Hsp70 Knockdown in the Brine Shrimp Artemia franciscana: Implication on Reproduction, Immune Response and Embryonic Cuticular Structure

The potential functional role(s) of heat shock protein 70 (Hsp70) in the brine shrimp, Artemia franciscana, a crucial crustacean species for aquaculture and stress response studies, was investigated in this study. Though we have previously reported that Hsp70 knockdown may have little or no impact on Artemia development, the gestational survival and number of offspring released by adult females were impaired by obscuring Hsp70 synthesis. Transcriptomic analysis revealed that several cuticle and chitin synthetic genes were downregulated, and carbohydrate metabolic genes were differentially expressed in Hsp70-knockdown individuals. A more comprehensive microscopic examination performed in this study revealed exoskeleton structural destruction and abnormal eye lenses featured in Hsp70-deficient adult females 48 h after Hsp70 dsRNA injection. Cysts produced by these Hsp70-deficient broods, instead, had a defective shell and were smaller in size, whereas nauplii had shorter first antennae and a rougher body epicuticle surface. Changes in carbohydrate metabolism caused by Hsp70 knockdown affected glycogen levels in adult Artemia females, as well as trehalose in cysts released from these broods, indicating that Hsp70 may play a role in energy storage preservation. Outcomes from this work provided novel insights into the roles of Hsp70 in Artemia reproduction performance, cyst formation, and exoskeleton structure preservation. The findings also support our previous observation that Hsp70 knockdown reduced Artemia nauplius tolerance to bacterial pathogens, which could be explained by the fact that loss of Hsp70 downregulated several Toll receptor genes (NT1 and Spaetzle) and reduced the integrity of the exoskeleton, allowing pathogens to enter and cause infection, ultimately resulting in mortality.

Diversity and connectedness of brine shrimp viruses in global hypersaline ecosystems

Brine shrimp (Artemia) has existed on Earth for 400 million years and has major ecological importance in hypersaline ecosystems. As a crucial live food in aquaculture, brine shrimp cysts have become one of the most important aquatic products traded worldwide. However, our understanding of the biodiversity, prevalence and global connectedness of viruses in brine shrimp is still very limited. A total of 143 batches of brine shrimp (belonging to seven species) cysts were collected from six continents including 21 countries and more than 100 geographic locations worldwide during 1977-2019. In total, 55 novel RNA viruses were identified, which could be assigned to 18 different viral families and related clades. Eleven viruses were dsRNA viruses, 16 were +ssRNA viruses, and 28 were-ssRNA viruses. Phylogenetic analyses of the RNA-directed RNA polymerase (RdRp) showed that brine shrimp viruses were often grouped with viruses isolated from other invertebrates and fungi. Remarkably, most brine shrimp viruses were related to those from different hosts that might feed on brine shrimp or share the same ecological niche. A notable case was the novel brine shrimp noda-like virus 3, which shared 79.25% (RdRp) and 63.88% (capsid proteins) amino acid identity with covert mortality nodavirus (CMNV) that may cause losses in aquaculture. In addition, both virome composition and phylogenetic analyses revealed global connectedness in certain brine shrimp viruses, particularly among Asia and Northern America. This highlights the incredible species diversity of viruses in these ancient species and provides essential data for the prevalence of RNA viruses in the global aquaculture industry. More broadly, these findings provide novel insights into the previously unrecognized RNA virosphere in hypersaline ecosystems worldwide and demonstrate that human activity might have driven the global connectedness of brine shrimp viruses.

The effects of Pandanus tectorius leaf extract on the resistance of White-leg shrimp Penaeus vannamei towards pathogenic Vibrio parahaemolyticus

Pandanus tectorius leaf extract effect on the White-leg shrimp Penaeus vannamei tolerance against Vibrio parahaemolyticus were investigated in this study. Thirty shrimp post-larvae measured at approximately 1 cm were exposed for 24 h to 0.5, 1, 2, 3, 4, 5 and 6 g/L leaf extract and subsequently observed for survival and immune-related genes expression (Hsp70, ProPO, peroxinectin, penaeidin, crustin and transglutaminase), followed by determination of their tolerance and histological tissue profiles upon Vibrio challenge. Survival of shrimps treated with 6 g/L of leaf extract improved by up to 95% to controls. Hsp70, crustin, and prophenoloxidase mRNA levels were observed to be 8.5, 10.4, and 1.5-fold higher, respectively. Histopathological analysis of the hepatopancreas and the muscle tissues revealed major tissue degeneration in Vibrio-challenged shrimps but not in shrimps primed with P. tectorius leaf extract. Of all the dose examined, the best pathogen resistance results were obtained with a 24 h incubation of shrimp in 6 g/L P. tectorius methanolic leaf extract. The tolerance towards V. parahaemolyticus might be associated with the increased regulation of Hsp70, prophenoloxidase and crustin upon exposure to the extract, all immune-related proteins essential for pathogen elimination in Penaeid shrimp. The present study primarily demonstrated that P. tectorius leaf extract is a viable alternative for enhancing P. vannamei post-larvae resistance against V. parahaemolyticus, a major bacterial pathogen in aquaculture.

Beneficial microbes to suppress Vibrio and improve the culture performance of copepod Tigriopus japonicus Mori

The use of beneficial microbes, i.e., probiotics, to reduce pathogens and promote the performance of the target species is an important management strategy in mariculture. This study aimed to investigate the potential of four microbes, Debaryomyces hansenii, Ruegeria mobilis, Lactobacillus plantarum, and Bacillus subtilis, to suppress Vibrio and increase survival, population growth and digestive enzyme activity (protease, lipase, and amylase) in the harpacticoid copepod, Tigriopus japonicus. Copepod, T. japonicus stock culture with an initial mean density of 50 individual/mL (25 adult male and 25 adult female) was distributed into five treatments (i.e., four experimental and a control, each with four replicates; repeated twice) using 20 beakers (100 mL capacity each). The copepods were fed a mixture of the dinoflagellate Alexandrium tamarense and the diatom Phyaeodactylum tricornutum (3 × 104 cells/mL-1). Each microbe's concentration was adjusted at 108 CFU/mL-1 and applied to the culture condition. D. hansenii, L. plantarum, and B. subtilis all improved the copepods' survival and population growth, likely by including a higher lipase activity (P < 0.05). In contrast, using R. mobilis did not improve the copepod's culture performance compared to control. B. subtilis was the most effective in decreasing the copepod's external and internal Vibrio loading. The probiotic concentrations in the copepod decreased within days during starvation, suggesting that routine re-application of the probiotics would be needed to sustain the microbial populations and the benefits they provide. Our results demonstrated that D. hansenii and B. subtilis are promising probiotics for mass copepod culture as live food for mariculture purposes.

