Combination of a pesticide exposure and a bacterial challenge: in vivo effects on immune response of Pacific oyster, Crassostrea gigas (Thunberg)

Histological, biochemical and immunohistochemical assessments of Roundup®, atrazine, and 2,4-D mixtures on tissue architecture, body fluid conditions, nitrotyrosine protein and Na+/K+-ATPase expressions in the American oyster, Crassostera virginica

Pesticides are widely used to control weeds and pests in agricultural settings but harm non-target aquatic organisms. In this study, our objective was to evaluate the effect of short-term exposure (one week) to environmentally relevant concentrations of pesticides mixture (low concentration: 0.4 μg/l atrazine, 0.5 μg/l Roundup®, and 0.5 μg/l 2,4-D; high concentration: 0.8 μg/l atrazine, 1 μg/l Roundup®, and 1 μg/l 2,4-D) on tissue architecture, body fluid conditions, and 3-nitrotyrosine protein (NTP) and Na+/K+-ATPase, expressions in tissues of American oyster (Crassostrea virginica) under controlled laboratory conditions. Histological analysis demonstrated the atrophy in the gills and digestive glands of oysters exposed to pesticides mixture. Periodic acid-Schiff (PAS) staining showed the number of hemocytes in connective tissue increased in low- and high-concentration pesticides exposure groups. However, pesticides treatment significantly (P < 0.05) decreased the amount of mucous secretion in the gills and digestive glands of oysters. The extrapallial fluid (i.e., body fluid) protein concentrations and glucose levels were dropped significantly (P < 0.05) in oysters exposed to high-concentration pesticides exposure groups. Moreover, immunohistochemical analysis showed significant upregulations of NTP and Na+/K+-ATPase expressions in the gills and digestive glands in pesticides exposure groups. Our results suggest that exposure to environmentally relevant pesticides mixture causes morphological changes in tissues and alters body fluid conditions and NTP and Na+/K+-ATPase expressions in tissues, which may lead to impaired physiological functions in oysters.

Propidium monoazide PCR, a method to determine OsHV-1 undamaged capsids and to estimate virus Lethal Dose 50

Ostreid herpes virus 1 (OsHV-1) has been classified within the Malacoherpesviridae family from the Herpesvirales order. OsHV-1 is the etiological agent of a contagious viral disease of Pacific oysters, C. gigas, affecting also other bivalve species. Mortality rates reported associated with the viral infection vary considerably between sites and countries and depend on the age of affected stocks. A variant called μVar has been reported since 2008 in Europe and other variants in Australia and in New Zealand last decade. These variants are considered as the main causative agents of mass mortality events affecting C. gigas. Presently there is no established cell line that allows for the detection of infectious OsHV-1. In this context, a technique of propidium monoazide (PMA) PCR was developed in order to quantify "undamaged" capsids. This methodology is of interest to explore the virus infectivity. Being able to quantify viral particles getting an undamaged capsid (not only an amount of viral DNA) in tissue homogenates prepared from infected oysters or in seawater samples can assist in the definition of a Lethal Dose (LD) 50 and gain information in the experiments conducted to reproduce the viral infection. The main objectives of the present study were (i) the development/optimization of a PMA PCR technique for OsHV-1 detection using the best quantity of PMA and verifying its effectiveness through heat treatment, (ii) the definition of the percentage of undamaged capsids in four different tissue homogenates prepared from infected Pacific oysters and (iii) the approach of a LD50 during experimental viral infection assays on the basis of a number of undamaged capsids. Although the developped PMA PCR technique was unable to determine OsHV-1 infectivity in viral supensions, it could greatly improve interpretation of virus positive results obtained by qPCR. This technique is not intended to replace the quantification of viral DNA by qPCR, but it does make it possible to give a form of biological meaning to the detection of this DNA.

Ancestors' Gift: Parental Early Exposure to the Environmentally Realistic Pesticide Mixture Drives Offspring Phenotype in a Larger Extent Than Direct Exposure in the Pacific Oyster, Crassostrea gigas

Marine organisms are threatened by the presence of pesticides in coastal waters. Among them, the Pacific oyster is one of the most studied invertebrates in marine ecotoxicology where numerous studies highlighted the multiscale impacts of pesticides. In the past few years, a growing body of literature has reported the epigenetic outcomes of xenobiotics. Because DNA methylation is an epigenetic mark implicated in organism development and is meiotically heritable, it raises the question of the multigenerational implications of xenobiotic-induced epigenetic alterations. Therefore, we performed a multigenerational exposure to an environmentally relevant mixture of 18 pesticides (nominal sum concentration: 2.85 μg·L-1) during embryo-larval stages (0-48 hpf) of a second generation (F1) for which parents where already exposed or not in F0. Gene expression, DNA methylation, and physiological end points were assessed throughout the life cycle of individuals. Overall, the multigenerational effect has a greater influence on the phenotype than the exposure itself. Thus, multigenerational phenotypic effects were observed: individuals descending from exposed parents exhibited lower epinephrine-induced metamorphosis and field survival rates. At the molecular level, RNA-seq and Methyl-seq data analyses performed in gastrula embryos and metamorphosis-competent pediveliger (MCP) larvae revealed a clear F0 treatment-dependent discrimination. Some genes implicated into shell secretion and immunity exhibited F1:F0 treatment interaction patterns (e.g., Calm and Myd88). Those results suggest that low chronic environmental pesticide contamination can alter organisms beyond the individual scale level and have long-term adaptive implications.

Inactivation of two oyster pathogens by photocatalysis and monitoring of changes in the microbiota of seawater: A case study on Ostreid herpes virus 1 μVar and Vibrio harveyi

The pollution of seawater by both biotic (bacteria, viruses) and abiotic contaminants (biocides, pharmaceutical residues) frequently leads to economic losses in aquaculture activities mostly mortality events caused by microbial infection. Advanced Oxidation Processes (AOPs) such as heterogeneous photocatalysis allow the removal of all organic contaminants present in water and therefore could reduce production losses in land-based farms. Oysters in land-based farms such as hatcheries and nurseries suffer from a large number of mortality events, resulting in significant losses. If photocatalysis has been widely studied for the decontamination, its application for disinfection is still overlooked, especially on seawater for viruses. We therefore studied seawater disinfection using the photocatalysis (UV365/TiO2) method in the context of Pacific oyster mortality syndrome (POMS). POMS has been defined as a polymicrobial disease involving an initial viral infection with Ostreid Herpes Virus 1, accompanied by multiple bacterial infections. We investigated the impact of treatment on Vibrio harveyi, a unique opportunistic pathogenic bacterium, and on a complex microbial community reflecting a natural POMS event. Viral inactivation was monitored using experimental infections to determine whether viral particles were still infectious after. Changes in the total bacterial community in seawater were studied by comparing UV365/TiO2 treatment with UV365-irradiated seawater and untreated seawater. In the case of OsHV-1, a 2-h photocatalytic treatment prevents POMS disease and oyster mortality. The same treatment also inactivates 80% of viable Vibrio harveyi culture (c.a. 1.5 log). Since OsHV-1 and Vibrio harveyi are effectively inactivated without long-term destabilization of the total bacterial microbiota in the seawater, photocatalysis appears to be a relevant alternative for disinfecting seawater in land-based oyster beds.

The Silent Threat: Exploring the Ecological and Ecotoxicological Impacts of Chlorinated Aniline Derivatives and the Metabolites on the Aquatic Ecosystem

The growing concern over the environmental impacts of industrial chemicals on aquatic ecosystems has prompted increased attention and regulation. Aromatic amines have drawn scrutiny due to their potential to disturb aquatic ecosystems. 4-chloroaniline and 3,4-dichloroaniline are chlorinated derivatives of aniline used as intermediates in the synthesis of pharmaceuticals, dyes, pesticides, cosmetics, and laboratory chemicals. While industrial applications are crucial, these compounds represent significant risks to aquatic environments. This article aims to shed light on aromatic amines' ecological and ecotoxicological impacts on aquatic ecosystems, given as examples 4-chloroaniline and 3,4-dichloroaniline, highlighting the need for stringent regulation and management to safeguard water resources. Moreover, these compounds are not included in the current Watch List of the Water Framework Directive, though there is already some information about aquatic ecotoxicity, which raises some concerns. This paper primarily focuses on the inherent environmental problem related to the proliferation and persistence of aromatic amines, particularly 4-chloroaniline and 3,4-dichloroaniline, in aquatic ecosystems. Although significant research underscores the hazardous effects of these compounds, the urgency of addressing this issue appears to be underestimated. As such, we underscore the necessity of advancing detection and mitigation efforts and implementing improved regulatory measures to safeguard the water bodies against these potential threats.

