Genomic expression responses toward bisphenol-A toxicity in Daphnia magna in terms of reproductive activity

Thresholds and interactive effects of BPA-gradient and temperature on life history traits of Daphnia magna

Bisphenol A (BPA), a synthetic organic compound widely used in the production of plastics, is recognized as an emerging contaminant because of its toxicity and the potential risks associated with bioaccumulation in organisms. Despite potential environmental hazards, there is a lack of studies examining BPA toxicity mechanisms and its potential impact on various trophic levels, with even fewer exploring whether global stressors such as temperature can affect the toxicity of BPA in organisms. Our aim was to assess the combined impact of BPA and varying temperature regimes on life-history traits in Daphnia magna. Our results revealed a significant impact of BPA on the growth, reproduction, and accumulated moulting of D. magna, with adverse effects primarily associated with the assimilation of BPA in algae rather than the BPA present in the medium, pointing to a trophic transfer mechanism. The interactive effect between BPA and temperature demonstrated a slight stimulatory effect of low BPA level on D. magna growth rate under warming constant conditions, but an inhibitory under warming fluctuating temperatures. Additionally, a BPA threshold was identified, below which growth became temperature-dependent. This study emphasizes the crucial role of considering temperature in predicting how toxins may affect Daphnia within aquatic food webs.

Transcriptome response of a marine copepod in response to environmentally-relevant concentrations of saxitoxin

Paralytic shellfish toxins (PSTs) can pose a serious threat to human health. Among them, saxitoxin (STX) is one of the most potent natural neurotoxins. Here, the copepod Tigriopus japonicus, was exposed to environmentally relevant concentrations (2.5 and 25 μg/L) STX for 48 h. Although no lethal effects were observed at both concentrations, the transcriptome was significantly altered, and displayed a concentration-dependent response. STX exposure decreased the copepod's metabolism and compromised immune defense and detoxification. Additionally, STX disturbed signal transduction, which might affect other cellular processes. STX exposure could inhibit the copepod's chitin metabolism, disrupting its molting process. Also, the processes related to damage repair and protection were up-regulated to fight against high concentration exposure. Collectively, this study has provided an early warning of PSTs for coastal ecosystem not only because of their potent toxicity effect but also their bioaccumulation that can transfer up the food chain after ingestion by copepods.

Unveiling the multilevel impact of four water-soluble polymers on Daphnia magna: From proteome to behaviour (a case study)

The ubiquitous presence of water-soluble polymers (WSPs) in freshwater environments raises concerns regarding potential threats to aquatic organisms. This study investigated, for the first time, the effects of widely used WSPs -polyvinyl alcohol (PVA), polyvinylpyrrolidone (PVP), polyacrylic acid (PAA), and polyethylene glycol (PEG)- using a multi-level approach in the freshwater biological model Daphnia magna. This integrated assessment employed a suite of biomarkers, evaluation of swimming behaviour, and proteomic analysis to investigate the effects of three environmentally relevant concentrations (0.001, 0.5, and 1 mg/L) of the tested WSPs from molecular to organismal levels, assessing both acute and chronic effects. Our findings reveal that exposure to different WSPs induces specific responses at each biological level, with PEG being the only WSP inducing lethal effects at 0.5 mg/L. At the physiological level, although all WSPs impacted both swimming performance and heart rate of D. magna specimens, PAA exhibited the greatest effects on the measured behavioural parameters. Furthermore, proteomic analyses demonstrated altered protein profiles following exposure to all WSPs, with PVA emerging as the most effective.

Toxicity of bisphenol A (BPA) and its derivatives in divers biological models with the assessment of molecular mechanisms of toxicity

The aim of the study was to determine totoxicity of bisphenol A (BPA) and its derivatives (bisphenol S (BPS), bisphenol F (BPF), and tetrabromobisphenol A (TBBPA)) due to its high accumulation in environment. The performed analysis revealed the toxicity of the BPA, BPF, and BPS against Kurthia gibsoni, Microbacterium sp., and Brevundimonas diminuta as the most sensitive, reaching microbial toxic concentrations in the range of 0.018-0.031 mg ∙ L^-1. Moreover, the genotoxicity assay shows the ability of all tested compounds to increase in the β-galactosidase level at the concentration range 7.81-500 µM (in Escherichia coli, PQ37). In turn, the matbolic activation of tested bishpenols has caused the enhacement of the genotoxicity and cytotoxicity effect. Interestingely, the highest phytotoxicity effect was pointed for BPA and TBBPA at the concentrations of 10 mg ∙ L^-1 and 50 mg ∙ L^-1, which cause the inhibition of root growth by 58% and 45%, respectively (especially for S. alba and S. saccharatum). Furthermore, the cytotoxicity analyses show the ability of BPA, BPS, and TBBPA to significantly decrease the metabolic activity of human keratynoctes in vitro after 24 h of treatment at the micromolar concentrations. Simialry, the impact of the certain bisphenols on proliferation-, apoptosis-, and inflammation-related mRNA expression was shown in tested cell line. Summarizing, the presented results have proved that BPA and its derrivatives are able to show high negative effect on certain living orgnisms such as bacteria, plants, and human cells, which is strict related to pro-apoptotic and genotoxic mechanism of action.

