Comet Assay on Daphnia magna in eco-genotoxicity testing

Evaluation of arsenic induced genotoxicity and its impact on life processes of Daphnia magna

Heavy metals like arsenic is ubiquitously present in the environment. Geologic and anthropogenic activities are the root cause behind high concentration of arsenic in natural water bodies demanding strict monitoring of water quality prior to human consumption and utilization. In the present study, we have employed Daphnia magna for studying the biological effects of environmentally relevant high concentration of arsenic in water. In acute toxicity study, the LC50 value for 24hr exposure was found to be 2.504 mg/L, which gradually decreased with increase in time period (24hr- 96hr) to 2.011 mg/ L at 96hr. Sub-chronic toxicity was evaluated over 12 days using sub-lethal concentrations (5 %, 10 %, 15 %, and 20 % of the 24-hr LC50). Survivability in Daphnia showed a decreasing trend from 96 % to 91 % with increase in arsenic concentrations from 5 % of LC50 24 hr value to 20 % of LC 50 24hr value respectively. Alongside decreased survivability, there was a significant reduction in body size, with organisms exposed to the highest concentration of arsenic measuring 0.87±0.01 mm compared to 1.51±0.10 mm in the control group. Reproductive potential declined concentration dependently with exposure, with the highest reduction observed at 20 % of LC50 24hr value, where offspring numbers decreased to 7±1 from 23±5 in the control. Heart rate decreased in concentration and time-dependent manners, with the lowest rates observed at the highest arsenic concentration (279±16 bpm after 24hr and 277±27 bpm after 48hr). Comet assay and micronucleus assay conducted after 48 hrs of exposure revealed concentration-dependent genotoxic effects in Daphnia magna. Our results indicate negative impact on physiology and reproduction of Daphnia magna at environmentally existent concentration of arsenic. Also Daphnia magna could serve as a sensitive test system for investigating arsenic contamination in water bodies.

Alkaline Comet Assay to Assess Genotoxicity in Zebrafish Larvae

The zebrafish (Danio rerio) is a model organism widely used in several research fields due to its characteristics and numerous advantages, such as optical embryo transparency, fully sequenced genome, orthologous genes to humans, small size, high reproductive rate, easy gene editing and relatively low costs. Thus, a number of protocols have been developed that allow the use of this vertebrate model for toxic effect evaluation at various biological levels, including genotoxicity, using the comet assay technique.The comet assay or single-cell gel electrophoresis is a popular and sensitive method to study DNA damage in cells, which is described in this chapter. Briefly, cells suspended in agarose on a microscope slide are lysed, denatured, electrophoresed, neutralized, and stained to study the migration of DNA strand breaks. As a result, cells with increased DNA damage present a high fluorescence intensity and an increase of comet tail length. For the visual score, comets are classified according to the head integrity, tail intensity, and tail length into five classes, namely, class 0 until class 4 (comets with high damage and with almost all the DNA in the tail). These data are used to calculate the Genetic Damage Index (GDI) expressed as Arbitrary Units (AU).

A review on aquatic toxins - Do we really know it all regarding the environmental risk posed by phytoplankton neurotoxins?

