Quick assessment of cytotoxins effect on Daphnia magna using in vivo fluorescence microscopy

Ecological risks of high-ammonia environment with inhibited growth of Daphnia magna: Disturbed energy metabolism and oxidative stress

High ammonia pollution is a common problem in water bodies. However, research on the mechanisms underlying the toxic effects on organisms at different nutritional levels is still insufficient. Herein, based on the environmental concentration, the toxic effects of high ammonia pollution on Daphnia magna were investigated. Overall, the feeding and filtration rates of D. magna were significantly decreased by ammonia. Growth inhibition of D. magna by ammonia was confirmed by the decreased body length. After ammonia exposure, the metabolic status of D. magna changed, the correlation network weakened, and the correlations between metabolites were disrupted. Changes occurred in metabolites primarily involved in oxidative stress, fatty acid oxidation, tricarboxylic acid cycle, and protein digestion, absorption, and synthesis, which were validated through alterations in multiple biomarkers. In addition, mitochondrial function was evaluated and was found to inhibit mitochondrial activity, which was accompanied by a decreased marker of mitochondrial activity contents and ATPase activity. Thus, the results suggested that energy metabolism and oxidative stress were involved in ammonia-induced growth toxicity. This study provides new insights into the impact of ammonia on aquatic ecological health.

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

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

Interactive effects of cyanobacterial metabolites aeruginosin-98B, anabaenopeptin-B and cylindrospermopsin on physiological parameters and novel in vivo fluorescent indicators in Chironomus aprilinus larvae

We aimed to determine the effects of single cyanobacterial metabolites aeruginosin-B (AER-B), anabaenopeptin-B (ANA-B), cylindrospermopsin (CYL), their binary and ternary mixtures on biomarkers of Chironomus aprilinus larvae: oxygen consumption, fat body structure and two novel fluorescent indicators: imaging of nuclei in cells of body integument, and the catecholamine level. The obtained results showed that oxygen consumption was inhibited by single tested cyanobacterial metabolites except for ANA-B at the lowest concentration (250 μg/L). Although the mixtures of the metabolites inhibited oxygen consumption with antagonistic interactions between the components stimulation was noted in the group exposed to the lowest concentrations of AER-B + CYL (125 μg/L + 125 μg/L, respectively) and the ternary mixture of AER-B + ANA-B + CYL (83.3 μg/L + 83.3 μg/L + 83.3 μg/L, respectively). In vivo fluorescent staining with Hoechst 34580 showed that single AER-B had lower cytotoxic potential on body integument cells than ANA-B and CYL and most binary mixtures except for AER-B + CYL induced synergistic toxicity. Catecholamine level was decreased in animals exposed to single metabolites, their binary and ternary mixtures; however, the interactions between the components in the ternary mixture were antagonistic. Fat body was found to be disrupted in the larvae exposed to single metabolites and their combinations. Antagonistic toxic interactions between the oligopeptide components were found in most binary and the ternary mixtures; however, synergistic effect was noted in the binary mixture of AER-B + CYL. The results suggest that in natural conditions Chironomus larvae and possibly other benthic invertebrates may be affected by cyanobacterial metabolites, however various components and in mixtures and their concentrations may determine varied physiological effects and diverse interactions.

Utilizing Extraepitopic Amino Acid Substitutions to Define Changes in the Accessibility of Conformational Epitopes of the Bacillus cereus HlyII C-Terminal Domain

