Dietary supplementation of recombinant antimicrobial peptide Epinephelus lanceolatus piscidin improves growth performance and immune response in Gallus gallus domesticus

The modulation of intestinal commensal bacteria possibly contributes to the growth and immunity promotion in Epinephelus akaara after feeding the antimicrobial peptide Scy-hepc

BACKGROUND

Our previous study revealed that feeding the antimicrobial peptide (AMP) product Scy-hepc significantly enhances the growth of mariculture fish through the activation of the GH-Jak2-STAT5-IGF1 axis. However, the contribution of gut microbiota to this growth enhancement remains unclear. This study aimed to elucidate the potential mechanism involved in intestinal absorption and modulation of gut microbiota in Epinephelus akaara following Scy-hepc feeding.

RESULTS

The results showed that a 35 day regimen of Scy-hpec markedly promoted the growth of E. akaara compared to groups supplemented with either florfenicol, B. subtilis, or a vector. The growth enhancement is likely attributed to alterations in microbiota colonization in the foregut and midgut, characterized by an increasing abundance of potential probiotics (Rhizobiaceae and Lysobacter) and a decreased abundance of opportunistic pathogens (Psychrobacter and Brevundimonas) as determined by 16S rRNA analysis. Additionally, similar to the effect of florfenicol feeding, Scy-hepc significantly improved host survival rate by over 20% in response to a lethal dose challenge with Edwardsiella tarda. Further investigations demonstrated that Scy-hepc is absorbed by the fish foregut (20-40 min) and midgut (20-30 min) as confirmed by Western blot, ELISA, and Immunofluorescence. The absorption of Scy-hepc affected the swimming, swarming and surfing motility of Vibrio harveyi and Bacillus thuringiensis isolated from E. akaara's gut. Moreover, Scy-hepc induced the downregulation of 40 assembly genes and the upregulation expression of 5, with the most significant divergence in gene expression between opportunistic pathogens and probiotics concentrated in their motility genes (PomA/B, MotA/B).

CONCLUSIONS

In summary, this study shows that feeding AMP Scy-hepc can promote growth and bolster immunity in E. akaara. These beneficial effects are likely due to the absorption of Scy-hepc in the fish's foregut and midgut, which modulates the colonization and motility of commensal bacteria, leading to favorable changes in the composition of the foregut and midgut microbiota. Therefore, a profound understanding of the mechanisms by which antimicrobial peptides affect host gut microbiota will contribute to a comprehensive assessment of their advantages and potential application prospects as substitutes for antibiotics in fish health and improving aquaculture practices.

Application of antimicrobial peptides in the poultry industry

Poultry meat production and exportation contribute significantly to the global economy. However, various infections affect poultry production and consequently affect the economy. Nowadays, antibiotics are widely used in infection treatment and prevention. Antibiotic overuse is problematic because may cause antimicrobial resistance, which can be transferred to humans directly or indirectly, affecting public health. In addition, since antibiotics for animal growth stimulation are banned, it is important to search for new molecules to overcome these difficulties. As an alternative, antimicrobial peptides (AMPs) can show immunomodulatory, antimicrobial, and growth stimulation, which makes these molecules interesting as alternatives to antibiotic use. Studying AMPs can provide new ideas for treating the most important infections that affect poultry. Besides, this can assist in reducing the resistance problem. This review aims to examine recent studies about AMPs used against pathogens that can affect the poultry industry.

Effects of antimicrobial peptides from dietary Hermetia illucens larvae on the growth, immunity, gene expression, intestinal microbiota and resistance to Aeromonas hydrophila of juvenile red claw crayfish (Cherax quadricarinatus)

