Effect of copper exposure on gene expression profiles in Chlamydomonas reinhardtii based on microarray analysis

Insertional mutagenesis of AIDA or CYP720B1 in the green alga Chlamydomonas reinhardtii confers copper(II) tolerance and increased biomass

The widespread use of copper (Cu) in industrial and agricultural settings leads to the accumulation of excess Cu within aquatic ecosystems, posing a threat to organism health. Microalgal bioremediation has emerged as a popular and promising solution to mitigate the risks. Nevertheless, the genetic underpinnings and engineering tactics involved in heavy metal bioremediation by microalgae remain inadequately elucidated. In this study, two mutants obtained from screening a Chlamydomonas reinhardtii (C. reinhardtii) mutant library were identified as insertional mutagenesis in the AIDA (Cre12.g487450) and CYP720B1 (Cre10.g426700) genes. Interestingly, these two mutants exhibited decreased cell size and ciliary length but increased cell growth rates. Under Cu(II) stress, the AIDA and CYP720B1 mutants presented dose-dependent tolerance to Cu(II), resulting in increased biomass and improved cellular morphology. Furthermore, the analysis for the antioxidant system suggested that increased Cu(II) tolerance was associated with a low-level response strategy to Cu(II) stress. Transmission electron microscopy images also revealed increased stress-related organelles (starch granules, acidocalcisomes, and plastoglobules) in these two mutants. Considering the excellent Cu(II) tolerance and biomass of these two mutants, our findings provide potential microalgal strains for further genetic modifications and performance mining to improve aquatic Cu(II) bioremediation through biomass enhancement.

Integration of Copper Toxicity Mechanisms in Raphidocelis subcapitata: Advancing Insights at Environmentally Relevant Concentrations

This work aimed to characterize the impact of copper (Cu), at environmentally relevant concentrations, using the freshwater microalga Raphidocelis subcapitata. Algae were incubated with 33 or 53 µg/L Cu, in OECD medium, and toxic impacts were evaluated over 72 h, using different cellular and biochemical biomarkers. The exposure to 33 µg/L Cu had an algistatic effect: slowing growth and reducing algal population (53%, at 72 h) without compromising the cell membrane. This Cu concentration promoted a transient reduction in chlorophyll a (chla) content and typical markers of oxidative stress: increased levels of reactive oxygen species (ROS), augmented catalase (CAT) activity, and lipid peroxidation (malondialdehyde, MDA). Algae exposed to 53 µg/L Cu, suffered a severe effect with a 93% reduction in the number of cells, 50% decrease in chla content, and diminished (17%) maximum photochemical quantum yield of PSII (Fv/Fm). This population also presented increased levels of ROS and MDA, 33 and 20 times higher than the control, respectively, at 72 h, augmented CAT activity, and permeabilized cell membrane (5%, at 72 h). These findings provide valuable insights into Cu toxicity in aquatic ecosystems, highlighting the biochemical and physiological impacts at environmentally relevant concentrations.

Differentiation between chemo- and radiotoxicity of 137Cs and 60Co on Lemna minor

The uptake and effects of stable Cs and Co on L.minor were extensively studied, together with the effects of gamma radiation using a 137Cs or 60Co source. Innovative is that we combined external irradiation (from 137Cs or 60Co sources) with the direct uptake of certain amounts of stable Cs or Co to simulate the impact of the same mass of a radioisotope compared with that of the stable element. Such approach allows to differentiate between chemo- and radiotoxicity of 137Cs or 60Co, permitting to study the 137Cs and 60Co uptake by L. minor without using high concentrations of these elements in solution. Our results indicate that radiotoxicity of both 137Cs and 60Co has a greater importance compared to their chemotoxicity. This was also supported by the independent action and concentration addition concepts. Both concepts resulted in a good prediction of the dose-response curve of the combination exposure. The maximal removal of 137Cs or 60Co per gram dry matter of L. minor was lower compared with the removal of the corresponding stable isotope. The toxicity of 60Co was higher compared to 137Cs based on EC50 values and uptake data. With respect to the effects on photosynthetic pigments, starch and soluble sugars contents, only starch increased in a concentration- and dose-dependent manner.

Palmelloid Formation and Cell Aggregation Are Essential Mechanisms for High Light Tolerance in a Natural Strain of Chlamydomonas reinhardtii

Photosynthetic organisms, such as higher plants and algae, require light to survive. However, an excessive amount of light can be harmful due to the production of reactive oxygen species (ROS), which cause cell damage and, if it is not effectively regulated, cell death. The study of plants' responses to light can aid in the development of methods to improve plants' growth and productivity. Due to the multicellular nature of plants, there may be variations in the results based on plant age and tissue type. Chlamydomonas reinhardtii, a unicellular green alga, has also been used as a model organism to study photosynthesis and photoprotection. Nonetheless, the majority of the research has been conducted with strains that have been consistently utilized in laboratories and originated from the same source. Despite the availability of many field isolates of this species, very few studies have compared the light responses of field isolates. This study examined the responses of two field isolates of Chlamydomonas to high light stress. The light-tolerant strain, CC-4414, managed reactive oxygen species (ROS) slightly better than the sensitive strain, CC-2344, did. The proteomic data of cells subjected to high light revealed cellular modifications of the light-tolerant strain toward membrane proteins. The morphology of cells under light stress revealed that this strain utilized the formation of palmelloid structures and cell aggregation to shield cells from excessive light. As indicated by proteome data, morphological modifications occur simultaneously with the increase in protein degradation and autophagy. By protecting cells from stress, cells are able to continue to upregulate ROS management mechanisms and prevent cell death. This is the first report of palmelloid formation in Chlamydomonas under high light stress.

Heavy metal-induced stress in eukaryotic algae-mechanisms of heavy metal toxicity and tolerance with particular emphasis on oxidative stress in exposed cells and the role of antioxidant response

Heavy metals is a collective term describing metals and metalloids with a density higher than 5 g/cm3. Some of them are essential micronutrients; others do not play a positive role in living organisms. Increased anthropogenic emissions of heavy metal ions pose a serious threat to water and land ecosystems. The mechanism of heavy metal toxicity predominantly depends on (1) their high affinity to thiol groups, (2) spatial similarity to biochemical functional groups, (3) competition with essential metal cations, (4) and induction of oxidative stress. The antioxidant response is therefore crucial for providing tolerance to heavy metal-induced stress. This review aims to summarize the knowledge of heavy metal toxicity, oxidative stress and antioxidant response in eukaryotic algae. Types of ROS, their formation sites in photosynthetic cells, and the damage they cause to the cellular components are described at the beginning. Furthermore, heavy metals are characterized in more detail, including their chemical properties, roles they play in living cells, sources of contamination, biochemical mechanisms of toxicity, and stress symptoms. The following subchapters contain the description of low-molecular-weight antioxidants and ROS-detoxifying enzymes, their properties, cellular localization, and the occurrence in algae belonging to different clades, as well as the summary of the results of the experiments concerning antioxidant response in heavy metal-treated eukaryotic algae. Other mechanisms providing tolerance to metal ions are briefly outlined at the end.

