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

Hemolymph microbiota and immune effectors' expressions driven by geographical rearing acclimation of the aquacultured Penaeus stylirostris

BACKGROUND

In holobiont, microbiota is known to play a central role on the health and immunity of its host. Then, understanding the microbiota, its dynamic according to the environmental conditions and its link to the immunity would help to react to potential dysbiosis of aquacultured species. While the gut microbiota is highly studied, in marine invertebrates the hemolymph microbiota is often set aside even if it remains an important actor of the hemolymph homeostasis. Indeed, the hemolymph harbors the factors involved in the animal homeostasis that interacts with the microbiota, the immunity. In the Southwest Pacific, the high economical valued shrimp Penaeus stylirostris is reared in two contrasted sites, in New Caledonia (NC) and in French Polynesia (FP).

RESULTS

We characterized the active microbiota inhabiting the hemolymph of shrimps while considering its stability during two seasons and at a one-month interval and evidenced an important microbial variability between the shrimps according to the rearing conditions and the sites. We highlighted specific biomarkers along with a common core microbiota composed of 6 ASVs. Putative microbial functions were mostly associated with bacterial competition, infections and metabolism in NC, while they were highly associated with the cell metabolism in FP suggesting a rearing site discrimination. Differential relative expression of immune effectors measured in the hemolymph of two shrimp populations from NC and FP, exhibited higher level of expression in NC compared to FP. In addition, differential relative expression of immune effectors was correlated to bacterial biomarkers based on their geographical location.

CONCLUSIONS

Our data suggest that, in Pacific shrimps, both the microbiota and the expression of the immune effectors could have undergone differential immunostimulation according to the rearing site as well as a geographical adaptative divergence of the shrimps as an holobiont, to their rearing sites. Further, the identification of proxies such as the core microbiota and site biomarkers, could be used to guide future actions to monitor the bacterial microbiota and thus preserve the productions.

Decoding the role of HIF-1α in immunoregulation in Litopenaeus vannamei under hypoxic stress

Hypoxia poses a significant challenge to aquatic organisms, especially Litopenaeus vannamei (L. vannamei), which play a vital role in the global aquaculture industry. Hypoxia-inducible factor 1α (HIF-1α) is a pivotal regulator of the organism's adaptation to hypoxic conditions. To understand of how HIF-1α affects the immunity of L. vannamei under hypoxic conditions, we conducted a thorough study involving various approaches. These included observing tissue morphology, analyzing the expression of immune-related genes, assessing the activities of immune-related enzymes, and exploring immune-related pathways. Our study revealed that RNA interference (RNAi)-mediated knockdown of HIF-1α markedly reduced HIF-1α expression in the gill (75-95 %), whereas the reduction ranged from 2 to 43 % in the hepatopancreas. Knockdown of HIF-1α resulted in increased damage to both gill and hepatopancreatic tissues in hypoxic conditions. Additionally, immune-related genes, including Astakine (AST), Hemocyanin (HC), and Ferritin (FT), as well as immune-related enzymes such as Acid Phosphatase (ACP), Alkaline Phosphatase (AKP), and Phenoloxidase (PO), exhibited intricate regulatory patterns in response to hypoxia stress following the knockdown of HIF-1α. Transcriptome analysis revealed that HIF-1α knockdown significantly impacts multiple signaling pathways, including the JAK-STAT signaling pathway, Th17 cell differentiation pathways, PI3K-Akt signaling pathway, ErbB signaling pathway, MAPK signaling pathway, chemokine signaling pathway, ribosomal pathways, apoptosis, lysosomes and arachidonic acid metabolism. These alterations disrupt the organism's immune balance and interfere with normal metabolic processes, potentially leading to various immune-related diseases. We speculate that the weakened immune response resulting from HIF-1 inhibition is due to the reduced metabolic capacity, and the existence of a direct regulatory relationship between them requires further exploration. This study greatly advances our understanding of the vital role that HIF-1α plays in regulating immune responses in shrimp under hypoxic conditions, thereby deepening our comprehension of this critical biological mechanism.