Antimicrobial peptides (AMPs), which are widely present in animals and plants, have a broad distribution, strong broad-spectrum antibacterial activity, low likelihood of developing drug resistance, high thermal stability and antiviral properties. The present study investigated the effects of adding AMPs from Hermetia illucens larvae on the growth performance, muscle composition, antioxidant capacity, immune response, gene expression, antibacterial ability and intestinal microbiota of Cherax quadricarinatus (red claw crayfish). Five experimental diets were prepared by adding 50 (M1), 100 (M2), 150 (M3) and 200 (M4) mg/kg of crude AMP extract from H. illucens larvae to the basal diet feed, which was also used as the control (M0). After an eight-week feeding experiment, it was discovered that the addition of 100-150 mg/kg of H. illucens larvae AMPs to the feed significantly improved the weight gain rate and specific growth rate of C. quadricarinatus. Furthermore, the addition of H. illucens larvae AMPs to the feed had no significant effect on the moisture content, crude protein, crude fat and ash content of the C. quadricarinatus muscle. The addition of 100-150 mg/kg of H. illucens larvae AMPs in the feed also increased the antioxidant capacity, nonspecific immune enzyme activity and related gene expression levels in C. quadricarinatus, thereby enhancing their antioxidant capacity and immune function. The H. illucens larvae AMPs improved the structure and composition of the intestinal microbiota of C. quadricarinatus, increasing the microbial community diversity of the crayfish gut. Finally, the addition of 100-150 mg/kg of H. illucens larvae AMPs in the feed enhanced the resistance of C. quadricarinatus against Aeromonas hydrophila, improving the survival rate of the crayfish. Based on the aforementioned findings, it is recommended that H. illucens larvae AMPs be incorporated into the C. quadricarinatus feed at a concentration of 100-150 mg/kg.

A systematical review on antimicrobial peptides and their food applications

Food safety issues are a major concern in food processing and packaging industries. Food spoilage is caused by microbial contamination, where antimicrobial peptides (APs) provide solutions by eliminating microorganisms. APs such as nisin have been successfully and commonly used in food processing and preservation. Here, we discuss all aspects of the functionalization of APs in food applications. We briefly review the natural sources of APs and their native functions. Recombinant expression of APs in microorganisms and their yields are described. The molecular mechanisms of AP antibacterial action are explained, and this knowledge can further benefit the design of functional APs. We highlight current utilities and challenges for the application of APs in the food industry, and address rational methods for AP design that may overcome current limitations.

Supplementing artemisinin positively influences growth, antioxidant capacity, immune response, gut health and disease resistance against Vibrio parahaemolyticus in Litopenaeus vannamei fed cottonseed protein concentrate meal diets

Artemisinin (ART) is a kind of Chinese herbal medicine worth exploring, which obtains various physiological activities. In order to study the prebiotic effect of ART on Litopenaeus vannamei fed cottonseed protein concentrate meal diets, six groups of isonitrogenous and isolipid diets were prepared (including the fish meal control group, FM; cottonseed protein concentrate replacing 30% fishmeal protein and supplementing ART groups: ART0, ART0.3, ART0.6, ART0.9, and ART1.2). The feeding trials was lasted for 56 days. The results showed that the final body weight, weight gain and specific growth rate of the ART0.6 group were the highest, yet the feed coefficient rate of the ART0.6 group was the lowest significantly (P < 0.05). There was no significant difference in survival rate among treatments (P > 0.05). In serum, the content of malondialdehyde in ART0 group was the highest (P < 0.05); the activities of superoxide dismutase, catalase, phenol oxidase and lysozyme increased firstly and then decreased among the ARTs groups (P < 0.05). The activities of intestinal digestive enzymes (including the trypsin, lipase and amylase) showed an upward trend among the ARTs groups (P < 0.05). The histological sections showed that the intestinal muscle thickness, fold height and fold width in the FM group were significantly better than those in the ART0 group; while the mentioned above morphological indexes in the ART0 group were significantly lowest among the ARTs groups (P < 0.05). Sequencing of intestinal microbiota suggested that the microbial richness indexes firstly increased and then decreased (P < 0.05); the bacterial community structure of each treatment group was almost close; the relative abundance of pathogenic bacteria decreased significantly (P < 0.05), such as the Proteobacteria and Cyanobacteria at phylum level, besides the Vibrio and Candidatus Bacilloplasma at genus level. In intestinal tissue, the relative expression levels of TOLL1, TRAF6 and Pehaeidih3 showed up-regulated trends, while the expression of Crustin and LZM firstly up-regulated and then down-regulated (P < 0.05). The challenge experiment suggested that the cumulative mortality of FM group was significantly lower than that of ART0 group; besides the cumulative mortality firstly increased and then decreased between the ARTs groups (P < 0.05). In conclusion, the dietary supplementation of ART can improve the growth, antioxidant capacity, immune response, gut health and disease resistance of the shrimp. To be considered as a dietary immune enhancer, the recommended supplementation level of ART in shrimp's cottonseed protein concentrate meal diets is 0.43%.

