The impact of elevated sulfur and nitrogen levels on cadmium tolerance in Euglena species.

Heavy metal (HM) pollution threatens human and ecosystem health. Current methods for remediating water contaminated with HMs are expensive and have limited effect. Therefore, bioremediation is being investigated as an environmentally and economically viable alternative. Freshwater protists Euglena gracilis and Euglena mutabilis were investigated for their tolerance to cadmium (Cd). A greater increase in cell numbers under Cd stress was noted for E. mutabilis but only E. gracilis showed an increase in Cd tolerance following pre-treatment with elevated concentrations of S or N. To gain insight regarding the nature of the increased tolerance RNA-sequencing was carried out on E. gracilis. This revealed transcript level changes among pretreated cells, and additional differences among cells exposed to CdCl2. Gene ontology (GO) enrichment analysis reflected changes in S and N metabolism, transmembrane transport, stress response, and physiological processes related to metal binding. Identifying these changes enhances our understanding of how these organisms adapt to HM polluted environments and allows us to target development of future pre-treatments to enhance the use of E. gracilis in bioremediation relating to heavy metals.

Agrobacterium tumefaciens-Mediated Nuclear Transformation of a Biotechnologically Important Microalga-Euglena gracilis.

Euglena gracilis (E. gracilis) is an attractive organism due to its evolutionary history and substantial potential to produce biochemicals of commercial importance. This study describes the establishment of an optimized protocol for the genetic transformation of E. gracilis mediated by Agrobacterium (A. tumefaciens). E. gracilis was found to be highly sensitive to hygromycin and zeocin, thus offering a set of resistance marker genes for the selection of transformants. A. tumefaciens-mediated transformation (ATMT) yielded hygromycin-resistant cells. However, hygromycin-resistant cells hosting the gus gene (encoding ß-glucuronidase (GUS)) were found to be GUS-negative, indicating that the gus gene had explicitly been silenced. To circumvent transgene silencing, GUS was expressed from the nuclear genome as transcriptional fusions with the hygromycin resistance gene (hptII) (encoding hygromycin phosphotransferase II) with the foot and mouth disease virus (FMDV)-derived 2A self-cleaving sequence placed between the coding sequences. ATMT of Euglena with the hptII-2A-gus gene yielded hygromycin-resistant, GUS-positive cells. The transformation was verified by PCR amplification of the T-DNA region genes, determination of GUS activity, and indirect immunofluorescence assays. Cocultivation factors optimization revealed that a higher number of transformants was obtained when A. tumefaciens LBA4404 (A600 = 1.0) and E. gracilis (A750 = 2.0) cultures were cocultured for 48 h at 19 °C in an organic medium (pH 6.5) containing 50 µM acetosyringone. Transformation efficiency of 8.26 ± 4.9% was achieved under the optimized cocultivation parameters. The molecular toolkits and method presented here can be used to bioengineer E. gracilis for producing high-value products and fundamental studies.

Internalization of polystyrene microplastics in Euglena gracilis and its effects on the protozoan photosynthesis and motility.

In this study, effects of polystyrene microplastics (MPS) on Euglena gracilis were investigated via examination on its photosynthesis and motility, two typical properties of the protozoan. No adverse effects were observed after 4-d exposure except for decrease in motility at two high MPS concentrations (5 and 25 mg/L). After 8-d duration, MPS at 1 mg/L had no obvious effects on E. gracilis, but two higher concentrations (5 and 25 mg/L) of MPS inhibited protozoan growth, motility, and photosynthesis. The reduced protozoan photosynthetic activity was reflected by changes in Fv/Fm (the maximum photochemical yield of PSII), ΔFIP (difference between FP and FI) and PIABS (the performance index), indicative of reduced quantum yield of electron transport and enhanced energy dissipation. A dose-dependent effect of MPS on E. gracilis was found in protozoan growth, photosynthesis and motility, especially photosynthetic indices. MPS of small size (75 nm) seemed more toxic to the protozoa than large size (1000 nm). Internalization of MPS in the cells and chloroplasts was observed clearly for the first time, likely responsible for their toxicity. Analysis on photosynthetic process and motility of E. gracilis could provide more comprehensive understanding of MPS toxicity in the aquatic environment, and may potentially serve as a biomonitoring tool.