Transcriptome analysis of response mechanism to Microcystin-LR and microplastics stress in Asian clam (Corbicula fluminea)

In this study, we analyzed the hepatopancreas tissues of Asian Clam (Corbicula fluminea) exposed to three different adverse environmental conditions from the same batch using RNA-seq. The four treatment groups included the Asian Clam group treated with Microcystin-LR (MC), the Microplastics-treated group (MP), the Microcystin-LR and Microplastics-treated group (MP-MC), and the Control group. Our Gene Ontology analysis revealed 19,173 enriched genes, and the Kyoto Encyclopedia of Genes and Genomes (KEGG) enrichment analysis identified 345 related pathways. The KEGG pathway analysis demonstrated that the MC vs control group and the MP vs control group were significantly enriched in immune and catabolic pathways such as Antigen processing and presentation, Rheumatoid arthritis, Lysosome pathway, Phagosome pathway, and Autophagy pathway. We also evaluated the effects of Microplastics and Microcystin-LR on the activities of eight antioxidant enzymes and immune enzymes in Asian clams. Our study enriched the genetic resources of Asian clams and provided valuable information for understanding the response mechanism of Asian clams to microplastics and microcystin in the environment, through the identification of differentially expressed genes and related pathway analyses from the large number of transcriptome sequences obtained.

Hallmarks of crustacean immune hemocytes at single-cell resolution

In invertebrates, hemocytes are the key factors in innate immunity. However, the types of invertebrate immune hemocytes are unclassified due to the limitation of morphological classification. To determine the immune hemocytes of crustaceans, the heterogeneity of hemocytes of shrimp Marsupenaeus japonicus and crayfish Procambarus clarkii, two representative crustacean species, were characterized in this study. The results of single-cell RNA sequencing indicated that shrimp and crayfish contained 11 and 12 types of hemocytes, respectively. Each of different types of hemocytes specifically expressed the potential marker genes. Based on the responses of shrimp and crayfish to the infection of white spot syndrome virus (WSSV) and the challenge of lipopolysaccharide (LPS), four types of immune hemocytes of crustaceans were classified, including semi-granular hemocytes involved in antimicrobial peptide production, granular hemocytes responsible for the production of antimicrobial peptides, hemocytes related to cell proliferation and hemocytes in immunity-activated state. Therefore, our study provided the first classification of crustacean hemocytes as well as of immune hemocytes of crustaceans at the single-cell resolution, which would be helpful to understand the innate immunity of invertebrates.

RNA-seq analysis revealing the immune response of Neocaridina denticulata sinensis gill to Vibrio parahaemolyticus infection

Vibrio parahaemolyticus causes serious economic losses to the shrimp farming industry. There is still a lack of adequate understanding of the changes in the overall response of N. denticulata sinensis caused by V. parahaemolyticus, particularly with respect to gill tissue, which is severely damaged by the pathogen. In this study, a total of 1358 differentially expressed genes were identified between the PBS control and Vibrio stimulation groups using transcriptome sequencing techniques. After further screening and analysis, many immune-related genes were obtained, involving lysosome pathway, metabolic process, chitin-binding protein, and serine protease family members. In addition, we randomly selected six DEGs in the lysosome pathway for qRT-PCR verification, and the results showed that their expression patterns were consistent with the RNA-seq. The results demonstrate the molecular regulation of the gill tissue response to V. parahaemolyticus infection in N. denticulata sinensis, contributing to the understand of the complex and efficient innate immune system and defense mechanisms in crustaceans.

Dietary recombinant human lysozyme improves the growth, intestinal health, immunity and disease resistance of Pacific white shrimp Litopenaeus vannamei

The present study was conducted to investigate the effects of dietary recombinant human lysozyme (RHL) on the growth, immune response, anti-oxidative activity, intestinal morphology, intestinal microflora and disease resistance of shrimp Litopenaeus vannamei. Shrimps with an initial body weight of 2.36 ± 0.02 g were fed diets supplemented with 0 (control group, R0), 0.0025% (R1), 0.005% (R2), 0.01% (R3), 0.02% (R4) and 0.04% (R5) of RHL, respectively. After a 10-week feeding trial, the final body weight, survival rate, weight gain ratio and protein efficiency rate of the shrimps in dietary RHL supplemented groups were significantly higher than that in the control group, while feed conversion ratio was significantly lower (P < 0.05). The total haemocyte count, total anti-oxidative capacity, respiratory burst, activities of phagocytosis, nitric oxide synthase, phenol oxidase and lysozyme in serum were significantly higher in dietary RHL supplemented groups than those in the control group (P < 0.05). Meanwhile, the intestinal pile height and wall thickness were significantly higher in dietary RHL supplemented groups than those in the control group (P < 0.05). Dietary RHL significantly improved the expressions of immune-related genes in gill, such as lipopolysaccharide-β-glucan binding protein, Toll, immune deficiency, heat shock protein 70 and Crustin (P < 0.05). The abundance of proteobacteria and bacteroidetes in intestine was higher, while the abundance of firmicutes and cyanobacteria was lower than those in the control group at the phylum level. In addition, dietary RHL supplementation significantly improved the protective ability of shrimp against V. parahaemolyticus infection (P < 0.05). Based on the broken-line model analysis for weight gain ratio after the feeding trial, the optimal level of dietary RHL supplementation for shrimp was estimated to be 0.006375%.

