Molecular Mechanisms in Ecotoxicology: An Interplay between Environmental Chemistry and Biology

A close collaboration between environmental chemistry and biological sciences is required for a complete understanding of ecotoxicological effects. Bioavailability and uptake of pollutants cannot be regarded as isolated chemical or biological questions. Knowledge of the effective concentrations in the organism or at the target site(s) is essential to link the fate and effects of a chemical and is a prerequisite for quantitative investigation of the modes of toxic action. These modes of action need to be unraveled using whole-organism or in vitro systems in order to be able to develop specific biomarkers and biosensors that can be applied as early warning systems. Our mode-of-action-based approaches, in which chemical and biological analytical tools are combined, should improve the understanding of ecotoxicological effects and should be implemented in the future in risk assessment

Characterization of extracellular polymeric substances (EPS) from periphyton using liquid chromatography-organic carbon detection-organic nitrogen detection (LC-OCD-OND)

A protocol was developed to extract, fractionate, and quantitatively analyze periphyton extracellular polymeric substances (EPS), which obtains both information on the molecular weight (M r) distribution and protein and polysaccharide content. The EPS were extracted from freshwater periphyton between July and December 2011. Organic carbon (OC) compounds from different EPS extracts were analyzed using liquid chromatography-organic carbon detection-organic nitrogen detection (LC-OCD-OND), and total protein and polysaccharide content were quantified. Four distinct OC fractions, on the basis of M r, were identified in all extracts, corresponding to high M r biopolymers (≥80-4kDa), degradation products of humic substances (M r not available), low M r acids (10-0.7kDa), and small amphiphilic/neutral compounds (3-0.5kDa). Low C/N ratios (4.3 ± 0.8) were calculated for the biopolymer fractions, which represented 16-38% of the measured dissolved organic carbon (DOC), indicating a significant presence of high M r proteins in the EPS. Protein and polysaccharide represented the two major components of EPS and, when combined, accounted for the measured DOC in extracts. Differences in specific OC fractions of EPS extracts over the course of the study could be quantified using this method. This study suggests that LC-OCD-OND is a new valuable tool in EPS characterization of periphyto

Function and regulation of the glutathione peroxidase homologous gene GPXH

When exposed to strong sunlight, photosynthetic organisms encounter photooxidative stress by the increased production of reactive oxygen species causing harmful damages to proteins and membranes. Consequently, a fast and specific induction of defense mechanisms is required to protect the organism from cell death. In Chlamydomonas reinhardtii, the glutathione peroxidase homologous gene GPXH/GPX5 was shown to be specifically upregulated by singlet oxygen formed during high light conditions presumably to prevent the accumulation of lipid hydroperoxides and membrane damage. We now showed that the GPXH protein is a thioredoxin-dependent peroxidase catalyzing the reduction of hydrogen peroxide and organic hydroperoxides. Furthermore, the GPXH gene seems to encode a dual-targeted protein, predicted to be localized both in the chloroplast and the cytoplasm, which is active with either plastidic TRXy or cytosolic TRXh1. Putative dual-targeting is achieved by alternative transcription and translation start sites expressed independently from either a TATA-box or an Initiator core promoter. Expression of both transcripts was upregulated by photooxidative stress even though with different strengths. The induction required the presence of the core promoter sequences and multiple upstream regulatory elements including a Sp1-like element and an earlier identified CRE/AP-1 homologous sequence. This element was further characterized by mutation analysis but could not be confirmed to be a consensus CRE or AP1 element. Instead, it rather seems to be another member of the large group of TGAC-transcription factor binding sites found to be involved in the response of different genes to oxidative stres

Environmental behavior and ecotoxicity of engineered nanoparticles to algae, plants, and fungi

Developments in nanotechnology are leading to a rapid proliferation of new materials that are likely to become a source of engineered nanoparticles (ENPs) to the environment, where their possible ecotoxicological impacts remain unknown. The surface properties of ENPs are of essential importance for their aggregation behavior, and thus for their mobility in aquatic and terrestrial systems and for their interactions with algae, plants and, fungi. Interactions of ENPs with natural organic matter have to be considered as well, as those will alter the ENPs aggregation behavior in surface waters or in soils. Cells of plants, algae, and fungi possess cell walls that constitute a primary site for interaction and a barrier for the entrance of ENPs. Mechanisms allowing ENPs to pass through cell walls and membranes are as yet poorly understood. Inside cells, ENPs might directly provoke alterations of membranes and other cell structures and molecules, as well as protective mechanisms. Indirect effects of ENPs depend on their chemical and physical properties and may include physical restraints (clogging effects), solubilization of toxic ENP compounds, or production of reactive oxygen species. Many questions regarding the bioavailability of ENPs, their uptake by algae, plants, and fungi and the toxicity mechanisms remain to be elucidate

