Chicken-type lysozyme functions in the antibacterial immunity in red swamp crayfish, Procambarus clarkii

Characterization and functional analysis of a novel goose-type lysozyme from teleost Sebastes schlegelii with implications for antibacterial defense and immune cell modulation

Lysozymes are crucial enzymes involved in the innate immune response against bacterial pathogens. In this study, we identified and characterized a goose-type lysozyme gene (SsLyG) from the black rockfish Sebastes schlegelii, an economically important aquaculture species. The deduced amino acid sequence of SsLyG contains 495 residues, which inculded a signal peptide, an immunoglobulin domain, and a goose egg-white lysozyme (GEWL) domain. Tissue expression analysis revealed the highest SsLyG levels in blood, and its transcription was significantly upregulated in the spleen and kidney upon bacterial and polyI:C challenges. Recombinant SsLyGE (rSsLyGE) exhibited lytic activity against Micrococcus lysodeikticus and concentration-dependent binding ability to Staphylococcus aureus and Micrococcus luteus. Furthermore, rSsLyGE promoted peripheral blood lymphocyte proliferation, enhanced macrophage respiratory burst activity, and increased reactive oxygen species production. RNA interference-mediated knockdown of SsLyG resulted in higher bacterial loads in the liver and spleen after Listonella anguillarum challenge, suggesting its role in early antibacterial defense. Collectively, these findings provide insights into the immune function of SsLyG and its potential application in developing antimicrobial strategies for aquaculture.

Ferritin Heavy-like subunit is involved in the innate immune defense of the red swamp crayfish Procambarus clarkii

Iron-binding proteins, known as ferritins, play pivotal roles in immunological response, detoxification, and iron storage. Despite their significance to organisms, little is known about how they affect the immunological system of the red swamp crayfish (Procambarus clarkii). In our previous research, one ferritin subunit was completely discovered as an H-like subunit (PcFeH) from P. clarkii. The full-length cDNA of PcFerH is 1779 bp, including a 5'-UTR (untranslated region, UTR) of 89 bp, 3'-UTR (untranslated region, UTR) of 1180 bp and an ORF (open reading frame, ORF) of 510 bp encoding a polypeptide of 169 amino acids that contains a signal peptide and a Ferritin domain. The deduced PcFerH protein sequence has highly identity with other crayfish. PcFerH protein's estimated tertiary structure is quite comparable to animal structure. The PcFerH is close to Cherax quadricarinatus, according to phylogenetic analysis. All the organs examined showed widespread expression of PcFerH mRNA, with the ovary exhibiting the highest levels of expression. Additionally, in crayfish muscles, intestines, and gills, the mRNA transcript of PcFerH was noticeably up-regulated, after LPS and Poly I:C challenge. The expression of downstream genes in the immunological signaling system was suppressed when the PcFerH gene was knocked down. All of these findings suggested that PcFerH played a vital role in regulating the expression of downstream effectors in the immunological signaling pathway of crayfish.

Effects of environmental pollutant benzop[α]yrene on the innate immunity of Scylla paramamosain and its mechanism

Benzo[α]pyrene (BaP), a polycyclic aromatic hydrocarbon, is present in the aquatic environment and may be harmful to aquatic animals. We exposed the mud crab Scylla paramamosain to BaP for 7 days, the of superoxide dismutase (SOD), catalase (CAT), phenoloxidase (PO), lysozyme (LZM), glutathione (GSH), glutathione-S-transferase (GST), and acid phosphatase (ACP) activities in the hemolymph of mud crab were reduced. Additionally, the reactive oxygen species content was increased in mud crabs after exposed to BaP. When BaP concentration was increased, the total hemocyte count (THC), the survival rate of hemocytes and their proliferation were decreased. Histopathology analysis revealed damaged hepatopancreas cells, which indicating that BaP exposure is cytotoxic to crab hemocytes. However, the degree of DNA damage did not worsen with increasing BaP concentration. The expression levels of p53, MCM7, Caspase-3, and Myosin were changed with increasing concentration of BaP, which indicated that BaP exposure may affect apoptosis and phagocytosis in mud crabs. As BaP concentration was increased, the apoptosis rate of hemocytes was increased and the phagocytosis was decreased. These results confirmed that BaP exposure inhibited the innate immune response of mud crabs. A possible explanation for this effect is that BaP reduces the antioxidant enzyme activity and increases the reactive oxygen species content in mud crabs, thereby oxidizing and damaging hemocytes, which stimulates phagocytosis and apoptosis and negatively affects the innate immunity of S. paramamosain.

