Identification and expression analysis of the g-type and c-type lysozymes in grass carp Ctenopharyngodon idellus

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

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

Expression characteristics and in vitro antibacterial properties of C-type lysozyme in crucian carp infected with Aeromonas salmonicida

Aeromonas salmonicida is an ancient fish pathogen. Lysozymes are important molecules in the innate immune system that fight bacterial infections. The expression characteristics of C-type lysozyme in crucian carp infected with A. salmonicida and its antibacterial effect against A. salmonicida had not been investigated. Thus, we used bioinformatics to analyze the gene and protein characteristics of C-type lysozymes in crucian carp. Changes in C-type lysozyme expression before and after crucian carp infection with A. salmonicida were detected, and the in vitro antibacterial effect of recombinant carp C-type lysozyme on A. salmonicida was validated. The results showed that the coding DNA sequence region of the lysozyme gene sequence was 438 bp long, encoding 145 amino acids and containing two conserved catalytic sites: Glu53 and Asp69. Phylogenetic analysis revealed that crucian carp C-type lysozymes clustered with Cyprinus carpio lysozyme C. After crucian carp were infected with A. salmonicida, the gene and protein expression of C-type lysozymes in the liver, spleen, kidney, and hindgut were significantly upregulated, with the liver showing the highest upregulation that was 15 times higher than that in the uninfected group. In addition, recombinant C-type lysozyme exhibited significant antibacterial activity against A. salmonicida, with an average inhibition zone radius of 0.92 cm when using 40 μg recombinant lysozyme. In conclusion, this study reveals the important role of C-type lysozymes in the innate immune response of crucian carp and provides a theoretical basis for preventing crucian carp infection with A. salmonicida.

Effects of Chinese herbal medicines on growth performance, intestinal flora, immunity and serum metabolites of hybrid grouper (Epinephelus fuscoguttatus♀×Epinephelus lanceolatu♂)

The immunomodulatory roles of Chinese herbal Medicine (CHM) in aquatic animals have been well-recorded. However, how CHM impacts the intestinal microbiota and serum metabolism is not fully understood. In this study, the effects of different additive levels of CHM on the growth performance, immunity, intestinal flora and serum metabolism of hybrid grouper (♀Epinephelus fuscoguttatus × ♂Epinephelus lanceolatu) were investigated. The addition of 0.5%, 1.0%, 1.5% and 2.0% Chinese herbal medicine compound to feed could significantly improve the weight gain rate (WGR), specific growth rate (SGR) and survival rate (SR) of grouper, reduced feed coefficient, while had no significant difference on morphometric parameter. The most significant improvement for the parameters above was observed in 1.5% group. Different addition levels of CHM could also significantly enhance the activities of ACP, AKP, SOD, CAT and LZM in serum. Accordingly, the supplementation of CHM significantly induced up-regulation of immune genes such as IL-8, IL-1β, TNF-α, Nrf2, Lzm in the liver, spleen and head kidney of grouper, improved the resistance of grouper to V. harveyi as well. The intestinal flora analysis showed that at the phylum level, the main dominant species of intestinal microorganisms were Firmicutes, Proteobacteria, Bacteroidota, Actinobacteriota, Gemmatimonadota, Desulfobacterota, Fusobacteriota and Myxococcota. At the genus level, the high abundance was Lactobacillus, Streptococcus, Bacteroides, Escherichia, Romboutsia, Sphingomonas and Muribaculaceae. The abundance of probiotics (such as Lachnospiraceae, Lactobacillaceae, Streptococcaceae, etc) in CHM-supplement groups were higher (highest in 1.5% group) compared with control group. Moreover, a total of 11 common differential metabolic pathways were screened by LC-MS metabolism analysis of serum, they were Neuroactive ligand-receptor interaction, Purine metabolism, Linoleic acid, Glycerophospholipid metabolism, Taurine and hypotaurine metabolism, Arginine and proline metabolism, ABC transporters, Aminoacyl-tRNA biosynthesis, Arachidonic acid metabolism, Drug metabolism-cytochrome P450, alpha-Linolenic acid metabolism. Also, three common differential metabolites (PI(20:4(5Z,8Z,11Z,14Z)/18:1(11Z)), PC(20:3(8Z,11Z,14Z)/22:1(13Z)), PC(22:0/20:4(5Z,8Z,11Z,14Z)) associated with intestinal health, growth and disease resistance was found. These data will contributes to a comprehensive understand for the regulatory roles of CHM on fish, which is also beneficial for the disease control and sustainable development of aquaculture.

Characterization and expression patterns of lysozymes reveal potential immune functions during male pregnancy of seahorse

Seahorses are one of the most amazing ovoviviparous fishes in the ocean because males, and not females, have evolved a brood pouch for incubating embryos. During male pregnancy, paternal seahorses need to develop effective immune protection for embryos in the brood pouch from potential infection by pathogens. Lysozymes (Lyz) are a group of antibacterial enzymes of the innate immune system that play an important role in resisting pathogen invasion. However, the immune function of lysozymes in the brood pouch of the pregnancy-lined seahorse (Hippocampus erectus) remains unknown. In this study, we found three different lysozymes in the lined seahorse: HeLyzC, HeLyzG1, and HeLyzG2. Synteny analysis revealed that HeLyzG1 and HeLyzG2 were generated by species-specific expansion rather than tandem duplication. Tissue expression patterns showed that the highest mRNA expression levels of the three lysozymes occurred in the brood pouches. Immunostimulation-induced expression analysis showed that all three HeLyzs in the brood pouches up-regulated their mRNA expression levels after Vibrio parahaemolyticus infection, but only the HeLyzG2 was upregulated after Poly(I:C) injection. Similarly, except for HeLyzC, upregulated expressions of HeLyzG1 and HeLyzG2 were found quickly in brood pouches injected with LPS. The upregulated levels of HeLyzC and HeLyzG2 in brood pouches during pregnancy were significantly higher than those in non-pregnancy, implying that seahorse lysozymes might function in the immune defense in brood pouches during pregnancy. In addition, the expression levels of HeLyzs were low in embryos in the brood pouch but significantly increased in neonates. This implies that embryos in the brood pouch might not necessarily express more lysozymes by themselves due to paternal immune protection. In conclusion, our study demonstrated that HeLyzs play an important role in immune protection during male seahorse gestation, and the synergistic effect of multiple HeLyzs may contribute to improved neonatal survival.

Immunity in Sea Turtles: Review of a Host-Pathogen Arms Race Millions of Years in the Running

The immune system of sea turtles is not completely understood. Sea turtles (as reptiles) bridge a unique evolutionary gap, being ectothermic vertebrates like fish and amphibians and amniotes like birds and mammals. Turtles are ectotherms; thus, their immune system is influenced by environmental conditions like temperature and season. We aim to review the turtle immune system and note what studies have investigated sea turtles and the effect of the environment on the immune response. Turtles rely heavily on the nonspecific innate response rather than the specific adaptive response. Turtles' innate immune effectors include antimicrobial peptides, complement, and nonspecific leukocytes. The antiviral defense is understudied in terms of the diversity of pathogen receptors and interferon function. Turtles also mount adaptive responses to pathogens. Lymphoid structures responsible for lymphocyte activation and maturation are either missing in reptiles or function is affected by season. Turtles are a marker of health for their marine environment, and their immune system is commonly dysregulated because of disease or contaminants. Fibropapillomatosis (FP) is a tumorous disease that afflicts sea turtles and is thought to be caused by a virus and an environmental factor. We aim, by exploring the current understanding of the immune system in turtles, to aid the investigation of environmental factors that contribute to the pathogenesis of this disease and provide options for immunotherapy.

Chicken-type lysozyme is a major bacteriolytic enzyme in the blood of the banded houndshark Triakis scyllium

We examined lysozyme activities in the serum and the leukocyte extracts of the banded houndshark Triakis scyllium. The serum exhibited lytic activity, but not the leukocyte extracts. The lytic substance in the serum was of approximately 14 kDa and the N-terminal amino acid sequence was YVYSK. cDNA cloning identified a C-type lysozyme (TsLysC) gene and two G-type lysozyme (TsLysG) cDNA clones of different lengths. The TsLysC gene encodes 149 amino acids residues, and the sequence derived from the N-terminal amino acid sequencing was displayed at position 17-21. TsLysG, on the other hand, contains two ORFs that are homologous to the N- and C-terminal regions of G-type lysozyme of other fish species. TsLysC mRNA levels were high in the liver. TsLysG mRNA level was significantly lower than TsLysC mRNA in the liver.

