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

Comprehensive review of Argulus infestations in aquaculture: Biological impacts and advanced management strategies

The aquaculture industry is hindered by various factors. One of the most noticeable factors is infection by parasites and pathogens. Argulus stands out as a prominent and economically significant ectoparasite in freshwater aquaculture. Argulus infestation causes severe immunomodulatory effects on its hosts by promoting argulosis, causing inflammation, extensive tissue damage, and death. Indian aquaculture sector faced a loss of 62.5 million USD due to Argulus infection. However, current control methods, such as pesticides, cause serious environmental damage. Herbal treatment methods are ineffective and have limitations. Hence, a more efficient and cost-effective control method is needed. In recent years, vaccine development has emerged as a promising avenue of research. Understanding the effect of the host-parasite relationship in the host immune system is essential to develop strategies for prevention, control, and management of argulosis. These interactions provide insights into the co-evolutionary dynamics between hosts and parasites. This review provides an overview of the current knowledge on the host-searching behaviour of Argulus, host-parasite interaction and control strategies. This review also highlights the need for further research and the development of sustainable control measures for Argulus infection.

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.

Antioxidant Defence in Labeo rohita to Biotic and Abiotic Stress: Insight from mRNA Expression, Molecular Characterization and Recombinant Protein-Based ELISA of Catalase, Glutathione Peroxidase, CuZn Superoxide Dismutase, and Glutathione S-Transferase

Fish possess numerous enzymatic antioxidant systems as part of their innate immunity. These systems have been poorly studied in Labeo rohita (rohu). The present study characterized and investigated the role of antioxidant genes in the defence mechanisms against two types of stressors, including infection and ammonia stress. Four key genes associated with antioxidant activity-catalase, glutathione peroxidase, glutathione S-transferase, and CuZn superoxide dismutase were successfully cloned and sequenced. These genes were found to be expressed in different tissues and developmental stages of rohu. The expression levels of these antioxidant genes in the liver and anterior kidney tissues of rohu juveniles were modulated in response to bacterial infection (Aeromonas hydrophila), parasite infection (Argulus siamensis), poly I:C stimulation and ammonia stress. Additionally, the recombinant proteins derived from these genes exhibited significant antioxidant and antibacterial activities. These proteins also demonstrated a protective effect against A. hydrophila infection in rohu and had an immunomodulatory role. Furthermore, indirect ELISA assay systems were developed to measure these protein levels in healthy as well as A. hydrophila and ammonia-induced rohu serum. Overall, this study characterized and emphasised the importance of the antioxidant mechanism in rohu's defence against oxidative damage and microbial diseases.

Transcriptomic Variation of Amphiprion Percula (Lacepède, 1802) in Response to Infection with Cryptocaryon Irritans Brown, 1951

Cryptocaryon irritans (Brown 1951) frequently infect the Pomacentridae fishes causing severe economic losses. However, the anti-C. irritans' molecular mechanism in these fishes remains largely unknown. To address this issue, we conducted RNA-Seq for C. irrtians-infected gills of the clownfish Amphiprion percula (Lacepède 1802) at the early (day 1) and late (day 3) stages of infection. A total of 1655 differentially expressed genes (DEGs) were identified. Gene Ontology (GO) and Kyoto Encyclopedia of Genes and Genomes (KEGG) pathway enrichment analyses of DEGs showed a vast genetic variation related to the following aspects: ECM-receptor interaction, P13K-Akt signalling, cytokine-cytokine receptor interaction, and endocytosis. During the early phase of infection, key genes involved in ATP production, energy homeostasis, and stress control were abruptly increased. In the late phase, however, acute response molecules of the peripheral nervous system (synaptic transmission and local immunity), metabolic system triggering glycogen synthesis, energy maintenance, and osmoregulation were found to be critical. The highest number of upregulated genes (URGs) recovered during the early phase was included under the 'biological process' category, which primarily functions as response to stimuli, signalling, and biological regulation. In the late phase, most of the URGs were related to gene regulation and immune system processes under 'molecular function' category. The immune-related URGs of early infection include major histocompatibility complex (MHC) class-II molecules apparently triggering CD4+ T-cell-activated Th responses, and that of late infection include MHC class-1 molecules for the possible culmination of CD8+ T-cell triggered cytotoxicity. The high level of genic single nucleotide polymorphisms (SNPs) identified during the late phase of infection is likely to influence their susceptibility to secondary infection. In summary, the identified DEGs and their related metabolic and immune-related pathways and the SNPs may provide new insights into coordinating the immunological events and improving resistance in Pomacentridae fishes against C. irritans.