Heavy metal detoxification mechanisms by microalgae: Insights from transcriptomics analysis

Heavy metal pollution in ecosystem is a global threat. The associated toxicity and carcinogenic nature of heavy metals/metalloids such as mercury, cadmium, lead, and arsenic are imposing a severe risk to both ecological diversity and human lives. Harnessing the adaptive feature of microalgae for remediating toxic heavy metal has reached a milestone in past few decades. Transcriptomics analyses have provided mechanistic insights to map the dynamics of cellular events under heavy metal stress, thus deciphering the strategic responses of microalgae. Here, the present review comprehensively addresses the elicited molecular responses of microalgae to detoxify the heavy metal stress. The review highlights the intricate role of biochemical components and signaling networks mediating stress responsive transitions of microalgae at physiological level. Furthermore, the differential gene expression signifying the transporters involved in uptake, distribution/sequestration, and efflux of heavy metal has also been reviewed. In a nutshell, this study provided a comprehensive understanding of the molecular mechanisms adopted by microalgae at transcriptome level to nullify the oxidative stress while detoxifying the heavy metals.

Adverse physiological and molecular level effects of polystyrene microplastics on freshwater microalgae

Microplastics have aroused widespread concern because of their adverse effects on aquatic organisms. However, the underlying toxicity mechanisms have not been examined in detail. This study investigated the interactions between polystyrene microplastics (PS-MPs) and the model freshwater microalgae Euglena gracilis. The results of transmission electron microscopy showed that the vacuoles of microalgae were induced after 24 h exposure to 1 mg/L PS-MPs (5 μm and 0.1 μm). Furthermore, PS-MPs significantly (p < 0.05) reduced pigment contents. Moreover, superoxide dismutase activities were significantly (p < 0.05) induced in all PS-MPs treated groups. Peroxidase activities were also significantly (p < 0.05) affected by two sizes of PS-MPs (5 μm and 0.1 μm), indicating that oxidative stress was induced after exposure to PS-MPs. At the molecular level, PS-MPs dysregulated the expression of genes involved in cellular processes, genetic information processing, organismal systems, and metabolisms. The KCS gene and the CTR1 gene may be key pathways to induce adverse effects on the E. gracilis after exposure to 5 μm PS-MPs. These findings will help to elucidate the underlying molecular mechanism of microplastics toxicity on freshwater organisms.

Metabolome response to anthropogenic contamination on microalgae: a review

BACKGROUND

Microalgae play a key role in ecosystems and are widely used in ecological status assessment. Research focusing on such organisms is then well developed and essential. Anyway, approaches for a better comprehension of their metabolome's response towards anthropogenic stressors are only emerging.

AIM OF REVIEW

This review presents the biochemical responses of various microalgae species towards several contaminants including metals and chemicals as pesticides or industrial compounds. We aim to provide a comprehensive and up-to-date overview of analytical approaches deciphering anthropogenic contaminants impact on microalgae metabolome dynamics, in order to bring out relevant biochemical markers that could be used for risk assessment.

KEY SCIENTIFIC CONCEPTS OF REVIEW

Studies to date on ecotoxicological metabolomics on microalgae are highly heterogeneous in both analytical techniques and resulting metabolite identification. There is a real need for studies using complementary approaches to determine biomarkers usable for ecological risk assessment.

The effects of copper on photosynthesis and biomolecules yield in Chlorolobion braunii

Our knowledge of the effects of copper on microalgal physiology is largely based on studies conducted with high copper concentrations; much less is known when environmentally relevant copper levels come into question. Here, we evaluated the physiology of Chlorolobion braunii exposed to free copper ion concentrations between 5.7 × 10^-9 and 5.0 × 10^-6  mol · L^-1 , thus including environmentally relevant values. Population growth and maximum photosynthetic quantum yield of PSII were determined daily during the 96 h laboratory controlled experiment. Exponentially-growing cells (48 h) were analyzed for effective quantum yield and rapid light curves (RLC), and total lipids, proteins, carbohydrates, chlorophyll a and carotenoids were determined. The results showed that growth rates and population density decreased gradually as copper increased in experiment, but the photosynthetic parameters (maximum and effective quantum yields) and photochemical quenching (qP) decreased only at the highest free copper concentration tested (5.0 × 10^-6 mol · L^-1 ); nonphotochemical quenching (NPQ) increased gradually with copper increase. The RLC parameters Ek and rETRmax were inversely proportional to copper concentration, while α and Im decreased only at 5.0 × 10^-6 mol · L^-1 . The effects of copper in biomolecules yield (mg · L^-1 ) varied depending on the biomolecule. Lipid yield increased at free copper concentration as low as 2.5 × 10^-8 mol · L^-1 , but proteins and carbohydrates were constant throughout.

When Unity Is Strength: The Strategies Used by Chlamydomonas to Survive Environmental Stresses

The unicellular green alga Chlamydomonas reinhardtii is a valuable model system to study a wide spectrum of scientific fields, including responses to environmental conditions. Most studies are performed under optimal growth conditions or under mild stress. However, when environmental conditions become harsher, the behavior of this unicellular alga is less well known. In this review we will show that despite being a unicellular organism, Chlamydomonas can survive very severe environmental conditions. To do so, and depending on the intensity of the stress, the strategies used by Chlamydomonas can range from acclimation to the formation of multicellular structures, or involve programmed cell death.

Comparative study of Cu uptake and early transcriptome responses in the green microalga Chlamydomonas reinhardtii and the macrophyte Elodea nuttallii

Microalgae are widely used as representative primary producers in ecotoxicology, while macrophytes are much less studied. Here we compared the bioavailability and cellular toxicity pathways of 2 h-exposure to 10^-6 mol L^-1 Cu in the macrophyte Elodea nuttallii and the green microalga Chlamydomonas reinhardtii. Uptake rate was similar but faster in the algae than in the macrophyte, while RNA-Sequencing revealed a similar number of regulated genes. Early-regulated genes were congruent with expected adverse outcome pathways for Cu with Gene Ontology terms including gene regulation, energy metabolism, transport, cell processes, stress, antioxidant metabolism and development. However, the gene regulation level was higher in E. nuttallii than in C. reinhardtii and several categories were more represented in the macrophyte than in the microalga. Moreover, several categories including oxidative pentose phosphate pathway (OPP), nitrate metabolism and metal handling were only found for E. nuttallii, whereas categories such as cell motility, polyamine metabolism, mitochondrial electron transport and tricarboxylic acid cycle (TCA) were unique to C. reinhardtii. These differences were attributed to morphological and metabolic differences and highlighted dissimilarities between a sessile and a mobile species. Our results highlight the efficiency of transcriptomics to assess early molecular responses in biota, and the importance of studying more aquatic plants for a better understanding on the impact and fate of environmental contaminants.