Applications of Lysozyme, an Innate Immune Defense Factor, as an Alternative Antibiotic

Lysozyme is a ~14 kDa protein present in many mucosal secretions (tears, saliva, and mucus) and tissues of animals and plants, and plays an important role in the innate immunity, providing protection against bacteria, viruses, and fungi. Three main different types of lysozymes are known: the c-type (chicken or conventional type), the g-type (goose type), and the i-type (invertebrate type). It has long been the subject of several applications due to its antimicrobial properties. The problem of antibiotic resistance has stimulated the search for new molecules or new applications of known compounds. The use of lysozyme as an alternative antibiotic is the subject of this review, which covers the results published over the past two decades. This review is focused on the applications of lysozyme in medicine, (the treatment of infectious diseases, wound healing, and anti-biofilm), veterinary, feed, food preservation, and crop protection. It is available from a wide range of sources, in addition to the well-known chicken egg white, and its synergism with other compounds, endowed with antimicrobial activity, are also summarized. An overview of the modified lysozyme applications is provided in the form of tables.

A new insight to characterize immunomodulation based on hepatopancreatic transcriptome and humoral immune factor analysis of the Cherax quadricarinatus infected with Aeromonas veronii

Cherax quadricarinatus is a type of large freshwater crayfish that is characterized by rapid growth and formidable adaptability. It has also been widely cultured and studied as a model organism. Aeromonas veronii is the dominant pathogen in aquatic environments and the primary threat to aquaculture's economic stability. To better understand the interactions between C. quadricarinatus and A. veronii, high-throughput RNA sequencing of the C. quadricarinatus hepatopancreas was carried out on a control group, susceptible group (6 h after infection), and resistant group (48 h after infection). A total of 65,850,929 genes were obtained. Compared with the control group, 2616 genes were up-regulated and 1551 genes were down-regulated in the susceptible group; while 1488 genes were up-regulated and 1712 genes were down-regulated in the resistant group. GO and KEGG analysis showed that these differentially expressed genes (DEGs) were associated with multiple immune pathways, including Toll-like receptors (TLRs), antigen processing and presentation, NOD-like receptor signaling pathway, phagosome, lysosome, JAK-STAT signaling pathway. qRT-PCR showed that infection by A. veronii changed the expression pattern of the serine proteinase inhibitor (SPI), crustacean hyperglycemic hormone (CHH), anti-lipopolysaccharide factor (ALF), and extracellular copper/zinc superoxide dismutase (SOD1), all of which were significantly higher than in the control group up to 48 h after infection. In addition, detection of superoxide dismutase (SOD), catalase (CAT), lysozyme (LZM), and phenoloxidase (PO) activity, as well as ceruloplasmin (CP) concentration at different times after infection showed diverse trends. Furthermore, pathological sections obtained 24 h after infection show lesions on the hepatopancreas and intestinal tissues caused by A. veronii. The results of this study provide a foundation for analyzing the immune mechanism of C. quadricarinatus infected with A. veronii at the transcriptional level and a theoretical basis for screening disease-resistant individuals to ensure healthy economic development of the aquatic industry.

Interleukin-2 enhancer binding factor 2 (ILF2) in pacific white shrimp (Litopenaeus vannamei): Alternatively spliced isoforms with different responses in the immune defenses against vibrio infection

Alternative splicing is an essential molecular mechanism that increase the protein diversity of a species to regulate important biological processes. As a transcription factor, Interleukin-2 enhancer binding factor 2 (ILF2) regulates the functions of interleukin-2 (IL-2) at the levels of transcription, splicing and translation, and plays other critical roles in the immune system. ILF2 is well-documented in vertebrates, while little is currently known in crustacean species such as the Pacific white shrimp (Litopenaeus vannamei). In the present study, five cDNA for spliced isoforms of Lv-ILF2 were identified, in which four of them are the full-length long isoforms (Lv-ILF2-L1, Lv-ILF2-L2, Lv-ILF2-L3 and Lv-ILF2-L4) and one of them is a truncated short isoform (Lv-ILF2-S). The whole sequence of ILF2 gene from L. vannamei was obtained, which is 11,680 bp in length with 9 exons separated by 8 introns. All five isoforms contain a domain associated with zinc fingers (DZF). Two alternative splicing types (alternative 5' splice site and alternative 3' splice site) were identified in the five isoforms. The Lv-ILF2 mRNA showed a broad distribution in all detected tissues, and the Lv-ILF2-L transcript levels were higher than those of Lv-ILF2-S in corresponding tissues. The mRNA levels of Lv-ILF2-S in the hepatopancreas, heart, muscle and stomach, but not in the eyestalk, were significantly increased after challenges with Vibrio harveyi or lipopolysaccharide (LPS), while no significant changes were observed for the transcript levels of Lv-ILF2-L in these tissues under the same immune stimulants. On the contrary, the transcript levels of neither Lv-ILF2-S nor Lv-ILF2-L were affected by challenges of polyinosinic: polycytidylic acid [Poly (I:C)]. In addition, after knockdown of the Lv-ILF2 mRNA level by siRNA, the mortality of shrimp and the hepatopancreatic bacterial numbers were significantly increased under V. harveyi challenge, indicating that Lv-ILF2 might participate in the immune defenses against V. harveyi invasion. Collectively, our study here supplied the first evidence for a novel splicing mechanism of ILF2 transcripts, and provided a functional link between the Lv-ILF2 isoforms and the capacity against pathogenic Vibrio in penaeid shrimp.