Hemolysin II (HlyII)-one of the pathogenic factors of Bacillus cereus, a pore-forming β-barrel toxin-possesses a C-terminal extension of 94 amino acid residues, designated as the C-terminal domain of HlyII (HlyIICTD), which plays an important role in the functioning of the toxin. Our previous work described a monoclonal antibody (HlyIIC-20), capable of strain-specific inhibition of hemolysis caused by HlyII, and demonstrated the dependence of the efficiency of hemolysis on the presence of proline at position 324 in HlyII outside the conformational antigenic determinant. In this work, we studied 16 mutant forms of HlyIICTD. Each of the mutations, obtained via multiple site-directed mutagenesis leading to the replacement of amino acid residues lying on the surface of the 3D structure of HlyIICTD, led to a decrease in the interaction of HlyIIC-20 with the mutant form of the protein. Changes in epitope structure confirm the high conformational mobility of HlyIICTD required for the functioning of HlyII. Comparison of the effect of the introduced mutations on the effectiveness of interactions between HlyIICTD and HlyIIC-20 and a control antibody recognizing a non-overlapping epitope enabled the identification of the amino acid residues N339 and K340, included in the conformational antigenic determinant recognized by HlyIIC-20.

Novel peptide identified from viable-cell based phage display technique regulates growth cycle of Daphnia magna

Phage display is a widely used technique for selecting specific binding peptides, but presenting antigens in their natural form can be challenging, as protein coating may induce structural changes. In this study, we employed a whole cell-based phage display technique without a coating step to select peptides that bind specifically to Daphnia magna eggs. Boiled eggs were used as a control to ensure that antigens were presented in their natural forms. We identified a peptide, DEP1 (LYALPLSHLKSHGGG), with the highest binding affinity to D. magna eggs. DEP1 did not affect zebrafish eggs, but it inhibited normal hatching and reproductive ability in D. magna eggs, and hindered growth in neonates before their first ecdysis. Morphological analysis revealed that DEP1 caused intestinal damage and tissue abnormalities. Our findings demonstrate that the whole cell-based phage display technique is successful in presenting antigens in their natural form, and that the DEP1 peptide can be applied to regulate the growth cycle of D. magna. These results have implications for the use of phage display in environmental research and the potential use of DEP1 for hazardous organisms in aquatic systems.

Behavioral disturbances induced by cyanobacterial oligopeptides microginin-FR1, anabaenopeptin-A and microcystin-LR are associated with neuromotoric and cytotoxic changes in Brachionus calyciflorus

Aquatic animals are exposed to various cyanobacterial products released concomitantly to the environment by decaying blooms. Although there exist results on the toxicity of cyanobacterial extracts little is known on the influence of pure oligopeptides or their mixtures and elucidated mechanisms of behavioral toxicity in zooplanktonic organisms. Therefore, the aim of the present study was to assess the effects of single and mixed pure cyanobacterial oligopeptides: microginin FR-1 (MG-FR1), anabaenopeptin-A (ANA-A) and microcystin-LR (MC-LR) at various concentrations on the swimming behavior and catecholamine neurotransmitter activity, muscular F-actin structure, DNA nuclear content and cell viability of a model rotifer Brachionus calyciflorus. Swimming behavior was analyzed with the use of video digital analysis. Fluorescent microscopy imaging was used to analyze neuromotoric biomarkers in the whole organisms: neuromediator release (by staining with EC517 probe), muscle F-actin filaments (by staining with blue phalloidin dye). DNA content and cytotoxicity was also determined by Hoechst 34580 and propidium iodide double staining, respectively. The results showed that single oligopeptides inhibited all the tested endpoints. The binary mixtures induced synergistic interaction on swimming speed except for MG-FR1 +MC-LR which was nearly additive. Both binary and ternary mixtures also synergistically degraded F-actin and triggered cytotoxic effects visible in the whole organisms. Antagonistic inhibitory effects of all the binary mixtures were found on catecholamine neurotransmitter activity, however the ternary mixture induced additive toxicity. Antagonistic effects of both binary and ternary mixtures were also noted on nuclear DNA content. The results of the study suggest that both depression of neurotransmission and impairment of muscle F-actin structure in muscles may contribute to mechanisms of Brachionus swimming speed inhibition by the tested single cyanobacterial oligopeptides and their mixtures. The study also showed that natural exposure of rotifers to mixtures of these cyanobacterial metabolites may result in different level of interactive toxicity with antagonistic, additive synergistic effects depending on the variants and concentrations present in the environment.