Trans- and Multigenerational Effects of Isothiazolinone Biocide CMIT/MIT on Genotoxicity and Epigenotoxicity in Daphnia magna

The mixture of 5-chloro-2-methylisothiazol-3(2H)-one and 2-methylisothiazol-3(2H)-one, CMIT/MIT, is an isothiazolinone biocide that is consistently detected in aquatic environments because of its broad-spectrum usage in industrial fields. Despite concerns about ecotoxicological risks and possible multigenerational exposure, toxicological information on CMIT/MIT is very limited to human health and within-generational toxicity. Furthermore, epigenetic markers altered by chemical exposure can be transmitted over generations, but the role of these changes in phenotypic responses and toxicity with respect to trans- and multigenerational effects is poorly understood. In this study, the toxicity of CMIT/MIT on Daphnia magna was evaluated by measuring various endpoints (mortality, reproduction, body size, swimming behavior, and proteomic expression), and its trans- and multigenerational effects were investigated over four consecutive generations. The genotoxicity and epigenotoxicity of CMIT/MIT were examined using a comet assay and global DNA methylation measurements. The results show deleterious effects on various endpoints and differences in response patterns according to different exposure histories. Parental effects were transgenerational or recovered after exposure termination, while multigenerational exposure led to acclimatory/defensive responses. Changes in DNA damage were closely associated with altered reproduction in daphnids, but their possible relationship with global DNA methylation was not found. Overall, this study provides ecotoxicological information on CMIT/MIT relative to multifaceted endpoints and aids in understanding multigenerational phenomena under CMIT/MIT exposure. It also emphasizes the consideration of exposure duration and multigenerational observations in evaluating ecotoxicity and the risk management of isothiazolinone biocides.

Chronic toxicity of diclofenac, carbamazepine and their mixture to Daphnia magna: a comparative two-generational study

The chronic toxicity of diclofenac (DCF) and carbamazepine (CBZ) as separate substances and in conjunction with their mixture on Daphnia magna was assessed in the parental (F0) and first filial (F1) generations. The second (F1-B2) and fifth (F1-B5) broods of F1 offspring were investigated and compared. Both drugs and their mixture were exposed to each generation of Daphnia magna for 21 days with life history, behavioural and gene expressions as measured endpoints. After the parental exposure, offspring from these two broods were transferred to a clean medium for a 21-day recovery. Exposure to diclofenac, carbamazepine and their mixture significantly inhibited growth, reproduction, swimming activities, heart rate, thoracic limb activities, reproductive and antioxidant-related genes in the parental as well as the first filial generations. These effects were relatively greater in the F1 generation. This indicates that Daphnia magna's sensitivity improved while its fitness declined over the two generations, which is an indicator of greater energy requirements for maintenance. Besides, the significant inhibition in the antioxidant-related genes implies that oxidative stress occurred in Daphnia magna under the exposure to these drugs. The significant reduction in the reproductive output, moulting frequency and cyp314 gene expression as a result of exposure to CBZ simultaneously obtained herein may indicate that this drug could act as an endocrine disruptor. Most of these significant effects were not recoverable after the 21-day recovery period. The findings reported herein highlight the necessity to include maternal effects in environmental risk assessment processes, considering that pollutant effects are underestimated during single-generational exposure.

