Application of Euglena gracilis cells to comet assay: evaluation of DNA damage and repair

Exposure to environmental levels of 2,4-di-tert-butylphenol affects digestive glands and induces inflammation in Asian Clam (Corbicula fluminea)

2,4-Di-tert-butylphenol (2,4-DTBP) is used as an antioxidant added to plastics. Due to its potential toxicity and relatively high concentrations in environments and presence in human tissue, concern has been raised for 2,4-DTBP as a contaminant associated with adverse health outcomes. However, studies on the toxicity of 2,4-DTBP are relatively limited, especially for benthic aquatic organisms. In this study, Asian clams (Corbicula fluminea) were exposed to environmentally relevant concentrations of 2,4-DTBP (0.01-1 μM, corresponding to 2.06-206.32 μg/L) for 21 days. Accumulation of 2,4-DTBP was noted in both gills and digestive glands, with the latter presenting as the primary target tissue. Increased damage rate of digestive tube and cellular DNA damage were observed in the digestive glands of 2,4-DTBP exposed clams. The injury was attributed to the imbalance of the antioxidant system, characterized by elevated oxidative stress and inflammation (upregulation of ROS, MDA, NO, and pro-inflammatory factors). In contrast, upon 2,4-DTBP exposure, antioxidant system in gills was activated, while ROS and NO were not promoted. Moreover, NF-κB and IL-1 were significantly decreased. These results suggested that biochemical mechanisms were activated in gills to maintain homeostasis. Internal exposure in the digestive gland was significantly correlated with the biochemical biomarkers tested, underscoring the potential risk associated with the bioaccumulation of 2,4-DTBP from contaminated environments. These findings provide novel insights into toxicity of 2,4-DTBP in bivalves, contributing valuable knowledge to risk assessment and chemical management.

Methodological advances and future directions of microalgal bioassays for evaluation of potential toxicity in environmental samples: A review

Microalgal bioassays are widely applied to evaluate the potential toxicity of various persistent toxic substances in environmental samples due to multiple advantages, including high sensitivity, short test duration, and cost-effectiveness. Microalgal bioassay is gradually developing in method, and the scope of application to environmental samples is also expanding. Here, we reviewed the published literature on microalgal bioassays for environmental assessments, focusing on types of samples, sample preparation methods, and endpoints, and highlighted key scientific advancements. Bibliographic analysis was performed with the keywords 'microalgae' and 'toxicity' or 'bioassay', and 'microalgal toxicity'; 89 research articles were selected and reviewed. Traditionally, most studies implementing microalgal bioassays focused on water samples (44%) with passive samplers (38%). Studies using the direct exposure method (41%) of injecting microalgae into sampled water mainly evaluated toxic effects by growth inhibition (63%). Recently, various automated sampling techniques, in situ bioanalytical methods with multiple endpoints, and targeted and non-targeted chemical analyses have been applied. More research is needed to identify causative toxicants affecting microalgae and to quantify the cause-effect relationships. This study provides the first comprehensive overview of recent advances in microalgal bioassays performed with environmental samples, suggesting future research directions based on current understanding and limitations.

The effects of benzo[a]pyrene on the composition of gut microbiota and the gut health of the juvenile sea cucumber Apostichopus japonicus Selenka

The gut microbiota is essential for health and physiological functions in the host organism. However, the toxicological evaluation of environmental pollutants on the gut microbiota is still insufficient. In the present study, the juvenile sea cucumber Apostichopus japonicus was exposed for 14 days to Benzo[a]pyrene (BaP), which is a model polycyclic aromatic hydrocarbon (PAH), at four different concentrations (0, 0.5, 5, and 25 μg/L). We analyzed the intestinal microbial community of A. japonicas using 16S rRNA gene amplicon sequencing. Our results demonstrate that BaP exposure caused alterations to the microbiome community composition in sea cucumbers. At the phylum level, Planctomycetes were significantly more abundant in BaP exposure groups at 14 d compared with the control group, and the abundance of Proteobacteria and Bacteroidetes increased while the abundance of Firmicutes decreased following BaP exposure. At the genus level, multiple beneficial and autochthonous genera declined in the BaP treatment groups compared to the control, including Lactococcus, Bacillus, Lactobacillus, Enterococcus, Leuconostoc and Weissella; however, a bloom of alkane-degrading bacteria was found in BaP-exposed guts and included Lutibacter, Pseudoalteromonas, Polaribacter, Rhodopirellula and Blastopirellula. Furthermore, histological morphology, enzymatic activity and gene expression analysis revealed that BaP exposure also negatively impacted gut structure and function and presented as inflammation or atrophy, oxidative stress and immune suppression in sea cucumber intestines. Collectively, these findings provide insights into the toxic effects of BaP exposure on A. japonicas associated with intestinal microbiota and health.

Comparative analysis of toxicity reduction of wastewater in twelve industrial park wastewater treatment plants based on battery of toxicity assays

Wastewater treatment plants (WWTPs) in industrial parks provide centralized treatment for industrial and domestic wastewater. However, the information on toxicity reduction of wastewater and its correlation with treatment process in industrial park is limited. This study compared the toxicity reduction of wastewater in 12 industrial park WWTPs based on battery of toxicity assays. Nine toxic endpoints involving microorganism, phytoplankton, zooplankton, plant and human cell lines were applied. All the influents of WWTPs induced high toxicities, which were significantly reduced after the treatments from 7 of the studied WWTPs. However, the effluents of five WWTPs induced higher toxicity in one or more toxic endpoints compared to the influents. This study also found that most of anaerobic-anoxic-oxic (A²/O)-based processes had good removal efficiency of wastewater toxicity, while the sequencing batch reactor (SBR)-based processes had the lowest removal efficiency. Moreover, low correlation coefficients were obtained among all toxic endpoints, indicating that battery of toxicity assays was necessary to completely characterize the toxicity and risk of wastewater in industrial parks. This study shed new lights to the toxicity reduction of wastewater and its correlation with treatment process, which is very useful for the design, management and operation of WWTPs in industrial parks.

