Expression and distribution of penaeidin antimicrobial peptides are regulated by haemocyte reactions in microbial challenged shrimp

Influence of stocking density on the growth, immune and physiological responses, and cultivation environment of white-leg shrimp (Litopenaeus vannamei) in biofloc systems

Biofloc (BF) stands out as a promising system for sustainable shrimp farming. Optimizing various culture conditions, such as stocking density, carbohydrate source, and feeding management, is crucial for the widespread adoption of the BF system. This study compares the growth performance of white-leg shrimp (Litopenaeus vannamei) in culture ponds at low density (LD) with 50 organisms/m2 and high density (HD) with 200 organisms/m2. Post-larvae of white-leg shrimp were stocked for 16 weeks in both LD and HD groups. The LD group exhibited a superior survival rate, growth rate, and feed consumption compared to the HD group. The BF from the LD system recorded a significantly higher protein content (16.63 ± 0.21%) than the HD group (15.21 ± 0.34%). Heterotrophic bacterial counts in water did not significantly differ with stocking density. However, Vibrio count in water samples was higher in the HD group (3.59 ± 0.35 log CFU/mL) compared to the LD group (2.45 ± 0.43 log CFU/mL). The whole shrimp body analysis revealed significantly higher protein and lipid content in the LD group. In contrast, the total aerobic bacterial count in shrimp from the HD group was high, with the identification of Salmonella enterica ssp. arizonae. Additionally, Vibrio counts in shrimp samples were significantly higher in the HD group (4.63 ± 0.32 log CFU/g) compared to the LD group (3.57 ± 0.22 log CFU/g). The expression levels of immune-associated genes, including prophenoloxidase, transglutaminase, penaiedin 3, superoxide dismutase, lysozyme, serine proteinase, and the growth-related gene ras-related protein (rap-2a), were significantly enhanced in the LD group. Conversely, stress-related gene expression increased significantly in the HD group. Hepatopancreases amylase, lipase, and protease were higher in the LD group, while trypsin activity did not differ significantly. Antioxidant enzyme activity (catalase, glutathione, glutathione peroxidase, and superoxide dismutase) significantly increased in the LD group. The histological structure of hepatopancreas, musculature, and female gonads remained similar in both densities. However, negative effects were observed in the gills' histology of the HD group. These results suggest that increasing stocking density is associated with significantly negative biological, microbial, and physiological effects on white-leg shrimp under the BF system.

Marine Arthropods as a Source of Antimicrobial Peptides

Peptide therapeutics play a key role in the development of new medical treatments. The traditional focus on endogenous peptides has shifted from first discovering other natural sources of these molecules, to later synthesizing those with unique bioactivities. This review provides concise information concerning antimicrobial peptides derived from marine crustaceans for the development of new therapeutics. Marine arthropods do not have an adaptive immune system, and therefore, they depend on the innate immune system to eliminate pathogens. In this context, antimicrobial peptides (AMPs) with unique characteristics are a pivotal part of the defense systems of these organisms. This review covers topics such as the diversity and distribution of peptides in marine arthropods (crustacea and chelicerata), with a focus on penaeid shrimps. The following aspects are covered: the defense system; classes of AMPs; molecular characteristics of AMPs; AMP synthesis; the role of penaeidins, anti-lipopolysaccharide factors, crustins, and stylicins against microorganisms; and the use of AMPs as therapeutic drugs. This review seeks to provide a useful compilation of the most recent information regarding AMPs from marine crustaceans, and describes the future potential applications of these molecules.

Control of vibriosis in shrimp through the management of the microbiota and the immune system

Shrimp aquaculture is constantly threatened by recurrent outbreaks of diseases caused by pathogenic bacteria of the genus Vibrio. Acute hepatopancreatic necrosis disease (AHPND) is one of the most aggressive vibriosis reported to date in the shrimp industry. AHPND provokes massive mortalities, causing economic losses with strong social impacts. Control of vibriosis requires the application of multifactorial strategies. This includes vibrio exclusion, shrimp microbiota, particularly in the digestive tract, and shrimp health management through immune stimulation. This paper reviews these two strategies for the prophylactic control of vibriosis. First, we describe the devastating effects of AHPND and the cellular and humoral effectors of the shrimp immune system to cope with this pathology. Secondly, the mechanisms of action of probiotics and their positive impacts are highlighted, including their immunostimulant effects and their role in the balance of the shrimp microbiota. Finally, we reviewed immunostimulants and prebiotics polysaccharides that together with probiotics act benefiting growth, feed efficiency and the microbiota of the digestive tract of farmed shrimp.

Shrimp thrombospondin (TSP): presence of O-β1,4 N-acetylglucosamine polymers and its function in TSP chain association in egg extracellular matrix

We characterized the existence of O-β(1,4)-GlcNAc polymers (β1,4GNP) that were anchored on the O-linked glycosylation sites of shrimp thrombospondin (pmTSP-II). There were five putative β1,4GNP linkages on the epithelial growth factor-like domain of pmTSP-II. Antibody against O-β-GlcNAc (CTD110.6) was used to prove the existence of linear and complex β1,4GNP. The antibody well reacted with linear chito-triose, -tetraose and -pentaose conjugated with phosphatidylethanolamine lipid. The immunoreactivity could also be detected with a complex β1,4GNP within pmTSP-II (at MW > 250 kDa). Upon denaturing the protein with SDS-PAGE buffer, the size of pmTSP-II was shifted to be 250 kDa, approximately 2.5 folds larger than the deduced molecular mass of pmTSP-II (110 kDa), suggesting additional association of pmTSP-II apart from its known disulfide bridging. This was confirmed by chitinase digestion on pmTSP-II protein leading to the subsequent smaller protein bands at 110–170 kDa in time- and concentration-dependent manners. These bands well reacted with CTD110.6 antibody and disappeared after extensive chitinase hydrolysis. Together, we believe that β1,4GNP on pmTSP-II serve the function in an inter-chain association to provide structural architecture of egg extracellular matrix, a novel function of pmTSP-II in reproductive biology.

Circulating Phylotypes of White Spot Syndrome Virus in Bangladesh and Their Virulence

White Spot Syndrome Virus (WSSV) has emerged as one of the most prevalent and lethal viruses globally and infects both shrimps and crabs in the aquatic environment. This study aimed to investigate the occurrence of WSSV in different ghers of Bangladesh and the virulence of the circulating phylotypes. We collected 360 shrimp (Penaeus monodon) and 120 crab (Scylla sp.) samples from the south-east (Cox’s Bazar) and south-west (Satkhira) coastal regions of Bangladesh. The VP28 gene-specific PCR assays and sequencing revealed statistically significant (p < 0.05, Kruskal–Wallis test) differences in the prevalence of WSSV in shrimps and crabs between the study areas (Cox’s Bazar and Satkhira) and over the study periods (2017–2019). The mean Log load of WSSV varied from 8.40 (Cox’s Bazar) to 10.48 (Satkhira) per gram of tissue. The mean values for salinity, dissolved oxygen, temperature and pH were 14.71 ± 0.76 ppt, 3.7 ± 0.1 ppm, 34.11 ± 0.38 °C and 8.23 ± 0.38, respectively, in the WSSV-positive ghers. The VP28 gene-based phylogenetic analysis showed an amino-acid substitution (E→G) at the 167th position in the isolates from Cox’s Bazar (referred to as phylotype BD2) compared to the globally circulating one (BD1). Shrimp PL artificially challenged with BD1 and BD2 phylotypes with filtrates of tissue containing 0.423 × 109 copies of WSSV per mL resulted in a median LT50 value of 73 h and 75 h, respectively. The in vivo trial showed higher mean Log WSSV copies (6.47 ± 2.07 per mg tissue) in BD1-challenged shrimp PL compared to BD2 (4.75 ± 0.35 per mg tissue). Crabs infected with BD1 and BD2 showed 100% mortality within 48 h and 62 h of challenge, respectively, with mean Log WSSV copies of 12.06 ± 0.48 and 9.95 ± 0.37 per gram tissue, respectively. Moreover, shrimp antimicrobial peptides (AMPs), penaeidin and lysozyme expression were lower in the BD1-challenged group compared to BD2 challenged shrimps. These results collectively demonstrated that relative virulence properties of WSSV based on mortality rate, viral load and expression of host immune genes in artificially infected shrimp PL could be affected by single aa substitution in VP28.

