First evidence for toxic defense based on the multixenobiotic resistance (MXR) mechanism in Daphnia magna

Microcystins bioaccumulate but do not biomagnify in an experimental aquatic food chain

Microcystins-common hepatotoxins produced by cyanobacteria-have been detected in a wide range of organisms, though research examining the trophic transfer of microcystins and whether microcystins bioaccumulate or biomagnify in food webs has generated contradictory results. Here, we explored the trophic transfer of microcystins from the herbivorous water flea, Daphnia pulex, to the predatory larvae of a damselfly, Enallagma sp. We tested the hypotheses that microcystins transfer from the tissue of herbivorus zooplankton to that of predatory invertebrates and that these toxins biomagnify across trophic levels. We also assessed the relative contribution of toxin transfer from the gut and tissue of Daphnia pulex to Enallagma sp. We found that microcystins are effectively sequestered in the tissue of Daphnia pulex, and that these sequestered toxins are then transferred to the tissue of Enallagma sp. The contribution of gut contents to toxin transfer was negligible. Contrary to the pattern predicted by biomagnification, we found that the concentration of microcystins decreased with increasing trophic levels. Our results support the hypothesis that microcystins can be transferred trophically, but do not support the hypothesis that microcystins biomagnify from lower to higher trophic levels. Conversly, we observe biodilution in this system. These results have consequences for the impact of microcystins across trophic levels in a changing world with increasing intensity and duration of harmful algal blooms.

Environmental risk assessment of pharmaceuticals in wastewaters and reclaimed water from catalan main river basins

Aquatic pollution from pharmaceuticals is a growing environmental concern globally, particularly in Catalonia's primary water bodies, the Llobregat and Besòs rivers. This study investigates pharmaceutical residues in reclaimed water effluents from the Llobregat River and a wastewater treatment plant (WWTP) in the Besòs River, critical contributors to the region's water resources. Employing LC-MS/MS, 85 pharmaceutical residues were monitored, revealing elevated concentrations of tramadol, losartan, and gemfibrozil, commonly prescribed drugs in Catalonia. Surprisingly, downstream concentrations exceeded upstream levels significantly, indicating the adverse impact of reclaimed water on water quality. Furthermore, evaluation of WWTP efficiency displayed varying removal rates, from 10 % to 99.8 %, highlighting treatment inadequacies for certain compounds. Predictive environmental concentrations (PECs) aligned closely with measured values, affirming the utility of predictive models in early-stage research. Risk assessment via the risk quotient (RQ) method identified atorvastatin and chlorpromazine as surpassing toxicity thresholds. This study underscores the urgent need to address pharmaceutical contamination in urban rivers and reclaimed waters in Catalonia. By highlighting treatment inefficacies and potential ecological risks, it contributes to the development of sustainable water management strategies and environmental conservation efforts in the region. Efforts should focus on continuously monitoring specific compounds, evaluating their individual toxicity, and implementing appropriate remediation techniques in WWTPs to safeguard water quality and aquatic ecosystems.

Size-dependent toxic interaction between polystyrene beads and mercury on the mercury accumulation and multixenobiotic resistance (MXR) of brackish water flea Diaphanosoma celebensis

Due to their worldwide distribution and persistence, mercury (Hg), and nano- and microplastics (NMPs) pose major threats to global ocean ecosystems. Hg and NMPs co-exist in the ocean and can interact with each other. However, information on the toxicity of this interaction to marine biota remains limited. Thus, we investigated the toxicological interaction between HgCl2 (Hg) and NMPs by studying the influence of different sizes of polystyrene beads (0.05-, 0.5-, and 6-μm) on Hg accumulation in the brackish water flea Diaphanosoma celebensis. The Hg adsorption capacity of NPs (0.05-μm) was higher than that of MPs (0.5- and 6-μm). Only the group co-exposed to both Hg and NPs showed increased Hg content in D. celebensis. Multixenobiotic resistance (MXR) activity and transcriptional modulation of transporter genes (ABCBs and ABCCs) were decreased by NMP exposure, particularly by NPs, suggesting MXR disruption by NPs. However, only the activity of multidrug resistance-associated proteins (MRPs; ABCCs) increased with Hg exposure and decreased upon NP+Hg co-exposure, indicating an important role of ABCC in Hg efflux. Furthermore, in vivo toxicity tests showed a synergistic toxic interaction between Hg and NPs on the reproduction of D. celebensis. Our findings suggest that NPs have the potential to enhance the toxicity of Hg, increasing Hg accumulation not only by serving Hg as a carrier but also by disrupting MXR.

Automated Image-Based Fluorescence Screening of Mitochondrial Membrane Potential in Daphnia magna: An Advanced Ecotoxicological Testing Tool

This study demonstrated the strengths of in vivo molecular staining coupled with automated imaging analysis in Daphnia magna. A multiwell plate protocol was developed to assess mitochondrial membrane potential using the JC-1 dye. The suitability of five common anesthetics was initially tested, and 5% ethanol performed best in terms of anesthetic effects and healthy recovery. The staining conditions were optimized to 30 min staining with 2 μM JC-1 for best J-aggregate formation. The protocol was validated with the model compound carbonyl cyanide 3-chlorophenylhydrazone (CCCP) and used to measure the effect of four environmental contaminants, 2,4-dinitrophenol, triclosan, n-(1,3-dimethylbutyl)-N'-phenyl-p-phenylenediamine (6PPD), and ibuprofen, on mitochondrial health. Test organisms were imaged using an automated confocal microscope, and fluorescence intensities were automatically quantified. The effect concentrations for CCCP were lower by a factor of 30 compared with the traditional OECD 202 acute toxicity test. Mitochondrial effects were also detected at lower concentrations for all tested environmental contaminants compared to the OCED 202 test. For 2,4-dinitrophenol, mitochondria effects were detectable after 2 h exposure to environmentally relevant concentrations and predicted organism death was observed after 24 h. The high sensitivity and time efficiency of this novel automated imaging method make it a valuable tool for advancing ecotoxicological testing.

Daphnia magna model for the study of mycotoxins present in food: Gliotoxin, ochratoxin A and its combination

Mycotoxins are low molecular weight compounds present in food and feed. Although their effects on human health have been widely described, their mechanisms of action are still undefined. Gliotoxin (GTX) and ochratoxin A (OTA) are among the most dangerous mycotoxins produced by Aspergillus spp. Therefore, their toxicity was studied in the Daphnia magna model, which has high capacity to predict cytotoxicity and assess ecotoxicity, comparable to mammalian models. The study consisted of a series of tests to evaluate the effects of mycotoxins GTX, OTA and their combinations at different dilutions on Daphnia magna that were conducted according to standardized OECD 202 and 211 guidelines. The following assays were carried out: acute toxicity test, heartbeat, delayed toxicity test, reproduction, growth rate test. Reproducibility was determined by observing the offspring after 21 days of GTX exposure. In acute and delayed toxicity transcript levels of genes involved in xenobiotic metabolism (mox, gst, abcb1, and abcc5), and oxidative stress (vtg-SOD) were analyzed by qPCR. GTX showed acute toxicity and decreased heart rate in D. magna compared to OTA. On the other hand, OTA showed a delayed effect as evidenced by the immobility test. Both mycotoxins showed to increase genes involved in xenobiotic metabolism, while only the mycotoxin mixture increased oxidative stress. These results suggest that the mycotoxins tested could have negative impact on the environment and human health.