Zambrano-Rodríguez P. The Use of Peptides in Veterinary Serodiagnosis of Infectious Diseases: A Review

Peptides constitute an alternative and interesting option to develop treatments, vaccines, and diagnostic tools as they demonstrate their scope in several health aspects; as proof of this, commercial peptides for humans and animals are available on the market and used daily. This review aimed to know the role of peptides in the field of veterinary diagnosis, and include peptide-based enzyme-linked immunosorbent assay (pELISA), lateral flow devices, and peptide latex agglutination tests that have been developed to detect several pathogens including viruses and bacteria of health and production relevance in domestic animals. Studies in cattle, small ruminants, dogs, cats, poultry, horses, and even aquatic organisms were reviewed. Different studies showed good levels of sensitivity and specificity against their target, moreover, comparisons with commercial kits and official tests were performed which allowed appraising their performance. Chemical synthesis, recombinant DNA technology, and enzymatic synthesis were reviewed as well as their advantages and drawbacks. In addition, we discussed the intrinsic limitations such as the small size or affinity to polystyrene membrane and mention several strategies to overcome these problems. The use of peptides will increase in the coming years and their utility for diagnostic purposes in animals must be evaluated.

Effects of recombinant anti-lipopolysaccharide factor expressed by Pichia pastoris on the growth performance, immune response and disease resistance of Litopenaeusvannamei

The codon-optimized anti-lipopolysaccharide factor (ALF) sequence was introduced into pPICZαA vector and transformed into Pichia pastoris GS115. The recombinant ALF yeast supernatant (rALF-mix) was freeze-dried and evaluated as a feed additive for Litopenaeus vannamei. It was found by antibacterial activity test in vitro that the rALF-mix had antibacterial activity under different pH and temperature conditions. The 0, 0.00375%, 0.0075%, 0.015%, 0.03% and 0.06% of rALF-mix were added respectively to make the six experimental diets. After a 10-week feeding trial with shrimps (2.36 ± 0.02 g), it was found that the weight gain rate (WGR) and protein efficiency ratio (PER) of shrimp in the groups with 0.0075%, 0.015% and 0.03% of dietary rALF-mix supplementation were significantly higher than those in the control group (P < 0.05). Dietary rALF-mix supplementation significantly increased the total haemocyte count, respiratory burst, phagocytic activity, total anti-oxidative capacity (T-AOC), phenol oxidase activity, nitric oxide synthase activity, lysozyme (LYZ) activity, serum antibacterial capacity in the hemolymph and the T-AOC, LYZ in the hepatopancreas of shrimps (P < 0.05). The malondialdehyde contents in hemolymph and hepatopancreas were significantly decreased (P < 0.05). Meanwhile, the expression levels of toll, immune deficiency, heat shock protein 70, crustin and lipopolysaccharide-β-glucan binding protein in the gill of shrimps were significantly increased (P < 0.05). After the challenge test, it was showed that dietary rALF-mix supplementation significantly improved the resistance of L. vannamei to Vibrio parahaemolyticus (P < 0.05). In conclusion, the rALF-mix can be used as a functional feed additive to improve the growth, immunity and disease resistance of shrimp. Based on the quadratic regression analysis for WGR, the optimal supplemental level of rALF-mix in diet for shrimp was estimated to be 0.02813%.