Sensitive detection of oxidative DNA damage in cyanobacterial cells using supercoiling-sensitive quantitative PCR

Supercoiling-sensitive quantitative PCR (ss-qPCR) is a sensitive technique to detect DNA damage in cultured animal cells and cultured/clinical human cells in vitro. In this study, we investigated whether the ss-qPCR method can be applied as a sensitive means to detect oxidative DNA damage in unicellular organisms. We used the model cyanobacterium Synechococcus elongatus PCC 7942 as a test organism and H₂O₂ as an exogenetic oxidative toxicant. Results showed that a significant increase in the plasmid DNA damage of S. elongatus PCC 7942 was induced by H₂O₂ in a dose- and time-dependent manner. The sensitivity of ss-qPCR in detecting DNA damage of the cyanobacterium was higher than the cell inhibition method (up to 255 times) as calculated from the slopes of fitted curves in the tested sub-toxic concentration range of 1-5 mM H₂O₂. Ss-qPCR also detected repairable low-intensity DNA damage in the cyanobacterium when DNA repair inhibitors were used. The detection limit of modified ss-qPCR was one tenth of that of previous methods. We also observed that ss-qPCR can be used to detect genomic DNA conformation change of cyanobacterium exposed to H₂O₂. Thus, this method will provide a powerful technical support for investigating the mechanisms of cyanobacterial DNA damage by environmental factors, especially intracellular reactive oxygen species enhancement-related factors.

Ecotoxicity evaluation of natural suspended particles using the microalga, Euglena gracilis

As vectors for pollutants, suspended particles (SPs) have been studied for many years. However, limited studies have focused on the ecotoxicity of natural SPs. This study examined ecotoxicity of natural SPs isolated from Gonghu Bay and its Ecological Restoration Area (ERA) water samples by Tangential Flow Filtration (TFF) using the microalga Euglena gracilis as a model organism. Effects of SPs on algae growth, photosynthesis pigment contents, superoxide dismutase (SOD) activity and DNA damage were characterized to determine the effects of ecological restoration. Additionally, SPs were separated into nanoscale (<1 μm diameter) and common-scale (≥1 μm diameter) groups by size, to compare the differences in toxicity of SPs with different sizes. We found, in naturally occurring concentrations in Gonghu Bay, nanoscale SPs were more toxic than common-scale ones. However, no significant adverse effects were detected in the nanoscale SPs from the ERA, which demonstrated that ecological restoration might reduce the toxicity of nanoscale SPs. The results were supported by the inhibition of growth, SOD activities and DNA damage, while no adverse influences were detected on pigment contents of E. gracilis in all the treated groups. Our study provides new insights into the toxic effects of SPs.

Expression profiles of different glutathione S-transferase isoforms in scallop Chlamys farreri exposed to benzo[a]pyrene and chrysene in combination and alone

Aquatic organisms are increasingly exposed to polycyclic aromatic hydrocarbons (PAHs) due to anthropogenic pressure. This study aimed at evaluating the response of Glutathione S-transferases (GSTs) in scallop Chlamys farreri against benzo[a]pyrene (BaP) and chrysene (CHR) exposure under laboratory conditions. Nine published GST genes were classified into six subfamilies and a new member of rho family was identified for the first time. Twelve GSTs (including nine published GST genes and three in transcriptome established by our laboratory) mRNA transcript levels in the gills, digestive glands, adductor muscle, mantle, testis, ovaries, blood cells of scallops were measured by real-time PCR. The results showed that the mRNA transcript levels of twelve GSTs, except GST-zeta, GST-mu and GST-microsomal, were highest in digestive gland. Accordingly, the mRNA expression levels of GSTs were measured in digestive glands of scallops exposed to BaP (0.1μg/L and 1μg/L), CHR (0.1μg/L and 1μg/L) and their mixtures (0.1μg/L BaP +0.1μg/L CHR and 1μg/L BaP +1μg/L CHR). The results indicated that different GST had specific response to different pollution exposure. In BaP exposure experiment, the mRNA expression level of GST-theta was a potential suitable biomarker. GST-sigma-2 and GST-3, which belonged to sigma class, were sensitive to CHR exposure while GST-microsomal was considered a potential ideal bioindicator to joint exposure of BaP and CHR. In summary, this study investigated the classification of GSTs and provided information about the expression profiles of different class GSTs after PAHs exposure.

