Antibacterial activity in four marine crustacean decapods

Transcriptome analysis of eyestalk ganglion provides new insights into the immune response of Eriocheir sinensis

Generally, eyestalk ganglion is regarded as a basic neuroendocrine tissue in decapods. In the past decades, increasing evidence has implied that the nervous system plays important roles in modulating the immune defense against pathogenic microorganisms. However, the molecular mechanisms of nervous system on the innate immunity of decapods remain largely unclear. In this study, we investigated the transcriptomic responses of eyestalk ganglion in Eriocheir sinensis challenged by Vibrio parahaemolyticus. A total of 77 differentially expressed genes (DEGs) were identified, and these DEGs were predicted to be involved in diverse biological pathways including thyroid hormone signaling pathway, peroxisome proliferator-activated receptor (PPAR) signaling pathway, ferroptosis, endocrine system, and neurotrophin signaling pathway. Furthermore, the results indicated that the eyestalk ganglion of E. sinensis could respond to the infection of V. parahaemolyticus by increasing the expression of antibacterial protein such as gillcin and ribosomal protein L27, meanwhile, weakening the inhibition of NF-κB pathway via down-regulating the expression of the suppressor genes such as sterile alpha and TIR motif-containing protein 1 and nicotinic acetylcholine receptor. These findings suggested that V. parahaemolyticus infection triggers the activation of immune response in eyestalk ganglion of E. sinensis, which throws lights on the crucial roles of eyestalk ganglion in crab antibacterial immunity and provides new clues and theoretical basis for disease prevention and control.

Effects of dietary 5-aminolevulinic acid on growth performance and nonspecific immunity of Litopenaeus vannamei, as determined by transcriptomic analysis

5-aminolevulinic acid (5-ALA) is an endogenous non-protein amino acid that is frequently used in modern agriculture. This study set out to determine how dietary 5-ALA affected the nonspecific immunity and growth performance of Litopenaeus vannamei. The shrimp were supplemented with dietary 5-ALA at 0, 15, 30, 45, and 60 mg/kg for three months. Transcriptome data of the control group and the group supplemented with 45 mg/kg dietary 5-ALA were obtained using transcriptome sequencing. 592 DEGs were identified, of which 426 were up-regulated and 166 were down-regulated. The pathways and genes associated with growth performance and nonspecific immunity were confirmed using qRT-PCR. The highest survival rate, body length growth rate, and weight gain values were observed in shrimp fed diets containing 45 mg/kg 5-ALA. L. vannamei in this group had a significantly higher total hemocyte count, phagocytosis rate and respiratory burst value than those in the control group. High doses of dietary 5-ALA (45 mg/kg, 60 mg/kg) significantly increased the activities of catalase, superoxide dismutase, oxidized glutathione, glutathione-peroxidase, phenoloxidase, lysozyme, acid phosphatase, and alkaline phosphatase. At the transcriptional level, dietary 5-ALA significantly up-regulated the expression levels of antioxidant immune-related genes. The optimal concentration of 5-ALA supplementation was 39.43 mg/kg, as indicated by a broken line regression. Our study suggested that dietary 5-ALA positively impacts the growth and nonspecific immunity of L. vannamei, providing a novel theoretical basis for further research into 5-ALA as a dietary supplement.

Effects of dietary melatonin on antioxidant and immune function of the Pacific white shrimp (Litopenaeus vannamei), as determined by transcriptomic analysis

Melatonin (MT) is regarded as an antioxidant and immunostimulant that can efficiently scavenge free radicals and activate antioxidant enzymes. The aim of this study was to investigate the effects of dietary MT on the growth performance and immune function of the Pacific white shrimp (Litopenaeus vannamei). Six groups of L. vannamei were supplemented with dietary MT at 0, 22.5, 41.2, 82.7, 165.1, and 329.2 mg/kg levels for 2 months. RNA-Seq analysis was performed to obtain transcriptome data of the control group and the group supplemented with dietary MT at 82.7 mg/kg BW. In total, 1220 DEGs (799 up-regulated and 421 down-regulated) were identified. Pathways and genes related to growth performance and immune function were verified by real-time quantitative polymerase chain reaction. The total hemocyte count, phagocytosis rate, and respiratory burst were significantly increased in the MT (82.7 mg/kg BW) group as compared to the control group. Analysis of antioxidant-related enzymes in the hepatopancreas showed that dietary MT (82.7 mg/kg BW) significantly increased activities of superoxide dismutase (SOD), glutathione peroxidase (GPx), and catalase, while dietary MT at 41.2 mg/kg BW significantly increased activities of glutathione S-transferase, lysozyme (LZM), and phenoloxidase (PO). At the transcriptional level, dietary MT up-regulated expression levels of genes associated with antioxidant immunity and growth, which included PO, SOD, LZM, GPx, chitin synthase, ecdysone receptor, calcium-calmodulin dependent protein kinase I, and retinoid X receptor. In conclusion, dietary MT may improve the growth performance and immune function of L. vannamei to some extent.

Effects of dietary bile acids levels on growth performance, anti-oxidative capacity, immunity and intestinal microbiota of abalone Haliotis discus hannai

Abalone Haliotis discus hannai (initial weight: 38.79 ± 0.70 g) was used as the experimental animal in a 105-day feeding trial to investigate the influence of dietary bile acids levels on the growth, anti-oxidation, immune response and intestinal microbiota. Six isonitrogenous and isolipidic diets were prepared by adding 0 (control group), 15, 30, 60, 120 and 240 mg/kg of bile acids, respectively (named BA0, BA15, BA30, BA60, BA120 and BA240, respectively). It was found that survival of abalone between groups had no significant difference (P > 0.05). Compared to the control, significant improvements in weight gain rate (WGR) were observed in the groups of BA30 and BA60 (P < 0.05). Based on WGR, the broken line regression model analysis showed that the optimum demand for dietary bile acids for abalone was 35.47 mg/kg. Dietary bile acids increased the total anti-oxidative capacity and activities of catalase, superoxide dismutase, lysozyme and alkaline phosphatase, meanwhile decreased the content of malondialdehyde, alanine aminotransferase and aspartate aminotransferase activities in the cell-free hemolymph (P < 0.05). When bile acids were added to the diets, mRNA levels of genes related to pro-inflammatory factors and apoptosis in the digestive gland were down-regulated (P < 0.05). In contrast, the expression of genes related to anti-oxidation was significantly up-regulated (P < 0.05). The Firmicutes, Actinobacteriota and Proteobacteria were the most abundant phyla in intestine. And dietary bile acids significantly decreased the abundance of Actinobacteria and increased the abundance of Firmicutes (P < 0.05). In conclusion, supplementation of dietary bile acids within 120 mg/kg significantly increased the growth of abalone. The 34.62 mg/kg of dietary bile acids significantly increased the anti-oxidative capacity of abalone. Appropriate levels of dietary bile acids (34.62-61.75 mg/kg) promote the immunity of abalone. Application of appropriate levels of bile acids in diets (34.62 mg/kg) changed the intestinal microbiota and promoted the intestinal health of abalone.

Novel Antimicrobial Peptide from the Hepatopancreas of the Red King Crab

Crustaceans have successfully adapted to survive in their natural habitat, rich in microorganisms, due to the presence of antimicrobial peptides (AMPs) in their organism. They achieve this adaptation despite lacking the highly specific adaptive immune system found in vertebrates. One valuable source of AMPs is the hepatopancreas, a waste product from crab fishery and its processing. Applying zymographic and spectrophotometric techniques, we discovered a small peptide (approximately 5 kDa) within a low molecular weight protein fraction extracted from the acetone powder of the red king crab hepatopancreas. This peptide hydrolyzes both M. lysodeikticus cell wall and M. lysodeikticus cell wall polysaccharide, while showing no activity against gelatin. The found peptide may be of interest for application in medicine, biotechnology, and the food industry, for example as a bio-preservative.

