Phenoloxidase activity in three commercial bivalve species. Changes due to natural infestation with Perkinsus atlanticus

Glyoxal oxidase-mediated detoxification of reactive carbonyl species contributes to virulence, stress tolerance, and development in a pathogenic fungus

Reactive carbonyl and oxygen species (RCS/ROS), often generated as metabolic byproducts, particularly under conditions of pathology, can cause direct damage to proteins, lipids, and nucleic acids. Glyoxal oxidases (Gloxs) oxidize aldehydes to carboxylic acids, generating hydrogen peroxide (H2O2). Although best characterized for their roles in lignin degradation, Glox in plant fungal pathogens are known to contribute to virulence, however, the mechanism underlying such effects are unclear. Here, we show that Glox in the insect pathogenic fungus, Metarhizium acridum, is highly expressed in mycelia and during formation of infection structures (appressoria), with the enzyme localizing to the cell membrane. MaGlox targeted gene disruption mutants showed RCS and ROS accumulation, resulting in cell toxicity, induction of apoptosis and increased autophagy, inhibiting normal fungal growth and development. The ability of the MaGlox mutant to scavenge RCS was significantly reduced, and the mutant exhibited increased susceptibility to aldehydes, oxidative and cell wall perturbing agents but not toward osmotic stress, with altered cell wall contents. The ΔMaGlox mutant was impaired in its ability to penetrate the host cuticle and evade host immune defense resulting in attenuated pathogenicity. Overexpression of MaGlox promoted fungal growth and conidial germination, increased tolerance to H2O2, but had little to other phenotypic effects. Transcriptomic analyses revealed downregulation of genes related to cell wall synthesis, conidiation, stress tolerance, and host cuticle penetration in the ΔMaGlox mutant. These findings demonstrate that MaGlox-mediated scavenging of RCS is required for virulence, and contributes to normal fungal growth and development, stress resistance.

Probiotics from kefir: Evaluating their immunostimulant and antioxidant potential in the carpet shell clam (Ruditapesdecussatus)

This study aimed to investigate the impact of incorporating kefir into the diet on biometric parameters, as well as the immune and antioxidant responses of the carpet shell clam (Ruditapes decussatus) after an experimental infection by Vibrio alginolyticus. Clams were divided into a control group and a treated group. The control group was fed on spirulina (Arthrospira platensis) alone. While, the treated group was fed on spirulina supplemented with 10% dried kefir. After 21 days, clams were immersed in a suspension of V. alginolyticus 5 × 105 CFU mL -1 for 30 min. Seven days after experimental infection, survival was 100% in both groups. The obtained results showed a slight increase in weight and condition index in clams fed with kefir-supplemented diet for 21 days compared to control clams. Regarding antioxidant responses, the treated group showed higher superoxide dismutase activity compared to the control group. However, the malondialdehyde level was lower in the treated clams than in the control. In terms of immune parameters, the treated group showed slightly elevated activities of phenoloxidase, lysozyme and alkaline phosphatase, whereas a decreased lectin activity was observed compared to the control group. The obtained results suggest that kefir enhanced both the antioxidant and immune response of infected clams.

Comparative study of immunological biomarkers in the carpet shell clams (Ruditapes decussatus) from metal-contaminated sites in the South Lagoon of Tunis (Tunisia)

The South Lagoon of Tunis (Tunisia) is a Mediterranean lagoon adversely affected by industrial contaminants, harbour activity and untreated urban sewage. In this lagoon, the clam Ruditapes decussatus has been widely used as a biomonitor of seawater pollution through measurements of parameters related to oxidative stress and neurotoxicity. However, few studies have considered parameters of the immune system of this species in the South Lagoon of Tunis. Therefore, the aim of the present work was to evaluate several immune-related parameters in the cell-free haemolymph of carpet shell clams sampled during August and February from three polluted sites in the South Lagoon of Tunis (S1, S2 and S3) and one less polluted site as a reference site (RS) in order to identify suitable biomarkers for environmental quality assessments of this ecosystem. Concerning the immune-related parameters, seasonal factors modulated phenoloxidase, lysozyme, protease and esterase activity, with lower values measured for samples collected in August than for samples collected in February. In fact, bactericidal activity against two of the pathogenic bacteria tested and the activity of most immune-related enzymes were reduced in the cell-free haemolymph of clams collected from the most sampling sites in August compared to February one. In addition, values of abiotic parameters (temperature, salinity and pH) and metal (cadmium, copper, iron, lead and zinc) concentrations in the clams' soft tissues, previously obtained and published by the authors, as well as the values of immune-related parameters were integrated using principal component analyses. Results indicated that the values of all measured immune-related parameters were negatively correlated with the temperature values and the variations most of these parameters highlighted that the chemical industrial area (S3) was the most impacted location within the South Lagoon of Tunis. The present study illustrates that the immune-related parameters measured in carpet shell clam cell-free haemolymph represent suitable biomarkers for environmental quality assessments because they provide effective seasonal and spatial discrimination.

A multi-biomarker approach to assess toxicity of diclofenac and 4-OH diclofenac in Mytilus trossulus mussels - First evidence of diclofenac metabolite impact on molluscs

Although the presence of pharmaceuticals in the environment is an issue widely addressed in research over the past two decades, still little is known about their transformation products. However, there are indications that some of these chemicals may be equally or even more harmful than parent compounds. Diclofenac (DCF) is among the most commonly detected pharmaceuticals in the aquatic environment, but the potential effects of its metabolites on organisms are poorly understood. Therefore, the present study aimed to evaluate and compare the toxicity of DCF and its metabolite, 4-hydroxy diclofenac (4-OH DCF), in mussels using a multi-biomarker approach. Mytilus trossulus mussels were exposed to DCF and 4-OH DCF at 68.22 and 20.85 μg/L (measured concentrations at day 0), respectively, for 7 days. In our work, we showed that both tested compounds have no effect on most of the enzymatic biomarkers tested. However, it has been shown that their action can affect the protein content in gills and also be reflected through histological markers. ENVIRONMENTAL IMPLICATION: Studies in recent years clearly prove that pharmaceuticals can negatively affect aquatic organisms. In addition to parent compounds, metabolites of pharmaceuticals can also be a significant environmental problem. In the present work, the effects of diclofenac and its main metabolite, 4-hydroxy diclofenac, on marine mussels were evaluated. Both compounds showed negative effects on mussels, which was primarily observed through histological changes. The present study therefore confirms that not only diclofenac, but also its main metabolite can have negative effects on aquatic organisms.

Two-sided effects of prolonged hypoxia and sulfide exposure on juvenile ark shells (Anadara broughtonii)

Oxygen deficit and sulfide have been restrictive factors in mariculture zones. However, the adaptive mechanism in aquatic lives is still unclear. The commercial ark shells Anadara broughtonii were selected to test the tolerance and adaptive responses to prolonged and intermittent hypoxia with or without exogenous sulfide (mild, moderate, high) by evaluating their behavior, mortality, oxidative level, antioxidant responses, and the MAPK-mediated apoptosis in gills. The results indicated that the clams were tolerant to hypoxia and sulfide exposure but vulnerable during reoxygenation from the challenges. Even so, sulfide had remarkable effect on attenuating the accumulation of reactive oxygen species (ROS) and lipid peroxides caused by reoxygenation from prolonged hypoxia. The increase of glutathione level was probably as an early and primary protective response to prevent the expected reperfusion injury from reoxygenation. The challenges suppressed the oxidative level with a dose-dependent effect of sulfide, with an exception when exposed to mild sulfide. Synchronously, biphasic effects of exogenous sulfide on apoptotic cascade, which was induced by mild sulfide while it was inhibited by higher sulfide, were also detected in gills. The induced or inhibited apoptosis by hypoxia and sulfide kept to a typical ROS-MAPK-CASPASE cascade, desiderating further investigation.