Chemical tolerance related to the ABC transporter gene and DNA methylation in cladocera (Daphnia magna)

We performed multigenerational tests to clarify the chemical tolerance mechanisms of a nontarget aquatic organism, Daphnia magna. We continuously exposed D. magna to a carbamate insecticide (pirimicarb) at lethal or sublethal concentrations (0, 3.8, 7.5, and 15 μg/L) for 15 generations (F0-F14). We then determined the 48 h-EC50 values and mRNA expression levels of acetylcholinesterase, glutathione S-transferase, and ATP (Adenosine triphosphate)-binding cassette transporter (ABCt) in neonates (<24 h old) from F0, F4, F9, and F14. To ascertain the effects of DNA methylation on pirimicarb sensitivity, we measured 5-methylcytosine levels (DNA methylation levels) in neonates of parents in the last generation (F14). In addition, we cultured groups exposed to 0 and 7.5 μg/L (the latter of which acquired chemical tolerance to pirimicarb) with or without 5-azacytidine (de-methylating agent) and determined methylation levels and 48 h-EC50 values in neonates (<24 h old) from the treated parents. The EC50 values (30.3-31.6 μg/L) in F14 of the 7.5 and 15 μg/L groups were approximately two times higher than that in the control (16.0 μg/L). A linear mixed model analysis showed that EC50 and ABCt mRNA levels were significantly increased with generational alterations; further analysis showed that the ABCt mRNA level was positively related to the EC50 . Therefore, ABCt may be associated with altered pirimicarb sensitivity. In addition, the EC50 value and DNA methylation levels in pirimicarb-tolerant clones decreased after exposure to 5-azacytidine, suggesting that DNA methylation contributes to chemical tolerance. These findings improved our knowledge regarding the acquisition of chemical tolerance in aquatic organisms.

Multixenobiotic response of Collembola to soil contamination, the phisiological basis for bioindicative environmental monitoring

Collembola are well-established models in ecotoxicological research, extensively employed to investigate the effects of various contaminants, including heavy metals. The Multixenobiotic Resistance Mechanism (MXR) is a physiological response based on transmembrane efflux proteins that play a pivotal role in pumping xenobiotics and conferring resistance. This mechanism is firmly established as a biomarker of aquatic contamination and has recently shown promise as a soil biomonitoring tool. In this study, we aimed to assess the feasibility of utilizing the MXR mechanism as a biomonitoring tool, specifically by investigating the response of two Collembola species exposed to soil contaminated in a real-life situation. Soil samples were obtained from the site of Brazil's largest mine disaster, a dam rupture in Brumadinho-MG. We explored MXR activity in the model species Folsomia candida and a tropical native species, Cyphoderus sp. Our findings reveal efflux activity in both species, confirmed by model MXR protein inhibitors. Moreover, we observed distinct MXR activity levels corresponding to the degree of heavy metal contamination in the soil samples. Consequently, our results underscore the potential of combining an established soil bioindicator, such as Collembola, with the physiological response of a molecular biomarker like MXR. This approach may represent a valuable strategy for biomonitoring terrestrial ecosystems.

Temperature related toxicity features of acute acetamiprid and thiacloprid exposure in Daphnia magna and implications on reproductive performance

This study investigated the potential for elevated temperature to alter the toxicity of acetamiprid (ACE) and thiacloprid (Thia) in the ecotoxicity model Daphnia magna. The modulation of CYP450 monooxygenases (ECOD), ABC transporter activity (MXR) and incident cellular reactive oxygen species (ROS) overproduction was screened in premature daphnids following acute (48 h) exposure to sublethal concentrations of ACE and Thia (0.1-, 1.0 μM) at standard 21 °C and elevated 26 °C temperatures. Delayed outcomes of acute exposures were further evaluated based on the reproduction performance of daphnids monitored over 14 days of recovery. Exposures to ACE and Thia at 21^o C elicited moderate induction of ECOD activity, pronounced inhibition of MXR activity and severe ROS overproduction in daphnids. In the high thermal regime, treatments resulted in significantly lower induction of ECOD activity and inhibition of MXR activity, suggesting a suppressed metabolism of neonicotinoids and less impaired membrane transport activity in daphnids. Elevated temperature on its own, caused a three-fold rise in ROS levels in control daphnids, while ROS overproduction upon neonicotinoid exposure was less accentuated. Acute exposures to ACE and Thia caused significant decreases also in the reproduction of daphnids, indicating delayed outcomes even at environmentally relevant concentrations. Both the cellular alterations in exposed daphnids and decreases in their reproductive output post exposures evidenced closely similar toxicity patterns and potentials for the two neonicotinoids. While elevated temperature elicited only a shift in baseline cellular alterations evoked by neonicotinoids, it significantly worsened the reproductive performance of daphnids following neonicotinoid exposures.

Alterations in Daphnia magna exposed to enniatin B and beauvericin provide additional value as environmental indicators

Mycotoxins beauvericin (BEA) and enniatin B (ENN B) affect negatively several systems and demand more studies as the mechanisms are still unclear. The simultaneous presence of contaminants in the environment manifests consequences of exposure for both animals and flora. Daphnia magna is considered an ideal invertebrate to detect effects of toxic compounds and environmental alterations. In this study, the potential toxicity and the basic mechanism of BEA and ENN B individually and combined were studied in D. magna. Acute and delayed toxicity were evaluated, and transcript levels of genes involved in xenobiotic metabolism (mox, gst, abcb1, and abcc5), reproduction, and oxidative stress (vtg-SOD) were analyzed by qPCR. Though no acute toxicity was found, results revealed a spinning around and circular profile of swimming, a strong decrease of survival after 72 h for BEA and ENN B at 16 µM and 6.25 µM, respectively, while for BEA + ENN B [8 + 1.6] µM after 96 h. The amount of mycotoxin remaining in the media revealed that the higher the concentration assayed the higher the amount remaining in the media. Differential regulation of genes suggests that xenobiotic metabolism is affected denoting different effects on transcription for tested mycotoxins. The results provide new insights into the underlying risk assessment of BEA and ENN B not only through food for consumers but also for the environment.

Cyclosporin A acts as a novel insecticide against Cry1Ac-susceptible and -resistant Helicoverpa armigera

Cotton bollworm (Helicoverpa armigera) is an economically important pest, which is difficult to manage due to its biological and ecological traits, and resistance to most insecticides. Alternative compounds for the sustainable management of H. armigera are needed. As a fungal metabolite, Cyclosporin A (CsA) has not been applied in agriculture pests. Here, CsA was evaluated as a propective insecticide for H. armigera. The results showed that CsA displayed high insecticidal activity against both Cry1Ac-susceptible and -resistant populations of H. armigera. Moreover, lower concentrations of CsA had clear effects, including significantly reduced pupal weight, pupation rate, emergence rate, ovary size, female fecundity and egg hatchability. Further study confirmed that CsA suppressed calcineurin activity and the subsequent expression of endogenous antimicrobial peptide genes (APMs), leading to impaired immunity, ultimately resulting in delayed development and increased mortality. Thus, CsA treatment could control the cotton bollworm population and even showed efficacy against those with Bt resistance. In addition, the morphological changes observed in insects fed CsA with lower concentrations provide insight into insect immunity, regulation of growth and development, regulation of body color, ovary development and sexual selection under external pressure. Overall, our study provides information on biological control potential of Cry1Ac-susceptible and -resistant populations of H. armigera to develop novel bioinsecticides.