Comparative immune responses of blue mussel and zebra mussel haemocytes to simultaneous chemical and bacterial exposure

Biomonitoring at the scale of the aquatic continuum and based on biomarkers, requires various representative species and a knowledge of their sensitivity to contaminants. Mussel immunomarkers are established tools for evaluating immunotoxic stress, but little is known about the consequences of an immune activation by local microorganisms on their response to pollution. This study aims to compare the sensitivity of cellular immunomarkers in two mussel species from different environments, the marine mussel Mytilus edulis (blue mussel) and the freshwater mussel Dreissena polymorpha (zebra mussel), to chemical stressors combined with bacterial challenge. Haemocytes were exposed ex vivo to the contaminants (bisphenol A, caffeine, copper chloride, oestradiol, ionomycin) for 4 h. The chemical exposures were coupled with simultaneous bacterial challenges (Vibrio splendidus and Pseudomonas fluorescens) to trigger activation of the immune response. Cellular mortality, phagocytosis efficiency and phagocytosis avidity were then measured by flow cytometry. The two mussel species had different basal levels since D. polymorpha showed higher cell mortality than M. edulis (23.9 ± 11% and 5.5 ± 3% dead cells respectively), and lower phagocytosis efficiency (52.6 ± 12% and 62.2 ± 9%), but similar phagocytosis avidity (17.4 ± 5 and 13.4 ± 4 internalised beads). Both bacterial strains led to an increase in cellular mortality (+8.4% dead cells in D. polymorpha, +4.9% in M. edulis), as well an activation of phagocytosis (+9.2% of efficient cells in D. polymorpha, +6.2% efficient cells and +3 internalised beads per cell in M. edulis). All chemicals triggered an increase in haemocyte mortality and/or phagocytotic modulations, except for bisphenol A. The two species differed in the amplitude of their response. The addition of a bacterial challenge significantly altered cell responses to chemicals with synergetic and antagonistic variations compared to a single exposure, depending on the compound used and the mussel species. This work highlights the species-specific sensitivity of mussel immunomarkers to contaminants, with or without bacterial challenge, and the necessity of considering the presence of in natura non-pathogenic microorganisms for future in situ applications of immunomarkers.

Response of Sabella spallanzanii to multiple stressors. The combined effect of infection and copper sulphate

The aim of this work is to study the immune responses of the polychaete Sabella spallanzanii after exposure to copper sulphate, an immunomodulating agent in marine organisms, and the multiple stresses caused by Escherichia coli infection, to validate the species as a model organism in marine-coastal biomonitoring programmes. Polychaetes were housed in laboratory and divided into five experimental groups: 1. Control (no microinjected), 2. filtered seawater + TBS injection (control of point 3), 3. filtered seawater + E. coli injection (control of point 4), 4. CuSO₄ + TBS injection (control of point 5), and 5. CuSO₄ + E. coli injection. The immune variables, esterase and alkaline phosphatase activity, cytotoxicity and detoxifying/antioxidant enzymes such as glutathione peroxidase were evaluated in total body extracts of the animals. Moreover, toll-like receptor, allograft inflammatory factor-1, lysozyme and haemagglutinating activity were investigated to highlight possible interactions. Indeed, the results of this work demonstrate the immunomodulating effect of copper sulphate on S. spallanzanii total body extracts related to oxidative stress and inflammatory markers.

Immunotoxicity pathway and mechanism of benzo[a]pyrene on hemocytes of Chlamys farreri in vitro

Benzo[a]pyrene (B[a]P), a typical PAHs widely existing in the marine environment, has been extensively studied for its immunotoxicity due to its persistence and high toxicity. Nevertheless, the immunotoxicity mechanism remain incompletely understood. In this study, isolated hemocytes of Chlamys farreri were exposed at three concentrations of B[a]P (5, 10 and 15 μg/mL), and the effects of B[a]P on detoxification metabolism, signal transduction, humoral immune factors, exocytosis and phagocytosis relevant proteins and immune function at 0, 6, 12, 24 h were studied. Results illustrated the AhR, ARNT and CYP1A1 were significantly induced by B[a]P at 12 h. Additionally, the content of B[a]P metabolite BPDE increased in a dose-dependent manner with pollutants. Under B[a]P stimulation, the expressions of PTK (Src, Fyn) and PLC-Ca²⁺-PKC pathway gene increased significantly, while the transcription level of AC-cAMP-PKA pathway gene decreased remarkably. Additionally, the expressions of nuclear transcription factors (CREB, NF-κB), complement system genes and C-type lectin genes up-regulated obviously. The gene expressions of phagocytosis and exocytosis related proteins were also notably affected. 5 μg/mL B[a]P could promote phagocytosis in a transitory time, but with the increase of exposure time and concentration of B[a]P, the phagocytosis, antibacterial and bacteriolytic activities gradually decreased. These results indicated that similar to vertebrates, BPDE, the metabolite of B[a]P, mediated downstream signal transduction via PTK in bivalves. The declined of the immune defense ability of hemocytes might be closely related to the inhibition of AC-cAMP-PKA pathway and the imbalance of intracellular Ca²⁺ pathway. In addition, the results manifested that complement and lectin systems play a significant role in regulating immune response. In this study, the direct relationship between detoxification metabolism and immune signal transduction in bivalves under B[a]P stress was demonstrated for the first time, which provided important information for the potential molecular mechanism of B[a]P-induced immune system disorder in bivalves.

Impact of Diuron contamination on blood cockles (Tegillarca granosa Linnaeus, 1758)

Examination of the impact of Diuron contamination on blood cockles (Tegillarca granosa) was conducted by combining field screening at three sampling events and a toxicity test. Diuron was extracted using the liquid-liquid extraction (LLE) technique and analyzed using HPLC-UV. The median lethal concentration (LC₅₀) of Diuron on T. granosa was tested under a 72-h exposure. Diuron in water samples ranged from not detected (ND) to 3910 ppb, which was the highest concentration detected in samples after the irrigation water was discharged from the paddy plantation. Diuron was not detected in sediment samples. Mortality of T. granosa ranged from 4.74 to 38.33% with the highest percentages recorded after the release of the irrigation water. The LC₅₀ value of Diuron was 1.84 ppm. This study suggests that irrigation water from paddy plantation that drifts to coastal areas containing Diuron harms T. granosa at the study area.

The neonicotinoid insecticide imidacloprid, but not salinity, impacts the immune system of Sydney rock oyster, Saccostrea glomerata

The broad utilisation of neonicotinoids, particularly imidacloprid (IMI), in agriculture has led to unplanned contamination of aquatic systems around the world. The sublethal effects of individual pesticides on the immune system of oysters, as well as their combined effects with other environmental stressors that fluctuate in estuarine environments, such as salinity, are yet to be investigated in ecotoxicology. We investigated the acute (4 d) toxicity of IMI in two salinity regimes on the immune parameters of Sydney rock oysters (SRO), including total hemocyte counts (THC), differential hemocyte counts (DHC), phagocytosis and hemocyte aggregation (HA), hemolymph protein expression and enzyme (catalase (CAT), glutathione S-transferase (GST) and acetylcholinesterase (AChE)) activities. Environmentally relevant concentrations of IMI were found to cause an increase in THC, induce GST activity, reduce HA, and inhibit AChE activity. However, DHC, CAT activity and phagocytosis were not significantly impacted at any test concentration at either salinity. IMI concentrations ≥0.01 mg/L significantly altered the expression of 28 proteins in the hemolymph of SRO, including an increase in the relative expression of extracellular superoxide dismutase, severin, ATP synthase subunit beta, as well as stress response proteins (heat shock proteins, serine/threonine-protein kinase DCLK3 and peroxiredoxin-1), and a decrease/absence of collagen alpha-4 (VI) and alpha-6 (VI) chain, metalloendopeptidase, L-ascorbate oxidase, transporter, CEP209_CC5 domain-containing protein and actin. This study indicates that the immune system of SRO can be impacted at environmentally relevant concentrations of IMI, but reduced salinity does not appear to influence the toxicity of this insecticide.

An environmentally realistic pesticide and copper mixture impacts embryonic development and DNA integrity of the Pacific oyster, Crassostrea gigas

Frequent occurrences of pesticides in the environment have raised concerns that combined exposure to these chemicals may result in enhanced toxicity through additive or synergistic interaction between compounds. Spermatozoa and embryos of the Pacific oyster, Crassostrea gigas, were exposed to different concentrations of a pesticide mixture with and without copper, mimicking the cocktail of pollutants occurring in the oyster culture area of Arcachon Bay. For the 1× exposure condition, measured concentration corresponds to a total concentration of 1.083 μg L^-1 for the mixture of 14 pesticides and to 6.330 μg L^-1 for copper (Cu). Several endpoints including larval abnormalities, DNA damage to spermatozoa and embryo and gene expression in D-larvae were investigated. Results demonstrated that pesticide mixtures in combination with or without copper induced a dose-dependent increase in embryotoxic and genotoxic effects on D-larvae from the lowest tested dose of 0.1×. Transcription of genes involved in anti-oxidative stress (cat), respiratory chain (coxI), metal detoxification (mt1 and mt2), and cell cycle arrest and apoptosis (p53) was found to be significantly downregulated while the xenobiotic biotransformation gene gst was significantly upregulated in embryos exposed to pesticide mixture with and without Cu. These findings raise the question of the possible impacts of mixtures of pesticides and metals on wild or farmed oyster populations from polluted coastal marine areas.