Sub-chronic ammonia exposure induces hepatopancreatic damage, oxidative stress, and immune dysfunction in red swamp crayfish (Procambarus clarkii)

Ammonia, as one of the primary water pollutants in aquaculture, has been shown to induce a wide range of ecotoxicological effects on aquatic animals. In order to investigate the antioxidant and innate immune responses in crustaceans disrupted by ammonia, red swamp crayfish (Procambarus clarkii) were exposed to 0, 15, 30, and 50 mg/L total ammonia nitrogen for 30 d, the alterations of antioxidant responses as well as innate immunity were studied. The results showed that the severity of hepatopancreatic injury were aggravated by the increasing ammonia levels, which were mainly characterized by tubule lumen dilatation and vacuolization. The swollen mitochondria and disappeared mitochondria ridges suggested that oxidative stress induced by ammonia targets the mitochondria. Concurrently, enhanced MDA levels, and decreased GSH levels as well as the decreased transcription and activity of antioxidant enzymes, including SOD, CAT, and GPx were noticed, which suggested that high concentrations of ammonia exposure induce oxidative stress in P. clarkii. Furthermore, a significant decrease of the hemolymph ACP, AKP, and PO along with the significant downregulation of immune-related genes (ppo, hsp70, hsp90, alf1, ctl) jointly indicated that ammonia stress inhibited the innate immune function. Our findings demonstrated that sub-chronic ammonia stress induced hepatopancreatic injury and exert suppressive effects on the antioxidant capacity as well as innate immunity of P. clarkii. Our results provide a fundamental basis for the deleterious effects of ammonia stress on aquatic crustaceans.

Andrographis paniculata improves growth and non-specific immunity of shrimp Litopenaeus vannamei, and protects it from Vibrio alginolyticus by reducing oxidative stress and apoptosis

Andrographis paniculata (AP) is a traditional medicinal plant with many pharmacological activities, including anti-inflammatory, antimicrobial, immunity stimulation and so on. Several studies have reported that AP plays a strong role in promoting the immune system of aquatic animals to resist several pathogens. In the present study, we investigate the effects of a diet containing AP on the immune responses, growth, and the resistance to Vibrio alginolyticus (V. alginolyticus) in Litopenaeus vannamei (L. vannamei). Four diets were formulated by adding AP at the dosage of 0% (Control), 0.25%, 0.5%, and 1% in the basal diet, respectively. Each diet was randomly fed to one group with three replicates of shrimps in a 28-day feeding trial. The results showed that dietary AP improved the growth performance and non-specific immune function of shrimps. To investigate the effect of AP on disease resistance of L. vannamei, shrimps fed with diet containing AP were challenged with V. alginolyticus. Compared with the control group, the shrimps fed diet containing AP showed significantly higher survival. Furthermore, the hepatopancreas injury in the shrimp fed with AP was less than control group at 6 h after V. alginolyticus infection. However, no difference was observed in the degree of hepatopancreas injury between AP groups and control group at 12 h and 24 h after V. alginolyticus infection. Based on this result, the samples at 6 h after V. alginolyticus infection was selected for subsequent detection. Reactive oxygen species (ROS) accumulation in hemocytes and O₂^- production in hepatopancreas caused by V. alginolyticus infection was significantly reduced after feeding a diet containing 0.25% and 0.5% AP (p < 0.05). In addition, we found that feeding AP significantly up-regulated the expression of pro-apoptotic genes (Bax, Caspase 3, p53) and down-regulated the expression of anti-apoptotic genes (Bcl-2) in hepatopancreas after V. alginolyticus infection. In conclusion, AP promote the growth and immunity of L. vannamei, and protects shrimps against V. alginolyticus by regulating the oxidative damage and apoptosis. These results provide useful information regarding the effects of AP extracts as a shrimp feed additive for sustainable shrimp culture.

Effects of berberine hydrochloride on immune response in the crab Charybdis japonica

Berberine hydrochloride is the main effective component of Coptis spp. used in Chinese herbal medicine and its underlying molecular mechanisms, responsible for inducing effects in crustacean species, are not fully understood. In this study, the molecular response of the crab Charybdis japonica to berberine hydrochloride exposure was studied using transcriptome sequencing. The survival rate, gene expression and activities of several immune enzymes were measured after berberine hydrochloride treatments, with or without injection of the pathogenic bacterium Aeromonas hydrophila. A total of 962 differentially expressed genes (464 up-regulated and 498 down-regulated) were observed during exposure to 100 mg/L of berberine hydrochloride and in the control group after 48 h. Enrichment analysis revealed that these genes are involved in metabolism, cellular processes, signal transduction and immune functions, indicating that exposure to berberine hydrochloride activated the immune complement system. This bioactive compound simultaneously activated fibrinogen beta (FGB), fibrinogen alpha (FGA), alpha-2-macroglobulin (A2M), kininogen (KNG), fibrinogen gamma chain (FGB), alpha-2-HS-glycoprotein (AHSG), caspase-8 (CASP8), cathepsin L (CTSL), adenylate cyclase 3 (Adcy3) and MMP1. Its action could significantly increase the survival rate of the crabs injected with A. hydrophila and promote the activity of LZM, Caspas8, FGA, ACP and AKP in the hepatopancreas. When A. hydrophila was added, the neutralization of 300 mg/L berberine hydrochloride maximized the activities of Caspas8, LZM, ACP and AKP. Our results provide a new understanding of the potential effects of berberine hydrochloride on the immune system mechanisms in crustaceans.

Effects of sulfated β-glucan from Saccharomyces cerevisiae on growth performance, antioxidant ability, nonspecific immunity, and intestinal flora of the red swamp crayfish (Procambarus clarkii)

The aim of this study was to examine the combined effects of sulfated β-Glucan from Saccharomyces cerevisiae (sGSC) on growth performance, antioxidant ability, nonspecific immunity, and intestinal flora of the red swamp crayfish (Procambarus clarkii). Four experimental diets (sGSC25, sGSC50, sGSC100 and sGSC200) with different levels of sGSC (0.025%, 0.05%, 0.1% and 0.2% in diet, respectively) were fed to juvenile crayfish (average weight: 2.5 ± 0.5 g) for 8 weeks. The control diet was given with 2000 mg/kg GSC (GSC200 group). The based control diet was given without sGSC or GSC (blank group). Each group had 3 parallel test pools, 20 crayfish were reared in each pool. At the end of the growth trial, adding dietary 0.025%-0.1% sGSC could significantly improve the growth performance, antioxidant capacity and immunity of crayfish. Compared with GSC, sGSC had a better effect at lower concentration. Higher concentration of sGSC (>0.1%) would cause some side effects. sGSC also could improve the structure of the intestinal flora and optimize the function of the flora. sGSC would increase the abundances of probiotics such as Hafnia and Acinetobacter, and decreases the abundances of maleficent bacteria such as Enterobacteriaceae. Higher concentration of sGSC (>0.1%) would increase the abundance of Aeromonas. To conclude, 0.025%-0.1% sGSC can be used as a supplement in crayfish feed to increase growth, immunity, and antioxidant capacity and improve the structure of intestinal flora. These results provided a theoretical basis for the application of sGSC instead of GSC in crayfish breeding. It will be necessary to further study the optimal concentration of sGSC in feed additives in different growth stages of crayfish in the future.

Dietary effects of Clostridium autoethanogenum protein substituting fish meal on growth, intestinal histology and immunity of Pacific white shrimp (Litopenaeus vannamei) based on transcriptome analysis

The study investigated the dietary effects of Clostridium autoethanogenum protein (CAP) substituting fish meal on the growth, intestinal histology, serum immune indexes and transcriptome of Pacific white shrimp, Litopenaeus vannamei. Four isonitrogenous and isolipidic diets were designed as the control diet (CON) containing 560 g/kg fish meal, and three fish meal-substituted diets in which 30% (CAP-30), 45% (CAP-45) and 70% (CAP-70) fish meal were replaced with CAP, respectively. The four diets were fed to shrimp with initial body weight of 2.78 ± 0.13 g for 8 weeks. The results showed that the weight gain, feed intake, survival and intestinal villus height in CAP-45 and CAP-70 groups were lower than those of the control and CAP-30 groups (P < 0.05). In addition, the serum aspartate aminotransferase and phenol oxidase activities in all fish meal-substituted groups, and the lysozyme activity in CAP-45 and CAP-70 groups were increased, while the total protein content in CAP-45 and CAP-70 groups was decreased when compared with the control (P < 0.05). Transcriptome profiling of hepatopancreas indicated that high inclusion of CAP negatively affected the protein synthesis and the utilization of nutrients by regulating pancreas secretion, protein digestion and absorption, ribosome pathways, and disturbed the immune system and metabolic processes by phagosomes and lysosomes pathways, thereby affecting the growth performance and immune function of shrimp. In conclusion, CAP could substitute 30% fish meal in a diet containing 560 g/kg fish meal without adverse effects on the growth, intestinal histology and immunity of Pacific white shrimp.