Improved Algal Toxicity Test System for Robust Omics-Driven Mode-of-Action Discovery in Chlamydomonas reinhardtii

Algae are key components of aquatic food chains. Consequently, they are internationally recognised test species for the environmental safety assessment of chemicals. However, existing algal toxicity test guidelines are not yet optimized to discover molecular modes of action, which require highly-replicated and carefully controlled experiments. Here, we set out to develop a robust, miniaturised and scalable Chlamydomonas reinhardtii toxicity testing approach tailored to meet these demands. We primarily investigated the benefits of synchronised cultures for molecular studies, and of exposure designs that restrict chemical volatilisation yet yield sufficient algal biomass for omics analyses. Flow cytometry and direct-infusion mass spectrometry metabolomics revealed significant and time-resolved changes in sample composition of synchronised cultures. Synchronised cultures in sealed glass vials achieved adequate growth rates at previously unachievably-high inoculation cell densities, with minimal pH drift and negligible chemical loss over 24-h exposures. Algal exposures to a volatile test compound (chlorobenzene) yielded relatively high reproducibility of metabolic phenotypes over experimental repeats. This experimental test system extends existing toxicity testing formats to allow highly-replicated, omics-driven, mode-of-action discovery.

Triclosan-induced transcriptional and biochemical alterations in the freshwater green algae Chlamydomonas reinhardtii

Triclosan (TCS) is an antibacterial and antifungal agent widely used in personal care products (PCPs). We investigated the effects of TCS (20μg/L, 100μg/L and 500μg/L) on Chlamydomonas reinhardtii by measuring the algal growth, chlorophyll content, lipid peroxidation, and transcription of the antioxidant-related genes (superoxide dismutase (SOD), glutathione peroxidase (GPX), catalase (CAT), glutathione S-transferase (GST), plastid terminal oxidase 2 (PTOX) and thioredoxin (TRX)) as well as biochemical alterations. The results showed significant dose-related effects of TCS on the algal species in terms of growth and chlorophyll content. Malondialdehyde (MDA) increased with increasing TCS concentrations and showed significant difference between the treatment of 405.3μg/L TCS and control group. Transcription analysis revealed that the expression of SOD mRNA was most sensitive to TCS among the selected genes. In addition, Fourier-transform infrared spectroscopy showed time- and concentration-specific biochemical responses in C. reinhardtii when exposed to TCS. The biochemical alterations associated with different doses of TCS were mainly attributed to structural changes associated with lipid, protein, nucleic acid and carbohydrate. The findings from this study reveal that TCS in the aquatic environment may affect algal growth, chlorophyll synthesis, oxidative stress responses and cause biochemical alterations. This study provided important information to achieve a better understanding of the toxic mechanism of triclosan on algae Chlamydomonas reinhardtii.

Photosynthetic and transcriptional responses of the marine diatom Thalassiosira pseudonana to the combined effect of temperature stress and copper exposure

A 96-h exposure experiment was conducted to elucidate the toxicity responses of the marine diatom Thalassiosira pseudonana upon exposure to different temperatures and copper (Cu) concentrations. Three Cu treatments (seawater control; 200μg/L Cu, EC₅₀ for the yield at 25°C; and 1000μg/L Cu, EC₅₀ for growth inhibition at 25°C) were conducted against four temperatures (10°C, 15°C, 25°C and 30°C). Growth rate and photosynthetic responses showed a significant interacting thermal-chemical effect with strong synergistic responses observed at 30°C treatments. Expression of heat shock protein (hsp) was positively modulated by increasing temperatures. Hsp 90, hsp90-2 and sit1 (related to silica shell formation) were highly expressed at 30°C under 1000μg/L Cu, while the genes encoding light harvesting proteins (3HfcpA and 3HfcpB) and silaffin precursor sil3 were significantly up-regulated at 15°C under 200μg/L Cu. Our results indicated an increase Cu toxicity to T. pseudonana under high temperature and Cu dose.

Towards elucidation of the toxic mechanism of copper on the model green alga Chlamydomonas reinhardtii

Toxic effects of copper on aquatic organisms in polluted water bodies have garnered particular attention in recent years. Microalgae play an important role in aquatic ecosystems, and they are sensitive to heavy metal pollution. Thus, it is important to clarify the mechanism of copper toxicity first for ecotoxicology studies. In this study, the physiological, biochemical and gene expression characteristics of a model green microalga, Chlamydomonas reinhardtii, with 0, 50, 150 and 250 μM copper treatments were investigated. The response of C. reinhardtii to copper stress was significantly shown at a dose dependent manner. Inhibition of cell growth and variation of total chlorophyll content were observed with copper treatments. The maximum photochemical efficiency of PSII, actual photochemical efficiency of PSII and photochemical quenching value decreased in the 250 μM copper treatment with minimum values equal to 28, 24 and 60 % of the control values respectively. The content of lipid peroxidation biomarker malondialdehyde with copper treatments increased with a maximum value sevenfold higher than the control value. Inhibition of cell growth and photosynthesis was ascribed to peroxidation of membrane lipids. The glutathione content and activities of antioxidant enzymes, glutathione S-transferase, glutathione peroxidase, superoxide dismutase and peroxidase were induced by copper. Interestingly, the expression of antioxidant genes and the photosynthetic gene decreased in most copper treatments. In conclusion, oxidative stress caused by production of excess reactive oxidative species might be the major mechanism of copper toxicity on C. reinhardtii.