Production of an invertebrate lysozyme of Scylla paramamosain in E.coli and evaluation of its antibacterial, antioxidant and anti-inflammatory effects

Lysozymes, which are secreted in many organisms, including invertebrates, mammals, plants, bacteria and fungus, exhibit antimicrobial, antiviral, antioxidant, and anti-inflammatory activities. Splys-i is an invertebrate-type (i-type) lysozyme isolated from Scylla paramamosain in 2017 and is involved in immune defense against bacteria. However, the antibacterial, antioxidant, and anti-inflammatory activities of Splys-i remain to be elucidated. In the current study, the expression parameters (including IPTG concentration, induction temperature, and induction duration) of Splys-i in Escherichia coli were optimized to achieve high-level yield through shake-flask cultivation with approximately 120 mg of Splys-i obtained from 1 L of LB medium. The purified Splys-i displayed low cytotoxicity to RAW264.7 macrophage cells and low hemolytic activity against erythrocytes of mouse, rat, and rabbit, respectively, and exhibited potent antibacterial activity against both Gram-positive and -negative bacteria with minimum concentrations ranging from 15 to 90 μg/mL. The antibacterial property of Splys-i was also unaffected when treated with various temperature, pHs, and salinity, respectively, and Splys-i showed resistance to proteinase digestion. Radical-scavenging rate assay (including ABTS⁺, DPPH, hydroyl free radical, and superoxide anion) indicated that Splys-i was an efficient antioxidant. Splys-i also exerted anti-inflammatory effect through the inhibition of IκBα and NF-κB(P65) phosphorylation, thereby reducing the secretion of pro-inflammatory cytokines. All these results suggested that Splys-i can be prepared from E. coli with potent biological property.

Shedding the Light on Litopenaeus vannamei Differential Muscle and Hepatopancreas Immune Responses in White Spot Syndrome Virus (WSSV) Exposure

White Spot Syndrome Virus (WSSV) is one of the main threats to farming Litopenaeus vannamei, the most important crustacean commercialized in aquaculture worldwide. Here, we performed RNA-seq analyses in hepatopancreas and muscle from WSSV-negative (healthy) and WSSV-positive (unhealthy) L. vannamei, previously exposed to the virus, to obtain new insights about the molecular basis of resistance to WSSV. We detected 71% of our reads mapped against the recently described L. vannamei genome. This is the first report mapping RNA-seq transcripts from shrimps exposed to WSSV against the species reference genome. Differentially expressed gene (DEG) analyses were performed for four independent comparisons, and 13,338 DEGs were identified. When the redundancies and isoforms were disregarded, we observed 8351 and 6514 DEGs, respectively. Interestingly, after crossing the data, we detected a common set of DEGs for hepatopancreas and healthy shrimps, as well as another one for muscle and unhealthy shrimps. Our findings indicate that genes related to apoptosis, melanization, and the Imd pathway are likely to be involved in response to WSSV, offering knowledge about WSSV defense in shrimps exposed to the virus but not infected. These data present potential to be applied in further genetic studies in penaeids and other farmed shrimp species.