Identification and characterization of l-amino acid oxidase 2 gene in orange-spotted grouper (Epinephelus coioides)

Recently, l-amino acid oxidases (LAAOs) have been identified in several fish species as first-line defense molecules against bacterial infection. Here, we report the cloning and characterization of a fish LAAO gene, EcLAAO2, from orange-spotted grouper (Epinephelus coioides). The full-length cDNA is 3030 bp, with an ORF encoding a protein of 511 amino acids. EcLAAO2 is mainly expressed in the fin, gill, and intestine. Its expression is upregulated in several immune organs after challenge with lipopolysaccharide (LPS) and poly (I:C). The recombinant EcLAAO2 protein (rEcLAAO2), expressed and purified from a baculovirus expression system, was determined to be a glycosylated dimer. According to a hydrogen peroxide-production assay, the recombinant protein was identified as having LAAO enzyme activity with substrate preference for L-Phe and L-Trp, but not L-Lys as other known fish LAAOs. rEcLAAO2 could effectively inhibit the growth of Vibrio parahaemolyticus, Staphylococcus aureus, and Bacillus subtilis while exhibiting less effective inhibition of the growth of Escherichia coli. Finally, protein models based on sequence homology were constructed to predict the three-dimensional structure of EcLAAO2 as well as to explain the difference in substrate specificity between EcLAAO2 and other reported fish LAAOs. In conclusion, this study identifies EcLAAO2 as a novel fish LAAO with a substrate preference distinct from other known fish LAAOs and reveals that it may function against invading pathogens.

RNase1 can modulate gut microbiota and metabolome after Aeromonas hydrophila infection in blunt snout bream

Pancreatic ribonuclease (RNase1) of Megalobrama amblycephala exhibits both antimicrobial and digestive activity. The gut microbiome improve the digestion and metabolic capacity and enhance the functioning of the immune system of the host against pathogenic bacteria. In this study, we aimed to assess the protective effect of RNase1 on Aeromonas hydrophila-induced inflammation and intestinal microbial metabolism. Megalobrama amblycephala were randomly divided into three groups: control (injected PBS), infection (A. hydrophila-injected), and treatment group (RNase1 pretreatment 24 h before the A. hydrophila injection). The morphological symptoms were significantly alleviated by RNase1. RNase1 reshaped the perturbed gut microbiota by upregulating Proteobacteria and Vibrio richness and downregulating Firmicutes, Chlamydiae, Bacillus, and Gemmobacter richness. The lysophosphatidylcholine, (±) 17 HETE, D- (+) -cellobiose, and PC (20:5) in the treatment group were restored by RNase 1 protein treatment to the level of the control group. In the treatment group, phospholipid metabolism, fatty acid metabolism, glucose metabolism and lipid metabolism were different from the control and infection groups. The proinflammatory factors concentration in intestinal samples significantly increased after A. hydrophila infection. Our results revealed that RNase1 plays an important role in resistance to pathogen invasion, reducing inflammation, and improving intestinal function, thus inhibiting the occurrence of disease.

The Bioactive Potential of Trawl Discard: Case Study from a Crinoid Bed Off Blanes (North-Western Mediterranean)

Although knowledge of the bioactive compounds produced by species inhabiting coastal waters is increasing, little is known about the bioactive potential produced by marine species occupying deeper habitats with high biodiversity and productivity. Here, we investigate about the bioactive potential of molecules produced by species that inhabit the crinoid beds, a poorly known essential fish habitat affected by trawling, wherein large amounts of commercial and noncommercial species are discarded. Based on a trawl survey conducted in 2019, 14% of the 64 species discarded on crinoid beds produce molecules with some type of bioactive potential, including; soft corals (Alcyonium palmatum); tunicates (Ascidia mentula); bony fish, such as horse mackerel (Trachurus trachurus); European hake (Merluccius merluccius); and chondrichthyans, such as small-spotted catshark (Scyliorhinus canicula). In addition, 16% of the discarded species had congeneric species that produce compounds with bioactive potential, indicating that such species might also possess similar types of bioactive molecules. Molecules with antioxidant, antitumour, antihypertensive, and antibacterial properties were the most frequent, which could provide the basis for future research aiming to discover new marine-based drugs and compounds for other human uses. Among all species or genera that produce compounds with bioactive potential, 68% presented medium or high vulnerability to trawling. Results show that the discarded catch contains many species, which produce different bioactive compounds that represent an added-value resource. These results highlight the importance of manage properly crinoid beds, to ensure that species that produce molecules with bioactive potential inhabiting these habitats are protected.

Dietary supplementation of marine yeast Yarrowia lipolytica modulates immune response in Litopenaeus vannamei

The immunostimulatory potential of the marine yeast Yarrowia lipolytica (D1 and N6 strains) administered orally was evaluated in the white shrimp Litopenaeus vannamei. Yeasts and commercial glucans were mixed with a commercial feed to formulate diets with a 1.1% concentration of immunostimulants. The shrimp were fed daily for a period of 21 days. Weekly determinations were performed for immunological parameters in hemolymph, such as total hemocyte count (THC), lysozyme activity (LYZ), prophenoloxidase activity, antioxidant enzymatic activities (superoxide dismutase [SOD], catalase [CAT], and peroxidases), and bactericidal activity against Vibrio parahaemolyticus. Expression profiles of penaeidin (PEN), lysozyme (LYZ), and prophenoloxidase (proPO) immune genes were evaluated in hemocytes. In general, an increase in the immune parameters was observed in shrimp fed yeast diet compared to glucan and the control diets. Yarrowia lipolytica, especially strain N6, provided maximum immunostimulatory effects evidenced by the increase of immune parameters (THC, LYZ, SOD, CAT) and gene expression profile. In conclusion, this study demonstrated that Y. lipolytica had immunostimulatory effects and increased bactericidal activity in L. vannamei hemocytes against V. parahaemolyticus. These findings open the path for the potential application of Y. lipolytica-based immunostimulant for shrimp aquaculture.

Antimicrobial Lipids from Plants and Marine Organisms: An Overview of the Current State-of-the-Art and Future Prospects

In the actual post-antibiotic era, novel ways of rethinking antimicrobial research approaches are more urgent than ever. Natural compounds with antimicrobial activity such as fatty acids and monoacylglycerols have been investigated for decades. Additionally, the interest in other lipid classes as antimicrobial agents is rising. This review provides an overview on the research about plant and marine lipids with potential antimicrobial activity, the methods for obtaining and analyzing these compounds, with emphasis on lipidomics, and future perspectives for bioprospection and applications for antimicrobial lipids. Lipid extracts or lipids isolated from higher plants, algae or marine invertebrates are promising molecules to inactivate a wide spectrum of microorganisms. These lipids include a variety of chemical structures. Present and future challenges in the research of antimicrobial lipids from natural origin are related to the investment and optimization of the analytical workflow based on lipidomics tools, complementary to the bioassay-guided fractionation, to identify the active compound(s). Also, further work is needed regarding the study of their mechanism of action, the structure-activity relationship, the synergistic effect with conventional antibiotics, and the eventual development of resistance to lipids, which, as far as is known, is unlikely.