Biological response of protists Haematococcus lacustris and Euglena gracilis to conductive polymer poly (3,4-ethylenedioxythiophene) polystyrene sulfonate.

Improving the growth and pigment accumulation of microalgae by electrochemical approaches was considered a novel and promising method. In this research, we investigated the effect of conductive polymer poly (3,4-ethylenedioxythiophene) polystyrene sulfonate (PEDOT:PSS) dispersible in water on growth and pigment accumulation of Haematococcus lacustris and Euglena gracilis. The results revealed that effect of PEDOT:PSS was strongly cell-dependent and each cell type has its own peculiar response. For H. lacustris, the cell density in the 50 mg·l-1 treatment group increased by 50·27%, and the astaxanthin yield in the 10 mg·l-1 treatment group increased by 37·08%. However, under the high concentrations of PEDOT:PSS treatment, cell growth was significantly inhibited, and meanwhile, the smaller and more active zoospores were observed, which reflected the changes in cell life cycle and growth mode. Cell growth of E. gracilis in all the PEDOT:PSS treatment groups were notably inhibited. Chlorophyll a content in E. gracilis decreased while chlorophyll b content increased in response to the PEDOT:PSS treatment. The results laid a foundation for further development of electrochemical methods to promote microalgae growth and explore the interactions between conductive polymers and microalgae cells.

Exposure of microalgae Euglena gracilis to polystyrene microbeads and cadmium: Perspective from the physiological and transcriptional responses.

Micro(nano)plastics (MPs/NPs) are already present as contaminants in the natural environment globally and have been shown to be difficult to degrade, resulting in the potential for ecological damage and public health concerns. However, the adverse effects of exposure to MPs/NPs by aquatic organisms, especially freshwater microalgae, remains unclear. In the present study, the growth, physiology and transcriptome of the freshwater microalgae Euglena gracilis were comprehensively analyzed following exposure to 1 mg/L of polystyrene (PS) microbeads (5 µm PS-MPs and 100 nm PS-NPs), 0.5 mg/L cadmium (Cd), or a mixture of PS microbeads and Cd for 96 h. Results showed that the toxicity of PS-MPs to microalgae was greater than PS-NPs, inducing increased growth inhibition, oxidative damage and decreased photosynthesis pigment concentrations. PS-MPs alone or in combination with Cd caused cavitation within microalgal cells, as well as increasing the number and volume of vacuoles. The combined exposure toxicity test showed that a combination of Cd + PS-NPs was more toxic than Cd + PS-MPs, which may be explained by the transcriptomic analysis results. Differentially expressed genes (DEGs) in the Cd + PS-NPs group were mainly enriched in metabolism-related pathways, suggesting that algal metabolism was hindered, resulting in aggravation of toxicity. The reduced toxicity induced by Cd + PS-MPs may indicate a response to resist external stress processes. In addition, no adsorption of 0.5 mg/L Cd to 1 mg/L PS microbeads was observed, suggesting that adsorption of MPs/NPs and Cd was not the key factor determining the combined toxicity effects in this study.

Toxicity of enzymatically decolored textile dyes solution by horseradish peroxidase.