Uranium (238U)-induced ROS and cell cycle perturbations, antioxidant responses and erythrocyte nuclear abnormalities in the freshwater iridescent shark fish Pangasius sutchi

The strategic plan of this study is to analyze any possible radiological impact on aquatic organisms from forthcoming uranium mining facilities around the Nagarjuna Sagar Dam in the future. The predominantly consumed and dominant fish species Pangasius sutchi, which is available year-round at Nagarjuna Sagar Dam, was selected for the study. To comprehend the outcome and to understand the mode of action of ²³⁸U, the fish species Pangasius sutchi was exposed to ¼ and ½ of the LC₅₀ doses of waterborne ²³⁸U in a static system in duplicate for 21 days. Blood and organs, including the gills, liver, brain and muscles, were collected at different time periods-0h, 24h, 48h, 72h, 96h, 7, days 14days and 21 days-using ICP-MS to determine the toxic effects of uranium and the accumulation of ²³⁸U concentrations. The bioaccumulation of ²³⁸U in P. sutchi tissues was dependent on exposure time and concentration. The accumulation of uranium was, in order of magnitude, measured as gills>liver>brain>tissue, with the highest accumulation in the gills. It was observed that exposure to ²³⁸U significantly reduced antioxidant enzymes such as superoxide dismutase, catalase, and lipid peroxidase. The analysis of DNA fragmentation by comet assay and cell viability by flow cytometry was performed at different time intervals. DNA histograms by flow cytometry analysis revealed an increase in the G2/M phase and the S phase. The long-term ²³⁸U exposure studies in fish showed increasing micronucleus frequencies in erythrocytes with greater exposure time. The higher the concentration of ²³⁸U is, the greater is the effect observed, suggesting a close relationship between accumulation and toxicity. A possible ROS-mediated ²³⁸U toxicity mechanism and antioxidant responses have been proposed.

Variability in antioxidant/detoxification enzymes of Sinonovacula constricta exposed to benzo[a]pyrene and phenanthrene

The purpose of this study was to investigate the toxic effects induced by benzo[a]pyrene and phenanthrene. For this purpose, a study was performed on the clam exposed to 0.0, 0.5, 4.5μgL(-1) B(a)P and PHE for 15days using parameters of antioxidant defenses and oxidative stress. Antioxidant biomarkers including ethoxyresorufin-O-deethylase, glutathione S-transferase, superoxide dismutase, and glutathione and rylhydrocarbon hydroxylasein gills of Sinonovacula constricta, were analyzed after a 1-, 3-, 9- and 15-day exposure to seawater containing B(a)P and PHE. Integrated biomarker response was calculated by combining multiple biomarkers into a single value. The results showed that the activity of all antioxidant biomarkers was induced throughout the exposure period, and different patterns of variations were detected with exposure time. In addition, the study showed that the two concentrations used caused the activation of different general detoxification mechanisms, and the same concentration at different two PAH compounds induced different toxicity responses.

In vitro study of the effect of metabolism enzymes on benzo(a)pyrene-induced DNA damage in the scallop Chlamys farreri

Acute toxicity effect of benzo(a)pyrene (BaP) on isolated scallop (Chlamys farreri) digestive gland cells was studied and a dose-dependent increase in toxicity was observed. The 8 μg/L of BaP had a significant toxic effect on isolated cells (p<0.05). In order to study the mechanism of CYP450, GST, SOD and MXR transporters involved in the production of DNA strand breakage such as DNA adduct formation and oxidative DNA damage by BaP were investigated in isolated digestive gland cells. Isolated cells were exposed in vitro to 0.8 μg/L of BaP for 24h in the dark at 25 °C in the absence or presence of cytochrome P450 inhibitor, GST inhibitor, Pgp inhibitor and antioxidant enzyme inhibitor. DNA adduct and 8-OHdG content were measured using the Enzyme-linked Immunosorbent Assay. The result indicated that DNA strand breakage was increased to 2 times compared with the control in the 0.8 μg/L of BaP treatment groups. The BaP-induced DNA adduct and 8-OHdG content increased significantly by inhibiting GST, while only 8-OHdG increased significantly when SOD was inhibited. The content of DNA adduct and 8-OHdG had no significant change when CYP450 was inhibited, while it decreased significantly when MXR transporters were inhibited. The result proved that GST play a key role in eliminating the BaP-induced DNA adduct and 8-OHdG, and SOD also had an important function in reducing the production of BaP-induced 8-OHdG.

Mercury-induced genotoxicity in marine diatom (Chaetoceros tenuissimus)

In this paper, we present an evaluation of genotoxic responses in marine diatom, Chaetoceros tenuissimus, isolated from Kandla Creek (lat 23.03° N, long 70.22° E), Gujarat, India, in terms of impairment of DNA integrity as a function of their exposure to elevated levels of mercury (Hg) under laboratory conditions. DNA integrity in C. tenuissimus was determined by partial alkaline unwinding assay. To our knowledge, this is the first such genotoxicity study to be conducted on marine diatom cultures towards understanding the relationship between Hg toxicity and DNA damage. Furthermore, we studied the impact of Hg on the growth of C. tenuissimus as a function of their exposure to enhanced levels of Hg in terms of decreasing chlorophyll a (chl a) concentrations. The data show the genotoxic effect of Hg on the growth of C. tenuissimus as well as DNA integrity to a great extent. Based on the results of our investigations, it is suggested that C. tenuissimus can be used as sentinel species for bio-monitoring of pollution due to genotoxic contaminants.

Acute effects of a prooxidant herbicide on the microalga Chlamydomonas reinhardtii: Screening cytotoxicity and genotoxicity endpoints

