Reactive oxygen species (ROS) and redox buffers as an interface between stress sensing, signalling and physiological responses in Daphnia magna

Phototoxicity and oxidative stress responses in Daphnia magna under exposure to sulfathiazole and environmental level ultraviolet B irradiation

Impact of black phosphorus nanosheet exposure on growth, reproduction, antioxidant mechanisms, and transcriptomic responses in Daphnia magna.

Ionizing radiation is known to induce oxidative stress and DNA damage as well as epigenetic effects in aquatic organisms. Epigenetic changes can be part of the adaptive responses to protect organisms from radiation-induced damage, or act as drivers of toxicity pathways leading to adverse effects. To investigate the potential roles of epigenetic mechanisms in low-dose ionizing radiation-induced stress responses, an ecologically relevant crustacean, adult Daphnia magna were chronically exposed to low and medium level external 60Co gamma radiation ranging from 0.4, 1, 4, 10, and 40 mGy/h for seven days. Biological effects at the molecular (global DNA methylation, histone modification, gene expression), cellular (reactive oxygen species formation), tissue/organ (ovary, gut and epidermal histology) and organismal (fecundity) levels were investigated using a suite of effect assessment tools. The results showed an increase in global DNA methylation associated with loci-specific alterations of histone H3K9 methylation and acetylation, and downregulation of genes involved in DNA methylation, one-carbon metabolism, antioxidant defense, DNA repair, apoptosis, calcium signaling and endocrine regulation of development and reproduction. Temporal changes of reactive oxygen species (ROS) formation were also observed with an apparent transition from ROS suppression to induction from 2 to 7 days after gamma exposure. The cumulative fecundity, however, was not significantly changed by the gamma exposure. On the basis of the new experimental evidence and existing knowledge, a hypothetical model was proposed to provide in-depth mechanistic understanding of the roles of epigenetic mechanisms in low dose ionizing radiation induced stress responses in D. magna.

Antibiotics represent a unique and diverse group of drugs, which are known to exert deleterious effects on non-target species and contribute to the phenomenon of antimicrobial resistance. With central inclusion on the EU Surface Water Watch List, and reported known affects in multiple model organisms, the importance of the sufficient monitoring of antibiotics in the aquatic environment has been highlighted. Most studies report the impact of individual antibiotics following exposure for a single generation in animals. In this study, we assessed the impact of four antibiotics with different modes of action (amoxicillin, trimethoprim, erythromycin, and sulfamethoxazole) and their mixture on the sentinel species Daphnia magna over three generations, via biochemical markers and a targeted metabolomic analysis of central metabolic pathways. No mortality was observed at 50 mg/L of each selected antibiotic and their composite mixture. Thus, a working concentration of 1 mg/L was chosen to progress this study. Results indicated that enzyme activity was particularly sensitive to exposure to amoxicillin and the mixture, whereas trimethoprim and the mixture induced the most metabolic changes in glycolysis and the TCA cycle. Additionally, the quaternary mixture had a stronger impact on the first generation of daphnids, altering the activity of β-galactosidase, glutathione S-transferase, and acid and alkaline phosphatase, suggesting that Daphnia can adapt to stress caused by antibiotics.

Polystyrene is widely used in disposable products and is now a ubiquitous plastic pollutant in aquatic environments, where it degrades into smaller particles that leach potentially toxic chemicals. However, knowledge regarding the impacts of plastic leachates remains limited. This study investigates the lethal and nonlethal effects of polystyrene leachate on two ecologically significant aquatic organisms, Daphnia magna (water flea) and Artemia salina (brine shrimp). Polystyrene leachates were prepared in seawater, freshwater, and sterile, pure water by incubating the material in each of the media under natural conditions for six months. D. magna and A. salina were exposed to varying concentrations of the leachates under controlled laboratory conditions, monitoring their survival, as well as measuring reactive oxygen species and antioxidant responses as superoxide dismutase and catalase activity. The data show that A. salina was more significantly affected with higher mortality observed at lower leachate concentrations, potentially linked to seawater enhancing the leaching of toxic additives. Moreover, at non-lethal concentrations, the antioxidative responses maintained homeostasis in both organisms. Considering the current reported microplastic concentrations in the aquatics and the adequate antioxidative response, leachate from plastic potentially does not pose a severe threat to these organisms. Nevertheless, hydrological characteristics of waterbodies may cause microplastic hotspots, which could significantly concentrate plastics and thus their leachates, necessitating action to reduce the current microplastic pollution level and avoid future surges. This study highlights the ecological significance of polystyrene pollution, emphasizing the need for more comprehensive regulatory measures and the development of sustainable alternatives to polystyrene-based products. The distinct responses of D. magna and A. salina imply that the impact of plastic pollution varies among species, necessitating further research to elucidate broader ecological consequences. Understanding how polystyrene leachate affects keystone species provides crucial insights into the overall implications for aquatic ecosystems.

