Ecotoxicity assessment of ashes from calcium-rich fuel combustion: contrasting results and regulatory implications.

The European Union's (EU) regulation for the waste classification based on their ecotoxicological hazard (hazardous property HP14) came into force on 5 July 2018. The regulation advocates the utilisation of computational formulae for the hazard classification of waste associated with hazardous property HP14. Concurrently, ecotoxicological testing remains an alternative. To date, the absence of a consensus regarding test organisms and methodologies has vested EU member states with autonomy in determining the approach for conducting ecotoxicity assessments. The discussions on waste classification are also ongoing globally, namely the discussions under the Basel Convention. This paper endeavours to elucidate whether the widely employed test organisms, Daphnia magna and Aliivibrio fischeri, may serve as suitable indicators for the evaluation of the ecotoxicity of waste. The research is grounded in the examination of ashes derived from a combustion process of calcium-rich fuel. Ecotoxicity testing was conducted on 14 ash samples with a liquid-to-solid ratio of 10:1. The results of the Aliivibrio fischeri testing indicated that all 14 ash samples were non-hazardous in terms of their ecotoxicity. However, the results of the Daphnia magna testing showed the opposite, suggesting that the ash samples may have the potential to be ecotoxic. This study offers valuable insights into ecotoxicity assessment and waste classification, emphasising the need for scientific rigour and comprehensive understanding before making regulatory decisions. It also situates its findings within the broader global context of waste management discussions, particularly those related to international agreements like the Basel Convention.

Can a shift in dominant species of Microcystis alter growth and reproduction of waterfleas?

The bloom-forming species Microcystis wesenbergii and M. aeruginosa occur in many lakes globally, and may exhibit alternating blooms both spatially and temporally. As environmental changes increase, cyanobacteria bloom in more and more lakes and are often dominated by M. wesenbergii. The adverse impact of M. aeruginosa on co-existing organisms including zooplanktonic species has been well-studied, whereas studies of M. wesenbergii are limited. To compare effects of these two species on zooplankton, we explored effects of exudates from different strains of microcystin-producing M. aeruginosa (Ma905 and Ma526) and non-microcystin-producing M. wesenbergii (Mw908 and Mw929), on reproduction by the model zooplankter Daphnia magna in both chronic and acute exposure experiments. Specifically, we tested physiological, biochemical, molecular and transcriptomic characteristics of D. magna exposed to Microcystis exudates. We observed that body length and egg and offspring number of the daphnid increased in all treatments. Among the four strains tested, Ma526 enhanced the size of the first brood, as well as total egg and offspring number. Microcystis exudates stimulated expression of specific genes that induced ecdysone, juvenile hormone, triacylglycerol and vitellogenin biosynthesis, which, in turn, enhanced egg and offspring production of D. magna. Even though all strains of Microcystis affected growth and reproduction, large numbers of downregulated genes involving many essential pathways indicated that the Ma905 strain might contemporaneously induce damage in D. magna. Our study highlights the necessity of including M. wesenbergii into the ecological risk evaluation of cyanobacteria blooms, and emphasizes that consequences to zooplankton may not be clear-cut when assessments are based upon production of microcystins alone.

Sol-Gel Synthesis of Silica-Poly (Vinylpyrrolidone) Hybrids with Prooxidant Activity and Antibacterial Properties.

The present work deals with the sol-gel synthesis of silica-poly (vinylpyrrolidone) hybrid materials. The nanohybrids (Si-PVP) have been prepared using an acidic catalyst at ambient temperature. Tetramethyl ortosilane (TMOS) was used as a silica precursor. Poly (vinylpyrrolidone) (PVP) was introduced into the reaction mixture as a solution in ethanol with a concentration of 20%. The XRD established that the as-prepared material is amorphous. The IR and 29Si MAS NMR spectra proved the formation of a polymerized silica network as well as the hydrogen bonding interactions between the silica matrix and OH hydrogens of the silanol groups. The TEM showed spherical particle formation along with increased agglomeration tendency. The efficacy of SiO2/PVP nanoparticles as a potential antimicrobial agent against a wide range of bacteria was evaluated as bacteriostatic, using agar diffusion and spot tests. Combined effects of hybrid nanomaterial and antibiotics could significantly reduce the bactericidal concentrations of both the antibiotic and the particles, and they could also eliminate the antibiotic resistance of the pathogen. The registered prooxidant activity of the newly synthesized material was confirmative and explicatory for the antibacterial properties of the tested substance and its synergetic combination with antibiotics. The effect of new hybrid material on Crustacea Daphnia magna was also estimated as harmless under concentration of 0.1 mg/mL.