Transcriptomic and Physiological Responses of the Green Microalga Chlamydomonas reinhardtii during Short-Term Exposure to Subnanomolar Methylmercury Concentrations

The effects of short-term exposure to subnanomolar methyl-mercury (MeHg) concentrations, representative of contaminated environments, on the microalga Chlamydomonas reinhardtii were assessed using both physiological end points and gene expression analysis. MeHg bioaccumulated and induced significant increase of the photosynthesis efficiency, while the algal growth, oxidative stress, and chlorophyll fluorescence were unaffected. At the molecular level, MeHg significantly dysregulated the expression of genes involved in motility, energy metabolism, lipid metabolism, metal transport, and antioxidant enzymes. Data suggest that the cells were able to cope with subnanomolar MeHg exposure, but this tolerance resulted in a significant cost to the cell energy and reserve metabolism as well as ample changes in the nutrition and motility of C. reinhardtii. The present results allowed gaining new insights on the effects and uptake mechanisms of MeHg at subnanomolar concentrations in aquatic primary producers.

Genome-wide analysis of transcription and photosynthesis inhibition in the harmful dinoflagellate Prorocentrum minimum in response to the biocide copper sulfate

Copper is an essential trace metal for organisms; however, excess copper may damage cellular processes. Their efficiency and physiological effects of biocides have been well documented; however, molecular transcriptome responses to biocides are insufficiently studied. In the present study, a 6.0K oligonucleotide chip was developed to investigate the molecular responses of the harmful dinoflagellate Prorocentrum minimum to copper sulfate (CuSO₄) treatment. The results revealed that 515 genes (approximately 8.6%) responded to CuSO₄, defined as being within a 2-fold change. Further, KEGG pathway analysis showed that differentially expressed genes (DEGs) were involved in ribosomal function, RNA transport, carbon metabolism, biosynthesis of amino acids, photosystem maintenance, and other cellular processes. Among the DEGs, 49 genes were related to chloroplasts and mitochondria. Furthermore, the genes involved in the RAS signaling pathway, MAPK signaling pathway, and transport pathways were identified. An additional experiment showed that the photosynthesis efficiency decreased considerably, and reactive oxygen species (ROS) production increased in P. minimum after CuSO₄ exposure. These results suggest that CuSO₄ caused cellular oxidative stress in P. minimum, affecting the ribosome and mitochondria, and severely damaged the photosystem. These effects may potentially lead to cell death, although the dinoflagellate has developed a complex signal transduction process to combat copper toxicity.

CrGNAT gene regulates excess copper accumulation and tolerance in Chlamydomonas reinhardtii

Excess copper (Cu) in environment affects the growth and metabolism of plants and green algae. However, the molecular mechanism for regulating plant tolerance to excess Cu is not fully understood. Here, we report a gene CrGNAT enconding an acetyltransferase in Chlamydomonas reinhardtii and identified its role in regulating tolerance to Cu toxicity. Expression of CrGNAT was significantly induced by 75-400μM Cu. The top induction occurred at 100μM. Transgenic algae overexpressing CrGNAT (35S::CrGNAT) in C. reinhardtii showed high tolerance to excess Cu, with improved cell population, chlorophyll accumulation and photosynthesis efficiency, but with low degree of oxidation with regard to reduced hydrogen peroxide, lipid peroxides and non-protein thiol compounds. In contrast, CrGNAT knock-down lines with antisense led to sensitivity to Cu stress. 35S::CrGNAT algae accumulated more Cu and other metals (Zn, Fe, Cu, Mn and Mg) than wild-type, whereas the CrGNAT down-regulated algae (35S::AntiCrGNAT) had moderate levels of Cu and Mn, but no effects on Zn, Fe and Mg accumulation as compared to wild-type. The elevated metal absorption in CrGNAT overexpression algae implies that the metals can be removed from water media. Quantitative RT-PCR analysis revealed that expression of two genes encoding N-lysine histone methyltransferases was repressed in 35S::CrGNAT algae, suggesting that CrGNAT-regulated algal tolerance to Cu toxicity is likely associated with histone methylation and chromatin remodeling. The present work provided an example a basis to develop techniques for environmental restoration of metal-contaminated aquatic ecosystems.

Responses of the alga Pseudokirchneriella subcapitata to long-term exposure to metal stress

The green alga Pseudokirchneriella subcapitata has been widely used in ecological risk assessment, usually based on the impact of the toxicants in the alga growth. However, the physiological causes that lead algal growth inhibition are not completely understood. This work aimed to evaluate the biochemical and structural modifications in P. subcapitata after exposure, for 72 h, to three nominal concentrations of Cd(II), Cr(VI), Cu(II) and Zn(II), corresponding approximately to 72 h-EC10 and 72 h-EC50 values and a high concentration (above 72 h-EC90 values). The incubation of algal cells with the highest concentration of Cd(II), Cr(VI) or Cu(II) resulted in a loss of membrane integrity of ~16, 38 and 55%, respectively. For all metals tested, an inhibition of esterase activity, in a dose-dependent manner, was observed. Reduction of chlorophyll a content, decrease of maximum quantum yield of photosystem II and modification of mitochondrial membrane potential was also verified. In conclusion, the exposure of P. subcapitata to metals resulted in a perturbation of the cell physiological status. Principal component analysis revealed that the impairment of esterase activity combined with the reduction of chlorophyll a content were related with the inhibition of growth caused by a prolonged exposure to the heavy metals.

Activation of Autophagy by Metals in Chlamydomonas reinhardtii

Autophagy is an intracellular self-degradation pathway by which eukaryotic cells recycle their own material in response to specific stress conditions. Exposure to high concentrations of metals causes cell damage, although the effect of metal stress on autophagy has not been explored in photosynthetic organisms. In this study, we investigated the effect of metal excess on autophagy in the model unicellular green alga Chlamydomonas reinhardtii. We show in cells treated with nickel an upregulation of ATG8 that is independent of CRR1, a global regulator of copper signaling in Chlamydomonas. A similar effect on ATG8 was observed with copper and cobalt but not with cadmium or mercury ions. Transcriptome sequencing data revealed an increase in the abundance of the protein degradation machinery, including that responsible for autophagy, and a substantial overlap of that increased abundance with the hydrogen peroxide response in cells treated with nickel ions. Thus, our results indicate that metal stress triggers autophagy in Chlamydomonas and suggest that excess nickel may cause oxidative damage, which in turn activates degradative pathways, including autophagy, to clear impaired components and recover cellular homeostasis.

Antagonistic and synergistic effects of light irradiation on the effects of copper on Chlamydomonas reinhardtii

The present study showed the important role of light intensity and spectral composition on Cu uptake and effects on green alga Chlamydomonas reinhardtii. High-intenisty light (HL) increased cellular Cu concentrations, but mitigated the Cu-induced decrease in chlorophyll fluorescence, oxidative stress and lipid peroxidation at high Cu concentrations, indicating that Cu and HL interact in an antagonistic manner. HL up-regulated the transcription of genes involved in the antioxidant response in C. reinhardtii and thus reduced the oxidative stress upon exposure to Cu and HL. Combined exposure to Cu and UVBR resulted in an increase of cellular Cu contents and caused severe oxidative damage to the cells. The observed effects were higher than the sum of the effects corresponding to exposure to UVBR or Cu alone suggesting a synergistic interaction.