The genome of the extremophile Artemia provides insight into strategies to cope with extreme environments

BACKGROUND

Brine shrimp Artemia have an unequalled ability to endure extreme salinity and complete anoxia. This study aims to elucidate its strategies to cope with these stressors.

RESULTS AND DISCUSSION

Here, we present the genome of an inbred A. franciscana Kellogg, 1906. We identified 21,828 genes of which, under high salinity, 674 genes and under anoxia, 900 genes were differentially expressed (42%, respectively 30% were annotated). Under high salinity, relevant stress genes and pathways included several Heat Shock Protein and Leaf Embryogenesis Abundant genes, as well as the trehalose metabolism. In addition, based on differential gene expression analysis, it can be hypothesized that a high oxidative stress response and endocytosis/exocytosis are potential salt management strategies, in addition to the expression of major facilitator superfamily genes responsible for transmembrane ion transport. Under anoxia, genes involved in mitochondrial function, mTOR signalling and autophagy were differentially expressed. Both high salt and anoxia enhanced degradation of erroneous proteins and protein chaperoning. Compared with other branchiopod genomes, Artemia had 0.03% contracted and 6% expanded orthogroups, in which 14% of the genes were differentially expressed under high salinity or anoxia. One phospholipase D gene family, shown to be important in plant stress response, was uniquely present in both extremophiles Artemia and the tardigrade Hypsibius dujardini, yet not differentially expressed under the described experimental conditions.

CONCLUSIONS

A relatively complete genome of Artemia was assembled, annotated and analysed, facilitating research on its extremophile features, and providing a reference sequence for crustacean research.

Pandanus tectorius fruit extract promotes Hsp70 accumulation, immune-related genes expression and Vibrio parahaemolyticus tolerance in the white-leg shrimp Penaeus vannamei

Plants and herbal extracts are indispensable for controlling the spread of disease-causing bacteria, including those that infect aquatic organisms used in aquaculture. The use of plant or herbal extract is expected to be safe for aquatic animals and less harmful to the environment, as opposed to conventional therapeutic alternatives such as antibiotics that promote the occurrence of potential antibiotic-resistant bacteria when used improperly. The efficacy of Pandanus tectorius fruit extract in the regulation of Hsp70 expression, pro-phenoloxidase (ProPO), peroxinectin, penaeidin, crustin and transglutaminase, all immune peptides essential for Vibrio tolerance in white leg shrimp, Penaeus vannamei, was investigated in this study, which included the determination of the safety levels of the extract. Tolerance of shrimp against Vibrio parahaemolyticus, a pathogenic bacteria that causes Acute Hepatopancreas Necrosis Disease (AHPND), was assessed on the basis of median lethal dose challenge survival (LD50 = 10⁶ cells/ml). Mortality was not observed 24 h after exposure of 0.5-6 g/L of the fruit extract, indicating that P. tectorius was not toxic to shrimp at these concentrations. A 24-h incubation of 2-6 g/L of the fruit extract increased shrimp tolerance to V. parahaemolyticus, with survival doubled when the maximum dose tested in this study was used. Concomitant with a rise in survival was the increase in immune-related proteins, with Hsp70, ProPO, peroxinectin, penaeidin, crustin and transglutaminase increased 10, 11, 11, 0.4, 8 and 13-fold respectively. Histological examination of the hepatopancreas and muscle tissues of Vibrio-infected shrimp primed with P. tectorius extract revealed reduced signs of histopathological degeneration, possibly due to the accumulation of Hsp70, a molecular chaperone crucial to cellular protein folding, tissue repair and immune response of living organisms, including Penaeid shrimp.

Cyst viability and stress tolerance upon heat shock protein 70 knockdown in the brine shrimp Artemia franciscana

Females of the brine shrimp Artemia franciscana produce either free-swimming nauplii via ovoviviparous pathway of reproduction or encysted embryos, known as cysts, via oviparous pathway, in which biological processes are arrested. While previous study has shown a crucial role of ATP-dependent molecular chaperone, heat shock protein 70 (Hsp70) in protecting A. franciscana nauplii against various abiotic and abiotic stressors, the function of this protein in diapausing embryos and cyst development, however, remains unknown. RNA interference (RNAi) was applied in this study to examine the role of Hsp70 in cyst development and stress tolerance, with the latter performed by desiccation and freezing, a common method used for diapause termination in Artemia cysts. Hsp70 knockdown was apparent in cysts released from females that were injected with Hsp70 dsRNA. The loss of Hsp70 affected neither the development nor morphology of the cysts. The time between fertilization and cyst release from Artemia females injected with Hsp70 dsRNA was delayed slightly, but the differences were not significant when compared to the controls. However, the hatching percentage of cysts which lacks Hsp70 were reduced following desiccation and freezing. Taken together, these results indicated that Hsp70 possibly plays a role in the stress tolerance but not in the development of diapause-destined embryos of Artemia. This research makes fundamental contributions to our understanding of the role molecular chaperone Hsp70 plays in Artemia, an excellent model organism for diapause studies of the crustaceans.

The blue mussel inside: 3D visualization and description of the vascular-related anatomy of Mytilus edulis to unravel hemolymph extraction

The blue mussel Mytilus edulis is an intensely studied bivalve in biomonitoring programs worldwide. The lack of detailed descriptions of hemolymph-withdrawal protocols, particularly with regard to the place from where hemolymph could be perfused from, raises questions regarding the exact composition of aspirated hemolymph and does not exclude the possibility of contamination with other body-fluids. This study demonstrates the use of high resolution X-ray computed tomography and histology combined with 3D-reconstruction using AMIRA-software to visualize some important vascular-related anatomic structures of Mytilus edulis. Based on these images, different hemolymph extraction sites used in bivalve research were visualized and described, leading to new insights into hemolymph collection. Results show that hemolymph withdrawn from the posterior adductor muscle could be extracted from small spaces and fissures between the muscle fibers that are connected to at least one hemolymph supplying artery, more specifically the left posterior gastro-intestinal artery. Furthermore, 3D-reconstructions indicate that puncturing hemolymph from the pericard, anterior aorta, atria and ventricle in a non-invasive way should be possible. Hemolymph withdrawal from the heart is less straightforward and more prone to contamination from the pallial cavity. This study resulted simultaneously in a detailed description and visualization of the vascular-related anatomy of Mytilus edulis.