Aquatic toxins are potent natural toxins produced by certain cyanobacteria and marine algae species during harmful cyanobacterial and algal blooms (CyanoHABs and HABs, respectively). These harmful bloom events and the toxins produced during these events are a human and environmental health concern worldwide, with occurrence, frequency and severity of CyanoHABs and HABs being predicted to keep increasing due to ongoing climate change scenarios. These contexts, as well as human health consequences of some toxins produced during bloom events have been thoroughly reviewed before. Conversely, the wider picture that includes the non-human biota in the assessment of noxious effects of toxins is much less covered in the literature and barely covered by review works. Despite direct human exposure to aquatic toxins and related deleterious effects being responsible for the majority of the public attention to the blooms' problematic, it constitutes a very limited fraction of the real environmental risk posed by these toxins. The disruption of ecological and trophic interactions caused by these toxins in the aquatic biota building on deleterious effects they may induce in different species is paramount as a modulator of the overall magnitude of the environmental risk potentially involved, thus necessarily constraining the quality and efficiency of the management strategies that should be placed. In this way, this review aims at updating and consolidating current knowledge regarding the adverse effects of aquatic toxins, attempting to going beyond their main toxicity pathways in human and related models' health, i.e., also focusing on ecologically relevant model organisms. For conciseness and considering the severity in terms of documented human health risks as a reference, we restricted the detailed revision work to neurotoxic cyanotoxins and marine toxins. This comprehensive revision of the systemic effects of aquatic neurotoxins provides a broad overview of the exposure and the hazard that these compounds pose to human and environmental health. Regulatory approaches they are given worldwide, as well as (eco)toxicity data available were hence thoroughly reviewed. Critical research gaps were identified particularly regarding (i) the toxic effects other than those typical of the recognized disease/disorder each toxin causes following acute exposure in humans and also in other biota; and (ii) alternative detection tools capable of being early-warning signals for aquatic toxins occurrence and therefore provide better human and environmental safety insurance. Future directions on aquatic toxins research are discussed in face of the existent knowledge, with particular emphasis on the much-needed development and implementation of effective alternative (eco)toxicological biomarkers for these toxins. The wide-spanning approach followed herein will hopefully stimulate future research more broadly addressing the environmental hazardous potential of aquatic toxins.

Measuring DNA modifications with the comet assay: a compendium of protocols

The comet assay is a versatile method to detect nuclear DNA damage in individual eukaryotic cells, from yeast to human. The types of damage detected encompass DNA strand breaks and alkali-labile sites (e.g., apurinic/apyrimidinic sites), alkylated and oxidized nucleobases, DNA-DNA crosslinks, UV-induced cyclobutane pyrimidine dimers and some chemically induced DNA adducts. Depending on the specimen type, there are important modifications to the comet assay protocol to avoid the formation of additional DNA damage during the processing of samples and to ensure sufficient sensitivity to detect differences in damage levels between sample groups. Various applications of the comet assay have been validated by research groups in academia, industry and regulatory agencies, and its strengths are highlighted by the adoption of the comet assay as an in vivo test for genotoxicity in animal organs by the Organisation for Economic Co-operation and Development. The present document includes a series of consensus protocols that describe the application of the comet assay to a wide variety of cell types, species and types of DNA damage, thereby demonstrating its versatility.

An integrated approach for chemical water quality assessment of an urban river stretch through Effect-Based Methods and emerging pollutants analysis with a focus on genotoxicity

The impact of emerging chemical pollutants, on both status and functionality of aquatic ecosystems is worldwide recognized as a relevant issue of concern that should be assessed and managed by researchers, policymakers, and all relevant stakeholders. In Europe, the Reach Regulation has registered more than 100.000 chemical substances daily released in the environment. Furthermore, the effects related to the mixture of substances present in aquatic ecosystems may not be predictable on the basis of chemical analyses alone. This evidence, coupled with the dramatic effects of climate changes on water resources through water scarcity and flooding, makes urgent the application of innovative, fast and reliable monitoring methods. In this context, Effect-Based Methods (EBMs) have been applied in the urban stretch of the Tiber River (Central Italy) with the aim of understanding if detrimental pressures affect aquatic environmental health. In particular, different eco-genotoxicological assays have been used in order to detect genotoxic activity of chemicals present in the river, concurrently characterized by chemical analysis. Teratogenicity and embryo-toxicity have been studied in order to cover additional endpoints. The EBMs have highlighted the presence of diffuse chemical pollution and ecotoxicological effects in the three sampling stations, genotoxicological effects have been also detected through the use of different tests and organisms. The chemical analyses confirmed that in the aquatic ecosystems there is a diffuse presence, even at low concentrations, of emerging contaminants such as pharmaceuticals, not routinely monitored pesticides, personal care products, PFAS. The results of this study can help to identify an appropriate battery of EBMs for future studies and the application of more appropriate measures in order to monitor, mitigate or eliminate chemical contamination and remediate its adverse/detrimental effects on the ecosystem health.