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

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

The Enhanced Immune Protection in Small Abalone Haliotis diversicolor Against a Secondary Infection With Vibrio harveyi

In recent years, more and more studies have shown that early pathogenic bacterial infection in invertebrates can enhance immunity and significantly reduce mortality when reinfected with the same pathogen. There are mechanisms to explain this phenomenon, but they are relatively few. In addition, dose-dependent primary infection is also associated with increased immunity. In the present study, the initial infection dose and mortality of abalone Haliotis diversicolor after reinfection with Vibrio harveyi were recorded, and the mechanism of immune enhancement was investigated by the transcriptomic response of abalone after two successive stimuli with V. harveyi. Priming with different concentrations of pathogen can enhance immunity; however, higher concentration is not always better. Compared with the first exposure, more genes were up-regulated after the second exposure. Among the commonly expressed genes, the immune related genes were significantly or persistently highly expressed after two infections and included pattern recognition receptors as well as immune effectors, such as toll-like receptors, perlucin 4, scavenger receptor class B-like protein, cytochrome P450 1B1-like, glutathione S-transferase 6, lysozyme and so on; in addition, these immune-related genes were mainly distributed in the pathways related to phagocytosis and calcium signaling. Among the specifically expressed genes, compared with the first infection, more genes were involved in the immune, metabolic and digestive pathways after the second infection, which would be more conducive to preventing the invasion of pathogens. This study outlined the mechanism of immune enhancement in abalone after secondary infection at the global molecular level, which is helpful for a comprehensive understanding of the mechanism of immune priming in invertebrates.

Differentially Expressed Genes in Hepatopancreas of Acute Hepatopancreatic Necrosis Disease Tolerant and Susceptible Shrimp (Penaeus vannamei)

Acute hepatopancreatic necrosis disease (AHPND) is a lethal disease in marine shrimp that has caused large-scale mortalities in shrimp aquaculture in Asia and the Americas. The etiologic agent is a pathogenic Vibrio sp. carrying binary toxin genes, pirA and pirB in plasmid DNA. Developing AHPND tolerant shrimp lines is one of the prophylactic approaches to combat this disease. A selected genetic line of Penaeus vannamei was found to be tolerant to AHPND during screening for disease resistance. The mRNA expression of twelve immune and metabolic genes known to be involved in bacterial pathogenesis were measured by quantitative RT-PCR in two populations of shrimp, namely P1 that showed susceptibility to AHPND, and P2 that showed tolerance to AHPND. Among these genes, the mRNA expression of chymotrypsin A (ChyA) and serine protease (SP), genes that are involved in metabolism, and crustin-P (CRSTP) and prophenol oxidase activation system 2 (PPAE2), genes involved in bacterial pathogenesis in shrimp, showed differential expression between the two populations. The differential expression of these genes shed light on the mechanism of tolerance against AHPND and these genes can potentially serve as candidate markers for tolerance/susceptibility to AHPND in P. vannamei. This is the first report of a comparison of the mRNA expression profiles of AHPND tolerant and susceptible lines of P. vannamei.

Marine actinomycetes Nocardiopsis alba MCCB 110 has immunomodulatory property in the tiger shrimp Penaeus monodon

Shrimp farming constitutes an important source of revenue and employment in many developing countries. However, the shrimp industry has always been plagued with infectious diseases having varied aetiologies. Dominated by non - specific immune mechanism, preventive health care strategy is the most appropriate approach to protect the crop. The present study evaluated the efficacy of an actinomycete, Nocardiopsis alba MCCB 110 in eliciting non - specific immune mechanism in Penaeus monodon having Vibrio harveyi as the challenge organism. Haemocyte count, total protein, phenoloxidase, reactive oxygen intermediates, acid and alkaline phosphatase as well as the gene expression of proPO, peroxinectin, transglutaminase, alpha 2-macroglobulin, astakine, crustin, and penaeidin-3 were evaluated. The results demonstrated that the phenoloxidase, respiratory burst, total protein, acid and alkaline phosphatases were higher in the haemolymph of shrimps fed with Nocardiopsis alba MCCB 110 incorporated feed before and after challenge with Vibrio harveyi, compared to those of placebo fed animals. Up-regulation of six immune genes (alpha 2 macroglobulin, penaeidin -3, transglutaminase, proPO, crustin and peroxinectin) during the post-challenge were recorded. Survival of shrimp among the Nocardiopsis alba administered ones was 83% while it was 50% in placebo fed group. The elevated levels of nonspecific immune gene transcripts and concurrent increase in non specific immunity besides the higher survival rate in the Nocardiopsis alba administered group demonstrated the immunomodulatory property of the marine actinomycete Nocardiopsis alba MCCB 110 in the tiger shrimp Penaeus monodon, and on administering it through diet shrimp could be protected from vibriosis especially of V. harveyi.

A Type IIa crustin from the pink shrimp Farfantepenaeus paulensis (crusFpau) is constitutively synthesized and stored by specific granule-containing hemocyte subpopulations

Crustins are cysteine-rich antimicrobial peptides (AMPs) widely distributed across crustaceans. From the four described crustin Types (I to IV), crustins from the subtype IIa are the most abundant and diverse members found in penaeid shrimp. Despite the critical role of Type IIa crustins in shrimp antimicrobial defenses, there is still limited information about their synthesis and antimicrobial properties. Here, we report the subcellular localization and the antibacterial spectrum of crusFpau, a Type IIa crustin from the pink shrimp Farfantepenaeus paulensis. The recombinantly expressed crusFpau showed antimicrobial activity against both Gram-positive and Gram-negative bacteria at low concentrations. Results from immunofluorescence using anti-rcrusFpau antiserum revealed that crusFpau is synthetized and stored by both granular and semigranular hemocytes, but not by hyaline cells. Interestingly, not all granular and semigranular hemocytes stained for crusFpau, revealing that this crustin is produced by specific granule-containing hemocyte subpopulations. Finally, we showed that the granule-stored peptides are not constitutively secreted into the plasma of healthy animals.

Dietary yeast hydrolysate and brewer's yeast supplementation could enhance growth performance, innate immunity capacity and ammonia nitrogen stress resistance ability of Pacific white shrimp (Litopenaeus vannamei)