Applications of Next-Generation Sequencing Technologies and Computational Tools in Molecular Evolution and Aquatic Animals Conservation Studies: A Short Review

Aquatic ecosystems that form major biodiversity hotspots are critically threatened due to environmental and anthropogenic stressors. We believe that, in this genomic era, computational methods can be applied to promote aquatic biodiversity conservation by addressing questions related to the evolutionary history of aquatic organisms at the molecular level. However, huge amounts of genomics data generated can only be discerned through the use of bioinformatics. Here, we examine the applications of next-generation sequencing technologies and bioinformatics tools to study the molecular evolution of aquatic animals and discuss the current challenges and future perspectives of using bioinformatics toward aquatic animal conservation efforts.

Penaeid shrimp genome provides insights into benthic adaptation and frequent molting

Crustacea, the subphylum of Arthropoda which dominates the aquatic environment, is of major importance in ecology and fisheries. Here we report the genome sequence of the Pacific white shrimp Litopenaeus vannamei, covering ~1.66 Gb (scaffold N50 605.56 Kb) with 25,596 protein-coding genes and a high proportion of simple sequence repeats (>23.93%). The expansion of genes related to vision and locomotion is probably central to its benthic adaptation. Frequent molting of the shrimp may be explained by an intensified ecdysone signal pathway through gene expansion and positive selection. As an important aquaculture organism, L. vannamei has been subjected to high selection pressure during the past 30 years of breeding, and this has had a considerable impact on its genome. Decoding the L. vannamei genome not only provides an insight into the genetic underpinnings of specific biological processes, but also provides valuable information for enhancing crustacean aquaculture.

The Pacific white shrimp Litopenaeus vannamei is an important aquaculture species and a promising model for crustacean biology. Here, the authors provide a reference genome assembly, and show that gene expansion is involved in the regulation of frequent molting as well as benthic adaptation of the shrimp.

Managing the Microbial Community of Marine Fish Larvae: A Holistic Perspective for Larviculture

The availability of high-quality juveniles is a bottleneck in the farming of many marine fish species. Detrimental larvae-microbe interactions are a main reason for poor viability and quality in larval rearing. In this review, we explore the microbial community of fish larvae from an ecological and eco-physiological perspective, with the aim to develop the knowledge basis for microbial management. The larvae are exposed to a huge number of microbes from external and internal sources in intensive aquaculture, but their relative importance depend on the rearing technology used (especially flow-through vs. recirculating systems) and the retention time of the water in the fish tanks. Generally, focus has been on microbes entering the system, but microbes from growth within the system is normally a substantial part of the microbes encountered by larvae. Culture independent methods have revealed an unexpected high richness of bacterial species associated with larvae, with 100-250 operational taxonomic units associated with one individual. The microbiota of larvae changes rapidly until metamorphosis, most likely due to changes in the selection pressure in the digestive tract caused by changes in host-microbe and microbe-microbe interactions. Even though the microbiota of larvae is distinctly different from the microbiota of the water and the live food, the microbiota of the water strongly affects the microbiota of the larvae. We are in the early phase of understanding larvae-microbe interactions in vivo, but some studies with other animals than fish emphasize that we so far have underestimated the complexity of these interactions. We present examples demonstrating the diversity of these interactions. A large variety of microbial management methods exist, focusing on non-selective reduction of microbes, selective enhancement of microbes, and on improvement of the resistance of larvae against microbes. However, relatively few methods have been studied extensively. We believe that there is a lot to gain by increasing the diversity of approaches for microbial management. As many microbial management methods are perturbations of the microbial community, we argue that ecological theory is needed to foresee and test for longer term consequences in microbe-microbe and microbe-larvae interactions. We finally make some recommendations for future research and development.

Ontogenesis of opercular deformities in gilthead sea bream Sparus aurata: a histological description

The aim of this study was to characterize histological changes during opercular osteogenesis in farmed gilthead sea bream Sparus aurata larvae from 7 to 69 days post hatching (dph) and compare normal osteogenesis with that of deformed opercles. Mild opercular deformities were first detected in 19 dph larvae by folding of the opercle's distal edge into the gill chamber. Here, the variation in the phenotype and the irregular bone structure at the curled part of the opercles is described and compared with the histology of normal opercles. Results indicated that deformed opercles still undergo bone growth with the addition of new matrix by osteoblasts at the opercular surface, especially at its edges. No significant difference was found in bone thickness between deformed and normal opercles. In addition to differences in bone architecture, differences in collagen fibre thickness between normal and deformed opercles were also found.

Isolation of Vibrionaceae from wild blue mussel (Mytilus edulis) adults and their impact on blue mussel larviculture

The blue mussel (Mytilus edulis) is known as a robust bivalve species, although its larviculture appears to be highly susceptible to diseases. In this study, we isolated 17 strains from induced mortality events in healthy wild-caught blue mussel adults and demonstrated that they caused between 17% and 98% mortality in blue mussel larvae in a newly developed, highly controlled immersion challenge test model. Eight of the isolates belong to the Splendidus clade of vibrios, while the other isolates belong to the genus Photobacterium. The genomes of the most virulent Vibrio isolate and the most virulent Photobacterium isolate were sequenced and contained several genes encoding factors that have previously been linked to virulence towards bivalves. In vitro tests confirmed that all 17 isolates were positive for these virulence factors. The sequenced genomes also contained a remarkably high number of multidrug resistance genes. We therefore assessed the sensitivity of all isolates to a broad range of antibiotics and found that there were indeed many strong positive correlations between the sensitivities of the isolates to different antibiotics. Our data provide an ecological insight into mass mortality in blue mussels as they indicate that wild mussels contain a reservoir of pathogenic bacteria.

Molecular characterization and functional analyses of a diapause hormone receptor-like gene in parthenogenetic Artemia

In arthropods, mature females under certain conditions produce and release encysted gastrula embryos that enter diapause, a state of obligate dormancy. The process is presumably regulated by diapause hormone (DH) and diapause hormone receptor (DHR) that were identified in the silkworm, Bombyx mori and other insects. However, the molecular structure and function of DHR in crustaceans remains unknown. Here, a DHR-like gene from parthenogenetic Artemia (Ar-DHR) was isolated and sequenced. The cDNA sequence consists of 1410bp with a 1260-bp open reading frame encoding a protein consisting of 420 amino acid residues. The results of real-time PCR (qRT-PCR) and Western blot analysis showed that the mRNA and protein of Ar-DHR were mainly expressed at the diapause stage. Furthermore, we found that Ar-DHR was located on the cell membrane of the pre-diapause cyst but in the cytoplasm of the diapause cyst by analysis of immunofluorescence. In vivo knockdown of Ar-DHR by RNA interference (RNAi) and antiserum neutralization consistently inhibited diapause cysts formation. The results indicated that Ar-DHR plays an important role in the induction and maintenance of embryonic diapause in Artemia. Thus, our findings provide an insight into the regulation of diapause formation in Artemia and the function of Ar-DHR.