Since recent evidence has demonstrated that many types of chemicals exhibit oxidative and/or genotoxic potential on living organisms, reactive oxygen species (ROS) formation and DNA damage are currently the best accepted paradigms to assess the potential hazardous biological effects of a wide range of contaminants. The goal of this study was to evaluate the sensitivity of different cytotoxicity and genotoxicity responses on the model microalga Chlamydomonas reinhardtii exposed to the prooxidant herbicide paraquat. In addition to the growth endpoint, cell viability, mitochondrial membrane potential and presence of reactive oxygen species (ROS) were assayed as potential markers of cytotoxicity using flow cytometry (FCM). To study the effects of paraquat on C. reinhardtii DNA, several genotoxicity approaches were implemented for the first time in an ecotoxicological study on microalgae. Oxidative DNA base damage was analysed by measuring the oxidative DNA lesion 8-OHdG by FCM. DNA fragmentation was analysed by different methods: comet assay, and cell cycle analysis by FCM, with a particular focus on the presence of subG1-nuclei. Finally, effects on morphology of nuclei were monitored through DAPI staining. The evaluation of these endpoints showed that several physiological and biochemical parameters reacted to oxidative stress disturbances with greater sensitivity than integrative parameters such as growth rates or cell viability. The experiments revealed concentration-dependent cytotoxicity (ROS formation, depolarization of mitochondrial membrane), genotoxicity (oxidative DNA damage, DNA strand breakage, alterations in nuclear morphology), and cell cycle disturbances (subG1-nuclei, decrease of 4N population) in paraquat-treated cells. Overall, the genotoxicity results indicate that the production of ROS caused by exposure to paraquat induces oxidative DNA damage followed by DNA single- and double-strand breaks and cell cycle alterations, possibly leading to apoptosis in C. reinhardtii cells. This is supported by the observation of typical hallmarks of apoptosis, such as mitochondrial membrane depolarization, alterations in nuclear morphology and subG1 nuclei in cells exposed to the highest assayed concentrations. To our knowledge, this is the first study that provides a comprehensive analysis of oxidative DNA base damage in unicellular algal cells exposed to a prooxidant pollutant, as well as of its possible relation with other physiological effects. These results reinforce the need for additional studies on the genotoxicity of environmental pollutants on ecologically relevant organisms such as microalgae that can provide a promising basis for the characterization of potential pollutant hazards in the aquatic environment.

Toxic effects upon exposure to benzo[a]pyrene in juvenile white shrimp Litopenaeus vannamei

The purpose of this study was to investigate the toxic effects induced by benzo[a]pyrene (BaP). In the present study, juvenile white shrimp Litopenaeus vannamei were exposed to BaP for 21 days at four different concentrations as 0, 0.03, 0.3 and 3μg/L. Detoxification system parameters, transcription of metabolism-related genes, and damage indexes were investigated for screening. It showed mRNA expression levels of superoxide dismutase (SOD), cytochrome P450 (CYP) 1A1 and glutathione-S-transferase (GST) in hepatopancreas were significantly induced at day 3 by 0.3 and 3μg/L BaP, and returned to the initial level afterwards. 7-Ethoxyresorufin O-deethylase (EROD), GST and SOD activities in gill and hepatopancreas were also induced by 0.3 and 3μg/L BaP, while T-AOC and GSH contents were reduced after BaP exposure. The study also showed that 0.3 and 3μg/L BaP caused damage effects, while 0.03μg/L BaP treatment did not exhibit any damage effects. Moreover, according to the correlation analysis results, we conclude that EROD activity, GST activity and GSH content in hepatopancreas can be used as defense biomarkers; DNA strand breaks, lipid peroxidation (LPO) level and protein carbonyl (PC) content in gill and hepatopancreas can be used as damage biomarkers; EROD activity, GST activity, GSH contents and damage effects of DNA strand breaks, LPO level and PC content in hepatopancreas can be used as combined biomarkers. These results will provide information not only on potential biomarkers that could be effectively applied to biomonitor aquatic environment to contamination, but also provide information on toxic effects of this specie.

Genotoxic effects of commercial formulations of Chlorpyrifos and Tebuconazole on green algae

The alkaline single-cell gel electrophoresis assay (comet assay) was used for the study of the genotoxic effects of insecticide Chlorpyrifos and fungicide Tebuconazole (commercial formulations) on two freshwater green algae species, Pseudokirchneriella subcapitata and Nannocloris oculata, after 24 h of exposure. The percentage of DNA in tail of migrating nucleoids was taken as an endpoint of DNA impairment. Cell viability was measured by fluorometric detection of chlorophyll "a" in vivo and the determination of cell auto-fluorescence. Only the higher concentration of Chlorpyrifos tested resulted to affect significantly the cell viability of P. subcapitata, whereas cells of N. oculata were not affected. Tebuconazole assayed concentrations (3 and 6 mg/l) did not affect cell viability of both species. The results of comet assay on P. subcapitata showed that Chlorpyrifos concentration evaluated (0.8 mg/l) exerted a genotoxic effects; while for the other specie a concentration of 10 mg/l was needed. Tebuconazole was genotoxic at 3 and 6 mg/l for both species. The comet assay evidenced damage at the level of DNA simple strains molecule at pesticide concentrations were cytotoxicity was not evident, demonstrating that algae are models to take into account in ecological risk assessments for aquatic environments.

Toxicity and genotoxicity of water and sediment from streams on dotted duckweed (Landoltia punctata)

Most rivers are used as a source to supply entire cities; the quality of water is directly related to the quality of tributaries. Unfortunately men have neglected the importance of streams, which receive domestic and industrial effluents and transport nutrients and pesticides from rural areas. Given the complexity of the mixtures discharged into these water bodies, this study aimed to evaluate the quality of water and sediment of ten tributaries of Pirapó River, in Maringá, Paraná State, Brazil. To this end, the free-floating macrophyte Landoltia punctata (G. Meyer) Les & D.J.Crawford was used as test organism in microcosm, and the toxicity of water and sediment samples was evaluated by the relative growth rate, dry/fresh biomass ratio, and genotoxic effects (comet assay). Samples of water and sediment of each stream were arranged in microcosms with L. punctata. Seven days later, plants were collected for analysis. Nutrient levels were higher than the reference location, indicating eutrophication, but the results indicated a toxic effect for only three streams, and a genotoxic effect for all streams.