An 8-week feeding trial was conducted to evaluate the effects of dietary yeast hydrolysate and brewer's yeast supplementation on growth, immune-related genes expression and ammonia nitrogen stress resistance of Pacific white shrimp (Litopenaeus vannamei). Three isonitrogenous and isolipidic practical diets were formulated to contain 0% (control diet), 1% yeast hydrolysate and 1% brewer's yeast, respectively. 360 juvenile L. vannamei with an initial weight (0.88 ± 0.01 g) was randomly divided into 3 treatments in four replicates (30 shrimp per replicate). The results indicated that shrimp fed the diet containing 1% yeast hydrolysate had a significantly higher weight gain (WG), and specific growth rate (SGR) than that fed the control diet, and the lowest feed conversion ratio (FCR) was occurred in the 1% yeast hydrolysate supplementation group. Proximate composition in whole body and muscle among all treatments was not significantly influenced by the dietary yeast hydrolysate or brewer's yeast supplementation. The challenge test with ammonia nitrogen showed that lower cumulative survival was observed in those fed the control diet, and the highest cumulative survival was occurred at shrimp fed the 1% yeast hydrolysate supplementation. Shrimp fed the control diet had higher inflammation-related genes expression levels of tnf-α and il-1β in the intestine than those fed the diets supplemented with 1% yeast hydrolysate or 1% brewer's yeast, however, there was no significant difference in expression level of alp in intestine among all treatments. The relative expression levels of mTOR signal pathway genes (eif4ebp, eif4e1a, eif4e2 and p70s6k) were significantly up-regulated in the shrimp fed the diets supplemented with 1% yeast hydrolysate, and the lowest gene expression levels of eif4ebp, eif4e1a, eif4e2 and p70s6k in the intestine were occurred at the control diet. The highest expression levels of the immune-related genes (dorsal, relish, and proPO) in the intestine were observed at shrimp fed the 1% yeast hydrolysate supplementation, and the lowest expression levels of these genes were occurred at shrimp fed the control diet, however, there was no significant difference in gene expression of lysozyme among all treatments. The expression levels of penaeidin3a, crustin, proPO, and IMD in the hepatopancreas were significantly influenced by the dietary yeast hydrolysate, brewer's yeast or no yeast product supplementation, shrimp fed the 1% yeast hydrolysate supplementation had higher expression levels of these genes than those fed the control diet. The present study indicated that dietary 1% yeast hydrolysate or brewer's yeast supplementation could improve growth performance, enhance innate immunity, and strengthen resistance of ammonia nitrogen stress, and dietary 1% yeast hydrolysate supplementation provides better immunostimulatory effects than brewer's yeast of L. vannamei.

White spot syndrome virus (WSSV) suppresses penaeidin expression in Marsupenaeus japonicus hemocytes

Penaeidins are a unique family of antimicrobial peptides specific to penaeid shrimp and have been reported mainly function as anti-bacterial and anti-fungal. In order to investigate whether penaeidins could also respond to virus or not, we examined the effect of WSSV on MjPen-II (penaeidin in kuruma shrimp, Marsupenaeus japonicus) expression. In the control group, MjPen-II transcript level can be detected in almost all test tissues but was expressed most strongly in hemocytes. After WSSV infection, MjPen-II transcript level was significantly downregulated in hemocytes. Moreover, the proportion of MjPen-II+ hemocytes was not significantly different between non-infected and WSSV-infected shrimp, but the number of MjPen-II+ highly expressing hemocytes decreased after infection. In addition, MjPen-II was observed in the cytoplasm of granule-containing hemocytes. These results suggest that WSSV suppresses MjPen-II expression in hemocytes.

An immune-related gene expression atlas of the shrimp digestive system in response to two major pathogens brings insights into the involvement of hemocytes in gut immunity

Much of our current knowledge on shrimp immune system is restricted to the defense reactions mediated by the hemocytes and little is known about gut immunity. Here, we have investigated the transcriptional profile of immune-related genes in different organs of the digestive system of the shrimp Litopenaeus vannamei. First, the tissue distribution of 52 well-known immune-related genes has been assessed by semiquantitative analysis in the gastrointestinal tract (foregut, midgut and hindgut) and in the hepatopancreas and circulating hemocytes of shrimp stimulated or not with heat-killed bacteria. Then, the expression levels of 18 genes from key immune functional categories were quantified by fluorescence-based quantitative PCR in the midgut of animals experimentally infected with the Gram-negative Vibrio harveyi or the White spot syndrome virus (WSSV). Whereas the expression of some genes was induced at 48 h after the bacterial infection, any of the analyzed genes showed to be modulated in response to the virus. Whole-mount immunofluorescence assays confirmed the presence of infiltrating hemocytes in the intestines, indicating that the expression of some immune-related genes in gut is probably due to the migratory behavior of these circulating cells. This evidence suggests the participation of hemocytes in the delivery of antimicrobial molecules into different portions of the digestive system. Taken all together, our results revealed that gut is an important immune organ in L. vannamei with intimate association with hemocytes.

Differentially expressed transcripts in stomach of Penaeus monodon in response to AHPND infection

Acute Hepatopancreatic Necrosis Disease (AHPND) is an emerging disease in aquacultured shrimp caused by a pathogenic strain of Vibrio parahaemolyticus. As with several pathogenic bacteria, colonization of the stomach appeared to be the initial step of the infection for AHPND-causing Vibrio. To understand the immune responses in the stomach of black tiger shrimp (Penaeus monodon), differentially expressed transcripts (DETs) in the stomach during V. parahaemolyticus strain 3HP (VP3HP) infection was examined using Ion Torrent sequencing. From the total 42,998 contigs obtained, 1585 contigs representing 1513 unigenes were significantly differentially expressed with 1122 and 391 unigenes up- and down-regulated, respectively. Among the DETs, there were 141 immune-related unigenes in 10 functional categories: antimicrobial peptide, signal transduction pathway, proPO system, oxidative stress, proteinases/proteinase inhibitors, apoptotic tumor-related protein, pathogen recognition immune regulator, blood clotting system, adhesive protein and heat shock protein. Expression profiles of 20 of 22 genes inferred from RNA sequencing were confirmed with the results from qRT-PCR. Additionally, a novel isoform of anti-lipopolysaccharide factor, PmALF7 whose transcript was induced in the stomach after challenge with VP3HP was discovered. This study provided a fundamental information on the molecular response in the shrimp stomach during the AHPND infection that would be beneficial for future research.

A hemocyte-expressed fibrinogen-related protein gene (LvFrep) from the shrimp Litopenaeus vannamei: Expression analysis after microbial infection and during larval development

Fibrinogen-related proteins (FREPs) comprise a large family of microbial recognition proteins involved in many biological functions in both vertebrate and invertebrate animals. By taking advantage of publicly accessible databases, we have identified a FREP-like homolog in the most cultivated penaeid shrimp, Litopenaeus vannamei (LvFrep). The obtained sequence showed a conserved fibrinogen-related domain (FReD) and displayed significant similarities to FREP-like proteins from other invertebrates and to ficolins from crustaceans. The expression of LvFrep appeared to be limited to circulating hemocytes. Interestingly, LvFrep gene expression was induced in shrimp hemocytes only in response to a Vibrio infection but not to the White spot syndrome virus (WSSV). Moreover, LvFrep transcript levels were detected early in fertilized eggs, suggesting the participation of this immune-related gene in the antimicrobial defenses during shrimp development.

A new antimicrobial peptide SCY2 identified in Scylla Paramamosain exerting a potential role of reproductive immunity

A new antimicrobial peptide named SCY2 with 65.08% identity in amino acid sequence to the known scygonadin (SCY1) was first characterized in Scylla paramamosain based on its cloned full-length cDNA and genomic DNA sequences. The SCY2 gene was dominantly expressed in the ejaculatory duct of male crabs and its mRNA transcripts were discerned mainly in the glandular epithelium of the inner wall and the secretion inside the ejaculatory duct. Although the SCY2 gene could not be induced with the challenge of the bacteria and fungi tested, its induction reached the highest level at the peak period of mating in mature male crabs either in June or November, suggesting its induction was likely related to seasonal reproduction changes. Moreover, it was interesting to note that, from analysis of its transcripts and protein, SCY2 was significantly expressed only in the ejaculatory duct of pre-copulatory males before mating, however it was clearly detected in the spermatheca of post-copulatory females after mating accompanied by the decreased level of SCY2 expression in the ejaculatory duct. These results suggested that the SCY2 was probably transferred from the male during mating action with the female for the purpose of protecting fertilization. The recombinant SCY2 was more active against the Gram-positive than the Gram-negative bacteria tested. It was further observed that the SCY2 transcripts were significantly increased with addition of exogenous progesterone in tissue cultures whereas the several other hormones tested had no any effect on SCY2 expression, indicating that there might be a relationship between the SCY2 expression and the induction of hormones in vivo. In summary, this study demonstrated that one role of SCY2 was likely to be involved in crab reproduction and it exerted its reproductive immune function through the mating action and the maintenance of inner sterility in the spermatheca of the female, thus leading to successful fertilization of S. paramamosain.