Effects of hesperidin on the growth performance, antioxidant capacity, immune responses and disease resistance of red swamp crayfish (Procambarus clarkii)

We evaluated the effects of hesperidin on the nonspecific immunity, antioxidant capacity and growth performance of red swamp crayfish (Procambarus clarkii). A total of 900 healthy crayfish were randomly divided into six groups: the control group (fed the basal diet) and the HES25, HES50, HES75, HES100 and HES150 groups, which were fed the basal diet supplemented with 25, 50, 75, 100 and 150 mg kg^-1 hesperidin, respectively. The feeding experiment lasted 8 weeks. The results indicated that compared with the control group, the crayfish groups supplemented with 50-150 mg kg^-1 hesperidin had a decreased feed conversion ratio (FCR) and increased final body weight (FBW), specific growth rate (SGR) and weight gain (WG) (P < 0.05). The protein carbonyl content (PCC), reactive oxygen species (ROS) level and malondialdehyde (MDA) level in the hepatopancreas and hemocytes were significantly lower, while the total antioxidant capacity (T-AOC), glutathione peroxidase (GPx) activity, and superoxide dismutase (SOD) activity were significantly higher in the crayfish groups supplemented with 50-150 mg kg^-1 hesperidin than in the control group. Supplementation with 50-150 mg kg^-1 hesperidin significantly increased the activities of acid phosphatase (ACP), alkaline phosphatase (AKP), lysozyme (LZM), and phenoloxidase (PO) compared with the control group (P < 0.05); upregulated the mRNA expression of cyclophilin A (CypA), extracellular copper-zinc superoxide dismutase (ecCuZnSOD), GPxs, crustin, astacidin, Toll3 and heat shock protein 70 (HSP70) (P < 0.05); and decreased crayfish mortality following white spot syndrome virus (WSSV) infection. These findings indicate that dietary hesperidin supplementation at an optimum dose of 50-150 mg kg^-1 may effectively improve nonspecific immunity, antioxidant capacity and growth performance in crayfish.

Induction of innate immune response in whiteleg shrimp (Litopenaeus vannamei) embryos

The immune response of commercially relevant marine invertebrates has been extensively studied, in search of new disease-control strategies. Immune training is considered a novel approach that could help improve resistance to different pathogens. Here, we stimulated the white shrimp (Litopenaeus vannamei) during embryo development by exposure to heat-killed bacteria and evaluated their effect on hatching, larval development, and the expression of immune-related genes. In addition, we evaluated its impact on the response of shrimp nauplii during a challenge with Vibrio parahaemolyticus. We observed that the percentage of hatching and the resistance to bacterial infection increased due to the treatment of embryos with heat-killed cells of Vibrio and Bacillus. Apparently different stimuli could generate a differential pattern of gene expression, e.g., Vibrio induced a strong effector immune response whereas Bacillus elicited a protective immune profile. In addition, each response was triggered by molecular patterns detected in the environment. The results obtained in this study provide new insights for immune training to improve shrimp farming.

Morphological and functional characterization of circulating hemocytes using microscopy techniques

In the present study, Microscopy studies were performed to characterize the blood cells of the mangrove crab Episesarma tetragonum. Three types of hemocytes were observed: granulocytes, semi-granulocytes, and hyalinocytes or agranulocytes. Hyalinocytes have a distinguished nucleus surrounded by the cytoplasm, and a peculiar cell type was present throughout the cytosol, lysosomes with hemocyte types (granules) stained red (pink). Giemsa staining was used to differentiate between the large and small hemocytes. Ehrlich's staining was used to differentiate granule-containing cells in acidophils (55%), basophils (44%), and neutrophils (<1%). Periodic acid-Schiff staining was used to identify the sugar molecules in the cytoplasm. Cell-mediated immune reactions including phagocytosis, encapsulation, agglutination, and peroxidase-mediated cell adhesion are the functions of hemocytes. Agglutination reaction involves both kind of cells involved in yeast and heme-agglutination responses in invertebrates. The beta glucan outer layer of yeast cells was recognized by hemocyte receptors. Human RBC cells were agglutinated via granulocytes. E. tetragonum hemocytes are an important animal model for studying both ultrastructural and functional activity of circulating cells. In addition, E. tetragonum hemocytes exhibited excellent antibacterial and antibiofilm activities were studied through plating and microplate assays. Biofilm inhibition was also visualized through changes in biochemical assays and morphological variations were visualized through levels in in situ microscopy analysis.

Isolation and Characterization of Antimicrobial Peptides with Unusual Disulfide Connectivity from the Colonial Ascidian Synoicum turgens

This study reports the isolation of two novel cysteine-rich antibacterial peptides, turgencin A and turgencin B, along with their oxidized derivatives, from the Arctic marine colonial ascidian Synoicum turgens. The peptides are post-translationally modified, containing six cysteines with an unusual disulfide connectivity of Cys¹-Cys⁶, Cys²-Cys⁵, and Cys³-Cys⁴ and an amidated C-terminus. Furthermore, the peptides contain methionine residues resulting in the isolation of peptides with different degrees of oxidation. The most potent peptide, turgencin A_Mox1 with one oxidized methionine, displayed antimicrobial activity against both Gram-negative and Gram-positive bacteria with a minimum inhibitory concentration (MIC) as low as 0.4 µM against selected bacterial strains. In addition, the peptide inhibited the growth of the melanoma cancer cell line A2058 (IC₅₀ = 1.4 µM) and the human fibroblast cell line MRC-5 (IC₅₀ = 4.8 µM). The results from this study show that natural peptides isolated from marine tunicates have the potential to be promising drug leads.

Effects of dietary supplementation with icariin on growth performance, antioxidant capacity and non-specific immunity of Chinese mitten crab (Eriocheir sinensis)

We investigated the effects of icariin (ICA) on growth performance, antioxidant capacity and non-specific immunity in Chinese mitten crab (Eriocheir sinensis). A total of 200 healthy crabs (average weight: 33.58 ± 0.05 g) were randomly assigned to four treatments with five replicates, each with ten individuals per pool. There were four dietary treatments: the control group (fed with the basal diet), the ICA 50 group, the ICA100 group, and the ICA 200 group (fed with the basal diet supplemented with 50, 100, and 200 mg/kg ICA, respectively). These diets were provided for 8 weeks. Results indicated that ICA100 crabs had higher weight gain (WG), specific growth rate (SGR) and survival rate (SR) than the controls. Protein carbonyl content (PCC) and malondialdehyde (MDA) concentrations in the haemolymph and hepatopancreas of ICA100 crabs were significantly lower than in the control group, while the superoxide dismutase (SOD) and glutathione peroxidase (GPx) activities were significantly higher. The activities of PO, LZM, ACP and AKP were significantly enhanced with ICA supplementation at 50 and 100 mg/kg, yet decreased subsequently at 200 mg/kg. Furthermore, supplementation of 100 mg/kg ICA up-regulated the mRNA expression of prophenoloxidase (proPO), catalase (CAT), mitochondrial manganese superoxide dismutase (mtMnSOD), thioredoxin-1 (Trx1) and peroxiredoxin 6 (Prx6), while the mRNA expression of toll like receptors (TLRs), NF-κB-like transcription factor Relish and lipopolysaccharide-induced TNF-α factor (LITAF) were down-regulated in the hepatopancreas (P < 0.05). These findings indicate that dietary ICA supplementation at an optimum dose of 100 mg/kg may be effective in improving growth performance, antioxidant capability and non-specific immunity of Chinese mitten crab.

Effectiveness of traditional Chinese herbal medicine, San-Huang-San, in combination with enrofloxacin to treat AHPND-causing strain of Vibrio parahaemolyticus infection in Litopenaeus vannamei

The effects of oral administration of enrofloxacin (ENR) and San-Huang-San (SHS), singly or in combination, on the survival performance, disease resistance, and immunity of Litopenaeus vannamei were investigated. After challenge with an AHPND-causing strain of Vibrio parahaemolyticus (VP_AHPND), shrimp were immediately fed a drug-free diet, diets containing only ENR (20 mg·kg^-1) or SHS (500 mg·kg^-1) or diets containing low-dose (10 mg·kg^-1 ENR + 250 mg ·kg^-1 SHS), medium-dose (20 mg·kg^-1 ENR + 500 mg ·kg^-1 SHS), and high-dose (40 mg·kg^-1 ENR + 1000 mg ·kg^-1 SHS) drug combinations for 5 days. The cumulative shrimp mortality over 5 days after injection of VP_AHPND in the ENR + SHS combination groups was significantly lower than that in the ENR or SHS alone groups (p < 0.05). Immune parameters, including the vibrio density, total hemocyte counts (THCs), hemocyanin (HEM) concentration, antibacterial activity, activity levels of lysozyme (LZM), acid phosphatase (ACP), alkaline phosphatase (AKP), and phenoloxidase (PO) in cell-free hemolymph, and the expression levels of the immune-related genes anti-lipopolysaccharide factor (ALF), cathepsin B (catB), crustin, lectin (Lec), lysozyme (LZM), and Toll-like receptor (TLR) in hemocytes were determined in the shrimp. The results showed that the shrimp in drug combination groups cleared more VP_AHPND than that in the ENR or SHS group in the same time. The values for other immune parameters in the drug combination groups were higher than those in the ENR or SHS group (p < 0.05). Finally, in the histological examinations, the histological structural alignment and integrity of the hepatopancreatic tubules in the drug combination groups were better than that in the ENR and SHS groups. Under the experimental conditions, compared with ENR or SHS used alone, the combination use of ENR and SHS could improve immunity and disease resistance in shrimp after VP_AHPND infection, and could reduce the use of ENR when the better therapeutic effect was achieved.