Given the risk of environmental pollution by pharmaceutical compounds and the effects of these compounds on exposed ecosystems, ecologically relevant and realistic assessments are required. However, many studies have been mostly focused on individual responses in a single generation exposed to one-effect concentrations. Here, transcriptional responses of the crustacean Daphnia magna to the antibiotic tetracycline across multiple generations and effect concentrations were investigated. The results demonstrated that tetracycline induced different transcriptional responses of daphnids that were dependent on dose and generation. For example, reproduction-related expressed sequence tags (ESTs), including vitellogenin, were distinctly related to the dose-dependent tetracycline exposure, whereas multigenerational exposure induced significant change of molting-related ESTs such as cuticle protein. A total of 65 ESTs were shared in all contrasts, suggesting a conserved mechanism of tetracycline toxicity regardless of exposure concentration or time. Most of them were associated with general stress responses including translation, protein and carbohydrate metabolism, and oxidative phosphorylation. In addition, effects across the dose-response curve showed higher correlative connections among transcriptional, physiological, and individual responses than multigenerational effects. In the multigenerational exposure, the connectivity between adjacent generations decreased with increasing generation number. The results clearly highlight that exposure concentration and time trigger different mechanisms and functions, providing further evidence that multigenerational and dose-response effects cannot be neglected in environmental risk assessment.

Manipulation of Reactive Oxygen Species, Redox and Nitric Oxide Signaling Systems to Activate Plant Innate Immunity for Crop Disease Management

Nickel and binary metal mixture responses in Daphnia magna: Molecular fingerprints and (sub)organismal effects

Suspended particles (SP) exist widely in various water systems and are able to adsorb other pollutants in water, producing ecotoxic effects on aquatic nontarget species. Until now, however, few studies have focused on the effects of SP on antibiotics. Therefore, the present study investigated the effects of the mixtures of SP and phenicol antibiotics (chloramphenicol [CAP], thiamphenicol [TAP]) on acute toxicity and oxidative stress responses in Daphnia magna. The results indicated that the acute toxicity of phenicol antibiotics in D. magna was increased when combined with SP. Besides, the immobilization of daphnids caused by phenicol drugs in the presence of 10 mg/L of SP was more intense than that with 200 mg/L of SP. Furthermore, the impact of SP with diverse concentrations on the activity of catalase and the level of reduced glutathione in D. magna was different. Notably, almost all CAP + TAP + SP treatments markedly increased malondialdehyde content in D. magna, causing potential cellular oxidative damage in D. magna. In summary, the present study provides insights into the toxic effects of phenicol antibiotic and SP mixtures on aquatic organisms. Environ Toxicol Chem 2021;40:2463-2473. © 2021 SETAC.

Natural populations are confronted with multiple selection pressures resulting in a mosaic of environmental stressors at the landscape level. Identifying the genetic underpinning of adaptation to these complex selection environments and assigning causes of natural selection within multidimensional selection regimes in the wild is challenging. The water flea Daphnia is a renowned ecological model system with its well-documented ecology, the possibility to analyse subfossil dormant egg banks and the short generation time allowing an experimental evolution approach. Capitalizing on the strengths of this model system, we here link candidate genome regions to three selection pressures, known to induce micro-evolutionary responses in Daphnia magna: fish predation, parasitism and land use. Using a genome scan approach in space, time and experimental evolution trials, we provide solid evidence of selection at the genome level under well-characterized environmental gradients in the wild and identify candidate genes linked to the three environmental stressors. Our study reveals differential selection at the genome level in Daphnia populations and provides evidence for repeatable patterns of local adaptation in a geographic mosaic of environmental stressors fuelled by standing genetic variation. Our results imply high evolutionary potential of local populations, which is relevant to understand the dynamics of trait changes in natural populations and their impact on community and ecosystem responses through eco-evolutionary feedbacks.