Insights in the Development and Uses of Alternatives to Antibiotic Growth Promoters in Poultry and Swine Production

The overuse and misuse of antibiotics has contributed to the rise and spread of multidrug-resistant bacteria. To address this global public health threat, many countries have restricted the use of antibiotics as growth promoters and promoted the development of alternatives to antibiotics in human and veterinary medicine and animal farming. In food-animal production, acidifiers, bacteriophages, enzymes, phytochemicals, probiotics, prebiotics, and antimicrobial peptides have shown hallmarks as alternatives to antibiotics. This review reports the current state of these alternatives as growth-promoting factors for poultry and swine production and describes their mode of action. Recent findings on their usefulness and the factors that presently hinder their broader use in animal food production are identified by SWOT (strength, weakness, opportunity, and threat) analysis. The potential for resistance development as well as co- and cross-resistance with currently used antibiotics is also discussed. Using predetermined keywords, we searched specialized databases including Scopus, Web of Science, and Google Scholar. Antibiotic resistance cannot be stopped, but its spreading can certainly be hindered or delayed with the development of more alternatives with innovative modes of action and a wise and careful use of antimicrobials in a One Health approach.

Biological Functions and Applications of Antimicrobial Peptides

Abstract:

Despite antimicrobial resistance, which is attributed to the misuse of broad-spectrum antibiotics, antibiotics can indiscriminately kill pathogenic and beneficial microorganisms. These events disrupt the delicate microbial balance in both humans and animals, leading to secondary infections and other negative effects. Antimicrobial peptides (AMPs) are functional natural biopolymers in plants and animals. Due to their excellent antimicrobial activities and absence of microbial resistance, AMPs have attracted enormous research attention. We reviewed the antibacterial, antifungal, antiviral, antiparasitic, as well as antitumor properties of AMPs and research progress on AMPs. In addition, we highlighted various recommendations and potential research areas for their progress and challenges in practical applications.

Multiple roles of ribosomal antimicrobial peptides in tackling global antimicrobial resistance

In the last century, conventional antibiotics have played a significant role in global healthcare. Antibiotics support the body in controlling bacterial infection and simultaneously increase the tendency of drug resistance. Consequently, there is a severe concern regarding the regression of the antibiotic era. Despite the use of antibiotics, host defence systems are vital in fighting infectious diseases. In fact, the expression of ribosomal antimicrobial peptides (AMPs) has been crucial in the evolution of innate host defences and has been irreplaceable to date. Therefore, this valuable source is considered to have great potential in tackling the antimicrobial resistance (AMR) crisis. Furthermore, the possibility of bacterial resistance to AMPs has been intensively investigated. Here, we summarize all aspects related to the multiple applications of ribosomal AMPs and their derivatives in combating AMR.

An IL-1β homologue induced inflammation and antibacterial immune defense in Siberian sturgeon (Acipenser baeri)

Interleukin-1β is a key pro-inflammatory cytokine functioning in initiation of inflammatory responses against bacterial- and viral-infections. In the present study, a putative IL-1β counterpart was identified from Siberian sturgeon (Acipenser baeri) and designated as AbIL-1β. The Abil-1β cDNA sequence consists of 1130 bp with an open reading frame (ORF) of 585 bp, which encodes a 194 amino acid (aa) protein. Multiple amino acid sequence alignment revealed that a possible mature peptide could start at Leu¹⁸, although no cut site for ICE (IL-1β converting enzyme) enzyme was present in Siberian sturgeon IL-1β. Even if AbIL-1β shares a relative low identity (33.6%) with another sturgeon type II IL-1β gene from Acipenser dabryanus, they still clustered together in phylogenetic tree. Endogenous Abil-1β was highly expressed in brain, blood, head kidney and spleen of healthy Siberian sturgeon, and remarkably up regulated in head kidney, spleen, and liver upon Aeromonas hydrophila (A.h) challenge. Consistently, in vitro stimulation test using heat-killed A.h and LPS significantly increased Abil-1β transcripts of primary spleen cells. To investigate the bactericidal capability of AbIL-1β, recombinant AbIL-1β (rAbIL-1β) was generated by prokaryotes. Pre-injection of rAbIL-1β reduced the bacterial load in sturgeon spleen after A.h infection. Further, rAbIL-1β was served as feed additive and demonstrated to enhance hybrid sturgeon's defense against A.h infection by increased expressional levels of immune-related genes (IL-1β, IL-6, IL-8, IgM and MHCIIβ), elevated activities of serum lysosome, ACH50, and MPO, as well as higher percent survival. In summary, the current results suggested that AbIL-1β functions in immune regulation and could improve sturgeon's resistance to bacterial infection.