Genome-wide identification and expression profiling of TYR gene family in Ruditapes philippinarum under the challenge of Vibrio anguillarum

Tyrosinase (EC1.14.18.1, TYR) is also called phenol oxidase, is not only involved in pigmentation but also plays an important role in modulating innate immunity in invertebrates. Tyrosinase is a copper containing metalloenzyme. The tyrosinase protein has two copper binding sites and three conserved histidines. In this study, 21 tyrosinase genes (RpTYR) were obtained from the whole genome of Ruditapes philippinarum. Their open reading frames were from 951 to 5424 aa, the range of predicted relative molecular weight from 36.72 to 203.81 kDa, and the range of isoelectric point from 4.72 to 9.88. Transcriptome analysis showed that RpTYR gene was expressed specifically in different developmental stages, adult tissues, four strains and two groups with different shell colors. Besides, the expression profiles of 21 RpTYRs were investigated against the immune response of R. philippinarum to a Vibrio challenge. The qPCR results showed that RpTYRs were involved in the immune response of R. philippinarum after Vibrio anguillarum challenge. This study provides preliminary evidence that the tyrosinases genes are involved in the immune defense and the potential immune function of R. philippinarum. Overall, these findings suggested that the expansion of TYR genes may play vital roles in larval development, the formation of shell color pattern, and immune response in R. philippinarum.

An efficient photograph-based quantitative method for assessing castrating trematode parasites in bivalve molluscs

Parasitic castration of bivalves by trematodes is common, and may significantly reduce the reproductive capacity of ecologically important species. Understanding the intensity of infection is desirable, as it can indicate the time that has passed since infection, and influence the host's physiological and reproductive response. In addition, it is useful to know the developmental stage of the trematode, to understand trematode population trends and reproductive success. However, most existing methods (e.g. visually estimating the degree of infection) to assess intensity are approximate only and not reproducible. Here, we present a method to accurately quantify the percentage of bivalve gonad filled with digenean trematode tissue, based on small squashes of gonad tissue rapidly photographed under light microscopy. A maximum of 15 photographs is required to determine the percentage of the whole gonad occupied by trematodes with a minimum of 90% confidence, with smaller mussels requiring fewer. In addition, the stage of trematode infection can be assessed because full sporocysts, spent sporocysts and free cercariae are clearly distinguishable. Although variation exists in the distribution of trematodes in gonad tissue, and thus in the estimate of percentage of the gonad filled with trematodes, this method represents a marked improvement on current coarse assessments of infection which typically focus on binary presence/absence measures. This technique can be used to facilitate a more sophisticated understanding of host–parasite interactions in bivalves, and can inform the conservation and reproductive biology of environmentally crucial species.

HPLC characterization of molluscicidal component of Tamarindus indica and its mode of action on nervous tissue of Lymnaea acuminata

BACKGROUND

Fasciolosis is a water-borne disease with gastropods snail (Lymnaea acuminata) act as key-link is still burden for mankind especially in developing countries. Snail control is one of the important tools to trim down the frequency of fasciolosis.

OBJECTIVE

To evaluate the toxic effect and inhibitory potential of plant Tamarindus indica and their active constituent on the key enzyme of nervous tissue of snail L. acuminata.

METHOD

The present study deals with the chromatographic isolation and identification of molluscicidal component from Tamarindus indica bark and its effects on enzymes activities of vector snail L. acuminata.

RESULT

The toxicity study reveals that among all organic extract ethanol extract of T. indica bark (96 h LC50:127.4 mgL-1) was more effective than other organic extracts. The 96 h LC50 of column purified fraction of T. indica bark was 13.78 mgL-1 respectively. Saponin was isolated, characterized and identified as active molluscicidal component in the bark of T. indica by column chromatography, TLC and HPLC chromatographic methods. The in vivo and in vitro treatment of column purified fraction and saponin has significant inhibition in enzyme AChE, ACP and ALP activities. The study of inhibition kinetics indicates that inhibition of AChE and ALP is competitive, while ACP is uncompetitive in both the treatments.

CONCLUSION

Thus inhibition of these enzyme activities by T. indica bark column purified fraction and saponin in the snail L. acuminata may be the cause of its molluscicidal activity which leads snail death.

Disruption of an adenylate-forming reductase required for conidiation, increases virulence of the insect pathogenic fungus Metarhizium acridum by enhancing cuticle invasion

BACKGROUND

Metarhizium acridum, is a specific acridid pathogen developed for use against the migratory locust (Locusta migratoria manilensis). Adenylate-forming reductases (AFRs) include enzymes that are involved in natural product biosynthesis. Here, we genetically characterize the functions of a class IV AFR in M. acridum (MaAfr^IV ) on fungal development and virulence.

RESULTS

Gene expression analyses indicated MaAfr^IV was induced on locust wings early during the infection process. Surprisingly, loss of MaAfr^IV increased virulence (25.20% decrease in the median lethal time) against the locust in topical bioassays but was no different than the wild type when the cuticle was bypassed by direct infection of conidia into the insect hemocoel. Virulence markers including protease (Pr1) expression and appressorial turgor pressure were higher in the mutant than the parent strain. No difference was seen in the expression of host immune genes (Toll pathway) or in polyphenol oxidase (PPO) activity in locusts infected by the ΔMaAfr^IV or wild type strains. However, the ΔMaAfr^IV strain was unable to successfully sporulate on dead cadavers.

CONCLUSION

Disruption of MaAfr^IV increased fungal virulence by promoting insect cuticle invasion without altering host immune response or fungal immune evasion. Although loss of MaAfr^IV conferred an apparent benefit to the fungus in terms of enhanced virulence, a significant trade-off was seen in the inability of the fungus to sporulate on the cadaver. As conidiation on the cadaver is essential for subsequent propagation in the environment, loss of MaAfr^IV can reduce the engineering strains survivability in the field and improve the safety. © 2019 Society of Chemical Industry.

Comparison of viability and phagocytic responses of hemocytes withdrawn from the bivalves Mytilus edulis and Dreissena polymorpha, and exposed to human parasitic protozoa

Bivalve molluscs are now considered indicator species of aquatic contamination by human parasitic protozoa. Nonetheless, the possible effects of these protozoa on the immune system of their paratenic hosts are poorly documented. The aim of this study was to evaluate the effects of two protozoa on hemocyte viability and phagocytosis from two mussels, the zebra mussel (freshwater habitat) and the blue mussel (seawater habitat). For these purposes, viability and phagocytic markers have been analysed on hemocytes from mussels without biological stress (control hemocytes), and on hemocytes exposed to a biological stress (Toxoplasma gondii and Cryptosporidium parvum oocysts). We report, for the first known time, the interactions between protozoa and hemocytes of mussels from different aquatic environments. Zebra mussel hemocytes showed a decrease in phagocytosis of fluorescent microbeads after exposure to both protozoa, while blue mussel hemocytes reacted only to T. gondii oocysts. These decreases in the ingestion of microbeads can be caused by competition between beads and oocysts and can be influenced by the size of the oocysts. New characterisations of their immune capacities, including aggregation, remain to be developed to understand the specificities of both mussels.