Impacts of endocrine disrupting chemicals on reproduction in wildlife and humans

Endocrine disrupting chemicals (EDCs) are ubiquitous in aquatic and terrestrial environments. The main objective of this review was to summarize the current knowledge of the impacts of EDCs on reproductive success in wildlife and humans. The examples selected often include a retrospective assessment of the knowledge of reproductive impacts over time to discern how the effects of EDCs have changed over the last several decades. Collectively, the evidence summarized here within reinforce the concept that reproduction in wildlife and humans is negatively impacted by anthropogenic chemicals, with several altering endocrine system function. These observations of chemicals interfering with different aspects of the reproductive endocrine axis are particularly pronounced for aquatic species and are often corroborated by laboratory-based experiments (i.e. fish, amphibians, birds). Noteworthy, many of these same indicators are also observed in epidemiological studies in mammalian wildlife and humans. Given the vast array of reproductive strategies used by animals, it is perhaps not surprising that no single disrupted target is predictive of reproductive effects. Nevertheless, there are some general features of the endocrine control of reproduction, and in particular, the critical role that steroid hormones play in these processes that confer a high degree of susceptibility to environmental chemicals. New research is needed on the implications of chemical exposures during development and the potential for long-term reproductive effects. Future emphasis on field-based observations that can form the basis of more deliberate, extensive, and long-term population level studies to monitor contaminant effects, including adverse effects on the endocrine system, are key to addressing these knowledge gaps.

Transcriptional responses of Daphnia magna exposed to Akaki river water

Pollution of the aquatic environment is a global problem, with industrial waste, farming effluents, sewage, and wastewater as the main contributors. Many pollutants are biologically active at low concentrations, resulting in sublethal effects, which makes it a highly complex situation and difficult to assess. In many places, such as the Akaki river in Ethiopia, the pollution situation has resulted in streams with minimal presence of invertebrates or vertebrates. As it is difficult to perform a complete chemical analysis of the waters, the present study focused on using gene expression analysis as a biological end point to determine the effects of Akaki river contaminants. The present study was conducted using the small planktonic crustacean Daphnia magna with toxicogenomic molecular markers. Daphnia magna neonates were exposed to Akaki water samples collected from two different sites on the river and analyzed for mortality and expression of genes involved in different biological pathways. Despite the poor quality of Akaki river water, 48 h acute toxicity tests showed no mortality. Interestingly, analysis of sublethal toxicogenomic responses showed that exposure to Akaki water altered the expression of 25 out of 37 genes involved in metal regulation, immune response, oxidative stress, respiration, reproduction, and development. The toxicogenomic data gives insight into the mechanisms involved in causing potential adverse effects to aquatic biota harboring the Akaki river system.

Juvenile hormone synthesis and signaling disruption triggering male offspring induction and population decline in cladocerans (water flea): Review and adverse outcome pathway development

Juvenile hormone (JH) are a family of multifunctional hormones regulating larval development, molting, metamorphosis, reproduction, and phenotypic plasticity in arthropods. Based on its importance in arthropod life histories, many insect growth regulators (IGRs) mimicking JH have been designed to control harmful insects in agriculture and aquaculture. These JH analogs (JHAs) may also pose hazards to nontarget species by causing unexpected endocrine-disrupting (ED) effects such as molting and metamorphosis defects, larval lethality, and disruption of the sexual identity. This critical review summarizes the current knowledge of the JH-mediated effects in the freshwater cladoceran crustaceans such as Daphnia species on JHA-triggered endocrine disruptive outputs to establish a systematic understanding of JHA effects. Based on the current knowledge, adverse outcome pathways (AOPs) addressing the JHA-mediated ED effects in cladoceran leading to male offspring production and subsequent population decline were developed. The weight of evidence (WoE) of AOPs was assessed according to established guidelines. The review and AOP development aim to present the current scientific understanding of the JH pathway and provide a robust reference for the development of tiered testing strategies and new risk assessment approaches for JHAs in future ecotoxicological research and regulatory processes.

In vitro effects of selected endocrine disruptors (DEHP, PCB118, BPA) on narrow-clawed crayfish (Astacus leptodactylus) primary cells

Environmental pollutants with endocrine-disrupting effect are of global importance due to their contribution to the aethiologies of variety of complex diseases. These lipophilic pollutants are persistent in the environment and able to bioaccummulate in nontarget organisms. BPA, DEHP and PCB118 (dioxin-like PCB) are associated with endocrine disruption effects, while information on their effects on aquatic invertebrates are limited. In the current study, the effects of these compounds, which are ubiqutous and present at low concentrations in the environment, are studied in the primary hepatopancreas, muscle, gill, intestine and gonadal cultures of narrow-clawed crayfish (Astacus leptodactylus Eschscholtz, 1823), a widely distributed freshwater crayfish in Turkey with high economic importance. IC50 values following MTT assay ranged 0.27-12.61 nM; when compared with other tissues, the gonads were more affected with lower IC50 values. PCB118 induced higher cytotoxicity, while DEHP was the least toxic compound. This is the first study on the primary culture of A. leptodactylus¸ and the toxic effects of these compounds in this organism providing mechanistic insights on the responses and detoxification capacity of the organs. This study provides basis to unravel the mechanism of action of the tested EDCs in crayfish and improvement of cell culture conditions for ecotoxicity and screening assays.