The specificity of immune priming in silkworm, Bombyx mori, is mediated by the phagocytic ability of granular cells

In the past decade, the phenomenon of immune priming was documented in many invertebrates in a large number of studies; however, in most of these studies, behavioral evidence was used to identify the immune priming. The underlying mechanism and the degree of specificity of the priming response remain unclear. We studied the mechanism of immune priming in the larvae of the silkworm, Bombyx mori, and analyzed the specificity of the priming response using two closely related Gram-negative pathogenic bacteria (Photorhabdus luminescens TT01 and P. luminescens H06) and one Gram-positive pathogenic bacterium (Bacillus thuringiensis HD-1). Primed with heat-killed bacteria, the B. mori larvae were more likely to survive subsequent homologous exposure (the identical bacteria used in the priming and in the subsequent challenge) than heterologous (different bacteria used in the priming and subsequent exposure) exposure to live bacteria. This result indicated that the B. mori larvae possessed a strong immune priming response and revealed a degree of specificity to TT01, H06 and HD-1 bacteria. The degree of enhanced immune protection was positively correlated with the level of phagocytic ability of the granular cells and the antibacterial activity of the cell-free hemolymph. Moreover, the granular cells of the immune-primed larvae increased the phagocytosis of a previously encountered bacterial strain compared with other bacteria. Thus, the enhanced immune protection of the B. mori larvae after priming was mediated by the phagocytic ability of the granular cells and the antibacterial activity of the hemolymph; the specificity of the priming response was primarily attributed to the phagocytosis of bacteria by the granular cells.

Rearing effect of biofloc on antioxidant and antimicrobial transcriptional response in Litopenaeus stylirostris shrimp facing an experimental sub-lethal hydrogen peroxide stress

This study compares the antioxidant and antimicrobial transcriptional expression of blue shrimps reared according to two different systems, BioFloc Technology (BFT) and Clear sea Water (CW) and their differential responses when facing an experimental sublethal hydrogen peroxide stress. After 30 days of rearing, juvenile shrimps were exposed to H2O2 stress at a concentration of 30 ppm during 6 h. The oxidative stress caused by H2O2 was examined in the digestive glands of the shrimp, in which antioxidant enzyme (AOE) and antimicrobial peptide (AMP) gene expression were analysed by quantitative real-time PCR. Results showed that rearing conditions did not affect the expression of genes encoding AOEs or AMPs. However, H2O2 stress induced a differential response in expression between shrimps from the two rearing treatments (BFT and CW). Comparative analysis of the expression profiles indicates that catalase transcripts were significantly upregulated by H2O2 stress for BFT shrimps while no change was observed for CW shrimps. In contrast, H2O2 caused down-regulation of superoxide dismutase and glutathione transferase transcripts and of the three AMP transcripts studied (penaeidin 2 and 3, and crustin) for CW shrimps, while no effect was observed on BFT shrimp transcript levels. These results suggested that BFT shrimps maintained antioxidant and AMP responses after stress and therefore can effectively protect their cells against oxidative stress, while CW shrimp immune competence seems to decrease after stress.

Immune gene expression for diverse haemocytes derived from pacific white shrimp, Litopenaeus vannamei

In this study, diverse haemocytes from Pacific white shrimp Litopenaeus vannamei were spread by flow cytometer sorting system. Using the two commonly flow cytometric parameters FSC and SSC, the haemocytes could be divided into three populations. Microscopy observation of L. vannamei haemocytes in anticoagulant buffer revealed three morphologically distinct cell types designated as granular cell, hyaline cell and semigranular cell. Immune genes, which includes prophenoloxidase (proPO), lipopolysaccharide-β-glucan binding protein (LGBP), peroxinectin, crustin, lysozyme, penaeid-3a and transglutaminase (TGase), expressed from different haemocyte were analysed by quantitative real time PCR (qPCR). Results from the mRNA expression was estimated by relative level of each gene to β-actin gene. Finally, the seven genes could be grouped by their dominant expression sites. ProPO, LGBP and peroxinectin were highly expressed in granular cells, while LGBP, crustin, lysozyme and P-3a were highly expressed in semigranular cells and TGase was highly expressed in hyaline cells. In this study, L. vannamei haemocytes were firstly grouped into three different types and the immune related genes expression in grouped haemocytes were estimated.

Characterization of a novel anti-lipopolysaccharide factor isoform (SpALF5) in mud crab, Scylla paramamosain

Anti-lipopolysaccharide factors (ALFs), the potential antimicrobial peptides that bind and neutralize lipopolysaccharide (LPS), are common effectors of innate immunity in crustaceans. In this study, a novel isoform of ALFs (SpALF5) was isolated from the hemocytes of mud crab Scylla paramamosain. The full-length 975bp SpALF5 contains a 375bp open reading frame (ORF) encoding 125 amino acids. Although SpALF5 exhibits a low degree of nucleotide homology with other reported ALFs, it contains the conserved amino acid sequence with a signal peptide and a LPS-binding domain including two conservative cysteine residues. The genomic organization of SpALF5 consists of four exons and three introns, with each intron containing one or more tandem repeats. Unlike most of ALFs mainly distributed in crab hemocytes, SpALF5 transcript was predominantly observed in the brain, muscle and skin, while barely detected in the hemocytes in our study. In situ hybridization assay also showed that SpALF5 mRNA was localized in brain, muscle and skin tissues of mud crab. Further, SpALF5 transcript was significantly up-regulated after challenge with LPS, polyinosinic polycytidylic acid (PolyI:C) (with the except of that in brain), Vibrio parahemolyticus or white spot syndrome virus (WSSV). The recombinant SpALF5 protein showed a varying degree of binding activity towards bacteria and fungus. Moreover, in vitro, the recombinant SpALF5 revealed a strong antimicrobial activity against Gram-negative bacteria (V. parahemolyticus, Vibrio alginolyticus, Escherichia coli, Aeromonas hydrophila) and fungus (Sacchromyces cerevisiae), but could only inhibited the growth of some Gram-positive bacteria like Staphylococcus aureus. The results suggest that SpALF5 is a potent immune protector and plays an important role in immune defense against invading pathogens in S. paramamosain.

Role of Marsupenaeus japonicus crustin-like peptide against Vibrio penaeicida and white spot syndrome virus infection

Crustins are important AMP that has been identified in crustaceans. In this study, the role of Marsupenaeus japonicus crustin-like peptide (MjCRS) was examined in vivo by RNA interference (RNAi) using double-stranded RNA (dsRNA). Tissue expression analysis revealed that MjCRS transcripts are expressed in different tissues tested with the highest expression observed in hemocytes. Treatment with double-stranded RNA specific to MjCRS led to a significant reduction of MjCRS transcripts within the hemocytes. When MjCRS was silenced and subsequently infected with Vibrio penaeicida final mortality was significantly higher compared with PBS and dsGFP treated groups. On the other hand, final mortalities of MjCRS silenced and PBS injected groups were not significantly different after infection with white spot virus, however, both are significantly higher compared with dsGFP treated group. V. penaeicida infection significantly decreased MjCRS expression at 3, 6, 12 and 24h followed by significant increase at 48 h post-infection. On the contrary, white spot infection significantly increased MjCRS expression at 6 and 12h and decreased at 48 h post-infection. dsRNA treatment alone decreased total hemocyte counts (THCs) and subsequent V. penaeicida or white spot virus infection further decreased THCs. VP28 gene expression was both similarly increased in PBS injected group and MjCRS silenced group at 24 and 48 h-post infection. Results suggest that MjCRS is involved in antibacterial defense and might not have critical function against viral infection.

