The Role of Lectins in Finfish: A Review

Identification, characterization, and functional verification of a novel fish-egg lectin (FEL) from the golden pompano, Trachinotus ovatus

Lectins play important roles in the innate immune response and therefore are of great interest for immunologists. Although different families of lectins have been increasingly documented in various fish species, our current understanding of fish-egg lectins (FELs) is still in paucity. In this study, a novel FEL (ToFEL) was identified in the commercially important marine fish golden pompano (Trachinotus ovatus) through transcriptomic screening. In addition to bioinformatic characterization, the expression of ToFEL in different tissues and upon pathogenic challenge were profiled. Moreover, the binding capacity of ToFEL to five bacteria and the agglutinating activity of ToFEL against bacteria as well as blood and sperm cells of donor species with and without Ca2+ were assessed using the recombinant T. ovatus FEL (rToFEL). Our results demonstrated that ToFEL had an open reading frame (ORF) of 786 bp, which encodes a putative protein with 261 amino acids including a signal peptide consists of 19 amino acids. In addition to harboring three typical TECPR domains, a Ca2+-binding site was also identified in ToFEL. The ToFEL was shown to be highly homology to FELs of other fish species investigated, especially to its close relatives Seriola dumerili and S. lalandi. The expression of ToFEL was detected in all the ten tissues examined (predominantly in gill, liver, and ovary) under normal condition and was significantly induced upon pathogenic challenge. In addition, in the presence of Ca2+, the rToFEL exhibited strong binding and agglutinating activity against both gram-positive and gram-negative bacteria as well as blood and/or sperm cells of donor species. Collectively, our data indicate that ToFEL is a constitutive and inducible acute-phase immune molecule of T. ovatus in response to a broad-spectrum alien substances.

Sexual Selection on Non-Ornamental Traits Is Underpinned by Evidence of Genetic Constraints on Sex-Biased Expression in Dusky Pipefish

Species lacking distinct secondary sex characteristics, such as differences in size or morphology, are often thought to experience lower levels of sex-specific selection in comparison to highly sexually dimorphic organisms. However, monomorphism in classic visible traits could be a result of genetic or physiological constraints that prevent the sexes from reaching divergent fitness optima. Additionally, biochemical and molecular work have revealed a variety of less easily observed phenotypes that nonetheless exhibit profound dimorphism. Sex-specific selection could act on these more subtle, less visible, traits. We investigate sex-specific selection in the polygynandrous dusky pipefish (Syngnathus floridae), which lacks distinct secondary sexual characteristics such as size, colour and morphological dimorphism. Using experimental breeding populations, we revealed that although males and females have similar opportunities for sexual selection, only males experience significant sexual selection pressures on body size. We also investigated patterns of sex-biased and sex-specific gene expression in gonads, livers and gills, and tested whether genes with highly divergent expression patterns between the sexes are more likely to be tissue-specific, and therefore relieved of genetic constraints. Sex bias in gene expression was widespread, although the reproductive organs had the most sex-biased and sex-specific genes. Sex-specific selection on gene expression in gills was primarily related to immune response, whereas the liver and gonads had a wide variety of cellular processes, as well as reproductive proteins, showing sex-biased expression. These sex-biased genes showed higher organ-specificity in their expression patterns, suggesting that pleiotropic constraints might have historically impacted the evolution of sex-specific expression patterns. Altogether, we find evidence for ongoing and historical sex-specific selection in the dusky pipefish.

Evaluation of potential antiviral activities of antimicrobial peptides in fish mucus

BACKGROUND

Fish skin mucus contains innate immune factors and acts as the first line of physical or chemical defense against pathogens.

OBJECTIVE

The primary aim of this study was to determine the antiviral activity of sea bream (SBr), rainbow trout (RT), and sea bass (SBa) fish skin mucus against herpes simplex virus (HSV)-1. In addition, it was aimed to associate possible antiviral activity with antimicrobial peptides (AMPs) such as cathelicidin, hepcidin, galectin 2, and C10ORF99, whose levels were determined in the mucus.

METHODS

The antiviral activity and oxidative/antioxidant status of mucus against HSV-1 virus was evaluated. In addition, AMPs, SOD, and CAT activities, and immunoglobulin M levels were also analyzed in mucus of fish.