Length- and polymer-dependent ecotoxicities of microfibers to the earthworm Eisenia andrei

Microfibers are widespread environmental pollutants introduced to the soil environment because of the increasing use of plastic polymers. However, research on the soil ecotoxicity of microfibers is limited, especially when compared to research on their aquatic toxicity. This study investigated the effects of sub-chronic microfiber exposure on the earthworm Eisenia andrei. We compared the effects of three types of microfibers: short lyocell microfibers (231 ± 126 μm long), short polypropylene microfibers (191 ± 107 μm long), and long polypropylene microfibers (891 ± 141 μm long). After exposure for 21 days, earthworm survival, coelomocyte viability, cast microbial viability, and gut microbial viability were assessed, and a histopathological examination of the digestive tract and reproductive tissues was conducted. In addition, long polypropylene microfibers egested by the earthworms were collected to explore the possibility of earthworm-driven biofragmentation. Results indicated that high exposure concentration (1000 mg/kg dry soil) negatively affected earthworm coelomocytes and intestinal tissue, gut, and cast microbiomes. Although all three microfiber types reduced earthworm survival, the short polypropylene microfibers were more toxic to the earthworms than the long polypropylene microfibers or short lyocell microfibers, which indicated that size-dependent soil ecotoxicity was induced. PP microfibers were found to more negatively affect cast microbial activity and intestinal tissue than lyocell microfibers, indicating polymer-dependent soil ecotoxicity potential against earthworm species. This study provides evidence that synthesized microfibers cause cytotoxicity and decrease gut microbiome viability in earthworms, and that they can be biofragmented by earthworms.

The C-terminal domain of Bacillus cereus hemolysin II oligomerizes by itself in the presence of cell membranes to form ion channels

Bacillus cereus hemolysin II, a pore-forming β-barrel toxin (HlyII), has a C-terminal extension of 94 amino acid residues, designated as the C-terminal domain of HlyII (HlyIICTD). HlyIICTD is capable of forming oligomers in aqueous solutions. Oligomerization of HlyIICTD significantly increased in the presence of erythrocytes and liposomes. Its affinity for erythrocytes of various origins differed insignificantly but was noticeably higher for T-cells. HlyIICTD destroyed THP-1 monocytes and J774 macrophages, acted most effectively on Jurkat T-lymphocytes and had virtually no impact on B-cell lines. HlyIICTD was able to form ion-conducting channels on an artificial bilayer membrane.

Effects of Different Ammonia Levels on Tribenuron Methyl Toxicity in Daphnia magna

The present study investigates the toxicity of the herbicide tribenuron methyl (TBM) as an anthropogenic agent and ammonia as an abiotic factor on Daphnia magna at environmentally relevant concentrations. These stressors may coexist in surface waters in agricultural regions. To achieve this objective, D. magna were exposed to TBM at a nominal concentration of 0.81 μg/L in association with a low ammonia (LA) concentration of 0.65 mg/L and a high ammonia (HA) concentration of 1.61 mg/L in acute toxicity tests of 96-h duration and chronic toxicity tests of 21-day duration. The D. magna also were exposed to TBM, HA, and LA singly. The D. magna were analysed for various biomarkers of sublethal toxicity. Glutathione peroxidase (GPx), glutathione S-transferase (GST), cholinesterase (ChE) enzyme activities, and levels of thiobarbituric acid reactive substances (TBARS) and total protein were determined spectrophotometrically. Mitochondrial membrane potential (MMP) was analysed by microscopy with fluorescence staining. Cytochrome c and 5' AMP-activated protein kinase (AMPK) were analysed by Western blotting. Morphometric properties were examined microscopically. This is the first study in which AMPK, an indicator of intracellular energy, was measured in D. magna. GST and ChE enzyme activities and TBARS and total protein levels did not change during acute exposures (i.e., 96 h) in all treatments. GPx activity increased in D. magna from the HA + TBM treatment compared with single-exposure groups. The level of cytochrome c protein was elevated in D. magna from the LA and LA + TBM treatments. AMPK protein levels increased in all treatments with daphnids, except in the LA group. MMP was depolarised in D. magna from all treatments, whereas the most notable change was observed in HA + TBM mixture group in chronic exposures. The results show that GST and ChE may not be sensitive biomarkers for evaluating the sublethal toxic effects to D. magna exposed to environmentally relevant concentrations of ammonia and TBM. Acute and chronic exposure to ammonia and TBM probably caused an energetic crisis in D. magna. Therefore, AMPK and MMP are promising biomarkers for these toxicants.