Influence of Microplastics on Microbial Structure, Function, and Mechanical Properties of Stream Periphyton

Este artículo contiene 17 páginas, 5 figuras, 4 tablas.Periphyton is a freshwater biofilm composed of prokaryotic and eukaryotic communities that occupy rocks and sediments, forming the base of the food web and playing a key role in nutrient cycling. Given the large surface that periphyton comprises, it may also act as a sink for a diverse range of man-made pollutants, including microplastics (MP). Here we investigated the effect of 1–4 μm and 63–75 µm sized, spherical polyethylene MP with native and ultraviolet (UV)-weathered surface on developing natural stream periphyton communities over 28 days. In order to ensure proper particle exposure, we first tested MP suspension in water or in water containing either Tween 80, extracellular polymeric substances – EPS, fulvic acids, or protein. We found the extract of EPS from natural periphyton to be most suitable to create MP suspensions in preparation of exposure. Upon exposure, all tested types of MP were found to be associated with the periphyton, independent of their size and other properties. While biomass accrual and phenotypic community structure of the photoautotrophs remained unchanged, the prokaryotic and eukaryotic communities experienced a significant change in composition and relative abundances. Moreover, alpha diversity was affected in eukaryotes, but not in prokaryotes. The observed changes were more prominent in periphyton exposed to UV-treated as compared with native surface MP. Mechanical properties, as assessed by compression rheology, showed that MP-exposed periphyton had longer filamentous streamers, higher stiffness, lower force recovery and a higher viscoelasticity than control periphyton. Despite the observed structural and mechanical changes of periphyton, functional parameters (i.e., photosynthetic yield, respiration and nutrient uptake efficiencies) were not altered by MP, indicating the absence of MP toxicity, and suggesting functional redundancy in the communities. Together, our results provide further proof that periphyton is a sink for MP and demonstrate that MP can impact local microbial community composition and mechanical properties of the biofilms. Consequences of these findings might be a change in dislodgement behavior of periphyton, a propagation through the food chains and impacts on nutrient cycling and energy transfer. Hence, taking the omnipresence, high persistence and material and size diversity of MP in the aquatic environment into account, their ecological consequences need further investigation.The study was financially supported by the Velux foundation, project number 1039, Switzerland. Additional lab work was funded by Tailwind grant of Eawag Switzerland. Open access funding was provided by Eawag–Swiss Federal Institute of Aquatic Science And Technology.Peer reviewe

Influence of Microplastics on Microbial Structure, Function, and Mechanical Properties of Stream Periphyton

Periphyton is a freshwater biofilm composed of prokaryotic and eukaryotic communities that occupy rocks and sediments, forming the base of the food web and playing a key role in nutrient cycling. Given the large surface that periphyton comprises, it may also act as a sink for a diverse range of man-made pollutants, including microplastics (MP). Here we investigated the effect of 1-4 mu m and 63-75 mu m sized, spherical polyethylene MP with native and ultraviolet (UV)-weathered surface on developing natural stream periphyton communities over 28 days. In order to ensure proper particle exposure, we first tested MP suspension in water or in water containing either Tween 80, extracellular polymeric substances - EPS, fulvic acids, or protein. We found the extract of EPS from natural periphyton to be most suitable to create MP suspensions in preparation of exposure. Upon exposure, all tested types of MP were found to be associated with the periphyton, independent of their size and other properties. While biomass accrual and phenotypic community structure of the photoautotrophs remained unchanged, the prokaryotic and eukaryotic communities experienced a significant change in composition and relative abundances. Moreover, alpha diversity was affected in eukaryotes, but not in prokaryotes. The observed changes were more prominent in periphyton exposed to UV-treated as compared with native surface MP. Mechanical properties, as assessed by compression rheology, showed that MP-exposed periphyton had longer filamentous streamers, higher stiffness, lower force recovery and a higher viscoelasticity than control periphyton. Despite the observed structural and mechanical changes of periphyton, functional parameters (i.e., photosynthetic yield, respiration and nutrient uptake efficiencies) were not altered by MP, indicating the absence of MP toxicity, and suggesting functional redundancy in the communities. Together, our results provide further proof that periphyton is a sink for MP and demonstrate that MP can impact local microbial community composition and mechanical properties of the biofilms. Consequences of these findings might be a change in dislodgement behavior of periphyton, a propagation through the food chains and impacts on nutrient cycling and energy transfer. Hence, taking the omnipresence, high persistence and material and size diversity of MP in the aquatic environment into account, their ecological consequences need further investigation