RESULTS

Antiviral activity mucus of SBr, RT, and SBa against HSV-1 were determined as 2-4, 2-5, and 2-2, respectively. The higher antiviral activity of SBr and RT mucus compared to the mucus of SBa can be associated with higher AMP levels in them.

CONCLUSION

The skin mucus of SBr and RT may be nutritional supplement, adjuvant, and a new agent that can potentiate the effects of antimicrobial/antiviral agents.

Effects of pejus and pessimum zone salinity stress on gill proteome networks and energy homeostasis in Oreochromis mossambicus

Salinity tolerance in fish involves a suite of physiological changes, but a cohesive theory leading to a mechanistic understanding at the organismal level is lacking. To examine the potential of adapting energy homeostasis theory in the context of salinity stress in teleost fish, Oreochromis mossambicus were acclimated to hypersalinity at multiple rates and durations to determine salinity ranges of tolerance and resistance. Over 3000 proteins were quantified simultaneously to analyze molecular phenotypes associated with hypersalinity. A species- and tissue-specific data-independent acquisition (DIA) assay library of MSMS spectra was created. Protein networks representing complex molecular phenotypes associated with salinity acclimation were generated. O. mossambicus has a wide "zone of resistance" from 75 g/kg salinity to 120 g/kg. Crossing into the zone of resistance resulted in marked phenotypic changes including blood osmolality over 400 mOsm/kg, reduced body condition, and cessation of feeding. Protein networks impacted by hypersalinity consist of electron transport chain (ETC) proteins and specific osmoregulatory proteins. Cytoskeletal, cell adhesion, and extracellular matrix proteins are enriched in networks that are sensitive to the critical salinity threshold. These network analyses identify specific proteome changes that are associated with distinct zones described by energy homeostasis theory and distinguish them from general hypersalinity-induced proteome changes.

Gut-immunity modulation in Lepidocephalichthys guntea during Aeromonas hydrophila-infection and recovery assessed with transcriptome data

The fish immune system, which consists of innate and adaptive immunologic processes, defends against viruses, bacteria, fungi, and parasites. The gut immunity is an integral part of the host immune system that controls immunological homeostasis, hosts' interactions with their microbiomes, and provides defence against a number of intestinal infections. Lepidocephalichthys guntea, a facultative air-breathing fish, was experimentally infected with Aeromonas hydrophila using intraperitoneal injection followed by bath challenge, and transcriptome data were used to examine the gut immune responses during disease progression and recovery from the diseased state without the use of medication. For the control or uninfected fish (FGC) and the infected fish that were kept for seven days (FGE1) and fifteen days (FGE2), separate water tanks were set up. Coding DNA sequences (CDS) for FGC and FGE1, FGC and FGE2, and FGE1 and FGE2 were analyzed for differential gene expression (DGE). The presence and expression of genes involved in the T cell receptor (TCR) signalling pathway, natural killer (NK) cell-mediated cytotoxicity pathway, and complement-mediated pathway, along with a large number of other immune-related proteins, and heat shock protein (HSPs) under various experimental conditions and its relationship to immune modulation of the fish gut was the primary focus of this study. Significant up-and-down regulation of these pathways shows that, in FGE1, the fish's innate immune system was engaged, whereas in FGE2, the majority of innate immune mechanisms were repressed, and adaptive immunity was activated. Expression of genes related to the immune system and heat-shock proteins was induced during this host's immunological response, and this information was then used to build a thorough network relating to immunity and the heat-shock response. This is the first study to examine the relationship between pathogenic bacterial infection, disease reversal, and modification of innate and adaptive immunity as well as heat shock response.