Confocal Surface-Enhanced Raman Imaging of the Intestinal Barrier Crossing Behavior of Model Nanoplastics in Daphnia Magna.

Nanoplastics (nP) pose hazards to aquatic animals once they are ingested. Significant knowledge gaps exist regarding the nP translocation across the animal intestine, which is the first barrier between the ingested nP and the animal body. We examined the intestinal barrier crossing behavior of nP in an aquatic animal model (Daphnia magna) and determined the translocation mechanism with the help of model "core-shell" polystyrene nanoplastics (nPS) and confocal surface-enhanced Raman spectroscopy (SERS). The Raman reporter (4-mercaptobenzoic acid)-tagged gold "core" of the model nPS enables sensitive and reliable particle imaging by confocal SERS. This method detected SERS signals of model nPS concentration as low as 4.1 × 109 particles/L (equivalent to 0.27 µg/L PS "shell" concentration). The translocation was observed with the help of multilayer stacked Raman maps of SERS signals of the model nPS. With a higher concentration or longer exposure time of the model nPS, uptake and translocation of the plastic particles increased. In addition, we demonstrated that clathrin-dependent endocytosis and macropinocytosis were two major mechanisms underlying the translocation. This study contributes to a mechanistic understanding of nP translocation by using the pioneering model nPS and an analytical toolkit, which undergird further investigations into nP behavior and health effects in aquatic species.

Aqueous degradation of tioxazafen: Kinetics, products, pathways, and toxicity.

Tioxazafen (TXF) is the first 1,2,4-oxadiazole nematicide. In the present study, the aqueous degradation of TXF was investigated in terms of hydrolysis and photolysis. Under the irradiation of simulated sunlight, TXF degraded very fast in ultrapure water and buffers with half-lives (t1/2s) <8.3 min. A sole photoproduct (PP) PP228a was isolated, and identified by spectroscopic means (UV, IR, HRMS, and 1H NMR) to be the thiophen-3-yl isomer converted from its thiophen-2-yl parent. Comparing with TXF, PP228a had quite extended t1/2s ranging from 6.9 to 7.9 d. The photolysis kinetics of TXF and PP228a showed no pH-dependence, and varied for each individual compound as affected by nitrate, fulvic acid, and humic acid. Besides, both compounds were hydrolytically stable. 6 PPs of PP228a were identified, with two of them being its isomers. The mechanisms involved in the process included the biradical photosensitization, photoinduced electron transfer, and ring contraction-ring expansion reactions. The 48 h-EC50 to Daphnia magna was 0.808 mg/L for PP228a comparing to >1.12 mg/L for TXF, while the results of Vibrio fischeri assays indicated that one or more PPs of PP228a might have higher toxicity.

Comparative toxicology of algal cell extracts and pure cyanotoxins: insights into toxic effects and mechanisms of harmful cyanobacteria Raphidiopsis raciborskii.