The oxidative systems including enzymatic systems have been widely studied as an alternative for textile effluents treatment. However, studies have shown that some oxidative processes can produce degradation products with higher toxicity than the untreated dye. In this work, enzymatic dye decolorization was evaluated by horseradish peroxidase enzyme (HRP) and the toxicity of discoloration products was evaluate against Daphnia magna, Euglena gracilis algae, and Vibrio fischeri. Dye decolorization kinetics data were evaluated and the pseudo-second-order model showed the best-fitting to the experimental data. In addition, it was observed an increased acute and chronic toxicity associated with the decolorization efficiency. The Reactive Blue 19 and Reactive Black dye showed the highest toxicity against D. Magna (16 toxicity factor) and V. Fischeri (32 toxicity factor) after enzymatic decolorization. For the chronic toxicity against D. Magna, Reactive Red was the only dye with no fertility inhibition. In relation to toxicity tests with E. gracilis algae, it was not observed photosynthetic inhibition for all dyes. This study verified the viability of the enzyme horseradish peroxidase in the textile dyes decolorization and the importance to evaluate the decolorization products.

Nickel accumulation by the green algae-like Euglena gracilis.

Nickel accumulation and nickel effects on cellular growth, respiration, photosynthesis, ascorbate peroxidase (APX) activity, and levels of thiols, histidine and phosphate-molecules were determined in Euglena gracilis. Cells incubated with 0.5-1mM NiCl2 showed impairment of O2 consumption, photosynthesis, Chl a+b content and APX activity whereas cellular integrity and viability were unaltered. Nickel accumulation was depressed by Mg2+ and Cu2+, while Ca2+, Co2+, Mn2+ and Zn2+ were innocuous. The growth half-inhibitory concentrations for Ni2+ in the culture medium supplemented with 2 or 0.2mM Mg2+ were 0.43 or 0.03mM Ni2+, respectively. Maximal nickel accumulation (1362mg nickel/Kg DW) was achieved in cells exposed to 1mM Ni2+ for 24h in the absence of Mg2+ and Cu2+; accumulated nickel was partially released after 72h. GSH polymers content increased or remained unchanged in cells exposed to 0.05-1mM Ni2+; however, GSH, cysteine, γ-glutamylcysteine, and phosphate-molecules all decreased after 72h. Histidine content increased in cells stressed with 0.05 and 0.5mM Ni2+ for 24h but not at longer times. It was concluded that E. gracilis can accumulate high nickel levels depending on the external Mg2+ and Cu2+ concentrations, in a process in which thiols, histidine and phosphate-molecules have a moderate contribution.

Interaction of silver nanoparticles with algae and fish cells: a side by side comparison.

BACKGROUND: Silver nanoparticles (AgNP) are widely applied and can, upon use, be released into the aquatic environment. This raises concerns about potential impacts of AgNP on aquatic organisms. We here present a side by side comparison of the interaction of AgNP with two contrasting cell types: algal cells, using the algae Euglena gracilis as model, and fish cells, a cell line originating from rainbow trout (Oncorhynchus mykiss) gill (RTgill-W1). The comparison is based on the AgNP behavior in exposure media, toxicity, uptake and interaction with proteins. RESULTS: (1) The composition of exposure media affected AgNP behavior and toxicity to algae and fish cells. (2) The toxicity of AgNP to algae was mediated by dissolved silver while nanoparticle specific effects in addition to dissolved silver contributed to the toxicity of AgNP to fish cells. (3) AgNP did not enter into algal cells; they only adsorbed onto the cell surface. In contrast, AgNP were taken up by fish cells via endocytic pathways. (4) AgNP can bind to both extracellular and intracellular proteins and inhibit enzyme activity. CONCLUSION: Our results showed that fish cells take up AgNP in contrast to algal cells, where AgNP sorbed onto the cell surface, which indicates that the cell wall of algae is a barrier to particle uptake. This particle behaviour results in different responses to AgNP exposure in algae and fish cells. Yet, proteins from both cell types can be affected by AgNP exposure: for algae, extracellular proteins secreted from cells for, e.g., nutrient acquisition. For fish cells, intracellular and/or membrane-bound proteins, such as the Na+/K+-ATPase, are susceptible to AgNP binding and functional impairment.

Production of a thermal stress resistant mutant Euglena gracilis strain using Fe-ion beam irradiation.