Stonefish (Synanceia spp.) Ichthyocrinotoxins: An ecological review and prospectus for future research and biodiscovery

Marine organisms possess a diverse array of unique substances, many with wide ranging potential for applications in medicine, industry, and other sectors. Stonefish (Synanceia spp.), a bottom-dwelling fish that inhabit shallow and intertidal waters throughout the Indo-Pacific, harbour two distinct substances, a venom, and an ichthyocrinotoxin. Stonefish are well-known for the potent venom associated with their dorsal spines as it poses a significant risk to public health. Consequently, much of the research on stonefish focusses on the venom, with the aim of improving outcomes in cases of envenomation. However, there has been a notable lack of research on stonefish ichthyocrinotoxins, a class of toxin that is synthesised within specialised epithelial cells (i.e., tubercles) and exuded onto the skin. This has resulted in a substantial knowledge gap in our understanding of these animals. This review aims to bridge this gap by consolidating literature on the ecological functions and biochemical attributes of ichthyocrinotoxins present in various fish species and juxtaposing it with the current state of knowledge of stonefish ecology. We highlight the roles of ichthyocrinotoxins in predator defence, bolstering innate immunity, and mitigating integumentary interactions with parasites and detrimental fouling organisms. The objective of this review is to identify promising research avenues that could shed light on the ecological functions of stonefish ichthyocrinotoxins and their potential practical applications as therapeutics and/or industrial products.

Identification, characterization, and agglutinating activity of a novel C-type lectin domain family 3 member B (CLEC3B) discovered in golden pompano, Trachinotus ovatus

The lectins are a large family of carbohydrate-binding proteins that play important roles in the innate immune response of various organisms. Although C-type lectin domain family 3 member B (CLEC3B), an important member of C-type lectin, has been well documented in humans and several other higher vertebrates, little is currently known about this molecule in economically important marine fish species. In this study, through transcriptomic and BLAST screening, a novel CLEC3B gene was identified in the golden pompano (Trachinotus ovatus). The T. ovatus CLEC3B (ToCLEC3B) was subsequently characterized by bioinformatic analysis and compared with those reported in other species. In addition, the expression patterns of ToCLEC3B in different tissues under normal condition and at different times post pathogen challenge were assessed. Furthermore, the agglutinating activity of ToCLEC3B with and without Ca2+ against different bacteria and blood cells of donor species were verified using the recombinant T. ovatus CLEC3B (rToCLEC3B). Our results demonstrated that ToCLEC3B is a Ca2+-dependent galactose-binding lectin with a single copy of carbohydrate recognition domain (CRD). Similar to CLEC3B reported in other species, the CRD domain of ToCLEC3B consists of two α-helices, six β-sheets, and four loops, forming two Ca2+- and a galactose-binding sites. According to the phylogenetic analysis, the ToCLEC3B was highly similar (similarity at 95.00%) to that of its relative, the greater amberjack (Seriola dumerili). The expression of ToCLEC3B was detected in all tissues examined under normal condition and was significantly up-regulated by injection of pathogenic microbes. In addition, the rToCLEC3B exhibited strong agglutinating activity against different bacteria and blood cells of donor species in the presence of Ca2+. Our results indicate that ToCLEC3B is a constitutive and inducible acute-phase immune factor in the host's innate immune response of T. ovatus.

Molecular Characterization of Galectin-3 in Large Yellow Croaker Larimichthys crocea Functioning in Antibacterial Activity

Galectins are proteins that play a crucial role in the innate immune response against pathogenic microorganisms. Previous studies have suggested that Galectin-3 could be a candidate gene for antibacterial immunity in the large yellow croaker Larimichthys crocea. In this study, we cloned the Galectin-3 gene in the large yellow croaker, and named it LcGal-3. The deduced amino acid sequence of LcGal-3 contains a carbohydrate recognition domain with two conserved β-galactoside binding motifs. Quantitative reverse transcription PCR (qRT-PCR) analysis revealed that LcGal-3 was expressed in all the organs/tissues that were tested, with the highest expression level in the gill. In Larimichthys crocea kidney cell lines, LcGal-3 protein was distributed in both the cytoplasm and nucleus. Moreover, we found that the expression of LcGal-3 was significantly upregulated upon infection with Pseudomonas plecoglossicida, as demonstrated by qRT-PCR analyses. We also purified the LcGal-3 protein that was expressed in prokaryotes, and found that it has the ability to agglutinate large yellow croaker red blood cells in a Ca²⁺-independent manner. The agglutination activity of LcGal-3 was inhibited by lipopolysaccharides (LPS) in a concentration-dependent manner, as shown in the sugar inhibition test. Additionally, LcGal-3 exhibited agglutination and antibacterial activities against three Gram-negative bacteria, including P. plecoglossicida, Vibrio parahaemolyticus, and Vibrio harveyi. Furthermore, we studied the agglutination mechanism of the LcGal-3 protein using blood coagulation tests with LcGal-3 deletion and point mutation proteins. Our results indicate that LcGal-3 protein plays a critical role in the innate immunity of the large yellow croaker, providing a basis for further studies on the immune mechanism and disease-resistant breeding in L. crocea and other marine fish.