Neural stem cell-based in vitro bioassay for the assessment of neurotoxic potential of water samples

Intensive agriculture activities, industrialization and growing numbers of wastewater treatment plants along river banks collectively contribute to the elevated levels of neurotoxic pollutants in natural water reservoirs across Europe. We established an in vitro bioassay based upon neural stem cells isolated from the subventricular zone of the postnatal mouse to evaluate the neurotoxic potential of raw wastewater, treated sewage effluent, groundwater and drinking water. The toxic potential of water samples was evaluated employing viability, proliferation, differentiation and migration assays. We found that raw wastewater could reduce the viability and proliferation of neural stem cells, and decreased the neuronal and astrocyte differentiation, neuronal neurite growth, astrocyte growth and cell migration. Treated sewage water also showed inhibitory effects on cell proliferation and migration. Our results indicated that relatively high concentrations of nitrogenous substances, pesticides, mercuric compounds, bisphenol-A, and phthalates, along with some other pollutants in raw wastewater and treated sewage water, might be the reason for the neuroinhibitory effects of these water samples. Our model successfully predicted the neurotoxicity of water samples collected from different sources and also revealed that the incomplete removal of contaminants from wastewater can be problematic for the developing nervous system. The presented data also provides strong evidence that more effective treatments should be used to minimize the contamination of water before release into major water bodies which may be considered as water reservoirs for human usage in the future.

Oxidative and apoptotic effects of fluoxetine and its metabolite norfluoxetine in Daphnia magna

The aim of this study was to investigate the oxidative and apoptotic potential of fluoxetine, a widely used antidepressant in Turkey and the world, and of its metabolite norfluoxetine on a model non-target organism, Daphnia magna to see how exposure to this group of antidepressants (specific serotonin reuptake inhibitors) could affect the aquatic environment in which they end up. Juvenile D. magna specimens were chronically exposed to fluoxetine and norfluoxetine alone and in combination at concentrations found in the aquatic environment (0.091 and 0.011 μg/L, respectively) and to their 10-fold environmental concentrations for 21 days. Another group of 17-day-old animals were subacutely exposed to 100-fold environmental concentrations for four days. After exposure, we measured their glutathione peroxidase (GPx) and cholinesterase (ChE) activities, thiobarbituric acid-reactive substances (TBARS), and total protein content spectrophotometrically, while mitochondrial membrane potential (MMP) was analysed by fluorescence staining, and cytochrome c and ERK1/2 protein content by Western blotting. This is the first-time cytochrome c and ERK1/2 were determined at the protein level in D. magna. We also measured their carapace length, width, and caudal spine length microscopically. At environmental concentrations fluoxetine and norfluoxetine caused an increase in ChE activity and brood production. They also caused a decrease in juvenile carapace length, width, and caudal spine length and depolarised the mitochondrial membrane. At 10-fold environmental concentrations, GPx activity, lipid peroxidation levels, cytochrome c, and ERK1/2 protein levels rose. The most pronounced effect was observed in D. magna exposed to norfluoxetine. Norfluoxetine also decreased brood production. Similar effects were observed with subacute exposure to 100-fold environmental concentrations. However, total protein content decreased. All this confirms that fluoxetine and norfluoxetine have oxidative and apoptotic potential in D. magna. Daphnia spp. have a great potential to give us precious insight into the mechanisms of environmental toxicants, but there is still a long way to go before they are clarified in these organisms.