Euglena gracilis is a common phytoplankton species, which also has motile flagellate characteristics. Recent research and development has enabled the industrial use of E. gracilis and selective breeding of this species is expected to further expand its application. However, the production of E. gracilis nuclear mutants is difficult because of the robustness of its genome. To establish an efficient mutation induction procedure for E. gracilis, we employed Fe-ion beam irradiation in the RIKEN RI beam factory. A decrease in the survival rate was observed with the increase in irradiation dose, and the upper limit used for E. gracilis selective breeding was around 50 Gy. For a practical trial of Fe-ion irradiation, we conducted a screening to isolate high-temperature-tolerant mutants. The screening yielded mutants that proliferated faster than the wild-type strain at 32 °C. Our results demonstrate the effectiveness of heavy-ion irradiation on E. gracilis selective breeding.

The effect of rapamycin on biodiesel-producing protist Euglena gracilis.

Rapamycin induces autophagy with lipid remodeling in yeast and mammalian cells. To investigate the lipid biosynthesis of Euglena gracilis, rapamycin was supplemented in comparison with two model algae, Chlamydomonas reinhardtii and Cyanidioschyzon merolae. In Euglena, rapamycin induced the reduction of chlorophylls and the accumulation of neutral lipids without deterring its cell proliferation. Its lipidomic profile revealed that the fatty acid composition did not alter by supplementing rapamycin. In Chlamydomonas, however, rapamycin induced serious growth inhibition as reported elsewhere. With a lower concentration of rapamycin, the alga accumulated neutral lipids without reducing chlorophylls. In Cyanidioschyzon, rapamycin did not increase neutral lipids but reduced its chlorophyll content. We also tested fatty acid elongase inhibitors such as pyroxasulfone or flufenacet in Euglena with no significant change in its neutral lipid contents. In summary, controlled supplementation of rapamycin can increase the yield of neutral lipids while the scheme is not always applicable for other algal species.

Assessment of the impact of chlorophyll derivatives to control parasites in aquatic ecosystems.

Several research groups have studied new biopesticides which are less toxic to the environment and capable of controlling the vectors of parasitic diseases, especially in aquatic ecosystems. Pest control by photodynamic substances is an alternative to chemical or other measures, with chlorophyll and its derivatives as the most studied substances supported by their easy availability and low production costs. The impact of chlorophyll derivatives on four different species, a small crustacean (Daphnia similis), a unicellular alga (Euglena gracilis) and two species of fish (Astyanax bimaculatus and Cyprynus carpio) were tested under short-term conditions. In addition, the effects of long-term exposure were evaluated in D. similis and E. gracilis. In short-term tests, mortality of D. similis (EC50 = 7.75 mg/L) was most strongly affected by chlorophyllin, followed by E. gracilis (EC50 = 12.73 mg/L). The fish species showed a greater resistance documented by their EC50 values of 17.58 and 29.96 mg/L in C. carpio and A. bimaculatus, respectively. A risk quotient is calculated by dividing an estimate of exposure by an estimate of effect. It indicated that chlorophyll derivatives can be applied in nature to control the vectors of parasitic diseases under short-term conditions, but long-term exposure requires new formulations.

Cadmium removal by Euglena gracilis is enhanced under anaerobic growth conditions.