Hybrid of Metapenaeus dobsoni lectin and platinum nanoparticles exert antimicrobial and immunostimulatory effects to reduce bacterial bioburden in infected Nile tilapia

A novel antibacterial immunostimulant using Platinum nanoparticles (PtNPs) and lectin from Metapenaeus dobsoni (Md-Lec) was developed. The Md-Lec and PtNPs (Pt-lec) hybrid formed through non-covalent interaction exhibits antimicrobial activity against fish specific pathogens by affecting membrane integrity and producing excess reactive oxygen species. The therapeutic efficacy of Pt-lec was demonstrated through rescuing Aeromonas hydrophila infected Nile Tilapia. Pt-lec prevents the infection spreading and reduces the bacterial bioburden in less than 12 h, and as a result of this the fish were restored to normalcy. To assess immunostimulation, we studied the expression of three different immune related genes, namely LEC, Myd88 and COX-2 in the gills, liver, spleen and kidney of fish under various experimental conditions. Our results showed that Pt-lec treatment appeared to be better when compared to lectin alone in enhancing the expression of Myd88 and COX-2, but LEC was not as expected. These results suggest that Pt-lec has the ability to protect Nile Tilapia against bacterial infection by restricting bacterial bioburden through their direct effects on the bacterial membrane and indirectly through their effects on host immune-related gene expression. This hybrid could have potential “green” application in fish farming in rescuing infected animals when compared to widely and unregulated antibiotics.

Hybrid of Metapenaeus dobsoni lectin and platinum nanoparticles exert antimicrobial and immunostimulatory effects to reduce bacterial bioburden in infected Nile tilapia

A novel antibacterial immunostimulant using Platinum nanoparticles (PtNPs) and lectin from Metapenaeus dobsoni (Md-Lec) was developed. The Md-Lec and PtNPs (Pt-lec) hybrid formed through non-covalent interaction exhibits antimicrobial activity against fish specific pathogens by affecting membrane integrity and producing excess reactive oxygen species. The therapeutic efficacy of Pt-lec was demonstrated through rescuing Aeromonas hydrophila infected Nile Tilapia. Pt-lec prevents the infection spreading and reduces the bacterial bioburden in less than 12 h, and as a result of this the fish were restored to normalcy. To assess immunostimulation, we studied the expression of three different immune related genes, namely LEC, Myd88 and COX-2 in the gills, liver, spleen and kidney of fish under various experimental conditions. Our results showed that Pt-lec treatment appeared to be better when compared to lectin alone in enhancing the expression of Myd88 and COX-2, but LEC was not as expected. These results suggest that Pt-lec has the ability to protect Nile Tilapia against bacterial infection by restricting bacterial bioburden through their direct effects on the bacterial membrane and indirectly through their effects on host immune-related gene expression. This hybrid could have potential "green" application in fish farming in rescuing infected animals when compared to widely and unregulated antibiotics.

Expression of Antimicrobic Peptide Piscidin1 in Gills Mast Cells of Giant Mudskipper Periophthalmodon schlosseri (Pallas, 1770)

The amphibious teleost Giant mudskipper (Periophthalmodon schlosseri, Pallas 1770) inhabit muddy plains and Asian mangrove forests. It spends more than 90% of its life outside of the water, using its skin, gills, and buccal-pharyngeal cavity mucosa to breathe in oxygen from the surrounding air. All vertebrates have been found to have mast cells (MCs), which are part of the innate immune system. These cells are mostly found in the mucous membranes of the organs that come in contact with the outside environment. According to their morphology, MCs have distinctive cytoplasmic granules that are released during the degranulation process. Additionally, these cells have antimicrobial peptides (AMPs) that fight a variety of infections. Piscidins, hepcidins, defensins, cathelicidins, and histonic peptides are examples of fish AMPs. Confocal microscopy was used in this study to assess Piscidin1 expression in Giant Mudskipper branchial MCs. Our results demonstrated the presence of MCs in the gills is highly positive for Piscidin1. Additionally, colocalized MCs labeled with TLR2/5-HT and Piscidin1/5-HT supported our data. The expression of Piscidin1 in giant mudskipper MCs highlights the involvement of this peptide in the orchestration of teleost immunity, advancing the knowledge of the defense system of this fish.

