The Erlanger flagellate test (EFT): photosynthetic flagellates in biological dosimeters

A Ten-Minute Bioassay to Test Metal Toxicity with the Freshwater Flagellate Euglena agilis

A chemical analysis of water quality cannot detect some toxicants due to time constraints, high costs, and limited interactions for detection. Bioassays would offer a complementary means to assess pollution levels in water. Euglena is a flagellate green alga and an excellent system for toxicity testing thanks to its ease of culture, rapid growth, and quick response to environmental stresses. Herein, we examined the sensitivity of E. agilis to seven heavy metals by analyzing six end-point parameters: motility, velocity, cell compactness, upward swimming, r-value, and alignment. Notably, the velocity of E. agilis was most sensitive to cadmium (96.28 mg·L−1), copper (6.51 mg·L−1), manganese (103.28 mg·L−1), lead (78.04 mg·L−1), and zinc (101.90 mg·L−1), while r-values were most sensitive to arsenic (12.84 mg·L−1) and mercury (4.26 mg·L−1). In this study, velocity and r-values are presented as useful biomarkers for the assessment of metal toxicity in Euglena. The metals As, Cd, Cu, and Pb were suitable for this test. The advantages of the ecotoxicity test are its rapidity: It takes 10 min to obtain results, as opposed to the typical 3–4 d of exposure time with intensive labor. Moreover, this test can be performed at room temperature under dark conditions.

A rapid phenol toxicity test based on photosynthesis and movement of the freshwater flagellate, Euglena agilis Carter

Phenol, a monosubstituted aromatic hydrocarbon with various commercial uses, is a major organic constituent in industrial wastewaters. The ecotoxic action of phenol for aquatic environment is well known. In this study, rapid phenol toxicity tests (1h) were developed based on chlorophyll a (Chl a) fluorescence and the movement parameters of the freshwater flagellate, Euglena agilis Carter. Phenol significantly reduced the maximum quantum yield (Fv/Fm) of photosystem II (PS II) and the maximum photosynthetic electron transport rate (rETRmax) with median effective concentration (EC50) values of 8.94 and 4.67 mM, respectively. Phenol reduced the motility and triggered change in the swimming velocity of the test organism. Among the parameters tested, velocity was the most sensitive biomarker with an EC50 of 3.17 mM. The EC50 values for Fv/Fm, motility, and velocity appear to overlap the permitted levels of phenol. In conclusion, the photosynthesis and movement of E. agilis can be fast and sensitive risk assessment parameters for the evaluation of phenol toxicity in municipal and industrial effluents.

Going with the flow: detection of drift in response to hypo-saline stress by the estuarine benthic diatom Cylindrotheca closterium

Avoidance response is a well-known mechanism for escaping environmental stress. For organisms with reduced active movement, such as benthic microalgae, drifting could be a specifically selected mean of avoiding less favorable environments. To test this hypothesis, a system was developed to assess if hypo-saline stress triggers drift in the estuarine benthic diatom Cylindrotheca closterium. Concurrently, the effects of salinity on growth inhibition were also investigated in order to compare the sensitivity of this endpoint with the drift response, and to estimate the immediate population decline caused by both drift and population growth responses. It was verified that the salinity value that inhibited the algal population growth by 50% (IGS₅₀) was 19, while the salinity value that triggered the drift response by 50% of the population (TDS₅₀) was 15. These results indicate that drift is an identifiable response triggered to escape stressful environments. The combination of the two responses (population growth and drift) showed that population decline based exclusively on the inhibition of population growth may result in an underestimation of the risk, compared with the decline when drifting to avoid stress is also taken into account.

UV-B affects photosynthesis, ROS production and motility of the freshwater flagellate, Euglena agilis Carter

