Effect of manganese and calcium deficiency on the growth and oxygen exchange of Scenedesmus intermedius cultured for successive generations

Quantitative structure-activity relationships for green algae growth inhibition by polymer particles

After use and disposal of chemical products, many types of polymer particles end up in the aquatic environment with potential toxic effects to primary producers like green algae. In this study, we have developed Quantitative Structure-Activity Relationships (QSARs) for a set of highly structural diverse polymers which are capable to estimate green algae growth inhibition (EC50). The model (N = 43, R² = 0.73, RMSE = 0.28) is a regression-based decision tree using one structural descriptor for each of three polymer classes separated based on charge. The QSAR is applicable to linear homo polymers as well as copolymers and does not require information on the size of the polymer particle or underlying core material. Highly branched polymers, non-nitrogen cationic polymers and polymeric surfactants are not included in the model and thus cannot be evaluated. The model works best for cationic and non-ionic polymers for which cellular adsorption, disruption of the cell wall and photosynthesis inhibition were the mechanisms of action. For anionic polymers, specific properties of the polymer and test characteristics need to be known for detailed assessment. The data and QSAR results for anionic polymers, when combined with molecular dynamics simulations indicated that nutrient depletion is likely the dominant mode of toxicity. Nutrient depletion in turn, is determined by the non-linear interplay between polymer charge density and backbone flexibility.

Use of lanthanides to alleviate the effects of metal ion-deficiency in Desmodesmus quadricauda (Sphaeropleales, Chlorophyta)

Lanthanides are biologically non-essential elements with wide applications in technology and industry. Their concentration as environmental contaminants is, therefore, increasing. Although non-essential, lanthanides have been proposed (and even used) to produce beneficial effects in plants, even though their mechanisms of action are unclear. Recently, it was suggested that they may replace essential elements. We tested the effect of low concentrations of lanthanides on the common freshwater microalga Desmodesmus quadricauda, grown under conditions of metal ion-deficiency (lower calcium or manganese concentrations). Our goal was to test if lanthanides can replace essential metals in their functions. Physiological stress was recorded by studying growth and photosynthetic activity using a pulse amplitude modulation (PAM) fluorimeter. We found that nutrient stress reduced parameters of growth and photosynthesis, such as maximal quantum yield, relative electron transport rate, photon capturing efficiency and light saturation irradiance. After adding low concentrations of five lanthanides, we confirmed that they can produce a stimulatory effect on microalgae, depending on the nutrient (metal) deprivation. In the case of a calcium deficit, the addition of lanthanides partly alleviated the adverse effects, probably by a partial substitution of the element. In contrast, with manganese deprivation (and at even lower concentrations), lanthanides enhanced the deleterious effect on cellular growth and photosynthetic competence. These results show that lanthanides can replace essential elements, but their effects on microalgae depend on stress and the nutritional state of the microalgae, raising the possibility of environmental impacts at even low concentrations.

Toxicological response of the green alga Scenedesmus bijuga to mercury and lead

Effect of mercury or lead on the growth, bioaccumulation and some enzyme activities of one of the most common algae in River Nile, Scenedesmus bijuga, was determined. The cell count and chlorophyll a content decreased with an increase in mercury or lead concentrations in a culture medium, particularly at higher doses. Higher mercury and lead uptake was observed with increasing concentration of the elements. The alga accumulated appreciably more mercury than lead. At higher doses, the two elements strongly suppressed some enzyme activities of primary S. bijuga metabolism.

Proline alleviates heavy metal stress in Scenedesmus armatus

Growth and some metabolic activities of Scenedesmus armatus grown in the presence of different heavy metals (Cd, Mn and Ni) with and without exogenously added proline (Pro) were monitored. The growth of S. armatus cells (cell concentration, pigment and dry mass) was inhibited by all these heavy metals. Addition of Pro to the culture medium minimized the toxic effect of the metals. The growth rate was somewhat higher in Pro-containing cultures and started to decline 1 d later than in cultures containing heavy metals alone. S. armatus cells accumulated the added Pro in response to heavy metals. The accumulation correlated with protein content. Cd was the strongest inducer of Pro accumulation, Mn being the weakest. Cells accumulated nickel more than cadmium and manganese. Heavy metal-treated cells had increased peroxidase and catalase activities.