Vulnerability of glutathione-depleted Crassostrea gigas oysters to Vibrio species

Glutathione (GSH) is a major cellular antioxidant molecule participating in several biological processes, including immune function. In this study, we investigated the importance of GSH to oysters Crassostrea gigas immune response. Oysters were treated with the GSH-synthesis inhibitor buthionine sulfoximine (BSO), and the function of immune cells and mortality were evaluated after a bacterial challenge with different Vibrio species. BSO caused a moderate decrease (20-40%) in GSH levels in the gills, digestive gland, and hemocytes. As expected, lower GSH decreased survival to peroxide exposure. Hemocyte function was preserved after BSO treatment, however, oysters became more susceptible to challenges with Vibrio anguillarum, V. alginolyticus, or V. harveyi, but not with V. parahaemolyticus and V. vulnificus, indicating a species-specific vulnerability. Our study indicates that in natural habitats or in mariculture farms, disturbances in GSH metabolism may pre-dispose oysters to bacterial infection, decreasing survival.

Realistic environmental exposure to microplastics does not induce biological effects in the Pacific oyster Crassostrea gigas

The aim of the present study was to evaluate the presence and potential toxic effects of plastic fragments (<400 μm) of polyethylene and polypropylene on the Pacific oyster Crassostrea gigas. Oysters were exposed to environmentally relevant concentrations (0, 0.008, 10, 100 μg of particles/L) during 10 days, followed by a depuration period of 10 days in clean seawater. Effects of microplastics were evaluated on the clearance rate of organisms, tissue alteration, antioxidant defense, immune alteration and DNA damage. Detection and quantification of microplastics in oyster's tissues (digestive gland, gills and other tissues) and biodeposits using infrared microscopy were also conducted. Microplastics were detected in oyster's biodeposits following exposure to all tested concentrations: 0.003, 0.006 and 0.05 particles/mg of biodeposits in oysters exposed to 0.008, 10 and 100 μg of particles/L, respectively. No significant modulation of biological markers was measured in organisms exposed to microplastics in environmentally relevant conditions.

Imidacloprid and formulated product impacts the fatty acids and enzymatic activities in tissues of Sydney rock oysters, Saccostrea glomerata

The use of imidacloprid (IMI) and its formulated products in agriculture is a risk to aquatic organisms due to deposition into waterways from runoff and aerial spraying. However, there is limited information on the potential effects of this pesticide on commercially important shellfish, such as oysters. We investigated the impacts of IMI and Spectrum 200SC (IMI formulation) on the activity of the enzymes Glutathione-S-transferase (GST), Catalase (CAT) and Acetylcholinesterase (AChE), in different oyster tissues including the gill, adductor muscle and digestive gland. We also investigated the condition index and fatty acid composition of the flesh of oysters after 2 weeks exposure. The concentrations of IMI in the different tissues was assessed using Liquid Chromatography-Mass Spectrometry (LC-MS) after QuEChERS extraction. Higher concentrations of IMI residues were detected in the adductor muscle of the oysters, followed by the gills and with the lowest amounts recovered from the digestive gland across all the concentrations tested. IMI and Spectrum 200SC significantly affected the gill AChE activity at 2 mg/L, but digestive gland CAT, and gill and digestive gland GST were impacted at environmentally relevant concentrations (0.01 and 0.05 mg/L). In the whole oyster, 2 weeks exposure to IMI (≥0.01 mg/L) resulted in a proportional increase in saturated fatty acids (SFA), altered the polyunsaturated fatty acid (PUFA) to SFA ratio and altered the omega 3 fatty acids (n-3) to omega 6 fatty acids (n-6) ratio, but there were no effects on the condition index of the oyster. Although the oysters responded differently to the formulated product, there was no consistent difference in the sublethal effects of analytical IMI and Spectrum 200SC. This study showed that exposure to IMI and Spectrum 200SC can significantly affect the biochemical processes and metabolites in oysters, with implications for food quality and safety.

Overlapping and unique toxic effects of three alternative antifouling biocides (Diuron, Irgarol 1051®, Sea-Nine 211®) on non-target marine fish

The use of alternative biocides has increased due to their economic and ecological relevance. Although data regarding the toxicity of commercial alternative biocides in marine organisms are accumulating, little is known about their toxic pathways or mechanisms. To compare the toxic effects of commercial alternative biocides on non-target pelagic fish (flounder) embryos, we investigated the adverse effects of developmental malformation and transcriptional changes. Three biocides including Diuron, Irgarol 1051^® and Sea-Nine 211^® produced a largely overlapping suite of developmental malformations, including tail-fin fold defects and dorsal body axis curvature. In our test, the potencies of these biocides were ranked in the following order with respect to malformation and mortalities: Sea-Nine 211^® > Irgarol 1051^® > Diuron. Consistent with the toxicity rankings, the expression of genes related to heart formation was greater in embryonic flounder exposed to Sea-Nine 211^® than in those exposed to Irgarol 1051^® or Diuron, while expression of genes related to fin malformation was greater in the Irgarol 1051^® exposure group. In analyses of differential gene expression (DEG) profiles (fold change of genes with a cutoff P < 0.05) by high-throughput sequencing (RNA-seq), genes associated with nervous system development, transmembrane transport activity, and muscle cell development were significantly changed commonly. Embryos exposed to Diuron showed changes related to cellular protein localization, whereas genes associated with immune system processes were up-regulated significantly in embryos exposed to Irgarol 1051^®. Genes related to actin filament organization and embryonic morphogenesis were up-regulated in embryos exposed to Sea-Nine 211^®. Overall, our study provides a better understanding of the overlapping and unique developmental toxic effects of three commercial booster biocides through transcriptomic analyses in a non-target species, embryonic flounder.

Host-microbiota interactions shed light on mortality events in the striped venus clam Chamelea gallina

Mass mortalities due to disease outbreaks have recently affected a number of major taxa in marine ecosystems. Climate- and pollution-induced stress may compromise host immune defenses, increasing the risk of opportunistic diseases. Despite growing evidence that mass mortality events affecting marine species worldwide are strongly influenced by the interplay of numerous environmental factors, the reductionist approaches most frequently used to investigate these factors hindered the interpretation of these multifactorial pathologies. In this study, we propose a broader approach based on the combination of RNA-sequencing and 16S microbiota analyses to decipher the factors underlying mass mortality in the striped venus clam, Chamelea gallina, along the Adriatic coast. On one hand, gene expression profiling and functional analyses of microbial communities showed the over-expression of several genes and molecular pathways involved in xenobiotic metabolism, suggesting potential chemical contamination in mortality sites. On the other hand, the down-regulation of several genes involved in immune and stress response, and the over-representation of opportunistic pathogens such as Vibrio and Photobacterium spp. indicates that these microbial species may take advantage of compromised host immune pathways and defense mechanisms that are potentially affected by chemical exposure, resulting in periodic mortality events. We propose the application of our approach to interpret and anticipate the risks inherent in the combined effects of pollutants and microbes on marine animals in today's rapidly changing environment.

The immune responses of the Chinese rare minnow (Gobiocypris rarus) exposed to environmentally relevant concentrations of cypermethrin and subsequently infected by the bacteria Pseudomonas fluorescens

In the present study, to assess the immunotoxicity of cypermethrin (CYP) in fish, Chinese rare minnows (Gobiocypris rarus) were exposed to environmentally relevant concentrations (0.15, 0.5, and 1.5 μg/L) of CYP for 28 d and subjected to pathogen challenge trials for 2 d. After 28 d of CYP exposure, the levels of Immunoglobulin M (IgM), Alkaline phosphatase (ALP), and C-reactive protein (CRP) were significantly decreased (p < 0.05) after treatment with 1.5 μg/L CYP. Moreover, an induction of inflammatory cytokine transcripts (tnfa, il-6, il-8, and il-12) was observed (p < 0.05) after treatment with 1.5 μg/L CYP. After challenge with Pseudomonas fluorescens (P. fluorescens), plasma lysozyme (LYS) activity at 24 and 48 hours post-injection (hpi) was significantly decreased in the 0.5 and 1.5 μg/L CYP treatment groups (p < 0.05). Moreover, liver Complement component 3 (C3) and CRP contents at 24 hpi were significantly decreased in the 1.5 μg/L CYP treatment group (p < 0.05), whereas significant decreases in liver C3 and IgM contents were observed at 48 hpi (p < 0.05). Inhibition of expression of Toll-like receptor-nuclear factor kappa B (TLR-NF-kB) signaling pathway-related genes was observed in the CYP treatment groups and resulted in significant down-regulation of inflammatory cytokines (il-1β and il-12) in the 1.5 μg/L CYP treatment group at 48 hpi (p < 0.05). Interestingly, the mortality in the 0.5 and 1.5 μg/L CYP treatments was significantly increased at 48 hpi (p < 0.05). These results indicated that environmentally relevant concentrations of CYP suppressed the Chinese rare minnow immune system and reduced immune defense against bacterial infection, thereby causing subsequent mortality. Meanwhile, our results demonstrated that a subsequent host resistance challenge is an effective method for determining the immunotoxicity of chemicals (e.g., CYP).