Cyclosporin A as a Potential Insecticide to Control the Asian Corn Borer Ostrinia furnacalis Guenée (Lepidoptera: Pyralidae)

The long-term use of chemical insecticides has caused serious problems of insect resistance and environmental pollution; new insecticides are needed to solve this problem. Cyclosporin A (CsA) is a polypeptide produced by many fungi, which is used to prevent or treat immune rejection during organ transplantation. However, little is known about the utility of CsA as an insecticide. Therefore, this study evaluated the insecticidal activity of CsA using Ostrinia furnacalis as a model. The results demonstrated that CsA was toxic to O. furnacalis with LC₅₀ values of 113.02 μg/g and 198.70 μg/g for newly hatched neonates and newly molted third-instar larvae, respectively. Furthermore, CsA treatment had sublethal effects on the development of O. furnacalis, and significantly reduced the fecundity of adults; this suggests that CsA has great potential to suppress O. furnacalis populations. Further analysis revealed that CsA suppressed calcineurin activity in larvae. CsA had independent or synergistic toxic effects on O. furnacalis when combined with β-cypermethrin, indoxacarb, emamectin benzoate, azadirachtin, and the Bacillus thuringiensis toxin Cry1Ac, which suggests that CsA can help prevent or manage resistance. Our study provides detailed information on the potential of CsA as an insecticide for controlling lepidopterans.

Interactions of Environmental Chemicals and Natural Products With ABC and SLC Transporters in the Digestive System of Aquatic Organisms

An organism’s diet is a major route of exposure to both beneficial nutrients and toxic environmental chemicals and natural products. The uptake of dietary xenobiotics in the intestine is prevented by transporters of the Solute Carrier (SLC) and ATP Binding Cassette (ABC) family. Several environmental chemicals and natural toxins have been identified to induce expression of these defense transporters in fish and aquatic invertebrates, indicating that they are substrates and can be eliminated. However, certain environmental chemicals, termed Transporter-Interfering Chemicals or TICs, have recently been shown to bind to and inhibit fish and mammalian P-glycoprotein (ABCB1), thereby sensitizing cells to toxic chemical accumulation. If and to what extent other xenobiotic defense or nutrient uptake transporters can also be inhibited by dietary TICs is still unknown. To date, most chemical-transporter interaction studies in aquatic organisms have focused on ABC-type transporters, while molecular interactions of xenobiotics with SLC-type transporters are poorly understood. In this perspective, we summarize current advances in the identification, localization, and functional analysis of protective MXR transporters and nutrient uptake systems in the digestive system of fish and aquatic invertebrates. We collate the existing literature data on chemically induced transporter gene expression and summarize the molecular interactions of xenobiotics with these transport systems. Our review emphasizes the need for standardized assays in a broader panel of commercially important fish and seafood species to better evaluate the effects of TIC and other xenobiotic interactions with physiological substrates and MXR transporters across the aquatic ecosystem and predict possible transfer to humans through consumption.

Comparative Toxicological Evaluation of Tattoo Inks on Two Model Organisms

Tattooing is a technique that introduces colored substances under the skin in order to color it permanently. Decomposition products of tattoo pigments produce numerous damages for the skin and other organs. We studied the effects of a commercial red ink tattoo, PR170, on Xenopus laevis embryos and Daphnia magna nauplii using concentrations of 10, 20, and 40 mg/L. For Xenopus, we applied the FETAX protocol analyzing survival, malformations, growth, heart rate, and the expression of genes involved in the development. In D. magna, we evaluated the toxicity with an immobilization test. Moreover, we investigated the production of ROS, antioxidant enzymes, and the expression of the ATP-binding cassette in both models. Our results indicate that PR170 pigment has nanoparticle dimensions, modifies the survival and the ATP-binding cassette activity, and induces oxidative stress that probably produces the observed effects in both models. Deformed embryos were observed in Xenopus, probably due to the modification of expression of genes involved in development. The expression of pro-inflammatory cytokines was also modified in this amphibian. We think that these effects are due to the accumulation of PR170 and, in particular, to the presence of the azoic group in the chemical structure of this pigment. Further studies needed to better understand the effects of commercial tattoo inks.

Long-term exposure of Daphnia magna to polystyrene microplastic (PS-MP) leads to alterations of the proteome, morphology and life-history

In the past years, the research focus on the effects of MP on aquatic organisms extended from marine systems towards freshwater systems. An important freshwater model organism in the MP field is the cladoceran Daphnia, which plays a central role in lacustrine ecosystems and has been established as a test organism in ecotoxicology. To investigate the effects of MP on Daphnia magna, we performed a chronic exposure experiment with polystyrene MP under strictly standardized conditions. Chronic exposure of D. magna to PS microparticles led to a significant reduction in body length and number of offspring. To shed light on underlying molecular mechanisms induced by microplastic ingestion in D. magna, we assessed the effects of PS-MP at the proteomic level, as proteins, e.g., enzymes, are especially relevant for an organism's physiology. Using a state-of-the-art mass spectrometry based approach, we were able to identify 28,696 different peptides, which could be assigned to 3784 different proteins. Using a customized bioinformatic workflow, we identified 41 proteins significantly altered in abundance (q-value <0.05) in the PS exposed D. magna. Among the proteins increased in the PS treated group were several sulfotransferases, involved in basic biochemical pathways, as well as GABA transaminase catalyzing the degradation of the neurotransmitter GABA. In the abundance decreased group, we found essential proteins such as the DNA-directed RNA polymerase subunit and other proteins connected to biotic and inorganic stress and reproduction. Strikingly, we further identified several digestive enzymes that are significantly downregulated in the PS treated animals, which could have interfered with the affected animal's nutrient supply. This may explain the altered morphological and life history traits of the PS exposed daphnids. Our results indicate that long-term exposure to PS microplastics, which are frequently detected in environmental samples, may affect the fitness of daphnids.

Combined exposure to microplastics and zinc produces sex-specific responses in the water flea Daphnia magna

Microplastics are ubiquitous environmental pollutants and a great threat to the aquatic environment. Due to their small size (ranging from 1 µm to 5 mm), microplastics be easily ingested by a wide range of organisms and can serve as a vector for various contaminants. In this study, additive or possible synergistic effects of microplastics and zinc were demonstrated through sex-specific alterations in behavior, redox status, and modulation of detoxification-related genes in Daphnia magna, with males being more sensitive than females with stronger modulations of antioxidant responses, particularly on glutathione S-transferases expressions. Furthermore, we demonstrated microplastics may act as vectors for metals (Zn²⁺) in the aquatic environment in D. magna, with reduced bio-concentration of the total Zn concentration, inducing greater toxicity. Our findings demonstrated synergistic toxicity of the heavy metal Zn and microplastics and could contribute to greater understanding of sex-specific effects of microplastics in aquatic organisms.

The genome of the European estuarine calanoid copepod Eurytemora affinis: Potential use in molecular ecotoxicology

In this study, we sequenced and assembled the genome of a European estuarine calanoid copepod using Oxford Nanopore PromethION and Illumina HiSeq 2500 platforms. The length of the assembled genome was 776.1 Mb with N50 = 474.9 kb (BUSCO 85.9%), and the genome consisted of 2473 contigs. A total of 18,014 genes were annotated and orthologous gene clusters were analyzed in comparison to other copepods. In addition, genome-wide identification of cytochrome P450s, glutathione S-transferases, and ATP-binding cassette transporters in E. affinis was performed to determine gene repertoire of these detoxification-related gene families. Results revealed the presence of species-specific gene inventories, indicating that these gene families have evolved through species-specific gene loss/expansion processes, possibly due to adaptation to different environmental stressors. Our study provides a new inventory of the European estuarine calanoid copepod E. affinis genome with emphasis on phase I, II, and III detoxification systems.