The facultative protist Euglena gracilis, a heavy metal hyper-accumulator, was grown under photo-heterotrophic and extreme conditions (acidic pH, anaerobiosis and with Cd(2+)) and biochemically characterized. High biomass (8.5×10(6)cellsmL(-1)) was reached after 10 days of culture. Under anaerobiosis, photosynthetic activity built up a microaerophilic environment of 0.7% O2, which was sufficient to allow mitochondrial respiratory activity: glutamate and malate were fully consumed, whereas 25-33% of the added glucose was consumed. In anaerobic cells, photosynthesis but not respiration was activated by Cd(2+) which induced higher oxidative stress. Malondialdehyde (MDA) levels were 20 times lower in control cells under anaerobiosis than in aerobiosis, although Cd(2+) induced a higher MDA production. Cd(2+) stress induced increased contents of chelating thiols (cysteine, glutathione and phytochelatins) and polyphosphate. Biosorption (90%) and intracellular accumulation (30%) were the mechanisms by which anaerobic cells removed Cd(2+) from medium, which was 36% higher versus aerobic cells. The present study indicated that E. gracilis has the ability to remove Cd(2+) under anaerobic conditions, which might be advantageous for metal removal in sediments from polluted water bodies or bioreactors, where the O2 concentration is particularly low.

Ecotoxicological effects of graphene oxide on the protozoan Euglena gracilis.

Potential environmental risks posed by nanomaterials increase with their extensive production and application. As a newly emerging carbon material, graphene oxide (GO) exhibits excellent electrochemical properties and has promising applications in many areas. However, the ecotoxicity of GO to organisms, especially aquatic organisms, remains poorly understood. Accordingly, this study examined the toxicity of GO with protozoa Euglena gracilis as test organism. Growth inhibition test was initially performed to investigate acute toxic effects. Protozoa were subsequently exposed to GO ranging from 0.5 mg L(-1) to 5 mg L(-1) for 10 d. The growth, photosynthetic pigment content, activities of antioxidant enzymes, ultrastructure of the protozoa, as well as the shading effect of GO, were analyzed to determine the mechanism of the toxicity effect. Results showed that the 96 h EC50 value of GO in E. gracilis was 3.76±0.74 mg L(-1). GO at a concentration of 2.5 mg L(-1) exerted significant (P<0.01) adverse effects on the organism. These effects were evidenced by the inhibition of growth and the enhancement of malondialdehyde content and antioxidant enzyme activities. Shading effect and oxidative stress may be responsible for GO toxicity.

Toxic effects of individual and combined effects of BTEX on Euglena gracilis.

BTEX is a group of volatile organic compounds consisting of benzene, toluene, ethylbenzene and xylenes. Environmental contamination of BTEX can occur in the groundwater with their effects on the aquatic organisms and ecosystem being sparsely studied. The aim of this study was to evaluate the toxic effects of individual and mixed BTEX on Euglena gracilis (E. gracilis). We examined the growth rate, morphological changes and chlorophyll contents in E. gracilis Z and its mutant SMZ cells treated with single and mixture of BTEX. BTEX induced morphological change, formation of lipofuscin, and decreased chlorophyll content of E. gracilis Z in a dose response manner. The toxicity of individual BTEX on cell growth and chlorophyll inhibition is in the order of xylenes>ethylbenzene>toluene>benzene. SMZ was found more sensitive to BTEX than Z at much lower concentrations between 0.005 and 5 µM. The combined effect of mixed BTEX on chlorophyll contents was shown to be concentration addition (CA). Results from this study suggested that E. gracilis could be a suitable model for monitoring BTEX in the groundwater and predicting the combined effects on aqueous ecosystem.

Comparative toxicity of physiological and biochemical parameters in Euglena gracilis to short-term exposure to potassium sorbate.

Potassium sorbate is the potassium salt of sorbic acid, is a widespread and efficient antioxidant that has multiple functions in plants, traditionally associated with the reactions of photosynthesis; however, it has moderate toxicity to various species including rat, fish, bacteria and human health. The effects of potassium sorbate on the movement and photosynthetic parameters of Euglena gracilis were studied during short-term exposure. Potassium sorbate showed acute toxicity to the green flagellate E. gracilis affecting different physiological parameters used as endpoints in an automatic bioassay such as motility, precision of gravitational orientation (r-value), upward movement and alignment, with mean EC50 values of 2867.2 mg L(-1). The concentrations above 625 mg L(-1) of potassium sorbate induce an inhibition of the photosynthetic efficiency and electron transport rate and, in concentrations more than 2500.0 mg L(-1), the Euglena cells undergo a complete inhibition of photosynthesis even at low light irradiation.