Long-term effects of copper on the structure of freshwater periphyton communities and their tolerance to copper, zinc, nickel and silver. Aquatic Toxicology 47

Abstract A community adapted to elevated ambient levels of a particular pollutant is expected, compared to a non-exposed community, to display an increased tolerance to that pollutant. The potential of tolerance measurements as a method to detect metal-induced structural impacts at the community level is poorly known. Particularly, the determination of increased tolerance to various metals may confound conclusions related to the causes of the impact. In this study the effects of long-term copper exposure on the community structure of freshwater periphyton, and the short-term community tolerance of photosynthesis to copper, zinc, nickel and silver were determined. Using an outdoor flow-through aquaria system, we carried out long-term exposure of freshwater periphyton communities to copper (0, 0.05, 0.1, 0.5, 1 and 5 mM copper). After 12 weeks we examined how the copper exposure affected the taxonomic composition, photosynthesis rate and tolerance thereof to copper, zinc, nickel and silver. Effects included changes in the distribution of algal classes from a community dominated by Cyanophyceae to one dominated by Chlorophyta. The relative abundance of Oocystis nephrocytioides increased from less than 1% in the control aquaria to 56% in the 5 mM copper treatments. Except at the highest copper exposure, communities did not significantly differ in their photosynthesis rate, although the short-term tolerance of photosynthesis to metals was affected by the copper treatments. Significant increases in tolerance to copper were found in communities previously exposed to ] 0.1 mM copper concentrations. Communities exposed to copper also displayed an increased co-tolerance to zinc, nickel and silver. These observations suggest that copper-induced structural impacts on periphyton communities can be evidenced as an increased tolerance to copper. However, because of the occurrence of co-tolerance, the identification of the metals that have induced the structural and tolerance changes may require metal determinations in organisms

Effects of Differently Coated Silver Nanoparticles on the Photosynthesis of Chlamydomonas reinhardtii

Various factors have been invoked to explain the toxicity of silver nanoparticles (AgNP) to microorganisms including particle size and the nature of stabilizing coatings as well as the amount of dissolved silver occurring in AgNP suspensions. In this study we have assessed the effects of nine differently coated AgNP (chitosan, lactate, polyvinylpyrrolidone, polyethelene glycol, gelatin, sodium dodecylbenzenesulfonate, citrate, dexpanthenol, and carbonate) and AgNO3 on the photosynthesis of the freshwater algae Chlamydomonas reinhardtii. We have thus examined how AgNP effects on algae relate to particle size, measured dissolved silver (Agd), and bioavailable silver (Agbioav). Agbioav was indirectly estimated in toxicity experiments by cysteine–silver complexation at the EC50. The EC50 calculated as a function of measured Agd concentrations showed for some coatings values similar to that of dissolved Ag, whereas other coated AgNP displayed lower EC50 values. In all cases, excess cysteine completely prevented effects on photosynthetic yield, confirming the role of Agd as a cause of the observed effect on the photosynthesis. Toxicity was related neither to particle size nor to the coatings. For all differently coated AgNP suspensions, the EC50 values calculated as a function of Agbioav were comparable to the value of AgNO3. Depending on the coatings Agbioav was comparable to or higher than measured Agd.. © 2015 American Chemical Society.This work was supported by the Swiss Federal Institute of Aquatic Science and Technology (Eawag) and by the Spanish Ministry of Economy and Competitiveness (National Research Plan, (GALC-002/2011). Authors also thank Dr. Andreas Gondikas from the University of Vienna, for his helpful comments on silver-cysteine binding dynamics. The corresponding author also received a research stay grant from Programa Europa XXI from Caja Inmaculada.Peer Reviewe