The effects of ultraviolet B (UV-B; 295-320 nm) radiation on certain vital physiological (photosynthesis), biochemical (production of reactive oxygen species - ROS) and behavioral (motility and orientation) characteristics were investigated in the unicellular photoautotroph, Euglena agilis Carter. The photosynthetic performance of E. agilis was recorded after exposure of between 15 and 60 min followed by a period of recovery lasting 6-24h under dim light (5-10 μmol photons m(-2) s(-1)). The maximum quantum yield of PS II (F(v)/F(m)) was reduced to 65% and 14% of initial values immediately following 15 and 30 min UV-B exposure, but recovered to 100 and 86% of the initials, respectively. Values of rETR(max) in E. agilis exposed to 15 min UV-B were similar to those of the initials, but a 30 min UV exposure resulted in 75% reduction of rETR(max) with only a 43% recovery as compared with the initial after 24h recovery. After a 60 min UV-B exposure, there were no Chl a fluorescence signals, and hence no F(v)/F(m) or rETR(max). A UV dose-dependent increase in DCFH-DA fluorescence was found in E. agilis cells, reflecting an increase in ROS production. After exposures to UV-B for between 15 and 60 min, the percentages of motile cells in the population decreased to 76, 39 and 15%, respectively. Following 24h in dim light, the percentage of motile cells increased to between 66% and 95% of the initial value. The velocity of non-irradiated cells was 60 μm s(-1), which decreased to 16-35 μm s(-1) immediately following exposure for 15-60 min. After periods of time in dim light (6, 12 and 24h) velocities had recovered to between 44 and 81% of the initial value. In untreated controls, the r-value was 0.23, indicating random movement of E. agilis, but it increased to 0.35 and 0.72 after exposure to UV-B for 30 and 60 min, respectively. There was a tendency towards vertical downward movement of cells proportional to the duration of exposure. The compactness of E. agilis decreased from 2.9 in controls to 1.8-2.3 in cells treated with UV-B although significant recovery followed. UV-B dose-dependent interaction between photosynthetic activity, ROS production and movement is discussed in terms of a UV-protective mechanism in E. agilis.

Tracking of mercury ions in living cells with a fluorescent chemodosimeter under single- or two-photon excitation

Tracking of Hg2+ in solutions as well as in living cells was conducted with a fluorescent chemodosimeter by measuring the spectral shift of its fluorescence under single- or two-photon excitation. The spectral hypsochromic shifts of this chemodosimeter when reacting with Hg2+ were found to be about 50 nm in acetonitrile/water solutions and 32 nm in Euglena gracilis 277 living cells. This chemodosimeter shows high sensitivity and selectivity, and is not influenced by the pH values. It can signal Hg2+ in solutions down to the ppb range under either single-photon excitation (SPE) at 405 nm or two-photon excitation (TPE) at 800 nm. However, with low cellular chemodosimeter concentrations, the SPE spectra were disturbed by the auto-fluorescence from the native fluorophore in the cell, while the TPE spectra were still of high quality since the two-photon absorption cross section of this chemodosimeter is much larger than that of the native fluorophores in the cell.

Effects of the herbicides Roundup and Avans on Euglena gracilis

Glyphosate is the active ingredient in a range of widely used herbicides. The aim of this work is to evaluate the effects of two commercial herbicides, Roundup and Avans, on the motility, velocity, and gravitactic orientation of the aquatic flagellate Euglena gracilis. An early warning system, called ECOTOX, has been used for monitoring the different parameters of movement. The motility was not affected by Roundup and Avans after short period tests (0, 30, and 60 s). However, gravitactic orientation of the cells was affected at concentrations of 1.25 g l(-1) and above when treated with Avans, whereas treatments with Roundup showed no specific changes after short period tests. Velocity of the cells was affected by both herbicides, but the effects of Avans were shown to occur at lower concentrations in comparison to Roundup. Avans showed lower no observable effect concentration (NOEC) values in comparison to Roundup for the different parameters after short period tests. After long period (7 days) tests, NOEC values were similar except for the upward swimming, where Avans had a NOEC value of 100 microg l(-1) and Roundup 200 microg l(-1). The results demonstrate that Avans containing trimethylsulfonium salt of glyphosate is more toxic to E. gracilis than Roundup, which contained isopropylamine salt of glyphosate.

Effects of pH on the growth rate, motility and photosynthesis in Euglena gracilis

The influence of pH 3-10 on the growth, motility and photosynthesis in Euglena gracilis was demonstrated during a 7-d cultivation. The cells did not survive at pH < 4 and > 8, highest growth rate being detected at pH 7. Motility followed a similar pattern as growth rate. Photosynthetic response curves were shown to be of the same type over the whole pH range. High respiration was characteristic for cells grown at pH 5 and 6, the lowest one at 7. At high and also at low pH more active respiration was found which can be considered as a protective response on proton stress. Respiration was not completely inhibited with potassium cyanide. Photosynthesis was the most effective at pH 6; lower and higher pH decreased photosynthetic efficiency. pH affected more the growth rate than the photosynthesis.