Adipose Fin as a Natural “Optical Window” for Implantation of Fluorescent Sensors into Salmonid Fish

Simple Summary

Novel optical sensors require implantation into the most transparent organs in order to ensure the most reliable and rapid monitoring of animal health. Widely farmed salmonid fish, such as rainbow trout, have highly translucent adipose fin, which we tested here and showed its high potential as the implantation site for the fluorescent sensors. The filamentous sensors were convenient to inject into the fin, and their optical signal was easily detectable using a simple hand-held device even without immobilization of the fish. Responsiveness of the sensors inside the adipose fin to bodily changes was shown under induced acidosis of fish fluids. The obtained results characterize adipose fin as the favorable site for implantation of optical sensors into salmonids for real-time tracking animal physiological status in basic research and aquaculture.

Abstract

Implantable optical sensors are emerging tools that have the potential to enable constant real-time monitoring of various internal physiological parameters. Such a possibility will open new horizons for health control not only in medicine, but also in animal husbandry, including aquaculture. In this study, we analyze different organs of commonly farmed rainbow trout (Oncorhynchus mykiss) as implantation sites for fluorescent sensors and propose the adipose fin, lacking an endoskeleton, as the optimal choice. The fin is highly translucent due to significantly thinner dermis, which makes the detectable fluorescence of an implanted sensor operating at the visible light range by more than an order of magnitude higher relative to the skin. Compared to the proximal parts of ray fins, the adipose fin provides easy implantation and visualization of the sensor. Finally, we tested fluorescent pH sensors inside the adipose fin and demonstrated the possibility of acquiring their signal with a simple hand-held device and without fish anesthesia. All these features will most likely make the adipose fin the main “window” into the internal physiological processes of salmonid fish with the help of implantable optical sensors.

An Update of Lectins from Marine Organisms: Characterization, Extraction Methodology, and Potential Biofunctional Applications

Lectins are a unique group of nonimmune carbohydrate-binding proteins or glycoproteins that exhibit specific and reversible carbohydrate-binding activity in a non-catalytic manner. Lectins have diverse sources and are classified according to their origins, such as plant lectins, animal lectins, and fish lectins. Marine organisms including fish, crustaceans, and mollusks produce a myriad of lectins, including rhamnose binding lectins (RBL), fucose-binding lectins (FTL), mannose-binding lectin, galectins, galactose binding lectins, and C-type lectins. The widely used method of extracting lectins from marine samples is a simple two-step process employing a polar salt solution and purification by column chromatography. Lectins exert several immunomodulatory functions, including pathogen recognition, inflammatory reactions, participating in various hemocyte functions (e.g., agglutination), phagocytic reactions, among others. Lectins can also control cell proliferation, protein folding, RNA splicing, and trafficking of molecules. Due to their reported biological and pharmaceutical activities, lectins have attracted the attention of scientists and industries (i.e., food, biomedical, and pharmaceutical industries). Therefore, this review aims to update current information on lectins from marine organisms, their characterization, extraction, and biofunctionalities.

Structural characterization of a galectin isolated from the marine sponge Chondrilla caribensis with leishmanicidal potential

BACKGROUND

Solving primary structure of lectins leads to an understanding of the physiological roles within an organism and its biotechnological potential. Only eight sponge lectins have had their primary structure fully determined.

METHODS

The primary structure of CCL, Chondrilla caribensis lectin, was determined by tandem mass spectrometry. The three-dimensional structure was predicted and the protein-carbohydrate interaction analysed by molecular docking. Furthermore, the anti-leishmanial activity was observed by assays with Leishmania infantum.