Immune response to temperature stress in three bivalve species: Pacific oyster Crassostrea gigas, Mediterranean mussel Mytilus galloprovincialis and mud cockle Katelysia rhytiphora

Summer mortality of some bivalve species is often associated with the change of environmental temperature. This study compares the response of immunological parameters to temperature change in three marine bivalves: Pacific oyster Crassostrea gigas, Mediterranean mussel Mytilus galloprovincialis and mud cockle Katelysia rhytiphora. Each species was exposed to three temperatures, 15 °C, 20 °C and 25 °C for 14 days. The total haemocyte count (THC), phagocytosis, reactive oxygen species (ROS) and the activity of antioxidant enzymes such as superoxide dismutase (SOD) and catalase (CAT) were used as indicators to measure the response of each species to different temperatures. The highest temperature (25 °C) significantly increased the THC and phagocysis of haemocytes in all species. The SOD and CAT activities in the haemocytes of M. galloprovincialis and K. rhytiphora rapidly increased with temperature elevation, concomitantly with the increase of ROS ions. In contrast, the increases of ROS and SOD in C. gigas only occurred from 20 °C to 25 °C, suggesting that this intertidal species is more adaptive to different temperature levels. This study indicates that the activities of antioxidant enzymes can reflect the immune response of marine bivalves to thermal stress. Intertidal species such as Pacific oysters have a greater tolerance to thermal stress than subtidal species (e.g. Mediterranean mussel) and demersal species buried in sand (e.g. cockle).

Use of multiple endpoints to investigate the ecotoxicological effects of abamectin and thiamethoxam on Theba pisana snails

The ecotoxicological effects of dietary exposure to sublethal concentration (1/20 LC₅₀) of abamectin (ABM) and thiamethoxam (TMX) for two weeks exposure and one week recovery on oxidative stress parameters; lipid peroxidation (LPO), reduced glutathione (GSH), catalase (CAT) and glutathione S-transferase (GST), Deoxyribonucleic acid (DNA) damage as well as immunological parameters; cell death, phagocytosis, lysosomal membrane stability (LMS), lectins, superoxide anion (O₂^-) generation, phenoloxidase (PO), peroxidase (POD) and hemocyanin (Hc) of the land snail, Theba pisana were examined. The results showed that both tested compounds significantly increased DNA damage, LPO content, the activity of CAT and GST, cell death, POD activity, Hc level, whereas, significantly declined in phagocytic activity, LMS, lectins level, O2^- generation, PO activity, and GSH content compared to the controls after two week exposure. After one week of recovery, the measured biochemical parameters of treated snails were slightly repaired but their levels were still less than that of the level of untreated animals. Overall, based on acute toxicity endpoints, ABM appeared to be more harmful than TMX against this animal. Indeed, the different patterns of endpoint responses could represent a useful picture to characterise exposure to these pesticides in the land snail, T. pisana. This battery of snail endpoints might be a promising option to biomonitor the health of the terrestrial ecosystem and to offer valuable insights to the pesticides toxicity mechanisms.

Effects of aminomethylphosphonic acid, the main breakdown product of glyphosate, on cellular and biochemical parameters of the mussel Mytilus galloprovincialis

The effects of the breakdown products of herbicides on aquatic species are largely unknown. In a recent study, we evaluated the effects of glyphosate on the mussel Mytilus galloprovincialis. This study was designed to evaluate for the first time the impact of aminomethylphosphonic acid (AMPA) - the main breakdown product of glyphosate - on cellular and biochemical parameters of the mussel Mytilus galloprovincialis. Bivalves were exposed for 7, 14 and 21 days to 1, 10 and 100 μg/L of AMPA and various biomarkers were measured in haemolymph (total haemocyte counts, haemocyte diameter and volume, haemolymph pH, haemocyte proliferation, haemolymph lactate dehydrogenase activity, haemocyte lysate lysozyme and acid phosphatase activities), as well as in gills and digestive gland (superoxide dismutase, catalase, glutathione S-transferase and acetylcholinesterase activities). AMPA concentrations in seawater samples from the experimental tanks were also measured in order to correlate the biomarker responses of mussels with their exposure to the actual concentrations of AMPA. The MANOVA analysis demonstrated that the experimental variables considered (exposure dose, exposure duration, and their interaction) affected significantly biomarker responses. Nevertheless, the two-way ANOVA analysis revealed significant effects of AMPA on most of the biomarkers measured. The overall results of this study demonstrated that AMPA can affect cellular and biochemical parameters in mussels, similarly to glyphosate.

Evaluation of dicloran phototoxicity using primary cardiomyocyte culture from Crassostrea virginica

Dicloran is a commonly used fungicide throughout the Southern and Western United States. Runoff of dicloran from agriculture systems to nearby waterbodies can accumulate in the organisms that inhabit those areas. Although severe damage of dicloran to ecological systems has not been reported, its toxicity has been modified by photodegradation. The objective of this study is to assess the changes of dicloran toxicities during photo exposure using a reliable in vitro biological model. In the present investigation, the photodegradation of dicloran in vitro showed over 90% of dicloran was degraded within 24h of UV exposure in water. Two major intermediate degradation products, 2-chloro-1,4-benzoquinone (CBQ) and 1,4-benzoquinone (BQ), were detected upon UV exposure of dicloran; however, they were rapidly degraded via photolysis. To estimate the impact of the phototoxicity of dicloran to aquatic organisms, we developed an in vitro cell culture system using the C. virginica cardiomyoctes (CvCMs) which were isolated from heart tissues and formed beating cell clusters. The CvCM clusters were treated with irradiated dicloran or the two intermediate standards, CBQ and BQ, and they showed up to 41% decrease in beating rates compared to control cell clusters. Expression levels of selected genes: def, hsp70, and cam, were upregulated in response to stimulations of UV irradiated dicloran and the two standard intermediates. The four-hour irradiated dicloran also resulted in more significant inhibition in the proliferation and small cardioactive peptide β production of CvCMs than other treatment. Tested solutions of photolyzed dicloran showed elevated toxicities opposed to the standard intermediates, CBQ and BQ, suggesting additive toxicity of these dicloran products or toxicity due to other unidentified degradation products. Results of this study supported our hypothesis that the degradation of dicloran caused by photo irradiation results in an elevated toxicity which can be evaluated by the in vitro CvCM model.

Immunocompetence analysis of the aquatic snail Lymnaea stagnalis exposed to urban wastewaters

Wastewater treatment plant effluents from urban area are a well-known source of chronic multiple micropollution to the downstream living organisms. In this study, ecologically relevant laboratory-bred freshwater gastropods, Lymnaea stagnalis, were exposed for 29 days to raw effluents of a wastewater treatment plant in Lyon area (France). A time-course analysis of individual markers of immunocompetence (hemocyte density and viability, hemocyte NADPH activity, phenol oxidase activity, and capacity of phagocytosis) has shown slight trends of inflammatory-like responses induced by the 100% effluents. So far, no short-term hazard for L. stagnalis can be revealed. However, over the long term, such environmental stress-stimulating immune responses could provoke deleterious life history trade-offs because the immune system is known to be highly energy-consuming.

Ecotoxicological risk assessment for the herbicide glyphosate to non-target aquatic species: A case study with the mussel Mytilus galloprovincialis

Glyphosate (GLY) is one of the most used herbicide worldwide. Considering that information concerning the impact of GLY on bivalves is scarce, in this study we evaluated for the first time the effects of environmentally realistic concentrations of GLY (10, 100 and 1000 μg/L) to the mussel Mytilus galloprovincialis. Mussels were exposed for 7, 14 and 21 days and several biomarkers were measured in haemocytes/haemolymph (total haemocyte counts, haemocyte diameter and volume, haemolymph pH, haemolymph lactate dehydrogenase activity, haemocyte lysate lysozyme and acid phosphatase activities), as well as in gills and digestive gland (antioxidant enzyme and acetylcholinesterase activities). The concentrations of GLY and its main metabolite aminomethylphosphonic acid in the experimental tanks were also measured. The MANOVA analysis demonstrated that the experimental variables considered (exposure concentration, exposure duration, and their interaction) affected significantly biomarker responses. In addition, the two-way ANOVA analysis indicated that GLY was able to affect most of the cellular parameters measured, whereas antioxidant enzyme activities resulted to be influenced moderately. Interestingly, exposure to GLY reduced significantly acetylcholinesterase activity in gills. Although preliminary, the results of this study demonstrated that GLY can affect both cellular and biochemical parameters in mussels, highlighting a potential risk for aquatic invertebrates.