RNAi knock-down of shrimp Litopenaeus vannamei Toll gene and immune deficiency gene reveals their difference in regulating antimicrobial peptides transcription

NF-κB dependent antimicrobial peptides (AMPs) are of critical importance in protecting insects or mammals from microorganisms infection. However, we still do not make clear signaling pathways in regulating AMPs expression in shrimps. In this study, RNAi approach was used to study differences between Toll signaling pathway and immune deficiency signaling pathway in regulating the transcription of NF-κB dependent AMPs post bacteria challenge. Results showed that the transcription level of anti-lipopolysaccharide factor was highly suppressed in Litopenaeus vannamei immune deficiency (LvIMD) silenced shrimps by gene specific dsRNA compared to Litopenaeus vannamei Toll (LvToll) silenced shrimps with or without Vibrio anguillarum and Micrococcus lysodeikticus challenge. Conversely the transcription level of penaeidin3a was significantly suppressed in LvToll silenced shrimps compared to LvIMD silenced shrimps. However, no obvious difference was found in regulating the transcription of CrustinP. Meanwhile, we found that silencing LvToll both down regulated the transcription of Dorsal and Relish while silencing LvIMD only down regulated the transcription of Relish. At last, shrimp survival experiment showed that post V. anguillarum challenge high mortality was found both in LvToll and LvIMD silenced groups while post M. lysodeikticus challenge we saw high mortality only in LvToll silenced group. Hence, we conclude that shrimp L. vannamei Toll pathway and IMD pathway might be different in regulating the transcription of NF-κB dependent AMPs and responding to bacteria challenge but not independent of each other.

Identification and functional studies of Akirin, a potential positive nuclear factor of NF-κB signaling pathways in the Pacific white shrimp, Litopenaeus vannamei

As conserved nuclear factors, Akirins play critical roles in regulating antimicrobial peptides (AMPs) transcription downstream of NF-κB dependent signaling pathways in insects and mammals. However, no any functional studies was reported in penaeid shrimp. The identification and functional analysis of Akirin in the Pacific white shrimp, Litopenaeus vannamei were made in this research. The 833 nucleotides cDNA of Litopenaeus vannamei Akirin (LvAkirin) was obtained with an open reading frame of 639 bp, which encodes a putative protein of 212 amino acids. The molecular weight of LvAkirin is about 23.7 kDa with theoretical pI of 9.05. Two predicted nuclear localization signals (NLSs) were found and amino acid sequence alignments showed that Akirins are highly conserved between insects and mammals. The constitutive expression of LvAkirin mRNA was confirmed in all the examined tissues and high level appeared in testis followed by hemocytes and gill. LvAkirin mRNA was strongly induced in response to Vibrio parahaemolyticus infection. Silencing LvAkirin by dsRNA significantly reduced the expression of NF-κB dependent anti-lipopolysaccharide factor, crustin and penaeidin3a as well as transcription factors, Dorsal and Relish post Vibrio anguillarum (V. anguillarum) and Micrococcus lysodeikticus (M. lysodeikticus) challenge. Antibacterial activities of shrimp plasma was analyzed and high cumulative mortality was found in LvAkirin-silenced shrimps post bacteria challenge. Hence, we proposed LvAkirin might function as a positive nuclear factor of NF-κB dependent signaling pathways in shrimp innate immunity.

Biotic stress resistance in agriculture through antimicrobial peptides

Antimicrobial peptides (AMPs) are the hosts' defense molecules against microbial pathogens and gaining extensive research attention worldwide. These have been reported to play vital role of host innate immunity in response to microbial challenges. AMPs can be used as a natural antibiotic as an alternative of their chemical counterpart for protection of plants/animals against diseases. There are a number of sources of AMPs including prokaryotic and eukaryotic organisms and are present, both in vertebrates and invertebrates. AMPs can be classified as cationic or anionic, based on net charges. Large number of databases and tools are available in the public domain which can be used for development of new genetically modified disease resistant varieties/breeds for agricultural production. The results of the biotechnological research as well as genetic engineering related to AMPs have shown high potential for reduction of economic losses of agricultural produce due to pathogens. In this article, an attempt has been made to introduce the role of AMPs in relation to plants and animals. Their functional and structural characteristics have been described in terms of its role in agriculture. Different sources of AMPs and importance of these sources has been reviewed in terms of its availability. This article also reviews the bioinformatics resources including different database tools and algorithms available in public domain. References of promising biotechnology research in relation to AMPs, prospects of AMPs for further development of genetically modified varieties/breeds are highlighted. AMPs are valuable resource for students, researchers, educators and medical and industrial personnel.

Expression, tissue localization and synergy of antimicrobial peptides and proteins in the immune response of the oyster Crassostrea gigas

Diverse families of antimicrobial peptides and proteins have been described in oysters. We investigated here how antimicrobials are involved in the immune response against a pathogenic strain of Vibrio splendidus. Oyster antimicrobials were shown to display a wide variety of expression profiles in hemocyte populations and tissues. Oyster defensins are constitutively expressed in specific tissues such as mantle (Cg-Defm) or hemocytes (Cg-Defhs), while Cg-BPI is inducible and Cg-Prp appears down-regulated in hemocytes upon infection. The migratory behavior of hemocytes that express the different antimicrobials was found to be involved in the oyster response to a pathogenic Vibrio infection. Indeed, it contributes to colocalize several antimicrobials that were shown here to have synergistic activities. We propose that such a synergy, which was evidenced both within and between families of antimicrobials, might compensate for the low concentration of antimicrobials in oyster tissues.

Immunodetection of hemocytes, peneidins and α2-macroglobulin in the lymphoid organ of white spot syndrome virus infected shrimp

Viral diseases restrict the development of the world shrimp industry and there are few studies on cell response to the presence of viral infections. We performed immunohistochemistry assays to characterize hemocytes subpopulations involved in the immune process occurring in the LO of Litopenaeus vannamei shrimp. Tissue sections of animals that increased their LO spheroids and hemocytes infiltration after WSSV induced infection, were used. Three MABs namely, 40E10 (recognizing small granule hemocytes), 40E2 (recognizing large granule hemocytes), and 41B12, which recognize α(2)-macroglobulin were used. Additionally one polyclonal antibody was used against the penaeidins antimicrobial peptides, and to detect WSSV a commercial immunohistochemistry kit (DiagXotics) was used. Numerous small granule hemocytes were detected in the stromal matrix of LO tubules, whereas large granule hemocytes were less numerous and located mainly in hemal sinuses. The exocytosis of two molecules, which have been related to the phagocytosis process, i.e. penaeidins, and α(2)-macroglobulin, was detected in the external stromal matrix and the outer tubule walls. α(2) -macroglobulin inhibits phenoloxidase activity and its strong release in LO tissue may explain the absence of melanization in the immune processes occurring in it. The immunolabeling of vesicles within the LO spheroids with MABs 41B12 40E10 and antipenaedin antibody suggests that LOS are formed by phagocytic cells derived from small granule and hyaline hemocytes, with a possible role of peneidins and α(2)-macroglobulin acting as opsonines.