The effect of white spot syndrome virus (WSSV) envelope protein VP28 on innate immunity and resistance to white spot syndrome virus in Cherax quadricarinatus

VP28 is the most abundant membrane protein of WSSV, and the recombinant protein VP28 (VP26 or VP24) was constructed for the immune protection experiment in this study. Crayfish were immunized by intramuscular injection of recombinant protein V28 (VP26 or VP24) at a dose of 2 μg/g. The survival rate of crayfish immunized by VP28 showed a higher value than by VP26 or VP24 after WSSV challenge. Compared with the WSSV-positive control group, the VP28-immunized group could inhibit the replication of WSSV in crayfish, increasing the survival rate of crayfish to 66.67% after WSSV infection. The results of gene expression showed that VP28 treatment could enhance the expression of immune genes, mainly JAK and STAT genes. VP28 treatment also enhanced total hemocyte counts and enzyme activities including PO, SOD, and CAT in crayfish. VP28 treatment reduced the apoptosis of hemocytes in crayfish, as well as after WSSV infection. In conclusion, VP28 treatment can enhance the innate immunity of crayfish and has a significant effect on resistance to WSSV, and can be used as a preventive tool.

A novel c-type lysozyme from Litopenaeus vannamei exhibits potent antimicrobial activity

Lysozyme is relevant to the innate immune system as a vital protein for crustaceans. In the present study, we cloned and characterized a novel c-type lysozyme gene (LvLYZ) from the Pacific white shrimp (Litopenaeus vannamei). The obtained full-length cDNA of LvLYZ was 990 bp and contained an open reading frame of 693 bp. Its deduced amino acid sequence consisted of 230 amino acids (aa) with a 17 aa signal peptide at the N-terminal and 130 aa functional domains. The multiple sequence alignment (MSA) indicated that the typical active sites in LvLYZ were similarly conserved as c-type lysozymes from other species. The transcription of LvLYZ appeared in all detected tissues and had relatively higher expression levels in hemocytes, hepatopancreas, gill and intestine. The mRNA expression profiles of LvLYZ were up-regulated in hemocyte and hepatopancreas post the stimulation of Vibrio parahaemolyticus or white spot syndrome virus (WSSV), respectively. The recombinant protein of LvLYZ (rLvLYZ) exhibited antibacterial activities against various microbes, including Escherichia coli, Vibrio splendidus, Micrococcaus luteus, Vibrio parahaemolyticus and Staphylococcus aureus. These results indicated that LvLYZ could cope with bacteria in L. vannamei and may play a significant role in immune response against invading pathogens.

Transcriptome analysis of the immunomodulatory effects of Salvia miltiorrhiza polysaccharide on hemocyte immune response in Procambarus clarkii

Natural plant polysaccharide as immune modulator is considered an effective strategy for healthy aquaculture to reduce medicine treatment. Salvia miltiorrhiza polysaccharides (SMP) had applications to regulate immune activity and enhance antioxidant in vertebrates, but the potential function has been rarely reported in crustaceans. In this study, the immunological effects of SMP on hemocytes of Procambarus clarkii were analyzed. Results showed that total superoxide dismutase (T-SOD), phenoloxidase (PO) activity and respiratory burst were up-regulated after SMP treatment. After high-throughput sequencing, 2170 differentially expressed genes (DEGs) including 1294 up-regulated and 876 down-regulated genes were identified. KEGG function enrichment analysis indicated that DEGs are involved in crustaceans cellular immune-related signaling pathways, including lysosome, phagosome and endocytosis. Transcriptome mining and qRT-PCR showed that SMP up-regulated humoral immunity factors gene expression. Diets supplemented with 0.8% SMP significantly up-regulated the total number of hemocytes (THC), T-SOD and PO activity, improved the survival of crayfish after Citrobacter freundii infection. This study suggested that SMP could improve the cellular and humoral immunity of P. clarkii. Furthermore, this finding supplied a molecular foundation for further comprehending the immunopotentiator effects of plant polysaccharides in crustaceans.

The exploration and utilization of functional substances in edible insects: a review

Edible insects as food have been considered as a core future protein source. Not only are edible insects abundant in nutrient value, but also have numbers of functional substances, which could provide a multiple valuable benefits for humans. This review examines and summarizes the functional substances in edible insects and their special effects for people, as well as the use and prospects for these functional substances. There are many functional substances in edible insects, such as antimicrobial peptides, interferon, sex attractant hormones, cordycepin, active polysaccharides, microelement, chitin/chitosan, steroidal material, vitamin, lecithin, etc., which could provide multiple benefits for human beings. These special functional substances could help people enhance immunity, inhibit tumor, regulate intestinal function, relieve fatigue, anti oxidation, protect against colds, improve sleeping, promote the growth and development, as well as reducing blood sugar and blood pressure, among others. According to these valuable efficacies, the functional substances extracted from edible insects can be exploited mainly in three ways: edible insects are used to discover new medicines or health care products for people; and edible insects are applied in chemical, agricultural, food technology, pollutant treatment and textile sectors; as well as being consumed as animal feedstuff for livestock and other animals, which indirectly meet the different requirements for humans. Currently, edible insects have generated global interest to be developed as different forms of products and has promoted more research and development. However, pupae and larvae are still the main consumption ways in the market, which is unacceptable to most people. It is expected that the edible insect industry would be prosperous and sustainable by integrating the power of beneficial policies and regulations, huge consumer demand and proper strategies of promotion and production.