A Possible Role of Crustacean Cardioactive Peptide in Regulating Immune Response in Hepatopancreas of Mud Crab

Crustacean cardioactive peptide (CCAP), a cyclic amidated non-apeptide, is widely found in arthropods. The functions of CCAP have been revealed to include regulation of heart rate, intestinal peristalsis, molting, and osmotic pressure. However, to date, there has not been any report on the possible involvement of CCAP in immunoregulation in crustaceans. In this study, a CCAP precursor (designated as Sp-CCAP) was identified in the commercially important mud crab Scylla paramamosain, which could be processed into four CCAP-associated peptides and one mature peptide (PFCNAFTGC-NH₂). Bioinformatics analysis indicated that Sp-CCAP was highly conserved in crustaceans. RT-PCR results revealed that Sp-CCAP was expressed in nerve tissues and gonads, whereas the Sp-CCAP receptor gene (Sp-CCAPR) was expressed in 12 tissues of S. paramamosain, including hepatopancreas. In situ hybridization further showed that an Sp-CCAPR-positive signal is mainly localized in the F-cells of hepatopancreas. Moreover, the mRNA expression level of Sp-CCAPR in the hepatopancreas was significantly up-regulated after lipopolysaccharide (LPS) or polyriboinosinic polyribocytidylic acid [Poly (I:C)] challenge. Meanwhile, the mRNA expression level of Sp-CCAPR, nuclear transcription factor NF-κB homologs (Sp-Dorsal and Sp-Relish), member of mitogen-activated protein kinase (MAPK) signaling pathway (Sp-P38), pro-inflammatory cytokines factor (Sp-TNFSF and Sp-IL16), and antimicrobial peptide (Sp-Lysozyme, Sp-ALF, Sp-ALF4, and Sp-ALF5) in the hepatopancreas were all up-regulated after the administration of synthetic Sp-CCAP mature peptide both in vivo and in vitro. The addition of synthetic Sp-CCAP mature peptide in vitro also led to an increase in nitric oxide (NO) concentration and an improved bacterial clearance ability in the hepatopancreas culture medium. The present study suggested that Sp-CCAP signaling system might be involved in the immune responses of S. paramamosain by activating immune molecules on the hepatopancreas. Collectively, our findings shed new light on neuroendocrine-immune regulatory system in arthropods and could potentially provide a new strategy for disease prevention and control for mud crab aquaculture.

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 characterization of a RNA polymerase (RNAP) II (DNA directed) polypeptide H (POLR2H) in Pacific white shrimp (Litopenaeus vannamei) and its role in response to high-pH stress

RNA polymerase (RNAP) II (DNA-directed) (POLR2) genes are essential for cell viability under environmental stress and for the transfer of biological information from DNA to RNA. However, the function and characteristics of POLR2 genes in crustaceans are still unknown. In the present study, a POLR2H cDNA was isolated from Pacific white shrimp (Litopenaeus vannamei) and designated as Lv-POLR2H. The full-length Lv-POLR2H cDNA is 772 bp in length and contains a 32-bp 5'- untranslated region (UTR), a 284-bp 3'- UTR with a poly (A) sequence, and an open reading frame (ORF) of 456 bp encoding an Lv-POLR2H protein of 151 amino acids with a deduced molecular weight of 17.21 kDa. The Lv-POLR2H protein only contains one functional domain, harbors no transmembrane domains and mainly locates in the nucleus. The expression of the Lv-POLR2H mRNA was ubiquitously detected in all selected tissues, with the highest level in the gills. In situ hybridization (ISH) analysis showed that Lv-POLR2H was mainly located in the secondary gill filaments, the transcript levels of Lv-POLR2H in the gills were found to be significantly affected after challenge by pH, low salinity and high concentrations of NO₂^- and NH₄⁺, indicating that Lv-POLR2H in gill tissues might play roles under various physical stresses. Specifically, under high-pH stress, knockdown of Lv-POLR2H via siRNA significantly decreased the survival rate of the shrimp, indicating its key roles in the response to high-pH stress. Our study may provide the first evidence of the role of POLR2H in shrimp responding to high-pH stress and provides new insight into molecular regulation in response to high pH in crustaceans.

The bacteriolytic mechanism of an invertebrate-type lysozyme from mollusk Octopus ocellatus