A critical review on genotoxicity potential of low dimensional nanomaterials

Low dimensional nanomaterials (LDNMs) have earned attention among researchers as they exhibit a larger surface area to volume and quantum confinement effect compared to high dimensional nanomaterials. LDNMs, including 0-D and 1-D, possess several beneficial biomedical properties such as bioimaging, sensor, cosmetic, drug delivery, and cancer tumors ablation. However, they threaten human beings with the adverse effects of cytotoxicity, carcinogenicity, and genotoxicity when exposed for a prolonged time in industry or laboratory. Among different toxicities, genotoxicity must be taken into consideration with utmost importance as they inherit DNA related disorders causing congenital disabilities and malignancy to human beings. Many researchers have performed NMs' genotoxicity using various cell lines and animal models and reported the effect on various physicochemical and biological factors. In the present work, we have compiled a comparative study on the genotoxicity of the same or different kinds of NMs. Notwithstanding, we have included the classification of genotoxicity, mechanism, assessment, and affecting factors. Further, we have highlighted the importance of studying the genotoxicity of LDNMs and signified the perceptions, future challenges, and possible directives in the field.

Outdoor disinfectant sprays for the prevention of COVID-19: Are they safe for the environment?

Due to the wide range of viability on inanimate surfaces and fomite transmission of SARS-CoV-2, hydrogen peroxide (0.5%, HP) and hypochlorite-based (0.1%, HC) disinfectants (common biocides) are proposed by World Health Organization to mitigate the spread of this virus in healthcare settings. They can be adopted and applied to outdoor environments. However, many studies have shown that these two disinfectants are toxic to fishes and aquatic non-target organisms (primary producers and macroinvertebrates). The global market of these disinfectants will increase in coming years due to COVID-19. Therefore, it is urgent to highlight the toxicities of these disinfectants. The main findings of this article allow the community to develop a new strategy to protect the environment against the hazardous effects of disinfectants. Therefore, we use the "toxicity calculated ratio (TC ratio)" that refers to the fold increase or decrease in the toxicities reported in the literature (NOEC, LOEC, LC50 and EC50) relative to the WHO-recommended dose of HP and HC. The calculated TC ratios are valuable for policy makers to formulate the regulations to prevent disinfectant exposure in the environment. Our results were collected via PRISMA (Preferred Reporting Items for Systematic Reviews and Meta-analysis) guidelines and showed that the TC ratios are from the single digits to several thousand-fold lower than the HP and HC recommended dose, which means these disinfectants are potentially dangerous to non-target organisms. The results also showed that HP and HC are toxic to the growth and reproduction of non-target organisms. Therefore, we recommend policymakers formulate protocols for critical assessment and monitoring of the environment-especially on non-target organisms in water bodies located in and around disinfectant-exposed areas to safeguard the environment in the future.

Light-Mediated Toxicity of Porphyrin-Like Pigments from a Marine Polychaeta

Porphyrins and derivatives form one of the most abundant classes of biochromes. They result from the breakdown of heme and have crucial physiological functions. Bilins are well-known representatives of this group that, besides significant antioxidant and anti-mutagenic properties, are also photosensitizers for photodynamic therapies. Recently, we demonstrated that the Polychaeta Eulalia viridis, common in the Portuguese rocky intertidal, holds a high variety of novel greenish and yellowish porphyrinoid pigments, stored as granules in the chromocytes of several organs. On the follow-up of this study, we chemically characterized pigment extracts from the worm’s skin and proboscis using HPLC and evaluated their light and dark toxicity in vivo and ex vivo using Daphnia and mussel gill tissue as models, respectively. The findings showed that the skin and proboscis have distinct patterns of hydrophilic or even amphiphilic porphyrinoids, with some substances in common. The combination of the two bioassays demonstrated that the extracts from the skin exert higher dark toxicity, whereas those from the proboscis rapidly exert light toxicity, then becoming exhausted. One particular yellow pigment that is highly abundant in the proboscis shows highly promising properties as a natural photosensitizer, revealing that porphyrinoids from marine invertebrates are important sources of these high-prized bioproducts.