Characterization and functional analysis of a c-type lysozyme gene from obscure puffer Takifugu obscurus

Lysozyme (Lyz) is an alkaline enzyme that hydrolyzes mucopolysaccharides in bacteria and is highly conserved vertebrates and invertebrates. In this study, a c-type lysozyme gene (named ToLyzC) from the obscure puffer Takifugu obscurus was cloned and characterized. The full-length cDNA of ToLyzC was 432 bp, encoding 143 amino acids, with a predicted molecular mass of 16.2 kDa and a theoretical pI of 8.86. The depicted protein sequence contained a LYZ1 domain from 16 to 142 amino acids, seven conserved cysteine residues. Phylogenetic analysis indicated that ToLyzC clustered with Lyzs from other teleost fishes. Quantitative real-time PCR analysis revealed that ToLyzC mRNA was mainly expressed in the liver. The transcript level of ToLyzC gene was significantly upregulated after Staphylococcus aureus and Vibrio harveyi challenge. The optimal pH and temperature of recombinant ToLyzC protein (rToLyzC) lytic activity was detected to be 7.5 and 35 °C, respectively. rToLyzC exhibited significant antibacterial and bacterial binding activities against S. aureus, Aeromonas hydrophila, V. harveyi, and Edwardsiella tarda at different time points. In addition, the morphological changes of V. harveyi cells treated with rToLyzC were observed under scanning electron microscope, which further confirmed the antibacterial and bacteriolytic activity of rToLyzC. Taken together, our current study indicated that ToLyzC is involved in the immune response to bacterial infection in obscure puffers.

Molecular characterization and antibacterial activities of a goose-type lysozyme gene from roughskin sculpin (Trachidermus fasciatus)

Lysozymes, acting as antimicrobial molecules, play a vital role in the host's innate immune response to pathogen infections. In the present study, a g-type lysozyme gene termed Tf-LyzG from roughskin sculpin, Trachidermus fasciatus was firstly reported. The deduced amino acid sequence of Tf-LyzG contained 188 residues and possessed conserved catalytic residues (Glu⁷¹, Asp⁸⁴, and Asp⁹⁵). Gene expression analysis revealed that Tf-LyzG was widely distributed in the tested eleven tissues with the highest expression in the gill and could be significantly induced post lipopolysaccharide (LPS) challenge. The lysozyme activity of the purified recombinant protein (rTf-LyzG) was found to be most active at pH 5.5 and 37 °C. rTf-LyzG exhibited a wide spectrum of potent bacteriolytic activity against four Gram-positive bacteria and six Gram-negative bacteria. It also displayed a high affinity to polysaccharides on bacteria surfaces including LPS, lipoteichoic acid (LTA), and peptidoglycan (PGN). rTf-LyzG was capable of binding and agglutinating all nine bacteria. Flow cytometry assay further revealed that rTf-LyzG could disrupt the membrane of Micrococcus lysodeikticus which is confirmed by scanning electron microscope (SEM) analysis that reveals blebs around the bacterial cell membrane. In summary, these data indicate that Tf-LyzG is of great importance in the fish immune response against pathogens invasion.

Aeromonas veronii infection remarkably increases expression of lysozymes in grass carp (Ctenopharyngodon idellus) and injection of lysozyme expression cassette along with QCDC adjuvant significantly upregulates immune factors and decreases cumulative mortality

Aeromonas veronii AvX005 is a pathogenic bacterium with high toxicity to grass carp (Ctenopharyngodon idellus). The expression levels of g-type (goose-type lysozyme, Lys-g) and c-type lysozyme (chicken-type lysozyme, Lys-c) in the spleen of grass carp infected with AvX005 were significantly increased by approximately 4.5 times and 27 times, respectively. The recombinant proteins rLys-g and rLys-c produced in a recombinant expression system of Escherichia coli showed significant antibacterial activity against the pathogenic bacteria AvX005. A challenge test was conducted after rLys-g and rLys-c were expressed in grass carp L8824 liver cells, and compared with the survival rate of the control cells (46.3%), the survival rate of the experimental cells (77.6% for rLys-g and 68.6% for rLys-c) was significantly increased. Grass carp were infected with AvX005 on the second day after delivering pcDNA3.1-lys-g and pcDNA-lys-c with the Quil A/cholesterol/DDA/Carbopol (QCDC) adjuvant, and both pcDNA3.1-lys-g and pcDNA-lys-c provided 70% relative protection for grass carp. The activity of lysozyme and alkaline phosphatase in the serum of grass carp was significantly increased after injection of DNA. The expression of the immune factors IgM, C3 and IL8 in the kidney was upregulated to varying degrees for pcDNA3.1-lys-g and immune factors C3 and IgM was upregulated for pcDNA-lys-c. The results indicated that pcDNA3.1-lys-g and pcDNA-lys-c may be used as immunostimulants to protect grass carp from the pathogenic bacterium AvX005.

Transcriptome analysis of grass carp (Ctenopharyngodon idella) and Holland's spinibarbel (Spinibarbus hollandi) infected with Ichthyophthirius multifiliis

Ichthyophthirius multifiliis is a protozoan ciliate that causes white spot disease (also known as ichthyophthiriasis) in freshwater fish. Holland's spinibarbel (Spinibarbus hollandi) was less susceptible to white spot disease than grass carp (Ctenopharyngodon Idella). In this study, grass carp and Holland's spinibarbel are infected by I. multifiliis and the amount of infection is 10,000 theronts per fish. All grass carp died within 12 days after infection, and the survival rate of Holland's spinibarbel was more than 80%. In order to study the difference in sensitivity of these two fish species to I. multifiliis, transcriptome analysis was conducted using gill, skin, liver, spleen and head kidney of Holland's spinibarbel and grass carp at 48 h post-infection with I. multifiliis. A total of 489,296,696 clean reads were obtained by sequencing. A total of 105 significantly up-regulated immune-related genes were obtained by Gene Ontology (GO) classification and Kyoto Encyclopedia of Genes and Genomes (KEGG) pathway enrichment analysis in grass carp. Cluster of differentiation 40 (CD40), cluster of differentiation 80 (CD 80), tumor necrosis factor-alpha (TNF-α), toll-like receptor 4 (TLR-4), interleukin 1 beta (IL-1β) and other inflammatory-related genes in grass carp were enriched in the cytokine-cytokine receptor interaction pathway and toll-like receptor pathway. In Holland's spinibarbel, a total of 46 significantly up-regulated immune-related genes were obtained by GO classification and KEGG pathway enrichment analysis. Immune-related genes, such as Immunoglobin heavy chain (IgH), cathepsin S (CTSS), complement C1q A chain (C1qA), complement component 3 (C3) and complement component (C9) were enriched in phagosome pathway, lysosome pathway and complement and coagulation concatenation pathway. C3 was significantly up-regulated in gill and head kidney. Fluorescence in situ hybridization (FISH) showed that the C3 gene was highly expressed in gill tissue of Holland's spinibarbel infected with I. multifiliis. A small amount of C3 gene was expressed in the gill arch of grass carp after infected with I. multifiliis. In conclusion, the severe inflammatory response in vivo after infecting grass carp with I. multifiliis might be the main cause of the death of grass carp. The extrahepatic expression of the gene of Holland's spinibarbel might play an important role in the immune defense against I. multifiliis.

Lysozymes in Fish

In recent years, the deterioration of the aquaculture ecological environment has led to a high incidence of fish diseases. Lysozymes, important antimicrobial enzymes, play an important role in the innate immune system of fish. The studies of fish lysozymes benefit the control of fish infections caused by pathogens. In this review, we reviewed recent progress in fish lysozymes, including their classification, structural characteristics, biological functions and mechanisms, tissue distributions, and properties of their recombinant proteins, which will help us to systematically understand the fish lysozymes and facilitate their applications in the fields of food and agriculture.

Identification and characterization of the c-type lysozyme gene from a marine fish, Bostrychus sinensis

In this study, a c-type lysozyme gene (BsLyzC) was identified and characterized from a marine fish, Bostrychus sinensis. The BsLyzC encodes 154 amino acids and contains a signal peptide of 17 amino acids, two catalytic residues and eight cysteine residues. The genomic DNA of BsLyzC consists of four exons and three introns. The BsLyzC shares high sequence similarity with c-type lysozyme from other fish species. The qPCR assays indicated that the BsLyzC exhibited a constitutive expression pattern in eleven examined tissues of healthy B. sinensis individuals. The transcripts of BsLyzC could be significantly induced after infection of Vibrio parahemolyticus in blood, spleen and head kidney. The optimal temperature and pH for recombinant BsLyzC (rBsLyzC) were found to be 50 °C and 6.0, respectively. The rBsLyzC exhibited antibacterial activities against two Gram-positive bacteria and two Gram-negative bacteria. These results indicate that the BsLyzC is involved in the antibacterial immunity of B. sinensis.

