Activation of stress reactions in the dinophyte microalga Prorocentrum cordatum as a consequence of the toxic effect of ZnO nanoparticles and zinc sulfate.

According to the results of the experimental study, the main regularities of changes in morphological, structural-functional and fluorescent indices of P. cordatum were established when zinc oxide nanoparticles ZnO NPs (0.3-6.4 mg L-1) and Zn in form of salt (0.09-0.4 mg L-1) were added to the medium. The studied pollutants have cytotoxic (growth inhibition, development of oxidative stress, destruction of cytoplasmic organelles, disorganization of mitochondria) and genotoxic (changes in the morphology of nuclei, chromatin condensation) effects on microalgae, affecting almost all aspects of cell functioning. Despite the similar mechanism of action of zinc sulfate and ZnO NPs on P. cordatum cells, the negative effect of ZnO NPs is also due to the inhibition of photosynthetic activity of cells (significant decrease in the maximum quantum yield of photosynthesis and electron transport rate), reduction of chlorophyll concentration from 3.5 to 1.8 pg cell-1, as well as mechanical effect on cells: deformation and damage of cell membranes, aggregation of NPs on the cell surface. Apoptosis-like signs of cell death upon exposure to zinc sulfate and ZnO NPs were identified by flow cytometry and laser scanning confocal microscopy methods: changes in cell morphology, cytoplasm retraction, development of oxidative stress, deformation of nuclei, and disorganization of mitochondria. It was shown that the first signs of cell apoptosis appear at 0.02 mg L-1 Zn and 0.6 mg L-1 ZnO NPs after 72 h of exposure. At higher concentrations of pollutants, a dose-dependent decrease in algal enzymatic activity (up to 5 times relative to control) and mitochondrial membrane potential (up to 4 times relative to control), and an increase in the production of reactive oxygen species (up to 4-5 times relative to control) were observed. The results of the presented study contribute to the disclosure of fundamental mechanisms of toxic effects of pollutants and prediction of ways of phototrophic microorganisms reaction to this impact.

Combined effect of light and glyphosate herbicide on growth rate of marine diatom algae.

The effect of glyphosate herbicide at concentrations of 25, 100, 150 and 200 µg.L-1 on growth characteristics of diatoms C. caspia and T. weissflogii under accumulative growth conditions was investigated. Increasing herbicide concentration in the medium resulted in growth suppression of both species and decreased the final abundance of the cultures in the stationary growth phase. The calculated concentrations of herbicide EC10 and EC50 (10 and 90 µg.L-1 for C. caspia and 7 and 25 µg·L-1 for T. weissflogii, respectively) led to a 10 and 50% reduction in the abundance of the studied cultures relative to the control, are ecologically significant and correspond to the values recorded in aquatic areas. The combined effect of light (in the range of 20-250 µE.m-2.s-1) and glyphosate (calculated concentrations of EC10 and EC50) on the growth characteristics of microalgae was evaluated. An increase in algal sensitivity to light was observed with glyphosate exposure. In both species, the increase in the concentration of glyphosate in the medium led to a decrease in the initial angle of slope of the light curve of growth under conditions of light limitation, a reduction in the value of light saturation of growth, narrowing of the boundaries of the light optimum and an increase in the degree of light inhibition. It is shown that the effect of the combined action of light and glyphosate exceeds the sum of the effects of each factor. This fact should be taken into account in ecotoxicological monitoring when assessing the risks of glyphosate ingress into aquatic ecosystems. An increase in glyphosate concentration in water during periods with high values of solar insolation is potentially dangerous due to a decrease in the photosynthetic activity of algae and a reduction in diatom algae abundance.

Physiological responses of the microalgae Thalassiosira weissflogii to the presence of the herbicide glyphosate in the medium.