Ralstonia eutropha, containing high poly-β-hydroxybutyrate levels, regulates the immune response in mussel larvae challenged with Vibrio coralliilyticus

Marine invertebrates rely mainly on innate immune mechanisms that include both humoral and cellular responses. Antimicrobial peptides (AMPs), lysozyme and phenoloxidase activity, are important components of the innate immune defense system in marine invertebrates. They provide an immediate and rapid response to invading microorganisms. The impact of amorphous poly-β-hydroxybutyrate (PHB-A) (1 mg PHB-A L^-1) on gene expression of the AMPs mytimycin, mytilinB, defensin and the hydrolytic enzyme lysozyme in infected blue mussel larvae was investigated during "in vivo" challenge tests with Vibrio coralliilyticus (10⁵ CFU mL^-1). RNAs were isolated from mussel larvae tissue, and AMPs were quantified by q-PCR using the 18srRNA gene as a housekeeping gene. Our data demonstrated that AMPs genes had a tendency to be upregulated in challenged mussel larvae, and the strongest expression was observed from 24 h post-exposure onwards. The presence of both PHB-A and the pathogen stimulated the APMs gene expression, however no significant differences were noticed between treatments or between exposure time to the pathogen V. coralliilyticus. Looking at the phenoloxidase activity in the infected mussels, it was observed that the addition of PHB-A significantly increased the activity.

Gene expression analysis of Ruditapes philippinarum haemocytes after experimental Perkinsus olseni zoospore challenge and infection in the wild

The production of Manila clam (Ruditapes philippinarum) is seriously threatened by the protistan parasite Perkinsus olseni. We characterized and compared gene expression of Manila clam haemocytes in response to P. olseni in a time-course (10 h, 24 h, 8 d) controlled laboratory challenge (LC), representing the first step of infection, and in a more complex infection in the wild (WI), using a validated oligo-microarray containing 11,232 transcripts, mostly annotated. Several immune-genes involved in NIK/NF-kappaB signalling, Toll-like receptor signalling and apoptosis were activated at LC-10 h. However, down-regulation of genes encoding lysozyme, histones, cathepsins and heat shock proteins indicated signals of immunodepression, which persisted at LC-24 h, when only down-regulated genes were detected. A rebound of haemocyte activity occurred at LC-8 d as shown by up-regulation of genes involved in cytoskeleton organization and cell survival. The WI study showed a more complex picture, and several immune-relevant processes including cytoskeleton organization, cell survival, apoptosis, encapsulation, cell redox- and lipid-homeostasis were activated, illustrating the main mechanism of host response. Our results provide useful information, including potential biomarkers, to develop strategies for controlling Manila clam perkinsosis.

Recent findings on phenoloxidases in bivalves

The production of melanin is a complex process involving biochemical cascades, such as the pro-phenoloxidase (proPO) system, and enzymes, such as phenoloxidases (POs). Different studies have shown a strong correlation between the decrease in PO activities and the occurrence of diseases in bivalve invertebrates, leading to mortalities in the host. Results of these studies suggest that POs could play a fundamental role in defense mechanisms in bivalves. This article reviews the fundamental knowledge on the proPO system in bivalves and the methods used to assess PO activities. Finally, this is the first report on the major findings of laboratory and field studies that indicate that a type of PO in bivalves, the laccase enzyme, is inducible and involved in the 1) immune 2) antioxidant and 3) detoxification roles in bivalves, and might be an ecological potential biomarker of environmental stress.

Combination of polycyclic aromatic hydrocarbons and temperature exposure: In vitro effects on immune response of European clam (Ruditapes decussatus)

Marine organisms are subjected to various biotic and abiotic factors such as changes of temperature and pollutants [e.g. polycyclic aromatic hydrocarbons (PAHs), polychlorinated biphenyls (PCBs), and heavy metals, which may affect their defense mechanisms. In this context, the aim was to evaluate the combined effects of temperature (20 and 30 °C) and PAHs (fluorene, phenanthrene and pyrene) at two concentrations (10^-5 and 10^-3 mg mL^-1) on the immune responses of the European clam Ruditapes decussatus were after 24 h of in vitro exposure. Total haemocyte count, cell viability, phenoloxidase, lysozyme, alkaline phosphatase, esterase, antibacterial and agglutinating activities were measured. Exposure to high temperatures resulted in lower phosphatase alkaline activity and higher haemocyte viability and antibacterial and haemagglutinating activities, compared with the values recorded for clams maintained at low temperature. Only pyrene induced a significant decrease in haemocyte lysozyme (at 20 and 30 °C) and esterase (at 30 °C) activities. The total haemocyte count was increased by phenanthrene and pyrene at 20 °C and at 30 °C, respectively. Alkaline phosphatase activity increased when haemocytes were exposed to pyrene at 30 °C but decreased in the presence of fluorene at 20 °C. Furthermore, haemocyte viability was low in the presence of pyrene and fluorene at 20 °C and 30 °C, respectively, but was unaffected by phenanthrene. Antibacterial activity was significantly increased and no-significantly affected by the presence of pyrene and fluorene at 20 °C and 30 °C, respectively. The present study demonstrates the strong effect of PAHs and high temperature on haemocyte viability and other important immune functions, including phosphatase alkaline and antibacterial activities. Furthermore, changes in the immune parameters of European clam resulting from high temperatures may modulate the effects of PAHs and vice versa.

Natural selection on immune defense: A field experiment

Predicting the evolution of phenotypic traits requires an understanding of natural selection on them. Despite its indispensability in the fight against parasites, selection on host immune defense has remained understudied. Theory predicts immune traits to be under stabilizing selection due to associated trade-offs with other fitness-related traits. Empirical studies, however, report mainly positive directional selection. This discrepancy could be caused by low phenotypic variation in the examined individuals and/or variation in host resource level that confounds trade-offs in empirical studies. In a field experiment where we maintained Lymnaea stagnalis snails individually in cages in a lake, we investigated phenotypic selection on two immune defense traits, phenoloxidase (PO)-like activity and antibacterial activity, in hemolymph. We used a diverse laboratory population and manipulated snail resource level by limiting their food supply. For six weeks, we followed immune activity, growth, and two fitness components, survival and fecundity of snails. We found that PO-like activity and growth were under stabilizing selection, while antibacterial activity was under positive directional selection. Selection on immune traits was mainly driven by variation in survival. The form of selection on immune defense apparently depends on the particular trait, possibly due to its importance for countering the present parasite community.