Identification and characterization of a Masculinizer (Masc) gene involved in sex differentiation in Artemia

The sex of relatively primitive animals such as invertebrates is mostly determined by environmental factors and chromosome ploidy. Heteromorphic chromosomes may also play an important role, as in the ZW system in lepidopterans. However, the mechanisms of these various sex determination systems are still largely undefined. In the present study, a Masculinizer gene (Ar-Masc) was identified in the crustacean Artemia franciscana Kellogg 1906. Sequence analysis revealed that the 1140-bp full-length open reading frame of Ar-Masc encodes a 380-aa protein containing two CCCH-type zinc finger domains having a high degree of shared identities with the MASC protein characterized in the silkworm Bombyx mori, which has been determined to participate in the production of male-specific splice variants. Furthermore, although Ar-Masc could be detected in almost all stages in both sexual and parthenogenetic Artemia, there were significant variations in expression between these two reproductive modes. Firstly, qRT-PCR and Western blot analysis showed that levels of both Ar-Masc mRNA and protein in sexual nauplii were much higher than in parthenogenetic nauplii throughout the hatching process. Secondly, both sexual and parthenogenetic Artemia had decreased levels of Ar-Masc along with the embryonic developmental stages, while the sexual ones had a relatively higher and more stable expression than those of parthenogenetic ones. Thirdly, immunofluorescence analysis determined that sexual individuals had higher levels of Ar-MASC protein than parthenogenetic individuals during embryonic development. Lastly, RNA interference with dsRNA showed that gene silencing of Ar-Masc in sexual A. franciscana caused the female-male ratio of progeny to be 2.19:1. These data suggest that Ar-Masc participates in the process of sex determination in A. franciscana, and provide insight into the evolution of sex determination in sexual organisms.

Environmental impact of non-certified versus certified (ASC) intensive Pangasius aquaculture in Vietnam, a comparison based on a statistically supported LCA

Pangasius production in Vietnam is widely known as a success story in aquaculture, the fastest growing global food system because of its tremendous expansion by volume, value and the number of international markets to which Pangasius has been exported in recent years. While certification schemes are becoming significant features of international fish trade and marketing, an increasing number of Pangasius producers have followed at least one of the certification schemes recognised by international markets to incorporate environmental and social sustainability practices in aquaculture, typically the Pangasius Aquaculture Dialogue (PAD) scheme certified by the Aquaculture Stewardship Council (ASC). An assessment of the environmental benefit of applying certification schemes on Pangasius production, however, is still needed. This article compared the environmental impact of ASC-certified versus non-ASC certified intensive Pangasius aquaculture, using a statistically supported LCA. We focused on both resource-related (water, land and total resources) and emissions-related (global warming, acidification, freshwater and marine eutrophication) categories. The ASC certification scheme was shown to be a good approach for determining adequate environmental sustainability, especially concerning emissions-related categories, in Pangasius production. However, the non-ASC certified farms, due to the large spread, the impact (e.g., water resources and freshwater eutrophication) was possibly lower for a certain farm. However, this result was not generally prominent. Further improvements in intensive Pangasius production to inspire certification schemes are proposed, e.g., making the implementation of certification schemes more affordable, well-oriented and facilitated; reducing consumed feed amounts and of the incorporated share in fishmeal, especially domestic fishmeal, etc. However, their implementation should be vetted with key stakeholders to assess their feasibility.

Effects of acute change in salinity and moulting on the infection of white leg shrimp (Penaeus vannamei) with white spot syndrome virus upon immersion challenge

In the field, moulting and salinity drop in the water due to excessive rainfall have been mentioned to be risk factors for WSSV outbreaks. Therefore, in this study, the effect of an acute change in environmental salinity and shedding of the old cuticle shell on the susceptibility of Penaeus vannamei to WSSV was evaluated by immersion challenge. For testing the effect of abrupt salinity stress, early premoult shrimp that were acclimated to 35 g L^-1 were subjected to salinities of 50 g L^-1 , 35 g L^-1 , 20 g L^-1 , 10 g L^-1 and 7 g L^-1 or 5 g L^-1 and simultaneously exposed to 10^5.5  SID₅₀ mL^-1 of WSSV for 5 h, after which the salinity was brought back to 35 g L^-1 . Shrimp that were transferred from 35 g L^-1 to 50 g L^-1 , 35 g L^-1 and 20 g L^-1 did not become infected with WSSV. Shrimp became infected with WSSV after an acute salinity drop from 35 g L^-1 to 10 g L^-1 and lower. The mortality in shrimp, subjected to a salinity change to 10 g L^-1 , 7 g L^-1 and 5 g L^-1 , was 6.7%, 46.7% and 53.3%, respectively (P < 0.05)_. For testing the effect of moulting, shrimp in early premoult, moulting and post-moult were immersed in sea water containing 10^5.5  SID₅₀ mL^-1 of WSSV. The resulting mortality due to WSSV infection in shrimp inoculated during early premoult (0%), ecdysis (53.3%) and post-moult (26.72%) demonstrated that a significant difference exists in susceptibility of shrimp during the short moulting process (P < 0.05). The findings of this study indicate that during a drop in environmental salinity lower than 10 g L^-1 and ecdysis, shrimp are at risk for a WSSV infection. These findings have important implications for WSSV control measures.

Priming the immune system of Penaeid shrimp by bacterial HSP70 (DnaK)

This study was conducted to test the effect of DnaK on priming immune responses in Penaeid shrimp. Juvenile-specific pathogen-free (SPF) P. vannamei shrimp were injected with 0.05 μg recombinant DnaK. One hour post-DnaK priming, a non-lethal dose of Vibrio campbellii (10(5) CFU shrimp(-1)) was injected. Other treatments include only DnaK or V. campbellii injection or control with blank inocula. The haemolymph of three shrimp from each treatment was collected at 1.5, 6, 9 and 12 h post-DnaK priming (hpp). It was verified that injection with DnaK and V. campbellii challenge affected the transcription of 3 immune genes, transglutaminase-1 (TGase-1), prophenoloxidase-2 (proPO-2) and endogenous HSP70 (lvHSP70). In P. monodon, shrimp were first injected with DnaK at a dose of 10 μg shrimp(-1) and one hour later with 10(6) CFU of V. harveyi (BB120) shrimp(-1). Shrimp injected with DnaK showed a significant increase in proPO expression compared to the control (P < 0.05). Yet a double injection (DnaK and Vibrio) seemed to cause an antagonistic response at the level of expression, which was not equalled at the level of PO activity. Those results suggest that DnaK is able to modulate immune responses in P. vannamei and P. monodon.