Effects of in situ exposure to tritiated natural environments: A multi-biomarker approach using the fathead minnow, Pimephales promelas

Aquatic ecosystems are chronically exposed to radionuclides as well as other pollutants. Increased concentrations of pollutants in aquatic environments can present a risk to exposed organisms, including fish. The goal of this study was to characterize the effects of tritium, in the context of natural environments, on the health of fathead minnow, Pimephales promelas. Fish were exposed to tritium (activity concentrations ranging from 2 to 23,000Bq/L) and also to various concentrations of several metals to replicate multiple-stressor environments. Fish were exposed for 60days, then transferred to the tritium background site where they stayed for another 60days. Tritium, in the forms of tritiated water (HTO) and organically bound tritium (OBT), and a series of fish health indicators were measured in fish tissues at seven time points throughout the 120days required to complete the exposure and the depuration phases. Results showed effects of environmental exposure following the increase of tritium activity and metals concentrations in water. The internal dose rates of tritium, estimated from tissue HTO and OBT activity concentrations, were consistently low (maximum of 0.2μGy/h) compared to levels at which population effects may be expected (>100μGy/h) and no effects were observed on survival, fish condition, gonado-somatic, hepato-somatic, spleno-somatic and metabolic indices (RNA/DNA, proteins/DNA and protein carbonylation (in gonads and kidneys)). Using multivariate analyses, we showed that several biomarkers (DNA damages, MN frequency, gamma-H2AX, SFA/MUFA ratios, lysosomal membrane integrity, AChE, SOD, phagocytosis and esterase activities) were exclusively correlated with fish tritium internal dose rate, showing that tritium induced genotoxicity, DNA repair activity, changes in fatty acid composition, and immune, neural and antioxidant responses. Some biomarkers were responding to the presence of metals, but overall, more biomarkers were linked to internalized tritium. The results are discussed in the context of multiple stressors involving metals and tritium.

Modulation of immune and antioxidant responses by azinphos-methyl in the freshwater mussel Diplodon chilensis challenged with Escherichia coli

The aim of the present study was to characterize the immune response-total hemocyte number, cell type proportion, hemocyte viability, lysosomal membrane stability, phagocytic activity, cellular acid and alkaline phosphatase activity, and humoral bacteriolytic and phenoloxidase activity--in Diplodon chilensis exposed to 0.2 mg/L of azinphos-methyl (AZM), using Escherichia coli as immunological and pro-oxidant challenges. In addition, glutathione-S-transferase and lipid peroxidation thiobarbituric acid reactive substances were analyzed in gill tissue. Mussels from an unpolluted site were treated for 3 d as follows: 1) experimental control; 2) solvent effects control (acetone 0.01%); 3) bacterial challenge effects control (E. coli, 5 cells/mL × 10⁴ cells/mL); 4) pesticide effects control (AZM in acetone); 5) control for combined effects of solvent and bacterial challenge; and 6) exposed to AZM, then challenged with E. coli. The results showed increased granulocyte proportion and phagocytic activity. Partial reversion of deleterious effects of E. coli on lysosomal membranes was observed in mussels exposed to AZM and then challenged with E. coli. Total hemocyte number and humoral bacteriolytic activity were increased only by E. coli challenge. Acid phosphatase activity was increased by both E. coli and AZM, whereas the stimulating effect of E. coli on alkaline phosphatase activity was negatively modulated by AZM. Azinphos-methyl inhibited phenoloxidase activity regardless of the E. coli challenge. Gill glutathione-S-transferase activity was increased by E. coli treatment either alone or pretreated with acetone or AZM and by AZM alone. Thiobarbituric acid reactive substance levels were reduced by AZM alone or combined with the E. coli challenge and by acetone followed by the E. coli challenge. Both acetone and AZM seem to be important modulators of immune and antioxidant responses in D. chilensis. Environ Toxicol Chem 2017;36:1785-1794. © 2016 SETAC.

Haemocytes collected from experimentally infected Pacific oysters, Crassostrea gigas: Detection of ostreid herpesvirus 1 DNA, RNA, and proteins in relation with inhibition of apoptosis

Recent transcriptomic approaches focused on anti-viral immunity in molluscs lead to the assumption that the innate immune system, such as apoptosis, plays a crucial role against ostreid herpesvirus type 1 (OsHV-1), infecting Pacific cupped oyster, Crassostrea gigas. Apoptosis constitutes a major mechanism of anti-viral response by limiting viral spread and eliminating infected cells. In this way, an OsHV-1 challenge was performed and oysters were monitored at three times post injection to investigate viral infection and host response: 2h (early after viral injection in the adductor muscle), 24h (intermediate time), and 48h (just before first oyster mortality record). Virus infection, associated with high cumulative mortality rates (74% and 100%), was demonstrated in haemocytes by combining several detection techniques such as real-time PCR, real-time RT PCR, immunofluorescence assay, and transmission electron microscopy examination. High viral DNA amounts ranged from 5.46×104 to 3.68×105 DNA copies ng-1 of total DNA, were detected in dead oysters and an increase of viral transcripts was observed from 2, 24, and 48hpi for the five targeted OsHV-1 genes encoding three putative membrane proteins (ORFs 25, 41, and 72), a putative dUTPase (ORF 75), and a putative apoptosis inhibitor (ORF 87). Apoptosis was studied at molecular and cellular levels with an early marker (phosphatidyl-serine externalisation measured by flow cytometry and epifluorescence microscopy) and a later parameter (DNA fragmentation by terminal deoxynucleotidyltransferase-mediated dUTP nick end labeling assay (TUNEL)). The down-regulation of genes encoding proteins involved in the activation of the apoptotic pathway (TNF and caspase 3) and the up-regulation of genes encoding anti-apoptotic proteins (IAP-2, and Bcl-2) suggested an important anti-apoptosis phenomenon in haemocytes from OsHV-1 infected oysters at 24 and 48hpi. Additionally, more phosphatidyl-serines were externalized and more cells with DNA fragmentation were observed in haemocytes collected from artificial seawater injected oysters than in haemocytes collected from OsHV-1 infected oysters at 24 and 48hpi, suggesting an inhibition of the apoptotic process in presence of the virus. In conclusion, this study is the first to focus on C. gigas haemocytes, cells involved in the host immune defense, during an OsHV-1 challenge in controlled conditions by combining various and original approaches to investigate apoptosis at molecular and cellular levels.

Concomitant effect of low dose of lindane and intranasal lipopolysaccharide on respiratory system of mice

Lindane is very commonly used organochlorine pesticide and has been reported to cause several toxic effects including respiratory insufficiency. However, effects of low concentration of lindane alone or in combination with microbial molecules on lungs are not fully understood. To understand the effects a preliminary study was designed on Swiss albino mouse. Male mice were divided into treatment and control group (20; each). Treatment mice were given lindane in ground nut oil orally at 0.25 mg kg^-1 day^-1 for 60 days. After treatment, 10 mice were challenged with intranasal Escherichia coli lipopolysaccharide (LPS; 80 μg per mice) and remaining 10 with normal saline. The mice were euthanized 16 h post-LPS exposure. Control mice (10 each) were given normal saline or the LPS alone. Mice exposed with lindane and in combination with LPS had increase in total cell counts and leukocyte counts in broncho-alveolar lavage. Histological examination showed lung injury in the lindane-treated mice. The histopathological changes were more pronounced in lindane along with LPS-exposed mice. Lindane alone and in combination with LPS showed expression of immunopositive Toll-like receptor (TLR)-4 and tumour necrosis factor-alpha (TNF-α) positive reaction in various cells of lungs. While LPS induced acute inflammation in the lungs, combination of lindane and LPS exacerbated histological signs of the inflammation. The data indicate that lindane alone or in combination with LPS caused changes in lung morphology and altered TLR-4 and TNF-α expression which may have led to altered response to LPS challenge.