Hypoxia-inducible factor-1α involved in macrophage regulation in ayu (Plecoglossus altivelis) under hypoxia

Hypoxia-inducible factor-1α (HIF-1α) plays a critical role in immune and inflammatory responses and is important in controlling a variety of processes in monocytes and macrophages. However, the role of HIF-1α in the teleost immune system remains less known. In this study, we cloned the cDNA sequence of HIF-1α from the ayu (Plecoglossus altivelis, PaHIF-1α). Sequence and phylogenetic tree analysis showed that PaHIF-1α clustered within the fish HIF-1α tree and was closely related to that of Northern pike (Esox lucius). PaHIF-1α was expressed in all tested tissues and expression increased in liver, head kidney, and body kidney upon Vibrio anguillarum infection. PaHIF-1α was found to regulate the expression of cytokines in ayu monocytes/macrophages (MO/MФ). PaHIF-1α mediated hypoxia-induced enhancement of MO/MФ phagocytic and bactericidal activities to enhance host defenses. Compared with the control, intermittent hypoxia further increased the expression of PaHIF-1α mRNA, improved the survival rate, and reduced the bacterial load of V. anguillarum-infected ayu. Therefore, PaHIF-1α may play a predominant role in the modulation of ayu MO/MФ function.

Effect of dietary isoleucine on skin mucus barrier and epithelial physical barrier functions of hybrid bagrid catfish Pelteobagrus vachelli × Leiocassis longirostris

The study investigated the effects of dietary isoleucine (Ile) on skin mucus barrier and epithelial physical barrier functions of hybrid bagrid catfish Pelteobagrus vachelli × Leiocassis longirostris. A total of 630 fish (33.11 ± 0.09 g) were fed semi-purified isonitrogenous diets containing 5.0 (control), 7.5, 10.0, 12.5, 15.0, 17.5, and 20.0 g Ile kg ^-1 diet for 8 weeks. The results indicated that dietary Ile increased (P < 0.05) in skin (1) mucus protein content and antimicrobial activity against three gram-negative bacteria (Aeromonas hydrophila, Escherichia coli, and Yersinia ruckeri) and two gram-positive bacteria (Streptococcus agalactiae and Staphylococcus aureus), (2) mucus lysofew information is available about the influencezyme (LZM), acid phosphatase (ACP), and alkaline phosphatase (AKP) activities, and complement 3 and 4 (C3 and C4) and immunoglobulin M (IgM) contents, (3) intelectin 1 (intl1), intelectin 2 (intl2), c-type-lysozyme (c-LZM), g-type-lysozyme (g-LZM), and β-defensin mRNA levels. Dietary Ile decreased (P < 0.05) reactive oxygen species (ROS), malondialdehyde (MDA), and protein carbonyl (PC) contents, and up-regulated (P < 0.05) CuZnSOD, GST, GPX1a, muc5ac, muc5b, zonula occludens-1 (ZO-1), zonula occludens-2 (ZO-2), occludin, and claudin 3 mRNA levels in skin. These results indicated that Ile improved skin mucus barrier function via increasing mucus protein, C3 and C4, and IgM contents and antibacterial factors activities, and promoted epithelial physical barrier function via decreasing skin antioxidant damage and improving tight junction structure in hybrid bagrid catfish.

Development of a SNP linkage map and genome-wide association study for resistance to Aeromonas hydrophila in pacu (Piaractus mesopotamicus)

BACKGROUND

Pacu (Piaractus mesopotamicus) is one of the most important Neotropical aquaculture species from South America. Disease outbreaks caused by Aeromonas hydrophila infection have been considered significant contributors to the declining levels of pacu production. The current implementation of genomic selection for disease resistance has been adopted as a powerful strategy for improvement in fish species. This study aimed to investigate the genetic architecture of resistance to A. hydrophila in pacu via Genome-Wide Association Study (GWAS), the identification of suggestive Quantitative Trait Loci (QTLs) and putative genes associated with this trait. The genetic data were obtained from 381 juvenile individuals belonging to 14 full-sibling families. An experimental challenge was performed to gain access to the levels of genetic variation for resistance against the bacteria using the following trait definitions: binary test survival (TS) and time of death (TD).

RESULTS

The analyses of genetic parameters estimated moderate heritability (h2) for both resistance traits: 0.20 (± 0.09) for TS and 0.35 (± 0.15) for TD. A linkage map for pacu was developed to enable the GWAS, resulting in 27 linkage groups (LGs) with 17,453 mapped Single Nucleotide Polymorphisms (SNPs). The length of the LGs varied from 79.95 (LG14) to 137.01 (LG1) cM, with a total map length of 2755.60 cM. GWAS identified 22 putative QTLs associated to A. hydrophila resistance. They were distributed into 17 LGs, and were considered suggestive genomic regions explaining > 1% of the additive genetic variance (AGV) for the trait. Several candidate genes related to immune response were located close to the suggestive QTLs, such as tbk1, trim16, Il12rb2 and lyz2.

CONCLUSION

This study describes the development of the first medium density linkage map for pacu, which will be used as a framework to study relevant traits to the production of this species. In addition, the resistance to A. hydrophila was found to be moderately heritable but with a polygenic architecture suggesting that genomic selection, instead of marker assisted selection, might be useful for efficiently improving resistance to one of the most problematic diseases that affects the South American aquaculture.

Immunization of a novel bivalent outer membrane protein simultaneously resisting Aeromonas hydrophila, Edwardsiella anguillarum and Vibrio vulnificus infection in European eels (Angullia angullia)

In cultivated European eels, Aeromonas hydrophila, Edwardsiella anguillarum and Vibrio vulnificus are three important bacterial pathogens. In this study, European eels (Anguilla anguilla) were immunized by the bivalent expression products of the outer membrane protein (Omp) gene from A. hydrophila (OmpⅡ) and E. anguillarum (OmpA), and the effects of the bivalent protein (rOmpⅡ-A) on the immune function of the European eel were detected. Three hundred eels were divided average into three groups of PBS, adjuvant and rOmp. Eels of three goups were injected intraperitoneal with 0.2 mL of PBS (0.01 mol/L, pH7.4), PBS + F (PBS mixed equal volume of freund's uncomplete adjuvant) or rOmpⅡ-A (1 mg mL^-1 rOmpⅡ-A mixed equal volume of freund's uncomplete adjuvant). Four immune-related genes expression, proliferation of whole blood cells, serum and skin mucus antibody titer, superoxide dismutase (SOD) activity and the relative percent of survival (RPS) were studied at different days (or hours) post the immunization. The results showed that the igm, lysC, mhc2 and sod gene in the liver, spleen, kidney and intestine tract were significant increased in the Omp group; On the 28 day post the immunization (dpi), blood cell proliferation was increased in the Omp group, and on the 14, 21, 28 and 42 dpi, antibody titers in serum and mucus of the Omp group were significantly higher than that of the PBS and adjuvant group, regardless of coating with bacteria or Omp antigen. The SOD activity of Omp group increased significantly in liver, kidney, skin mucus and serum from 14 to 42 dpi, especially in serum. Eels chanllenged by A. hydrophila, E. anguillarum and V. vulnificus in the bivalent Omp group showed the RPS were 83.33%, 55.56% and 44.44%, respectively. The results of this study showed that immunization of the bivalent Omp could effectively improve the immune function of European eels, and produced effectively protection to A. hydrophila and E. anguillarum infection. Simultaneously, the bivalent Omp also produced distinct cross-protection to the eels challenged by V. vulnificus.