Activity changes of antioxidant and detoxifying enzymes in Tenebrio molitor (Coleoptera: Tenebrionidae) larvae infected by the entomopathogenic nematode Heterorhabditis beicherriana (Rhabditida: Heterorhabditidae)

Entomopathogenic nematodes (EPNs) of the genera Steinernema and Heterorhabditis are lethal parasites of many insect species. To investigate defensive mechanisms towards EPNs in relation to antioxidative and detoxifying enzymes, we chose Tenebrio molitor (Coleoptera: Tenebrionidae) as experimental insect. We studied the activity changes of superoxide dismutases (SODs), peroxidases (PODs), and catalases (CATs), as well as tyrosinase (TYR), acetylcholinesterase (AChE), carboxylesterase (CarE), and glutathione S-transferase (GSTs) for 40 h in T. molitor larvae infected with Heterorhabditis beicherriana infective juveniles (IJs) at 5 rates (0, 20, 40, 80, and 160 IJs/larva). We found that when T. molitor larvae infected with H. beicherriana at higher rates (80 and 160 IJs/larva), SOD activity quickly increased to more than 70 % higher than that control levels. The activities of POD and CAT increased after 24 h. TYR activity increased slowly at lower rates of infection for 16 h, followed by a slight decrease, and then increasing from 32 to 40 h. The other detoxifying enzymes (GST, CarE, and AChE) were enhanced at lower infection rates, but were inhibited at higher rates. Our results suggested that host antioxidative response and detoxification reactions played a central role in the defensive reaction to EPNs, and that this stress which was reflected by the higher level enzymes activity contributed to the death of hosts. Further study should explore the exact function of these enzymes using different species of EPNs and investigate the links between enzyme activity and host susceptibility to EPNs.

Estimating Genetic and Maternal Effects Determining Variation in Immune Function of a Mixed-Mating Snail

Evolution of host defenses such as immune function requires heritable genetic variation in them. However, also non-genetic maternal effects can contribute to phenotypic variation, thus being an alternative target for natural selection. We investigated the role of individuals' genetic background and maternal effects in determining immune defense traits (phenoloxidase and antibacterial activity of hemolymph), as well as in survival and growth, in the simultaneously hermaphroditic snail Lymnaea stagnalis. We utilized the mixed mating system of this species by producing full-sib families in which each parental snail had produced offspring as both a dam and as a sire, and tested whether genetic background (family) and non-genetic maternal effects (dam nested within family) explain trait variation. Immune defense traits and growth were affected solely by individuals' genetic background. Survival of snails did not show family-level variation. Additionally, some snails were produced through self-fertilization. They showed reduced growth and survival suggesting recessive load or overdominance. Immune defense traits did not respond to inbreeding. Our results suggest that the variation in snail immune function and growth was due to genetic differences. Since immune traits did not respond to inbreeding, this variation is most likely due to additive or epistatic genetic variance.

Immunological properties of oxygen-transport proteins: hemoglobin, hemocyanin and hemerythrin

It is now well documented that peptides with enhanced or alternative functionality (termed cryptides) can be liberated from larger, and sometimes inactive, proteins. A primary example of this phenomenon is the oxygen-transport protein hemoglobin. Aside from respiration, hemoglobin and hemoglobin-derived peptides have been associated with immune modulation, hematopoiesis, signal transduction and microbicidal activities in metazoans. Likewise, the functional equivalents to hemoglobin in invertebrates, namely hemocyanin and hemerythrin, act as potent immune effectors under certain physiological conditions. The purpose of this review is to evaluate the true extent of oxygen-transport protein dynamics in innate immunity, and to impress upon the reader the multi-functionality of these ancient proteins on the basis of their structures. In this context, erythrocyte-pathogen antibiosis and the immune competences of various erythroid cells are compared across diverse taxa.

Evaluation of Functionality and Biological Responses of Mytilus galloprovincialis after Exposure to Quaternium-15 (Methenamine 3-Chloroallylochloride)

Although the irritant effects of quaternium-15 have been established, little is known about the toxicological consequences induced by this xenobiotic on aquatic invertebrates. The present article reports toxicological, histological and physiological effects of quaternium-15 following the exposure of Mytilus galloprovincialis for 18 days at three different concentrations (0.1, 1.0 and 2.0 mg/L). The results demonstrate that at higher concentrations histological damages to M. galloprovincialis gills occur, like melanosis, light exfoliations, increase of mucus production and infiltrative inflammation. In addition digestive gland cells of M. galloprovincialis, were not able to perform the regulation volume decrease (RVD) owing to osmotic stress following the exposure to the preservative. Overall, this first study on quaternium-15 highlights that it can jeopardize both the morphology and vital physiological processes in marine invertebrates, depending on the duration of exposure and the concentration of the preservative, indicating that further studies are necessary to increase our knowledge about the effects of this substance, commonly added to our products of daily use.

Immune responses to infectious diseases in bivalves

Many species of bivalve mollusks (phylum Mollusca, class Bivalvia) are important in fisheries and aquaculture, whilst others are critical to ecosystem structure and function. These crucial roles mean that considerable attention has been paid to the immune responses of bivalves such as oysters, clams and mussels against infectious diseases that can threaten the viability of entire populations. As with many invertebrates, bivalves have a comprehensive repertoire of immune cells, genes and proteins. Hemocytes represent the backbone of the bivalve immune system. However, it is clear that mucosal tissues at the interface with the environment also play a critical role in host defense. Bivalve immune cells express a range of pattern recognition receptors and are highly responsive to the recognition of microbe-associated molecular patterns. Their responses to infection include chemotaxis, phagolysosomal activity, encapsulation, complex intracellular signaling and transcriptional activity, apoptosis, and the induction of anti-viral states. Bivalves also express a range of inducible extracellular recognition and effector proteins, such as lectins, peptidoglycan-recognition proteins, thioester bearing proteins, lipopolysaccharide and β1,3-glucan-binding proteins, fibrinogen-related proteins (FREPs) and antimicrobial proteins. The identification of FREPs and other highly diversified gene families in bivalves leaves open the possibility that some of their responses to infection may involve a high degree of pathogen specificity and immune priming. The current review article provides a comprehensive, but not exhaustive, description of these factors and how they are regulated by infectious agents. It concludes that one of the remaining challenges is to use new "omics" technologies to understand how this diverse array of factors is integrated and controlled during infection.

A review of the immune molecules in the sea cucumber

It is very important to identify and characterize the immune-related genes that respond to pathogens. Until recently, only some of the immune-related genes in sea cucumbers had been characterized. Their expression patterns after pathogen challenges have been analyzed via expressed sequence tag libraries, microarray studies and proteomic approaches. These genes include lectins, antimicrobial peptides, lysozyme, enzymes, clotting protein, pattern recognition proteins, Toll receptors, complement C3 and other humoral factors that might participate in the innate immune system of sea cucumbers. Although the participation of some of these immune molecules in the sea cucumber's innate immune defense against invading pathogens has been demonstrated, the functions of many of the molecules remain unclear. This review focuses on the discovery and functional characterization of the immune-related molecules from the sea cucumber for the first time and provides new insights into the immune mechanisms of the sea cucumber, which opens new possibilities for developing drugs for novel anti-bacterial and antiviral applications in fisheries.