CRISPR/Cas9 mutagenesis reveals a role for ABCB1 in gut immune responses to Vibrio diazotrophicus in sea urchin larvae

The ABC transporter ABCB1 plays an important role in the disposition of xenobiotics. Embryos of most species express high levels of this transporter in early development as a protective mechanism, but its native substrates are not known. Here, we used larvae of the sea urchin Strongylocentrotus purpuratus to characterize the early life expression and role of Sp-ABCB1a, a homolog of ABCB1. The results indicate that while Sp-ABCB1a is initially expressed ubiquitously, it becomes enriched in the developing gut. Using optimized CRISPR/Cas9 gene editing methods to achieve high editing efficiency in the F0 generation, we generated ABCB1a crispant embryos with significantly reduced transporter efflux activity. When infected with the opportunistic pathogen Vibrio diazotrophicus, Sp-ABCB1a crispant larvae demonstrated significantly stronger gut inflammation, immunocyte migration and cytokine Sp-IL-17 induction, as compared with infected control larvae. The results suggest an ancestral function of ABCB1 in host-microbial interactions, with implications for the survival of invertebrate larvae in the marine microbial environment.

Perturbation of calcium homeostasis and multixenobiotic resistance by nanoplastics in the ciliate Tetrahymena thermophila

Microplastics (MPs) are an environmental hazard of growing concern, including their potential toxic effects on the biota of different trophic levels. Nevertheless, the molecular mechanisms underlying MP-induced toxicity remain largely unknown. In the present study, Tetrahymena thermophila was exposed to polystyrene nanoplastics (PS-NPs) and the responses of this relatively sensitive ciliate were then followed using transcriptome analysis together with several other verification methods. The results showed that PS-NPs perturbed calcium (Ca) homeostasis, by inducing the inositol-1,4,5-trisphosphate-dependent liberation of Ca from the endoplasmic reticulum into the cytosol. The high cytosolic concentration of Ca induced Ca accumulation in mitochondria, which increased mitochondrial permeability and the generation of reactive oxygen species, finally leading to growth inhibition. Such toxicity is the so-called direct effects of PS-NPs. By contrast, PS-NPs also inhibited the activity of multixenobiotic resistance transporter, by down-regulating the ATP-binding cassette transporter genes Abcb15 and Abcc52. This additional effect may alter cellular responses to other pollutants and implicates PS-NPs in the risks to the organism posed by subsequent toxic exposures, which was named as the indirect effects of PS-NPs. Our study highlights the importance of considering both direct and indirect biological effects of MPs in evaluations of their environmental and health risks.

Detoxification and reproductive system-related gene expression following exposure to Cu(OH)2 nanopesticide in water flea (Daphnia magna Straus 1820)

The extensive use of copper-based nanopesticides in agriculture has led to their release into the aquatic environment and causes a potential risk to aquatic biota. However, there is a lack of knowledge regarding the possible toxic effect of these nanopesticides on non-target aquatic organisms including invertebrates. Therefore, in this study, effects of commonly used copper-based nanopesticide "Kocide 3000" on gene expression related to detoxification (cyp360a8, gst, P-gp, and hr96) and reproductive system (cut, cyp314, dmrt93, and vtg) in Daphnia magna was investigated through an acute toxicity test. In general, exposure to the nanopesticide caused significant down-regulation of detoxification genes after 24 h and then significant up-regulation after 48 h. Exposure to the nanopesticide, however, significantly induced cut expression after 24 h. Moreover, dmrt93 and vtg genes were up-regulated after 48 h exposure to the nanopesticide. On the other hand, the expression of dmrt93 and vtg down-regulated at high concentration of Cu(OH)₂ nanopesticide (1.5 ppm) after 96 h. The results of this study provide first evidence into the crucial role of genes related to detoxification and reproductive system in response to Cu(OH)₂ nanopesticide. The use of physiological, biochemical bioassays, as well as gene expression, can help explain the toxic effect of copper-based nanopesticides and provide more insight into the exact mechanism of toxicity in non-target aquatic organisms.

Physiological and pharmacological characterization of a molluscan neuronal efflux transporter; evidence for age-related transporter impairment

Plasma membrane efflux transporters play crucial roles in the removal and release of both harmful and beneficial substances from the interior of cells and tissue types in virtually every extant species. They contribute to the clearance of a broad spectrum of exogenous and endogenous toxicants and harmful metabolites, including the reactive lipid aldehyde byproducts of lipid peroxidation that are a hallmark of cellular ageing. Here, we tested whether declining transporter functionality may contribute to functional decline in a snail model of neuronal ageing. Through measuring the removal of 5(6)-carboxyfluorescein, a known substrate for membrane efflux transporters, we provide, for the first time, physiological evidence for the existence of probenecid-, MK571- and glutathione-sensitive efflux transporters in (gastropod) neurons and demonstrate that their functionality declines with age. Our data support the idea that waning cellular detoxification capacity might be a significant factor in the escalation of (lipo-)toxicity observed in neuronal ageing.

Cerium and erbium effects on Daphnia magna generations: A multiple endpoints approach

Cerium (Ce, CeCl₃) and Erbium (Er, ErCl₃) are increasingly used in many electronic devices facilitating the alteration of their biogeochemical cycles (e.g. e-waste). Previous surveys stated that their environmental concentrations due to natural or anthropogenic events can reach up to 161 μg/L in ore mine effluent for Ce with a mean water concentration of 0.79 μg/L, and 11.9 μg/L for Er in ore mine effluents with a mean water concentration of 0.004 μg/L. Their potential effects onto aquatic organisms are still relatively unexplored. In this study, long-term multigenerational effects on Daphnia magna were assessed using various exposure times (3, 7, 14, and 21 days) in three generations (F0, F1 and F2). Each generation was exposed to environmental concentrations of Ce and Er (0.54 and 0.43 μg/L, respectively - mean values) and effects included organisms' size, parental reproduction, and survival, determination of reactive oxygen species (ROS), enzymatic activity (superoxide dismutase (SOD), catalase (CAT), and glutathione S-transferase (GST)), gene expression of ATP-binding cassette (ABC) transporter, and uptake. Results evidenced that chronic multi-generational exposure of daphnids to Ce and Er reduced survival, growth and reproduction, decreasing ROS, SOD and CAT from F0 to F2. Ce reduced the number of generated offsprings after each generation, while Er delayed the time of offsprings emergence, but not their number. ROS, SOD, CAT and GST evidenced that Er is slightly more toxic than Ce. Up- and downregulation of genes was limited, but Ce and Er activated the ABC transporters. Uptake of Ce and Er decreased through exposure time and generations.

Simvastatin affect the expression of detoxification-related genes and enzymes in Daphnia magna and alter its life history parameters

Simvastatin (SV), as an hypocholesterolaemic drug, has been detected in various aquatic environment. However, limited information is available on the effects of SV on freshwater invertebrates. In the present study, we investigated the toxic effects of SV on Daphnia. magna (D. magna) through measuring the physiological changes (e.g., survival, growth rate, and reproduction) in a 21-d chronic toxicity test We also determined the expression of seven detoxification and reproduction-related genes (i.e. HR96, P-gp, CYP360A8, GST, CYP314, EcR and Vtg) and several enzymes (i.e. APND, ERND, GST and CAT) in a acute test (24 h). Results showed that high concentration (e.g. 50 μg L^-1) of SV for short time exposure (e.g. 24 h) significantly induced the expression of HR96 and P-gp (e.g. up to 2.5 folds)and enzymes (e.g. increasing 4.0 folds for ERND and GST activity) in D. magna.. The long-term chronic exposure (21 days) may cause the changes of life history parameters such as decreasing total egg production number per individual and intrinsic growth rates etc. SV may act as a potential endocrine disruptor to D. magna and the reproduction parameters were more sensitive endpoints than the survival and growth for evaluating SV exposure.