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.

An insight into the interaction between Argulus siamensis and Labeo rohita offers future therapeutic strategy to combat argulosis

Aquaculture and fisheries are salient flourishing sectors in the world but their sustainability is often afflicted by several pathogenic diseases. Among all the pathogenic diseases of fish, parasitic diseases are found to be a major cause of concern. Argulosis is one of the dominant parasitic problems encountered in Indian aquaculture practices. Argulus siamensis is the most prevalent argulid species harming the Indian major carp species including Labeo rohita. The major carps respond to parasitic infestation by elevating various immune relevant genes. The therapeutic chemicals, synthetic drugs and other plant extracts have made a progress in the fight against argulosis. However, there is no effective vaccine and drugs are available for this disease. Thus, designing efficient, cost-effective and eco-friendly control and treatment strategies for argulosis is presently needed. Keeping the aforementioned facts in mind, the current review elaborated the immunological interaction between A. siamensis and L. rohita, available combat tactics, highlighted the already identified vaccine candidates to design effective control measures and illustrated the use of omics technology in future to combat argulosis.

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.

Effects of dietary black soldier fly (Hermetia illucens Linnaeus) on the disease resistance of juvenile grouper (Epinephelus coioides)

An experiment was performed to study the effects of dietary levels of black soldier fly larva meal (BSFLM) on the growth performance, immunity and disease resistance of juvenile grouper (Epinephelus coioides). Four isoproteic and isoenergetic diets were formulated with dietary BSFLM levels of 0 g/kg (T0), 25 g/kg (T2.5), 50 g/kg (T5) and 100 g/kg (T10). Each diet was randomly fed to triplicate groups, each containing 40 fish. The results of the 30-day study indicated that fish growth performance was not affected in the T2.5 and T5 groups compared with the T0 group. In the group with a dietary BSFLM level of 100 g/kg, the feed coefficient was significantly higher than that in the other three groups. The superoxide dismutase, catalase, glutathione peroxidase, lysozyme activity, and malondialdehyde content in the liver, and the interleukin-1 beta (IL-1β), gamma interferon (IFN-γ), tumor necrosis factor alpha (TNF-α) and heat shock protein 70 (HSP70) expression in the gills, head kidney, liver and spleen remained consistent in all groups. In addition, no significant differences in the cumulative mortality or parasite abundance in groupers after Vibrio harveyi and Cryptocaryon irritans infection were observed. These results suggested that BSFLM supplemented diets did not inhibit disease resistance in groupers.

Parallel Independent Losses of G-Type Lysozyme Genes in Hairless Aquatic Mammals

Lysozyme enzymes provide classic examples of molecular adaptation and parallel evolution, however, nearly all insights to date come from chicken-type (c-type) lysozymes. Goose-type (g-type) lysozymes occur in diverse vertebrates, with multiple independent duplications reported. Most mammals possess two g-type lysozyme genes (Lyg1 and Lyg2), the result of an early duplication, although some lineages are known to have subsequently lost one copy. Here we examine g-type lysozyme evolution across >250 mammals and reveal widespread losses of either Lyg1 or Lyg2 in several divergent taxa across the mammal tree of life. At the same time, we report strong evidence of extensive losses of both gene copies in cetaceans and sirenians, with an additional putative case of parallel loss in the tarsier. To validate these findings, we inspected published short-read data and confirmed the presence of loss of function mutations. Despite these losses, comparisons of selection pressures between intact g- and c-type lysozyme genes showed stronger purifying selection in the former, indicative of conserved function. Although the reasons for the evolutionary loss of g-type lysozymes in fully aquatic mammals are not known, we suggest that this is likely to at least partially relate to their hairlessness. Indeed, although Lyg1 does not show tissue-specific expression, recent studies have linked Lyg2 expression to anagen hair follicle development and hair loss. Such a role for g-type lysozyme would explain why the Lyg2 gene became obsolete when these taxa lost their body hair.