Graphical Abstract

Transcriptomic analysis of Neocaridina denticulate sinensis hepatopancreas indicates immune changes after copper exposure

Neocaridina denticulate sinensis is a promising crustacean model species due to its merits in raising and breeding. However, its molecular responses to copper remains largely unknown. In the present research, RNA-seq was used to mine the alteration in transcriptome of N. denticulate sinensis hepatopancreas under copper exposure. A total of 16,423 DEGs was identified between control and Cu²⁺ treatment groups. GO enrichment analysis of all DEGs suggested down-regulated genes exceeded up-regulated genes in all the significantly enriched terms, except for RNA polymerase III complex (GO:0005666). KEGG analysis showed Cu exposure only induced two significantly enriched pathways, including Phagosome (ko04145) and Pathogenic Escherichia coli infection (ko05130). Besides, pattern recognition receptors as Toll, lectin B, CTL1 and SRB, AMPs as crustin type I, lysozyme, and NOS were down-regulated after Cu²⁺ exposure, while hemocyanin, MT, HSP70 and HSP90 were significantly up-regulated, implying these molecules may play vital role in Cu²⁺ detoxification of N. denticulate sinensis. Our results here provide research direction of heavy metal detoxification of N. denticulate sinensis, simultaneously enriched its genomic information.

The potential of antimicrobial peptides isolated from freshwater crayfish species in new drug development: A review

The much-publicised increased resistance of pathogenic bacteria to conventional antibiotics has focused research effort on the characterization of new antimicrobial drugs. In this context, antimicrobial peptides (AMPs) extracted from animals are considered a promising alternative to conventional antibiotics. In recent years, freshwater crayfish species have emerged as an important source of bioactive compounds. In fact, these invertebrates rely on an innate immune system based on cellular responses and on the production of important effectors in the haemolymph, such as AMPs, which are produced and stored in granules in haemocytes and released after stimulation. These effectors are active against both Gram-positive and Gram-negative bacteria. In this review, we summarise the recent progress on AMPs isolated from the several species of freshwater crayfish and their prospects for future pharmaceutical applications to combat infectious agents.

Immunotoxicity of polychlorinated biphenyls (PCBs) to the marine crustacean species, Scylla paramamosain

Polychlorinated biphenyls (PCBs) are persistent organic pollutants in environments, and they can negatively affect aquatic animal health. After 7 days of PCBs exposure, the activities of catalase, phenoloxidase, and superoxide dismutase and the total hemocyte count in the haemolymph were significantly decreased and the reactive oxygen species (ROS) content and phagocytic rate of hemocytes were significantly increased in mud crab Scylla paramamosain. Additionally, serum lysozyme, glutathione, glutathione-S-transferase, and glutathione peroxidase activities were significantly down-regulated in mud crab after PCBs exposure. The survival rate of crab hemocytes significantly declined as the PCBs concentration increased, indicating that PCBs had a cytotoxic effect on hemocytes. Exposure to increasing concentrations of PCBs also increased the degree of DNA damage in crab hemocytes. After PCBs exposure, the expression levels of P53 and caspase-3 in hemocytes were significantly up-regulated, which suggests that apoptosis was occurring. The apoptosis rate of hemocytes was up-regulated as the PCBs concentration increased, indicating that apoptosis was induced by the PCBs-activated caspase-3 pathway. These data suggest that exposure to PCBs hampered the immune response of mud crabs, most likely by (1) inducing ROS, causing DNA damage, and reducing the viability of hemocytes, (2) reducing the activities of antioxidant enzymes, and (3) inducing phagocytosis and apoptosis of hemocytes. And the final result of PCBs-induced immunotoxicity to mud crabs is the reduced bacterial disease resistance and survival rate of crabs under Vibrio alginolyticus challenge.

Identification and characterization of two highly homologous lysozymes from red swamp crayfish, Procambarus clarkii

Lysozyme is an important immune effector in innate immunity against pathogen infection. But the study on the active region of lysozyme is limited. In this study, two highly homologous lysozymes were identified from crayfish (designated as PcLysi4 and PcLysi5). The molecular structures of PcLysi4 and PcLysi5 were predicted by SWISS-MODEL with the structure of lysozyme (PDB accession No. 4PJ2.2.B) as model. The results suggested that the structure of PcLysi4 and PcLysi5 were highly similar, but there were more α-helices at positions (127–139) and longer β-sheet at positions (49–57) in the structure of PcLysi5 than in that of PcLysi4. The antibacterial and antiviral functions of the two lysozymes were investigated. PcLysi4 and PcLysi5 could promote the bacterial clearance ability of crayfish, and increase the survival rate of Vibrio-infected crayfish. Further study showed that PcLysi5 inhibited WSSV replication, and enhanced the survival rate of WSSV-infected crayfish. There was no evidence that PcLysi4 has an influence on WSSV replication. Furthermore, PcLysi5 was detected to interact with envelope protein VP24 of WSSV. Our results would provide a new reference for the study on active region of lysozyme.