Optimal dietary curcumin improved growth performance, and modulated innate immunity, antioxidant capacity and related genes expression of NF-κB and Nrf2 signaling pathways in grass carp (Ctenopharyngodon idella) after infection with Aeromonas hydrophila

This study investigated the effects of dietary curcumin on growth performance, non-specific immunity, antioxidant capacity and related genes expression of NF-κB and Nrf2 signaling pathways in grass carp (Ctenopharyngodon idella). A total of 525 juvenile grass carps with mean initial body weight of (5.30 ± 0.10) g were randomly distributed into five groups with three replicates each, fed five diets containing graded levels of curcumin (0, 196.11, 393.67, 591.46 and 788.52 mg/kg diet) for 60 days. After feeding trial, fifteen fish per tank were challenged with Aeromonas hydrophila and the mortalities were recorded for 7 days. The results showed that optimal dietary curcumin (393.67 mg/kg diet) improved the weight gain (WG) and specific growth rate (SGR) of juvenile grass carp, reduced feed conversion ratio (FCR) and the mortalities after challenge (P < 0.05). Moreover, optimal dietary curcumin increased the activities of lysozyme (LYZ) and acid phosphatase (ACP), and complement 3 (C3) and C4 levels, decreased alanine aminotransferase (ALT) and aspartate aminotransferase (AST) activities in serum of grass carp after injection with A. hydrophila (P < 0.05). Meanwhile, optimal dietary curcumin up-regulated the mRNA levels of LYZ, C3 and antimicrobial peptides [hepcidin, liver-expressed antimicrobial peptide-2 (LEAP-2), β-defensin], and anti-inflammatory cytokines of interleukin-10 (IL-10) and transforming growth factor β1 (TGF-β1), and inhibitor of κBα (IκBα), whereas down-regulated pro-inflammatory cytokines of tumor necrosis factor-α (TNF-α), IL-1β, IL-6 and IL-8, and nuclear factor kappa B p65 (NF-κB p65), IκB kinases (IKKα, IKKβ and IKKγ) mRNA levels in the liver and blood of grass carp after injection with A. hydrophila (P < 0.05). In addition, optimal dietary curcumin increased the reduced glutathione (GSH) content and activities of superoxide dismutase (SOD), catalase (CAT), glutathione peroxidase (GPx), glutathione S-transferase (GST) and glutathione reductase (GR), reduced reactive oxygen species (ROS) and malondialdehyde (MDA) levels in the liver of grass carp after injection with A. hydrophila (P < 0.05). Meanwhile, optimal dietary curcumin up-regulated the mRNA levels of these antioxidant enzymes and nuclear factor erythroid 2-related factor 2 (Nrf2), whereas down-regulated Kelch-like ECH-associated protein (Keap) 1a and Keap 1b mRNA levels (P < 0.05) in the liver and blood of grass carp after injection with A. hydrophila. Thus, optimal dietary curcumin supplementation could promote growth of juvenile grass carp, reduce FCR, and enhance disease resistance, innate immunity and antioxidant capacity of fish, attenuating inflammatory response. However, dietary excessive curcumin had negative effect on fish. Based on second-order regression analysis between dietary curcumin contents and weight gain, the optimum requirement of dietary curcumin in juvenile grass carp was determined to be 438.20 mg/kg diet.

Two Distinct C-Type Lysozymes in Goldfish: Molecular Characterization, Antimicrobial Potential, and Transcriptional Regulation in Response to Opposing Effects of Bacteria/Lipopolysaccharide and Dexamethasone/Leptin

Lysozymes are key antimicrobial peptides in the host innate immune system that protect against pathogen infection. In this study, the full-length cDNAs of two c-type lysozymes (gfLyz-C1 and gfLyz-C2) were cloned from goldfish (Carassius auratus). The structural domains, three-dimensional structures, and amino acid sequences of gfLyz-C1 and gfLyz-C2 were highly comparable, as the two proteins shared 89.7% sequence identity. The gfLyz-C1 and gfLyz-C2 recombinant proteins were generated in the insoluble fractions of an Escherichia coli system. Based on the results of lysoplate and turbidimetric assays, gfLyz-C1 and gfLyz-C2 showed broad-spectrum antimicrobial properties with high levels of activity against Micrococcus lysodeikticus, Vibrio parahemolyticus, and Edwardsiella tarda, and relatively low activity against E. coli. Both gfLyz-C1 and gfLyz-C2 mRNAs were mainly expressed in the trunk kidney and head kidney, and gfLyz-C1 was expressed at much higher levels than gfLyz-C2 in the corresponding tissues. The expression of the gfLyz-C1 and gfLyz-C2 transcripts in the trunk kidney and head kidney was induced in these tissues by challenge with heat-inactivated E. coli and lipopolysaccharides (LPS), and the transcriptional responses of gfLyz-C1 were more intense. In goldfish primary trunk kidney cells, the levels of the gfLyz-C1 and gfLyz-C2 transcripts were upregulated by heat-inactivated E. coli, V. parahemolyticus, and E. tarda, as well as LPS, and downregulated by treatment with dexamethasone and leptins. Overall, this study may provide new insights that will improve our understanding of the roles of c-type lysozymes in the innate immunity of cyprinid fish, including the structural and phylogenetic characteristics, antimicrobial effects, and regulatory mechanism.

Molecular cloning, expression analyses and functional characterization of a goose-type lysozyme gene from Bostrychus sinensis (family: Eleotridae)

In this study, we sequenced and characterized the goose-type lysozyme gene, termed as BsLysG, from the Chinese black sleeper (Bostrychus sinensis). The BsLysG encodes 196 amino acids and contains a soluble bacterial lytic transglycosylases domain, three catalytic residues (Glu⁷², Asp⁸⁵ and Asp¹⁰²) and the GLMQ motif (Gly⁹⁷, Leu⁹⁸, Met⁹⁹ and Gln¹⁰⁰). No signal peptide was observed in the BsLysG protein. The genomic DNA of BsLysG contains five exons and four introns. The sequence analyses showed that the BsLysG exhibits high similarity with LysG from other fishes. Phylogenetic analyses showed that the BsLysG is clustered together with its counterparts from other teleost fishes. The Real-time PCR analyses showed that the BsLysG was found to be ubiquitously expressed in ten examined organs in Chinese black sleeper, with predominant expression in spleen, followed by head kidney and peripheral blood. Expression analyses showed that the BsLysG was significantly upregulated in vivo after either pathogen Vibrio parahemolyticus infection or poly (I:C) challenge in peripheral blood, head kidney, liver and spleen organs. The purified recombinant BsLysG (rBsLysG) has optimal activity at 35 °C and pH 5.5. The rBsLysG exhibited antimicrobial activity against two Gram-positive bacteria (Micrococcus lysodeikticus and Staphylococcus aureus) and two Gram-negative bacteria (Escherichia coli and V. parahemolyticus). The Scanning electron microscope (SEM) imaging analyses showed that the rBsLysG-treated V. parahemolyticus cells displayed morphological deformation. These results indicate that the BsLysG is involved in host immune defense against bacterial infection.

Immuno-stimulatory effects of sulfated polysaccharides isolated from Codium fragile in olive flounder, Paralichthys olivaceus

Sulfated polysaccharides isolated from Codium fragile have been previously demonstrated to possess immune-stimulating effects on murine cell lines and the fraction F2 (F2) isolated by ion exchange chromatography was the most effective. In this study, the effects of the fraction F2 were evaluated on the expressions of immune genes including IL-1β, TNF-α, IL-8, IFN-γ and lysozyme in vitro and in vivo as well as lysozyme and complement activities in serum of olive flounder, Paralichthys olivaceus. In vitro, these gene expressions were up-regulated by F2 in head kidney cells. In vivo, IL-1β and IL-8 gene expressions were up-regulated in peritoneal cells, head kidney, liver, gill and spleen, while TNF-α, IFN-γ and lysozyme gene expressions were mostly up-regulated but varied depending on tissue types or time points. Indeed, lysozyme and complement activities in serum were increased. Overall, these results indicate that the sulfated polysaccharides from C. fragile have immuno-stimulatory effects on olive flounder and may be used to enhance immunity during aquaculture.