As an important economic mollusk in coastal areas, Octopus ocellatus dependents on innate immune system to resist the invasion of microorganisms. Lysozyme is a crucial effector owing to its significant lytic activity against bacterial pathogens during the immune responses. In this study, characteristic and immune function of an I-type lysozyme from O. ocellatus (OoLyz) was investigated. OoLyz shared a close relationship with the lysozymes from other bivalve mollusks. The mRNA of OoLyz exhibited a broad transcript in different tissues/organs, and with the greatest expression in hepatopancreas. The expression of OoLyz was significantly raised when O. ocellatus was infected by Vibrio anguillarum or Micrococcus luteus, suggesting OoLyz participated in innate immune response of host. Prokaryotic recombinant OoLyz (rOoLyz) exhibited obvious bacteriolysis ability towards both gram-negative bacteria V. anguillarum and Escherichia coli, and gram-positive bacteria M. luteus and Staphylococcus aureus. The bacteriolysis activities of rOoLyz towards gram-negative but not gram-positive bacteria was heat stable, indicating that OoLyz might clear gram-positive bacterium by enzyme-dependent mechanisms, but eliminate gram-negative microbe via enzymatic activity independent way. Scanning electron microscopy analysis showed that rOoLyz destroyed microbes by damaging cell wall. More importantly, the fact that rOoLyz could directly degrade the peptidoglycan, further revealed its bactericidal mechanism as a muramidase. Our results revealed the essential role of I-type lysozyme in the innate immunity of O. ocellatus, and shed new light to understand the mechanism of immune defense of mollusks.

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.

Heat Shock Protein 40 (HSP40) in Pacific White Shrimp (Litopenaeus vannamei): Molecular Cloning, Tissue Distribution and Ontogeny, Response to Temperature, Acidity/Alkalinity and Salinity Stresses, and Potential Role in Ovarian Development

Heat shock proteins (HSPs), a family of conserved proteins that are produced by cells in response to stresses, are known as molecular chaperones with a range of housekeeping and cellular protective functions. The 40 kD heat shock protein (HSP40) is a co-chaperone for HSP70 in the regulation of ATP hydrolysis. Unlike its well-documented cofactor HSP70, little is currently known regarding the biological functions of HSP40 in crustacean species such as penaeid shrimp. In the present study, the cDNA encoding HSP40 (Lv-HSP40) was identified from the Pacific white shrimp Litopenaeus vannamei, a highly significant commercial culture species. The structural organization indicates that Lv-HSP40 belongs to the type-I HSP40s. The muscle, gill, and hepatopancreas are the main sites of Lv-HSP40 transcript expression. Within these tissues, Lv-HSP40 mRNA were predominantly exhibited in the myocytes, epithelial cells and hepatopancreatic cells, respectively. Under acute thermal stress in the culture environment, Lv-HSP40 transcript levels are significantly induced in these three tissues, while low pH stress only upregulates Lv-HSP40 mRNA in the hepatopancreas and gill. During ontogenesis, Lv-HSP40 transcript levels are high at early embryonic stages and drop sharply at late embryonic and early larval stages. The ovary is another major organ of Lv-HSP40 mRNA expression in female shrimp, and Lv-HSP40 transcripts were mainly presented in the follicle cells but only weekly detected in the oocytes. Ovarian Lv-HSP40 mRNA levels increase continuously during gonadal development. Silencing of the Lv-HSP40 gene by RNA interference may effectively delay ovarian maturation after unilateral eyestalk ablation. The roles of Lv-HSP40 in ovarian development are speculated to be independent of its cofactor HSP70, and the vitellogenesis factor vitellogenin (Vg) and vitellogenin receptor (VgR). Our study, as a whole, provides new insights into the roles of HSP40 in multiple physiological processes in L. vannamei: (1) HSP40 is a responding factor during stressful conditions; and (2) HSP40 participates in embryonic and ovarian development.

Effects of 5-Aminolevulinic Acid on Gene Expression, Immunity, and ATP Levels in Pacific White Shrimp, Litopenaeus vannamei

With the emergence of several infectious diseases in shrimp aquaculture, there is a growing interest in the use of feed additives to enhance shrimp immunity. Recently, the use of 5-aminolevulinic acid (5-ALA), a non-protein amino acid that plays a rate-limiting role in heme biosynthesis, has received attention for its positive effect on immunity in livestock animals. To evaluate the effect of 5-ALA in the Pacific white shrimp, Litopenaeus vannamei, we conducted microarray analysis, a Vibrio parahaemolyticus immersion challenge test, an ATP level assay, and gene expression analysis of some hemoproteins and genes associated with heme synthesis and degradation. Out of 15,745 L. vannamei putative genes on the microarray, 101 genes were differentially expressed by more than fourfold (p < 0.05) between 5-ALA-supplemented and control shrimp hepatopancreas. 5-ALA upregulated 99 of the 101 genes, 41 of which were immune- and defense-related genes based on sequence homology. Compared to the control, the 5-ALA-supplemented group had a higher survival rate in the challenge test, higher transcript levels of porphobilinogen synthase, ferrochelatase, catalase, nuclear receptor E75, and heme oxygenase-1 and higher levels of ATP. These findings suggest that dietary 5-ALA enhanced the immune response of L. vannamei to V. parahaemolyticus, upregulated immune- and defense-related genes, and enhanced aerobic energy metabolism, respectively. Further studies are needed to elucidate the extent of 5-ALA use in shrimp culture.