Ongoing research on cyanotoxins, driven by the socioeconomic impact of harmful algal blooms, emphasizes the critical necessity of elucidating the toxicological profiles of algal cell extracts and pure toxins. This study comprehensively compares Raphidiopsis raciborskii dissolved extract (RDE) and cylindrospermopsin (CYN) based on Daphnia magna assays. Both RDE and CYN target vital organs and disrupt reproduction, development, and digestion, thereby causing acute and chronic toxicity. Disturbances in locomotion, reduced behavioral activity, and weakened swimming capability in D. magna have also been reported for both RDE and CYN, indicating the insufficiency of conventional toxicity evaluation parameters for distinguishing between the toxic effects of algal extracts and pure cyanotoxins. Additionally, chemical profiling revealed the presence of highly active tryptophan-, humic acid-, and fulvic acid-like fluorescence compounds in the RDE, along with the active constituents of CYN, within a 15-day period, demonstrating the chemical complexity and dynamics of the RDE. Transcriptomics was used to further elucidate the distinct molecular mechanisms of RDE and CYN. They act diversely in terms of cytotoxicity, involving oxidative stress and response, protein content, and energy metabolism, and demonstrate distinct modes of action in neurofunctions. In essence, this study underscores the distinct toxicity mechanisms of RDE and CYN and emphasizes the necessity for context- and objective-specific toxicity assessments, advocating nuanced approaches to evaluate the ecological and health implications of cyanotoxins, thereby contributing to the precision of environmental risk assessments.

Exploring structure/property relationships to health and environmental hazards of polymeric polyisocyanate prepolymer substances-3. Aquatic exposure and hazard of aliphatic diisocyanate-based prepolymers.

The water extractability and acute aquatic toxicity of seven aliphatic diisocyanate-based prepolymer substances were investigated to determine if lesser reactivity of the aliphatic isocyanate groups, as well as increased ionization potential of the expected (aliphatic amine-terminated) polymeric hydrolysis products, would influence their aquatic behavior compared to that of previously investigated aromatic diisocyanate-based prepolymers. At loading rates of 100 and 1,000 mg/L, only the substances having log Kow ≤9 exhibited more than 1% extractability in water, and a maximum of 66% water extractability was determined for a prepolymer having log Kow = 2.2. For the more hydrophobic prepolymer substances (log Kow values from 18-37), water extractability was negligible. High-resolution mass spectrometric analyses were performed on the water-accommodated fractions (WAF) of the prepolymers, which indicated the occurrence of primary aliphatic amine-terminated polymer species having backbones and functional group equivalent weights aligned to those of the parent prepolymers. Measurements of reduced surface tension and presence of suspended micelles in the WAFs further supported the occurrence of these surface-active cationic polymer species as hydrolysis products of the prepolymers. Despite these characteristics, the water-extractable hydrolysis products were practically non-toxic to Daphnia magna. All of the substances tested exhibited 48-h EL50 values of >1,000 mg/L, with one exception of EL50 = 157 mg/L. The results from this investigation support a grouping of the aliphatic diisocyanate-based prepolymers as a class of water-reactive polymer substances having predictable aquatic exposure and a uniformly low hazard potential, consistent with that previously demonstrated for the aromatic diisocyanate-based prepolymers.

Effects of food quantity on the ingestion and egestion of MPs with different colors by Daphnia magna.

Aquatic organism uptake and accumulate microplastics (MPs) through various pathways, with ingestion alongside food being one of the primary routes. However, the impact of food concentration on the accumulation of different types of MPs, particularly across various colors, remains largely unexplored. To address this gap, we selected Daphnia magna as a model organism to study the ingestion/egestion kinetics and the preference for different MP colors under varying concentrations of Chlorella vulgaris. Our findings revealed that as the concentration of Chlorella increased, the ingestion of MPs by D. magna initially increased and then showed a decline. During the egestion phase within clean medium without further food supply, an increase in food concentration during the ingestion phase led to a slower rate of MP discharge; while when food was present during the egestion phase, the discharge rate accelerated for all treatments, indicating the importance of food ingestion/digestion process on the MPs bioaccumulation. Furthermore, in the presence of phytoplankton, D. magna demonstrated a preference for ingesting green-colored MPs, especially at low and medium level Chlorella supply, possibly due to the enhanced food searching activities. Beyond gut passage, we also examined the attachment of MPs to the organism's body surface, finding that the number of adhered MPs increased with increasing food concentration, likely due to the intensified filtering current during food ingestion. In summary, this study demonstrated that under aquatic environment with increasing phytoplankton concentrations, the ingestion and egestion rates, color preferences, as well as surface adherence of MPs to filter feeding zooplanktons will be significantly influenced, which may further pose ecological risks. Our results offer novel insights into the unintentional accumulation of MPs by zooplankton, highlighting the complex interactions between food availability and MPs accumulation dynamics.