Molecular cloning, sequence analysis and expression of Fein-Penaeidin from the haemocytes of Indian white shrimp Fenneropenaeus indicus

Penaeidins are members of a special family of antimicrobial peptide existing in penaeid shrimp and play an important role in the immunological defense of shrimp. Here, we report a penaeidin sequence cloned from the Indian white shrimp Fenneropenaus indicus (Fein-Penaeidin). The Fein-Penaeidin open reading frame encodes a 77 amino acid peptide including a 19 amino acid signal peptide. The deduced amino acid sequences of Fein-Penaeidin include a proline rich N-terminal domain and a carboxyl-domain that contains six cysteine residues. Structural analysis revealed an alpha-helix in its secondary structure and the predicted 3D structure indicated two-disulphide bridges in the alpha-helix. Phylogenetic analysis and sequence comparison with other known peaneidin suggest the gene shows high similarity to that of penaeidin from Peneaus monodon (95%), F. indicus (80%) and Fenneropenaeus chinensis (74%). Fein-Penaeidin was examined in normal and microbial challenged shrimp and was found to be constitutively expressed in haemocytes, Heart, gills, muscles, intestine, hepatopancreas and eyestalk. Bacterial challenge resulted in mRNA up-regulation, inducing expression at 6 h post injection indicating the penaeidin involved in the innate immunity.

Big defensins, a diverse family of antimicrobial peptides that follows different patterns of expression in hemocytes of the oyster Crassostrea gigas

Background

Big defensin is an antimicrobial peptide composed of a highly hydrophobic N-terminal region and a cationic C-terminal region containing six cysteine residues involved in three internal disulfide bridges. While big defensin sequences have been reported in various mollusk species, few studies have been devoted to their sequence diversity, gene organization and their expression in response to microbial infections.

Findings

Using the high-throughput Digital Gene Expression approach, we have identified in Crassostrea gigas oysters several sequences coding for big defensins induced in response to a Vibrio infection. We showed that the oyster big defensin family is composed of three members (named Cg-BigDef1, Cg-BigDef2 and Cg-BigDef3) that are encoded by distinct genomic sequences. All Cg-BigDefs contain a hydrophobic N-terminal domain and a cationic C-terminal domain that resembles vertebrate β-defensins. Both domains are encoded by separate exons. We found that big defensins form a group predominantly present in mollusks and closer to vertebrate defensins than to invertebrate and fungi CSαβ-containing defensins. Moreover, we showed that Cg-BigDefs are expressed in oyster hemocytes only and follow different patterns of gene expression. While Cg-BigDef3 is non-regulated, both Cg-BigDef1 and Cg-BigDef2 transcripts are strongly induced in response to bacterial challenge. Induction was dependent on pathogen associated molecular patterns but not damage-dependent. The inducibility of Cg-BigDef1 was confirmed by HPLC and mass spectrometry, since ions with a molecular mass compatible with mature Cg-BigDef1 (10.7 kDa) were present in immune-challenged oysters only. From our biochemical data, native Cg-BigDef1 would result from the elimination of a prepropeptide sequence and the cyclization of the resulting N-terminal glutamine residue into a pyroglutamic acid.

Conclusions

We provide here the first report showing that big defensins form a family of antimicrobial peptides diverse not only in terms of sequences but also in terms of genomic organization and regulation of gene expression.

Expression of a novel antimicrobial peptide Penaeidin4-1 in creeping bentgrass (Agrostis stolonifera L.) enhances plant fungal disease resistance

Background

Turfgrass species are agriculturally and economically important perennial crops. Turfgrass species are highly susceptible to a wide range of fungal pathogens. Dollar spot and brown patch, two important diseases caused by fungal pathogens Sclerotinia homoecarpa and Rhizoctonia solani, respectively, are among the most severe turfgrass diseases. Currently, turf fungal disease control mainly relies on fungicide treatments, which raises many concerns for human health and the environment. Antimicrobial peptides found in various organisms play an important role in innate immune response.

Methodology/Principal Findings

The antimicrobial peptide - Penaeidin4-1 (Pen4-1) from the shrimp, Litopenaeus setiferus has been reported to possess in vitro antifungal and antibacterial activities against various economically important fungal and bacterial pathogens. In this study, we have studied the feasibility of using this novel peptide for engineering enhanced disease resistance into creeping bentgrass plants (Agrostis stolonifera L., cv. Penn A-4). Two DNA constructs were prepared containing either the coding sequence of a single peptide, Pen4-1 or the DNA sequence coding for the transit signal peptide of the secreted tobacco AP24 protein translationally fused to the Pen4-1 coding sequence. A maize ubiquitin promoter was used in both constructs to drive gene expression. Transgenic turfgrass plants containing different DNA constructs were generated by Agrobacterium-mediated transformation and analyzed for transgene insertion and expression. In replicated in vitro and in vivo experiments under controlled environments, transgenic plants exhibited significantly enhanced resistance to dollar spot and brown patch, the two major fungal diseases in turfgrass. The targeting of Pen4-1 to endoplasmic reticulum by the transit peptide of AP24 protein did not significantly impact disease resistance in transgenic plants.

Conclusion/Significance

Our results demonstrate the effectiveness of Pen4-1 in a perennial species against fungal pathogens and suggest a potential strategy for engineering broad-spectrum fungal disease resistance in crop species.

Cationic antimicrobial peptides in penaeid shrimp

Penaeid shrimp aquaculture has been consistently affected worldwide by devastating diseases that cause a severe loss in production. To fight a variety of harmful microbes in the surrounding environment, particularly at high densities (of which intensive farming represents an extreme example), shrimps have evolved and use a diverse array of antimicrobial peptides (AMPs) as part of an important first-line response of the host defense system. Cationic AMPs in penaeid shrimps composed of penaeidins, crustins, and anti-lipopolysaccharide factors are comprised of multiple classes or isoforms and possess antibacterial and antifungal activities against different strains of bacteria and fungi. Shrimp AMPs are primarily expressed in circulating hemocytes, which is the main site of the immune response, and hemocytes expressing AMPs probably migrate to infection sites to fight against pathogen invasion. Indeed, most AMPs are produced as early as the nauplii developmental stage to protect shrimp larvae from infections. In this review, we discuss the sequence diversity, expression, gene structure, and antimicrobial activities of cationic AMPs in penaeid shrimps. The information available on antimicrobial activities indicates that these shrimp AMPs have potential therapeutic applications in the control of disease problems in aquaculture.

Enhanced cellular immunity in shrimp (Litopenaeus vannamei) after 'vaccination'

It has long been viewed that invertebrates rely exclusively upon a wide variety of innate mechanisms for protection from disease and parasite invasion and lack any specific acquired immune mechanisms comparable to those of vertebrates. Recent findings, however, suggest certain invertebrates may be able to mount some form of specific immunity, termed ‘specific immune priming’, although the mechanism of this is not fully understood (see Textbox S1). In our initial experiments, either formalin-inactivated Vibrio harveyi or sterile saline were injected into the main body cavity (haemocoel) of juvenile shrimp (Litopenaeus vannamei). Haemocytes (blood cells) from V. harveyi-injected shrimp were collected 7 days later and incubated with a 1∶1 mix of V. harveyi and an unrelated Gram positive bacterium, Bacillus subtilis. Haemocytes from ‘vaccinated’ shrimp showed elevated levels of phagocytosis of V. harveyi, but not B. subtilis, compared with those from saline-injected (non-immunised) animals. The increased phagocytic activity was characterised by a significant increase in the percentage of phagocytic cells. When shrimp were injected with B. subtilis rather than vibrio, there was no significant increase in the phagocytic activity of haemocytes from these animals in comparison to the non-immunised (saline injected) controls. Whole haemolymph (blood) from either ‘immunised’ or non-immunised’ shrimp was shown to display innate humoral antibacterial activity against V. harveyi that was absent against B. subtilis. However, there was no difference in the potency of antibacterial activity between V. harveyi-injected shrimp and control (saline injected) animals showing that ‘vaccination’ has no effect on this component of the shrimp's immune system. These results imply that the cellular immune system of shrimp, particularly phagocytosis, is capable of a degree of specificity and shows the phenomenon of ‘immune priming’ reported by other workers. However, in agreement with other studies, this phenomenon is not universal to all potential pathogens.