Microalga Euglena as a bioindicator for testing genotoxic potentials of organic pollutants in Taihu Lake, China

The microalga Euglena was selected as a bioindicator for determining genotoxicity potencies of organic pollutants in Meiliang Bay of Taihu Lake, Jiangsu, China among seasons in 2008. Several methods, including the comet assay to determine breaks in DNA and quantification of antioxidant enzymes were applied to characterize genotoxic effects of organic extracts of water from Taihu Lake on the flagellated, microalga Euglena gracilis. Contents of photosynthetic pigments, including Chl a, Chl b and carotenoid pigments were inversely proportion to concentrations of organic extracts to which E. gracilis was exposed. Organic extracts of Taihu Lake water also affected activities of superoxide dismutase (SOD) and peroxidase (POD) of E. gracilis. There were no statistically significant differences in SOD activities among seasons except in June but significant differences in POD activities were observed among all seasons. The metrics of DNA fragmentation in the alkaline unwinding assay (Comet assay), olive tail moment (OTM) and tail moment (TM), used as measurement endpoints during the genotoxicity assay were both greater when E. gracilis was exposed to organic of water collected from Taihu Lake among four seasons. It is indicated that the comet assay was useful for determining effects of constituents of organic extracts of water on E. gracilis and this assay was effective as an early warning to organic pollutants.

Potential health impact and genotoxicity analysis of drinking source water from Liuxihe Reservoir (P.R. China)

Water from the Liuxihe Reservoir (a source of drinking water for Guangzhou City, P. R. China) was analyzed for semi-volatile organic compounds (SVOCs) and the results were used for a potential health impact assessment and genotoxicity test with the microalgae Euglena gracilis. The SVOCs were tested using USEPA Method 525.2, and the health risk assessment was conducted at a screening level using the hazard quotient (HQ) approach. Alkaline single-cell gel electrophoresis (comet assay) was used to evaluate DNA damage and determine the genotoxicity of the source water. The concentrations of the SVOCs in Liuxihe Reservoir were very low and phthalic acid esters were the main SVOCs present. The mean HQ values of pollutants were all less than one, indicating no risk. However, the lifetime carcinogenic risks (LCRs) were found to be close to the threshold of 1.00E-5. The results show that the water in the Liuxihe Reservoir might pose a potential carcinogenic risk to local residents. The highly concentrated extracts of the water samples could induce DNA damage in the microalgal cells and a dose-effect relationship was identified. These results showed that Liuxihe Reservoir water, as a source of drinking water, could pose a potential LCR to local consumers.

Assessment of trophic transfer of benzo(a)pyrene genotoxicity from the post-larval pink shrimp F. brasiliensis to the juvenile Florida pompano T. carolinus

In the present study, the polycyclic aromatic hydrocarbon (PAH) genotoxicity was investigated in a one-step predator-prey relationship with the trophic-related marine species. Florida pompanos were fed for 5 and 10 days with pink shrimp post larvae previously exposed to benzo(a)pyrene (BaP) concentrations. Parent BaP body burden was measured in samples of Farfantepenaeus brasiliensis. BaP metabolites were determined in bile samples of Trachinotus carolinus and DNA damage was assessed through the comet and erythrocyte nuclear abnormalities (ENAs) assays in fish erythrocytes. BaP body burden increased significantly with the PAH concentration in pink shrimp PLs as well as the fish bile BaP metabolites. Both, comet and ENAs assays indicated significant increase on erythrocyte DNA damage of Florida pompanos fed with BaP-exposed pink shrimp on both feeding periods. The trophic route of BaP genotoxicity is discussed as well as the PAH biotransformation as the inducing mechanism for the DNA damages observed.

EROD activity and genotoxicity in the seabob shrimp Xiphopenaeus kroyeri exposed to benzo[a]pyrene (BaP) concentrations

Seabob shrimp Xiphopenaeus kroyeri is a marine species that lives in shallow waters of coastal environments, often impacted by polycyclic aromatic hydrocarbons (PAH) pollution. In the present study, seabob shrimp were exposed for 96 h to benzo[a]pyrene (BaP) at the nominal concentrations of 100, 200, 400 and 800 microg-L(-1). Animals of the control groups were exposed either to clean water or to the BaP-carrier (DMSO). At the end of the exposures, muscle tissues were sampled for BaP uptake assessment and hepatopancreas and hemolymph for EROD enzyme activity and hemocytes DNA damage, respectively. EROD activity and DNA damage increased significantly as a function of BaP exposure concentrations. Significant correlations between BaP uptake and both EROD activity and DNA damage suggest that they can be used as suitable tools for integrated levels of study on the biomarkers of PAH exposure.

On-chip continuous monitoring of motile microorganisms on an ePetri platform

Self-imaging Petri dish platforms with microscopy resolution, which we term 'ePetri', can significantly streamline cell cultures and/or other longitudinal biological studies. In this paper, we demonstrate high-resolution imaging and long-term culture of motile microorganisms in a specialized ePetri platform by taking advantage of the inherent motion. By applying a super-resolution algorithm to a set of low-resolution images of the microorganisms as they move across the sensing area of a complementary metal oxide semiconductor (CMOS) image sensor chip, we can render an improved-resolution image of the microorganisms. We perform a longitudinal study of Euglena gracilis cultured in an ePetri platform, and image-based analysis on the motion and morphology of the cells. As a miniaturized and automated culture monitoring platform, this ePetri technology can greatly improve studies and experiments with motile microorganisms.

