi:10.1186/1471-2164-15-1102) contains supplementary material, which is available to authorized users.

Expression and purification of soluble porcine cystatin 11 in Pichia pastoris

Cystatin 11 (CST11) belongs to the cystatin type 2 family of cysteine protease inhibitors and exhibits antimicrobial activity in vitro. In this study, we describe the expression and purification of recombinant porcine CST11 in the Pichia pastoris system. We then assess its antimicrobial activity against Escherichia coli, Staphylococcus aureus, Staphylococcus epidermidis, and Bacillus subtilis by liquid growth inhibition assay. Kinetic studies indicate that the recombinant porcine CST11 has high potency against E. coli and S. aureus. Scanning electronic microscope analysis showed that CST11 might be targeting the bacterial membrane and, thus, could potentially be developed as a therapeutic agent for inhibiting microbe infection without the risk of antibiotic resistance.

Epinecidin-1 has immunomodulatory effects, facilitating its therapeutic use in a mouse model of Pseudomonas aeruginosa sepsis

Antimicrobial peptides (AMPs) are garnering attention as possible alternatives to antibiotics. Here, we describe the antimicrobial properties of epinecidin-1 against a multidrug-resistant clinical isolate of P. aeruginosa (P. aeruginosa R) and a P. aeruginosa strain from ATCC (P. aeruginosa ATCC 19660) in vivo. The MICs of epinecidin-1 against P. aeruginosa R and P. aeruginosa ATCC 19660 were determined and compared with those of imipenem. Epinecidin-1 was found to be highly effective at combating peritonitis infection caused by P. aeruginosa R or P. aeruginosa ATCC 19660 in mouse models, without inducing adverse behavioral effects or liver or kidney toxicity. Taken together, our results indicate that epinecidin-1 enhances the rate of survival of mice infected with the bacterial pathogen P. aeruginosa through both antimicrobial and immunomodulatory effects.

Turbot (Scophthalmus maximus) hepcidin-1 and hepcidin-2 possess antimicrobial activity and promote resistance against bacterial and viral infection

Hepcidin is an antimicrobial peptide and a regulator of iron homeostasis. In turbot (Scophthalmus maximus), two types of hepcidins have been identified, which share approximately 50% sequence identity. In this study, we examined the antimicrobial potentials of the two hepcidins in the form of synthesized peptides, SmHep1P and SmHep2P. We found that SmHep1P and SmHep2P exhibited apparent bactericidal activities against both Gram-positive and Gram-negative bacteria in a dose-dependent manner. The bactericidal effect of SmHep1P was stronger against Gram-positive bacteria, while the bactericidal effect of SmHep2P was stronger against Gram-negative bacteria. Fluorescence and electron microscopy showed that both peptides were able to bind to the target bacterial cells and alter the surface structure of the cells. In vitro studies showed that SmHep1P and SmHep2P reduced bacterial invasion into cultured fish cells. In vivo studies showed that turbot administered with SmHep1P and SmHep2P exhibited significantly enhanced resistance against bacterial and viral infection. In both in vivo and in vitro studies, the antimicrobial activities of SmHep2P were in most cases significantly stronger than those of SmHep1P. Together these results indicate that the two hepcidins of turbot most likely possess antimicrobial properties and play a role in the innate immune defense against bacterial and viral pathogens.

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.