Isolation of an invertebrate-type lysozyme from the nephridia of the echiura, Urechis unicinctus, and its recombinant production and activities

Invertebrates, unlike vertebrates which have adaptive immune system, rely heavily on the innate immune system for the defense against pathogenic bacteria. Lysozymes, along with other immune effectors, are regarded as an important group in this defense. An invertebrate-type (i-type) lysozyme, designated Urechis unicinctus invertebrate-type lysozyme, Uu-ilys, has been isolated from nephridia of Urechis unicinctus using a series of high performance liquid chromatography (HPLC), and ultrasensitive radial diffusion assay (URDA) as a bioassay system. Analyses of the primary structure and cDNA cloning revealed that Uu-ilys was approximately 14 kDa and composed of 122 amino acids (AAs) of which the precursor had a total of 160 AAs containing a signal peptide of 18 AAs and a pro-sequence of 20 AAs encoded by the nucleotide sequence of 714 bp that comprises a 5' untranslated region (UTR) of 42 bp, an open reading frame (ORF) of 483 bp, and a 3' UTR of 189 bp. Multiple sequence alignment showed Uu-ilys has high homology to i-type lysozymes from several annelids. Relatively high transcriptional expression levels of Uu-ilys was detected in nephridia, anal vesicle, and intestine. The native Uu-ilys exhibited comparable lysozyme enzymatic and antibacterial activities to hen egg white lysozyme. Collectively, these data suggest that Uu-ilys, the isolated antibacterial protein, plays a role in the immune defense mechanism of U. unicinctus. Recombinant Uu-ilys (rUu-ilys) produced in a bacterial expression system showed significantly decreased lysozyme lytic activity from that of the native while its potency on radial diffusion assay detecting antibacterial activity was retained, which may indicate the non-enzymatic antibacterial capacity of Uu-ilys.

Engineering Pichia pastoris for Efficient Production of a Novel Bifunctional Strongylocentrotus purpuratus Invertebrate-Type Lysozyme

Lysozymes are known as ubiquitously distributed immune effectors with hydrolytic activity against peptidoglycan, the major bacterial cell wall polymer, to trigger cell lysis. In the present study, the full-length cDNA sequence of a novel sea urchin Strongylocentrotus purpuratus invertebrate-type lysozyme (sp-iLys) was synthesized according to the codon usage bias of Pichia pastoris and was cloned into a constitutive expression plasmid pPIC9K. The resulting plasmid, pPIC9K-sp-iLys, was integrated into the genome of P. pastoris strain GS115. The bioactive recombinant sp-iLys was successfully secreted into the culture broth by positive transformants. The highest lytic activity of 960 U/mL of culture supernatant was reached in fed-batch fermentation. Using chitin affinity chromatography and gel-filtration chromatography, recombinant sp-iLys was produced with a yield of 94.5 mg/L and purity of > 99%. Recombinant sp-iLys reached its peak lytic activity of 8560 U/mg at pH 6.0 and 30 °C and showed antimicrobial activities against Gram-negative bacteria (Vibrio vulnificus, Vibrio parahemolyticus, and Aeromonas hydrophila) and Gram-positive bacteria (Staphylococcus aureus and Bacillus subtilis). In addition, recombinant sp-iLys displayed isopeptidase activity which reached the peak at pH 7.5 and 37 °C with the presence of 0.05 M Na⁺. In conclusion, this report describes the heterologous expression of recombinant sp-iLys in P. pastoris on a preparative-scale, which possesses lytic activity and isopeptidase activity. This suggests that sp-iLys might play an important role in the innate immunity of S. purpuratus.

Newly identified invertebrate-type lysozyme (Splys-i) in mud crab (Scylla paramamosain) exhibiting muramidase-deficient antimicrobial activity