Global transcriptional profiles of the copper responses in the cyanobacterium Synechocystis sp. PCC 6803

Copper is an essential element involved in fundamental processes like respiration and photosynthesis. However, it becomes toxic at high concentration, which has forced organisms to control its cellular concentration. We have recently described a copper resistance system in the cyanobacterium Synechocystis sp. PCC 6803, which is mediated by the two-component system, CopRS, a RND metal transport system, CopBAC and a protein of unknown function, CopM. Here, we report the transcriptional responses to copper additions at non-toxic (0.3 µM) and toxic concentrations (3 µM) in the wild type and in the copper sensitive copR mutant strain. While 0.3 µM copper slightly stimulated metabolism and promoted the exchange between cytochrome c6 and plastocyanin as soluble electron carriers, the addition of 3 µM copper catalyzed the formation of ROS, led to a general stress response and induced expression of Fe-S cluster biogenesis genes. According to this, a double mutant strain copRsufR, which expresses constitutively the sufBCDS operon, tolerated higher copper concentration than the copR mutant strain, suggesting that Fe-S clusters are direct targets of copper toxicity in Synechocystis. In addition we have also demonstrated that InrS, a nickel binding transcriptional repressor that belong to the CsoR family of transcriptional factor, was involved in heavy metal homeostasis, including copper, in Synechocystis. Finally, global gene expression analysis of the copR mutant strain suggested that CopRS only controls the expression of copMRS and copBAC operons in response to copper.

The antidepressant drug carbamazepine induces differential transcriptome expression in the brain of Atlantic salmon, Salmo salar

Concerns are being expressed recently over possible environmental effects of human pharmaceuticals. Although the likelihood of acute toxicity is low, the continuous discharge of pharmaceuticals into the aquatic environment means that sublethal effects on non-target organisms need to be seriously considered. One-year-old Atlantic salmon parr were exposed to 7.85±0.13μgL(-1) of the antidepressant drug Carbamazepine (CBZ) for five days to investigate changes of mRNA expression in the brain by means of a custom 17k Atlantic salmon cDNA microarray. The selected concentration is similar to upper levels that can be found in hospital and sewage treatment plant effluents. After treatment, 373 features were differently expressed with 26 showing up- or down-regulation of ≥2-fold (p≤0.05). Among the mRNAs showing the highest change were the pituitary hormones encoding features somatolactin, prolactin and somatotropin, or growth hormone. Functional enrichment and network analyses of up- and down-regulated genes showed that CBZ induced a highly different gene expression profile in comparison to untreated organisms. CBZ induced expression of essential genes of the focal adhesion and extracellular matrix - receptor interaction pathways most likely through integrin alpha-6 (itga6) activation. Negative regulation of apoptotic process, extracellular matrix organization and heme biosynthesis were the most enriched biological process related GO-terms, with the simultaneous enrichment of collagen and extracellular region related cellular component GO-terms, and extracellular matrix structural constituent, hormone activity and chromatin binding molecular function related GO-terms. These results show that relatively low doses of CBZ may affect brain physiology in exposed salmon parr, targeting similar processes as in human, indicating a high degree of conservation of targets of CBZ action. However, and since the mRNAs showing most changes in expression are critical for adaptation to different stressors and life history transitions in Atlantic salmon, more research should be undertaken to assess CBZ effects to avoid impairment of normal development and maintenance of natural populations.

Using transcriptomic profiles in the diatom Phaeodactylum tricornutum to identify and prioritize stressors

The transcriptomic profile of the marine diatom, Phaeodactylum tricornutum, exposed to several ecologically relevant stressors, was used to develop toxicity identification evaluation (TIE)-like gene expression assays. Algal growth inhibition was measured by flow cytometry to determine exposure concentrations that elicited a sublethal toxic response. P. tricornutum was exposed to concentrations of copper (2 μg L⁻¹), cadmium (5 μg L⁻¹), silver (20 μg L⁻¹), simazine (75 μg L⁻¹), the water accommodated fraction (WAF) of weathered crude oil (5 mg L⁻¹), 50 μg L⁻¹ ammonia, a decreased salinity treatment (15‰), and a mixture exposure of ammonia, decreased salinity and cadmium (10 μg L⁻¹). Analysis of the gene expression via microarray indicated that unique transcriptomic signals were generated for each of the individual treatments. Transcriptomic profiles of ammonia and the mixture treatment overlapped substantially. Photosynthesis related transcripts were altered in the simazine (herbicide) treatment. A transcript involved in degrading hydrocarbons, dioxygenase, had increased abundance after crude oil exposure. Overall, transcriptomic responses in the different treatments were associated with stress responses, membrane transport, transcription and translation and could be linked to contaminant mode of action. The transcriptomic profiles were used to design real-time (quantitative) polymerase chain reaction (qPCR) assays that would link changes in transcript abundance to a particular stressor in a TIE-based approach. At least one transcript for each contaminant tested (copper, cadmium, silver, salinity and ammonia) responded exclusively to that contaminant. With further development of additional transcriptomic markers for each contaminant, this new approach has potential to enhance traditional toxicology bioassays by providing additional lines of evidence to identify biologically relevant stressors within a contaminated ecosystem based on changes in the transcriptomic profile.

Transcriptome sequencing (RNA-seq) analysis of the effects of metal nanoparticle exposure on the transcriptome of Chlamydomonas reinhardtii

The widespread use of nanoparticles (NPs) raises concern over their potential toxicological effects in humans and ecosystems. Here we used transcriptome sequencing (RNA-seq) to evaluate the effects of exposure to four different metal-based NPs, nano-Ag (nAg), nano-TiO2 (nTiO2), nano-ZnO (nZnO), and CdTe/CdS quantum dots (QDs), in the eukaryotic green alga Chlamydomonas reinhardtii. The transcriptome was characterized before and after exposure to each NP type. Specific toxicological effects were inferred from the functions of genes whose transcripts either increased or decreased. Data analysis resulted in important differences and also similarities among the NPs. Elevated levels of transcripts of several marker genes for stress were observed, suggesting that only nZnO caused nonspecific global stress to the cells under environmentally relevant conditions. Genes with photosynthesis-related functions were decreased drastically during exposure to nTiO2 and slightly during exposures to the other NP types. This pattern suggests either toxicological effects in the chloroplast or effects that mimic a transition from low to high light. nAg exposure dramatically elevated the levels of transcripts encoding known or predicted components of the cell wall and the flagella, suggesting that it damages structures exposed to the external milieu. Exposures to nTiO2, nZnO, and QDs elevated the levels of transcripts encoding subunits of the proteasome, suggesting proteasome inhibition, a phenomenon believed to underlie the development and progression of several major diseases, including Alzheimer's disease, and used in chemotherapy against multiple myeloma.