Antimicrobial peptides (AMPs): A promising class of antimicrobial compounds

Antimicrobial peptides (AMPs) are compounds, which have inhibitory activity against microorganisms. In the last decades, AMPs have become powerful alternative agents that have met the need for novel anti-infectives to overcome increasing antibiotic resistance problems. Moreover, recent epidemics and pandemics are increasing the popularity of AMPs, due to the urgent necessity for effective antimicrobial agents in combating the new emergence of microbial diseases. AMPs inhibit a wide range of microorganisms through diverse and special mechanisms by targeting mainly cell membranes or specific intracellular components. In addition to extraction from natural sources, AMPs are produced in various hosts using recombinant methods. More recently, the synthetic analogues of AMPs, designed with some modifications, are predicted to overcome the limitations of stability, toxicity and activity associated with natural AMPs. AMPs have potential applications as antimicrobial agents in food, agriculture, environment, animal husbandry and pharmaceutical industries. In this review, we have provided an overview of the structure, classification and mechanism of action of AMPs, as well as discussed opportunities for their current and potential applications.

Antimicrobial peptides used as growth promoters in livestock production

Antibiotic growth promoters (AGPs) have been administered in livestock for decades to improve food digestion in growing animals, while also contributing to the control of microbial pathogens. The long-term and indiscrimate use of AGPs has generated genetic modifications in bacteria, leading to antimicrobial resistance (AMR), which can be disseminated to commensal and pathogenic bacteria. Thus, antimicrobial peptides (AMPs) are used to replaced AGPs. AMPs are found in all domains of life, and their cationic characteristics can establish electrostatic interactions with the bacterial membrane. These molecules used as growth promoters can present benefits for nutrient digestibility, intestinal microbiota, intestinal morphology, and immune function activities. Therefore, this review focuses on the application of AMPs with growth promoting potential in livestock, as an alternative to conventional antibiotic growth promoters, in an attempt to control AMR. KEY POINTS: • The long-term and indiscriminate use of AGPs in animal food can cause AMR. • AMPs can be used as substitute of antibiotics in animal food suplementation. • Animal food suplementated with AMPs can provied economic efficiency and sustainable livestock production.

Peptides Affecting the Outer Membrane Lipid Asymmetry System (MlaA-OmpC/F) Reduce Avian Pathogenic Escherichia coli (APEC) Colonization in Chickens

Avian pathogenic Escherichia coli (APEC), an extraintestinal pathogenic E. coli (ExPEC), causes colibacillosis in chickens and is reportedly associated with urinary tract infections and meningitis in humans. Development of resistance is a major limitation of current ExPEC antibiotic therapy. New antibacterials that can circumvent resistance problem such as antimicrobial peptides (AMPs) are critically needed. Here, we evaluated the efficacy of Lactobacillus rhamnosus GG (LGG)-derived peptides against APEC and uncovered their potential antibacterial targets. Three peptides (NPSRQERR [P1], PDENK [P2], and VHTAPK [P3]) displayed inhibitory activity against APEC. These peptides were effective against APEC in biofilm and chicken macrophage HD11 cells. Treatment with these peptides reduced the cecum colonization (0.5 to 1.3 log) of APEC in chickens. Microbiota analysis revealed two peptides (P1 and P2) decreased Enterobacteriaceae abundance with minimal impact on overall cecal microbiota of chickens. Bacterial cytological profiling showed peptides disrupt APEC membranes either by causing membrane shedding, rupturing, or flaccidity. Furthermore, gene expression analysis revealed that peptides downregulated the expression of ompC (>13.0-fold), ompF (>11.3-fold), and mlaA (>4.9-fold), genes responsible for the maintenance of outer membrane (OM) lipid asymmetry. Consistently, immunoblot analysis also showed decreased levels of OmpC and MlaA proteins in APEC treated with peptides. Alanine scanning studies revealed residues crucial (P1, N, E, R and P; P2, D and E; P3, T, P, and K) for their activity. Overall, our study identified peptides with a new antibacterial target that can be developed to control APEC infections in chickens, thereby curtailing poultry-originated human ExPEC infections. IMPORTANCE Avian pathogenic Escherichia coli (APEC) is a subgroup of extraintestinal pathogenic E. coli (ExPEC) and considered a foodborne zoonotic pathogen transmitted through consumption of contaminated poultry products. APEC shares genetic similarities with human ExPECs, including uropathogenic E. coli (UPEC) and neonatal meningitis E. coli (NMEC). Our study identified Lactobacillus rhamnosus GG (LGG)-derived peptides (P1 [NPSRQERR], P2 [PDENK], and P3 [VHTAPK]) effective in reducing APEC infection in chickens. Antimicrobial peptides (AMPs) are regarded as ideal candidates for antibacterial development because of their low propensity for resistance development and ability to kill resistant bacteria. Mechanistic studies showed peptides disrupt the APEC membrane by affecting the MlaA-OmpC/F system responsible for the maintenance of outer membrane (OM) lipid asymmetry, a promising new druggable target to overcome resistance problems in Gram-negative bacteria. Altogether, these peptides can provide a valuable approach for development of novel anti-ExPEC therapies, including APEC, human ExPECs, and other related Gram-negative pathogens. Furthermore, effective control of APEC infections in chickens can curb poultry-originated ExPEC infections in humans.