RNase1 alleviates the Aeromonas hydrophila-induced oxidative stress in blunt snout bream

RNase1 is an enzyme important in host defense in vertebrates where it degrades the RNA of bacteria and viruses. We evaluated the effect of RNase1 on the resistance to Aeromonas hydrophila infection in Megalobrama amblycephala. The fish were randomly divided into four groups: a blank group (none-treated M. amblycephala), a control group (injected PBS), a challenge group (A. hydrophila-injected) and a treatment group (pre-treated with RNase1 24 h before the A. hydrophila injection), and we collected five tissues of each group. Then we recorded changes in the levels of glutathione (GSH), oxidized glutathione (GSSG), hepatic catalase (CAT), superoxide dismutase (SOD), malondialdehyde (MDA) and lysozyme; and the relative mRNA expression of catalase (CAT), selenium-dependent glutathione peroxidase (GPx), Cu/Superoxide dismutase (Cu/Zn-SOD), glutamate-cysteine ligase (GCLC), glutathione reductase (GR) and nuclear factor erythroid 2-related factor 2 (Nrf2) for four groups. The expression of six genes was highest in liver and blood of the blank group. It was significantly higher in the gut of the treatment group (compared to control and challenge groups) 12 h after the infection. The treatment group exhibited a significant increase in GSH, SOD and CAT activity, and a decrease in GSSG, MDA and lysozyme content (compared to the control and challenge groups) 6 and 12 h after infection. These results suggest that supplementation with RNase1 protein can enhance resistance against A. hydrophila infections in M. amblycephala.

Comparative transcriptomic analysis of crab hemocytes in response to white spot syndrome virus or Vibrio alginolyticus infection

To assess the immune response of hemocytes to white spot syndrome virus (WSSV) or Vibrio alginolyticus infection in the mud crab Scylla paramamosain, a transcriptome analysis was performed. We report the analysis of 45131 transcripts from S. paramamosain hemocytes by de novo assembly. A comparison with GenBank protein and nucleotide sequences identified 33699 genes as previously known. The length distribution of the genes was 8147 genes ≥200 bp, 4714 genes ≥300 bp, and 3517 genes ≥2000 bp. A total of 21579 simple sequence repeats (SSRs) were found in the transcriptomic dataset, including 9% monomers, 53.34% dimers and 32.55% trimers. A total of 13172 and 5087 differentially expressed transcripts were found in the V. alginolyticus-infected group and WSSV-infected group, respectively. Of these, 5920 transcripts were up-regulated and 7252 were down-regulated in the V. alginolyticus-infected crabs and 2302 transcripts were up-regulated and 2785 were down-regulated in the WSSV-infected crabs. Additionally, 3096 transcripts were differentially expressed simultaneously in the V. alginolyticus-infected crabs and the WSSV-infected crabs. Several known immune-related genes such as heat shock protein, Janus kinase, STAT, relish, caspase, Ca²⁺-transporting ATPase and lysosomal alpha-mannosidase were found among the differentially expressed transcripts. Transcription and its regulation were significant biological processes, and ATP binding and zinc ion binding were significant molecular functions. This is the first report of comparative transcriptomic analysis of crab hemocytes in response to WSSV or V. alginolyticus infection. These findings will contribute to our understanding of the immune response to WSSV and V. alginolyticus infection in crustaceans.

Potential virulence factors of bacteria associated with tail fan necrosis in the spiny lobster, Jasus edwardsii

Tail fan necrosis (TFN) is a common condition found in commercially exploited spiny lobsters that greatly diminishes their commercial value. Bacteria possessing proteolytic, chitinolytic and lipolytic capabilities were associated with TFN in spiny lobsters, Jasus edwardsii. In this study, 69 bacterial isolates exhibiting all the three enzymatic capabilities from the haemolymph and tail fans of J. edwardsii with and without TFN were further characterized and compared, including morphology, biofilm formation, antimicrobial activity, antimicrobial resistance, and production of siderophores, melanin and ammonia. The genomic patterns of the most common Vibrio crassostreae isolates were also compared between TFN-affected and unaffected lobsters. Biofilm formation was stronger in bacterial isolates from both haemolymph and tail fans of TFN-affected lobsters compared to those from the unaffected lobsters, while melanin production and siderophore production were stronger in the isolates from tail fans of lobsters with TFN. By contrast, the other characteristics of isolates were similar in lobsters with and without TFN. The Vib. crassostreae isolates from the affected lobsters had similar genomic patterns. Overall, the results indicate that in addition to proteolytic, chitinolytic and lipolytic activities, the bacteria associated with TFN commonly have enhanced activity of important virulence factors, including biofilm formation, melanin production and siderophore production.

Paralithocins, Antimicrobial Peptides with Unusual Disulfide Connectivity from the Red King Crab, Paralithodes camtschaticus

As part of an ongoing exploration of marine invertebrates as a source of new antimicrobial peptides, hemocyte extracts from the red king crab, Paralithodes camtschaticus, were studied. Three cationic cysteine (Cys)-rich peptides, named paralithocins 1-3, were isolated by bioassay-guided purification, and their amino acid sequences determined by Edman degradation and expressed sequences tag analysis. Disulfide bond mapping was performed by high-resolution tandem mass spectrometry. The peptides (38-51 amino acids in length) share a unique Cys motif composed of eight Cys, forming four disulfide bridges with a bond connectivity of (Cys relative position) Cys1-Cys8, Cys2-Cys6, Cys3-Cys5, and Cys4-Cys7, a disulfide arrangement that has not been previously reported among antimicrobial peptides. Thus, paralithocins 1-3 may be assigned to a previously unknown family of antimicrobial peptides within the group of Cys-rich antimicrobial peptides. Although none of the isolated peptides displayed antimicrobial activity against the target strains Escherichia coli, Pseudomonas aeruginosa, or Staphylococcus aureus, they inhibited the growth of several marine bacterial strains with minimal inhibitory concentrations in the 12.5-100 μM range. These findings corroborate the hypothesis that marine organisms are a valuable source for discovering bioactive peptides with new structural motifs.

A Proteomic Study of Hemocyte Proteins from Mud Crab (Scylla paramamosain) Infected with White Spot Syndrome Virus or Vibrio alginolyticus

In this study, we investigated the hemocytes' immune response to white spot syndrome virus (WSSV) or Vibrio alginolyticus infection at the protein level. The differential proteomes from crab hemocytes infected with WSSV or V. alginolyticus were analyzed using the isobaric tags for relative and absolute quantitation approach immediately after infection. Using this approach, we identified 1,799 proteins by their by LC-MS/MS spectra and sequencing data. These included 157 upregulated proteins and 164 downregulated proteins after WSSV infection. Similarly, 243 proteins were determined to be differentially expressed during V. alginolyticus infection, of these, 121 were upregulated and 122 were downregulated after infection. Interestingly, among these differentially expressed proteins, 106 were up- or downregulated significantly in both WSSV and V. alginolyticus infection. Six genes, β-actin, myosin-9, anti-lipopolysaccharide factor isoform 4, anti-lipopolysaccharide factor 4, transketolase-like protein 2-like isoform 1, and sarcoplasmic calcium-binding protein 1 were chosen for further study. The expression of these genes all showed a trend of upregulation at 24 h post-WSSV or V. alginolyticus infection except for myosin-9 in response to WSSV. To confirm the protective effects of the six genes, crabs were injected with specific dsRNAs before WSSV or V. alginolyticus challenge. The results showed that the knockdown of these genes led to an increase in the morbidity and mortality (P < 0.01) rate, and a decrease in infection time in WSSV-infected crabs. During the first 84 h, knockdown of these genes also led to an increase in the morbidity rates in V. alginolyticus -infected crabs, and results of four genes showed a higher mortality rate than that of the control after they were knocked down. This is the first report of the proteome response in crab hemocytes during WSSV or V. alginolyticus infection. These findings will contribute to our understanding of the immune response to WSSV and V. alginolyticus infection in crabs.