Identification and functional characterization of a g-type lysozyme gene of Labeo rohita, an Indian major carp species

Lysozyme, an important secretory innate immune component, possesses antimicrobial activity against broad spectrum of bacteria and viruses. In the present study, complete CDs (558 bps) of g-type lysozyme of rohu (Labeo rohita) was amplified and translated for a putative protein of 185 amino acids. The domain architecture and tertiary structure was also predicted for the protein. Its expression profile was studied in three infection models (bacteria: Aeromonas hydrophila, poly I:C, a dsRNA viral analogue and an ectoparasite: Argulus siamensis) in liver and kidney tissues of rohu. An up-regulation of 630-fold and 420-fold of the gene was observed at 48 h in liver and anterior kidney tissues respectively, after A. hydrophila infection. Significant increase in transcript level was noticed in both liver (0.8-fold) and kidney (480-fold) after 1 h and 12 h of poly I:C induction, respectively. Similarly, expression of lysozyme g transcripts was increased 6000-fold after 7 d of A. siamensis infection in liver tissue. The recombinant protein of g-type lysozyme of rohu (rLr-lysG) of 20.19 kDa was produced in Escherichia coli system and the lysozyme activity of rLr-lysG was found to be most active at pH 6.0 and temperature 35 °C. The potential lytic activity was found to be against A. hydrophila (U_L = 0.53) followed by for E. tarda (U_L = 0.45) whereas the lytic activity was the least against S. aureus (U_L = 0.35) and M. lysodeikticus (U_L = 0.34), at pH 6.0 and temperature 35 °C. The normal serum level of protein was estimated using indirect ELISA and was found to be very low (0.12-0.15 μg/ml). These results suggested that g-type lysozyme of rohu might be a potent immunostimulant against microbial infections, with a major role in innate immunity.

Molecular cloning, expression and antibacterial activity of goose-type lysozyme gene in Microptenus salmoides

It is well known that lysozymes are key proteins to teleosts in the innate immune system and possess high bactericidal properties. In the present study, a g-type lysozyme gene was cloned from Microptenus salmoides. The g-type sequence consisted of 582 bp, which translated into a 193 amino acid (AA) protein (GenBank accession no: MH087462). The predicted molecular weight and theoretical isoelectric point were 21.36 kDa and 6.91 respectively and no signal peptide was observed. The qRT-PCR analysis showed that the g-type lysozyme gene was differentially expressed in various tissues under normal conditions and the highest g-type lysozyme level was observed in liver, gill and spleen while there seemed to be low expression in the muscle, heart and head-kidney. The expression of g-type lysozyme was differentially upregulated in the spleen, gill and intestine after stimulation with heat stress and Aeromonas hydrophila (A. hydrophila). Under heat stress and A. hydrophila injection, the g-type lysozyme mRNA levels all in spleens, gill and intestine tissues increased significantly (P < 0.05), with the maximum levels attained at 12 h, 24 h (or 12 h) and 24 h. Thereafter, they all decreased significantly (P < 0.01) and the expression in gill returned to nearly the basal value within 72 h. Those results suggested that g-type lysozyme was involved in the immune response to heat stress and bacterial challenge. The cloning and expression analysis of the g-type lysozyme provide theoretical basis to further study the mechanism of anti-adverseness in Microptenus salmoides. The g-type lysozyme gene perhaps also played an important role in the immune responses against bacterial invasion.

Molecular characterization, expression, and antibacterial activity of a c-type lysozyme isolated from the manila clam, Ruditapes philippinarum

Lysozyme is an antibacterial enzyme that is widely distributed in nature and plays an important role in the prevention of bacterial infections. In this study, a c-type lysozyme (designated as "RpCLYZ") was cloned and characterized from the manila clam, Ruditapes philippinarum. The full-length cDNA was 619 bp with an open reading frame (ORF) of 447 bp, and encoded a polypeptide of 148 amino acids with a calculated molecular mass of 17.0 kDa and an isoelectric point of 4.83. RpCLYZ was found to share high sequence similarity with c-type lysozymes from other invertebrates. The mRNA transcript of RpCLYZ was universally expressed in a wide range of tissues, especially in gills and mantle. Challenge with Vibrio anguillarum, significantly induced mRNA expression of RpCLYZ, which reached a maximum level 48 h after bacterial challenge. Recombinant RpCLYZ (rRpCLYZ) exhibited antibacterial activities against both Gram-positive and Gram-negative bacteria. Additionally, the optimal pH and temperature for rRpCLYZ activity were determined to be 4.5 and 20 °C, respectively. These results suggest that RpCLYZ participates in innate immune responses against bacterial invasion.

Molecular, transcriptional and functional insights into duplicated goose-type lysozymes from Sebastes schlegelii and their potential immunological role

Black rockfish (Sebastes schlegelii), an important aquaculture species in Korea, has been affected by bacterial diseases leading to a drastic decline in production. Goose-type lysozyme (LysG) is a key enzyme of the innate immune system to eradicate bacterial infections. In this study, two isoforms of LysG from black rockfish, designated as RfLysG1 and RfLysG2, have been identified and characterized at the molecular, transcriptional, and functional levels. The deduced amino acid sequences had the LysG family characteristics and exhibited conserved properties, including active residues and domains. The cDNA sequences of RfLysG1 and RfLysG2 were 1514 bp and 900 bp in length, respectively. The 567-bp open reading frame (ORF) of RfLysG1 encoded a protein of 188 amino acids with molecular mass 20.11 kDa, and the 600-bp ORF of RfLysG2 encoded a polypeptide with 199 amino acids and molecular mass of 22.19 kDa. Homology studies indicated that RfLysG1 showed the highest identity (84.6%) with LysG-B of Oplegnathus fasciatus, while RfLysG2 showed the highest identity (74.4%) with LysG of Siniperca chuatsi. Both sequences possessed a soluble lytic trans-glycosylase domain. Both lacked signal peptide and they were not identified as proteins secreted by non-classical pathway by the SecretomeP server. Transcriptional analysis of the two genes showed constitutive expression, where both genes were highly expressed in blood under normal physiological conditions. In response to the immune challenges lipopolysaccharide (LPS), Streptococcus iniae, and poly I:C injection, the expression of RfLysG1 and RfLysG2 was significantly upregulated in blood and spleen tissues in a time-dependent manner. Turbidimetric assays indicated that both recombinant proteins tagged with maltose-binding protein (MBP) were reactive against several Gram-positive and Gram-negative bacteria, but MBP was inactive. Optimum temperatures for the recombinant RfLysG1 and RfLysG2 were 40 °C and 50 °C, respectively, and both were highly active at pH 3.0. The results provide evidence for the vital immunological role and bacteriolytic potential of RfLysG1 and RfLysG2.

Molecular characterization, expression and antimicrobial activities of two c-type lysozymes from manila clam Venerupis philippinarum

Lysozymes play an important role in the innate immune responses with which mollusks respond to bacterial invasion through its lytic activity. In the present study, two c-type lysozymes (designed as VpCLYZ-1 and VpCLYZ-2, respectively) were identified and characterized from the manila clam Venerupis philippinarum. The full-length cDNA of VpCLYZ-1 and VpCLYZ-2 was of 629 and 736 bp, encoding a polypeptide of 156 and153 amino acid residues, respectively. The deduced amino acid sequences of VpCLYZs showed high similarity to other known invertebrate c-type lysozymes. Multiple alignments and phylogenetic relationship strongly suggested that VpCLYZ-1 and VpCLYZ-2 belonged to the c-type lysozyme family. Both VpCLYZ-1 and VpCLYZ-2 transcripts were constitutively expressed in a wide range of tissues with different levels. The VpCLYZ-1 transcript was dominantly expressed in hepatopancreas and hemocytes, while VpCLYZ-2 transcript was mainly expressed in the tissues of hepatopancreas and gills. Both the mRNA expression of VpCLYZ-1 and VpCLYZ-2 was significantly up-regulated at 12 h post Vibrio anguillarum challenge. The recombinant VpCLYZ-1 and VpCLYZ-2 (designed as rVpCLYZ-1 and rVpCLYZ-2) exhibited lytic activity against all tested bacteria, and rVpCLYZ-1 showed higher activities than rVpCLYZ-2 in killing Micrococcus luteus and V. anguillarum. Overall, our results suggested that VpCLYZ-1 and VpCLYZ-2 belonged to the c-type lysozyme family, and played important roles in the immune responses of manila clam, especially in the elimination of pathogens.

Analysis on the expression and function of a chicken-type and goose-type lysozymes in Chinese giant salamanders Andrias davidianus

Lysozymes as an important immune factor, play vital roles in innate immune response against pathogen infection. In the present study, one c-type and g-type lysozymes were identified from Chinese giant salamander (Andrias davidianus). They shared highly conserved structural features with lysozymes from other species. Spatial expression analysis revealed that AdlysC transcript was most abundant in liver and stomach, and least in muscle and brain. In contrast, the expression level of AdlysG was most abundant in liver and least in muscle and skin. The transcription level of c-type and g-type lysozymes were up-regulated after Aeromonas hydrophila infection in liver and spleen, indicating their participations in the immune response. Moreover, the recombinant AdlysC and AdlysG protein were produced and purified, and were used to investigate the lysozyme activity at different pH and temperatures. The optimal lytic activity was determined at pH 6.0 and at a temperature of 30 °C. Through the minimal inhibitory concentration test, the rAdlysC and rAdlysG exhibited apparent antibacterial activity against both Gram-positive and Gram-negative bacteria with a variable concentration. In conclusion, it is the first report of lysozymes in A. davidianus, and c-type and g-type lysozymes should be involved in the innate immune response of A. davidianus.