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.

Wastewater disinfection with photodynamic treatment and evaluation of its ecotoxicological effects.

Research has demonstrated the presence of viruses in wastewater (WW), which can remain viable for a long period, posing potential health risks. Conventional WW treatment methods involving UV light, chlorine and ozone efficiently reduce microbial concentrations, however, they produce hazardous byproducts and microbial resistance that are detrimental to human health and the ecosystem. Hence, there is a need for novel disinfection techniques. Antimicrobial Photodynamic Inactivation (PDI) emerges as a promising strategy, utilizing photosensitizers (PS), light, and dioxygen to inactivate viruses. This study aims to assess the efficacy of PDI by testing methylene blue (MB) and the cationic porphyrin TMPyP as PSs, along a low energy consuming white light source (LED) at an irradiance of 50 mW/cm2, for the inactivation of bacteriophage Phi6. Phi6 serves as an enveloped RNA-viruses surrogate model in WW. PDI experiments were conducted in a buffer solution (PBS) and real WW matrices (filtered and non-filtered). Considering the environmental release of the treated effluents, this research also evaluated the ecotoxicity of the resulting solution (post-PDI treatment effluent) on the model organism Daphnia magna, following the Organisation for Economic Cooperation and Development (OECD) immobilization technical 202 guideline. Daphnids were exposed to WW containing the tested PS at different concentrations and dilutions (accounting for the dilution factor during WW release into receiving waters) over 48 h. The results indicate that PDI with MB efficiently inactivated the model virus in the different aqueous matrices, achieving reductions superior to 8 log10 PFU/mL, after treatments of 5 min in PBS and of ca. 90 min in WW. Daphnids survival increased when subjected to the PDI-treated WW with MB, considering the dilution factor. Overall, the effectiveness of PDI in eliminating viruses in WW, the fading of the toxic effects on daphnids after MB' irradiation and the rapid dilution effect upon WW release in the environment highlight the possibility of using MB in WW PDI-disinfection.

Inhibitory Effects on Staphylococcus aureus Sortase A by Aesculus sp. Extracts and Their Toxicity Evaluation.

A promising strategy for combating bacterial infections involves the development of agents that disarm the virulence factors of pathogenic bacteria, thereby reducing their pathogenicity without inducing direct lethality. Sortase A, a crucial enzyme responsible for anchoring virulence factors to the cell surface of several pathogenic bacteria, has emerged as a possible target for antivirulence strategies. A series of hippocastanum species (Aesculus pavia, A. parviflora, Aesculus x carnea, and A. hippocastanum) were used to prepare ethanol- and water-based extracts for assessing their effect on Staphylococcus aureus sortase A. The extracts were characterized through HPLC analysis, and their polyphenols content was determined using the Folin-Ciocalteu method. The specific toxicity profile was evaluated in Daphnia magna using the median lethal concentration (LC50) and against the fibroblast MRHF cell line. The half maximal inhibitory concentration (IC50) values on sortase A, determined after 30 min of incubation, ranged from 82.70 to 304.31 µg/mL, with the A. pavia water extract exhibiting the highest inhibitory effect. The assessment of the A. pavia water extract on human fibroblasts revealed no significant signs of toxicity, even at a concentration of 500 µg/mL. This reduced toxicity was further validated through the Daphnia assay. These findings highlight the low toxicity and the potential of this extract as a promising source of future development of bacteria antivirulence solutions.

An Integrated Testing Strategy (ITS) to assess the environmental compatibility of wood protection techniques.