Antimicrobial peptides from marine invertebrates: challenges and perspectives in marine antimicrobial peptide discovery

The emergence of pathogenic bacteria resistance to conventional antibiotics calls for an increased focus on the purification and characterization of antimicrobials with new mechanisms of actions. Antimicrobial peptides are promising candidates, because their initial interaction with microbes is through binding to lipids. The interference with such a fundamental cell structure is assumed to hamper resistance development. In the present review we discuss antimicrobial peptides isolated from marine invertebrates, emphasizing the isolation and activity of these natural antibiotics. The marine environment is relatively poorly explored in terms of potential pharmaceuticals, and it contains a tremendous species diversity which evolved in close proximity to microorganisms. As invertebrates rely purely on innate immunity, including antimicrobial peptides, to combat infectious agents, it is believed that immune effectors from these animals are efficient and rapid inhibitors of microbial growth.

Modulation and Interaction of Immune-Associated Parameters with Antioxidant in the Immunocytes of Crab Scylla paramamosain Challenged with Lipopolysaccharides

Invertebrates are dependent on cellular and humoral immune defences against microbial infection. Scylla paramamosain is an important commercial species, but the fundamental knowledge on its immune defense related to the antioxidant and immune-associated reactions is still lacking. The study was to differentiate the responses of immune-associated parameters of haemolymph components in S. paramamosain when challenged with bacterial lipopolysaccharides (LPSs). The immunostimulating effects of LPS in crab by triggering various immune parameters (phagocytosis, lysozyme, antibacterial activity, phenoloxidase, and the generation of superoxide and nitric oxide) were investigated. Results showed that the generation of free radicals, phenoloxidase, lysozyme and antibacterial activities was significantly increased through the exposure periods. Conversely, total hemocyte count and lysosomal membrane stability decreased significantly as the exposure period extended to 96 h. The relationship between the antioxidant enzymes and immune reactions due to LPS was highly significant. In addition, ROS production was positively correlated with antioxidant showing immediate response of antioxidant defense to the oxyradicals generated. Overall, the study indicated that nonspecific immune components in hemocytes of crab showed active response to the LPS stimulation, and their responses suggested that many immune-associated parameters could be modulated and interrelated with the influence of antioxidants in crustaceans.

Immunological function in marine invertebrates: responses to environmental perturbation

The inception of ecological immunology has led to an increase in the number of studies investigating the impact of environmental stressors on host immune defence mechanisms. This in turn has led to an increased understanding of the importance of invertebrate groups for immunological research. This review discusses the advances made within marine invertebrate ecological immunology over the past decade. By demonstrating the environmental stressors tested, the immune parameters typically investigated, and the species that have received the greatest level of investigation, this review provides a critical assessment of the field of marine invertebrate ecological immunology. In highlighting the methodologies employed within this field, our current inability to understand the true ecological significance of any immune dysfunction caused by environmental stressors is outlined. Additionally, a number of examples are provided in which studies successfully demonstrate a measure of immunocompetence through alterations in disease resistance and organism survival to a realized pathogenic threat. Consequently, this review highlights the potential to advance our current understanding of the ecological and evolutionary significance of environmental stressor related immune dysfunction. Furthermore, the potential for the advancement of our understanding of the immune system of marine invertebrates, through the incorporation of newly emerging and novel molecular techniques, is emphasized.

Primary structure and cellular localization of callinectin, an antimicrobial peptide from the blue crab

We report the complete amino acid sequence of callinectin, a 32 amino acid, proline-, arginine-rich antimicrobial peptide (AMP) with four cysteines and having the sequence WNSNRRFRVGRPPVVGRPGCVCFRAPCPCSNY-amide. The primary structure of callinectin is highly similar to arasins, AMPs recently identified in the small spider crab (Hyas araneus). Callinectin exists in three isomers that vary in the functional group on the tryptophan (W) residue. The most prevalent isomer had a hydroxy-N-formylkynurenine group, while the other two isomers had either N-formylkynurenine or hydroxy-tryptophan. Using a sequence highly similar to native callinectin, we chemically synthesized a peptide which we called callinectin-like peptide (CLP). Via immuno-electron microscopy, affinity-purified rabbit antibodies raised to CLP successfully localized the site of callinectin in blue crab hemocytes to the large electron-dense granules that are found primarily in large granule hemocytes.

Molecular characterization of a novel big defensin from clam Venerupis philippinarum

Antimicrobial peptides (AMPs) are important mediators of the primary defense mechanism against microbial invasion. In the present study, a big defensin was identified from Venerupis philippinarum haemocytes (denoted as VpBD) by RACE and EST approaches. The VpBD cDNA contained an open reading frame (ORF) of 285 bp encoding a polypeptide of 94 amino acids. The deduce amino acid sequence of VpBD shared the common features of big defensin including disulfide array organization and helix structure, indicating that VpBD should be a new member of the big defensin family. The mRNA transcript of VpBD was up-regulated significantly during the first 24 hr after Vibrio anguillarum challenge, which was 7.4-fold increase compared to that of the control group. Then the expression decreased gradually from 24 hr to 96 hr, and the lowest expression level was detected at 96 hr post-infection, which was still 3.9-fold higher than that of control. The mature peptide of VpBD was recombined in Escherichia coli and purified for minimum inhibitory concentration (MIC) determination. The rVpBD displayed broad-spectrum inhibitory activity towards all tested bacteria with the highest activity against Staphyloccocus aureus and Pseudomonas putida. These results indicated that VpBD was involved in the host immune response against bacterial infection and might contribute to the clearance of invading bacteria.

Cationic antimicrobial peptides in penaeid shrimp

Penaeid shrimp aquaculture has been consistently affected worldwide by devastating diseases that cause a severe loss in production. To fight a variety of harmful microbes in the surrounding environment, particularly at high densities (of which intensive farming represents an extreme example), shrimps have evolved and use a diverse array of antimicrobial peptides (AMPs) as part of an important first-line response of the host defense system. Cationic AMPs in penaeid shrimps composed of penaeidins, crustins, and anti-lipopolysaccharide factors are comprised of multiple classes or isoforms and possess antibacterial and antifungal activities against different strains of bacteria and fungi. Shrimp AMPs are primarily expressed in circulating hemocytes, which is the main site of the immune response, and hemocytes expressing AMPs probably migrate to infection sites to fight against pathogen invasion. Indeed, most AMPs are produced as early as the nauplii developmental stage to protect shrimp larvae from infections. In this review, we discuss the sequence diversity, expression, gene structure, and antimicrobial activities of cationic AMPs in penaeid shrimps. The information available on antimicrobial activities indicates that these shrimp AMPs have potential therapeutic applications in the control of disease problems in aquaculture.

Expression of antimicrobial peptides from Hyas araneus haemocytes following bacterial challenge in vitro

Circulating haemocytes play major roles in the host defense reactions of decapods, including the synthesis and release of antimicrobial peptides (AMPs). Unlike the AMPs from insects, those in decapods are constitutively expressed. This study aims to establish primary cell cultures of the three main haemocyte types in Hyas araneus haemocytes, and to measure the in vitro expression of AMP genes in the cells following microbial challenge. The haemocyte populations were separated on Percoll gradients and cultured in modified L-15 medium. Expression analysis by real-time RT-PCR showed that the granular cells are the main producers of crustin, hyastatin and arasin 1 AMPs, but the hyaline cells and semigranular cells also show some expression of these genes. Incubating the cell populations with Aerococcus viridans var. homari (a Gram-positive bacterium) or Listonella anguillarum (a Gram-negative pathogen) provoked no dramatic changes in the gene expression of any of the AMP, and although there was a small (single doubling) significant increase in expression of the crustin gene in granular cells 24h after exposure to L. anguillarum, it is unclear if this is biologically relevant under in vitro conditions. The results presented in this study are in accordance with several in vivo studies.