Per os infectivity of white spot syndrome virus (WSSV) in white-legged shrimp (Litopenaeus vannamei) and role of peritrophic membrane

As earlier observations on peroral infectivity of WSSV in white-legged shrimp are conflicting, here, a standardized peroral intubation technique was used to examine (i) the role of the physical composition of the viral inoculum and (ii) the barrier function of the PM. In a first experiment, the infectivity of a WSSV stock was compared by determining the SID₅₀ by intramuscular injection, peroral inoculation or via feeding. The following titers were obtained: 10^8.77 SID₅₀/g by intramuscular injection, 10^1.23 SID₅₀/g by peroral inoculation and 10^0.73 SID₅₀/g by feeding. These results demonstrated that 10^7.54–10^8.03 infectious virus is needed to infect shrimp by peroral inoculation and via feeding. Next, it was examined if damage of the PM may increase the susceptibility for WSSV by peroral route. The infectivity of a virus stock was tested upon peroral inoculation of shrimp with and without removal of the PM and compared with the infectivity upon intramuscular inoculation. The virus titers obtained upon intramuscular injection and peroral inoculation of shrimp with and without PM were 10^8.63, 10^1.13 and 10^1.53 SID₅₀/mL, respectively. This experiment confirmed the need of 10^7.1–10^7.5 infectious virus to infect shrimp via peroral route and showed that the removal of the PM slightly but not significantly (p > 0.05) facilitated the infection of shrimp. This study indicated that WSSV contaminated feed is poorly infectious via peroral route, whereas it is highly infectious when injected into shrimp. The PM plays a minor role as internal barrier of shrimp against WSSV infection.

Reactive oxygen species generated by a heat shock protein (Hsp) inducing product contributes to Hsp70 production and Hsp70-mediated protective immunity in Artemia franciscana against pathogenic vibrios

The cytoprotective role of heat shock protein (Hsp70) described in a variety of animal disease models, including vibriosis in farmed aquatic animals, suggests that new protective strategies relying upon the use of compounds that selectively turn on Hsp genes could be developed. The product Tex-OE® (hereafter referred to as Hspi), an extract from the skin of the prickly pear fruit, Opuntia ficus indica, was previously shown to trigger Hsp70 synthesis in a non-stressful situation in a variety of animals, including in a gnotobiotically (germ-free) cultured brine shrimp Artemia franciscana model system. This model system offers great potential for carrying out high-throughput, live-animal screens of compounds that have health benefit effects. By using this model system, we aimed to disclose the underlying cause behind the induction of Hsp70 by Hspi in the shrimp host, and to determine whether the product affects the shrimp in inducing resistance towards pathogenic vibrios. We provide unequivocal evidences indicating that during the pretreatment period with Hspi, there is an initial release of reactive oxygen species (hydrogen peroxide and/or superoxide anion), generated by the added product, in the rearing water and associated with the host. The reactive molecules generated are the triggering factors responsible for causing Hsp70 induction within Artemia. We have also shown that Hspi acts prophylactically at an optimum dose regimen to confer protection against pathogenic vibrios. This salutary effect was associated with upregulation of two important immune genes, prophenoloxidase and transglutaminase of the innate immune system. These findings suggest that inducers of stress protein (e.g. Hsp70) are potentially important modulator of immune responses and might be exploited to confer protection to cultured shrimp against Vibrio infection.

Poly-ß-hydroxybutyrate content and dose of the bacterial carrier for Artemia enrichment determine the performance of giant freshwater prawn larvae

The beneficial effects of poly-β-hydroxybutyrate (PHB) for aquaculture animals have been shown in several studies. The strategy of applying PHB contained in a bacterial carrier has, however, hardly been considered. The effect of administering PHB-accumulated Alcaligenes eutrophus H16 containing 10 or 80 % PHB on dry weight, named A10 and A80, respectively, through the live feed Artemia was investigated on the culture performance of larvae of the giant freshwater prawn (Macrobrachium rosenbergii). Feeding larvae with Artemia nauplii enriched in a medium containing 100 and 1,000 mg L(-1) A80 significantly increased the survival with about 15 % and the development of the larvae with a larval stage index of about 1 as compared to feeding non-enriched Artemia. The survival of the larvae also significantly increased with about 35 % in case of a challenge with Vibrio harveyi. The efficiency of these treatments was equal to a control treatment of Artemia enriched in an 800 mg L(-1) PHB powder suspension, while Artemia enriched in 10 mg L(-1) A80, 100 mg L(-1) A10, and 1,000 mg L(-1) A10 did not bring similar effects. From our results, it can be concluded that PHB supplemented in a bacterial carrier (i.e., amorphous PHB) can increase the larviculture efficiency of giant freshwater prawn similar to supplementation of PHB in powdered form (i.e., crystalline PHB). When the level of PHB in the bacterial carrier is high, similar beneficial effects can be achieved as crystalline PHB, but at a lower live food enrichment concentration expressed on PHB basis.

Purification of white spot syndrome virus by iodixanol density gradient centrifugation

Up to now, only a few brief procedures for purifying white spot syndrome virus (WSSV) have been described. They were mainly based on sucrose, NaBr and CsCl density gradient centrifugation. This work describes for the first time the purification of WSSV through iodixanol density gradients, using virus isolated from infected tissues and haemolymph of Penaeus vannamei (Boone). The purification from tissues included a concentration step by centrifugation (2.5 h at 60,000 g) onto a 50% iodixanol cushion and a purification step by centrifugation (3 h at 80,000 g) through a discontinuous iodixanol gradient (phosphate-buffered saline, 5%, 10%, 15% and 20%). The purification from infected haemolymph enclosed a dialysis step with a membrane of 1,000 kDa (18 h) and a purification step through the earlier iodixanol gradient. The gradients were collected in fractions and analysed. The number of particles, infectivity titre (in vivo), total protein and viral protein content were evaluated. The purification from infected tissues gave WSSV suspensions with a very high infectivity and an acceptable purity, while virus purified from haemolymph had a high infectivity and a very high purity. Additionally, it was observed that WSSV has an unusually low buoyant density and that it is very sensitive to high external pressures.