RESULTS

The amino acid sequence consists of 142 amino acids with a calculated molecular mass of 15,443 Da. The lectin has a galectin-like domain architecture. As observed in other sponge galectins, the signature sequence of a highly conserved domain was also identified in CCL with some modifications. CCL exhibits a typical galectin structure consisting of a β-sandwich. Molecular docking showed that the amino acids interacting with CCL ligands at the monosaccharide binding site are mostly the same as those conserved in this family of lectins. Through its interaction with L. infantum glycans, CCL was able to inhibit the development of this parasite. CCL also induced apoptosis after eliciting ROS production and altering the membrane integrity of Leishmania infantum promastigote.

CONCLUSIONS

CCL joins the restricted group of sponge lectins with determined primary structure and very high biotechnological potential owing to its promising results against pathogens that cause Leishmaniasis.

GENERAL SIGNIFICANCE

As the determination of primary structure is important for biological studies, now CCL can become a sponge galectin with an exciting future in the field of human health.

Biofilm-Integrated Glycosylated Membrane for Biosuccinic Acid Production

Biofilm-based cell-immobilized fermentation technology is regarded as the technique with the most potential for biobased product (chemicals, biofuelss materials, etc.) production in industry. Glycosylated membrane can mimic natural extracellular matrix (ECM) and improve cell adhesion and biofilm formation based on carbohydrate-microbial lectin interaction. Here, we applied glycosylated membrane with rhamnose modified surface for constructing Actinobacillus succinogenes biofilm and producing biosuccinic acid. Polymer hollow fiber (PHF) membrane surface was first modified by glycosylation based on physical adsorption approach. The approach is simple, green, and suitable for scale-amplification. Then, the microbial biofilm formed dramatically on the modified membrane surface. And for subsequent biosuccinic acid production, the maximum titer of succinic acid reached 67.3 g/L, and the yield was 0.82 g/g. Compared with free cell fermentation, the titer and yield increased by 18% and 9% in this biofilm-based cell-immobilized fermentation system, respectively. Importantly, the production efficiency of biosuccinic acid increased obviously for subsequent biofilm-based cell-immobilized fermentation. In addition, the biofilm-integrated glycosylated membrane showed high reusability for succinic acid production. This result is important for developing biofilms for a wide range of applications in bioproduct (chemicals, biofuels, materials, etc.) production.

Scale Drop Disease Virus (SDDV) and Lates calcarifer Herpes Virus (LCHV) Coinfection Downregulate Immune-Relevant Pathways and Cause Splenic and Kidney Necrosis in Barramundi Under Commercial Farming Conditions

Marine farming of barramundi (Lates calcarifer) in Southeast Asia is currently severely affected by viral diseases. To better understand the biological implications and gene expression response of barramundi in commercial farming conditions during a disease outbreak, the presence of pathogens, comparative RNAseq, and histopathology targeting multiple organs of clinically “sick” and “healthy” juveniles were investigated. Coinfection of scale drop disease virus (SDDV) and L. calcarifer herpes virus (LCHV) were detected in all sampled fish, with higher SDDV viral loads in sick than in healthy fish. Histopathology showed that livers in sick fish often had moderate to severe abnormal fat accumulation (hepatic lipidosis), whereas the predominant pathology in the kidneys shows moderate to severe inflammation and glomerular necrosis. The spleen was the most severely affected organ, with sick fish presenting severe multifocal and coalescing necrosis. Principal component analysis (PC1 and PC2) explained 70.3% of the observed variance and strongly associated the above histopathological findings with SDDV loads and with the sick phenotypes, supporting a primary diagnosis of the fish being impacted by scale drop disease (SDD). Extracted RNA from kidney and spleen of the sick fish were also severely degraded likely due to severe inflammation and tissue necrosis, indicating failure of these organs in advanced stages of SDD. RNAseq of sick vs. healthy barramundi identified 2,810 and 556 differentially expressed genes (DEGs) in the liver and muscle, respectively. Eleven significantly enriched pathways (e.g., phagosome, cytokine-cytokine-receptor interaction, ECM-receptor interaction, neuroactive ligand-receptor interaction, calcium signaling, MAPK, CAMs, etc.) and gene families (e.g., tool-like receptor, TNF, lectin, complement, interleukin, chemokine, MHC, B and T cells, CD molecules, etc.) relevant to homeostasis and innate and adaptive immunity were mostly downregulated in sick fish. These DEGs and pathways, also previously identified in L. calcarifer as general immune responses to other pathogens and environmental stressors, suggest a failure of the clinically sick fish to cope and overcome the systemic inflammatory responses and tissue degeneration caused by SDD.