The genome of the freshwater water flea Daphnia magna: A potential use for freshwater molecular ecotoxicology

The water flea Daphnia magna is a small planktonic cladoceran. D. magna has been used as a model species for ecotoxicology, as it is sensitive to environmental stressors and environmental changes. Since Daphnia is affected by culture environment and each population/strain has its own ecological and genetic characteristics, its population/strain-based genome information is useful for environmental genomic studies. In this study, we assembled and characterized the genome of D. magna. Using a high-density genetic map of D. magna xinb3, the draft genome was integrated to 10 linkage groups (LGs). The total length of the integrated genome was about 123 Mb with N50 = 10.1 Mb, and the number of scaffolds was 4193 including 10 LGs. A total of 15,721 genes were annotated after manual curation. Orthologous genes were characterized in the genome and compared with other genomes of Daphnia. In addition, we identified defense related genes such as cytochrome P450 (CYP) genes, glutathione S-transferase (GST) genes, and ATP-binding cassette (ABC) genes from the assembled D. magna genome for its potential use in molecular ecotoxicological studies in the freshwater environment. This genomic resource will be helpful to study for a better understanding on molecular mechanism in response to various pollutants.

Tryptophan hydroxylase (TRH) loss of function mutations in Daphnia deregulated growth, energetic, serotoninergic and arachidonic acid metabolic signalling pathways

Serotonin has a pivotal function regulating development, growth, reproduction and behavior in animals. In this paper, we studied the deregulatory effects of the deprivation of serotonin in Daphnia magna TRH CRISPR-Cas9 mutants. Bi-allelic in-del THR mutants and, to a lesser extent, mono-allelic ones grew less, reproduced later, and produced smaller clutches than wild type clones. Transcriptomic and functional gene analyses showed a down-regulation of growth/molting and energy metabolism signaling pathways in TRH mutants, while revealing marked differences between mono- and bi-allelic clones. Bi-allelic mutants, lacking serotonin, presented the serotonergic synapse and arachidonic acid metabolic pathways down-regulated while the tryptophan to kynurenine was upregulated, thus indicating a cross-talk between the serotonergic and arachidonic acid metabolic pathways. Finally, the effects on the insulin growth factor-mediated signaling pathway were marginal. These changes in functional and metabolic pathways are consistent with previously reported effects in D. magna exposed to pharmaceuticals that inhibited arachidonic metabolism or enhanced the levels of serotonin.

Impact of an immunosuppressive human pharmaceutical on the interaction of a bacterial parasite and its invertebrate host

The interaction of pollutants and pathogens may result in altered and often enhanced effects of the chemical, the biotic stressor or both. These interaction effects cannot be reliably predicted from the toxicity of the chemical or the virulence of the pathogen alone. While standardized detection methods for immunotoxic effects of chemicals exist with regard to human health, employing host-resistance assays with vertebrates, such standardized test systems are completely lacking for invertebrate species and no guidance is available on how immunotoxic effects of a chemical in invertebrates could be definitively identified. In the present study, we investigated the impact of the immunosuppressive pharmaceutical cyclosporine A (CsA) on the invertebrate host-pathogen system Daphnia magna - Pasteuria ramosa. CsA is a calcineurin-inhibitor in vertebrates and also known to have antibiotic as well as antifungal properties. Juvenile D. magna were exposed to CsA for 21 days with or without additional pathogen challenge during the first 72 h of exposure. Long-term survival of the host D. magna was synergistically impacted by co-exposure to the chemical and the pathogen, expressed e.g. in significantly enhanced hazard ratios. Additionally, enhanced virulence of the pathogen upon chemical co-exposure was expressed in an increased proportion of infected hosts and an increased speed of Pasteuria-induced host sterilization. In contrast, effects on reproduction were additive in Pasteuria-challenged, but finally non-infected D. magna. The enhancing effects of CsA occurred at and below 3 μg/L, which was in the absence of the pathogen the lowest concentration significantly impacting the standard toxicity endpoint 'reproduction' in D. magna. Hence, the present study provides evidence that a pharmaceutical intended to suppress the human immune system can also suppress disease resistance of an aquatic invertebrate organism at otherwise non-toxic concentrations. Plausible ways of direct interactions of CsA with the host's immune system are discussed, e.g. interference with phagocytosis or Toll-like receptors. Experimental verification of such a direct interference would be warranted to support the strong evidence for immunotoxic activity of CsA in invertebrates. While it remains open whether CsA concentrations in the environment are high enough to trigger adverse effects in environmental organisms, our findings highlight the need to consider immunotoxicity in an environmental risk assessment, and to develop suitable standardized methods for this purpose.

Differential gene transcription across the life cycle in Daphnia magna using a new all genome custom-made microarray

Background

Unravelling the link between genes and environment across the life cycle is a challenging goal that requires model organisms with well-characterized life-cycles, ecological interactions in nature, tractability in the laboratory, and available genomic tools. Very few well-studied invertebrate model species meet these requirements, being the waterflea Daphnia magna one of them. Here we report a full genome transcription profiling of D. magna during its life-cycle. The study was performed using a new microarray platform designed from the complete set of gene models representing the whole transcribed genome of D. magna.

Results

Up to 93% of the existing 41,317 D. magna gene models showed differential transcription patterns across the developmental stages of D. magna, 59% of which were functionally annotated. Embryos showed the highest number of unique transcribed genes, mainly related to DNA, RNA, and ribosome biogenesis, likely related to cellular proliferation and morphogenesis of the several body organs. Adult females showed an enrichment of transcripts for genes involved in reproductive processes. These female-specific transcripts were essentially absent in males, whose transcriptome was enriched in specific genes of male sexual differentiation genes, like doublesex.

Conclusion

Our results define major characteristics of transcriptional programs involved in the life-cycle, differentiate males and females, and show that large scale gene-transcription data collected in whole animals can be used to identify genes involved in specific biological and biochemical processes.

Electronic supplementary material

The online version of this article (10.1186/s12864-018-4725-7) contains supplementary material, which is available to authorized users.

Novel approach for evaluating pharmaceuticals toxicity using Daphnia model: analysis of the mode of cytochrome P450-generated metabolite action after acetaminophen exposure

Because of its widespread use, the pharmaceutical acetaminophen (APAP) is frequently detected in aquatic environments. APAP can have serious physiological effects, such as reduced reproduction, low growth rates, and abnormal behavior, in aquatic organisms. However, the methods available for evaluation of the aquatic toxicity of APAP are of limited usefulness. The present study aimed to develop reliable and sensitive markers for evaluation of APAP toxicity using Daphnia as a model organism. We focused on N-acetyl-p-benzoquinoneimine (NAPQI) production from APAP via cytochrome P450 metabolism because NAPQI causes APAP toxicity. Daphnia magna were exposed to APAP (0, 50, or 100 mg/L for 12 h or 24 h), and the total metabolites were extracted and analyzed for NAPQI. Direct detection of NAPQI was difficult because of its high reactivity, and its peak was close to that for APAP. Therefore, we tried to identify molecular and biochemical indicators associated with NAPQI generation, elimination, and its interactions with macromolecules. We identified changes in CYP370A13 gene expression, glutathione depletion, inhibition of thioredoxin reductase activity, and production of reactive oxygen species as indicators of D. magna exposure to APAP. These indicators could be used to develop sensitive and accurate techniques to evaluate the environmental toxicity of APAP.