A first AFLP-based genetic linkage map for brine shrimp Artemia franciscana and its application in mapping the sex locus

We report on the construction of sex-specific linkage maps, the identification of sex-linked markers and the genome size estimation for the brine shrimp Artemia franciscana. Overall, from the analysis of 433 AFLP markers segregating in a 112 full-sib family we identified 21 male and 22 female linkage groups (2n = 42), covering 1,041 and 1,313 cM respectively. Fifteen putatively homologous linkage groups, including the sex linkage groups, were identified between the female and male linkage map. Eight sex-linked AFLP marker alleles were inherited from the female parent, supporting the hypothesis of a WZ-ZZ sex-determining system. The haploid Artemia genome size was estimated to 0.93 Gb by flow cytometry. The produced Artemia linkage maps provide the basis for further fine mapping and exploring of the sex-determining region and are a possible marker resource for mapping genomic loci underlying phenotypic differences among Artemia species.

New approaches for Artemia pond culture

A project for intensive culture of Artemia in Vinhchau solar saltwork was funded by Soctrang Authority. The aim of this project is to increase the average cyst yield of 50kg.ha-1.crop, and to build up a stable culture technique with a better yield for local farmers. Multiple laboratory experiments were set up with inert food including fermented rice bran, tiger shrimp feed (PL15), as well as their combination with live algae (Chaetoceros). Results showed that, under laboratory conditions, fermented rice bran and tiger shrimp feed can be used as supplemental food sources. The shrimp feed alone or in combination with algae always gave better cyst production compared to the others, but should not account for more than 50% of the diet. In the field trials, aeration of Artemia ponds also increased cyst yields (from 195.8+/-44.2 to 207+/-46.1kg.ha-1.crop with 6 and 12 aeration a day, respectively) compared to ponds with no aeration (88.2+/-27.5kg.ha-1.crop), however the returns on investment (ROI=2.73-2.71 with aera tion vs. 2.24 without) are not significantly different. Utilization of fermented rice bran (20kg.ha-1.day) and shrimp feed (6kg.ha-1.day) as a supplementary feed during pond production in combination with greenwater supplies (10% of pond volume daily) resulted in higher yields (96.0+/-15.9 and 157.2+/-15.0kg.ha-1.crop, respectively) than traditional culture; Shrimp feed as a supplemental feed supported the cyst yield but their negative effect was at a high cost vs. traditional culture and use of fermented rice bran. Based on the cyst yield and ROI, fermented rice bran should be a promising item for poor farmers.

Feeding truncated heat shock protein 70s protect Artemia franciscana against virulent Vibrio campbellii challenge

The 70 kDa heat shock proteins (Hsp70s) are highly conserved in evolution, leading to striking similarities in structure and composition between eukaryotic Hsp70s and their homologs in prokaryotes. The eukaryotic Hsp70 like the DnaK (Escherichia coli equivalent Hsp70) protein, consist of three functionally distinct domains: an N-terminal 44-kDa ATPase portion, an 18-kDa peptide-binding domain and a C-terminal 10-kDa fragment. Previously, the amino acid sequence of eukaryotic (the brine shrimp Artemia franciscana) Hsp70 and DnaK proteins were shown to share a high degree of homology, particularly in the peptide-binding domain (59.6%, the putative innate immunity-activating portion) compared to the N-terminal ATPase (48.8%) and the C-terminal lid domains (19.4%). Next to this remarkable conservation, these proteins have been shown to generate protective immunity in Artemia against pathogenic Vibrio campbellii. This study, aimed to unravel the Vibrio-protective domain of Hsp70s in vivo, demonstrated that gnotobiotically cultured Artemia fed with recombinant C-terminal fragment (containing the conserved peptide binding domain) of Artemia Hsp70 or DnaK protein were well protected against subsequent Vibrio challenge. In addition, the prophenoloxidase (proPO) system, at both mRNA and protein activity levels, was also markedly induced by these truncated proteins, suggesting epitope(s) responsible for priming the proPO system and presumably other immune-related genes, consequently boosting Artemia survival upon challenge with V. campbellii, might be located within this conserved region of the peptide binding domain.

Susceptibility of juvenile Macrobrachium rosenbergii to different doses of high and low virulence strains of white spot syndrome virus (WSSV)

As some literature on the susceptibility of different life stages of Macrobrachium rosenbergii to white spot syndrome virus (WSSV) is conflicting, the pathogenesis, infectivity and pathogenicity of 2 WSSV strains (Thai-1 and Viet) were investigated here in juveniles using conditions standardized for Penaeus vannamei. As with P. vannamei, juvenile M. rosenbergii (2 to 5 g) injected with a low dose of WSSV-Thai-1 or a high dose of WSSV-Viet developed comparable clinical pathology and numbers of infected cells within 1 to 2 d post-infection. In contrast, a low dose of WSSV-Viet capable of causing mortality in P. vannamei resulted in no detectable infection in M. rosenbergii. Mean prawn infectious dose 50% endpoints (PID₅₀ ml⁻¹) determined in M. rosenbergii were in the order of 100-fold higher for WSSV-Thai-1 (105.3 ± 0.4 PID₅₀ ml⁻¹) than for WSSV-Viet (103.2 ± 0.2 PID₅₀ ml⁻¹), with each of these being about 20-fold and 400-fold lower, respectively, than found previously in P. vannamei. The median lethal dose (LD₅₀ ml⁻¹) determined in M. rosenbergii was also far higher (~1000-fold) for WSSV-Thai-1 (105.4 ± 0.4 LD₅₀ ml⁻¹) than for WSSV-Viet (102.3 ± 0.3 LD₅₀ ml⁻¹). Based on these data, it is clear that juvenile M. rosenbergii are susceptible to WSSV infection, disease and mortality. In comparison to P. vannamei, however, juvenile M. rosenbergii appear more capable of resisting infection and disease, particularly in the case of a WSSV strain with lower apparent virulence.