Different transcriptional responses of heat shock protein 70/90 in the marine diatom Ditylum brightwellii exposed to metal compounds and endocrine-disrupting chemicals

Environmental hazard assessments using diatoms have been well documented; however, their molecular toxicology has not been sufficiently studied. In this study, we characterized heat shock protein (HSP) 70/90 of the diatom Ditylum brightwellii (Db) and evaluated their transcriptional profiles in response to various environmental stresses (e.g., thermal shocks and metal and non-metal pollutants). Putative DbHSP70 (658aa, 71.7 kDa) and DbHSP90 (707aa, 80.2 kDa) proteins had conserved HSP family motifs but different C-terminus motifs, that is, "EEVD" in DbHSP70 and "MEEVD" in DbHSP90. Phylogenetic analyses of both proteins showed that D. brightwellii was well clustered with other diatoms. Real-time PCR analysis showed that thermal stress considerably upregulated DbHSP70 and DbHSP90. As for chemical pollutants, DbHSP70 greatly responded to CuSO4 and NiSO4 exposure, but not CuCl2 or NiCl2. However, DbHSP90 was significantly upregulated by all the metal compounds tested (CuSO4, NiSO4, CuCl2, and NiCl2). Strikingly, the expression of both genes was not induced by the organic pollutants tested, such as endocrine-disrupting chemicals. These data suggest that DbHSP70 and DbHSP90 are differentially involved in the defense response against various environmental stressors. Moreover, metal toxicity may be specifically affected by the conjugated anion in the metal compounds (e.g., SO4(2-) and Cl(-)).

An omics based assessment of cadmium toxicity in the green alga Chlamydomonas reinhardtii

The effects of cadmium were assessed in the freshwater alga Chlamydomonas reinhardtii. Algae were exposed to concentrations of 0, 8.1 or 114.8 μM of cadmium and growth rates, gene transcription and metabolite profiles were examined after 48 and 72 h of exposure. In algae exposed to 8.1 μM Cd, several genes were differentially transcribed after 48 h but no adverse growth related effects were detected. A transient effect on both gene transcription patterns and metabolite profiles could be discerned after 48 h of exposure but the majority of these changes disappeared after 72 h. In contrast, all effects were more pronounced at the 114.8 μM cadmium exposure. Here growth was clearly reduced and transcription of a large number of genes involved in oxidative stress defense mechanisms was differentially increased. Metabolites involved in the glutathione synthesis pathway (an important antioxidant defense) were also affected but the effects of cadmium were found to be more pronounced at the transcript level than in the metabolome, suggesting that the former exhibits greater sensitivity toward cadmium exposure.

Transcriptional responses of heat shock protein 70 (Hsp70) to thermal, bisphenol A, and copper stresses in the dinoflagellate Prorocentrum minimum

The heat shock protein 70 (Hsp70) family is an important part of the cell's machinery for protein folding, and helps to protect cells from environmental stress. Although Hsp70 functions have been discovered in various organisms, studies on dinoflagellate Hsps are limited, except for a few phylogenetic attempts. In this study, we sequenced the complete open reading frame of the dinoflagellate Prorocentrum minimum Hsp70 (PmHsp70), and characterized its molecular functions. The putative PmHsp70 protein contained 3 signature patterns of the Hsp70 family. Phylogenetic analysis revealed that PmHsp70 belonged to the dinoflagellate clade. Real-time (RT)-PCR analyses revealed that PmHsp70 was upregulated by thermal stress. Further, we examined the transcriptional response of PmHsp70 to copper (Cu) and bisphenol A (BPA) exposures. In toxicity assays, Cu and BPA exhibited EC(50)-72 h values of 1.07 ± 0.138 mg L(-1) and 1.51 ± 0.110 mg L(-1), respectively, in P. minimum. Expression of PmHsp70 was significantly upregulated in response to Cu and BPA exposures (one-way ANOVA, P<0.05). PmHsp70 displayed different expression patterns in response to different concentrations of Cu and BPA. This study evaluated typical characteristics and, for the first time, toxicant-related functions of PmHsp70. The results suggest that Hsp70 genes may play a vital role in the environmental stress responses of dinoflagellates.

Myo-inositol prevents copper-induced oxidative damage and changes in antioxidant capacity in various organs and the enterocytes of juvenile Jian carp (Cyprinus carpio var. Jian)

Although oxidative stress has been demonstrated to be involved in copper (Cu)-induced toxicity, information regarding the effect of antioxidants on Cu toxicity is still scarce. This study assessed the possible protective effects of myo-inositol (MI) against subsequent Cu exposure in juvenile Jian carp (Cyprinus carpio var. Jian) in vivo and in their enterocytes in vitro. First, oxidative stress was established by exposing fish to different concentrations of Cu (0-7.2 mg Cu/L water) for 4 days. Next, the protective effects of MI (administered as a dietary supplement for 60 days) against subsequent Cu exposure (0.6 mg Cu/L water for 4 days) were studied in fish. The third trial determined the effects of Cu exposure (0-6.0 mg Cu/L of medium for 24h) on enterocytes in vitro. Finally, enterocytes were pre-incubated with graded levels of MI (0-75 mg MI/L of medium) for 72 h and exposed to 6.0 mg Cu/L of medium for 24h. The results indicated that ≥ 0.6 mg Cu/L water could induce oxidative stress in fish (P<0.05). Cu exposure significantly induced increases in lipid peroxidation and protein oxidation in the gill, hepatopancreas and intestine in fish. However, these oxidative effects were prevented by MI pre-supplementation. MI also prevented the toxic effects of Cu on anti-superoxide anion (ASA), anti-hydroxyl radical (AHR), superoxide dismutase (SOD), catalase (CAT), glutathione-S-transferase (GST), glutathione peroxidase (GPx) and glutathione reductase (GR) activities and glutathione (GSH) content in these organs. In vitro, enterocytes exposed to Cu displayed a dose-dependent injury. Moreover, cell viability, protein retention (PR), alkaline phosphatase, total-SOD (T-SOD) and Cu/ZnSOD activities were all depressed by Cu (P<0.05). Interestingly, the final experiment showed that MI pre-supplementation could block the toxic effects of Cu on the antioxidant system, and thus protect enterocytes from Cu-induced oxidative damage. All of these results indicated that the induction of key antioxidant defenses by MI pre-supplementation, including SOD, CAT, GPx, GST and GSH, may play an important role in the protection of fish against oxidative stress.