To quantify the possible impact of different wood protection techniques on the aquatic environment, we applied a tiered Integrated Testing Strategy (ITS) on leachates obtained from untreated (UTW) Norway spruce (Picea abies), specimens treated with a copper-ethanolamine-based preservative solution, complying with the Use Class 3 (UC3), and specimens thermally modified (TM). Different maturation times in water were tested to verify whether toxicant leaching is time-dependent. Tier I tests, addressing acute effects on Aliivibrio fischeri, Raphidocelis subcapitata, and Daphnia magna, evidenced that TM toxicity was comparable or even lower than in UTW. Conversely, UC3 significantly affected all species compared to UTW, also after 30 days of maturation in water, and was not considered an environmentally acceptable wood preservation solution. Tier II (effects on early-life stages of Lymnea auricularia) and III (chronic effects on D. magna and L. auricularia) performed on UTW and TM confirmed the latter as an environmentally acceptable treatment, with increasing maturation times resulting in decreased adverse effects. The ITS allowed for rapid and reliable identification of potentially harmful effects due to preservation treatments, addressed the choice for a less impacting solution, and can be effective for manufacturers in identifying more environmentally friendly solutions while developing their products.

The analysis of inducible family members in the water flea Daphnia magna led to the identification of an uncharacterized lineage of heat shock protein 70.

To explore the function and evolutionary relationships of inducible heat shock protein 70 (Hsp70) in Daphnia magna, cDNAs of four Hsp70 family members (DmaHsp70, DmaHsp70-2, DmaHsp70-12, DmaHsp70-14) were cloned. While all DmaHsp70s possess three function domains, it is noteworthy that only DmaHsp70 ends with a "EEVD" motif. Phylogenetic analysis indicates that the Hsp70-12 lineage is distanced from the rest, and therefore it is an uncharacterized lineage of Hsp70. The differences in isoelectric point and 3-dimensional (3D) conformation of the N-terminal nucleotide binding domain (NBD) of DmaHsp70s further support the theory. DmaHsp70s exhibit varied motif distribution patterns and the logo sequences of motifs have diverse signature characteristics, indicating that different mechanisms are involved in the regulation of ATP binding and hydrolysis for the DmaHsp70s. Protein-protein network together with the predicted subcellular locations of DmaHsp70s suggest that they likely fulfill distinct roles in cells. The transcription of four DmaHsp70s were changed during the recovery stage after thermal stress or oxidative stress. But the expression pattern of them were dissimilar. Collectively, these results collectively elucidated the identification of a previously uncharacterizedHsp70 lineage in animal and extended our understanding of the Hsp70 family.

Fishmeal substitution by zooplankton or Daphnia magna biomass meals in the diet of Nile tilapia: Effects on growth, gut histological changes, bacterial abundance and stress tolerance.

Fishmeal substitution with sustainable feed sources is highly essential towards sustainable production. This study aimed to investigate the effects of substituting fishmeal (FM) with Daphnia magna biomass meal (DBM) or zooplankton biomass meal (ZBM) on growth performance, liver and intestinal histology, gut bacterial abundance and stress tolerance of Nile tilapia, Oreochromis niloticus, fry. Nile tilapia fry (0.23 ± 0.04 g) were randomly assigned to five groups of three replicates. The control diet comprised 300 g/kg FM, and the FM was substituted with DBM or ZBM at levels of 25% and 50% (DBM-25, DBM-50, ZBM-25 and ZBM-50 respectively) in the other experimental diets. The experiment lasted 56 days in 1.5 m3 concrete tanks. The results revealed that weight gain and feed conversion ratio (FCR) significantly (p ≤ 0.035 and 0.025 respectively) improved with a polynomial response with a peak at 25% ZBM and a linear increase with DBM up to 50% of FM. Histometric indices of the distal intestine showed improvements (p ≤ 0.001) in villus height, villus width, crypt depth and muscle thickness of fish fed DBM or ZBM compared to the control. In the meantime, there were no histological abnormalities in the liver sections. The replacement of FM with DBM or ZBM could modulated gut bacterial abundance, including total bacterial count, Escherichia coli, Bacillus subtilis, and Lactobacillus sp. The fish-fed DBM or ZBM-containing diets had higher (p ≤ 0.05) tolerances to salinity stress than the control group. In conclusion, DBM or ZBM could replace FM up to 50% and 25%, respectively with improved fish growth performance, FCR, gut histology and tolerance to salinity stress.