Immune responses of phenoloxidase and superoxide dismutase in the manila clam Venerupis philippinarum challenged with Vibrio tapetis--part II: combined effect of temperature and two V. tapetis strains

Manila clams, Venerupis philippinarum (Adams and Reeve, 1850), were experimentally infected with two different bacterial strains and challenged with two different temperatures. Bacterial strains used in this study were Vibrio tapetis strain CECT4600(T), the causative agent of Brown Ring Disease (BRD) and V. tapetis strain LP2, supposed less virulent to V. philippinarum. V. tapetis is considered to proliferate at low temperatures, i.e. under 21 °C. In a global warming context we could hypothesize a decrease of mass mortalities caused by V. tapetis but these thermal changes could also directly impact the immune system of the host V. philippinarum. Thus, the aim of this study was to investigate the effects of the extrapallial injection with V. tapetis combined with temperature challenge on two enzymes activities in V. philippinarum. More precisely, after infection, phenoloxidase (PO) and superoxide dismutase (SOD), two major enzymes involved in immune response, were studied for 30 days in two compartments: the mantle and the hemolymph. Conchyolin Deposit Stages (CDS) and Shell Repair Stages (SRS) were also determined 30 days post-injection as a proxy of the virulence of the tested strains. In this study, we highlighted that host-pathogen interaction in a varying environment affects the enzymatic response of the host. The coupled effect of V. tapetis injection and temperature challenge was detected 30 days post injection and resulted in virulence differences. These findings were supported by CDS and SRS determination in clams and lead to the conclusion that clam's immunity could be enhanced at 22 °C while V. tapetis virulence is lowered at this temperature. Another result of our study was the increase of PO and SOD basal activities as clams are exposed to warmer temperature.

Parasites infecting the cultured oyster Crassostrea gasar (Adanson, 1757) in Northeast Brazil

The oyster Crassostrea gasar is a species widely used as food and a source of income for the local population of the estuaries of Northeast Brazil. Perkinsus marinus and Perkinsus olseni are deleterious parasites for oyster farming and were recently detected in Brazil. In this study, a histopathologic survey of the oyster C. gasar cultured in the estuary of the River Mamanguape (Paraíba State) was performed. Adult oysters were collected in December 2011 and March, May, August and October 2012 and processed for histology and Perkinsus sp. identification by molecular analyses. Histopathological analysis revealed the presence of parasitic organisms including viral gametocytic hypertrophy, prokaryote-like colonies, protozoans (Perkinsus sp. and Nematopsis sp.) and metazoans (Tylocephalum sp. and cestodes). Other commensal organisms were also detected (the protozoan Ancistrocoma sp. and the turbellarian Urastoma sp.). The protozoan parasite Perkinsus sp. had the highest overall prevalence among the symbiotic organisms studied (48·9%), followed by Nematopsis sp. (36·3%). The other organisms were only sporadically observed. Only the protozoan Perkinsus sp. caused alterations in the oysters’ infected organs. Molecular analyses confirmed the presence of P. marinus, P. olseni and Perkinsus beihaiensis infecting the oyster C. gasar. This is the first report of P. beihaiensis in this oyster species.

Infectious microbial diseases and host defense responses in Sydney rock oysters

Aquaculture has long been seen as a sustainable solution to some of the world's growing food shortages. However, experience over the past 50 years indicates that infectious diseases caused by viruses, bacteria, and eukaryotes limit the productivity of aquaculture. In extreme cases, these types of infectious agents threaten the viability of entire aquaculture industries. This article describes the threats from infectious diseases in aquaculture and then focuses on one example (QX disease in Sydney rock oysters) as a case study. QX appears to be typical of many emerging diseases in aquaculture, particularly because environmental factors seem to play a crucial role in disease outbreaks. Evidence is presented that modulation of a generic subcellular stress response pathway in oysters is responsible for both resistance and susceptibility to infectious microbes. Understanding and being able to manipulate this pathway may be the key to sustainable aquaculture.

Characterization of phenoloxidase from the sea cucumber Apostichopus japonicus

Phenoloxidase (PO) is a crucial immune-related enzyme in invertebrates. In this study, three POs of the sea cucumber Apostichopus japonicus were detected in coelomic fluid using linear-gradient native-PAGE combined with catechol staining and then partially purified by gel excising. The results showed that the three POs had a color of mahogany (AjPO1), yellow (AjPO2) and purple (AjPO3) respectively with molecular weights smaller than 21kDa in native-PAGE after staining with catechol. Enzymatic activities analysis revealed that AjPO1, AjPO2 and AjPO3 had optimal temperature of 45, 95 and 85°C and pH of 5.0, 8.0 and 8.0, respectively. Kinetic analysis showed that the Km values of AjPO1 for catechol, l-DOPA, dopamine and hydroquinone were 3.23, 0.86, 3.98 and 1.20mmol/l, respectively, those of AjPO2 were 0.31, 0.38, 2.05 and 1.30mmol/l, respectively, and those of AjPO3 were 5.95, 1.28, 5.81 and 0.62mmol/l, respectively. These results suggest that the three POs are laccase-type phenoloxidase. The activities of all three A. japonicus POs were significantly promoted by Ca(2+), Mg(2+) and Mn(2+), and strongly inhibited by ethylenediamine tetraacetic acid disodium (EDTA), sodium diethyldithiocarbamate (DETC) and some common antioxidants. The inhibitions by EDTA and DETC suggest that the three A. japonicus POs are copper-containing metalloenzymes. Immune-responsive analysis showed that the total PO activities in coelomocytes (TPAC) increased greatly after lipopolysaccharide (LPS) challenge and declined significantly after polyinosinic-polycytidylic acid (PolyI:C) challenge, implying that A. japonicus PO immune system, which is composed of several isoenzymes with different characteristics, is closely involved in the defense against the infection of Gram-negative bacteria and double-stranded RNA viruses.

Phenoloxidase from the sea cucumber Apostichopus japonicus: cDNA cloning, expression and substrate specificity analysis

Phenoloxidase (PO) is a crucial component of the immune system of echinoderms. In the present study, the full-length cDNA of PO (AjPO) was cloned from coelomocytes of the sea cucumber Apostichopus japonicus using 3'- and 5'-rapid amplification of cDNA ends (RACE) PCR method, which is 2508 bp, with an open reading frame (ORF) of 2040 bp encoding 679 amino acids. AjPO contains a transmembrane domain, and three Cu-oxidase domains with copper binding centers formed by 10 histidines, one cysteine and one methionine respectively. Phylogenetic analysis revealed that AjPO was clustered with laccase-type POs of invertebrates. Using the isolated membrane proteins as crude AjPO, the enzyme could catalyze the substrates catechol, L-3,4-dihydroxyphenylalanine (L-DOPA), dopamine and hydroquinone, but failed to oxidize tyrosine. The results described above collectively proved that AjPO was a membrane-binding laccase-type PO. The quantitative real-time PCR (qRT-PCR) analysis revealed that AjPO mRNA was expressed in muscle, body wall, coelomocytes, tube feet, respiratory tree and intestine with the highest expression level in coelomocytes. AjPO could be significantly induced by lipopolysaccharide (LPS), peptidoglycan (PGN), Zymosan A and polyinosinic-polycytidylic acid (PolyI:C), suggesting AjPO is closely involved in the defense against the infection of bacteria, fungi and double-stranded RNA viruses.