Effects of a cationic PAMAM dendrimer on photosynthesis and ROS production of Chlamydomonas reinhardtii

Poly(amidoamine) (PAMAM) dendrimers hold great promises for biomedicine. This study sought to examine the toxicity of generation 4 (G4) cationic PAMAM dendrimer to the green microalga, Chlamydomonas reinhardtii, using physiological and molecular biomarkers. Results revealed that the G4 dendrimer at 15 and 25 nM stimulated the photosynthetic process and the production of reactive oxygen species (ROS) in algae. However, the over-production of ROS did not induce the expression of antioxidant enzyme genes, catalase and glutathione peroxidase. In addition, genes encoding light-harvesting proteins (lhca and lhcb), a ferredoxin (fdx) and an oxygen-evolving enhancer protein (psb) involved in photosynthesis were repressed after treatment. Nevertheless, the expression of the lhcbm9 gene, encoding a major light harvesting polypeptide, was increased. These results suggest that the strong modulation of photosynthesis induced by the dendrimer could lead to elevated ROS levels in microalgae.

Systems biology approach in Chlamydomonas reveals connections between copper nutrition and multiple metabolic steps

In this work, we query the Chlamydomonas reinhardtii copper regulon at a whole-genome level. Our RNA-Seq data simulation and analysis pipeline validated a 2-fold cutoff and 10 RPKM (reads per kilobase of mappable length per million mapped reads) (~1 mRNA per cell) to reveal 63 CRR1 targets plus another 86 copper-responsive genes. Proteomic and immunoblot analyses captured 25% of the corresponding proteins, whose abundance was also dependent on copper nutrition, validating transcriptional regulation as a major control mechanism for copper signaling in Chlamydomonas. The impact of copper deficiency on the expression of several O₂-dependent enzymes included steps in lipid modification pathways. Quantitative lipid profiles indicated increased polyunsaturation of fatty acids on thylakoid membrane digalactosyldiglycerides, indicating a global impact of copper deficiency on the photosynthetic apparatus. Discovery of a putative plastid copper chaperone and a membrane protease in the thylakoid suggest a mechanism for blocking copper utilization in the chloroplast. We also found an example of copper sparing in the N assimilation pathway: the replacement of copper amine oxidase by a flavin-dependent backup enzyme. Forty percent of the targets are previously uncharacterized proteins, indicating considerable potential for new discovery in the biology of copper.

Evaluation and decontamination of crude oil-polluted soils using Centrosema pubescen Benth and amendment-support options

Growth performance and phytoremediation of soil of the Niger Delta Region of Nigeria artificially-contaminated with crude oil (up to 100 mL/2 kg soil) using centrosema pubescen Benth was investigated for 12 weeks. The soil samples in which the plants were established were either un-amended, or amended with NPK, or UREA or chicken manure. The extents of removal of PAHs and BTEX were measured as well as the rates of growth of the plants. Gas Chromatographic analysis confirmed the degradation of carcinogenic hydrocarbons like BTEXs and PAHs with this technique. At the highest dose of crude, the contaminant concentrations were 43 mg/kg PAHs, 10 mg/kg BTEX, and 5,613 mg/kg O&G. The greatest percent removal of BTEX was observed at the highest contaminant dose, and with the manure amendment. Similar trends were observed with PAHs and although they were less marked, the trends with PAHs may have been more highly statistically significant. There was no measurable plant uptake of contaminants. Inhibition of plant growth (measured as leaf area, shoot length and production of dry weight) was proportional to the dose of crude oil, but the manure amendment was very effective at reducing the growth inhibition. Interestingly, manure amendment reduced the phytotoxicity significantly in this study.

Changes in transcript abundance in Chlamydomonas reinhardtii following nitrogen deprivation predict diversion of metabolism

Like many microalgae, Chlamydomonas reinhardtii forms lipid droplets rich in triacylglycerols when nutrient deprived. To begin studying the mechanisms underlying this process, nitrogen (N) deprivation was used to induce triacylglycerol accumulation and changes in developmental programs such as gametogenesis. Comparative global analysis of transcripts under induced and noninduced conditions was applied as a first approach to studying molecular changes that promote or accompany triacylglycerol accumulation in cells encountering a new nutrient environment. Towards this goal, high-throughput sequencing technology was employed to generate large numbers of expressed sequence tags of eight biologically independent libraries, four for each condition, N replete and N deprived, allowing a statistically sound comparison of expression levels under the two tested conditions. As expected, N deprivation activated a subset of control genes involved in gametogenesis while down-regulating protein biosynthesis. Genes for components of photosynthesis were also down-regulated, with the exception of the PSBS gene. N deprivation led to a marked redirection of metabolism: the primary carbon source, acetate, was no longer converted to cell building blocks by the glyoxylate cycle and gluconeogenesis but funneled directly into fatty acid biosynthesis. Additional fatty acids may be produced by membrane remodeling, a process that is suggested by the changes observed in transcript abundance of putative lipase genes. Inferences on metabolism based on transcriptional analysis are indirect, but biochemical experiments supported some of these deductions. The data provided here represent a rich source for the exploration of the mechanism of oil accumulation in microalgae.

Knock-down of the COX3 and COX17 gene expression of cytochrome c oxidase in the unicellular green alga Chlamydomonas reinhardtii

The COX3 gene encodes a core subunit of mitochondrial cytochrome c oxidase (complex IV) whereas the COX17 gene encodes a chaperone delivering copper to the enzyme. Mutants of these two genes were isolated by RNA interference in the microalga Chlamydomonas. The COX3 mRNA was completely lacking in the cox3-RNAi mutant and no activity and assembly of complex IV were detected. The cox17-RNAi mutant presented a reduced level of COX17 mRNA, a reduced activity of the cytochrome c oxidase but no modification of its amount. The cox3-RNAi mutant had only 40% of the wild-type rate of dark respiration which was cyanide-insensitive. The mutant presented a 60% decrease of H(2)O(2) production in the dark compared to wild type, which probably accounts for a reduced electron leakage by respiratory complexes III and IV. In contrast, the cox17-RNAi mutant showed no modification of respiration and of H(2)O(2) production in the dark but a two to threefold increase of H(2)O(2) in the light compared to wild type and the cox3-RNAi mutant. The cox17-RNAi mutant was more sensitive to cadmium than the wild-type and cox3-RNAi strains. This suggested that besides its role in complex IV assembly, Cox17 could have additional functions in the cell such as metal detoxification or Reactive Oxygen Species protection or signaling. Concerning Cox3, its role in Chlamydomonas complex IV is similar to that of other eukaryotes although this subunit is encoded in the nuclear genome in the alga contrary to the situation found in all other organisms.