Pulmonary innate inflammatory responses to agricultural occupational contaminants

Agricultural workers are exposed to many contaminants and suffer from respiratory and other symptoms. Dusts, gases, microbial products and pesticide residues from farms have been linked to effects on the health of agricultural workers. Growing sets of data from in vitro and in vivo models demonstrate the role of the innate immune system, especially Toll-like receptor 4 (TLR4) and TLR9, in lung inflammation induced following exposure to contaminants in agricultural environments. Interestingly, inflammation and lung function changes appear to be discordant indicating the complexity of inflammatory responses to exposures. Whereas the recent development of rodent models and exposure systems have yielded valuable data, we need new systems to examine the combined effects of multiple contaminants in order to increase our understanding of farm-exposure-induced negative health effects.

Use of a suite of biomarkers to assess the effects of carbamazepine, bisphenol A, atrazine, and their mixtures on green mussels, Perna viridis

The present study investigated the toxicity of several emerging contaminants: the pharmaceutical drug carbamazepine (CBZ), the plasticizer bisphenol A (BPA), and the herbicide atrazine (ATZ) in a marine bivalve. Green mussels (Perna viridis) were exposed to different concentrations of CBZ, BPA, and ATZ, either individually or as mixtures over a 7-d period, and a suite of molecular and cellular biomarkers were analyzed: biomarkers of immunotoxicity (total hemocyte count, phagocytosis, extracellular lysozyme), genotoxicity (Comet assay), neurotoxicity (inhibition of acetylcholinesterase [AChE]), endocrine disruption (vitellin-like proteins), and detoxification enzymes (cytochrome P4501A [CYP1A], 7-ethoxyresorufin O-deethylase [EROD], and glutathione-S-transferase [GST]). Results of the single-chemical exposure tests highlighted the relatively low toxicity of CBZ because most biomarker responses observed were recorded at concentrations well above environmental levels. Bisphenol A exposure at environmentally realistic concentrations resulted in clear immunomodulatory, genotoxic, and endocrine-disruptive effects. Similarly, 3 of the 10 biomarkers tested on green mussels (genotoxicity, inhibition of AchE, and EROD) responded after exposure to ATZ at environmentally relevant doses or below, and confirmed the potency of this herbicide to marine bivalves. Exposure tests using mixtures of CBZ, BPA, and ATZ also revealed that these 3 substances were generally acting in an additive manner on the selected biomarkers, at environmental doses, with some exceptions (antagonism and/or synergy) at low and high concentrations. The present study also confirms that most of the biomarkers used are suitable for biomonitoring studies with green mussels. Environ Toxicol Chem 2017;36:429-441. © 2016 SETAC.

Effects of Antifouling Biocides on Molecular and Biochemical Defense System in the Gill of the Pacific Oyster Crassostrea gigas

Antifouling biocides such as organotin compounds and their alternatives are potent toxicants in marine ecosystems. In this study, we employed several molecular and biochemical response systems of the Pacific oyster Crassostrea gigas to understand a potential mode of action of antifouling biocides (i.e. tributyltin (TBT), diuron and irgarol) after exposure to different concentrations (0.01, 0.1, and 1 μg L^-1) for 96 h. As a result, all the three antifouling biocides strongly induced the antioxidant defense system. TBT reduced both enzymatic activity and mRNA expression of Na⁺/K⁺-ATPase and acetylcholinesterase (AChE). Lower levels of both Na⁺/K⁺-ATPase activity and AChE mRNA expression were observed in the diuron-exposed oysters compared to the control, while the irgarol treatment reduced only the transcriptional expression of AChE gene. We also analyzed transcript profile of heat shock protein (Hsp) superfamily in same experimental conditions. All antifouling biocides tested in this study significantly modulated mRNA expression of Hsp superfamily with strong induction of Hsp70 family. Taken together, overall results indicate that representative organotin TBT and alternatives have potential hazardous effects on the gill of C. gigas within relatively short time period. Our results also suggest that analyzing a series of molecular and biochemical parameters can be a way of understanding and uncovering the mode of action of emerging antifouling biocides. In particular, it was revealed that Pacific oysters have different sensitivities depend on the antifouling biocides.

Effect of 4-nonylphenol on the immune response of the Pacific oyster Crassostrea gigas following bacterial infection with Vibrio campbellii

The xenoestrogen 4-nonylphenol (NP) is a ubiquitous aquatic pollutant and has been shown to impair reproduction, development, growth and, more recently, immune function in marine invertebrates. We investigated the effects of short-term (7 d) exposure to low (2 μg l^-1) and high (100 μg l^-1) levels of NP on cellular and humoral elements of the innate immune response of Crassostrea gigas to a bacterial challenge. To this end, we measured 1) total hemocyte counts (THC), 2) relative transcript abundance of ten immune-related genes (defh1, defh2, bigdef1, bigdef2, bpi, lysozyme-1, galectin, C-type lectin 2, timp, and transglutaminase) in the hemocytes, gill and mantle, and 3) hemolymph plasma lysozyme activity, following experimental Vibrio campbellii infection. Both low and high levels of NP were found to repress a bacteria-induced increase in THC observed in the control oysters. While several genes were differentially expressed following bacterial introduction (bigdef2, bpi, lysozyme-1, timp, transglutaminase), only two genes (bpi in the hemocytes, transglutaminase in the mantle) exhibited a different bacteria-induced expression profile following NP exposure, relative to the control oysters. Independently of infection-status, exposure to NP also altered mRNA transcript abundance of several genes (bpi, galectin, C-type lectin 2) in naïve, saline-injected oysters. Finally, plasma lysozyme activity levels were significantly higher in low dose NP-treated oysters (both naïve and bacteria challenged) relative to control oysters. Combined, these results suggest that exposure to ecologically-relevant (low) and extreme (high) levels of NP can alter both cellular and humoral elements of the innate immune response in C. gigas, an aquaculture species of global economic importance.

Comparative embryotoxicity and genotoxicity of the herbicide diuron and its metabolites in early life stages of Crassostrea gigas: Implication of reactive oxygen species production

Herbicides are one of the major classes of pollutants contaminating coastal waters over the world. Among them, diuron (3-(3,4-dichlorophenyl)-1,1-dimethylurea) is a phenylurea herbicide frequently detected in oyster-producing area, known to be toxic for this important exploited non-target species. With the aim to investigate the mechanisms by which diuron displays its toxicity in oyster, the implication of both biotransformation and oxygen reactive species (ROS) production was studied considering embryotoxicity and genotoxicity as endpoints. Comparative embryotoxicity and genotoxicity of diuron and its main metabolites (DCPMU, DCPU and 3,4-DCA) were thus studied on oyster larvae by the embryo-larval bioassay on D larvae and the comet assay on trochophore larvae, respectively. Exposures were also performed in presence and absence of known ROS scavenger compounds - ascorbic acid and N-acetylcysteine, to evaluate the involvement of oxyradicals in the toxic responses. In the case of diuron, the production of ROS on exposed oyster larvae was also measured using 2',7'-dichlorodihydrofluorescein diacetate as a probe for flow cytometric analysis. The results we obtained showed the embryotoxicity and genotoxicity of diuron and its metabolites in early life stages of the Pacific oyster. For concentrations ranging from 0.05 to 0.5μgL(-1), diuron appeared significantly more embryotoxic than DCPMU and DCPU (p<0.001). Embryotoxicity decreased with diuron metabolism as follows: diuron≥DCPMU=DCPU, highlighting that biotransformation can constitute a true detoxication pathways in oyster larvae by decreasing the toxicity of the parent compound. In the opposite, no difference was observed between diuron and its metabolites concerning larval development when considering a lower and more environmentally realistic range of concentrations (0.002-0.050μgL(-1)). 3,4-DCA was the only compound that did not show any sign of embryotoxicity, even at concentrations up to 5μgL(-1). Concerning genotoxicity, no significant difference was observed between diuron and all of its metabolites including 3, 4 DCA with damages detected from the concentration of 0.05μgL(-1). As for diuron, the toxicity of the metabolites seems to be mediated in some part by ROS production as clearly demonstrated by the decrease in genotoxicity and developmental abnormalities in the presence of the oxidant scavenger, ascorbic acid.

Effects of an environmentally relevant concentration of diuron on oyster genitors during gametogenesis: responses of early molecular and cellular markers and physiological impacts

Genitors of the Pacific oyster Crassostrea gigas were submitted during gametogenesis to a short pulse exposure to the herbicide diuron at a realistic environmental concentration. Histological analysis showed no effect of diuron on gametogenesis course, sex ratio and reproductive effort. A non-significant increase in testosterone and progesterone levels was observed in genitors exposed to the herbicide. At cell level, diuron exposure was shown to modulate the phagocytic activity of circulating hemocytes. The results of a transcriptional analysis showed that diuron affected the expression of genes belonging to functions known to play a major role during oyster gametogenesis such as gene transcription regulation, DNA replication and repair, DNA methylation and cytokinesis. Taking into account the results we previously obtained on the same genitors, this study showed a negative effect of diuron on oyster reproduction by inducing both structural and functional modifications of the DNA.