The effects of Caulerpa microphysa enzyme-digested extracts on ACE-inhibitory activity and in vitro anti-tumour properties

The aim of this study was to determine the ACE inhibitory activity and its anti-cancer properties of Caulerpa microphysa extracts. C. microphysa samples were digested with Flavourzyme, Alcalase, and pepsin. The ACE inhibitory activity of enzyme-digested C. microphysa decreased in the order of digestion with pepsin>Flavourzyme>Alcalase; that is, pepsin-extracted samples had significantly higher activity than the other enzyme extractions. To test its anti-tumour effects in vitro C. microphysa pepsin-digested extracts were applied to BALB/c mice with transplanted myelomonocytic leukaemia (WEHI-3) and Human promyelocytic leukaemia (HL-60) cell lines. The growth of both cell lines was inhibited, and extracts induced DNA damage, evaluated with a comet assay. The data demonstrate that C. microphysa pepsin-digested extract had the ability to anti-tumour effects. Further application as a health food is worthy of investigation.

Organic pollutants and ambient severity for the drinking water source of western Taihu Lake

Measurement of the organic compounds found in western Taihu Lake and evaluation of the ambient severity (AS) of the water using multimedia environmental goals (MEG) was conducted. The comet assay and the antioxidant enzyme approach were used to test the potential toxicity of water samples on the microalgae Euglena gracilis. Total concentrations of 25 organic pollutants in samples from two sites were 6.700 and 14.655 μg/l, respectively, with a calculated total ambient severity (TAS) of less than 1 and therefore minimal risk to human and ecological health. Organic extracts from the samples at these two sites was found to induce dose-dependent DNA damage on microalgae cells. DNA damage together with changes in superoxide dismutase (SOD) and peroxidase (POD) activities indicated that the potential pollutant toxicity was far higher at one of the two sites than at the other site. The comet assay combined with the activities of antioxidant enzymes may be of value as a biomarker for presence of organic pollutants in drinking water sources.

A convenient fluorescent-labeled assay for in vitro measurement of DNA mismatch repair activity

OBJECTIVE

The assay of DNA mismatch repair (MMR) activity can be used as a biomarker for environmental condition detection and human disease diagnosis. Radioactive ³²P-endlabeled DNA containing mismatch is extensively used as the substrate for MMR activity analyses. The aim of the present study is to develop a simple non-radioactive, but equally specific and sensitive method for the MMR activity assay.

METHODS

A fluorescent label was chosen to replace the radioactive isotope label. Sensitive evaluation of the fluorescent label was carried out for the first time, and then the fluorescent label was compared with the isotope label in the MMR activity and DNA binding assays.

RESULT

LOD (limit of detection) of the fluorescent label was about 0.1 fmol and the relative signal strength displayed a pretty good linear relationship. Moreover, the fluorescent label method has equivalent sensitivity and performance as compared with the classical radioactive method in experiments.

CONCLUSION

In light of the sensitivity, reproducibility, safety, rapidity and long lifespan of the fluorescent label, this improved method can be applied to evaluation of biologic and toxic effects of environmental pollutants on man and other forms of life.

Antimicrobial activity of commercial zeolite A on Acinetobacter junii and Saccharomyces cerevisiae

The influence of three samples of commercially produced zeolite A (named A, M and R) in water medium on the bacterium Acinetobacter junii and yeast Saccharomyces cerevisiae was investigated. These microorganisms were used in the bioassay and are not specifically related to the use of zeolite A. All zeolite samples showed the negative influence on the survival and physiological status of A. junii and S. cerevisiae. The EC(50) values for the inhibition of CFU of A. junii were 0.328, 0.138 and 0.139 g l(-1) for zeolite sample A, M and R, respectively. The EC(50) values of tested zeolites for S. cerevisiae, estimated by fermentation and fluorescence microscopy assay, ranged from 2.88 to 5.47 g l(-1). The genotoxic effect of three samples of zeolite to S. cerevisiae was shown by the alkaline comet assay. When assuming all the aspects of zeolite toxicity to bacterium and yeast, the zeolite sample R appeared to be less toxic than the samples A and M. The hydrolysis of zeolite crystals, amorphous aluminosilicate and unreacted gel fraction in water medium and consecutive dissolution and leaching of aluminium and silicon in the form of aluminosilicate molecules (700-1300 Da) was detected.

Effects of pesticides on freshwater diatoms

The study of pesticide effects on algae, and diatoms in particular, was focused on photosynthesis and biomass growth disturbances. Few studies have been performed to investigate the effects of these toxic agents on intracellular structures of diatom cells. Nuclear alterations and cell wall abnormalities were reported for diatoms exposed to toxic compounds. Nevertheless, the cellular mechanisms implicated in the development of such alterations and abnormalities remain unclear. Sensitivity to pesticides is known to be quite different among different diatom species. Eutrophic and small species are recognized for their tolerance to pesticides exposure. More pronounced cell defenses against oxidative stress may explain this absence of sensitivity in species of smaller physical size. Notwithstanding, on the whole, explaining the rationale behind tolerance variations among species has been quite difficult, thus far. In this context, the understanding of intracellular toxicity in diatoms and the relation between these intracellular effects and the disturbance of species composition in communities represent a key target for further research. The original community species structure determines the response of a diatom community to toxic agent exposure. Diatom communities that have species capable of switching from autotrophic to heterotrophic modes, when photosynthesis is inhibited (e.g., after pesticide exposure), can continue to grow, even in the presence of high pesticide pollution. How diatoms respond to toxic stress, and the degree to which they respond, also depends on cell and community health, on ecological interactions with other organisms, and on general environmental conditions. The general structural parameters of diatom communities (biomass, global cell density) are less sensitive to pesticide effects than are the specific structural parameters of the unicellular organisms themselves (cell density by species, species composition). For benthic species, biofilm development and grazing on this matrix as a source of food for invertebrates and fishes may also modify the response of diatom communities. Environmental parameters (light exposure, nutrient concentrations, and hydraulic conditions) affect, and often interfere with, the response of diatoms to pesticides. Therefore, the complexity of aquatic ecosystems and the complexity of pesticide to easily detect the effects of such pollutants on diatoms. Clearly more research will be required to address this problem.