Identification and functional study of a shrimp Dorsal homologue

Rel/NF-kappaB transcription factors play central roles in induction and regulation of innate immune responses. Here, identification and functional analysis of LvDorsal, a Dorsal homologue from the Pacific white shrimp Litopenaeus vannamei, were described. The full-length cDNA of LvDorsal is 2204bp with an open reading frame that encodes 400 amino acids. The deduced LvDorsal contains a conserved Rel homology domain (RHD), an IPT (Ig-like, plexins and transcription factors) domain and a nucleus localization signal, suggesting that it belongs to the class II NF-kappaB. RT-PCR analysis showed that LvDorsal mRNAs were expressed in all the tissues tested, including gill, epidermis, hemocytes, intestine, stomach, eyestalk, brain, hepatopancreas, muscle, heart and pyloric caecum. Immunofluorescence assay showed that recombinant LvDorsal was translocated into the nucleus of Drosophila S2 cells. Electrophoretic mobility shift assay illustrated that recombinant LvDorsal RHD from S2 cells bound specifically with D. melanogaster kappaB motifs. Additionally, the dual-luciferase reporter assays indicated that LvDorsal could transactivate the reporter gene controlled by the 5' flanking region of shrimp penaeidin-4 and Drosophila attacin genes, suggesting that LvDorsal can regulate the transcription of shrimp penaeidin-4 gene. Study of LvDorsal will help us to better understand shrimp immunity and may help to obtain more effective methods to prevent shrimp diseases.

Time-course analysis of peroxinectin mRNA in the shrimp Litopenaeus vannamei after challenge with Vibrio campbellii

Peroxinectin (Pox), which promotes cell adhesion and encapsulation of bacteria in crustaceans, is synthesized in granular and semigranular hemocytes. In this study, real-time PCR was used to quantify Pox transcripts in individual tissues of the Pacific white shrimp, Litopenaeus vannamei, over 48 h following injection of a sublethal dose of the shrimp pathogen Vibrio campbellii. The resulting data were used to infer the movements of hemocytes among the tissues in response to bacterial challenge. Over all times and treatments, Pox transcripts (ng total RNA)(-1) varied by orders of magnitude among individual tissues, such that circulating hemocytes >> gills >> heart lymphoid organ hepatopancreas approximately muscle. Relatively low constitutive expression of Pox in the lymphoid organ compared to circulating hemocytes, gills, and heart supports a primary role for this organ in bacteriostasis and degradation, rather than encapsulation of invasive bacteria. Numbers of Pox transcripts increased significantly at the injection site within 4 h and remained significantly elevated for 48 h, consistent with a rapid and sustained recruitment of hemocytes to the site of injection. Transcripts increased significantly in the gill but not in other tissues over the time-course of this experiment. These expression data reinforce the role of the gill in trapping and encapsulating invasive bacteria as a primary strategic focus during the early phase of the crustacean immune response and, by comparison with earlier studies of lysozyme expression in the same tissues, suggest differential roles for various tissues in a successful immune response.

Identification and functional study of a shrimp Relish homologue

Rel/NF-kappaB transcription factors play central roles in induction and regulation of innate immune responses. Here we describe the identification and functional analysis of a Relish homologue, LvRelish and its shorter isoform sLvRelish, from the Pacific white shrimp, Litopenaeus vannamei. The LvRelish gene has 22 exons in approximately 15 kb genomic sequence. The full-length cDNA of LvRelish is 4071 bp with an open reading frame that encodes 1207 amino acids. LvRelish contains a conserved Rel homology domain (RHD), a nucleus localization signal, an IkappaB-like domain (six ankyrin repeats), and a death domain, suggesting that it belongs to the class I NF-kappaB. sLvRelish cDNA is 1051 bp encoding 317 amino acids. It shares the RHD region with LvRelish. RT-PCR analysis showed that LvRelish and sLvRelish mRNAs were expressed at different levels in tissues. Western blot analysis showed that recombinant intact LvRelish could be cleaved into two fragments in S2 cells, and immunofluorescence assay showed that the plasmid-expressed LvRelish protein was seen both in the cytoplasm and the nucleus. Electrophoretic mobility shift assay showed that recombinant RHD of LvRelish in S2 cells bound specifically with Drosophila melanogaster kappaB motifs in vitro. Both the LvRelish and its RHD domain transactivated the reporter gene controlled by the 5' flanking region of penaeidin 4, an antibacterial peptide of shrimp, suggesting that LvRelish can regulate the transcription of penaeidin 4 gene. Identification of LvRelish will help us better understand shrimp immunity and may help obtain more effective methods to prevent shrimp diseases.

Cloning of penaeidin gene promoter in tiger shrimp (Penaeus monodon)

Penaeidins belong to a family of antimicrobial peptides that are expressed in the hemocytes of penaeid shrimps. Using an extender PCR method and a nested PCR, we cloned two types of genomic fragment flanking the 5' end of penaeidin gene in tiger shrimp (Penaeus monodon): Type536 and Type411 sequences. Both fragments contained TATA box, GATA, dorsal and AP-1 motifs and were ligated to an expression vector with a luciferase reporter gene. The constructs were then delivered into Drosophila S2 cell line. The promoter functions of the two fragments were determined using a luciferase expression assay. The study demonstrated that Type411 sequence performed higher transcriptional activity than Type536. Alignment of the upstream sequences of penaeidin genes in P. monodon and Litopenaeus vannamei showed that the promoter regions were obviously more diverse than the 5'UTRs. Phylogenetic analysis indicated the presence of two types of promoters that are not species-specific in the two shrimps.

Review: Immunity mechanisms in crustaceans

Crustacean aquaculture represents a major industry in tropical developing countries. As a result of high culture densities and increasing extension of aquaculture farms, the presence of diseases has also increased, inducing economic losses. Invertebrates, which lack adaptive immune systems, have developed defense systems that respond against antigens on the surface of potential pathogens. The defense mechanisms of crustaceans depend completely on the innate immune system that is activated when pathogen-associated molecular patterns are recognized by soluble or by cell surface host proteins, such as lectins, antimicrobial, clotting, and pattern recognition proteins, which, in turn, activate cellular or humoral effector mechanisms to destroy invading pathogens. This work is aimed at presenting the main characteristics of the crustacean proteins that participate in immune defense by specific recognition of carbohydrate containing molecules, i.e. glycans, glycolipids, glycoproteins, peptidoglycans, or lipopolysaccharides from Gram-negative and Gram-positive bacteria, viruses, or fungi. We review some basic aspects of crustacean effector defense processes, like agglutination, encapsulation, phagocytosis, clottable proteins, and bactericidal activity, induced by these carbohydrate-driven recognition patterns.

Characterization of crustins from the hemocytes of the spider crab, Hyas araneus, and the red king crab, Paralithodes camtschaticus

Crustins are distributed across the decapods and are believed to play a significant part in the humoral defense system of their host. In this study, two crustin isoforms from Hyas araneus hemocytes were purified and tested for antimicrobial activity against selected microorganisms. They show both antibacterial and antifungal activity, with highest activity against the Gram-positive bacteria Corynebacterium glutamicum. Sequencing of the transcripts showed them to have a mature peptide of 90 amino acids and differing in three positions in the mature peptide. They were named CruHa1 and CruHa2. Real-time RT-PCR revealed that they mainly are expressed in hemocytes. Screening a cDNA library detected a crustin sequence in Paralithodes camtschaticus hemocytes, coding for a mature peptide of 98 amino acids. It was named CruPc. Based on phylogenetic inference and primary structure, CruHa1 and CruHa2 were placed within the Type I group of crustins, while CruPc belongs to the Type II.