Algal toxicity and food chain transport characteristics of three common bisphenols and their mixtures.

Various bisphenols (BPs) have been frequently detected in the aquatic environment and coexist in the form of mixtures with potential huge risks. As we all know, food chain is a media by which BPs mixtures and their mixtures probably enter the organisms at different trophic levels due to their environmental persistence. As a result, the concentrations of BPs and their mixtures may continuously magnify to varying degrees, which can produce higher risks to different levels of organisms, and even human health. However, the related researches about mixtures are few due to the complexity of mixtures. So, the ternary BP mixtures were designed by the uniform design ray method using bisphenol A (BPA), bisphenol S (BPS) and bisphenol F (BPF) to investigate their food chain effects including bioconcentration and biomagnification. Here, Chlorella pyrenoidosa (C. pyrenoidosa) and Daphnia magna (D. magna) were selected to construct a food chain. The toxic effects of single BPs and their mixtures were also systematically investigated by the time-dependent microplate toxicity analysis (t-MTA) method. Toxicity interaction within the ternary mixture was analyzed by the concentration addition model (CA) and the deviation from the CA model (dCA). The results show that the C. pyrenoidosa and D. magna had obvious bioconcentration and biomagnification effects on BPs and their mixture. The mixture had the potential to enrich at higher nutrient levels. And BPF had the largest bioconcentration effect (BCF1 = 481.86, BCF2 = 772.02) and biomagnification effect (BMF = 1.6). Three BPs were toxic to C. pyrenoidosa by destroying algal cells and decreasing protein and chlorophyll contents, and their toxicity order was BPF > BPA > BPS. Moreover, their ternary mixture exhibits synergism with time/concentration-dependency. The obtained results are of significant reference value for objectively and accurately assessing the ecological and environmental risks of bisphenol pollutants.

Combined exposure to hypoxia and nanoplastics leads to negative synergistic oxidative stress-mediated effects in the water flea Daphnia magna.

In this study, we investigated the combined effects of hypoxia and NPs on the water flea Daphnia magna, a keystone species in freshwater environments. To measure and understand the oxidative stress responses, we used acute toxicity tests, fluorescence microscopy, enzymatic assays, Western blot analyses, and Ingenuity Pathway Analysis. Our findings demonstrate that hypoxia and NPs exhibit a negative synergy that increases oxidative stress, as indicated by heightened levels of reactive oxygen species and antioxidant enzyme activity. These effects lead to more severe reproductive and growth impairments in D. magna compared to a single-stressor exposure. In this work, molecular investigations revealed complex pathway activations involving HIF-1α, NF-κB, and mitogen-activated protein kinase, illustrating the intricate molecular dynamics that can occur in combined stress conditions. The results underscore the amplified physiological impacts of combined environmental stressors and highlight the need for integrated strategies in the management of aquatic ecosystems.

Quantitative structure-activity relationship predicting toxicity of pesticides towards Daphnia magna.

Global pesticide usage reaching 2.7 million metric tons annually, brings a grave threat to non-target organisms, especially aquatic organisms, resulting in serious concerns. Predicting aquatic toxicity of pesticides towards Daphnia magna is significant. In this work, random forest (RF) algorithm, together with ten Dragon molecular descriptors, was successfully utilized to develop a quantitative structure-activity/toxicity relationship (QSAR/QSTR) model for the toxicity pEC50 of 745 pesticides towards Daphnia magna. The optimal QSTR model (RF Model I) based on the RF parameters of ntree = 50, mtry = 3 and nodesize = 5, yielded R2 = 0.877, MAE = 0.570, rms = 0.739 (training set of 596 pEC50), R2 = 0.807, MAE = 0.732, rms = 0.902 (test set of 149 pEC50), and R2 = 0.863, MAE = 0.602, rms = 0.774 (total set of 745 pEC50), which are accurate and satisfactory. The optimal RF model is comparable to other published QSTR models for Daphnia magna, although the optimal RF model possessed a small descriptor subset and dealt with a large dataset of pesticide toxicity pEC50. Thus, the investigation in this work provides a reliable, applicable QSTR model for predicting the toxicity pEC50 of pesticides towards Daphnia magna.