Genotoxicity of organic pollutants in source of drinking water on microalga Euglena gracilis

The potential toxicities of organic pollutants in the drinking water source at Meiliang Bay of Lake Taihu were investigated by comet assay and antioxidant enzyme approach on microalgae Euglena gracilis. The organic extracts of the water samples could induce DNA damage on microalgae cells. Statistically significant differences (P < 0.05) were observed at groups of 0.3x, 3x and 10x concentrations compared with the control and a solvent control (DMSO). The organic extracts also affected antioxidant enzyme activity and induced lipid peroxidation in the microalga. In the high dose group, there was an obvious increase in SOD content (P < 0.05). The results suggest that the concentrated organics from water sample extracts have adversary effects on E. gracilis and could possibly damage the ecosystem.

Comparison of the sensitivity of different toxicity test endpoints in a microalga exposed to the herbicide paraquat

The use of herbicides constitutes the principal method of weed control but the introduction of these compounds into the aquatic environment can provoke severe consequences for non-target organisms such as microalgae. Toxic effects of these pollutants on microalgae are generally evaluated using phytotoxicity tests based on growth inhibition, a population-based parameter. However, physiological cellular endpoints could allow early detection of cell stress and elucidate underlying toxicity mechanisms. Effects of the herbicide paraquat on the freshwater microalga Chlamydomonas moewusii were studied to evaluate growth rate and cellular parameters such as cellular viability and metabolic activity assayed by flow cytometry and DNA damage assayed by the comet assay. Sensitivity of growth and parameters assayed by flow cytometry were similar, showing a significant effect in cultures exposed to a paraquat concentration of 0.1 microM or higher, although in cultures exposed during 48 h to 0.05 microM, a significant stimulation of cellular fluorescein fluorescence was observed, related to cellular metabolic activity. After only 24 h of herbicide exposure significant DNA damage was observed in microalgal cells exposed to all paraquat concentrations assayed, with a 23.67% of comets in cultures exposed to 0.05 microM, revealing the genotoxicity of this herbicide. Taking into account the results obtained, comet assay provides a sensitive and rapid system for measuring primary DNA damage in Chlamydomonas moewusii, which could be an important aspect of environmental genotoxicity monitoring in surface waters.

Comet assay in phytoplankton as biomarker of genotoxic effects of environmental pollution

The alkaline comet assay was tested on different microalgae: the dinoflagellates, Karenia mikimotoi and Alexandrium minutum, and the diatom, Chaetoceros gracilis. The microalgae were exposed during their exponential growth to the model direct genotoxicant, hydrogen peroxide (1h, 5 and 100muM H2O2). Following H2O2 exposure, the comet assay was validated only for K. mikimotoi for which genotoxicity was observed from the lowest tested concentration of 5 microM with a concentration-dependent effect. C. gracilis was too small in size (4 microm) to be correctly analysed. For A. minutum, our lysis buffer was not strong enough to digest the cellulosic thecal plates. For K. mikimotoi, the comet assay was thus applied for the study of the genotoxic effects of different pesticides: epoxiconazole (as Opus formulation), chlorpyriphos-ethyl (as Dursban formulation) and endosulfan at 1, 10 and 100 microg of active substance/L for 24h. Exposure to epoxiconazole in formulation resulted in an increase in the extent of DNA strand breaks at the highest tested concentration icro/L. Endosulfan exposure resulted in DNA damage for K. mikimotoi nuclei. Genotoxicity was observed from 1 microg/L of endosulfan and was not concentration dependent.

Comet assay: a reliable tool for the assessment of DNA damage in different models

New chemicals are being added each year to the existing burden of toxic substances in the environment. This has led to increased pollution of ecosystems as well as deterioration of the air, water, and soil quality. Excessive agricultural and industrial activities adversely affect biodiversity, threatening the survival of species in a particular habitat as well as posing disease risks to humans. Some of the chemicals, e.g., pesticides and heavy metals, may be genotoxic to the sentinel species and/or to non-target species, causing deleterious effects in somatic or germ cells. Test systems which help in hazard prediction and risk assessment are important to assess the genotoxic potential of chemicals before their release into the environment or commercial use as well as DNA damage in flora and fauna affected by contaminated/polluted habitats. The Comet assay has been widely accepted as a simple, sensitive, and rapid tool for assessing DNA damage and repair in individual eukaryotic as well as some prokaryotic cells, and has increasingly found application in diverse fields ranging from genetic toxicology to human epidemiology. This review is an attempt to comprehensively encase the use of Comet assay in different models from bacteria to man, employing diverse cell types to assess the DNA-damaging potential of chemicals and/or environmental conditions. Sentinel species are the first to be affected by adverse changes in their environment. Determination of DNA damage using the Comet assay in these indicator organisms would thus provide information about the genotoxic potential of their habitat at an early stage. This would allow for intervention strategies to be implemented for prevention or reduction of deleterious health effects in the sentinel species as well as in humans.