DNA damage detection by Comet Assay on Daphnia magna: Application in freshwater biomonitoring

Monitoring of water genotoxicity still remains underexploited in risk assessment. The present study aimed at standardizing and evaluating the sensitivity and applicability of the Comet Assay adapted for Daphnia magna in genotoxicological investigations in freshwater environments. Two sampling campaigns (2014-2015) were performed in the watercourses of a pilot basin located in the Parma district (Italy). Fourteen sampling stations with different Ecological Status and/or EBI values were selected, all with a good Chemical Status according to the EU-Water Framework Directive 2000/60. The Alkaline Comet Assay was performed on 48 h-aged daphnids exposed (24 h) to 23 water samples. In parallel, the acute toxicity test was carried out. Daphnids exposed to samples, collected upstream the main watercourses in non-impacted areas, showed low DNA migration (Tail Intensity percentage - TI% - in the range 2.97-13.21), similar to laboratory controls. An increase in genotoxicity (TI% in the range 20-40) proceeding from the mountain towards the plain area was observed, in agreement with the land uses and the ES/EBI values of the stations. The highest genotoxic damage was observed after exposure to samples from watercourses of the minor hydrographic network in the plain area and waterbodies receiving wastewater treatment plant outflows. A modified version of the Comet Assay able to identify the presence of genotoxins inducing DNA oxidative damage, after standardization, was applied to daphnids treated with waters from 4 selected monitoring stations. The presence of oxidative contaminants was detected downstream a wastewater treatment plant outflow. The Comet Assay on D. magna has proven to be sensitive and able to discriminate among differently impacted areas and might be applied routinely. The FPG-Comet proved to be able to highlight the presence of contaminants causing oxidative stress. In our knowledge, this is the first time that Comet Assay on Daphnia magna is successfully applied for freshwater monitoring.

Seasonal ecotoxicological monitoring of freshwater zooplankton in Bir Mcherga dam (Tunisia)

Dams represent large semi-closed reservoirs of pesticides and various organic and inorganic pollutants from agricultural and human activities, and their monitoring should receive special attention. This study evaluated the environmental health status of Bir Mcherga dam using zooplankton species. The dam has a capacity of 130 Mm³ and its waters are used for irrigation, water drinking supply, and fishery. Copepods and cladocerans (crustaceans) were collected in situ monthly between October and August 2012. Oxidative stress (CAT, MDA), neurotoxicity (AChE), and genotoxicity (micronucleus test) biomarkers were analyzed in two zooplankton species: Acanthocyclops robustus and Diaphanosoma mongolianum. High values of cells with a micronucleus were observed during summer. AChE activities were inhibited during early winter and summer. The high seasonal variability of CAT and MDA levels indicates that zooplankton is continuously exposed to different oxidative stresses. These results suggest that there is an obvious and continuous multi-faceted stress in Bir Mcherga reservoir and, consequently, an urgent monitoring of freshwater environments in Tunisia is needed, particularly those intended for human consumption and irrigation.

Controlling micropollutants in tertiary municipal wastewater by O3/H2O2, granular biofiltration and UV254/H2O2 for potable reuse applications