A quorum sensing-disrupting brominated thiophenone with a promising therapeutic potential to treat luminescent vibriosis

Vibrio harveyi is amongst the most important bacterial pathogens in aquaculture. Novel methods to control this pathogen are needed since many strains have acquired resistance to antibiotics. We previously showed that quorum sensing-disrupting furanones are able to protect brine shrimp larvae against vibriosis. However, a major problem of these compounds is that they are toxic toward higher organisms and therefore, they are not safe to be used in aquaculture. The synthesis of brominated thiophenones, sulphur analogues of the quorum sensing-disrupting furanones, has recently been reported. In the present study, we report that these compounds block quorum sensing in V. harveyi at concentrations in the low micromolar range. Bioluminescence experiments with V. harveyi quorum sensing mutants and a fluorescence anisotropy assay indicated that the compounds disrupt quorum sensing in this bacterium by decreasing the ability of the quorum sensing master regulator LuxR to bind to its target promoter DNA. In vivo challenge tests with gnotobiotic brine shrimp larvae showed that thiophenone compound TF310, (Z)-4-((5-(bromomethylene)-2-oxo-2,5-dihydrothiophen-3-yl)methoxy)-4-oxobutanoic acid, completely protected the larvae from V. harveyi BB120 when dosed to the culture water at 2.5 µM or more, whereas severe toxicity was only observed at 250 µM. This makes TF310 showing the highest therapeutic index of all quorum sensing-disrupting compounds tested thus far in our brine shrimp model system.

Monitoring of Vibrio harveyi quorum sensing activity in real time during infection of brine shrimp larvae

Quorum sensing, bacterial cell-to-cell communication, has been linked to the virulence of pathogenic bacteria. Indeed, in vitro experiments have shown that many bacterial pathogens regulate the expression of virulence genes by this cell-to-cell communication process. Moreover, signal molecules have been detected in samples retrieved from infected hosts and quorum sensing disruption has been reported to result in reduced virulence in different host-pathogen systems. However, data on in vivo quorum sensing activity of pathogens during infection of a host are currently lacking. We previously reported that quorum sensing regulates the virulence of Vibrio harveyi in a standardised model system with gnotobiotic brine shrimp (Artemia franciscana) larvae. Here, we monitored quorum sensing activity in Vibrio harveyi during infection of the shrimp, using bioluminescence as a read-out. We found that wild-type Vibrio harveyi shows a strong increase in quorum sensing activity early during infection. In this respect, the bacteria behave remarkably similar in different larvae, despite the fact that only half of them survive the infection. Interestingly, when expressed per bacterial cell, Vibrio harveyi showed around 200-fold higher maximal quorum sensing-regulated bioluminescence when associated with larvae than in the culture water. Finally, the in vivo quorum sensing activity of mutants defective in the production of one of the three signal molecules is consistent with their virulence, with no detectable in vivo quorum sensing activity in AI-2- and CAI-1-deficient mutants. These results indicate that AI-2 and CAI-1 are the dominant signals during infection of brine shrimp.

Effects of poly-β-hydroxybutyrate (PHB) on Siberian sturgeon (Acipenser baerii) fingerlings performance and its gastrointestinal tract microbial community

Poly-β-hydroxybutyrate (PHB) is a natural polymer that can be depolymerized into water-soluble short-chain fatty acid monomers. These monomers can act as microbial control agents. In this study, the effects of partially replacing the diet of Siberian sturgeon fingerlings with 2% and 5% PHB were investigated. Replacing 2% of the diet with PHB improved weight gain, specific growth rate (SGR) and survival in the sturgeon fingerlings during the 10-week experimental period. Community-level physiological profiling and PCR-denaturing gradient gel electrophoresis (PCR-DGGE) were used to analyze the microbial community diversity and community organization in the sturgeon gastrointestinal tract. DGGE analysis revealed that PHB affected the intestinal microbial species richness and diversity. The highest species richness was observed with 2% PHB. DNA sequencing of the dominant bands in 2% and 5% PHB treatments revealed that PHB stimulated bacteria belonging to the genera Bacillus and Ruminococcaceae. Principal component analysis, Lorenz curves and the Shannon index of Biolog Ecoplate data revealed that aerobic metabolic potential of the bacterial community was different in the PHB-treated fishes as compared with the control situation. Overall, our results indicate that PHB act as microbial control agents and replacement of 2% of Siberian sturgeon fingerling diet with PHB has beneficial effects.

Bacterial host interaction of GFP-labelled Vibrio anguillarum HI-610 with gnotobiotic sea bass, Dicentrarchus labrax (L.), larvae

The location and cell damage caused by Vibrio anguillarum, the causative agent of classical vibriosis, within the developing gut of the newly hatched sea bass, Dicentrarchus labrax (L.), is unknown. A gnotobiotic sea bass model was used to investigate the early interactions of V. anguillarum with sea bass larvae. In the present study, germ-free sea bass larvae were orally exposed to a V. anguillarum HI-610 pathogen labelled with the green fluorescent protein (GFP-HI-610) and sampled at regular intervals. Pathogenic colonization of gut enterocytes was observed 2 h post-exposure (p.e.) and onwards, whereas bacteria within the swim bladder were visualized 48 h p.e and onwards. Ultrastructural findings demonstrated direct bacterial contact with the host cell in the oesophageal mucosa and putative attachment to microvilli of mid- and hindgut enterocytes. The present findings form a starting point for studies assessing the impact of potential candidates (probiotics, prebiotics, antimicrobial peptides) to mitigate bacterial virulence.

Priming the prophenoloxidase system of Artemia franciscana by heat shock proteins protects against Vibrio campbellii challenge

Like other invertebrates, the brine shrimp Artemia franciscana relies solely on innate immunity, which by definition lacks adaptive characteristics, to combat against invading pathogens. One of the innate mechanisms is melanisation of bacteria mediated by the activation of the prophenoloxidase (proPO) system. The 70 kDa heat shock proteins (Hsp70) derived from either prokaryote (Escherichia coli) or eukaryote (Artemia), well conserved and immune-dominant molecules, protect Artemia against Vibrio campbellii. However, the molecular mechanisms by which these proteins protect Artemia against Vibrio campbellii infection are unknown. Here we demonstrated that feeding gnotobiotically grown Artemia with either Artemia Hsp70 or the E. coli Hsp70 equivalent DnaK, each overproduced in E. coli, followed by V. campbellii challenge enhanced the proPO system, at both mRNA and protein activity levels. Additionally, the Artemia fed with these proteins survived well in a Vibrio challenge assay. These results indicated that Hsp70s derived from either prokaryotic or eukaryotic sources generate protective immunity in the crustacean Artemia against V. campbellii infection by priming the proPO system. This is apparently the first in vivo report on priming activity of Hsp70 in an invertebrate.