Lysozymes are widely distributed immune effectors exerting muramidase activity against the peptidoglycan of the bacterial cell wall to trigger cell lysis. However, some invertebrate-type (i-type) lysozymes deficient of muramidase activity still exhibit antimicrobial activity. To date, the mechanism underlying the antimicrobial effect of muramidase-deficient i-type lysozymes remains unclear. Accordingly, this study characterized a novel i-type lysozyme, Splys-i, in the mud crab Scylla paramamosain. Splys-i shared the highest identity with the Litopenaeus vannamei i-type lysozyme (Lvlys-i2, 54% identity) at the amino acid level. Alignment analysis and 3D structure comparison show that Splys-i may be a muramidase-deficient i-type lysozyme because it lacks the two conserved catalytic residues (Glu and Asp) that are necessary for muramidase activity. Splys-i is mainly distributed in the intestine, stomach, gills, hepatopancreas, and hemocytes, and it is upregulated by Vibrio harveyi or Staphylococcus aureus challenge. Recombinant Splys-i protein (rSplys-i) can inhibit the growth of Gram-negative bacteria (V. harveyi, Vibrio alginolyticus, Vibrio parahemolyticus, and Escherichia coli), Gram-positive bacteria (S. aureus, Bacillus subtilis, and Bacillus megaterium), and the fungus Candida albicans to varying degrees. In this study, two binding assays and a bacterial agglutination assay were conducted to elucidate the potential antimicrobial mechanisms of Splys-i. Results demonstrated that rSplys-i could bind to all nine aforementioned microorganisms. It also exhibited a strong binding activity to lipopolysaccharide from E. coli and lipoteichoic acid and peptidoglycan (PGN) from S. aureus but a weak binding activity to PGN from B. subtilis and β-glucan from fungi. Moreover, rSplys-i could agglutinate these nine types of microorganisms in the presence of Ca²⁺ at different protein concentrations. These results suggest that the binding activity and its triggered agglutinating activity might be two major mechanisms of action to realize the muramidase-deficient antibacterial activity. In addition, rSplys-i can hydrolyze the peptidoglycan of some Gram-positive bacteria because it exhibits weak isopeptidase activities in salt and protein concentration-dependent manner. This result indicates that such an isopeptidase activity may contribute to the muramidase-deficient antimicrobial activity to a certain degree. In conclusion, Splys-i is upregulated by pathogenic bacteria, and it inhibits bacterial growth by binding and agglutination activities as well as isopeptidase activity, suggesting that Splys-i is involved in immune defense against bacteria through several different mechanisms of action.

Transcriptomic analyses on muscle tissues of Litopenaeus vannamei provide the first profile insight into the response to low temperature stress

The Pacific white shrimp (Litopenaeus vannamei) is an important cultured crustacean species worldwide. However, little is known about the molecular mechanism of this species involved in the response to cold stress. In this study, four separate RNA-Seq libraries of L. vannamei were generated from 13°C stress and control temperature. Total 29,662 of Unigenes and overall of 19,619 annotated genes were obtained. Three comparisons were carried out among the four libraries, in which 72 of the top 20% of differentially-expressed genes were obtained, 15 GO and 5 KEGG temperature-sensitive pathways were fished out. Catalytic activity (GO: 0003824) and Metabolic pathways (ko01100) were the most annotated GO and KEGG pathways in response to cold stress, respectively. In addition, Calcium, MAPK cascade, Transcription factor and Serine/threonine-protein kinase signal pathway were picked out and clustered. Serine/threonine-protein kinase signal pathway might play more important roles in cold adaptation, while other three signal pathway were not widely transcribed. Our results had summarized the differentially-expressed genes and suggested the major important signaling pathways and related genes. These findings provide the first profile insight into the molecular basis of L. vannamei response to cold stress.

Dietary effect of apple cider vinegar and propionic acid on immune related transcriptional responses and growth performance in white shrimp, Litopenaeus vannamei

This experiment was conducted to study the effect of various levels of ACV^® and Propionic acid (PA) on expression of immune related genes and growth performance in white shrimp (Litopenaeus vannamei). Three hundred and seventy-five shrimps with an average initial weight of 10.2 ± 0.04 g were collected and acclimatized for two weeks. Five experimental diets including control diet, 0.5% PA diet and 1%, 2% and 4% ACV^® diets were applied to feed the shrimps. They were fed 4 times a day with 2.5% of body weight. After 60 days of culture, shrimps fed with ACV^® and PA diets showed no significant difference in growth performance. Expression of prophenoloxidase (proPo), lysozyme (Lys), penaeidin-3a (Pen-3a) and Crustin (Cru) genes were determined from hepatopancreas, using the real-time PCR after 15, 30 and 60 days. Expression of Lys and proPo genes was significantly up regulated in shrimps fed with ACV^® and PA diets compared to the control group after 30 and 60 days of treatment. After 15 days, Pen-3a gene expression was significantly higher in PA group compared to the control group. Also, shrimps fed with 1% and 4% ACV^® and PA diets showed significantly increased expression of Pen-3a after 30 days. In contrast, expression of Cru was significantly down regulated in response to ACV^® diets, but, Cru expression in treated shrimps with PA diet was greater than the control group after 30 and 60 days. Overall, the results provided evidence that ACV^® could be used as a natural immunostimulant for shrimps in order to adjust and enhance expression of the immune related genes.