Influence of different light-dark cycles on motility and photosynthesis of Euglena gracilis in closed bioreactors.

Abstract The unicellular photosynthetic freshwater flagellate Euglena gracilis is a promising candidate as an oxygen producer in biological life-support systems. In this study, the capacity of Euglena gracilis to cope with different light regimes was determined. Cultures of Euglena gracilis in closed bioreactors were exposed to different dark-light cycles (40 W/m(2) light intensity on the surface of the 20 L reactor; cool white fluorescent lamps in combination with a 100 W filament bulb): 1 h-1 h, 2 h-2 h, 4 h-4 h, 6 h-6 h, and 8 h-16 h, respectively. Motility and oxygen development in the reactors were measured constantly. It was found that, during exposure to light-dark cycles of 1 h-1 h, 2 h-2 h, 4 h-4 h, and 6 h-6 h, precision of gravitaxis as well as the number of motile cells increased during the dark phase, while velocity increased in the light phase. Oxygen concentration did not yet reach a plateau phase. During dark-light cycles of 8 h-16 h, fast changes of movement behavior in the cells were detected. The cells showed an initial decrease of graviorientation after onset of light and an increase after the start of the dark period. In the course of the light phase, graviorientation increased, while motility and velocity decreased after some hours of illumination. In all light profiles, Euglena gracilis was able to produce sufficient oxygen in the light phase to maintain the oxygen concentration above zero in the subsequent dark phase.

Ecotoxicological studies of micro- and nanosized barium titanate on aquatic photosynthetic microorganisms.

The interaction between live organisms and micro- or nanosized materials has become a current focus in toxicology. As nanosized barium titanate has gained momentum lately in the medical field, the aims of the present work are: (i) to assess BT toxicity and its mechanisms on the aquatic environment, using two photosynthetic organisms (Anabaena flos-aquae, a colonial cyanobacteria, and Euglena gracilis, a flagellated euglenoid); (ii) to study and correlate the physicochemical properties of BT with its toxic profile; (iii) to compare the BT behavior (and Ba(2+) released ions) and the toxic profile in synthetic (Bold's Basal, BB, or Mineral Medium, MM) and natural culture media (Seine River Water, SRW); and (iv) to address whether size (micro, BT MP, or nano, BT NP) is an issue in BT particles toxicity. Responses such as growth inhibition, cell viability, superoxide dismutase (SOD) activity, adenosine-5-triphosphate (ATP) content and photosynthetic efficiency were evaluated. The main conclusions are: (i) BT have statistically significant toxic effects on E. gracilis growth and viability even in small concentrations (1µgmL(-1)), for both media and since the first 24 h; on the contrary of on A. flos-aquae, to whom the effects were noticeable only for the higher concentrations (after 96 h: ≥75 µg mL(-1) for BT NP and =100 µg mL(-1) for BT MP, in BB; and ≥75 µg mL(-1) for both materials in SRW), in spite of the viability being affected in all concentrations; (ii) the BT behaviors in synthetic and natural culture media were slightly different, being the toxic effects more pronounced when grown in SRW - in this case, a worse physiological state of the organisms in SRW can occur and account for the lower resistance, probably linked to a paucity of nutrients or even a synergistic effect with a contaminant from the river; and (iii) the effects seem to be mediated by induced stress without a direct contact in A. flos-aquae and by direct endocytosis in E. gracilis, but in both organisms the contact with both BT MP and BT NP increased SOD activity and decreased photosynthetic efficiency and intracellular ATP content; and (iv) size does not seem to be an issue in BT particles toxicity since micro- and nano-particles produced significant toxic for the model-organisms.

Potential environmental toxicity from hemodialysis effluent.