A comprehensive pilot study was carried out to experimentally assess the potential of newly developed treatment trains integrating two-stage AOPs and biofiltration to reach potable reuse water quality standards from municipal wastewater. The processes consisted of a two-stage AOPs with (carbon or limestone) biofiltration, the first AOP (O₃/H₂O₂) serving as pre-treatment to biofiltration and the second AOP (UV₂₅₄/H₂O₂) serving as post-biofiltration finishing step to ensure advanced disinfection. A comprehensive monitoring campaign was put in place resulting from the combination of targeted, non-targeted and suspect screening measurements. It was found that 13 organic micropollutants were detected from a list of 219 suspects although at ng/L level only. For the treatment conditions piloted in this study (O₃ = 13 ± 0.5 mg/L, H₂O₂ = 11 ± 0.4 mg/L for the O₃/H₂O₂ process, and UV = 410 ± 63.5 mJ/cm², H₂O₂ = 5 mg/l for the UV₂₅₄/H₂O₂ process), it was possible to estimate the overall removal efficacy for each unit process, which was found to follow this order: RO (99%)  > BAC (87%) > O₃-H₂O₂ (78%)  > BAL (67%)  > UV/H₂O₂ (43%)  > AOP contact chamber (19%)  > UF(0%), with the treatment train integrating two AOPs and granular biofiltration with activated carbon (O₃/H₂O₂ + BAC + UV₂₅₄/H₂O₂) showing superior performance with a 99% abatement in total micropollutants. No ecotoxicologically-positive response was generally observed for any of the effluent samples from the tested trains, even when pre-concentration factors up to 100-1000 times were employed to increase the sensitivity of the bioassay methods.

Ageing differently: Sex-dependent ageing rates in Daphnia magna

Ageing is defined as the gradual decline of normal physiological functions in a time-dependent manner. Significant progress has been made in characterising the regulatory processes involved in the mechanisms of ageing which would have been hindered without the use of model organisms. Use of alternative model organisms greatly diversifies our understanding of different factors underpinning the ageing process and the potential translation for human application. Unique characteristics make Daphnia an attractive model organism for research into mechanisms underlying ageing, such as transparent body, short generation time, well-characterised methylome, regenerative capabilities and available naturally occurring ecotypes. Most interestingly, genetically identical female and male Daphnia have evolved different average lifespans, providing a unique opportunity for understanding the underlying mechanisms of ageing and regulation of lifespan. Investigating sex differences in longevity could provide insight into principal mechanisms of ageing and lifespan regulation. In this study we provide evidence in support of establishing genetically identical female and male Daphnia as unique and valuable resources for research into mechanisms of ageing and begin to delineate the mechanisms involved in sex differences in lifespan. We identify significant differences between genders in physiological markers such as lifespan, growth rate, heart rate and swimming speed in addition to molecular markers such as lipid peroxidation product accumulation, thiol content decline and age-dependent decline in DNA damage repair efficiency. Overall, our data indicates that investigating sex differences in longevity in the clonal organism Daphnia under controlled laboratory conditions can provide insight into principal mechanisms of ageing and lifespan regulation.

Effects of pharmaceuticals used to treat salmon lice on non-target species: Evidence from a systematic review

Aquaculture is currently one of the best prospects to help meet the growing need for protein in the human diet. However, aquaculture development and production result in consequences for the environment and also impact other productive activities. Salmon and trout cage culture has required the use of large quantities of pharmaceuticals in order to control outbreaks and the persistence of different pathogens, including sea lice (parasitic copepods), which cause economic losses of around 0.39 € Kg^-1 of salmon produced. The pharmaceuticals currently used for the control of sea lice (cypermethrin, deltamethrin, azamethiphos, hydrogen peroxide) are applied by in situ immersion treatments, enclosing net pens using tarpaulin and then bathing fish with the pharmaceutical. After treatment the pharmaceuticals are released into the surrounding environment, exposing non-target species. Although the effects of such pharmaceutical exposure has been studied in some species, to date a systematic and exhaustive review of these potential effects has not yet been performed. In this study, an exhaustive review of the literature evaluating lethal and sub-lethal effects of anti-sea lice pharmaceuticals on non-target crustaceans and bivalves was performed, in order to assess the extent of the effects, toxicity, variables affecting such toxicity and identify potential synergistic effects previously unexplored. Our results show clear negative effects at concentrations lower than those used in treatments against sea lice in all of the species studied. Likewise, this study demonstrates knowledge gaps that need to be addressed in order to improve our understanding of the effects of these pharmaceuticals on non-target species, ecosystems in general and other productive activities.