The polymorphism of chicken-type lysozyme gene in Japanese flounder (Paralichthys olivaceus) and its association with resistance/susceptibility to Listonella anguillarum

Lysozyme is a crucially spread hydrolase in organisms that can defend against bacterial infection in innate immunity. In this study, we successfully sequenced the coding region of chicken-type lysozyme gene (PoLysC) in Paralichthys olivaceus and identified nine single nucleotide polymorphisms (SNPs). We then amplified the 2500 bp promoter region of lysozyme and identified the eight sites of polymorphisms. All SNPs were genotyped between susceptible and resistance groups after Listonella anguillarum challenge. One of these SNP sites in the codon of PoLysC was genotyped and determined to be a significant marker by analyzing its distribution in the susceptible and resistant groups. As a nonsynonymous mutation, the frequency of 140G/C genotype in the resistant group was higher (67.74%) than that in the susceptible group (32.26%). The linkage between SNP140 and polymorphisms in the promoter region was also studied. Results revealed that the frequency of haplotype CC_-536/CC_-1200/GG₁₄₀ in the resistance group was significantly higher than that in the susceptible group. The quantitative expression of lysozyme gene in the resistant group was also higher than that in the susceptible group. This finding indicated that the linkage between polymorphism -536 and -1200 sites in promoter and SNP140 in codon sequence was associated with the resistance of P. olivaceus to L. anguillarum. All these results suggest that the mutations in promoter and coding region were related to changes in PoLysC for resisting L. anguillarum. The haplotype CC_-536/CC_-1200/GG₁₄₀ was a potential marker and can thus be applied to selective breeding for the disease resistance of P. olivaceus.

Transcription of immune related genes in Solea senegalensis vaccinated against Photobacterium damselae subsp. piscicida. Identification of surrogates of protection

Solea senegalensis is a flatfish with a great potential for aquaculture, but infectious diseases restrict its production, being this fish species highly susceptible to Photobacterium damselae subsp. piscicida (Phdp) infections. A better understanding of the mechanisms related to fish immune response is crucial for the development of effective approaches in disease management. In the present work, transcriptional changes of immune related genes have been evaluated in farmed S. senegalensis specimens vaccinated against Phdp by intraperitoneal injection (IP) and immersion (IM). IP fish showed higher antibody levels and increased transcription of genes encoding lysozyme C1, complement factors involved in the classical pathway and components involved in the opsonization and the limitation of free iron availability, all of them facilitating the faster elimination of the pathogen and promoting higher RPS after the infection with Phdp. The results of this study seem to support a different intensity of the specimens immune response in the head kidney. Analysis of the immune response in 15 day post-challenged fish showed up-regulation of genes involved in all stages of S. senegalensis immune response, but especially those genes encoding proteins related to the innate response such as complement, lysozyme and iron homeostasis in the head kidney. On the other hand, liver transcription was higher for genes related to inflammation, apoptosis and cell mediated cytotoxicity (CMC). Furthermore, comparison of the differential response of S. senegalensis genes in vaccinated and unvaccinated fish to Phdp infection allowed the identification of a potential biosignature, consisting in 10 genes, as a surrogate of protection and therefore, as indicator of vaccine success against fotobacteriosis after IP vaccination. These results provide important insights into the S. senegalensis protection against Phdp induced by vaccination.

Molecular characteristics of lysozyme G in Euryglossa orientalis; cDNA cloning, phylogenic analysis, physicochemical properties and tissue gene expression

Lysozymes are the key molecules of innate immune system against bacterial infections. In the present study, we identified the molecular characteristics, physicochemical properties, antibacterial activity, evolutionary relationship and tissue expression pattern of g-type lysozyme in Euryglossa orientalis (EuOr LysG). The full-length EuOr LysG cDNA is composed of 588 nucleotides and an open reading frame encoding a protein with 195 amino acids with more than 65 % identity to g-type lysozyme of Solea senegalensis (73 %) and Scophthalmus rhombus (64 %). Amino acid sequence alignment showed that EuOr LysG protein possessed a conserved catalytic motif (Glu71-Asp84-Asp101) and one predicted disulfide bond between Cys32 and Cys122. Phylogenetic analysis based on the g-type lysozyme sequences indicated that E. orientalis and other fish of Pleuronectiformes were diverged together in the evolutionary history. The K _m and V _max values of the recombinant EuOr LysG were 0.266 mg/ml of Micrococcus lysodeikticus as substrate and 667 U/mg of protein, respectively. The optimum temperature and pH of recombinant EuOr LysG were 45 and 6 °C, respectively. Real-time PCR analysis showed that EuOr LysG transcript was most abundant in head kidney and gill and less in muscle. We also showed that the EuOr LysG had potent lytic activity against major fish bacterial pathogens with the highest activity against Bacillus cereus and Aeromonas hydrophila. Bacterial challenge with Vibrio parahaemolyticus could upregulate LysG in immune-related tissues. Our results help to understand the molecular and physicochemical characteristics of g-type lysozyme in E. orientalis which might play an important role in host defense against the bacterial infection.

Molecular identification and expression analysis of a goose-type lysozyme (LysG) gene in yellow catfish Pelteobagrus fulvidraco

Lysozymes, innate immunity molecules, play a vital role in immune response to pathogens. The yellow catfish Pelteobagrus fulvidraco (Siluriformes: Bagridae) is an economically important fish in China. The aim of this study was to quantify expression of the P. fulvidraco LysG gene (a g-type lysozyme) in response to pathogen-associated molecular patterns (PAMP) challenge. First, the P. fulvidraco LysG gene (PfLysG) was cloned and characterized. The full-length cDNA of PfLysG is 1323 bp, including a 5'-untranslated region (UTR) of 131 bp, a 3'-UTR of 634 bp, and an open reading frame of 558 bp encoding a polypeptide of 185 amino acids, which contains a transglycosylase SLT domain (Pfam01464). The predicted molecular weight of the protein is 20.52 kDa with a pI of 9.08. Two catalytic residues and seven N-acetyl-D-glucosamine binding sites are conserved in the sequence and there is no predicted signal peptide. The deduced PfLysG protein sequence has 84%, 76% and 69% percent identity with the LysGs from Ictalurus furcatus, Danio rerio, and Salmo salar, respectively. The predicted tertiary structure of PfLysG is very similar to that from other animals. Phylogenetic analysis showed that PfLysG is closely related to those from Teleostei. Real-time quantitative reverse transcription-PCR (qPCR) analysis showed that PfLysG was expressed in all examined tissues and most highly expressed in head kidney, spleen, and intestine. After simulated pathogen challenge with lipopolysaccharide and polyriboinosinic polyribocytidylic acid, respectively, the mRNA expression of PfLysG was upregulated significantly at different time points. The results suggest that the identified g-type lysozyme of P. fulvidraco is involved in innate immune responses.

Effects on intestinal microbiota and immune genes of Solea senegalensis after suspension of the administration of Shewanella putrefaciens Pdp11

The interaction host-intestinal microbiota is essential for the immunological homeostasis of the host. Probiotics, prebiotics and synbiotics are promising tools for the manipulation of the intestinal microbiota towards beneficial effects to the host. The objective of this study was to evaluate the modulation effect on the intestinal microbiota and the transcription of genes involved in the immune response in head kidney of Solea senegalensis after administration of diet supplemented with the prebiotic alginate and the probiotic Shewanella putrefaciens Pdp11 CECT 7627 (SpPdp11). The results showed higher adaptability to dietary changes in the intestinal microbiota of fish fed diet with alginate and SpPdp11 together compared to those fish that received an alginate-supplemented diet. The alginate-supplemented diet produced up-regulation of genes encoding proteins involved in immunological responses, such as complement, lysozyme G and transferrin, and oxidative stress, such as NADPH oxidase and glutation peroxidase. On the other hand, the administration of alginate combined with SpPdp11 resulted in a significant increase of the transcription of genes encoding for glutation peroxidase and HSP70, indicating a potential protective effect of SpPdp11 against oxidative stress. In addition, these effects were maintained after the suspension of the probiotic treatment. The relationship between the modulation of the intestinal microbiota and the expression of genes with protective effect against the oxidative stress was demonstrated by the Principal Components Analysis.