Activation of the immune defence of the freshwater snail Lymnaea stagnalis by different immune elicitors

Understanding the outcomes of host-parasite interactions in nature is in high demand as parasites and pathogens are important for several ecological and evolutionary processes. Ecological immunology (ecoimmunology) has a key role in reaching this goal because immune defence is the main physiological barrier against infections. To date, ecoimmunological studies largely lean on measuring constitutive immune defences (components of defence that are always active). However, understanding the role of inducible components of immune function is important as the immune system is largely an inducible defence. Measuring such defences can be complicated as different parasites may activate different immune cascades, and expression of different immune traits may not be independent. We examined the suitability of different immune activation techniques for the freshwater snail Lymnaea stagnalis. By experimentally challenging snails with different immune elicitors [injection with snail saline (i.e. wounding), lyophilized Escherichia coli cells, lyophilized Micrococcus lysodeikticus cells, healthy snail gonad, and trematode-infected snail gonad; maintenance in microorganism-enriched water] and measuring phenoloxidase-like and antibacterial activity of their haemolymph, we found increased immune activity against some immune elicitors, but also decreased activity. Our findings suggest potentially complicated relationships among immune traits, and propose suitable techniques for ecological studies in this study system.

Laccase-like activity in the hemolymph of Venerupis philippinarum: characterization and kinetic properties

The phenoloxidases (POs) include tyrosinases (EC 1.14.18.1), catecholases (EC 1.10.3.1) and laccases (EC 1.10.3.2) and are known to play a role in the immune defences of many invertebrates. For the Manila clam, Venerupis philippinarum, the exact role is not known, especially with regard to defences against Brown Ring Disease (BRD), which leads to high mortalities along European coasts. In order to understand the role and functioning of PO in V. philippinarum, the first step, and aim of this study, was to biochemically characterize the PO activity in the circulating hemolymph. Various substrates were tested and the common PO substrates L-DOPA, Catechol and dopamine exhibited good affinity with the enzyme and consequent low K(m) values (3.75, 1.97, 4.91 mM, respectively). A single tyrosinase-specific substrate, PHPPA, was oxidized, but the affinity for it was low (K(m) = 47.33 mM). Three tested laccase-specific substrates were oxidized by V. philippinarum PO (PPD, OPD and hydroquinone) and affinity was higher than for PHPPA. The results obtained with the substrate were confirmed by the use of different inhibitors: CTAB, a laccase-specific inhibitor inhibited PO activity greatly but not completely, whereas 4-Hr, specific to catecholases and tyrosinases, inhibited PO activity to a lesser extent. The results lead us to conclude that V. philippinarum PO activity in the circulating hemolymph, is mainly a laccase-like activity but there is also a smaller-scale tyrosinase-like activity. The inhibition mechanisms were also determined using dose-response substrate concentration for an inhibitor concentration equal or close to the IC50. Optimal conditions for the enzyme activity were also determined using L-DOPA as substrate, showing that its optimal temperature and pH are around 40 °C and 8.4 respectively. The enzyme is denatured for temperatures above 50 °C.

Shell colour polymorphism, injuries and immune defense in three helicid snail species, Cepaea hortensis, Theba pisana and Cornu aspersum maximum

Shell colour polymorphism is a widespread feature of various land snail species. In our study we aimed at elucidating the question whether there is a correlation between shell colouration and immune defense in three land snail species by comparing phenoloxidase (PO) activity levels of different morphs after immunostimulation via Zymosan A-injection. Since phenoloxidase is involved both in immune defense as well as in melanin production, the PO activity level is particularly interesting when trying to resolve this question. Even though Zymosan A failed to induce PO activity rendering a comparison of inducible PO activity impossible, an interesting difference between pale and dark morphs of all tested species could be observed: dark snails were less affected by hemolymph withdrawal and were able to maintain or regenerate a significantly higher PO activity level after hemolymph withdrawal than pale snails. Possible implications of this observation are discussed.

Sequencing and characterization of striped venus transcriptome expand resources for clam fishery genetics

Background

The striped venus Chamelea gallina clam fishery is among the oldest and the largest in the Mediterranean Sea, particularly in the inshore waters of northern Adriatic Sea. The high fishing pressure has lead to a strong stock abundance decline, enhanced by several irregular mortality events. The nearly complete lack of molecular characterization limits the available genetic resources for C. gallina. We achieved the first transcriptome of this species with the aim of identifying an informative set of expressed genes, potential markers to assess genetic structure of natural populations and molecular resources for pathogenic contamination detection.

Methodology/Principal Findings

The 454-pyrosequencing of a normalized cDNA library of a pool C. gallina adult individuals yielded 298,494 raw reads. Different steps of reads assembly and filtering produced 36,422 contigs of high quality, one half of which (18,196) were annotated by similarity. A total of 111 microsatellites and 20,377 putative SNPs were identified. A panel of 13 polymorphic transcript-linked microsatellites was developed and their variability assessed in 12 individuals. Remarkably, a scan to search for contamination sequences of infectious origin indicated the presence of several Vibrionales species reported to be among the most frequent clam pathogen's species. Results reported in this study were included in a dedicated database available at http://compgen.bio.unipd.it/chameleabase.

Conclusions/Significance

This study represents the first attempt to sequence and de novo annotate the transcriptome of the clam C. gallina. The availability of this transcriptome opens new perspectives in the study of biochemical and physiological role of gene products and their responses to large and small-scale environmental stress in C. gallina, with high throughput experiments such as custom microarray or targeted re-sequencing. Molecular markers, such as the already optimized EST-linked microsatellites and the discovered SNPs will be useful to estimate effects of demographic processes and to detect minute levels of population structuring.

The phenoloxidase activity and antibacterial function of a tyrosinase from scallop Chlamys farreri

Tyrosinase (TYR), also known as monophenol monooxygenase, is a ubiquitous binuclear copper-containing enzyme which catalyzes the hydroxylation of phenols to catechols and the oxidation of catechols to quinones. In the present study, the cDNA of a tyrosinase (CfTYR) was identified from scallop Chlamys farreri, which encoded a polypeptide of 486 amino acids. The CfTYR mRNA transcripts were expressed in all the tested tissues, including haemocytes, adductor muscle, kidney, hepatopancreas, gill, gonad and mantle, with the highest level in mantle. The expression level of CfTYR mRNA in haemocytes decreased significantly during 3-6 h after LPS stimulation, and reached the lowest level at 6 h (0.05-fold, P < 0.05). Then, it began to increase at 12 h (0.32-fold, P > 0.05), and reached the highest level at 24 h (2.91-fold, P < 0.05). At 3 h after LPS stimulation, the phenoloxidase activity catalyzing L-dopa and dopamine in haemolymph increased significantly to 53.13 and 40.36 U mg(-1) respectively, but it decreased to 10.82 U mg(-1) and even undetectable level after CfTYR activity was inhibited. Furthermore, the antibacterial activity of haemolymph against Escherichia coli was also increased significantly at 3 h after LPS stimulation, but it decreased significantly when the haemolymph was treated by TYR inhibitor. The recombinant protein of the mature CfTYR peptide expressed in the in vitro Glycoprotein Expression Kit displayed phenoloxidase activity of 64.36 ± 5.51 U mg(-1) in the present of trypsinase and Cu(2+). These results collectively suggested that CfTYR was a homologue of tyrosinase in scallop C. farreri with the copper-dependence phenoloxidase activity, and it could be induced after immune stimulation and mediate immune response for the elimination of invasive pathogens in scallop.