Gamma radiation induces dose-dependent oxidative stress and transcriptional alterations in the freshwater crustacean Daphnia magna

Among aquatic organisms, invertebrate species such as the freshwater crustacean Daphnia magna are believed to be sensitive to gamma radiation, although information on responses at the individual, biochemical and molecular level is scarce. Following gamma radiation exposure, biological effects are attributed to the formation of free radicals, formation of reactive oxygen species (ROS) and subsequently oxidative damage to lipids, proteins and DNA in exposed organisms. Thus, in the present study, effects and modes of action (MoA) have been investigated in D. magna exposed to gamma radiation (dose rates: 0.41, 1.1, 4.3, 10.7, 42.9 and 106 mGy/h) after short-term exposure (24 and 48 h). Several individual, cellular and molecular endpoints were addressed, such as ROS formation, lipid peroxidation, DNA damage and global transcriptional changes. The results showed that oxidative stress is one of the main toxic effects in gamma radiation exposed D. magna, mediated by the dose-dependent increase in ROS formation and consequently oxidative damage to lipids and DNA over time. Global transcriptional analysis verified oxidative stress as one of the main MoA of gamma radiation at high dose rates, and identified a number of additional MoAs that may be of toxicological relevance. The present study confirmed that acute exposure to gamma radiation caused a range of cellular and molecular effects in D. magna exposed to intermediate dose rates, and highlights the need for assessing effects at longer and more environmentally relevant exposure durations in future studies.

Assessment of the ecotoxicity of urban estuarine sediment using benthic and pelagic copepod bioassays

Urban estuarine sediments are sinks to a range of contaminants of anthropogenic origin, and a key challenge is to characterize the risk of these compounds to receiving environments. In this study, the toxicity of urban estuarine sediments was tested using acute and chronic bioassays in the benthic harpacticoid Quinquelaophonte sp., and in the planktonic calanoid Gladioferens pectinatus, two New Zealand copepod species. The sediment samples from the estuary tributary sites significantly impacted reproduction in Quinquelaophonte sp. However, results from one of the estuary sites were not significantly different to those from the tributaries sites, suggesting that chemicals other than trace metals, polycyclic aromatic hydrocarbons and ammonia may be the causative stressors. Sediment elutriate samples had significant effects on reproductive endpoints in G. pectinatus, and on the induction of DNA damage in cells, as shown by the comet assay. The results indicate that sediment contamination at the Ahuriri Estuary has the potential to impact biological processes of benthic and pelagic organisms. The approach used provides a standardized methodology to assess the toxicity of estuarine sediments.

Effects of a hypothetical escape of CO2 gas from subterranean storage sites on water flea Daphnia magna

The impacts of a hypothetical CO₂ gas leak from freshwater sediments on the survival and reproduction of freshwater flea Daphnia magna were analyzed. Another objective was to assess the performance of standard toxicity testing protocols for CO₂-induced acidification research in freshwaters. Four pH levels (7.5, 7.0, 6.5, and 6.0) and two sediments with different contamination level were tested. The results revealed that the D. magna are susceptible to a gradual but relatively rapid CO₂ enrichment of the water column causing a change from circumneutral to acidic conditions. Standard 48-h immobilization test with D. magna tended to underestimate the toxicity at CO₂-induced acidity condition. Dissolved aluminum may be implicated in the toxicity to the parental daphnids exposed. Metal outflux from sediments and behavior in elutriate have been discussed.

The various aspects of genetic and epigenetic toxicology: testing methods and clinical applications

Genotoxicity refers to the ability of harmful substances to damage genetic information in cells. Being exposed to chemical and biological agents can result in genomic instabilities and/or epigenetic alterations, which translate into a variety of diseases, cancer included. This concise review discusses, from both a genetic and epigenetic point of view, the current detection methods of different agents’ genotoxicity, along with their basic and clinical relation to human cancer, chemotherapy, germ cells and stem cells.