Molecular characterization, transcriptional profiling, and antibacterial potential of G-type lysozyme from seahorse (Hippocampus abdominalis)

Lysozymes are a family of enzymes that catalyze the hydrolysis of bacterial cell wall, acting as antimicrobial effectors of the innate immune system. In the present study, an ortholog of goose-type lysozyme (ShLysG) from the big-belly seahorse (Hippocampus abdominalis) was identified and characterized structurally and functionally. The full-length cDNA sequence (1213 bp) of ShLysG is comprised of an open reading frame made up of 552 bp, encoding a polypeptide of 184 amino acid (aa) with a predicted molecular mass of 20 kDa. In silico analysis of ShLysG revealed the absence of signal peptide and the presence of a characteristic bacterial soluble lytic transglycosylase (SLT) domain bearing three catalytic residues (Glu⁷¹, Asp⁸⁴, and Asp⁹⁵) and seven N-acetyl-d-glucosamine binding sites (Glu⁷¹, Asp⁹⁵, Tyr⁹⁸, His⁹⁹, Ile¹¹⁷, Tyr¹⁴⁵, and Asn¹⁴⁶). Homology analysis demonstrated that the aa sequence of ShLysG shared 60.7-67.4% identity and 72.6-79.3% similarity with the orthologs of other teleosts. Phylogenetic analysis of ShLysG indicated a closest relationship with the ortholog from Gadus morhua. In healthy seahorse, ShLysG mRNA showed a constitutive expression in all the tissues examined, with the highest expression in kidney and the least expression in liver. The ShLysG mRNA levels were also shown significant elevation upon the bacterial and pathogen-associated molecular pattern (PAMPs) challenges. Furthermore, lytic activities of ShLysG recombinant protein were detected against several Gram-negative and Gram-positive bacterial species. Taken together, these results suggest that ShLysG might possess a potential immune defensive role against invading microbial pathogens in seahorse.

Expression and antimicrobial activity of c-type lysozyme in taimen (Hucho taimen, Pallas)

Lysozymes are important defense proteins of the innate immune system and possess high antibacterial activities. In the present study, a full-length c-type lysozyme cDNA (HtLysC) was cloned and characterized from taimen (Hucho taimen, Pallas). The cDNA contains an open reading frame (ORF) of 432 bp encoding 143 amino acid (aa), with 97% identity to LysC of Rainbow trout (Oncorhynchus mykiss). The amino acid sequence possessed a LYZ1 domain (16-140 aa) which contained two conserved residues (Glu 50 and Asp 67), eight conserved cysteine residues and a calcium binding site. RT-PCR analysis showed that HtLysC transcripts were most abundant in liver and less in muscle. The expression of HtLysC was up-regulated in the liver when challenged with Yersinia ruckeri. The recombinant HtLysC (rHtLysC) had lytic activities against Micrococcus lysodeikticus, Aeromonas salmonicida and Y. ruckeri. Enzyme assay showed that the optimal temperature and pH of rHtLysC were 55 °C and 6.0, respectively. Taken together, these results indicated that HtLysC might play an important role in innate immune defense against bacterial pathogens as a functional lysozyme.

Molecular cloning, inducible expression and antibacterial analysis of a novel i-type lysozyme (lyz-i2) in Pacific white shrimp, Litopenaeus vannamei

The full-length cDNA coding for a novel invertebrate (i-type) lysozyme was identified in Pacific white shrimp (Litopenaeus vannamei). The newly obtained L. vannamei lysozyme is similar to the Penaeus monodon i-type lysozyme 2, but it is distant from the known L. vannamei c-type lysozyme and i-type lysozyme 1 in protein sequence; therefore, it was defined as L. vannamei i-type lysozyme 2 (lyz-i2). Expression of L. vannamei lyz-i2 transcripts were ubiquitously detected in all tissues we selected, with the highest abundance observed in the hemolymph. Challenge with Vibrio harveyi might elicit L. vannamei lyz-i2 mRNA expression in the hepatopancreas, intestine, muscle, gill and hemolymph. In the themolymph, specifically, the stimulatory effects of Vibrio and lipopolysaccharide (LPS) on lyz-i2 transcript levels were durable and transient, respectively; while Polyinosinic:polycytidylic acid [Poly (I:C)] treatment did not affect lyz-i2 expression. L. vannamei lyz-i2 recombinant protein was generated in an Escherichia coli system. By lysoplate and turbidimetric assays, the L. vannamei lyz-i2 recombinant protein showed a broad spectrum of antimicrobial properties with high activities against Micrococcaceae lysodeikticus and various Vibrio species and relatively low activity against E. coli. In conclusion, L. vannamei lyz-i2 might be a potent antibacterial protein with a role in innate immunity in Penaeid shrimp.

Cloning and expression analysis of c-type lysozyme gene in golden pompano, Trachinotus ovatus

It is well known that lysozymes are key proteins to teleosts in the innate immune system and possess high bactericidal properties. In the present study, a c-type lysozyme gene (To-lysC) was cloned from golden pompano, Trachinotus ovatus. The To-lysC cDNA is composed of 743 bp with a 36 bp of 5'-UTR, 432 bp open reading frame (ORF) and 275 bp 3'-UTR, encoding a polypeptide of 144 amino acids (GenBank accession no: KT935522). Phylogenetic analysis revealed that To-lysC showed highest similarity to Perca flavescens lysC. Quantitative real-time PCR (qRT-PCR) analysis showed that To-lysC had relatively high expression level in the head kidney, gill and brain. After Vibrio harveyi infection, transcripts of To-lysC increased and reached its peak at 12 h p.i. These results indicated that To-lysC may play an important role in innate immune response to bacteria.

Molecular characterization and expressing analysis of the c-type and g-type lysozymes in Qihe crucian carp Carassius auratus

Lysozyme as an important nonspecific immune factor, can kill bacteria by hydrolyzing β-1,4-glycosidic linkages of peptidoglycan layer, and plays an important role in innate immune response against pathogen infection. In the present study, we report molecular cloning, tissue distribution and functional characterization of the c-type and g-type lysozymes in Qihe crucian carp Carassius auratus (designated as Ca-clys and Ca-glys, respectively). The full-length of Ca-clys and Ca-glys cDNA were cloned using RT-PCR and RACE methods. Catalytic and other conserved residues, required for functionality, were identified by multiple sequence alignment and structure predicted. The findings indicating the Ca-clys with signal peptide sequence, while the Ca-glys without, imply that the two isozymes function in different sites of cell. Phylogenetic analysis revealed that Ca-clys and Ca-glys genes evolve at different rates. Moreover, spatial expression analysis showed that Ca-clys transcript was most abundant in kidney and least in gill. However, the expression level of Ca-glys was significantly lower compared with Ca-clys in various tissues, which was the most abundant in spleen and least in brain. After intraperitoneal injection with A. hydrophila and lipopolysaccharide (LPS), the mRNA levels of Ca-clys and Ca-glys were generally up-regulated in liver and gill, but indicated the different expression changes in spleen, kidney and head kidney. With regard to the lysozyme activity, it was showed that the total enzyme activities generally increased in liver, gill, spleen, and head kidney after stimulation. These results confirmed that both Ca-clys and Ca-glys play an important role in non-specific immunity after A. hydrophila invasion. In this study, it was speculated that expressions of Ca-clys and Ca-glys were regulated in different patterns against pathogens.