Phenoloxidase in the scallop Chlamys farreri: purification and antibacterial activity of its reaction products generated in vitro

Phenoloxidase (PO) was purified from hemocytes of the scallop Chlamys farreri using native-PAGE and gel permeation column chromatography, and then substrate specificity and antibacterial activity generated from reaction products of purified PO were analyzed. The results showed purified PO had a molecular mass of 576 kDa in native-PAGE and 53 kDa in denatured PAGE, and could catalyze the substrates L-3,4-dihydroxyphenylalanine (L-DOPA), dopamine, catechol and hydroquinone suggesting it is a type of p-diphenoloxidase. Using dopamine as a substrate, PO reaction products significantly inhibited the growth of Vibrio alginolyticus, Vibrio parahaemolyticus and Aeromonas salmonicida. No significant inhibition was found in Streptococcus dysgalactiae, Streptococcus iniae, Micrococcus lysodeikticus and Edwardsiella tarda. When L-DOPA was used as a substrate, significant inhibition occurred in A. salmonicida only.

Short-term physiological effects of a xenobiotic mixture on the freshwater mussel Elliptio complanata exposed to municipal effluents

The aim of this study was to investigate the short-term effects of tertiary-treated municipal effluents on the freshwater mussel Elliptio complanata. Caged mussels were immersed during 2 weeks in a river located North of Montreal Island, upstream/downstream the outfall and in one reference site located at the beginning of the Rivière des Prairies. A selection of biomarkers was analyzed to depict changes on various physiological systems: general physiology (mussel viability, condition index and gonado-somatic index), immune status (hemocyte viability, cellularity, phagocytosis efficiency, NK-like cytotoxic activity and lysozyme activity), inflammation (cyclo-oxygenase activity), detoxification (glutathione-S-transferases activity) and vitellogenesis (alkali-labile phosphate level). The analysis of total and fecal coliform counts in water and of heterotrophic bacteria levels in mussel tissues showed that the bacteriological quality of the water strongly decreased from the reference site to the downstream site. This was correlated with a significant loss of weight and an increase of mussel mortality. Cellularity and phagocytosis efficiency were significantly increased in the downstream site compared to the reference site. Though not statistically significant, lysozyme activity was also increased. NK-like cytotoxicity, activity of the pro-inflammatory enzyme COX and the levels of ALP and MT were not significantly changed. Conversely, the municipal effluents induced a significant increase of GST activity in downstream site, indicating a stimulation of detoxification metabolism. Altogether, these results confirm that a short-term exposure to a mixture of bacterial and chemical compounds released by the wastewater treatment plant La Pinière induces adverse physiological effects in E. complanata, as observed with the modulation of immune response and induction of detoxification metabolism.

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.

Maintenance of genetic variation in immune defense of a freshwater snail: role of environmental heterogeneity

Natural populations often show genetic variation in pathogen resistance, which is paradoxal because natural selection is expected to erode genetic variation in fitness-related traits. Several different factors have been suggested to maintain such variation, but their relative importance is still poorly understood. Here we examined if environmental heterogeneity and genetic trade-offs could contribute to the maintenance of genetic variation in immune function of a freshwater snail Lymnaea stagnalis. We assessed the immunocompetence of snails originating from different families and maintained in different feeding treatments (ad libitum feeding, no food) by measuring the density of circulating hemocytes, phenoloxidase activity, and antibacterial activity of snail hemolymph. Food limitation reduced snail immune function, and we found significant among-family variation in hemocyte concentration and PO activity, but not in antibacterial activity. Interestingly, food availability modified the family-level variation observed in PO activity so that the relative immunocompetence of different snail families changed over environmental conditions (G x E interaction). We found no evidence for genetic trade-offs between snail growth and immune defense nor among immune traits. Thus, our findings support the idea that environmental heterogeneity may promote maintenance of genetic variation in immune defense, but also suggest that different immune traits might not respond similarly to environmental variation.

Detection of phenoloxidase activity in early stages of the Pacific oyster Crassostrea gigas (Thunberg)

The presence of phenoloxidase (PO) activity was detected in different developmental stages of the Pacific oyster, Crassostrea gigas. A significant reduction in PO activity was observed from the 6h embryo stage to the day 11 larvae by spectrophotometry. A progressive increase was also observed from the day 13 larvae right through to the juvenile stage. The microscopy studies with '6h embryo' and adult samples confirmed the presence of PO activity. Various modulators of PO activity were used to study the triggering of pro-phenoloxidase (proPO) activating system of C. gigas but also to confirm the exact nature of the monitored activity. The enzyme activation mechanisms appear to differ with the developmental stage: bacterial lipopolysaccharides constitute an early elicitor of the proPO-PO system, whereas a purified trypsin triggers proPO-PO system in C. gigas spat. Phenoloxidase activity was totally suppressed by PO-specific inhibitors such as beta-2-mercaptoethanol, sodium diethyldithiocarbonate and tropolone. This study demonstrated the selective response of PO-like activity by different elicitors and suggested that proPO-PO activating system, which is supposed to play an important function in non-self recognition and host immune reactions in oyster, is expressed early in the Pacific oyster, C. gigas.

Contamination of bivalve haemolymph samples by adductor muscle components: implications for biomarker studies

Haemolymph samples and haemocytes collected via the adductor muscles of bivalve molluscs are extensively used in ecotoxicological studies. Withdrawal of haemolymph from mussels, Mytilus edulis, via the posterior adductor muscle, may lead to contamination with the intracellular contents of adductor myocytes. Lysopine dehydrogenase (LyDH) activity, an adductor myocyte marker, was used to investigate the impact of this potential contamination on levels of total glutathione, glutathione peroxidase (GPx) and acetylcholinesterase (AChE) measured in cell-free haemolymph. The mean glutathione content of cell-free haemolymph from 28 mussels was 3.2 +/- 1.8 microM (mean +/- SD). There was a linear relationship (slope = 0.28 +/- 0.03 min; mean +/- SE; P < 0.0001, n = 28) with haemolymph LyDH levels suggesting that at least some of the glutathione measured in cell-free haemolymph had arisen from contamination. Haemolymph LyDH activity was significantly higher in samples extracted using larger diameter needles, and also in samples where there had been some difficulty in the extraction. Exposure of mussels to oxidative stress using 40 microg l(-1) Cu for 5 days resulted in a 1.7 fold increase in glutathione (P = 0.033), but no increase (P = 0.810) in LyDH activity in adductor muscle. This was reflected in a similar increase in the slope of a plot of cell-free haemolymph glutathione versus LyDH activity (P = 0.011), consistent with both of these having originated from the adductor muscle. Cell-free haemolymph GPx and AChE activities also correlated with LyDH activity (Spearman rank correlation coefficients of 0.531 (P = 0.0068) and 0.537 (P = 0.0062), respectively, n = 27) suggesting that these also arise from contamination of the haemolymph. For GPx there was a significant linear relationship (P = 0.025) with haemolymph LyDH levels consistent with both enzymes originating from the myocytes. However, there was hyperbolic relationship (P = 0.0004) between haemolymph AChE and LyDH activities. It appears that this is because the AChE originates from a different compartment to the LyDH, i.e. cholinergic neuromuscular junctions in the adductor muscle. We conclude that it would be prudent, when considering the possibility of using a biomarker in cell-free haemolymph from bivalve molluscs, to check whether contamination could be an issue.