Chronic effects of temperature and nitrate pollution on Daphnia magna: Is this cladoceran suitable for widespread use as a tertiary treatment?

Effluent clarification and disinfection are major challenges in wastewater management. The cladoceran Daphnia magna has been proposed as a cost-effective and ecosystem-friendly option to clarify and disinfect secondary effluents, but its efficacy has not been fully tested under different sewage conditions. The present study explores the effects of temperature and nitrate on the efficacy of D. magna as a tertiary treatment at two different scales (individual assays and microcosms). Individual assays were employed to determine direct effects of temperature and/or nitrate on D. magna cultured in a suspension of organic matter. Using microcosms under the same environmental conditions, we explored the clearing efficacy of D. magna interacting with a natural microbial community. Individual assays revealed that D. magna mortality increased by 17% at 26 °C, 21% at >250 mg NO3(-)/l and by 60% at 26 °C and at >250 mg NO3(-)/l, and individuals displayed reduced body size, filtering rates and fecundity when compared to those at 21 °C and <40 mg NO3(-)/l. Improved performance under these conditions was also mirrored in the microcosms, with a higher density of D. magna (>100 ind/l) at 21 °C and <40 mg NO3(-)/l compared to the number (0-21 ind/l) at 26 °C and/or >250 mg NO3(-)/l. In the microcosms at 21 °C and <40 mg NO3(-)/l, turbidity and the density of bacteria, protists and micro-metazoa decreased in relation to those at 26 °C and/or >250 mg NO3(-)/l. Each treatment developed a unique and characteristic microbial assemblage, and D. magna was identified as the major driver of the community structure of protists and micro-metazoa. This enabled us to determine taxa vulnerability to D. magna grazing, and to re-define their tolerance thresholds for nitrate. In conclusion, this study increases our knowledge of how microbes respond to temperature and nitrate pollution, and highlights that D. magna efficacy as a tertiary treatment can be seriously compromised by variable environmental conditions.

Integrated analysis of the ecotoxicological and genotoxic effects of the antimicrobial peptide melittin on Daphnia magna and Pseudokirchneriella subcapitata

Melittin is a major constituent of the bee venom of Apis mellifera with a broad spectrum of activities. Melittin therapeutical potential is subject to its toxicity and the assessment of ecotoxicity and genotoxicity is of particular interest for therapeutic use. Here we analyzed the biological effects of melittin on two aquatic species, which are representative of two different levels of the aquatic trophic chain: the invertebrate Daphnia magna and the unicellular microalgae Pseudokirchneriella subcapitata. The attention was focused on the determination of: i) ecotoxicity; ii) genotoxicity; iii) antigenotoxicity. Our main finding is that melittin is detrimental to D. magna reproduction and its sub-lethal concentrations create an accumulation dependent on exposition times and a negative effect on DNA. We also observed that melittin significantly delayed time to first eggs. Moreover, results showed that melittin exerted its toxic and genotoxic effects in both species, being a bit more aggressive towards P. subcapitata.

Genotoxic potency of mercuric chloride in gill cells of marine gastropod Planaxis sulcatus using comet assay

In vivo and in vitro exposures were used to investigate the genotoxicity of mercuric chloride (HgCl2) to the marine snail, Planaxis sulcatus. The comet assay protocol was validated on gill cells exposed in vitro to hydrogen peroxide (H2O2, 0-50 μM). Snails were exposed in vivo for 96 h to HgCl2 (10, 20, 50, and 100 μg/l). Our results showed significant concentration-dependent increase in the tail DNA (TDNA) and olive tail moment (OTM) in exposed snails for all doses compared with controls. In vitro exposure to HgCl2 (10-100 μg/l) resulted in significantly higher values for TDNA at all concentrations. Our results showed that DNA damage increased in the gill cell with increasing exposure time. This study demonstrates the usefulness of comet assay for detection of DNA damage after exposure to HgCl2 and the sensitivity of marine snail P. sulcatus as a good candidate species for metal pollution.