Evaluation of DNA dosimetry to assess ozone-mediated variability of biologically harmful radiation in Antarctica

In this study we investigated the use of a DNA dosimeter to accurately measure changes in ultraviolet B radiation (UVBR; 280-315 nm) under Antarctic ozone hole conditions. Naked DNA solution in quartz tubes was exposed to ambient solar radiation at Rothera Research Station, Antarctica, between October and December 1998 for 3 h during UVBR peak hours (1200-1500 h). Trends in UVBR-mediated DNA damage (formation of cyclobutane pyrimidine dimers [CPD]) were related to cloud cover, ozone-column depth and spectroradiometric measurements of ambient radiation. Ozone-column depths ranged from 130 to 375 DU during the study period, resulting in highly variable UVBR doses, from 1.6 to 137 kJ m(-2) over the 3 h exposure, as measured by spectroradiometry. There was a strong positive correlation (86%) between dosimeter CPD concentrations and DNA-weighted UVBR doses. Ozone depth was a strong predictor of DNA damage (63%), and there was no significant relationship between CPD formation and cloud cover. Subtle changes in spectral characteristics caused by ozone depletion were detected by the biodosimeter; the highest CPD concentrations were observed in October when ozone-mediated shifts favored shorter wavelengths of UVBR. We conclude that the DNA biodosimeter is an accurate indicator of biologically effective UVBR, even under highly variable ozone conditions.

Applicability of growth rate, cell shape, and motility of Euglena gracilis as physiological parameters for bioassessment at lower concentrations of toxic substances: an experimental approach

The responses of the growth rate, motility, and cell shape in the green flagellate Euglena gracilis to different concentrations of waste water substances from the pulp and paper industry were tested in a long-term study (7 days). Samples before (uncleaned sample) and after (cleaned sample) the treatment in a cleaning system were studied. The influence of different doses of UV-B radiation on cell shape and motility was also investigated. No statistically significant effects of increasing concentrations of the waste substances both before and after the cleaning process (except inhibition by the undiluted uncleaned effluent) on the growth rate in E. gracilis were observed. Cell shape turned out to be an unreliable physiological parameter for assessing the toxicity at lower concentrations of waste water substances. No significant patterns could be observed in the response of the cell shape to the different concentrations of the waste water substances or to UV-B radiation. Motility has been concluded to be a more sensitive parameter than cell shape. However, no clear patterns were observed in the response of the motility to the different concentrations of the waste water substances studied. Increasing concentrations of the uncleaned sample demonstrated a defense against UV-B radiation, due to the high absorbance in the UV-B range, when effects on motility were examined. We conclude that contrary to the results reported in the literature earlier, cell shape and motility of E. gracilis are not universal physiological parameters for bioassessment at lower concentrations of toxic substances, including metals such as copper and zinc from the pulp and paper industry. The long-duration tests had, in general, higher significance than those of short duration.

A novel express bioassay for detecting toxic substances in water by recording rhodopsin-mediated photoelectric responses in Chlamydomonas cell suspensions

The influence of Cu2+, Zn2+, Cd2+, Pb2+ and formaldehyde on rhodopsin-mediated photoelectric responses in the green flagellate Chlamydomonas reinhardtii was investigated using three modifications of a recently developed population method for electrical recording (in nonoriented, phototactically preoriented (PO) and gravitactically preoriented cell suspensions). The addition of the heavy metal ions at concentrations several times lower than those known to affect swimming velocity and other physiological parameters in photosynthetic flagellates led to a rapid (one to several minutes) inhibition of the responses. Formaldehyde induced a significant temporary increase in the gravi-orientation of the cells simultaneously with an inhibition of their photoelectric cascade, photo-orientation and motility. The signals recorded in PO suspensions were more sensitive to all tested toxic substances than those recorded from nonoriented cells and indicated a switch from negative to positive phototaxis in the presence of the toxic substances. Of the two major components of the photoelectric cascade, the regenerative response was more sensitive to the tested heavy metal ions, but not to formaldehyde, than the photoreceptor current. The results obtained show that measurement of the photoinduced electrical responses in Chlamydomonas cell suspensions is a powerful novel bioassay for testing environmental pollutants in water samples.