Effects of mixed antimicrobial peptide on the growth performance, antioxidant and immune responses and disease resistance of Pengze crucian carp (Carassius auratus var. Pengze)

Antimicrobial peptides have broad-spectrum antibacterial properties and low drug resistance, and they demonstrate great potential as antibiotic substitutes. In this study, five dietary mixed antimicrobial peptide supplement groups were set and fed to Pengze crucian carp for 10 weeks. The 6 groups were G0 (control group) and 5 additional groups: G1 (100 mg/kg), G2 (200 mg/kg), G3 (400 mg/kg), G4 (800 mg/kg) and G5 (1600 mg/kg). The results showed that the final body weight (FBW), weight gain rate (WGR) and specific growth rate (SGR) of fish in G1 and G2 were higher than those of fish in the control group, and G1 was significantly higher than G0 (P < 0.05). In addition, the FBW, WGR, and SGR of the G3 group were significantly lower than those of the G0 group. The chymotrypsin, lipase and amylase activities of G1 and G2 were significantly upregulated compared with G0 and reached peak values in G1. The activity of T-AOC and SOD in the addition group was higher (except G2 and G4) than that in the control groups, and significantly increased in G3 compared to the control group. The activity of MDA in the addition group was lower than that in the control group (p > 0.05). The expression levels of TLR-4, MYD88 and TNF-α in the three organs of the addition group were higher than those in G0 and reached the peak value in G3 (p < 0.05). Furthermore, the expression levels of TLR-4, MYD88 and TNF-α in the three organs of G3 were significantly lower than those in G0 and lower than those in the other supplemented groups. The expression levels of IL-10 and IL-11 tended to be upregulated after A. hydrophila challenge, and G3 in different organs was significantly higher than that in other supplemented groups and G0. The results of this study show that an appropriate amount of mixed antimicrobial peptides can improve the growth performance and antioxidant and immune capabilities of Pengze crucian carp and can also play a positive role in the treatment of A. hydrophila infection.

Challenge in the Discovery of New Drugs: Antimicrobial Peptides against WHO-List of Critical and High-Priority Bacteria

Bacterial resistance has intensified in recent years due to the uncontrolled use of conventional drugs, and new bacterial strains with multiple resistance have been reported. This problem may be solved by using antimicrobial peptides (AMPs), which fulfill their bactericidal activity without developing much bacterial resistance. The rapid interaction between AMPs and the bacterial cell membrane means that the bacteria cannot easily develop resistance mechanisms. In addition, various drugs for clinical use have lost their effect as a conventional treatment; however, the synergistic effect of AMPs with these drugs would help to reactivate and enhance antimicrobial activity. Their efficiency against multi-resistant and extensively resistant bacteria has positioned them as promising molecules to replace or improve conventional drugs. In this review, we examined the importance of antimicrobial peptides and their successful activity against critical and high-priority bacteria published in the WHO list.