Effects of Hg sublethal exposure in the brain of peacock blennies Salaria pavo: Molecular, physiological and histopathological analysis

Marine environments are affected by large amounts of toxicants among those mercury (Hg). The aim of this study was to assess potential neurotoxic effects of Hg in the peacock blenny Salaria pavo. A sublethal contamination to 66 μg HgCl₂ L^-1 over periods of 1, 4, 10 and 15 days was performed. Total Hg concentrations measured in the brain highlighted the detection of Hg at days 1 and 4 following the exposure but no concentration of the metal was further detected. Partial-length cDNA of genes coding ABC transporters (abcb1, abcc1, abcc2, abcg2) and acetylcholinesterase (ache) were characterized. Results from mRNA expression levels displayed an up-regulation of abcb1 mRNA while a down-regulation of abcc1 and abcc2 mRNA was observed. No change in abcg2 and ache mRNA expression was noted throughout the experiment. At each sampling time, Hg exposure did not affect the activity of the AChE enzyme. The histological analysis indicated that fish exhibited several damages in the optic tectum and the cerebellum and 3 reaction patterns were identified for each organ: circulatory disturbances, regressive and progressive changes. Molecular, physiological and histological biomarkers assessed in the present study highlighted that peacock blennies were able to detoxify Hg from the brain tissue by developing defense mechanisms. More globally, neurotoxic effects of a sublethal Hg exposure in the brain of peacock blennies and the adaptation capacity of this species were evaluated.

The impact of chemosensitisation on bioaccumulation and sediment toxicity

Cellular multixenobiotic resistance (MXR) transport proteins enhance the efflux of numerous organic pollutants. However, MXR proteins may be blocked or saturated by xenobiotic compounds, acting as inhibitors - also called chemosensitisers. Although effective on a cellular level, the environmental relevance of chemosensitisers has not been conclusively demonstrated. Since sediments are an important source of bioaccumulating compounds in aquatic ecosystems, sediments and sediment-associated hydrophobic pollutants were investigated for their potential to increase exposure and toxicity in the presence of chemosensitisation. In this study, we address this issue by (1) comparing the net uptake of 17 hydrophobic environmental pollutants by zebrafish (Danio rerio) embryos in the presence and absence of the model chemosensitiser verapamil and (2) investigating the impact of verapamil on the dose-dependent effect on zebrafish embryos exposed to polluted sediment extracts. None of the 17 pollutants showed a reproducible increase in bioaccumulation upon chemosensitisation with verapamil. Instead, internal concentrations were subject to intra-species variation by a factor of approximately two. However, a significant increase in toxicity was observed upon embryo co-exposure to verapamil for one of three sediment extracts. In contrast, another sediment extract exhibited less toxicity when combined with verapamil. In general, the results indicate only a minor impact of verapamil on the uptake of moderately hydrophobic chemicals in zebrafish embryos.

Characterization of MXR activity in the sea anemone Bunodosoma cangicum exposed to copper

Transmembrane proteins of the ABC family contribute to a multiple xenobiotic resistance (MXR) phenotype in cells, driving the extrusion of toxic substances. This phenotype promotes a high degree of protection against xenobiotics. The present study provides a better understanding of the MXR activity in the podal disk cells of Bunodosoma cangicum exposed to copper, and further establishes the relationship between protein activity (measured by accumulation of rhodamine-B) and bioaccumulation of copper in these cells. Sea anemone cells were exposed for 24h to copper (0, 7.8 and 15.6μg/L) in presence and absence of MXR blocker (verapamil 50μM). Results indicate that copper exposure increases intracellular metal content when ABC proteins were blocked, causing an increase in cellular death. The present study also verified the relationship between MXR activity, ATP depletion, and general metabolic activity (by MTT). MXR activity decreased in treatment groups exposed to copper concentrations of 15.6μg/L and 10mM energy depleting potassium cyanide. Metabolic activity increased in cells exposed to 7.8μgCu/L, but 15.6μgCu/L was similar to 0 and 7.8μg/L. The presence of copper decreased the ABC proteins expression. The present study improves the knowledge of MXR in anemone cells and shows that this activity is closely associated with copper extrusion. Also, the copper exposure is able to modify the metabolic state and to lead to cytotoxicity when cells cannot defend themselves.

ATP-binding cassette (ABC) proteins in aquatic invertebrates: Evolutionary significance and application in marine ecotoxicology

The ATP-binding cassette (ABC) protein superfamily is known to play a fundamental role in biological processes and is highly conserved across animal taxa. The ABC proteins function as active transporters for multiple substrates across the cellular membrane by ATP hydrolysis. As this superfamily is derived from a common ancestor, ABC genes have evolved via lineage-specific duplications through the process of adaptation. In this review, we summarized information about the ABC gene families in aquatic invertebrates, considering their evolution and putative functions in defense mechanisms. Phylogenetic analysis was conducted to examine the evolutionary significance of ABC gene families in aquatic invertebrates. Particularly, a massive expansion of multixenobiotic resistance (MXR)-mediated efflux transporters was identified in the absence of the ABCG2 (BCRP) gene in Ecdysozoa and Platyzoa, suggesting that a loss of Abcg2 gene occurred sporadically in these species during divergence of Protostome to Lophotrochozoa. Furthermore, in aquatic invertebrates, the ecotoxicological significance of MXR is discussed while considering the role of MXR-mediated efflux transporters in response to various environmental pollutants.

Toxic effects of diclofenac on life history parameters and the expression of detoxification-related genes in Daphnia magna

Diclofenac (DCF), as a widely used drug, has been detected in various environmental media such as municipal wastewater effluent. However, there is little information on the effects of DCF on freshwater invertebrates potentially exposing to its residues in surface water. In the present study, we investigated the toxic effects of DCF on the physiological parameters (e.g., survival, growth rate, and reproduction) of a crustacean, Daphnia magna, via a 21-d chronic toxicity test, and we also evaluated the effects of DCF on the expression of the genes related to the detoxification metabolism, growth, development and reproduction (e.g., HR96, P-gp, CYP360A8, CYP314, GST, EcR and Vtg) in acute exposure (up to 96h) with RT-PCR. Significant toxic effects of DCF to D. magna were observed at 50μgL^-1, the expression of these selected genes was inhibited with 24h of exposure, and induced after 48h to some extents. The expression of Vtg was induced at high concentrations of DCF (500μgL^-1 and 5000μgL^-1) after 24h and 48h of exposure, but also significantly induced at low concentration (50μgL^-1) after 96h of exposure. Dose- and time-dependent relationships were observed for gene expression of the seven selected genes. In the 21-d chronic toxicity test, the days to the first brood and the days to the first egg production were both significantly delayed at 50μgL^-1. However, there were no significant differences observed among the molting frequency, number of eggs produced in the first brood, total number of eggs per individual, total number of broods per individual, body length and intrinsic growth rate. Our results suggested that the reproduction parameters are more sensitive endpoints than the survival and growth for evaluating the toxicity of DCF to aquatic invertebrates.