Persistence of DNA damage in the freshwater mussel Unio pictorum upon exposure to ethyl methanesulphonate and hydrogen peroxide

An important endpoint in assessing pollution-related toxicity is genotoxicity. To obtain insight into the time-course of oxidative- and alkylation-induced DNA damage in the freshwater mussel, Unio pictorum, mussels were exposed for 24 hr to concentration gradients of pro-oxidant hydrogen peroxide (H(2)O(2)) and a mono-functional alkylating agent, ethyl methanesulfonate (EMS). DNA damage was assessed in haemocytes immediately upon exposure and over the recovery period of up to 72 days by means of comet and micronucleus assays. Following exposure to H(2)O(2), DNA damage as detected by the comet assay returned to control values after one day, except for the mussels exposed to the highest dose when damage was detectable for the next 3 days. In contrast, alkylation-induced DNA damage was detectable even after 72 days of recovery in de-chlorinated water, with a dose-response relationship observable throughout the whole recovery period. Micronucleus frequency was the highest on Day 3 after exposure to EMS; it decreased considerably by Day 7 and returned almost to the control levels 19 days after exposure, while no significant induction of micronuclei was observed in mussels exposed to H(2)O(2). Although the comet assay is considered a biomarker of recent genotoxic exposure, detecting DNA damage of shorter longevity than with the micronucleus assay, results presented here show that in the case of alkylation damage the comet assay reveals genotoxic exposure of U. pictorum in a dose-dependent manner even after 2 months.

Genotoxicity of cadmium in marine diatom Chaetoceros tenuissimus using the alkaline Comet assay

Genotoxic effects of cadmium on phytoplankton Chaetoceros tenuissimus have been evaluated using DNA damage by Comet assay. Cadmium concentrations ranging from 2.4 to 10 mg/l were used to evaluate the effects. Results showed that as the concentration of Cd increased growth of the diatom decreased. Alkaline single-cell gel electrophoresis (Comet assay) method, which is highly sensitive in detection of DNA damage in eukaryotic cells, was used to observe genomic changes in marine diatom cells. DNA damage was measured as percent number of comets and normal cells. 65% cells were found to be damaged at 10 mg/l concentration of Cd as compared to 23% in 2.4 mg/l and only 5% in controls. More than 50% apoptotic cells were observed on 8th day at 10 mg/l and 12th day at 7.5 mg/l concentrations. At lower Cd concentrations (4.5 mg/l and below) the damage was below 30% till the last day. This suggested that higher Cd levels have early damaging effects on cell nuclear material and that % injury increases with advancement of exposure period. One advantage of use of C. tenuissimus is the ease with which it can be cultured in a defined medium. C. tenuissimus diatom can be used as an in vivo model for ecogenotoxicity assessment using the Comet assay.

Application of methods for assessing the geno- and cytotoxicity of Triclosan to C. ehrenbergii

The toxic effects of Triclosan (2,4,4'-trichloro-2'-hydroxydiphenyl ether) on morphology and sexual and asexual reproduction of C. ehrenbergii were examined. In addition, the genotoxic effects of Triclosan were evaluated on the same alga using the microgel electrophoresis test, also-called Comet assay. Increasing Triclosan concentrations in the range 0.125-5 mg L(-1) did not affect size and shape of the cells but had relevant effects on both chloroplast morphology and dimension. Triclosan inhibited the vegetative growth of C. ehrenbergii at 0.5 mg L(-1). The effects on sexual reproduction indicate that the number of C. ehrenbergii zygospores was significantly reduced by the application of 0.937 mg L(-1). The Comet assay showed that Triclosan treatments led to a dose-dependent DNA damage of C. ehrenbergii; 0.25 mg L(-1)caused significant genotoxic effects and higher concentrations irreversibly altered the DNA strands. These results suggest that C. ehrenbergii could represent a useful organism to evaluate the whole toxicity of pharmaceuticals and personal care products (PPCPs), giving valuable information for a risk assessment.

Detection and quantification of genotoxicity in wastewater-treated Tetrahymena thermophila using the comet assay

In the present study, the comet, or single-cell, gel electrophoresis assay was adapted for use with the ubiquitous unicellular protozoan Tetrahymena thermophila, and the method was evaluated for its ability to detect DNA damage induced by known genotoxins and wastewater samples. The original comet assay protocol was substantially modified (e.g., lower concentrations of detergents were used in the lysis buffer; electrophoresis time was reduced). Using the modified method, T. thermophila were subjected to short exposures of phenol, hydrogen peroxide, and formaldehyde, leading to concentration-dependent increases in DNA damage. The genotoxic potential of influent and effluent water samples from a local municipal wastewater treatment plant was evaluated. The results indicated that the influent wastewater was genotoxic and that the genotoxicity in the effluent water was substantially reduced. We assume employing T. thermophila in the use of the comet assay may become a cost-effective and reliable tool for genotoxicity screening and monitoring of wastewater and similar systems.

Light dependency of resistance to ionizing radiation in Euglena gracilis

The resistance of Euglena gracilis strains Z (wild type) and SM-ZK (chloroplast-deficient mutant) to ionizing radiation was investigated. The colony forming ability of E. gracilis strain Z was higher than that of strain SM-ZK after 60Cogamma-irradiation. For both strains, the resistance of light-grown cells was higher than that of dark-grown cells, suggesting that the light conditions during culture contribute to the radiation resistance of E. gracilis. The comet assay showed that the ability of rejoining DNA double-strand breaks (dsb) was much higher in the light-grown cells. These results suggest that E. gracilis possesses a light-induced repair system to cope with DNA dsb.