Development of EST-Molecular Markers from RNA Sequencing for Genetic Management and Identification of Growth Traits in Potato Grouper (Epinephelus tukula)

Simple Summary

The potato grouper is a novel aquaculture species in Taiwan. Due to the lack of genetic information concerning this species, we have developed molecular markers based on transcriptome sequencing and further characterized their association with gene diversity and growth traits of this species. Ultimately, these markers could be utilized as accurate and efficient tools for genetic management and marker-assisted selection of potato grouper with distinct growth traits.

Abstract

The accuracy and efficiency of marker-assisted selection (MAS) has been proven for economically critical aquaculture species. The potato grouper (Epinephelus tukula), a novel cultured grouper species in Taiwan, shows large potential in aquaculture because of its fast growth rate among other groupers. Because of the lack of genetic information for the potato grouper, the first transcriptome and expressed sequence tag (EST)-derived simple sequence repeat (SSR) and single nucleotide polymorphism (SNP) markers were developed. Initially, the transcriptome was obtained from seven cDNA libraries by using the Illumina platform. De novo transcriptome of the potato grouper yielded 51.34 Gb and 111,490 unigenes. The EST-derived SSR and SNP markers were applied in genetic management, in parentage analysis, and to discover the functional markers of economic traits. The F₁ juveniles were identified as siblings from one pair of parents (80 broodstocks). Fast- and slow-growth individuals were analyzed using functional molecular markers and through their association with growth performance. The results revealed that two SNPs were correlated with growth traits. The transcriptome database obtained in this study and its derived SSR and SNP markers may be applied not only for MAS but also to maintain functional gene diversity in the novel cultured grouper.

Effects of compound antimicrobial peptides on the growth performance, antioxidant and immune responses and disease resistance of grass carp (Ctenopharyngodon idellus)

In this study, the compound antimicrobial peptides was added to the basic diet to probe its effects on grass carp for 8 weeks. There were 6 groups in our study, including M0 (0 mg/kg) and 5 additional groups: M1 (100 mg/kg), M2 (200 mg/kg), M3 (400 mg/kg), M4 (800 mg/kg) and M5 (1600 mg/kg). The results are as follows: (1) The grass carp's FBW, WGR and SGR in M4 were significantly increased than M0 (p < 0.05). (2) In the hepatopancreas, the amylase activity of M2, M3 and M5 were significant up-regulation than other groups (p < 0.05). (3) The activity of T-AOC in the M3 and M4 was significantly higher compared to the other groups in grass carp hepatopancreas, while MDA was significantly reduced compared to the control group (p < 0.05). The activity of SOD in M5 was significantly increased than the other groups (p < 0.05). (4) The expression of MnSOD (except head kidney), IL8 and TNF-α and IL-1β (except hepatopancreas) were significantly increased (p < 0.05), while TGF-β and were significantly reduced in the hepatopancreas, spleen and head kidney at M3 (p < 0.05), and IL10 were significantly decreased in the hepatopancreas at M3 (p < 0.05). In addition, expression of IL8 and TNF-α were significant down-regulation, whereas TGF-β (expect head kidney) were significant up-regulation in hepatopancreas, spleen and head kidney in M3 after challenge with A. hydrophila. The expression of IL-1β in spleen and head kidney were also down-regulated, whereas IL10 were significantly up-regulated in the hepatopancreas at M3 after challenge with A. hydrophila (p < 0.05). The results of this study showed that grass carp fed a diet supplemented compound antimicrobial peptides was added with 400-800 mg/kg, which could improve the growth performance, antioxidant and digestive capabilities, and could also enhance the expression of immune-related genes and control to A. hydrophila.

A Pilot Safety Assessment for Recombinant Epinephelus lanceolatus Piscidin Yeast Powder as a Drug Food Additive after Subacute and Subchronic Administration to SD Rats

Recombinant Epinephelus lanceolatus piscidin (RELP) was previously shown to improve growth performance and immune response when used as a feed additive for Gallus gallus domesticus. However, the long-term toxicity of RELP has not be thoroughly investigated. In the present study, we evaluated the subacute and subchronic oral toxicities of RELP in SD rats by hematological, biochemical, and histopathological analyses. To determine subacute and subchronic toxicities, male and female rats were fed with RELP 1000 mg/kg bodyweight/day for 28 and 90 days, respectively. Bodyweight and food intake were unchanged by RELP treatment over the course of the studies. After exposure, samples of blood, heart, lung, liver, and kidney were collected and analyzed. Results demonstrated that RELP exposure did not cause any observable hematological, biochemical, or histological abnormalities in SD rats. Thus, RELP may be a safe feed additive for use in agriculture and aquaculture.