Ectopical expression of bacterial collagen-like protein supports its role as adhesin in host-parasite coevolution.

For a profound understanding of antagonistic coevolution, it is necessary to identify the coevolving genes. The bacterium Pasteuria and its host, the microcrustacean Daphnia, are a well-characterized paradigm for co-evolution, but the underlying genes remain largely unknown. A genome-wide association study suggested a Pasteuria collagen-like protein 7 (Pcl7) as a candidate mediating parasite attachment and driving its coevolution with the host. Since Pasteuria ramosa cannot currently be genetically manipulated, we used Bacillus thuringiensis to express a fusion protein of a Pcl7 carboxy-terminus from P. ramosa and the amino-terminal domain of a B. thuringiensis collagen-like protein (CLP). Mutant B. thuringiensis (Pcl7-Bt) spores but not wild-type B. thuringiensis (WT-Bt) spores attached to the same site of susceptible hosts as P. ramosa. Furthermore, Pcl7-Bt spores attached readily to susceptible host genotypes, but only slightly to resistant host genotypes. These findings indicated that the fusion protein was properly expressed and folded and demonstrated that indeed the C-terminus of Pcl7 mediates attachment in a host genotype-specific manner. These results provide strong evidence for the involvement of a CLP in the coevolution of Daphnia and P. ramosa and open new avenues for genetic epidemiological studies of host-parasite interactions.

Effect of chlorpyrifos-exposure on the expression levels of CYP genes in Daphnia magna and examination of a possibility that an up-regulated clan 3 CYP, CYP360A8, reacts with pesticides.

Daphnia magna is a test organism used for ecological risk assessments of pesticides, but little is known about the expression levels of cytochrome P450s (CYP)s and their changes after pesticide exposure in the less than 24-h-olds used for ecotoxicity tests. In this study, D. magna juveniles were exposed to 0.2 µg/L of chlorpyrifos under the conditions for acute immobilization test as specified by the OECD test guideline for 24 h, and then the gene expression was compared between the control and chlorpyrifos-exposure groups by RNA-sequencing analysis, with a focus on CYP genes. Among 38 CYP genes expressed in the control group, seven were significantly up-regulated while two were significantly down-regulated in the chlorpyrifos-exposure group. Although the sublethal concentration of chlorpyrifos did not change their expression levels so drastically (0.8 < fold change < 2.6), CY360A8 of D. magna (DmCYP360A8), which had been proposed to be responsible for metabolism of xenobiotics, was abundantly expressed in controls yet up-regulated by chlorpyrifos. Therefore, homology modeling of DmCYP360A8 was performed based on the amino acid sequence, and then molecular docking simulations with the insecticides that were indicated to be metabolized by CYPs in D. magna were conducted. The results indicated that DmCYP360A8 could contribute to the metabolism of diazinon and chlorfenapyr but not chlorpyrifos. These findings suggest that chlorpyrifos is probably detoxified by other CYP(s) including up-regulated and/or constitutively expressed one(s).

Ecological consequences when organisms avoid a contaminated environment: A study evaluating the toxicity of fipronil.

The ability of aquatic organisms to sense the surrounding environment chemically and interpret these signals correctly is crucial to their survival and ecological niche. This study applied the Heterogenous Multi-Habitat Assay System - HeMHAS to evaluate the avoidance potential of Daphnia magna to detect fipronil-contaminated habitats in a connected landscape after a short (48 h), previous, forced exposure to an environmentally relevant concentration of the same insecticide. The swimming of daphnids was also analyzed by recording the total distance covered. D. magna preferred areas with less contamination, although the effect of fipronil on their swimming ability (a decrease) was observed for all the concentrations tested. The application of non-forced multi-compartment exposure methodologies is a recent trend and is ecologically relevant as it is based on how contamination can really produce changes in an organism's habitat selection. Finally, we consider the importance of more non-forced exposure approaches where Stress Ecology can be aggregated to improve systemic understanding of the risk that contaminants pose to aquatic ecosystems from a broader landscape perspective.