Dose-dependent effects of morphine on lipopolysaccharide (LPS)-induced inflammation, and involvement of multixenobiotic resistance (MXR) transporters in LPS efflux in teleost fish

Opioid drugs, such as morphine (MO), detected in aquatic environments worldwide, may harm fish due to their semi-persistence and ability to potently interact with molecular targets conserved across vertebrates. Here, we established a waterborne bacterial lipopolysaccharide (LPS) challenge assay with zebrafish embryos as a model to investigate chemically-induced disruption of the innate immune system, and used it to study the effects of MO exposure. Exposure to 1 mg/L MO resulted in pronounced immunosuppression, reflected in downregulation of several inflammation-related genes, including myd88, trif, traf6, p38, nfκb2, il-1β, il-8 and ccl34a. Fish exposed to 1 mg/L MO accumulated 11.7 ng/g (wet weight) of MO, a concentration comparable to that reported in blood of chronic drug abusers subject to higher infection rates. Surprisingly, exposure to lower MO concentrations (100 ng/L-100 μg/L) led to exacerbation of LPS-induced inflammation. Two ATP-binding cassette (ABC) transporters known to be involved in the xenobiotic efflux - abcb4 and abcc2, also known as multixenobiotic resistance (MXR) transporters - were downregulated at 100 ng/L MO. We hypothesized that ABC/MXR transporters could modulate the severity of inflammation by being involved in efflux of LPS, thus regulating its accumulation in the organism. Indeed, we could demonstrate that blocking of ABC/MXR transporters by an inhibitor, cyclosporine A, results in stronger inflammation, coinciding with higher LPS accumulation, as visualized with fluorescently labeled LPS. Our work demonstrates that MO can disrupt fish innate immune responses at environmentally relevant concentrations. We also provide evidence for a role of ABC/MXR transporters in LPS efflux in fish. These finding may be applicable across other taxa, as ABC transporters are evolutionary conserved. Since diverse environmentally present chemicals are known to interfere with ABC/MXR transporters' expression or activity, our discovery raises concerns about potential adverse effects of such compounds on the immune system responses in aquatic organisms.

Inhibition of multixenobiotic resistance transporters (MXR) by silver nanoparticles and ions in vitro and in Daphnia magna

The P-glycoprotein (P-gp, ABCB1) and multidrug resistance associated protein 1 (MRP1), important members of the ABC (ATP-binding cassette) transporters, protect cells and organisms via efflux of xenobiotics and are responsible for the phenomenon of multidrug or multixenobiotic resistance (MXR). In this study we first evaluated, in vitro, the interaction of silver nanoparticles (Ag NPs, 20, 23 and 27nm), Ag 200nm particles and Ag ions (AgNO3) with MXR efflux transporters using MDCKII and the P-gp over-expressing MDCKII-MDR1 cells and calcein-AM as a substrate of the transporters. Next the in vivo modulation of MXR activity was studied in Daphnia magna juveniles with the model P-gp and MRP1 inhibitors verapamil-HCl and MK571, respectively. The common environmental contaminants perfluorooctane sulfonate and bisphenol A, previously observed to interfere with the P-gp in vitro, also inhibited the efflux of calcein in vivo. Small-sized Ag NPs (with biomolecules present on the surface) and AgNO3 inhibited the MXR activity in daphnids and MDCKII-MDR1 cells, but abcb1 gene expression remained unchanged. Both Ag NPs and dissolved ions contributed to the effects. This study provides evidence of the interference of Ag NPs and AgNO3 with the MXR activity both in vitro and in D. magna, and should be taken into account when Ag NP toxicity is assessed.

Organic UV filters inhibit multixenobiotic resistance (MXR) activity in Tetrahymena thermophila: investigations by the Rhodamine 123 accumulation assay and molecular docking

Multixenobiotic resistance (MXR) transporters, which belong to ATP-binding cassette (ABC) family proteins, are present in living organisms as a first line of defense system against xenobiotics and environmental contaminants. The effects of six organic UV filters (4-methyl -benzylidene camphor, 4-MBC; benzophenone-3, BP-3; butyl methoxydibenzoyl-methane, BM-DBM; ethylhexyl methoxy cinnamate, EHMC; octocrylene, OC and homosalate, HMS) on multixenobiotic resistance (MXR) in Tetrahymena thermophila were investigated in this study. It was found that 4-MBC, BP-3 and BM-DBM could significantly inhibit activity of the MXR system, causing concentration dependent accumulation of rhodamine 123; while EHMC, OC and HMS had weak MXR inhibition. The IC50 (50 % inhibition concentration) values of 4-MBC, BP-3 and BM-DBM were 23.54, 40.59 and 26.37 μM, respectively, with inhibitory potentials of 23.1, 13.4 and 20.6 % relative to verapamil (VER, a model inhibitor of P-glycoprotein). Our results firstly provide the evidence for UV filters inhibition effect on MXR in aquatic organisms. In addition, it was revealed by molecular docking analysis that the selected six UV filters can occupy the same binding site on T. thermophila P-gp as VER does; and form H-bonds with residues Ser 328 and/or Asn 281. This study raises the awareness of aquatic ecological risk from the organic UV filters exposure, as they would be involved in potentiating toxic effects by chemosensitizing.

Induction of multixenobiotic defense mechanisms in resistant Daphnia magna clones as a general cellular response to stress

Multixenobiotic resistance mechanisms (MXR) were recently identified in Daphnia magna. Previous results characterized gene transcripts of genes encoding and efflux activities of four putative ABCB1 and ABCC transporters that were chemically induced but showed low specificity against model transporter substrates and inhibitors, thus preventing us from distinguishing between activities of different efflux transporter types. In this study we report on the specificity of induction of ABC transporters and of the stress protein hsp70 in clones selected to be genetically resistant to ABCB1 chemical substrates. Clones resistant to mitoxantrone, ivermectin and pentachlorophenol showed distinctive transcriptional responses of transporter protein coding genes and of putative transporter dye activities. Expression of hsp70 proteins also varied across resistant clones. Clones resistant to mitoxantrone and pentachlorophenol showed high constitutive levels of hsp70. Transcriptional levels of the abcb1 gene transporter and of putative dye transporter activity were also induced to a greater extent in the pentachlorophenol resistant clone. Observed higher dye transporter activities in individuals from clones resistant to mitoxantrone and ivermectin were unrelated with transcriptional levels of the studied four abcc and abcb1 transporter genes. These findings suggest that Abcb1 induction in D. magna may be a part of a general cellular stress response.

Differences in tolerance to anthropogenic stress between invasive and native bivalves

Tolerance towards environmental stress has been frequently considered as one of the key determinants of invasion success. However, empirical evidence supporting the assumption that invasive species can better endure unfavorable conditions compared with native species is limited and has yielded opposing results. In this study, we examined the tolerance to different stress conditions (thermal stress and trace metal zinc pollution stress) in two phylogenetically related and functionally similar freshwater bivalve species, the native Anodonta anatina and the invasive Sinanodonta woodiana. We assessed potential differences in response to stress conditions using several cellular response assays: efficiency of the multixenobiotic resistance mechanism, respiration estimate (INT reduction capacity), and enzymatic biomarkers. Our results demonstrated that the invasive species overall coped much better with unfavorable conditions. The higher tolerance of S. woodiana was evident from (i) significantly decreased Rhodamine B accumulation indicating more efficient multixenobiotic resistance mechanism; (ii) significantly higher INT reduction capacity and (iii) less pronounced alterations in the activity of stress-related enzymes (glutathione-S-transferase, catalase) and of a neurotoxicity biomarker (cholinesterase) in the majority of treatment conditions in both stress trials. Higher tolerance to thermal extremes may provide physiological benefit for further invasion success of S. woodiana in European freshwaters, especially in the context of climate change.

Is chemosensitisation by environmental pollutants ecotoxicologically relevant?

The active cellular efflux of toxicants is an efficient biological defense mode present in all organisms. By blocking this so-called multixenobiotic resistance transport-a process also referred to as chemosensitisation-, cellular bioaccumulation and the sensitivity of organisms towards environmental pollutants can increase. So far, a wide range of compounds, including pesticides, pharmaceuticals, fragrances, and surfactants, have been identified as chemosensitisers. Although, significant on a cellular level, the environmental impact of chemosensitisation on the organism level is not yet understood. Critically evaluating existing data, this paper identifies research needs to support our tentative conclusion that chemosensitisation may well enhance the risks of chemical exposure to aquatic organisms. Our conclusion is based on studies investigating the impact of individual chemicals and complex environmental mixtures on aquatic wildlife and a chemosensitiser mixture toxicity model which, however, is subject to great uncertainty due to substantial knowledge gaps. Those uncertainties include the inconsistent reporting of effect data, the lack of representative environmental contaminants tested for chemosensitisation, and the publishing of highly unreliable nominal exposure concentrations. In order to confirm the tentative conclusion of this paper, we require the significant and systematic investigation of a broader set of chemicals and environmental samples with a harmonised set of bioassays and rigorously controlled freely dissolved effect concentrations.