Multilevel ecotoxicity assessment of environmentally relevant bisphenol F concentrations in Daphnia magna

With the pressure to ban or limit the use of Bisphenol A (BPA), substitutes such as bisphenol F (BPF) are applied to various commodities and generally detected in aquatic systems worldwide. To understand the potential ecological risk of BPF, the acute toxicity as well as behavioural, physiological and biochemical parameters of the water flea Daphnia magna were assessed. Following BPF exposure at concentrations ranging from 0.1 μg L^-1 to 100 μg L^-1, phenotypic traits including growth development, fecundity and swimming activity were significantly inhibited in response to exposure to sublethal concentrations (1-100 μg L^-1) of BPF, which had a positive relationship with the activity of antioxidant enzymes. Moreover, the acetylcholinesterase (AChE) activity, which was strictly associated with the behavioural changes, was clearly inhibited, which was also obviously related to the heart rate and thoracic limb activity. Compared to the toxicity of BPA, BPF induces similar toxic effects, and the health concerns regarding the use of these alternatives should be highlighted.

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.

Transcriptomic responses of Artemia salina exposed to an environmentally relevant dose of Alexandrium minutum cells or Gonyautoxin2/3

Toxicities of the marine algae Alexandrium minutum and its excreted gonyautoxins (GTXs) to the marine crustacean Artemia salina were investigated. Mortality was observed for neither larvae nor adult A. salina exposed to A. minutum at a density of 5000 cells/mL or 0.5 μM GTX2/3. After exposure, the full transcriptome of adult A. salina was assembled and functionally annotated. A total of 599,286 transcripts were obtained, which were clustered into 515,196 unigenes. Results of the transcriptional effect level index revealed that direct exposure to the toxic algae A. minutum caused greater alterations in the transcriptome than did exposure to the extracellular product GTX2/3. Mechanisms of effects were different between exposure of A. salina to A. minutum cells or GTX2/3. Exposure to A. minutum modulated formation of the ribonucleoprotein complex and metabolism of amino acids and lipids in A. salina. Exposure to GTX2/3 exposure inhibited expression of genes related to metabolism of chitin, which might result in disruption of molting process or disturbed sheath morphogenesis. Overall, effects on transcription observed in this study represent the first report based on application of next generation sequencing techniques to investigate the transcriptomic response of A. salina exposed to an environmentally realistic level of A. minutum or GTX2/3.

Time-dependent transcriptomic responses of Daphnia magna exposed to metabolic disruptors that enhanced storage lipid accumulation

The analysis of lipid disruption in invertebrates is limited by our poor knowledge of their lipidomes and of the associated metabolic pathways. For example, the mechanism by which exposure of the crustacean Daphnia magna to tributyltin, juvenoids, or bisphenol A increase the accumulation of storage lipids into lipid droplets is largely unknown/presently unclear. Here we analyze transcriptome changes subsequent to this lipid accumulation effect induced by either the pesticide pyriproxyfen (a juvenoid agonist), the plasticizer bisphenol A, or the antifouling agent tributyltin. Changes in the whole transcriptome were assessed after 8 and 24 h of exposure, the period showing the greatest variation in storage lipid accumulation. The three compounds affected similarly to a total of 1388 genes (965 overexpressed and 423 underexpressed transcripts), but only after 24 h of exposure. In addition, 225 transcripts became up-regulated in samples exposed to tributyltin for both 8 h and 24 h. Using D. melanogaster functional annotation, we determined that upregulated genes were enriched in members of KEGG modules implicated in fatty acid, glycerophospholipid, and glycerolipid metabolic pathways, as well as in genes related to membrane constituents and to chitin and cuticle metabolic pathways. Conversely, down-regulated genes appeared mainly related to visual perception and to oocyte development signaling pathways. Many tributyltin specifically upregulated genes were related to neuro-active ligand receptor interaction signaling pathways. These changes were consistent with the phetotypic effects reported in this and in previous studies that exposure of D. magna to the tested compounds increased lipid accumulation and reduced egg quantity and quality.