In vivo assessment of pathogens toxicity on Daphnia magna using fluorescent dye staining

Daphnia has been widely used as an indicator species in aquatic biomonitoring for decades. Traditional toxicity assays based on lethality take a long time to assess, and the effect mode of contaminants is not clear. Because of the translucency of the Daphnia body and the application of fluorescent probes in cell staining, different intoxicated parts can be visualized. In this study, a double-staining method using two fluorescent dyes, Calcein AM (cell-permeant dye) and Propidium Iodide (cell-impermeant dye), was carried out on Daphnia magna exposed to six pathogens: Salmonella spp. (four strains) and Shigella spp. (two strains). The results showed that those bacteria caused different infections on daphnia depending on the age of this organism and bacterial concentrations. In detail, S. dublin and S. sonnei are the most harmful to Daphnia when they cause damage at smaller concentrations at the younger stage (3 weeks old). Interestingly, older Daphnia can give responses to nearly 10 CFU/ml to less than 100 CFU/ml of some bacteria strains. In another experiment, S. sonnei disturbed Daphnia after just 10 min of exposure, and Daphnia adapted to S. choleraesuis, S. typhi, and S. flexneri at the early stage (3 weeks old) after 1 h of exposure. Moreover, the damaged areas of the daphnia body were directly observed via a microscope, contributing to the understanding and the prediction of toxicity mechanisms.

Physiological endpoints in daphnid acute toxicity tests

Daphnids are freshwater crustaceans used in toxicity tests. Although lethality and immobilisation are the most commonly used endpoints in those tests, more sensitive parameters are required for determination of sublethal acute effects of toxicants. The use of various physiological endpoints in daphnids is considered as a low-cost and simple alternative that meets the 3R's rule (Replacement, Reduction, Refinement) criteria. However, currently there is no review-based evaluation of their applicability in toxicity testing. This paper presents the results on the most commonly determined physiological parameters of Daphnia in ecotoxicological studies and human drug testing, such as feeding activity, thoracic limb movement, heart rate, cardiac area, respiratory activity, compound eye, mandible movements and post-abdominal claw contractions. Furthermore, their applicability as promising endpoints in the assessment of water quality or drug testing is discussed.

Soil ecotoxicity study of DEHP with respect to multiple soil species

Di (2-ethylhexyl) phthalate or DEHP is classified as an endocrine-disrupting chemical. It is used as a plasticizer and pesticide additive. Moreover, it has a half-life of about 150-300 days. Thus, it is present in the soil environment and soil risk assessments for DEHP are needed. However, a number of studies have focused on the effects of DEHP in a single soil species. In this study, we conducted acute and chronic toxicity testing for DEHP using varied soil species, including plants, earthworms, soil algae, Collembola, and soil nematodes. In the plant toxicity test, no effect was observed at very high concentration except at some endpoints, and no effect was observed in the earthworm toxicity test. However, there were adverse effects on soil algae, Collembola, and nematodes. Notably, in the Collembola assays, the survival of adults decreased significantly at very high concentrations, whereas reproduction was hindered at low concentrations. Similar inhibition of reproduction was noted in the soil nematode assay. This suggests that DEHP has a greater influence on fertility than survival in the adult test species. However, besides hindered reproduction, no effect was observed on soil species at environmentally relevant concentrations.

Assessing applicability of the paper-disc method used in combination with flow cytometry to evaluate algal toxicity

Soil algal bioassays have been limited by their inability to evaluate several toxic endpoints because it is difficult to collect pure soil algae growing on and beneath the soil surface. This study describes the extension of a previously developed paper-disc method for analyzing soil toxicity to algae. The method can be used in conjunction with flow cytometric analysis and facilitates the assessment of previously proposed toxicity endpoints, such as the growth zone, biomass, and photosynthetic activity. We assessed the applicability of this paper-disc soil method using the green algae Chlamydomonas reinhardtii and Pseudokirchneriella subcapitata exposed to nickel-contaminated soil; examined cell sizes, cell granularity, enzyme activity, and oxidative stress as new toxicity endpoints using flow cytometry; and identified morphological changes in green algae assayed. The results showed that, used in conjunction with flow cytometry, the extended paper-disc soil method is sufficiently sensitive to detect decreases in cell granularity in C. reinhardtii and esterase activity in P. subcapitata. The method also revealed decreases in growth zone, biomass, and electron transfer from the reaction center to the quinone pool. Collectively, the results of this study indicate that soil algal bioassays using nonspecific algae can be used to assess soil quality, to derive several toxicity endpoints for individual cells, and to evaluate previously established flow cytometric toxicity endpoints.