A new antimicrobial peptide isoform, Pc-crustin 4 involved in antibacterial innate immune response in fresh water crayfish, Procambarus clarkii

The main advantage of antimicrobial peptides (AMPs) used as the effectors in the innate immunity system of invertebrates is that the high specificity is not indispensable. And they play important roles in the systemic defenses against microbial invasion. In this study, a new full-length cDNA of the crustins molecule was identified in red swamp crayfish, P. clarkii (named Pc-crustin 4). The ORF of Pc-crustin 4 contained 369 bp which encoded a protein of 122 amino acids, with a 20-amino-acid signal peptide sequence. On the base of the classification method established by Smith et al., Pc-crustin 4 belonged to Type Ⅰ crustin molecule. The Pc-crustin 4 transcripts were expressed in hemocytes at relatively high level, and relatively low level in hepatopancreas, gills, and intestine in normal crayfish. After respectively challenged with S. aureus or E. ictaluri, the expression levels of Pc-crustin 4 showed up-regulation trends at different degrees in the hemocytes, hepatopancreas, gills, and intestine tissues. Besides, the results of liquid antibacterial assay showed that rPc-crustin 4 inhibited obviously the growth of S. aureus and E. ictaluri. The results of bacteria binding assay showed that rPc-crustin 4 could bind strongly to S. aureus and E. ictaluri. Finally, RNAi assay was performed to study the immunity roles of Pc-crustin 4 in crayfish in vivo. Taken together, Pc-crustin 4 is an important immunity effector molecule, which plays crucial roles in defending against bacterial infection in crayfish.

Molecular characterization, expression and antimicrobial activities of a c-type lysozyme from the mud crab, Scylla paramamosain

Lysozyme is an important immune protein involved in the first line of defense for crustaceans. In the present study, a c-type lysozyme gene (SpLyzC) was cloned and characterized from the mud crab, Scylla paramamosain. The full-length cDNA was 849 bp with an open reading frame of 669 bp, and encoded a polypeptide of 223 amino acids with a calculated molecular mass of 23.7 kDa and an isoelectric point of 8.90. SpLyzC shared conserved active sites with c-type lysozymes from other species, detected in all tested tissues and had higher expression levels in hepatopancreas and gill tissues. The expression of SpLyzC was up-regulated in hepatopancreas and gill after infection with Vibrio parahaemolyticus and Staphylococcus aureus. The density of bacteria in the hemolymph and the mortality of crabs increased following infection with V. parahaemolyticus after SpLyzC expression was silenced by injecting double-strand RNA of SpLyzC. The recombinant protein of the S. paramamosain c-type lysozyme (rSpLyzC) exhibited antibacterial activities against Micrococcus lysodeikticus, S. aureus, Vibrio harveyi and V. parahaemolyticus. These results indicate that SpLyzC could help eliminate bacteria in S. paramamosain and may play an important role in resistance to bacterial infection.

Identification and functional characterization of a c-type lysozyme from Fenneropenaeus penicillatus

Lysozyme is an important defense molecule of the innate immune system and possess high antimicrobial activities. In this study, a full-length c-type lysozyme cDNA (Fplysc) was cloned and characterized from Fenneropenaeus penicillatus. The cDNA contains an open reading frame of 477 bp encoding 158 amino acids, with 53-94% identity with those of other crustaceans. The recombinant Fplysc had antibacterial activities against Gram-positive bacteria (Streptococcus agalactiae and Micrococcus luteus) and Gram-negative bacteria (Vibrio alginolyticus and Escherichia coli), and showed antiviral activity against WSSV and IHHNV. The qRT-PCR analysis showed that Fplysc expression levels were most abundant in hemocytes and less in eyestalk. The expression levels of Fplysc were significantly upregulated in gill, intestine and hemocytes when challenged with WSSV and V. alginolyticus. Fplysc-silencling suppressed Fplysc expression in cephalothoraxes and increased mortality caused by WSSV and V. alginolyticus, and exogenous rFplysc led to a significant decrease of shrimp mortality by injecting rFplysc into Fplysc silenced shrimp, suggesting Fplysc is the important molecule in shrimp antimicrobial and antiviral response. In conclusion, the results provide some insights into the function of Fplysc in shrimp against bacterial and viral infection.