Regulation of virulence factors by quorum sensing in Vibrio harveyi

Vibrio harveyi is an important aquatic pathogen that produces several virulence factors. In this study, the effect of quorum sensing, bacterial cell-to-cell communication, on the production of the virulence factors caseinase, gelatinase, lipase, hemolysin, and phospholipase, was investigated. The activity of virulence factors was studied through enzymatic plate assays using V. harveyi wild type and mutants with constitutively maximal or minimal quorum sensing activity. The results showed that quorum sensing negatively regulates phospholipase activity as higher activity was observed in mutants with minimal quorum sensing activity than in the mutant with maximal quorum sensing activity.Reverse transcriptase real-time PCR with specific primers revealed that the expression level of three phospholipase genes was 2-fold higher [corrected] in the mutant with minimal quorum sensing activity than in the mutant with maximal quorum sensingactivity. As far as we know, this is the first report of quorum sensing regulation of phospholipase. Finally, caseinase and gelatinase activity were positively regulated by quorum sensing, which is consistent with previous reports, and lipase and hemolysin activity were found to be independent of quorum sensing. Hence, the regulation is different for different virulence factors, with some being either positively or negatively regulated, and others being independent of quorum sensing. This might reflect the need to produce the different virulence factors at different stages during infection.

Quorum quenching bacteria protect Macrobrachium rosenbergii larvae from Vibrio harveyi infection

AIMS

In this study, we investigated the effect of N-acyl homoserine lactone-degrading bacterial enrichment cultures (ECs) on larviculture of the giant freshwater prawn Macrobrachium rosenbergii.

METHODS AND RESULTS

The larval performance in terms of larval growth, larval survival, larval quality, duration of the larval rearing process and microflora levels in the rearing water as well as inside the prawn gut was investigated. The application of the EC bacteria was performed in two ways: by adding them directly into the larval rearing water and via enriched Artemia nauplii used for larval feeding. The results of the study demonstrated that both ECs that were tested had a similar positive effect on larval survival and larval quality, whereas they did not affect larval growth or the duration of the larval rearing process.

CONCLUSIONS

Under normal hatchery conditions, the optimal EC densities were found to be 10(6) CFU ml(-1) for adding into the rearing water and 5 × 10(8) CFU ml(-1) for enrichment of Artemia nauplii used for feeding of the larvae. In the hatchery, the ECs can be grown on waste streams of Artemia hatching.

SIGNIFICANCE AND IMPACT OF THE STUDY

Application of this kind of ECs could lead to a more sustainable aquaculture production, by replacing the use of antibiotics to control diseases.

Disruption of bacterial cell-to-cell communication by marine organisms and its relevance to aquaculture

Bacterial disease is one of the most critical problems in commercial aquaculture. Although various methods and treatments have been developed to curb the problem, yet they still have significant drawbacks. A novel and environmental-friendly approach in solving this problem is through the disruption of bacterial communication or quorum sensing (QS). In this communication scheme, bacteria regulate their own gene expression by producing, releasing, and sensing chemical signals from the environment. There seems to be a link between QS and diseases through the regulation of certain phenotypes and the induction of virulence factors responsible for pathogen-host association. Several findings have reported that numerous aquatic organisms such as micro-algae, macro-algae, invertebrates, or even other bacteria have the potential to disrupt QS. The mechanism of action varies from degradation of signals through enzymatic or chemical inactivation to antagonistic as well as agonistic activities. This review focuses on the existing marine organisms that are able to interfere with QS with potential application for aquaculture as bacterial control.

SNP detection in Na/K ATP-ase gene α1 subunit of bisexual and parthenogenetic Artemia strains by RFLP screening

In order to find a marker for differentiating between a bisexual and a parthenogenetic Artemia strain, Exon-7 of the Na/K ATPase α(1) subunit gene was screened by RFLP technique. The results revealed a constant synonymous SNP (single nucleotide polymorphism) in digestion by the Tru1I enzyme that was consistent with these two types of Artemia. This SNP was identified as an accurate molecular marker for discrimination between bisexual and parthenogenetic Artemia. According to the Nei's genetic distance (1973), the lowest genetic distance was found between individuals from Artemia urmiana Günther 1890 and parthenogenetic populations, making the described marker the first marker to easily distinguish between these two cooccurring species.

Investigation into the possible natural occurence of semicarbazide in Macrobrachium rosenbergii prawns

In the past year there has been an increased incidence in Belgium of cases of positive semicarbazide (SEM) tests in imported freshwater Macrobrachium rosenbergii prawns, seemingly indicating the possible abuse of nitrofurazone, a banned antimicrobial agent. This was in contrast to all other European countries where no significant increase in SEM-positive samples was detected. A possible explanation for this discrepancy between Belgium and the other European Union member states could be the fact that only in Belgium were whole prawns (meat + shell) analyzed for the presence of tissue-bound metabolites of nitrofurans, whereas in the other countries only the edible part (meat) of these prawns was analyzed. To investigate the possible natural occurrence of SEM in freshwater prawns, an animal trial was set up. In this experiment two groups of 10 juvenile M. rosenbergii, previously raised under standardized laboratory conditions, were stocked into two separate aquaria, a control group under reference conditions (no addition of nitrofurazone) and a group exposed to a daily dose of 50 mg of nitrofurazone L(-1) of culture water. Results of this animal trial proved that SEM naturally occurs in M. rosenbergii prawns but that at the current minimum required performance limit (MRPL) no tissue-bound SEM can be found in the meat of nontreated animals. In addition to this animal trial, commercial samples of other crustacean species, the shell and meat of which were analyzed separately, were also analyzed for the presence of SEM.

Efficacy of heterologous and homologous heat shock protein 70s as protective agents to Artemia franciscana challenged with Vibrio campbellii

The Hsp70 class of heat shock proteins (Hsps) has been implicated at multiple points in the immune response of both vertebrates and invertebrates. This class of chaperones is highly conserved in both sequence and structure, from prokaryotes to higher eukaryotes. In view of their high degree of homology, it was assumed that these Hsp70 proteins derived either from the prokaryotes or eukaryotes would have similar functions, especially in relation to their protective ability in a challenge assay. To verify this, we compared two evolutionary diverse Hsp70s, Artemia Hsp70 and Escherichia coli Hsp70 equivalent DnaK (each overproduced in E.coli), for their ability to protect Artemia against Vibrio challenge. Results showed that Artemia fed with E. coli producing Artemia Hsp70 or DnaK proteins, as assessed by immune-probing in western blots, survived better in a Vibrio challenge assay. The observed effects could be due to enhancement of the Artemia immune system as phenoloxidase activity was found to be increased by these proteins. These two Hsp70 proteins exhibit a high degree of homology, particularly in the peptide-binding domain (the putative innate immunity-activating portion) with 59.6% identity, indicating that the observed protective capacity of homologous or heterologous Hsp70 proteins might reside within this peptide-binding domain.