Quantification of silver nanoparticle toxicity to algae in soil via photosynthetic and flow-cytometric analyses

Soil algae, which have received attention for their use in a novel bioassay to evaluate soil toxicity, expand the range of terrestrial test species. However, there is no information regarding the toxicity of nanomaterials to soil algae. Thus, we evaluated the effects of silver nanoparticles (0-50 mg AgNPs/kg dry weight soil) on the soil alga Chlamydomonas reinhardtii after six days, and assessed changes in biomass, photosynthetic activity, cellular morphology, membrane permeability, esterase activity, and oxidative stress. The parameters measured were markedly affected by AgNP-induced stress at 50 mg AgNPs/kg dry weight soil, where soil algal biomass, three measures of photosynthetic activity (area, reaction center per absorption flux, and reaction center per trapped energy flux), and esterase activity decreased. AgNPs also induced increases in both cell size and membrane permeability at 50 mg AgNPs/kg dry weight soil. In addition to the increase in cell size observed via microscopy, a mucilaginous sheath formed as a protective barrier against AgNPs. Thus, the toxicity of AgNPs can be effectively quantified based on the physiological, biochemical, and morphological responses of soil algae, where quantifying the level of toxicity of AgNPs to soil algae could prove to be a useful method in terrestrial ecotoxicology.

Effects of silver nanowire length and exposure route on cytotoxicity to earthworms

To accurately evaluate the environmental toxicity of silver nanowires (AgNWs), it is necessary to characterize how the cytotoxicity of these nanomaterials is affected by the route of exposure. However, few studies have addressed the exposure route or mechanism of toxicity of nanomaterials, particularly of nanowires, in living organisms. In this study, we therefore analyzed the main exposure route of AgNWs in vitro, using earthworms (Eisenia andrei) as a model system, via flow cytometry. We subsequently examined the in vivo toxicity of AgNWs to earthworms in soil. These tests revealed that intracellular esterase activity was correlated with adsorption of the nanowires to the surfaces of coelomocytes in vitro, and that in vivo cytotoxicity resulted mainly from oral, rather than dermal, exposure to the nanowires. Overall, shorter AgNWs (10 μm) were more toxic than longer AgNWs (20 μm). To our knowledge, this study is the first report regarding the ecotoxicity of nanowires to earthworms in soil. Our findings provide important information to help assess the risk of toxic AgNW contamination of soil ecosystems.

A new and sensitive method for measuring in vivo and in vitro cytotoxicity in earthworm coelomocytes by flow cytometry

This study describes a new and sensitive method for measuring the in vivo and in vitro cytotoxicity of 2 earthworm species, Eisenia andrei and Perionyx excavatus, exposed to copper. Specifically, we measured the number of coelomocyte cells that were affected by copper following in vivo and in vitro exposure by flow cytometry, after calcein acetoxymethyl ester (calcein-AM) staining. We found that the coelomocyte viability of both earthworm species was noticeably reduced in the in vivo cytotoxicity test at concentrations of 100mg/kg copper in dry soil. However, pathological symptoms, such as mucous secretion and bleeding, swelling, thinning, and fragmentation, and burrowing symptoms were not evident following exposure to copper levels of <400mg/kg dry soil. In conclusion, the present study demonstrates that calcein-AM is a more sensitive test of earthworm coelomocyte cytotoxicity compared to the traditional individual level toxicity test. Therefore, this test could be used to detect low levels of metal contamination in soils.