Novel Antimicrobial Peptides EeCentrocins 1, 2 and EeStrongylocin 2 from the Edible Sea Urchin Echinus esculentus Have 6-Br-Trp Post-Translational Modifications

The global problem of microbial resistance to antibiotics has resulted in an urgent need to develop new antimicrobial agents. Natural antimicrobial peptides are considered promising candidates for drug development. Echinoderms, which rely on innate immunity factors in the defence against harmful microorganisms, are sources of novel antimicrobial peptides. This study aimed to isolate and characterise antimicrobial peptides from the Edible sea urchin Echinus esculentus. Using bioassay-guided purification and cDNA cloning, three antimicrobial peptides were characterised from the haemocytes of the sea urchin; two heterodimeric peptides and a cysteine-rich peptide. The peptides were named EeCentrocin 1 and 2 and EeStrongylocin 2, respectively, due to their apparent homology to the published centrocins and strongylocins isolated from the green sea urchin Strongylocentrotus droebachiensis. The two centrocin-like peptides EeCentrocin 1 and 2 are intramolecularly connected via a disulphide bond to form a heterodimeric structure, containing a cationic heavy chain of 30 and 32 amino acids and a light chain of 13 amino acids. Additionally, the light chain of EeCentrocin 2 seems to be N-terminally blocked by a pyroglutamic acid residue. The heavy chains of EeCentrocins 1 and 2 were synthesised and shown to be responsible for the antimicrobial activity of the natural peptides. EeStrongylocin 2 contains 6 cysteines engaged in 3 disulphide bonds. A fourth peptide (Ee4635) was also discovered but not fully characterised. Using mass spectrometric and NMR analyses, EeCentrocins 1 and 2, EeStrongylocin 2 and Ee4635 were all shown to contain post-translationally brominated Trp residues in the 6 position of the indole ring.

Nitric oxide synthase-dependent immune response against gram negative bacteria in a crustacean, Litopenaeus vannamei

Nitric oxide (NO) is a short-lived radical generated by nitric oxide synthases (NOS). NO is involved in a variety of functions in invertebrates, including host defense. In previous studies, we isolated and sequenced for the first time the NOS gene from hemocytes of Panulirus argus, demonstrating the inducibility of this enzyme by lipopolysaccharide in vitro e in vivo. Hyperimmune serum was obtained from rabbits immunized with a P. argus -NOS fragment of 31 kDa produced in Escherichia coli, which specifically detected the recombinant polypeptide and the endogenous NOS from lobster hemocytes by western blotting and immunofluorescence. In the present work, we demonstrate that the hyperimmune serum obtained against P. argus NOS also recognizes Litopenaeus vannamei NOS in hemocytes by western blotting and immunofluorescence. Our data also show that while the hemolymph of L. vannamei has a strong antibacterial activity against the Gram negative bacteria Aeromonas hydrophila, the administration of the anti NOS serum reduce the natural bacterial clearance. These results strongly suggest that NOS is required for the shrimp immune defense toward Gram negative bacteria. Therefore, the monitoring of induction of NOS could be an important tool for testing immunity in shrimp farming.

Evidence of Antibacterial Activities in Peptide Fractions Originating from Snow Crab (Chionoecetes opilio) By-Products

Antibacterial peptide fractions generated via proteolytic processing of snow crab by-products exhibited activity against Gram-negative and Gram-positive bacteria. Among the bacterial strains tested, peptide fractions demonstrated inhibitory activity against the Gram-negative bacteria such as Aeromonas caviae, Aeromonas hydrophila, Campylobacter jejuni, Listonella anguillarum, Morganella morganii, Shewanella putrefasciens, Vibrio parahaemolyticus and Vibrio vulnificus and against a few Gram-positive bacteria such as Listeria monocytogenes, Staphylococcus epidermidis and Streptococcus agalactiae. The principal bioactive peptide fraction was comprised mainly of proteins and minerals (74.3 and 15.5%, respectively). Lipids were not detected. The amino acid content revealed that arginine (4.6%), glutamic acid (5.3%) and tyrosine (4.8%) residues were represented in the highest composition in the antibacterial peptide fraction. The optimal inhibitory activity was observed at alkaline pH. The V. vulnificus strain, most sensitive to the peptide fraction, was used to develop purification methods. The most promising chromatography resins selected for purification, in order to isolate peptides of interest and to carry out their detailed biochemical characterization, were the SP-Sepharose™ Fast Flow cation exchanger and the Phenyl Sepharose™ High Performance hydrophobic interaction media. The partially purified antibacterial peptide fraction was analyzed for minimum inhibitory concentration (MIC) determination, and the value obtained was 25 μg ml(-1). Following mass spectrometry analysis, the active peptide fraction seems to be a complex of molecules comprised of several amino acids and other organic compounds. In addition, copper was the main metal found in the active peptide fraction. Results indicate the production of antibacterial molecules from crustacean by-products that support further applications for high-value bioproducts in several areas such as food and health.

Effects of perfluorooctane sulfonate on the immune responses and expression of immune-related genes in Chinese mitten-handed crab Eriocheir sinensis

Perfluorooctane sulfonate (PFOS) has been widely studied due to its global distribution, slow degradation, high bioaccumulation and toxicological effects on vertebrates. However, the potential toxicity of PFOS to crustaceans is little known. The present study investigated the effects of PFOS on the immune responses and expression of immune-related genes in the Chinese mitten-handed crab Eriocheir sinensis. Crabs were exposed to 0, 0.01, 0.1, 1.0 and 10mg/L of PFOS, and sampled on 1, 4, 7, 14 and 21days respectively. The total hemocyte count and lysozyme activity in PFOS-treated crab were significantly lower than in the control. The exposure to 10mg/L of PFOS led to a marked inhibition in phenoloxidase and superoxide dismutase activities. At other PFOS levels, phenoloxidase and superoxide dismutase showed an initial increase and a subsequent decrease over time. The alkaline and acid phosphatase activities were stimulated in 10mg/L PFOS until 21days. The mRNA expression of immune related genes including hepatopancreas-specific C-type lectin and prophenoloxidase activating factors were up-regulated after the exposure to the concentrations of 1 and 10mg/L of PFOS, while the expression of lysozyme gene was up-regulated only in the crab exposed to 0.1mg/L PFOS. The results demonstrate that the high dose of PFOS leads to immune toxicity and the hepatopancreas is a major target organ for PFOS accumulation and immunotoxicity. Hemocyte counts, phenoloxidase and acid phosphatase are useful biomarkers for the risk assessment of PFOS toxicity to crustaceans.

Antimicrobial activity in the cuticle of the American lobster, Homarus americanus

American lobster, Homarus americanus, continues to be an ecologically and socioeconomically important species despite a severe decline in catches from Southern New England and Long Island Sound (USA) and a high prevalence of epizootic shell disease in these populations. A better understanding of lobster immune defenses remains necessary. Cuticle material collected from Long Island Sound lobsters was found to be active against a broad spectrum of bacteria, including Gram-negative and -positive species. The antimicrobial activity was characterized by boiling, muffling, and size fractioning. Boiling did not significantly reduce activity, while muffling did have a significant effect, suggesting that the active component is organic and heat stable. Size fractioning with 3 and 10 kDa filters did not significantly affect activity. Fast protein liquid chromatography fractions were also tested for antimicrobial activity, and fractions exhibiting protein peaks remained active. MALDI mass spectrometry revealed peptide peaks at 1.6, 2.8, 4.6, and 5.6 kDa. The data presented suggest that one or several antimicrobial peptides contribute to antimicrobial activity present in the American lobster cuticle.