Evidence of an inflammatory-like response in non-normally pigmented tissues of two scleractinian corals

Increasing evidence of links between climate change, anthropogenic stress and coral disease underscores the importance of understanding the mechanisms by which reef-building corals resist infection and recover from injury. Cellular inflammation and melanin-producing signalling pathway are two mechanisms employed by invertebrates to remove foreign organisms such as pathogens, but they have not been recorded previously in scleractinian corals. This study demonstrates the presence of the phenoloxidase (PO) activating melanin pathway in two species of coral, Acropora millepora and a massive species of Porites, which both develop local pigmentation in response to interactions with a variety of organisms. L-DOPA (3-(3,4-dihydroxyphenyl)-L-alanine) substrate-based enzyme activation assays demonstrated PO activity in healthy tissues of both species and upregulation in pigmented tissues of A. millepora. Histological staining conclusively identified the presence of melanin in Porites tissues. These results demonstrate that the PO pathway is active in both coral species. Moreover, the upregulation of PO activity in areas of non-normal pigmentation in A. millepora and increased melanin production in pigmented Porites tissues suggest the presence of a generalized defence response to localized stress. Interspecific differences in the usage of pathways involved in innate immunity may underlie the comparative success of massive Porites sp. as long-lived stress tolerators.

Variations of enzyme activities in the haemocytes of scallop Chlamys farreri after infection with the acute virus necrobiotic virus (AVNV)

Acute virus necrobiotic virus (AVNV) is one of the main pathogens for large scale mortality of Chinese scallop Chlamys farreri. In this paper, C. farreri were infected by different dilutions of AVNV supernatant (5(0), 5(-1), 5(-2), 5(-3), 5(-4), 5(-5), 5(-6), 5(-7), respectively), and dead individuals were counted every day for 15 days. Samples from groups of 5(-3) and 5(-5) were taken every day till 15 days and the activities of acid phosphatase (ACP), alkaline phosphatase (ALP), superoxide dismutase (SOD), myeloperoxidase (MPO), phenoloxidase (PO), peroxidase (POD) and catalase (CAT) in haemocytes were measured. The results of virus challenge showed that survival rates of scallops in groups of 5(0) and 5(-1) decreased sharply after the first day and died out completely on the 5th and 4th day, respectively. In other groups (5(-2), 5(-3), 5(-4), 5(-5), 5(-6) and 5(-7)), survival rates decreased gradually till 6 or 7 days, then kept steady till 15 days, and they were dose-dependent, increasing from 12% to 80% as the dose decreased from 5(-2) to 5(-7) viral supernatant. In the control group, survival rate was 88%. Enzyme activities for groups of 5(-3) and 5(-5) illustrated that activities of ACP, SOD, MPO, PO in groups of 5(-3) and 5(-5) were significantly higher than the control group in the first 9 or 10 days, and went back to the control group levels gradually after 10 days. Moreover, their activities in group of 5(-3) varied more than that in the group of 5(-5), especially activities of MPO, PO. Differently, the activities of POD and CAT were reduced or induced by virus infection and showed no regular trends in the experiments. The activity of ALP was not detected.

Effects of hypercapnic hypoxia on inactivation and elimination of Vibrio campbellii in the Eastern oyster, Crassostrea virginica

The Eastern oyster, Crassostrea virginica, inhabits shallow coastal waters that frequently experience periods of low dissolved oxygen (hypoxia) and elevated CO(2) (hypercapnia) levels. Bacteria are extremely abundant in these environments and accumulate in large numbers in filter-feeding oysters, which can act as passive carriers of human pathogens. Although hypercapnic hypoxia (HH) can affect certain specific immune mechanisms, its direct effect on the inactivation, degradation and elimination of bacteria in oysters is unknown. This research was conducted to determine whether exposure to HH reduces the ability of C. virginica to inactivate and eliminate Vibrio campbellii following its injection into the adductor muscle. Oysters were held in fully air-saturated (normoxic; partial O(2) pressure [P(O2)] = 20.7 kPa, CO(2) < 0.06 kPa, pH 7.8 to 8.0) or HH (P(O2) = 4 kPa, CO(2) = 1.8 kPa, pH 6.5 to 6.8) seawater at 25 degrees C for 4 h before being injected in the adductor muscle with 10(5) live Vibrio campbellii bacteria and remained under these conditions for the remainder of the experiment (up to 24 h postinjection). Real-time PCR was used to quantify the number of intact V. campbellii bacteria, while selective plating was used to quantify the number of injected bacteria remaining culturable in whole-oyster tissues, seawater, and feces/pseudofeces at 0, 1, 4, and 24 h postinjection. We found that oysters maintained under normoxic conditions were very efficient at inactivating and degrading large numbers of injected bacteria within their tissues. Moreover, a small percentage ( approximately 10%) of injected bacteria were passed into the surrounding seawater, while less than 1% were recovered in the feces/pseudofeces. In contrast, HH increased the percentage of culturable bacteria recovered from the tissues of oysters, suggesting an overall decrease in bacteriostasis. We suggest that poor water quality may increase the risk that oysters will harbor and transmit bacterial pathogens hazardous to human and ecosystem health.

Ecotoxicity of CdTe quantum dots to freshwater mussels: impacts on immune system, oxidative stress and genotoxicity

The purpose of this study was to examine the toxic effects of cadmium-telluride (CdTe) quantum dots on freshwater mussels. Elliption complanata mussels were exposed to increasing concentrations of CdTe (0, 1.6, 4 and 8 mg/L) and cadmium sulfate (CdSO(4), 0.5mg/L) for 24h at 15 degrees C. After the exposure period, they were removed for assessments of immunocompetence, oxidative stress (lipid peroxidation) and genotoxicity (DNA strand breaks). Preliminary experiments revealed that CdTe dissolved in aquarium water tended to aggregate in the particulate phase (85%) while 15% of CdTe was found in the dissolved phase. Immunotoxicity was characterized by a significant decrease in the number of hemocytes capable of ingesting fluorescent beads, and hemocyte viability. The cytotoxic capacity of hemocytes to lyse mammalian K-562 cells was significantly increased, but the number of circulating hemocytes remained unchanged. Lipid peroxidation was significantly increased at a threshold concentration of 5.6 mg/L in gills and significantly reduced in digestive glands at a threshold concentration <1.6 mg/L CdTe. The levels of DNA strand breaks were significantly reduced in gills at <1.6 mg/L CdTe. In digestive glands, a transient but marginal increase in DNA strand breaks occurred at the lowest concentration and dropped significantly at the higher concentrations. A multivariate analysis revealed that the various response patterns differed based on the concentration of CdTe, thus permitting the identification of biomarkers associated with the form (colloidal vs. molecular) of cadmium.