Seroconversion and Skin Mucosal Parameters during Koi Herpesvirus Shedding in Common Carp, Cyprinus carpio

Seroconversion and the mucosal lysozyme G (lysG), complement 3 (c3), and immunoglobulins M (IgMsec) and Z2 (IgZ2) were measured for up to 900 degree days (DD) in skin swabs from common carp exposed to koi herpesvirus (KHV or CyHV-3) at either a non-permissive temperature (12 °C) or permissive temperatures (17 and 22 °C), and in survivors subjected to temperature increase to 22 °C 500 DD after the initial exposure. The survival rate at 22 °C varied from 100% in fish initially exposed at 12 °C, to 20% at 17 °C and 0% at 22 °C. Viral shedding episodes lasted for up to 29 days (493 DD) for fish clinically infected at 17 °C, and up to 57 days (684 DD) for asymptomatic fish held at 12 °C. Up-regulation of lysG transcripts was measured at 17 and 22 °C. Down-regulation of c3 and IgMsec transcripts was measured independent of the water temperature, followed by up-regulation after the temperature increase coinciding with seroconversion and clearance of KHV from the skin mucus. IgZ2 mRNA showed a negative correlation with IgM transcripts. KHV subversion of the complement system at the mucosal site coupled with poor immunoglobulin secretion during the viral replication might contribute to the long window of viral shedding, thus facilitating viral transmission.

Cloning and functional characterisation of natural killer enhancing factor-B (NKEF-B) gene of Labeo rohita: Anti-oxidant and antimicrobial activities of its recombinant protein

Natural killer enhancing factor (NKEF) of peroxiredoxin family is an important innate immune molecule with having anti-oxidant activity. Although this gene has already been studied in a few fish species, it is yet to be identified and functionally characterised in Indian major carps. In the present study, the complete NKEF-B cDNA of rohu, Labeo rohita was cloned that encoded a putative protein of 197 amino acids. The phylogenetic study showed that L. rohita NKEF-B (LrNKEF-B) is closely related to NKEF-B of Cyprinus carpio and Danio rerio species. Tissue-specific expression of LrNKEF-B gene revealed the highest transcript level in the liver tissue. In the ontogeny study, the highest level of the expression was observed in milt and at 18 h post-development. The expression pattern of this gene was also studied in various pathogen models viz., Gram-negative bacteria (Aeromonas hydrophila), ectoparasite (Argulus siamensis) and a dsRNA viral analogue (poly I:C) in the liver and anterior kidney tissues of L. rohita juveniles. During A. hydrophila infection, the increase in expression of transcripts was observed at 3 h post-infection in both liver (15-fold) and anterior kidney (8-fold). In A. siamensis infection, the expression gradually increased up to 3 d post-infection in the anterior kidney, whereas in liver 3-fold up-regulation was noticed at 12 h post-infection. Similarly, during poly I:C stimulation, up-regulation of NKEF-B transcript was observed in anterior kidney from 1 h to 24 h post-stimulation and down-regulated afterwards whereas, the transcript level increased gradually from 6 h to 15 d post-stimulation in liver tissue. In vitro exposure to concanavalin, A and formalin-killed A. hydrophila upregulated NKEF-B gene expression in anterior kidney and peripheral blood leukocytes of L. rohita, however, down-regulated the same in the splenic leukocytes. A recombinant protein of LrNKEF-B (rLrNKEF-B) of 22 kDa was produced and it showed anti-oxidant activity by protecting supercoiled DNA and reducing insulin disulfide bonds. The minimum bactericidal concentration of this recombinant protein was found to be 4.54 μM against A. hydrophila and Staphylococcus aureus. Interestingly, rLrNKEF-B showed relative percent survival of 72.6 % in A. hydrophila challenged L. rohita, and the survival was found to be associated with a high level of expression of different cytokines, anti-oxidant genes and perforin in the rLrNKEF-B treated L. rohita. An indirect ELISA assay for estimation of NKEF was developed in L. rohita, and the concentrations of NKEF-B increased with time periods post A. hydrophila challenge viz., 0 h (42.56 ng/mL), 12 h (174 ng/mL) and 48 h (370 ng/mL) in rohu serum. Our results suggest a crucial role of LrNKEF-B in innate immunity against biotic stress and oxidative damage and also having antibacterial activity.

Characterization of immune response against Mycobacterium marinum infection in the main hematopoietic organ of adult zebrafish (Danio rerio)

Tuberculosis remains a major global health challenge. To gain information about genes important for defense against tuberculosis, we used a well-established tuberculosis model; Mycobacterium marinum infection in adult zebrafish. To characterize the immunological response to mycobacterial infection at 14 days post infection, we performed a whole-genome level transcriptome analysis using cells from kidney, the main hematopoietic organ of adult zebrafish. Among the upregulated genes, those associated with immune signaling and regulation formed the largest category, whereas the largest group of downregulated genes had a metabolic role. We also performed a forward genetic screen in adult zebrafish and identified a fish line with severely impaired survival during chronic mycobacterial infection. Based on transcriptome analysis, these fish have decreased expression of several immunological genes. Taken together, these results give new information about the genes involved in the defense against mycobacterial infection in zebrafish.

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.