We evaluated changes in growth, chlorophyll fluorescence and basic physiological and biochemical parameters of the microalgae Thalassiosira weissflogii cells under the influence of the herbicide glyphosate in concentrations 0, 25, 95 and 150µgL-1 . The toxic effect of glyphosate on algae is weakly dependent on the level of cell mineral nutrition. High concentrations of the herbicide do not lead to the death of microalgae but block the process of algae cell division. An increase in the glyphosate concentration in the medium leads to a slowdown or stop of algal growth, a decrease in their final biomass, an increase in the production of reactive oxygen species (ROS), depolarisation of mitochondrial membranes and metabolic activity of algae. Glyphosate inhibits the photosynthetic activity of cells and inhibits the relative rate of electron transport in the photosynthetic apparatus. Glyphosate at the studied concentrations does not affect the size characteristics of cells and the intracellular content of chlorophyll in T. weissflogii . The studied herbicide or products of its decay retain their toxic properties in the environment for at least 9days. This result shows the need for further in-depth studies to assess the physiological response and possible acclimation changes in the functional state of oxygenic phototrophs in response to the herbicide action. The species specificity of microalgae to the effects of glyphosate in natural conditions is potentially dangerous due to a possible change in the species structure of biocoenoses, in particular, a decrease in the contribution of diatoms.

Application of confocal microscopy and flow cytometry to identify physiological responses of Prorocentrum micans to the herbicide glyphosate.

The physiological response of the dinoflagellate P. micans to the effect of the herbicide glyphosate at a concentration of 25-200 µg L-1 was evaluated. It has been shown that P. micans is able to grow due to the consumption of dissolved organic phosphorus formed as a result of the mineralization of glyphosate by bacteria. The addition of glyphosate to the medium inhibits the photosynthetic activity of cells; there is a pronounced inhibition of the relative electron transfer rate along the electron transport chain and the maximum quantum efficiency of the use of light energy. Morphological and ultrastructural changes in P. micans cells were evaluated at sublethal (150 µg L-1) and lethal (200 µg L-1) glyphosate concentrations. It has been shown that at a herbicide concentration of 150 µg L-1, the first signs of apoptosis appear in most P. micans cells: a decrease in lateral light scattering, cytoplasmic retraction, partial destruction of cytoplasmic organelles, a change in the morphology of nuclei, mitochondria, a change in the potential of mitochondrial membranes, and a decrease in the autofluorescence of chlorophyll in cells. At a glyphosate concentration of 200 µg L-1, P. micans showed signs of a late stage of apoptosis: violation of the integrity of intracellular organelles and chromatin organization, fragmentation of nuclei, condensation of cytoplasm, disorganization of chloroplasts in the cells, and the release of cell contents beyond the cell membrane. The effectiveness of using flow cytometry and laser scanning confocal microscopy methods for identifying signs and stages of cell apoptosis when exposed to glyphosate is discussed.

The comprehensive effect of copper oxide nanoparticles on the physiology of the diatom microalga Thalassiosira weissflogii.

The high rate of production and use of copper oxide nanoparticles (CuO NPs) results in its accumulation in the environment. However, the effect of large quantities of CuO NPs on aquatic ecosystems is not fully known. In aquatic ecosystems, phytoplankton is the primary producer of organic matter and the basis of all the trophic interactions; accordingly, the potential effect of CuO NPs on the microalgae community is of great concern. This study established the main patterns of changes in morphological, structural, functional, fluorescent and cytometric parameters in the marine diatom Thalassiosira weissflogii after adding CuO NPs to the medium at concentrations of 250-2500µgL-1 . As shown, the investigated pollutant has cytotoxic, genotoxic and mechanical effect on the microalga covering almost all the aspects of cell functioning. A two-fold decrease in the culture abundance relative to the control is observed at the toxicant content of 550µgL-1 in the medium. At CuO NPs content above 750µgL-1 , a pronounced inhibition of the alga growth is recorded, as well as a decrease in the efficiency of its photosynthetic apparatus, a disturbance of membrane integrity, an increase in cell volume, a rise in abundance of dead/inactive cells in the culture, enlargement and deformation of nuclei, an increase in reactive oxygen species production, and depolarisation of the mitochondrial membrane. Our results show that high CuO NPs concentrations in water can cause serious disruptions in phytoplankton functioning and in equilibrium of aquatic ecosystems in general.