Selective Amino Acid-Only in Vivo NMR: A Powerful Tool To Follow Stress Processes

In vivo NMR of small 13C-enriched aquatic organisms is developing as a powerful tool to detect and explain toxic stress at the biochemical level. Amino acids are a very important category of metabolites for stress detection as they are involved in the vast majority of stress response pathways. As such, they are a useful proxy for stress detection in general, which could then be a trigger for more in-depth analysis of the metabolome. 1H-13C heteronuclear single quantum coherence (HSQC) is commonly used to provide additional spectral dispersion in vivo and permit metabolite assignment. While some amino acids can be assigned from HSQC, spectral overlap makes monitoring them in vivo challenging. Here, an experiment typically used to study protein structures is adapted for the selective detection of amino acids inside living Daphnia magna (water fleas). All 20 common amino acids can be selectively detected in both extracts and in vivo. By monitoring bisphenol-A exposure, the in vivo amino acid-only approach identified larger fluxes in a greater number of amino acids when compared to published works using extracts from whole organism homogenates. This suggests that amino acid-only NMR of living organisms may be a very sensitive tool in the detection of stress in vivo and is highly complementary to more traditional metabolomics-based methods. The ability of selective NMR experiments to help researchers to "look inside" living organisms and only detect specific molecules of interest is quite profound and paves the way for the future development of additional targeted experiments for in vivo research and monitoring.

Evaluation of 4-nonylphenol and bisphenol A toxicity using multiple molecular biomarkers in the water flea Daphnia magna

Alkylphenols are well-known endocrine disruptors and may cause developmental and reproductive disorders in aquatic organisms. Daphnia magna is commonly used in ecotoxicological studies as a promising model species to investigate the effects of endocrine distruptors. In the present study, transcriptional modulation of eleven potential molecular indicators related to detoxification, antioxidant, development, and cellular stress was analyzed in D. magna exposed to different concentrations of bisphenol A (BPA) and 4-nonylphenol (4-NP) for 24 h and 48 h, using real-time qPCR. A hierarchical clustering analysis was applied to investigate relations among molecular markers depending on the compound, exposure duration, and concentration. Our findings suggested that GSH-related systems and stress proteins may be involved in cellular defense against BPA and 4-NP-mediated toxicity with different modes of action. Furthermore, these compounds may interrupt molting and reproduction in daphnids. In particular, D. magna GSH-related genes seem to be strongly affected by 4-NP exposure, indicating their potential as molecular biomarkers.

Allocation of glycerolipids and glycerophospholipids from adults to eggs in Daphnia magna: Perturbations by compounds that enhance lipid droplet accumulation

Analysis of the disruptive effects of chemicals on lipids in invertebrates is limited by our poor knowledge of the lipid metabolic pathways and the complete lipidome. Recent studies shown that juvenoids and bisphenol A disrupted the dynamics of lipid droplets in the crustacean Daphnia magna. This study used ultra-high performance liquid chromatography/time-of-flight mass spectrometry (UHPLC/TOFMS) to study how juvenoids (pyriproxyfen and methyl farnesoate) and bisphenol A disrupt the dynamics of glycerophospholipids and glycerolipids in Daphnia adults and their allocation to eggs. Lipidomic analysis identified 234 individual lipids corresponding to three classes of glycerolipids, seven of glycerophospholipids, and one of sphingolipids, of which 194 changed according to the chemical treatments and time. Adult females in the control and bisphenol A treatment groups had low levels of triacylglycerols but high levels of glycerophospholipids, whereas those in the juvenoid treatment groups had high levels of triacylglycerols and low levels of glycerophospholipids. The opposite trend was observed for the lipid contents in the eggs produced. Because the juvenoids reduced reproduction dramatically, the females allocated less triacylglycerols to their eggs than the controls did. Interestingly, females exposed to bisphenol A allocated less triacylglycerols to their eggs despite producing a similar number of eggs as that of the controls. Thin-layer chromatography analyses confirmed the UHPLC/TOFMS results and allowed qualitative determination of cholesterol, which was also accumulated in females exposed to the juvenoids.