Potential Application of Combined Therapy with Lectins as a Therapeutic Strategy for the Treatment of Bacterial Infections

Antibiotic monotherapy may become obsolete mainly due to the continuous emergence of resistance to available antimicrobials, which represents a major uncertainty to human health. Taking into account that natural products have been an inexhaustible source of new compounds with clinical application, lectins are certainly one of the most versatile groups of proteins used in biological processes, emerging as a promising alternative for therapy. The ability of lectins to recognize carbohydrates present on the cell surface allowed for the discovery of a wide range of activities. Currently the number of antimicrobials in research and development does not match the rate at which resistance mechanisms emerge to an effective antibiotic monotherapy. A promising therapeutic alternative is the combined therapy of antibiotics with lectins to enhance its spectrum of action, minimize adverse effects, and reduce resistance to treatments. Thus, this review provides an update on the experimental application of antibiotic therapies based on the synergic combination with lectins to treat infections specifically caused by multidrug-resistant and biofilm-producing Staphylococcus aureus, Escherichia coli, and Pseudomonas aeruginosa. We also briefly discuss current strategies involving the modulation of the gut microbiota, its implications for antimicrobial resistance, and highlight the potential of lectins to modulate the host immune response against oxidative stress.

Dietary Inclusion of Black Soldier Fly (Hermetia Illucens) Larvae Meal and Paste Improved Gut Health but Had Minor Effects on Skin Mucus Proteome and Immune Response in Atlantic Salmon (Salmo Salar)

The present study investigated effects of dietary inclusion of black soldier fly larvae (BSFL) (Hermetia illucens) meal and paste on gut health, plasma biochemical parameters, immune response and skin mucus proteome in pre-smolt Atlantic salmon (Salmo salar). The seven-week experiment consisted of seven experimental diets: a control diet based on fishmeal and plant protein (Control-1); three BSFL meal diets, substituting 6.25% (6.25IM), 12.5% (12.5IM) and 25% (25IM) of protein; two BSFL paste diets, substituting 3.7% (3.7IP) and 6.7% (6.7IP) of protein and an extra control diet with 0.88% of formic acid (Control-2). The 6.25IM diet reduced enterocyte steatosis in pyloric caeca, improved distal intestine histology, and reduced IgM in distal intestine. The fish fed 12.5IM diet reduced enterocyte steatosis in pyloric caeca, improved distal intestine histology, had a higher plasma lysozyme content compared to 6.25IM, and tend to increase phagocytic activity in head-kidney macrophages-like cells. On the other hand, 25IM diet improved distal intestine histology, but showed mild-moderate enterocyte steatosis in pyloric caeca, increased IFNγ and reduced IgM in distal intestine. In the case of BSFL paste diets, 3.7IP diet caused mild inflammatory changes in distal intestine, although it reduced enterocyte steatosis in pyloric caeca. The 6.7IP diet reduced enterocyte steatosis in pyloric caeca and improved distal intestine histology. Increasing level of BSFL meal in the diet linearly decreased plasma C-reactive protein, whereas increasing level of BSFL paste linearly increased plasma antioxidant capacity. Dietary inclusion of BSFL meal and paste had minor effects on the expression profile of proteins in skin mucus and no effects on immune markers in splenocytes. BSFL meal showed no negative effect on liver and muscle health as indicated by plasma alanine aminotranseferase, asparate aminotransferase and creatine kinase. The present study showed that replacing conventional protein sources with low to moderate levels of BSFL meal (6.25% and 12.5%) or paste (3.7% and 6.7%) reduced enterocyte steatosis in pyloric caeca, while replacing up to 25% with BSFL meal or 6.7% with paste improved distal intestine histology. Further, dietary inclusion of BSFL meal and paste had minor effects on skin mucus proteome and immune response in Atlantic salmon.