Effect of dietary carbohydrate on non-specific immune response, hepatic antioxidative abilities and disease resistance of juvenile golden pompano (Trachinotus ovatus)

The present study was conducted to investigate the effects of dietary carbohydrate (CHO) levels on non-specific immune responses, hepatic antioxidative status and disease resistance of juvenile golden pompano. Fish were fed six isonitrogenous and isoenergetic diets containing various CHO levels for 8 weeks. After the feeding trial, fish were challenged by Vibrio harveyi and survival rate was recorded for the next 12 days. Plasma total protein and albumin content, respiratory burst activity, alkaline phosphatase, slightly increased with dietary starch level from 0% to 16.8%, but significantly decreased at dietary starch levels of 16.8%-28%. Plasma lysozyme, complement 3 and complement 4 levels increased with increasing dietary carbohydrate up to 11.2% and then declined (P < 0.05). Contrary to glutamic-oxalacetic transaminase and triiodothyronine, plasma cortisol content increased with increasing dietary carbohydrate up to 22.4%, and then levelled off. The hepatic total antioxidative capacity, reduced glutathione and catalase levels reached the peak at the fish fed diet with 16.8% carbohydrate (P < 0.05). This also held true for hepatic superoxide dismutase activities, whereas the hepatic malondialdehyde content of fish fed dietary starch level of 16.8% was significantly lower than that of fish fed no CHO diet, but showed little difference (P > 0.05) with those of the other treatments. After challenge, fish fed 11.2% and 16.8% dietary CHO showed higher survival rate than that of fish in 0% CHO group (P < 0.05). However, survival rate showed little difference among 0%, 5.6%, 22.4% and 28% CHO groups (P > 0.05). The results of this study suggest that ingestion of 11.2-16.8% dietary CHO can enhance the non-specific immune responses, increase the hepatic antioxidant abilities, and improve resistance to V. harveyi infection of juvenile golden pompano.

Role of Marsupenaeus japonicus crustin-like peptide against Vibrio penaeicida and white spot syndrome virus infection

Crustins are important AMP that has been identified in crustaceans. In this study, the role of Marsupenaeus japonicus crustin-like peptide (MjCRS) was examined in vivo by RNA interference (RNAi) using double-stranded RNA (dsRNA). Tissue expression analysis revealed that MjCRS transcripts are expressed in different tissues tested with the highest expression observed in hemocytes. Treatment with double-stranded RNA specific to MjCRS led to a significant reduction of MjCRS transcripts within the hemocytes. When MjCRS was silenced and subsequently infected with Vibrio penaeicida final mortality was significantly higher compared with PBS and dsGFP treated groups. On the other hand, final mortalities of MjCRS silenced and PBS injected groups were not significantly different after infection with white spot virus, however, both are significantly higher compared with dsGFP treated group. V. penaeicida infection significantly decreased MjCRS expression at 3, 6, 12 and 24h followed by significant increase at 48 h post-infection. On the contrary, white spot infection significantly increased MjCRS expression at 6 and 12h and decreased at 48 h post-infection. dsRNA treatment alone decreased total hemocyte counts (THCs) and subsequent V. penaeicida or white spot virus infection further decreased THCs. VP28 gene expression was both similarly increased in PBS injected group and MjCRS silenced group at 24 and 48 h-post infection. Results suggest that MjCRS is involved in antibacterial defense and might not have critical function against viral infection.

Anti-stress properties and two HSP70s mRNA expressions of blunt snout bream (Megalobrama amblycephala) fed with all-plant-based diet

The influence of all-plant-based diet on fingerling blunt snout breams (Megalobrama amblycephala) was tested by examining growth performance, anti-stress properties and related gene expression. Healthy fish were randomly divided into triplicate groups per dietary treatment and fed with different formulated diets. The results showed that both weight gain, specific growth rate and protein efficiency ratio of all-plant-based diet group were significant higher than those of the control (p < 0.05). In contrast, FCR of all-plant-based diet group was significantly lower than that of the control (p < 0.05). Therefore, all-plant-based diets could not affect the growth performance of blunt snout breams. Compared to the control group, the lysozyme levels in serum and mucus, and glutamic-oxaloacetic transaminase activities in serum and liver decreased significantly (p < 0.05). In contrast, the glutamic-pyruvic transaminase activities in serum and liver increased significantly (p < 0.05). For blunt snout breams fed with all-plant-based diets, the superoxide dismutase activities in mucus, serum and liver as well as catalase activity in serum and liver were decreased significantly (p < 0.05) comparing with that of the control group. But malondialdehyde contents were higher (p < 0.05) in serum and liver than that of control group. The expression of HSC70 mRNA increased significantly (p < 0.05) in blunt snout breams fed with all-plant-based diet, whereas the HSP70 mRNA expression decreased significantly (p < 0.05) when compared with control group. In conclusion, all these results indicated that the application of all-plant-based diet could decrease the anti-stress properties (non-specific immunity, stress resistance and antioxidant ability) and HSP70 mRNA expression in blunt snout breams fingerling. Although all-plant-based diets could not affect the growth performance of blunt snout breams, the application of all-plant-based diet should be discreet in the production practice.

Effects of anthraquinone extract from Rheum officinale Bail on the physiological responses and HSP70 gene expression of Megalobrama amblycephala under Aeromonas hydrophila infection

We evaluated the effect of dietary supplementation with anthraquinone extract (from Rheum officinale Bail) on the resistance to Aeromonas hydrophila infection in Megalobrama amblycephala. The fish were randomly divided into two groups: a control group (fed a standard diet) and a treatment group (standard diet supplemented with 0.1% anthraquinone extract) and fed for 10 weeks. We then challenged the fish with A. hydrophila and recorded mortality and changes in serum cortisol, lysozyme, alkaline phosphatase (ALP), total protein, aspartate aminotransferase (AST), alanine aminotransferase (ALT), and hepatic catalase (CAT), superoxide dismutase (SOD), malondialdehyde (MDA) and the relative expression of heat shock protein 70 (HSP70) mRNA for a period of 5 d. Supplementation with 0.1% anthraquinone extract significantly increased serum lysozyme activity before infection, serum ALP activity at 24 h after infection, serum total protein concentration 12 h after infection, hepatic CAT activity 12 h after infection, hepatic SOD activity before infection, and the relative expression of hepatic HSP70 mRNA both before infection and 6 h after infection. In addition, the supplemented group had decreased levels of serum cortisol 6 h after infection, serum AST and ALT activities 12 h after infection, and hepatic MDA content 12 h after infection. Mortality was significantly lower in the treatment group (86.67%) than the control (100%). Our results suggest that ingestion of a basal diet supplemented with 0.1% anthraquinone extract from R. officinale Bail can enhance resistance against pathogenic infections in M. amblycephala.

Antimicrobial peptides from marine invertebrates: challenges and perspectives in marine antimicrobial peptide discovery

The emergence of pathogenic bacteria resistance to conventional antibiotics calls for an increased focus on the purification and characterization of antimicrobials with new mechanisms of actions. Antimicrobial peptides are promising candidates, because their initial interaction with microbes is through binding to lipids. The interference with such a fundamental cell structure is assumed to hamper resistance development. In the present review we discuss antimicrobial peptides isolated from marine invertebrates, emphasizing the isolation and activity of these natural antibiotics. The marine environment is relatively poorly explored in terms of potential pharmaceuticals, and it contains a tremendous species diversity which evolved in close proximity to microorganisms. As invertebrates rely purely on innate immunity, including antimicrobial peptides, to combat infectious agents, it is believed that immune effectors from these animals are efficient and rapid inhibitors of microbial growth.

Centrocins: isolation and characterization of novel dimeric antimicrobial peptides from the green sea urchin, Strongylocentrotus droebachiensis

As immune effector molecules, antimicrobial peptides (AMPs) play an important role in the invertebrate immune system. Here, we present two novel AMPs, named centrocins 1 (4.5kDa) and 2 (4.4kDa), purified from coelomocyte extracts of the green sea urchin, Strongylocentrotus droebachiensis. The native peptides are cationic and show potent activities against Gram-positive and Gram-negative bacteria. The centrocins have an intramolecular heterodimeric structure, containing a heavy chain (30 amino acids) and a light chain (12 amino acids). The cDNA encoding the peptides and genomic sequences were cloned and sequenced. One putative isoform (centrocin 1b) was identified and one intron was found in the genes coding for the centrocins. The full length protein sequence of centrocin 1 consists of 119 amino acids, whereas centrocin 2 consists of 118 amino acids which both include a preprosequence of 51 or 50 amino acids for centrocins 1 and 2, respectively, and an interchain of 24 amino acids between the heavy and light chain. The difference of molecular mass between the native centrocins and the deduced sequences from cDNA indicates that the native centrocins contain a post-translational brominated tryptophan. In addition, two amino acids at the C-terminal, Gly-Arg, were removed from the light chains during the post-translational processing. The separate peptide chains of centrocin 1 were synthesized and the heavy chain alone was shown to be sufficient for antimicrobial activity. The genome of the closely related species, the purple sea urchin (S. purpuratus), was shown to contain two putative proteins with high similarity to the centrocins.