Parental exposure to the herbicide diuron results in oxidative DNA damage to germinal cells of the Pacific oyster Crassostrea gigas

Chemical pollution by pesticides has been identified as a possible contributing factor to the massive mortality outbreaks observed in Crassostrea gigas for several years. A previous study demonstrated the vertical transmission of DNA damage by subjecting oyster genitors to the herbicide diuron at environmental concentrations during gametogenesis. This trans-generational effect occurs through damage to genitor-exposed gametes, as measured by the comet-assay. The presence of DNA damage in gametes could be linked to the formation of DNA damage in other germ cells. In order to explore this question, the levels and cell distribution of the oxidized base lesion 8-oxodGuo were studied in the gonads of exposed genitors. High-performance liquid chromatography coupled with UV and electrochemical detection analysis showed an increase in 8-oxodGuo levels in both male and female gonads after exposure to diuron. Immunohistochemistry analysis showed the presence of 8-oxodGuo at all stages of male germ cells, from early to mature stages. Conversely, the oxidized base was only present in early germ cell stages in female gonads. These results indicate that male and female genitors underwent oxidative stress following exposure to diuron, resulting in DNA oxidation in both early germ cells and gametes, such as spermatozoa, which could explain the transmission of diuron-induced DNA damage to offspring. Furthermore, immunostaining of early germ cells seems indicates that damages caused by exposure to diuron on germ line not only affect the current sexual cycle but also could affect future gametogenesis.

Risk assessment of environmental mixture effects

Determining interactions of multi-component environmental mixtures towards accurate risk assessment.

Immunotoxicological effects of environmental contaminants on marine bivalves

Coastal areas are complex environments frequently contaminated by numerous pollutants that represent a potential threat to marine organisms, especially bivalves. These pollutants may have major ecological consequences. Although effects of different environmental contaminants on the immune system in marine bivalves have been already reported, a few of reviews summarizes these effects. The main purpose of this chapter relies on summarizing recent body of data on immunotoxicity in bivalves subjected to contaminants. Immune effects of heavy metals, pesticides, HAP, PCB and pharmaceuticals are presented and discussed and a particular section is devoted to nanoparticle effects. A large body of literature is now available on this topic. Finally, the urgent need of a better understanding of complex interactions between contaminants, marine bivalves and infectious diseases is noticed.

Dose-dependent effects of metals on gene expression in the sydney rock oyster, Saccostrea glomerata

In the current study, we tested the effects of common environmental contaminants (the metals zinc and lead) on gene expression in Sydney rock oysters (Saccrostrea glomerata). Oysters were exposed to a range of metal concentrations under controlled laboratory conditions. The expression of 14 putative stress response genes was then measured using quantitative, real-time (q) PCR. The expression of all 14 genes was significantly affected (p < 0.05 vs. nonexposed controls) by at least one of the metals, and by at least one dose of metal. For 5 of the 14 target genes (actin, calmodulin, superoxide dismutase, topoisomerase I, and tubulin) the alteration of expression relative to controls was highest at intermediate (rather than high) doses of metals. Such responses may reflect adaptive (acclimation) reactions in gene expression at low to intermediate doses of contaminants, followed by a decline in expression resulting from exposure at higher doses. The data are discussed in terms of the intracellular pathways affected by metal contamination, and the relevance of such gene expression data to environmental biomonitoring.

Effects of subchronic exposure to glyphosate in juvenile oysters (Crassostrea gigas): From molecular to individual levels

Glyphosate-based herbicides are extensively used and can be measured in aquatic ecosystems, including coastal waters. The effect of glyphosate on non-target organisms is an issue of worldwide concern. The aim of this study was to investigate the effects of subchronic exposure to glyphosate in juvenile oysters, Crassostrea gigas. Yearling oysters were exposed to three concentrations of glyphosate (0.1, 1 and 100μgL(-1)) for 56days. Various endpoints were studied, from the individual level (e.g., gametogenesis and tissue alterations) to the molecular level (mRNA quantification), including biochemical endpoints such as glutathione-S-transferase (GST) and catalase activities and malondialdehyde content. No mortality and growth occurred during the experiment, and individual biomarkers revealed only slight effects. The levels of gene expression significantly increased in oysters exposed to the highest glyphosate concentration (GST and metallothioneins) or to all concentrations (multi-xenobiotic resistance). These results suggested an activation of defence mechanisms at the molecular level.

Pesticides and Ostreid Herpesvirus 1 Infection in the Pacific Oyster, Crassostrea gigas

Since 2008, mass mortality outbreaks have been reported in all French regions producing Pacific oysters, and in several Member States of the European Union. These mass mortality events of Pacific oysters are related to OsHV-1 infection. They occur during spring and summer periods leaving suspect the quality of the marine environment and the role of seasonal use of pesticides associated with the arrival of freshwater in oyster rearing areas. Pesticides have been also detected in French coastal waters, especially in areas of oyster production. Using PMA real-time PCR we showed that a mixture of 14 pesticides has no effect on the integrity of virus capsids from viral suspension in the conditions tested. A contact of oysters with this pesticide mixture was related to higher mortality rates among experimentally infected animals in comparison with control ones (no previous pesticide exposure before experimental infection). We therefore suggest that pesticides at realistic concentration can exert adverse effects on Pacific oysters and causes an increased susceptibility to the viral infection in experimental conditions.

In vivo effects of metaldehyde on Pacific oyster, Crassostrea gigas: comparing hemocyte parameters in two oyster families

Pollutants via run-off into the ocean represent a potential threat to marine organisms, especially bivalves such as oysters living in coastal environments. These organisms filter large volumes of seawater and may accumulate contaminants within their tissues. Pesticide contamination in water could have a direct or indirect toxic action on tissues or cells and could induce alteration of immune system. Bivalve immunity is mainly supported by hemocytes and participates directly by phagocytosis to eliminate pathogens. Some studies have shown that pesticides can reduce immune defences and/or modify genomes in vertebrates and invertebrates. Metaldehyde is used to kill slugs, snails and other terrestrial gastropods. Although metaldehyde has been detected in surface waters, its effects on marine bivalves including the Pacific oyster, Crassostrea gigas, have never been studied. Given the mode of action of this molecule and its targets (molluscs), it could be potentially more toxic to oysters than other pesticides (herbicides, fungicides, insecticides, etc.). Effects of metaldehyde on oyster hemocyte parameters were thus monitored through in vivo experiments based on a short-term exposure. In this work, metaldehyde at 0.1 μg/L, which corresponds to an average concentration detected in the environment, modulated hemocyte activities of Pacific oysters after an in vivo short-term contact. Individuals belonging to two families showed different behaviours for some hemocyte activities after contamination by metaldehyde. These results suggested that effects of pollutants on oysters may differ from an individual to another in relation to genetic diversity. Finally, it appears essential to take an interest in the effects of metaldehyde on a wide variety of aquatic invertebrates including those that have a significant economic impact.

Identification and expression of antioxidant and immune defense genes in the surf clam Mesodesma donacium challenged with Vibrio anguillarum

The immune system in marine invertebrates is mediated through cellular and humoral components, which act together to address the action of potential pathogenic microorganisms. In bivalve mollusks biomolecules implicated in oxidative stress and recognition of pathogens have been involved in the innate immune response. To better understand the molecular basis of the immune response of surf clam Mesodesma donacium, qPCR approaches were used to identify genes related to its immune response against Vibrio anguillarum infection. Genes related to oxidative stress response and recognition of pathogens like superoxide dismutase (MdSOD), catalase (MdCAT), ferritin (MdFER) and filamin (MdFLMN) were identified from 454-pyrosequencing cDNA library of M. donacium and were evaluated in mantle, adductor muscle and gills. The results for transcripts expression indicated that MdSOD, MdFLMN and MdFER were primarily expressed in the muscle, while MdCAT was more expressed in gills. Challenge experiments with the pathogen V. anguillarum had showed that levels of transcript expression for MdSOD, MdCAT, MdFER, and MdFLMN were positively regulated by pathogen, following a time-dependent expression pattern with significant statistical differences between control and challenge group responses (p<0.05). These results suggest that superoxide dismutase, catalase, ferritin and filamin, could be contributing to the innate immune response of M. donacium against the pathogen V. anguillarum.

Dual transcriptomics of virus-host interactions: comparing two Pacific oyster families presenting contrasted susceptibility to ostreid herpesvirus 1

BACKGROUND

Massive mortality outbreaks affecting Pacific oyster (Crassostrea gigas) spat in various countries have been associated with the detection of a herpesvirus called ostreid herpesvirus type 1 (OsHV-1). However, few studies have been performed to understand and follow viral gene expression, as it has been done in vertebrate herpesviruses. In this work, experimental infection trials of C. gigas spat with OsHV-1 were conducted in order to test the susceptibility of several bi-parental oyster families to this virus and to analyze host-pathogen interactions using in vivo transcriptomic approaches.