Graphene could be modified by functional groups through a series of transformation processes after being released into environment.Meanwhile, the properties of graphene, such as solubility and biotoxicity, could be altered by surface modification.It is important to investigate the aquatic toxicity of graphene and its surface functionalized derivatives for assessing their ecological risks.Oxidative stress is one of the main toxicity mechanisms of graphene nanomaterials, but the effect mechanism of different surface functional groups (amino and thiol) on the oxidative stress induced by graphene is still unclear.In order to illuminate the toxicity mechanism and evaluate the extent of oxidative stress, a series of graphene nanomaterials including unfunctionalized grapheme (u-G), carboxylated grapheme (G-COOH), aminated grapheme (G-NH 2 ), hydroxylated grapheme (G-OH) and sulfydryl grapheme (G-SH) were selected to determine the levels of reactive oxygen species(ROS), antioxidant enzymes, antioxidant and lipid peroxidation in Daphnia magna induced by these graphene nanomaterials.Daphnia magna were exposed to graphene and its surface functionalized derivatives during 24 h period.Following treatment, the parameters reflecting oxidative stress such as ROS, superoxide dismutase (SOD), catalase (CAT), glutathione (GSH) and malondialdehyde in Daphnia magna were measured.The results showed that malondialdehyde, a marker of lipid peroxidation in Daphnia magna, was significantly increased by u-G, G-COOH and G-OH, respectively.The level of malondialdehyde was significantly higher under u-G exposure than that under G-COOH or G-OH exposure.It is indicated that the degree of oxidative damage induced by u-G in Daphnia magna was more serious than that of G-COOH and G-OH.In addition, the three nanomaterials also caused the changes in ROS and glutathione (GSH) levels, and activities of superoxide dismutase (SOD) and catalase (CAT) were decreased by u-G and G-OH.However, G-SH and G-NH 2 did not cause oxidative damage within 24 h exposure period.Marked inactivation of antioxidant enzymes in an ROS-independent manner was observed in response to G-SH, suggesting that G-SH may cause a structural change in enzymes, leading to functional inactivity.G-NH 2 did not affect the levels of ROS, antioxidant enzymes, antioxidant and lipid peroxidation.At 24 h after stopping exposure, Daphnia magna can alleviate the oxidative damage induced by u-G, G-COOH and G-OH to a certain extent by its own regulation.The ability of graphene nanomaterials to cause oxidative stress in Daphnia magna is as follows: u-G>G-COOH≈G-OH>G-SH>G-NH 2 .The main reasons of oxidative stress in Daphnia Magna induced by u-G, G-COOH and G-OH were the generation of ROS, which led to the imbalance of antioxidant defense system and lipid peroxidation.G-SH mainly inhibited the activities of SOD and CAT antioxidant enzymes and affected the antioxidant defense system.However, there were no significant changes in ROS levels and antioxidant enzymes in Daphnia magna under G-NH 2 exposure.graphene, Daphnia magna, oxidative stress, reactive oxygen species (ROS), lipid peroxidation

With global warming, it is crucial to recognise that temperature changes can influence the ecotoxicity of pollutants in natural ecosystems. 4-Chloroaniline (4-CA) is an emerging contaminant due to its environmental persistence, bioaccumulation potential, and toxicity to aquatic organisms. This study intends to assess the effects of environmentally relevant concentrations of 4-CA (0.09-9.65µg/L) on Daphnia magna under two temperatures: 20°C (standard) and 26°C (global warming). A 21-day reproduction assay evaluated the life-history traits and biomarkers related to oxidative stress, metabolism, neurotoxicity, genotoxicity, and cellular energy allocation. Results revealed an interaction between temperature and 4-CA exposure. At 26°C, D. magna exhibited anticipation of reproduction and increased brood frequency but with fewer offspring per brood. Thermal stress also intensified metabolism and antioxidant defences, with elevated superoxide dismutase and glutathione peroxidase activities, suggesting a compensatory mechanism to mitigate oxidative damage. Genotoxicity was more pronounced at 26°C, highlighting an increased risk of DNA damage. The combined stress of 4-CA and temperature negatively impacted energy allocation, reproductive success, and overall fitness. The results underscore the importance of incorporating climate change scenarios into ecotoxicological assessments of emergent contaminants, reinforcing the need to include 4-CA in the Water Framework Directive Watch List.

Redox homeostasis is achieved by antioxidant systems, involving a large collection of enzymes that scavenge or degrade Reactive Oxygen Species (ROS) produced endogenously at low levels during cell growth. Besides the enzymatic protection against ROS, cells also contain small antioxidant molecules, such as glutathione (GSH). With an intracellular concentration between 1 and 10 mM, GSH is the most abundant non-protein thiol in the cell and is considered as the major redox buffer of the cell. In a previous study, we showed that only scarce amounts of intracellular GSH are required to protect yeast nuclear activities during oxidative stress. Surprisingly, such protection is sufficient for cell survival despite the strong oxidation of cytosolic proteins and the complete inhibition of protein synthesis (Hatem et al., 2014). GSH synthesis is a two-step process involving the gamma-glutamylcysteine (g-GC) synthetase Gsh1, which produces the g-GC intermediate from glutamate and cysteine, and the glutathione synthetase Gsh2, which adds a glycine to g-GC to release the final tripeptide. Deletion of GSH2 leads to yeast cells accumulating abnormal amounts of g-GC. It has been suggested that this molecule could replace GSH during oxidative stress exposure as the viability of ∆gsh2 cells, unable to synthesize GSH, is only mildly affected in oxidative stress conditions. Because our previous study revealed that the antioxidant protection of all cellular components and activities is not strictly required to preserve cell viability during oxidative stress, we decided to better characterize the physiological response of ∆gsh2 cells submitted to hydrogen peroxide treatments. Here we present the main results of this study and discuss the potential role of g-GC in the cellular protection against oxidative injury, compare to GSH.

Ecological risks of combination of multiple pollutants at environmentally relevant concentrations: Insights from the changes in life history traits, gut microbiota, and transcriptomic responses in Daphnia magna

Systemic and metabolic responses in Daphnia magna to anoxia