Effects of anthraquinone extract from Rheum officinale Bail on the growth performance and physiological responses of Macrobrachium rosenbergii under high temperature stress

In order to study the effects of anthraquinone extract from Rheum officinale Bail on Macrobrachium rosenbergii under high temperature stress, freshwater prawns were randomly divided into five groups: a control group was fed with basal diet, and four treatment groups fed with basal diet supplemented with 0.05%, 0.1%, 0.2%, and 0.4% anthraquinone extracts for 10 weeks, respectively. Then, freshwater prawns were exposed to high temperature stress at 35 degrees C for 48h. The growth, changes in haemolymph total protein, aspartate aminotransferase (AST), alanine aminotransferase (ALT), alkaline phosphatase (ALP), lysozyme, nitrogen monoxide (NO) and hepatic catalase (CAT), superoxide dismutase (SOD) and malondialdehyde (MDA) were investigated. The results showed that compared the control group, the specific growth rates, feed conversion efficiency, haemolymph ALP and lysozyme activities, total protein contents, hepatic CAT and SOD activities increased while haemolymph AST, ALT and hepatic MDA contents decreased in treatment groups before the stress, but their levels did not correlate with the doses of anthraquinone extracts. The specific growth rate (SGR), feed conversion efficiency and haemolymph lysozyme activity significantly increased but haemolymph AST activity decreased in 0.1% dose group; whereas haemolymph ALP activity and feed conversion efficiency increased but ALT activity and hepatic MDA contents significantly decreased in 0.2% dose group before the stress compared with the control. After high temperature stress, 0.1-0.2% anthraquinone extract also could improve the haemolymph total proteins, lysozyme and ALP activities, hepatic catalase, and superoxide dismutase, and reduce haemolymph ALT and AST activities, hepatic malondialdehyde contents. The cumulative mortality in the control was about 100% at 48h after high temperature stress while the cumulative mortality in the treatment groups supplemented with 0.1-0.2% anthraquinone extract were about 48-65%. The artificial infection with Vibrio anguillarum also showed the cumulative mortality in the control was about 100% while the cumulative mortality in the treatment groups supplemented with 0.1-0.2% anthraquinone extracts were about 57-80%. The present study suggested that ingestion of a basal diet supplemented with 0.1-0.20% anthraquinone extracts could prevent high temperature stress and promote the growth of prawns.

Condition-dependent ecdysis and immunocompetence in the amphipod crustacean, Gammarus pulex

The exoskeleton of arthropods forms an efficient protection against pathogens, but this first line of defence is periodically weakened during ecdysis, increasing the opportunity for surrounding pathogens to invade the body cavity. Since the richness of pathogens in the environment can be spatially and temporally variable, arthropods may have a fitness advantage in moulting in a place and time of low infection risk. Consistent with this hypothesis, we found that the amphipod crustacean, Gammarus pulex, exhibits temporal adjustment of the moult cycle in response to elevated risks of infection. Interestingly, this phenomenon is variable between two populations and independent of levels of immune defences. These results suggest that plasticity of the moult cycle in response to elevated risks of infection is adaptive and may result from adaptation to local variations in the risk of infection.

The role of haemocytes from the crab Carcinus aestuarii (Crustacea, Decapoda) in immune responses: A first survey

For the first time, a functional study of haemocytes from the crab Carcinus aestuarii was performed in order to evaluate their involvement in immune responses. Total haemocyte count (THC), phagocytosis, haemolymph opsonisation properties, hydrolytic and oxidative enzyme activities, and production of intracellular superoxide anion were evaluated. A great variability in THC was recorded among individuals, and haemocyte mean number was 6.4 (x10(6)) cells/ml haemolymph. Although only hyalinocytes were able to phagocytose yeast cells or Zymosan, phagocytic index was low (3%) and did not increase significantly (4%) after pre-incubation of yeast and Zymosan in cell-free haemolymph, suggesting that haemolymph did not have opsonising properties. All haemocyte types produced superoxide anion, whereas only granulocytes were positive to the hydrolytic enzymes assayed. In addition, only granulocytes were positive to phenoloxidase activity. Both Petri dish and spectrophotometric assays revealed a very low lysozyme-like activity in cell-free haemolymph (CFH) and haemocyte lysate (HL), although enzyme activity was higher in CFH than in HL. Interestingly, normalisation of data as to total protein content in CFH and HL resulted in an opposite situation, lysozyme-like activity being higher in HL than in CFH. This demonstrated that haemolymph of C. aestuarii has a high quantity of total proteins, functional properties of which need to be better investigated in future studies. Overall, the results obtained in the present study indicated that C. aestuarii haemocytes are not very active phagocytic cells, but they are more active in terms of both hydrolytic and oxidative enzyme activities and superoxide anion production.

Two recombinant peptides, SpStrongylocins 1 and 2, from Strongylocentrotus purpuratus, show antimicrobial activity against Gram-positive and Gram-negative bacteria

The cysteine-rich strongylocins were the first antimicrobial peptides (AMPs) discovered from the sea urchin species, Strongylocentrotus droebachiensis. Homologous putative proteins (called SpStrongylocin) were found in the sister species, S. purpuratus. To demonstrate that they exhibit the same antibacterial activity as strongylocins, cDNAs encoding the 'mature' peptides (SpStrongylocins 1 and 2) were cloned into a direct expression system fusing a protease cleavage site and two purification tags to the recombinant peptide. Both recombinant fusion peptides were expressed in a soluble form in an Escherichia coli strain tolerant to toxic proteins. Enterokinase was used to remove the fusion tags and purified recombinant SpStrongylocins 1 and 2 showed antimicrobial activity against both Gram-negative and Gram-positive bacteria. The results of membrane integrity assays against cytoplasmic membranes of E. coli suggest that both recombinant SpStrongylocins 1 and 2 conduct their antibacterial activity by intracellular killing mechanisms because no increase in membrane permeability was detected.

Antimicrobial lipids from the hemolymph of brachyuran crabs

The potential of marine crabs as a source of biologically active products is largely unexplored. In the present study, antimicrobial activity of the hemolymph (plasma) and hemocytes (plasma cells) of six brachyuran crabs was investigated against 16 pathogenic strains. Among the 16 strains tested maximum zone of inhibition was recorded in the hemolymph of Hyas araneus against Shigella flexineri. Interestingly Staphylococcus aureus and Salmonella typhi were susceptible to all the hemolymph and hemocytes samples. Likewise, the highest zone of inhibition was exhibited by both hemolymph and hemocytes samples against Vibrio cholerae. On the basis of TLC, 1HNMR, and 13CNMR it may be concluded that the antimicrobial activity in the hemolymph extract is due to the presence of lipids. This observation is further supported by the ESI-MS of the methanolic extract of hemolymph of H. araneus. ESI-MS shows cluster of peaks in the region m/z 445 to m/z 491 due to lysoglycerolipids/glycerides and cluster of signals between m/z 216 and 246, due to fatty acids/esters present in the sample.

Characterization of crustins from the hemocytes of the spider crab, Hyas araneus, and the red king crab, Paralithodes camtschaticus

Crustins are distributed across the decapods and are believed to play a significant part in the humoral defense system of their host. In this study, two crustin isoforms from Hyas araneus hemocytes were purified and tested for antimicrobial activity against selected microorganisms. They show both antibacterial and antifungal activity, with highest activity against the Gram-positive bacteria Corynebacterium glutamicum. Sequencing of the transcripts showed them to have a mature peptide of 90 amino acids and differing in three positions in the mature peptide. They were named CruHa1 and CruHa2. Real-time RT-PCR revealed that they mainly are expressed in hemocytes. Screening a cDNA library detected a crustin sequence in Paralithodes camtschaticus hemocytes, coding for a mature peptide of 98 amino acids. It was named CruPc. Based on phylogenetic inference and primary structure, CruHa1 and CruHa2 were placed within the Type I group of crustins, while CruPc belongs to the Type II.