Comparative Transcriptome Analysis for Understanding Predator-Induced Polyphenism in the Water Flea Daphnia pulex

The crustacean Daphnia pulex is one of the best model organisms for studying inducible defense mechanisms due to their inducible morphology in response to the predator Chaoborus larvae. In this study, multiple developmental stages of D. pulex were exposed to C. flavicans larvae and transcriptome profiles of samples from late embryo to fifth instar were sequenced by the RNA-seq technique to investigate the genetic background underlying inducible defenses. In comparison, differentially expressed genes between defensive and normal morphs were identified, including 908 genes in late embryo, 1383 genes in the first-third (1–3) instar, and 1042 genes in fourth-fifth (4–5) instar. Gene ontology enrichment analysis showed that structural constituents of the cuticle and structural molecule activity genes were prominent up-regulated genes in late embryos. Down-regulated genes in late embryos and 1–3 instar comprised metabolic process, hydrolase activity, and peptidase activity gene classes. Pathway analysis indicated that small molecule neurotransmitter pathways were potentially involved in the development of inducible defenses. The characterization of genes and pathways in multiple developmental stages can improve our understanding of inducible defense responses of D. pulex to predation at the molecular level.

Controversial use of vitellogenin as a biomarker of endocrine disruption in crustaceans: New adverse pieces of evidence in the copepod Eurytemora affinis

In recent years, the interest in the use of vitellogenin (VTG) as a biomarker of endocrine disruption in fish has led to VTG being considered as a potential tool in invertebrates. Among aquatic invertebrate models in ecotoxicology, the copepods are considered as reference species in marine, estuarine and freshwater ecosystems. In this context, we identified a VTG cDNA in Eurytemora affinis. The Ea-VTG2 cDNA is 5416bp in length with an open reading frame (ORF) of 5310bp that encodes a putative protein of 1769 amino acids residues. Phylogenetic analysis confirmed the hypothesis of a VTG duplication event before the emergence of the copepod species. The analysis of the Ea-VTG2 expression by qPCR in males and females according to their reproductive stages allowed transcript basal levels to be determined. The expression pattern revealed a gradual increase of transcript levels during maturation in females. Important inter-sex differences were observed with a VTG level in males ranging from about 1900- to 6800-fold lower than in females depending on their stage. Moreover, the protein was only detected in ovigerous females. The inducibility of Ea-VTG2 by chemicals was studied in males exposed to either a model of endocrine disruptor in vertebrates i.e. 4-nonylphenol (4-NP) or a crustacean hormone i.e. Methyl Farnesoate (MF), and in males sampled from a multi-contaminated estuary. No induction was highlighted. The VTG should not be considered as an appropriate biomarker in E. affinis as previously suggested for other crustaceans.

Sublethal and Reproductive Effects of Acute and Chronic Exposure to Flowback and Produced Water from Hydraulic Fracturing on the Water Flea Daphnia magna

Hydraulic fracturing is an industrial process allowing for the extraction of gas or oil. To fracture the rocks, a proprietary mix of chemicals is injected under high pressure, which later returns to the surface as flowback and produced water (FPW). FPW is a complex chemical mixture consisting of trace metals, organic compounds, and often, high levels of salts. FPW toxicity to the model freshwater crustacean Daphnia magna was characterized utilizing acute (48 h median lethal concentrations; LC₅₀) and chronic (21 day) exposures. A decrease in reproduction was observed, with a mean value of 18.5 neonates produced per replicate over a 21 day chronic exposure to 0.04% FPW, which was a significant decrease from the average of 64 neonates produced in the controls. The time to first brood was delayed in the highest FPW (0.04%) treatment. Neonates exhibited an LC₅₀ of 0.19% of full-strength FPW, making them more sensitive than adults, which displayed an LC₅₀ value of 0.75%. Quantitative PCR highlighted significant changes in expression of genes encoding xenobiotic metabolism (cyp4) and moulting (cut). This study is the first to characterize chronic FPW toxicity and will help with the development of environmental monitoring and risk assessment of FPW spills.

Endocrine-disruption potential of perfluoroethylcyclohexane sulfonate (PFECHS) in chronically exposed Daphnia magna

Perfluoroethylcyclohexane sulfonate (PFECHS), mainly used in hydraulic fluids in aircrafts, is a member of the perfluoroalkyl sulfonate family which includes the regulated perfluorooctane sulfonate (PFOS). PFECHS has been reported in environmental samples but its toxicity to aquatic organisms is unknown. The objectives of this study were to identify biological pathways altered by sublethal exposure (12 d) of D. magna to PFECHS (0.06, 0.6, and 6 mg/L) using microarray and quantitative real-time PCR and to identify potential biomarkers to link transcriptomic to phenotypic responses. PFECHS was also quantified in surface water samples (1.04-1.38 ng/L) collected from the St. Lawrence River, Canada. Transcriptomic analyses indicated the under-regulation of vitellogenin-related genes (VTG1) in PFECHS-exposed groups. PFECHS exposure also led to the up-regulation of genes related to cuticle. VTG was selected as a potential cellular marker and identified in D. magna using an immuno-specific assay and quantified using Western blot and LC/MS/MS. Results indicated a decrease of VTG content in exposed D. magna which was in concordance with the transcription of VTG-related genes. No effects were observed on survival, molting, or reproduction at the individual/population levels. Overall, results suggest endocrine disruption potential for PFECHS in D. magna at concentrations higher than levels reported in the aquatic environment.