Shrimp lectin (Md-Lec) conjugated copper sulfide nanoparticles enhance the elimination of aquatic pathogens in infected Nile tilapia (Oreochromis niloticus)

Lectins are known for their ability to bind to cell surface glycans, and are useful to develop a glycan-targeted drug delivery system. This study aimed to evaluate the capacity of pectin capped copper sulfide nanoparticles (pCuS NPs) to modulate the antibacterial activity of a lectin, Md-Lec, purified from the shrimp, Metapenaeus dobsoni. Fluorescence spectroscopy revealed that Md-Lec has the ability to form a complex with pCuS NPs. Haemagglutination assay showed that the carbohydrate binding site of the lectin was preserved even after complexing with pCuS. The minimum inhibitory concentrations (MICs) obtained for Md-Lec and pCuS NPs against the tested aquatic pathogens were 50 μg ml-1 and 12.5 μM, respectively. Interestingly, the MIC of Md-Lec-pCuS NPs complex was four fold lower than that of pCuS, which was attributed to the bacterial cell surface glycan recognization activity of Md-Lec. Zone of inhibition assay showed that the zone size was highest for the lectin conjugated nanoparticles. Mechanistic study revealed that Md-Lec-pCuS NPs affect the bacterial membrane integrity and produce a large volume of reactive oxygen species to kill the bacteria. The practical aspect of using this lectin-pCuS NPs complex was evaluated by treating bacteria infected Nile tilapia (Oreochromis niloticus). The bacterial load was much less in the lectin-pCus NPs complex treated fish; moreover, the fish fully recovered from the infection. It was concluded that the conjugate of antibacterial lectin and NPs is more effective than the individual components.

Antibacterial functions of a novel fish-egg lectin from spotted knifejaw (Oplegnathus punctatus) during host defense immune responses

Fish-egg lectins (FELs) have been identified in several teleost species and have been proved to play important roles in innate immune system against pathogen infection. In this study a novel fish-egg lectin (OppFEL) was identified from spotted knifejaw (Oplegnathus punctatus), and the expression patterns against bacterial infection was characterized. The amino acid sequence is highly homologous to other teleost FELs, containing five repeats of the conserved TECPR domain. Expression of OppFEL was widely observed in examined tissues, with the most abundant transcripts observed in gill, showing a pattern of tissue specific expression. The OppFEL expression was significantly up-regulated following a Gram-negative bacterium (Vibrio anguillarum) challenge in vivo, suggesting participation in host antibacterial immune responses. Recombinant OppFEL protein (rOppFEL) possessed calcium dependent binding capacities and agglutination to four Gram-negative bacterium and two Gram-positive bacterium. Sugar binding assay revealed that rOppFEL specifically bound to insoluble lipopolysaccharide and peptidoglycan. In addition, rOppFEL was also proved to have hemagglutinating activity against erythrocytes from Mus musculus, O. punctatus, Sebastes schlegelii and Paralichthys olivaceus. Dual-luciferase analysis showed that overexpression of OppFEL could suppress the activity of NF-κB in a dose dependent manner. Taken together, these results suggest that OppFEL is a unique fish-egg lectin that possesses apparent immunomodulating property and is involved in host defense against pathogens invasion.

Antimicrobial properties and phenoloxidase activation of the lectin isolated from kadal shrimp (Metapenaeus dobsoni)

The present study reveals purification and characterization of the lectin from the haemolymph of Metapenaeus dobsoni. The Md-Lec was purified by affinity chromatography with mannose coupled sepharose CL-4B column and it exhibits single band with a molecular weight of 68 kDa in SDS-PAGE. Furthermore, the molecular mass was confirmed by MALDI-TOF and functional groups present were analysed by FTIR. The surface morphology of purified Md-Lec displays the homogeneous nature of protein. The X-ray diffraction (XRD) analysis expresses three peaks at 10.7716̊, 21.6258̊ and 31.7523̊which indicate the crystalline nature of the protein and the retention time of 3.068 min evident from HPLC reveals the purity of the sample. Functional analysis of purified Md-Lec exhibits yeast agglutination activity against Saccharomyces cerevisiae and has the ability to agglutinate the human erythrocytes, which was observed by light microscopy. It also exhibited phenoloxidase activation, encapsulation and phagocytic activities. In addition, purified Md-Lec showed the broad spectrum of bacterial agglutination activity against Gram negative Vibrio parahaemolyticus and Aeromonas hydrophila, important fish pathogens. Antiviral potential and anticancer activity of purified Md-Lec against CyHV-2 virus and MDA-MB-231 breast cancer cell lines were also evaluated in this study.