Understanding the toxicity of certain potentially toxic compounds on various aquatic organisms allows to assess the impact that these pollutants on the aquatic biota. One source of pollution is the wastewater from hemodialysis. The process of sewage treatment is inefficient in inhibition and removal of pathogenic bacteria resistant to antibiotics in this wastewater. In many countries, such as Brazil, during emergencies, sewage and effluents from hospitals are often dumped directly into waterways without any previous treatment. The objective of this study was to characterize the effluents generated by hemodialysis and to assess the degree of acute and chronic environmental toxicity. The effluents of hemodialysis showed high concentrations of nitrites, phosphates, sulfates, ammonia, and total nitrogen, as well as elevated conductivity, turbidity, salinity, biochemical and chemical oxygen demand, exceeding the thresholds defined in the CONAMA Resolution 430. The samples showed acute toxicity to the green flagellate Euglena gracilis affecting different physiological parameters used as endpoints in an automatic bioassay such as motility, precision of gravitational orientation (r-value), compactness, upward movement, and alignment, with mean EC50 values of recalculate as 76.90 percent (±4.68 percent) of the undiluted effluents. In tests with Daphnia magna, the acute toxicity EC50 was 86.91 percent (±0.39 percent) and a NOEC value of 72.97 percent and a LEOC value 94.66 percent.

Assessing benzene-induced toxicity on wild type Euglena gracilis Z and its mutant strain SMZ.

Benzene is a representative member of volatile organic compounds and has been widely used as an industrial solvent. Groundwater contamination of benzene may pose risks to human health and ecosystems. Detection of benzene in the groundwater using chemical analysis is expensive and time consuming. In addition, biological responses to environmental exposures are uninformative using such analysis. Therefore, the aim of this study was to employ a microorganism, Euglena gracilis (E. gracilis) as a putative model to monitor the contamination of benzene in groundwater. To this end, we examined the wild type of E. gracilis Z and its mutant form, SMZ in their growth rate, morphology, chlorophyll content, formation of reactive oxygen species (ROS) and DNA damage in response to benzene exposure. The results showed that benzene inhibited cell growth in a dose response manner up to 48 h of exposure. SMZ showed a greater sensitivity compared to Z in response to benzene exposure. The difference was more evident at lower concentrations of benzene (0.005-5 µM) where growth inhibition occurred in SMZ but not in Z cells. We found that benzene induced morphological changes, formation of lipofuscin, and decreased chlorophyll content in Z strain in a dose response manner. No significant differences were found between the two strains in ROS formation and DNA damage by benzene at concentrations affecting cell growth. Based on these results, we conclude that E. gracilis cells were sensitive to benzene-induced toxicities for certain endpoints such as cell growth rate, morphological change, depletion of chlorophyll. Therefore, it is a potentially suitable model for monitoring the contamination of benzene and its effects in the groundwater.

Ecotoxicity evaluation of a liquid detergent using the automatic biotest ECOTOX.

Synthetic detergents are common pollutants reaching aquatic environments in different ways after usage at homes, institutions and industries. In this study a liquid detergent, used for dish washing, was evaluated for its toxicity during long- and short-term tests using the automatic biotest ECOTOX. Different parameters of Euglena gracilis like motility, swimming velocity, gravitactic orientation, cell compactness and cell growth were used as end points. In short-term experiments, the maximum adverse effects on motility, velocity, cell shape and gravitaxis were observed after 1 h of exposure. With further increase in exposure time to the detergent a slight recovery of these parameters was observed. In long-term experiments, the detergent caused severe disturbances to E. gracilis. Motility, cell growth and cell compactness (shape) with EC50 values of 0.064, 0.18 and 2.05 %, respectively, were found as the most sensitive parameters to detergent stress. There was a slight positive effect on gravitactic orientation at the lowest two concentrations; at higher concentrations of the detergent cells orientation was highly impaired giving EC50 values of 1.75 and 2.52 % for upward swimming and r-value, respectively.