RESULTS

The divergent response of these oyster families in terms of mortality confirmed that susceptibility to OsHV-1 infection has a significant genetic component. Two families with contrasted survival rates were selected. A total of 39 viral genes and five host genes were monitored by real-time PCR. Initial results provided information on (i) the virus cycle of OsHV-1 based on the kinetics of viral DNA replication and transcription and (ii) host defense mechanisms against the virus.

CONCLUSIONS

In the two selected families, the detected amounts of viral DNA and RNA were significantly different. This result suggests that Pacific oysters are genetically diverse in terms of their susceptibility to OsHV-1 infection. This contrasted susceptibility was associated with dissimilar host gene expression profiles. Moreover, the present study showed a positive correlation between viral DNA amounts and the level of expression of selected oyster genes.

First description of French V. tubiashii strains pathogenic to mollusk: I. Characterization of isolates and detection during mortality events

Nine dominant bacterial isolates were obtained from different batches of Crassostrea gigas spat experiencing high mortality rates in a French experimental hatchery/nursery in 2007. Using phenotypic analysis combined with multilocus sequence analysis, the isolates were shown to be genetically close to the Vibrio tubiashii type strain. Based on (1) analyses of the recA gene sequences; (2) the results of DNA-DNA hybridization assays between 07/118 T2 (LMG 27884=CECT 8426), which is a representative strain, and the V. tubiashii type strain (69%); and (3) phenotypic traits, the bacteria were classified in a group close to American V. tubiashii strain. Its virulence (70% of mortalities) and the toxicity of the extracellular products of 07/118 T2 was demonstrated (41% of mortalities). Moreover, a QPCR diagnostic tool targeting the gyrB gene was developed to investigate the epidemiological significance of V. tubiashii in French oyster mortality outbreaks recorded by the national surveillance network. Of the 21 batches originating from hatcheries, only two were positive, whereas V. tubiashii DNA could not be detected in any of the batches of moribund animals collected in field/outdoor facilities. These results demonstrate the existence of a group of virulent V. tubiashii in France that episodically infect C. gigas.

Health status and bioremediation capacity of wild freshwater mussels (Diplodon chilensis) exposed to sewage water pollution in a glacial Patagonian lake

Deleterious effects on health and fitness are expected in mussels chronically exposed to sewage water pollution. Diplodon chilensis inhabiting SMA, an area affected by untreated and treated sewage water, shows increased hemocyte number and phagocytic activity, while bacteriolytic and phenoloxidase activities in plasma and reactive oxygen species production in hemocytes are lower compared to mussels from an unpolluted area (Yuco). There are not differences in cell viability, lysosomal membrane stability, lipid peroxidation and total oxygen scavenging capacity between SMA and Yuco mussels' hemocytes. Energetic reserves and digestive gland mass do not show differences between groups; although the condition factor is higher in SMA than in Yuco mussels. Gills of SMA mussels show an increase in mass and micronuclei frequency compared to those of Yuco. Mussels from both sites reduce bacterial loads in polluted water and sediments, improving their quality with similar feeding performance. These findings suggest that mussels exposed to sewage pollution modulate physiological responses by long-term exposure; although, gills are sensitive to these conditions and suffer chronic damage. Bioremediation potential found in D. chilensis widens the field of work for remediation of sewage bacterial pollution in water and sediments by filtering bivalves.

Pacific oyster (Crassostrea gigas) hemocyte are not affected by a mixture of pesticides in short-term in vitro assays

Pesticides are frequently detected in estuaries among the pollutants found in estuarine and coastal areas and may have major ecological consequences. They could endanger organism growth, reproduction, or survival. In the context of high-mortality outbreaks affecting Pacific oysters, Crassostrea gigas, in France since 2008, it appears of importance to determine the putative effects of pesticides on oyster susceptibility to infectious agents. Massive mortality outbreaks reported in this species, mainly in spring and summer, may suggest an important role played by the seasonal use of pesticides and freshwater input in estuarine areas where oyster farms are frequently located. To understand the impact of some pesticides detected in French waters, their effects on Pacific oyster hemocytes were studied through short-term in vitro experiments. Bivalve immunity is mainly supported by hemocytes eliminating pathogens by phagocytosis and producing compounds including lysosomal enzymes and antimicrobial molecules. In this study, oyster hemocytes were incubated with a mixture of 14 pesticides and metaldehyde alone, a molecule used to eliminate land mollusks. Hemocyte parameters including dead/alive cells, nonspecific esterase activities, intracytoplasmic calcium, lysosome number and activity, and phagocytosis were monitored by flow cytometry. No significant effect of pesticides tested at different concentrations was reported on oyster hemocytes maintained in vitro for short-term periods in the present study. It could be assumed that these oyster cells were resistant to pesticide exposure in tested conditions and developing in vivo assays appears as necessary to better understand the effects of pollutants on immune system in mollusks.

The impacts of handling and air exposure on immune parameters, gene expression, and susceptibility to vibriosis of European abalone Haliotis tuberculata

Wild or farmed abalone are regularly exposed to stressors, such as air exposure and handling. Immune and transcriptional responses as well as susceptibility to vibriosis of sexually mature or immature European abalone acclimated at 16 or 19 °C were determined following handling or air exposure. Hemocyte density and H2O2 production increased while hemocyte viability and phagocytic index decreased following handling. Air exposure induces a decrease of hemocyte density and phagocytic index. Measurement of the expression of genes implicated in general metabolic, immunological and stress responses in gills, foot-muscle and hemocytes by real time q-PCR suggested that both stressors lead to a metabolic rate depression, characterized by a general inhibition of transcription. Finally, following handling a Vibrio harveyi challenge enhances almost 100% mortality of sexually immature animals at 19 °C while it has been previously demonstrated that only mature are susceptible to vibriosis.

Study of genetic damage in the Japanese oyster induced by an environmentally-relevant exposure to diuron: evidence of vertical transmission of DNA damage

Pesticides represent a major proportion of the chemical pollutants detected in French coastal waters and hence a significant environmental risk with regards to marine organisms. Commercially-raised bivalves are particularly exposed to pollutants, among them pesticides, as shellfish farming zones are subject to considerable pressure from agricultural activities on the mainland. The aims of this study were to determine (1) the genotoxic effects of diuron exposure on oyster genitors and (2) the possible transmission of damaged DNA to offspring and its repercussions on oyster fitness. To investigate these points, oysters were exposed to concentrations of diuron close to those detected in the Marennes-Oleron Basin (two 7-day exposure pulses at 0.4 and 0.6 μg L(-1)) during the gametogenesis period. Genomic abnormalities were characterized using two complementary approaches. The Comet assay was applied for the measurement of early and reversible primary DNA damage, whereas flow cytometry was used to assess the clastogenic and aneugenic effect of diuron exposure. Polar Organic Chemical Integrative Samplers (POCIS) were used in exposed and assay tanks to confirm the waterborne concentration of diuron reached during the experiment. The results obtained by the Comet assay clearly showed a higher level of DNA strand breaks in both the hemocytes and spermatozoa of diuron-exposed genitors. The transmission of damaged genetic material to gamete cells could be responsible for the genetic damage measured in offspring. Indeed, flow cytometry analyses showed the presence of DNA breakage and a significant decrease in DNA content in spat from diuron-exposed genitors. The transmission of DNA damage to the offspring could be involved in the negative effects observed on offspring development (decrease in hatching rate, higher level of larval abnormalities, delay in metamorphosis) and growth. In this study, the vertical transmission of DNA damage was so highlighted by subjecting oyster genitors to short exposures to diuron at medium environmental concentrations. The analysis of POCIS showed that oysters were exposed to integrated concentrations as low as 0.2 and 0.3 μg L(-1), emphasizing the relevance of the results obtained and the risk associated to chemical contamination for oyster recruitment and fitness.

Variability of the hemocyte parameters of cultivated mussel Mytilus galloprovincialis (Lmk 1819) in Sabaudia (Latina, Italy) coastal lagoon

The Sabaudia's lake consists of a protected coastal lagoon, located in the central Italy, historically characterized by recurrent mortality events of marine fauna during warmer months. A field study was monthly conducted on mussels Mytilus galloprovincialis cultivated inside the lagoon, measuring hemocyte parameters as total circulating count (THC), viability (HV), spreading and oxidative response to in vitro phagocytosis stimulation. A depression of the immune response was observed during the spring season, as indicated by higher values of hemocyte circularity and lower luminescence levels related to respiratory burst, also associated to modulation of THC and HV. The water temperature and the oxygen concentration appeared as the major environmental factors having influence on the phagocytosis activity. Therefore, the hemocyte variations have been intended as early danger signal to evaluate the immunodepression induced by the environmental stressors which could reveal in advance the development of critical situations for mussel survival.