A Survey of the ATP-Binding Cassette (ABC) Gene Superfamily in the Salmon Louse (Lepeophtheirus salmonis)

Salmon lice, Lepeophtheirus salmonis (Krøyer, 1837), are fish ectoparasites causing significant economic damage in the mariculture of Atlantic salmon, Salmo salar Linnaeus, 1758. The control of L. salmonis at fish farms relies to a large extent on treatment with anti-parasitic drugs. A problem related to chemical control is the potential for development of resistance, which in L. salmonis is documented for a number of drug classes including organophosphates, pyrethroids and avermectins. The ATP-binding cassette (ABC) gene superfamily is found in all biota and includes a range of drug efflux transporters that can confer drug resistance to cancers and pathogens. Furthermore, some ABC transporters are recognised to be involved in conferral of insecticide resistance. While a number of studies have investigated ABC transporters in L. salmonis, no systematic analysis of the ABC gene family exists for this species. This study presents a genome-wide survey of ABC genes in L. salmonis for which, ABC superfamily members were identified through homology searching of the L. salmonis genome. In addition, ABC proteins were identified in a reference transcriptome of the parasite generated by high-throughput RNA sequencing (RNA-seq) of a multi-stage RNA library. Searches of both genome and transcriptome allowed the identification of a total of 33 genes / transcripts coding for ABC proteins, of which 3 were represented only in the genome and 4 only in the transcriptome. Eighteen sequences were assigned to ABC subfamilies known to contain drug transporters, i.e. subfamilies B (4 sequences), C (11) and G (2). The results suggest that the ABC gene family of L. salmonis possesses fewer members than recorded for other arthropods. The present survey of the L. salmonis ABC gene superfamily will provide the basis for further research into potential roles of ABC transporters in the toxicity of salmon delousing agents and as potential mechanisms of drug resistance.

Identification of a putatively multixenobiotic resistance related Abcb1 transporter in amphipod species endemic to the highly pristine Lake Baikal

The fauna of Lake Baikal in Eastern Siberia, the largest freshwater body on Earth, is characterized by high degrees of biodiversity and endemism. Amphipods, a prominent taxon within the indigenous fauna, occur in an exceptionally high number of endemic species. Considering the specific water chemistry of Lake Baikal with extremely low levels of potentially toxic natural organic compounds, it seems conceivable that certain adaptions to adverse environmental factors are missing in endemic species, such as cellular defense mechanisms mitigating toxic effects of chemicals. The degree to which the endemic fauna is affected by the recently occurring anthropogenic water pollution of Lake Baikal may depend on the existence of such cellular defense mechanisms in those species. We here show that endemic amphipods express transcripts for Abcb1, a major component of the cellular multixenobiotic resistance (MXR) defense against toxic chemicals. Based on a partial abcb1 cDNA sequence from Gammarus lacustris, an amphipod species common across Northern Eurasia but only rarely found in Lake Baikal, respective homologous sequences were cloned from five amphipods endemic to Lake Baikal, Eulimnogammarus verrucosus, E. vittatus, E. cyaneus, E. marituji, and Gmelinoides fasciatus, confirming that abcb1 is transcribed in those species. The effects of thermal (25 °C) and chemical stress (1-2 mg L(-1) phenanthrene) in short-term exposures (up to 24 h) on transcript levels of abcb1 and heat shock protein 70 (hsp70), used as a proxy for cellular stress in the experiments, were exemplarily examined in E. verrucosus, E. cyaneus, and Gammarus lacustris. Whereas increases of abcb1 transcripts upon treatments occurred only in the Baikalian species E. verrucosus and E. cyaneus but not in Gammarus lacustris, changes of hsp70 transcript levels were seen in all three species. At least for species endemic to Lake Baikal, the data thus indicate that regulation of the identified amphipod abcb1 is triggered within the general cellular stress response. This is the first report presenting molecular data on a MXR transporter in amphipods, an ecotoxicologically important but with regard to gene sequence data comparatively little explored taxon.

Multixenobiotic resistance efflux activity in Daphnia magna and Lumbriculus variegatus

Multixenobiotic resistance is a phenomenon in which ATP-binding cassette (ABC) family proteins transfer harmful compounds out of cells. Daphnia magna and Lumbriculus variegatus are model species in aquatic ecotoxicology, but the presence and activity of ABC proteins have not been well described in these species. The aim of this work was to study the presence, activity, and inhibition of ABC transport proteins in D. magna and L. variegatus. The presence of abcb1 and abcc transcripts in 8-9-day-old D. magna was investigated by qRT-PCR. The activity of MXR in D. magna and L. variegatus was explored by influx of the fluorescent ABC protein substrates rhodamine B and calcein-AM, with and without the model inhibitors verapamil (unspecific ABC inhibitor), reversin 205 (ABCB1 inhibitor) and MK571 (ABCC inhibitor). Juvenile D. magna possessed all examined abcb and abcc transcripts, but only reversin 205 inhibited MXR activity. The MXR activity in L. variegatus was inhibited by MK571, and to a lesser extent by verapamil, whereas reversin 205 seemed to stimulate the transport activity. Whereas calcein-AM worked better as an MXR substrate in D. magna, rhodamine B was a better substrate for L. variegatus MXR activity measurements. This is the first report on MXR activity in the order Lumbriculida, subclass Oligochaeta, and class Clitellata.

Transcriptomic, biochemical and individual markers in transplanted Daphnia magna to characterize impacts in the field

Daphnia magna individuals were transplanted across 12 sites from three Spanish river basins (Llobregat, Ebro, Jucar) showing different sources of pollution. Gene transcription, feeding and biochemical responses in the field were assessed and compared with those obtained in re-constituted water treatments spiked with organic eluates obtained from water samples collected at the same locations and sampling periods. Up to 166 trace contaminants were detected in water and classified by their mode of action into 45 groups that included metals, pharmaceuticals, pesticides, illicit drugs, and other industrial compounds. Physicochemical water parameters differentiated the three river basins with Llobregat having the highest levels of conductivity, metals and pharmaceuticals, followed by Ebro, whereas the Jucar river had the greatest levels of illicit drugs. D. magna grazing rates and cholinesterase activity responded similarly than the diversity of riparian benthic communities. Transcription patterns of 13 different genes encoding for general stress, metabolism and energy processes, molting and xenobiotic transporters corroborate phenotypic responses differentiated sites within and across river basins. Principal Component Analysis and Partial Least Square Projections to Latent Structures regression analyses indicated that measured in situ responses of most genes and biomarkers and that of benthic macroinvertebrate diversity indexes were affected by distinct environmental factors. Conductivity, suspended solids and fungicides were negatively related with the diversity of macroinvertebrates cholinesterase, and feeding responses. Gene transcripts of heat shock protein and metallothionein were positively related with 11 classes of organic contaminants and 6 metals. Gene transcripts related with signaling paths of molting and reproduction, sugar, protein and xenobiotic metabolism responded similarly in field and lab exposures and were related with high residue concentrations of analgesics, diuretics, psychiatric drugs, β blockers, illicit drugs, trizoles, bisphenol A, caffeine and pesticides. These results indicate that application of omic technologies in the field is a promising subject in water management.