Reproductive switching analysis of Daphnia similoides between sexual female and parthenogenetic female by transcriptome comparison

The water flea Daphnia are planktonic crustaceans commonly found in freshwater environment that can switch their reproduction mode from parthenogenesis to sexual reproduction to adapt to the external environment. As such, Daphnia are great model organisms to study the mechanism of reproductive switching, the underlying mechanism of reproduction and development in cladocerans and other animals. However, little is known about the Daphnia's reproductive behaviour at a molecular level. We constructed a genetic database of the genes expressed in a sexual female (SF) and a parthenogenetic female (PF) of D. similoides using Illumina HiSeq 2500. A total of 1,763 differentially expressed genes (865 up- and 898 down-regulated) were detected in SF. Of the top 30 up-regulated SF unigenes, the top 4 unigenes belonged to the Chitin_bind_4 family. In contrast, of the top down-regulated SF unigenes, the top 3 unigenes belonged to the Vitellogenin_N family. This is the first study to indicate genes that may have a crucial role in reproductive switching of D. similoides, which could be used as candidate genes for further functional studies. Thus, this study provides a rich resource for investigation and elucidation of reproductive switching in D. similoides.

Hazard identification and risk characterization of bisphenols A, F and AF to aquatic organisms

Production of bisphenol A (BPA) analogues such as bisphenol F (BPF) and bisphenol AF (BPAF) has recently increased, due to clear evidence of adverse effects of BPA on humans and wildlife. Bisphenols (BPs) have already been released into aquatic environment without previous available information about potential adverse effects of BPs and their potential risk to aquatic ecosystems. In this study, lethal and sublethal effects of BPF and BPAF to bacteria, algae, crustacea and fish embryos were investigated and the results were compared to the adverse effects obtained for BPA. We found that BPAF was the most toxic compound to Daphnia magna, Danio rerio and Desmodesmus subspicatus; the lowest 72 h EC50 (median effective concentration) and 21 d NOEC (no observed effect concentration) values were determined at 2.2 mg/L regarding zebrafish hatching success and 0.23 mg/L of BPAF obtained for growth and reproduction of water fleas, respectively. In most cases, BPA was more toxic to D. magna, D. rerio and D. subspicatus in comparison to BPF, but pigmentation of zebrafish embryos after 48 h of exposure and reproduction of water fleas after 21-day D. magna reproductive test exposure to BPF were much more impaired. Risk quotients (measured environmental concentration/21 d NOEC) showed that BPA, BPF and BPAF are recently not chronically hazardous to the survival, reproduction and growth of water fleas in surface waters. On the other hand, we importantly show that currently present BPAF concentrations in surface waters could cause a potential ecological risk to aquatic organisms. In the near future, higher concentrations of BPF and BPAF in surface waters are anticipated and for this reason further testing using test systems with various aquatic species and endpoints are needed to provide additional information about toxic impacts of BPF and BPAF on aquatic biota.

Metabolomics reveals energetic impairments in Daphnia magna exposed to diazinon, malathion and bisphenol-A

