USING A FLUORESCENT CELL-BASED APPROACH IN THE EVALUATION OF AQUATIC POLLUTION

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Use of a fluorescence-based approach to assess short-term responses of the alga Pseudokirchneriella subcapitata to metal stress

Publication . Machado, Manuela D.; Soares, Eduardo V.

This work explores the use of fluorescent probes to evaluate the responses of the green alga Pseudokirchneriella subcapitata to the action of three nominal concentrations of Cd(II), Cr(VI), Cu(II) and Zn(II) for a short time (6 h). The toxic effect of the metals on algal cells was monitored using the fluorochromes SYTOX Green (SG, membrane integrity), fluorescein diacetate (FDA, esterase activity) and rhodamine 123 (Rh123, mitochondrial membrane potential). The impact of metals on chlorophyll a (Chl a) autofluorescence was also evaluated. Esterase activity was the most sensitive parameter. At the concentrations studied, all metals induced the loss of esterase activity. SG could be used to effectively detect the loss of membrane integrity in algal cells exposed to 0.32 or 1.3 μmol L−1 Cu(II). Rh123 revealed a decrease in the mitochondrial membrane potential of algal cells exposed to 0.32 and 1.3 μmol L−1 Cu(II), indicating that mitochondrial activity was compromised. Chl a autofluorescence was also affected by the presence of Cr(VI) and Cu(II), suggesting perturbation of photosynthesis. In conclusion, the fluorescence-based approach was useful for detecting the disturbance of specific cellular characteristics. Fluorescent probes are a useful diagnostic tool for the assessment of the impact of toxicants on specific targets of P. subcapitata algal cells.

2015Journal article

Open access

Sensitivity of freshwater and marine green algae to three compounds of emerging concern

Publication . Machado, Manuela Dias; Soares, Eduardo V.

In this study, the toxicity of three compounds of emerging concern (CEC) belonging to different classes [metolachlor (herbicide), erythromycin (antibiotic) and triclosan (antiseptic)], were evaluated and compared using the freshwater alga Pseudokirchneriella subcapitata and the marine alga Dunaliella tertiolecta. Toxicity assays were performed by exposing algal cells, in exponential phase of growth, to the toxicants for 72 h (P. subcapitata) or 96 h (D. tertiolecta). The toxicant concentrations that induced an inhibition of 50% of algal growth (EC50) of P. subcapitata or D. tertiolecta were 118 and 11.3 × 103 μg L−1 for metolachlor (MTC), 38 and 5.75 × 103 μg L−1 for erythromycin (ERT) and 27.1 and 93 μg L−1 for triclosan (TCS), respectively. Based on these EC50 values, it was possible to hierarchize (decreasing order) the toxicity of the CEC studied: TCS > ERT > MTC. The EC50 values achieved for P. subcapitata were between 3.4- and 151-fold lower than those observed with D. tertiolecta, which demonstrated the higher sensitivity of the freshwater alga comparatively to the marine alga. All 72 h-EC10 or 72 h-EC50 values determined in this study with P. subcapitata are within the concentration range of these pollutants described in the literature, in ground and surface waters, which underlines the significance of this alga in the ecotoxicity assessment of freshwaters.

2018Journal article

Restricted access

Impact of erythromycin on a non-target organism: Cellular effects on the freshwater microalga Pseudokirchneriella subcapitata

Publication . Machado, Manuela Dias; Soares, Eduardo V.

The increasing and indiscriminate use of antibiotics is the origin of their introduction in aquatic systems through domestic and livestock effluents. The occurrence of erythromycin (ERY), a macrolide antibiotic, in water bodies raises serious concerns about its potential toxic effect in aquatic biota (non-target organisms), particularly in microalgae, the first organisms in contact with aquatic contaminants. This study aimed to evaluate the possible toxic effects of ERY on relevant cell targets of the freshwater microalga Pseudokirchneriella subcapitata. Algal cells incubated with significant environmental ERY concentrations presented disturbance of the photosynthetic apparatus (increased algal autofluorescence and reduction of chlorophyll a content) and mitochondrial function (hyperpolarization of mitochondrial membrane). These perturbations can apparently be attributed to the similarity of the translational machinery of these organelles (chloroplasts and mitochondria) with the prokaryotic cells. P. subcapitata cells treated with ERY showed a modification of metabolic activity (increased esterase activity) and redox state (alteration of intracellular levels of reactive oxygen species and reduced glutathione content) and an increased biovolume. ERY induced an algistatic effect: reduction of growth rate without loss of cell viability (plasma membrane integrity). The present study shows that chronic exposure (72 h), at low (μg L-1) ERY concentrations (within the range of concentrations detected in surface and ground waters), induce disturbances in the physiological state of the alga P. subcapitata. Additionally, this work alerts to the possible negative impact of the uncontrolled use of ERY on the aquatic systems.

2019Journal article

Restricted access