A novel antimicrobial peptide derived from fish goose type lysozyme disrupts the membrane of Salmonella enterica

In aquaculture, accumulation of antibiotics resulted in development of resistance among bacterial pathogens. Consequently, it became mandatory to find alternative to synthetic antibiotics. Antimicrobial peptides (AMPs) which are described as evolutionary ancient weapons have been considered as promising alternates in recent years. In this study, a novel antimicrobial peptide had been derived from goose type lysozyme (LyzG) which was identified from the cDNA library of freshwater fish Channa striatus (Cs). The identified lysozyme cDNA contains 585 nucleotides which encodes a protein of 194 amino acids. CsLyzG was closely related to Siniperca chuatsi with 92.8% homology. The depicted protein sequence contained a GEWL domain with conserved GLMQ motif, 7 active residues and 2 catalytic residues. Gene expression analysis revealed that CsLyzG was distributed in major immune organs with highest expression in head kidney. Results of temporal expression analysis after bacterial (Aeromonas hydrophila) and fungal (Aphanomyces invadans) challenges indicated a stimulant-dependent expression pattern of CsLyzG. Two antimicrobial peptides IK12 and TS10 were identified from CsLyzG and synthesized. Antibiogram showed that IK12 was active against Salmonella enterica, a major multi-drug resistant (MDR) bacterial pathogen which produces beta lactamase. The IK12 induced loss of cell viability in the bacterial pathogen. Flow cytometry assay revealed that IK12 disrupt the membrane of S. enterica which is confirmed by scanning electron microscope (SEM) analysis that reveals blebs around the bacterial cell membrane. Conclusively, CsLyzG is a potential innate immune component and the identified antimicrobial peptide has great caliber to be used as an ecofriendly antibacterial substance in aquaculture.

Transcriptional response of Atlantic salmon families to Piscirickettsia salmonis infection highlights the relevance of the iron-deprivation defence system

Background

Piscirickettsiosis or Salmonid Rickettsial Septicaemia (SRS) is a bacterial disease that has a major economic impact on the Chilean salmon farming industry. Despite the fact that Piscirickettsia salmonis has been recognized as a major fish pathogen for over 20 years, the molecular strategies underlying the fish response to infection and the bacterial mechanisms of pathogenesis are poorly understood. We analysed and compared the head kidney transcriptional response of Atlantic salmon (Salmo salar) families with different levels of susceptibility to P. salmonis infection in order to reveal mechanisms that might confer infection resistance.

Results

We ranked forty full-sibling Atlantic salmon families according to accumulated mortality after a challenge with P. salmonis and selected the families with the lowest and highest cumulative mortalities for microarray gene expression analysis. A comparison of the response to P. salmonis infection between low and high susceptibility groups identified biological processes presumably involved in natural resistance to the pathogen. In particular, expression changes of genes linked to cellular iron depletion, as well as low iron content and bacterial load in the head kidney of fish from low susceptibility families, suggest that iron-deprivation is an innate immunity defence mechanism against P. salmonis. To complement these results, we predicted a set of iron acquisition genes from the P. salmonis genome. Identification of putative Fur boxes and expression of the genes under iron-depleted conditions revealed that most of these genes form part of the Fur regulon of P. salmonis.

Conclusions

This study revealed, for the first time, differences in the transcriptional response to P. salmonis infection among Atlantic salmon families with varied levels of susceptibility to the infection. These differences correlated with changes in the abundance of transcripts encoding proteins directly and indirectly involved in the immune response; changes that highlighted the role of nutritional immunity through iron deprivation in host defence mechanisms against P. salmonis. Additionally, we found that P. salmonis has several mechanisms for iron acquisition, suggesting that this bacterium can obtain iron from different sources, including ferric iron through capturing endogenous and exogenous siderophores and ferrous iron. Our results contribute to determining the underlying resistance mechanisms of Atlantic salmon to P. salmonis infection and to identifying future treatment strategies.

Electronic supplementary material

The online version of this article (doi:10.1186/s12864-015-1716-9) contains supplementary material, which is available to authorized users.

Transcriptional Onset of Lysozyme Genes during Early Development in Olive Flounder (Paralichthys olivaceus)

The immune system in teleost fish is not completely developed during embryonic and larval stages, therefore effective innate mechanisms is very important for survival in such an environment. However, the knowledge of the development of immune system assumed to be restricted. In many species, lysozymes have been considered as important genes of the first line immune defense. The early detection of lysozyme mRNA in previous reports, led to the investigation of its presence in oocytes. As a result, c-type lysozyme mRNA transcripts were detected in unfertilized oocytes indicating maternal transfer. Therefore, we investigated the expression patterns of lysozymes in flounder, including the matured oocyte. In our results, c-type lysozyme mRNA was first detected in unfertilized oocyte stage, observed the significantly decreased until hatching stage, and was significantly increased after hatching stage. On the other hand, g-type lysozyme mRNA transcripts were first detected at late neurula stage, and the mRNA level was significantly increased after 20 dph. It may be suggest that maternally supplied mRNAs are selectively degraded prior to the activation of embryonic transcription. This study will be help in understanding the maturation and onset of humoral immunity during development of olive flounder immune system.

Transcriptional Onset of Lysozyme Genes during Early Development in Olive Flounder (Paralichthys olivaceus)

The immune system in teleost fish is not completely developed during embryonic and larval stages, therefore effective innate mechanisms is very important for survival in such an environment. However, the knowledge of the development of immune system assumed to be restricted. In many species, lysozymes have been considered as important genes of the first line immune defense. The early detection of lysozyme mRNA in previous reports, led to the investigation of its presence in oocytes. As a result, c-type lysozyme mRNA transcripts were detected in unfertilized oocytes indicating maternal transfer. Therefore, we investigated the expression patterns of lysozymes in flounder, including the matured oocyte. In our results, c-type lysozyme mRNA was first detected in unfertilized oocyte stage, observed the significantly decreased until hatching stage, and was significantly increased after hatching stage. On the other hand, g-type lysozyme mRNA transcripts were first detected at late neurula stage, and the mRNA level was significantly increased after 20 dph. It may be suggest that maternally supplied mRNAs are selectively degraded prior to the activation of embryonic transcription. This study will be help in understanding the maturation and onset of humoral immunity during development of olive flounder immune system.

Molecular cloning and characterization of a new G-type lysozyme gene (Ec-lysG) in orange-spotted grouper, Epinephelus coioides

Lysozyme acts as an innate immunity molecule against pathogen infection. In this study, a new G-type lysozyme gene with a typical G-type lysozyme domain (designated as Ec-lysG) was cloned and characterized from the orange-spotted grouper, Epinephelus coioides. The full-length Ec-lysG cDNA contains 1419 bp and encodes a 256-residue protein containing a 25-residue signal peptide at the N-terminus. BLAST analysis reveals Ec-lysG shares 64% identity with Siniperca chuatsi, but 63% to another reported G-type lysozyme from orange-spotted grouper (OSG-lysG). The genomic DNA of Ec-lysG contains four exons and three introns, with a total length of 2062 bp. An amino acid sequence alignment showed that Ec-lysG shares the fundamental structural features of G-type lysozyme, including the catalytic residues, substrate binding sites, and soluble lytic transglycosylase domain. Quantitative PCR showed that Ec-lysG transcript is most abundant in the head kidney, and less abundant in the heart. The expression of Ec-lysG was differentially upregulated in the head kidney after stimulation with lipopolysaccharide, Vibrio alginolyticus, and Singapore grouper iridovirus (SGIV). A subcellular localization analysis showed that Ec-lysG is distributed predominantly in the cytoplasm. Recombinant Ec-lysG (rEc-lysG) has optimal activity at pH 7.5 and 35°C. rEc-lysG showed lytic activities against Gram-positive bacterium Streptococcus iniae, Staphylococcus aureus, and Micrococcus lysodeikticus, and the Gram-negative bacterium V. alginolyticus. Scanning electron microscopy (SEM) showed that rEc-lysG acts on M. lysodeikticus cell walls. The overexpression of Ec-lysG in grouper cells did not significantly delay the occurrence of the cytopathic effect (CPE) induced by SGIV, and did not inhibit viral gene transcription. In conclusion, Ec-lysG might be a potent antibacterial protein, with a role in innate immunity.

Identification and characterization of a goose-type lysozyme from sewage snail Physa acuta

Freshwater snail Physa acuta has been considered as an important invasive species and medical mollusc. Field investigation has shown that this snail could survive better than other snails in polluted water bodies. To understand the immune mechanisms of P. acuta, suppression subtractive hybridization hepatopancreas cDNA library has been constructed with bacterial challenge. In this study, a full-length cDNA of a novel goose-type lysozyme (PALysG) has been identified from P. acuta by EST and RACE technique. The conservative structure domains share high homology with other molluscan g-type lysozymes including the SLT domain, the substrate binding sites, the catalytic residues, three alpha-helices structures and six molluscan specific cysteines. Meanwhile, PALysG is the first record of goose-type lysozyme in Gastropoda. Real-time PCR indicated that PALysG mRNA had been expressed significantly at high levels in hepatopancreas for 8-48 h. PALysG recombinant protein displayed the lytic activity of g-type lysozyme with other organisms against Micrococcus lysodikicus.