(1)H nuclear magnetic resonance (NMR)-based metabolomics was used to study the response of Daphnia magna to increasing sub-lethal concentrations of either an organophosphate (diazinon or malathion) or bisphenol-A (BPA). Principal component analysis (PCA) of (1)H NMR spectra were used to screen metabolome changes after 48h of contaminant exposure. The PCA scores plots showed that diazinon exposures resulted in aberrant metabolomic profiles at all exposure concentrations tested (0.009-0.135 μg/L), while for malathion the second lowest (0.08μg/L) and two highest exposure concentrations (0.32μg/L and 0.47μg/L) caused significant shifts from the control. Individual metabolite changes for both organophosphates indicated that the response to increasing exposure was non-linear and described perturbations in the metabolome that were characteristic of the severity of exposure. For example, intermediate concentrations of diazinon (0.045μg/L and 0.09μg/L) and malathion (0.08μg/L) elicited a decrease in amino acids such as leucine, valine, arginine, glycine, lysine, glutamate, glutamine, phenylalanine and tyrosine, with concurrent increases in glucose and lactate, suggesting a mobilization of energy resources to combat stress. At the highest exposure concentrations for both organophosphates there was evidence of a cessation in metabolic activity, where the same amino acids increased and glucose and lactate decreased, suggesting a slowdown in protein synthesis and depletion of energy stocks. This demonstrated a similar response in the metabolome between two organophosphates but also that intermediate and severe stress levels could be differentiated by changes in the metabolome. For BPA exposures, the PCA scores plot showed a significant change in metabolome at 0.1mg/L, 1.4mg/L and 2.1mg/L of exposure. Individual metabolite changes from 0.7 to 2.1mg/L of BPA exposure showed increases in amino acids such as alanine, valine, isoleucine, leucine, arginine, phenylalanine and tyrosine. These metabolite changes were correlated with decreases in glucose and lactate. This pattern of response was also seen in the highest organophosphate exposures and suggested a generalized stress response that could be related to altered energy dynamics in D. magna. Through studying increasing exposure responses, we have demonstrated the ability of metabolomics to identify discrete differences between intermediate and severe stress, and also to characterize how systemic stress is manifested in the metabolome.

Chronic toxicity evaluation of the flame retardant tris (2-butoxyethyl) phosphate (TBOEP) using Daphnia magna transcriptomic response

Tris (2-butoxyethyl) phosphate (TBOEP) is an organophosphorous-containing flame retardant (OPFR) of high production volume used in a broad range of applications. The use of TBOEP containing products has resulted in its release and ubiquitous occurrence in the aquatic environment. In this study, Daphnia magna transcriptomic response was measured by microarray to evaluate sublethal effects of TBOEP as part of a multi-level biological approach including specific gene transcription measured by qRT-PCR, enzyme activity, and life-history endpoints (i.e., survival, growth and reproduction). Chronic exposure (21 d) to a range of sublethal concentrations of TBOEP (14.7-1470μgL(-1)) did not impact growth, survival or reproduction, although the number of offspring decreased between the lowest and the highest dose. Gene transcription profiling by microarray analysis revealed that 101 genes were differentially transcribed in response to TBOEP (fold change treated/control ±1, p<0.05). Most of the responding genes were involved in protein metabolism (9), biosynthesis (4) and energy metabolism (6) indicating that TBOEP could have chronic toxic effects on aquatic organisms at sublethal doses by disrupting essential biological pathways. Nine genes were found to be commonly affected by more than one dose, including a gene coding for cathepsin D and multiple isoforms of genes coding for hemoglobin, suggesting potential biomarkers of interest. Microarray results were confirmed by qRT-PCR and measurements at the protein level as cathepsin D enzymatic activity increased significantly in the highest dose treatment. Results highlight the relevance of using the transcriptomic response of D. magna as a first line of evidence to unravel the mode of action of chemicals.

Ecotoxicogenomic approaches for understanding molecular mechanisms of environmental chemical toxicity using aquatic invertebrate, Daphnia model organism

Due to the rapid advent in genomics technologies and attention to ecological risk assessment, the term “ecotoxicogenomics” has recently emerged to describe integration of omics studies (i.e., transcriptomics, proteomics, metabolomics, and epigenomics) into ecotoxicological fields. Ecotoxicogenomics is defined as study of an entire set of genes or proteins expression in ecological organisms to provide insight on environmental toxicity, offering benefit in ecological risk assessment. Indeed, Daphnia is a model species to study aquatic environmental toxicity designated in the Organization for Economic Co-operation and Development’s toxicity test guideline and to investigate expression patterns using ecotoxicology-oriented genomics tools. Our main purpose is to demonstrate the potential utility of gene expression profiling in ecotoxicology by identifying novel biomarkers and relevant modes of toxicity in Daphnia magna. These approaches enable us to address adverse phenotypic outcomes linked to particular gene function(s) and mechanistic understanding of aquatic ecotoxicology as well as exploration of useful biomarkers. Furthermore, key challenges that currently face aquatic ecotoxicology (e.g., predicting toxicant responses among a broad spectrum of phytogenetic groups, predicting impact of temporal exposure on toxicant responses) necessitate the parallel use of other model organisms, both aquatic and terrestrial. By investigating gene expression profiling in an environmentally important organism, this provides viable support for the utility of ecotoxicogenomics.

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.