Piscidin 4: Genetic expression and comparative immunolocalization in Nile tilapia (Oreochromis niloticus) following challenge using different local bacterial strains

The antimicrobial activity of tilapia piscidin 4 (TP4) was determined in vitro against four bacterial strains, Aeromonas hydrophilla, Pseudomonas fluorescens, Streptococcus iniae and Vibrio anguillarum. Nile tilapia were infected with low and high doses of the tested pathogens; after 3, 6, 24 h and 7 days of the specific TP4 gene expression, tissue immunolocalization was also performed. Histopathological examination revealed septicaemia and necrosis of hemopoietic tissue for all of the tested bacteria. Immunolocalization showed abundance in S. iniae-infected fish tissues. Quantitative RT-PCR analysis revealed that high doses raised mRNA expression levels compared to low doses and expression levels increased in the infected fish, particularly after 24 h, indicating that TP4 exerts potent bactericidal activity against some fish pathogens and plays an essential role in fish immunity.

Lack of Acute Toxicity and Mutagenicity from Recombinant Epinephelus lanceolatus Piscidin Expressed in Pichia pastoris

The antimicrobial peptide (AMP) piscidin was identified from Epinephelus lanceolatus and demonstrated to possess antimicrobial and immune-related functions. Supplementation of feed with recombinant Epinephelus lanceolatus piscidin (rEP)-expressing yeast pellets may minimize the excessive use of antibiotics and control pathogens in aquaculture or animal husbandry. However, before implementing rEP as a supplement, it is necessary to understand whether it harbors any toxicity. Since toxicological information on the topic is scarce, the present investigation was carried out to test whether rEP exhibits allergenic and/or toxic effects. In an oral acute toxicity test (OECD 425), Sprague Dawley (SD) rats were administered rEP dissolved in reverse osmosis water, yielding an LD₅₀ > 5000 mg/kg (no observed animal death). The compound was therefore classified as non-toxic by oral administration. In an acute respiratory toxicity test (OECD 403), heads and noses of SD rats were exposed to liquid aerosol for 4 h (the highest concentration that could be administered without causing any animal death), and a lethal concentration (LC₅₀) > 0.88 mg/L was obtained. The mass medium aerodynamics diameter (MMAD) of rEP aerosol particles was 8.18 μm and mass medium aerodynamics diameter (GSD) was 3.04, which meant that 25.90% could enter the airway (<4 μm) of a rat, and 58.06% (<10 μm) could be inhaled by humans. An ocular irritation test (OECD 405) with rEP powder was performed on New Zealand White (NZW) rabbits. Signs of irritation included conjunctival swelling and diffuse flushing 1 h after administration. The signs were less apparent after 24 h and disappeared after 72 h. The classification assigned to the powder was mild eye irritation. Skin sensitization was performed for a local lymphoproliferative test (OECD 442B) using BALB/c mice, with the highest soluble concentration of the rEP considered to be 100% test substance; formulations were diluted to 50% and 25%, and bromodeoxyuridine (BrdU) incorporation was used to measure the degree of lymphocyte proliferation. The stimulation indexes (SIs) were 1.06 (100%), 0.44 (50%), and 0.77 (25%), all of which were less than the cutoff value for a positive sensitization result (1.6). Negative response was also seen in the bacterial reverse mutation test (OECD 471), and no chromosomal effects on Chinese hamster ovary (CHO)-K1 cells were observed (OECD 487). Based on these six toxicity tests, rEP showed neither acute toxic effects in experimental animals nor mutagenicity. Thus, rEP can be considered safe for use in subsequent research on its application as a feed additive for poultry, cattle, or aquatic animals.