Proteomic analysis of the response of an acidophilic strain of Chlamydomonas sp. (Chlorophyta) to natural metal-rich water

A proteomic approach including 2-DE and MALDI-TOF analysis has been developed to identify the soluble proteins of the unicellular photosynthetic algae Chlamydomonas sp. isolated from an extreme acidic environment, Río Tinto (southwest Spain). We have analyzed the soluble proteome obtained from whole cells growing on metal-rich natural acidic water from the river in comparison with the same strain growing in artificial BG-11 media. The most drastic effect was the decrease in the abundance of the ribulose-1,5-biphosphate carboxylase as well as other enzymes related to photosynthesis. However, phytochrome B, phosphoribulokinase, and phosphoglycerate kinase were upregulated when cells were grown in metal-rich acidic water. Besides, increased accumulation of two Hsps, Hsp70 and Hsp90 as well as other stress-related enzymes were also found in the cells growing in natural acidic water. These results suggest that naturally occurring metal-rich water induces a stress response in acidophilic Chlamydomonas forcing algal cells to reorganize their metabolic pathways as an adaptive response to these environmental conditions.

Toxicogenomics using yeast DNA microarrays

Development of genomics and bioinformatics enable us to analyze the global gene expression profiles of cells by DNA microarray. Changes in gene expression patterns indicate changes in its physiological conditions. Following the exposure of an organism or cell to toxic chemicals or other environmental stresses, the global genetic responses can be expeditiously and easily analyzed. Baker's yeast, Saccharomyces cerevisiae, is one of the most studied and useful model eukaryotes. The biggest advantage of yeast genomics is the available functional information for each gene and a considerable number of data are accumulating in the field of toxicity assessment using yeast DNA microarray. In this review, we discuss the toxicogenomics of metal ions, alcohols and aldehydes, and other chemicals.

Effect assessment of the herbicide paraquat on a green alga using differential gene expression and biochemical biomarkers

Effects of the herbicide paraquat were assessed on the green freshwater alga Chlamydomonas reinhardtii using different endpoints of toxicity. Cell concentration and growth rate were monitored, whereas flow cytometry was applied to determine changes in chlorophyll content, viability and presence of reactive oxygen species. Furthermore, a transcriptomics approach using microarray hybridizations was applied to elucidate the mechanisms of toxicity. The results reveal that paraquat concentrations above 0.25 microM induce toxic effects in C. reinhardtii, reflected in a significantly reduced growth rate and cell concentration with a corresponding median effective concentration (EC50) value of 0.26 microM. With increasing paraquat concentrations, an increase in cell volume was registered with a particle counter as well as in the forward scattering signal of flow cytometric measurements, which is a measure of cell size. Flow cytometry, moreover, showed an increase in reactive oxygen species with increasing exposure concentration, corroborating the general knowledge that this herbicide exerts its toxicity through the generation of oxidative stress. At the same time, several genes involved in oxidative stress defense mechanisms, such as L-ascorbate peroxidase, glutaredoxin, and a possible glutathione-S-transferase were differentially expressed, demonstrating the value of microarrays for elucidating possible mechanisms of toxicity. The fact that several genes were differentially expressed at paraquat concentrations that caused no adverse effects on higher levels of biological organization indicates that a transcriptomics approach allows for the detection of early effects, even before they become manifest at higher levels.

Isolation and characterization of a cDNA encoding a heat shock protein 70 from a sterile mutant of Ulva pertusa (Ulvales, Chlorophyta)

Synthesis and accumulation of molecular chaperones are universal responses found in all cellular organisms when exposed to a variety of unfavorable conditions. Heat shock protein 70 (Hsp70), which is one of the major classes of molecular chaperones, plays a particularly important role in cellular stress responses, and the Hsp70 system is the most intensely studied in higher plants and algae. Therefore, we isolated and characterized a cDNA clone encoding Hsp70 from a sterile strain of Ulva pertusa (Ulvales, Chlorophyta). The sterile U. pertusa Hsp70 (UpHsp70) cDNA consisted of 2,272 nucleotides and had an open reading frame encoding a polypeptide of 663 amino acid (AA) residues with a molecular mass of 71.7 kDa. Amino acid alignment and phylogenetic analysis of Hsp70s from other organisms showed that UpHsp70 was more similar to cytoplasmic Hsp70s from green algae and higher plants (> or =75%) than to those from other algae and microorganisms. Southern blot analysis indicated that the sterile U. pertusa genome had at least four cytoplasmic Hsp70-encoding genes. UpHsp70 mRNA levels were significantly affected by diurnal changes, rapidly increased by high-temperature stress, and gradually increased by exposure to copper, cadmium, and lead. These results suggest that UpHsp70 plays particularly important roles in adaptation to high-temperature conditions and diurnal changes, and is potentially involved in tolerance to heavy metal toxicity.

METAL-INDUCED REACTIVE OXYGEN SPECIES PRODUCTION IN CHLAMYDOMONAS REINHARDTII (CHLOROPHYCEAE)(1)

Toxic effects of metals appear to be partly related to the production of reactive oxygen species (ROS), which can cause oxidative damage to cells. The ability of several redox active metals [Fe(III), Cu(II), Ag(I), Cr(III), Cr(VI)], nonredox active metals [Pb(II), Cd(II), Zn(II)], and the metalloid As(III) and As(V) to produce ROS at environmentally relevant metal concentrations was assessed. Cells of the freshwater alga Chlamydomonas reinhardtii P. A. Dang. were exposed to various metal concentrations for 2.5 h. Intracellular ROS accumulation was detected using an oxidation-sensitive reporter dye, 5-(and-6)-carboxy-2',7'-dihydrodifluorofluorescein diacetate (H2 DFFDA), and changes in the fluorescence signal were quantified by flow cytometry (FCM). In almost all cases, low concentrations of both redox and nonredox active metals enhanced intracellular ROS levels. The hierarchy of maximal ROS induction indicated by the increased number of stained cells compared to the control sample was as follows: Pb(II) > Fe(III) > Cd(II) > Ag(I) > Cu(II) > As(V) > Cr(VI) > Zn(II). As(III) and Cr(III) had no detectable effect. The effective free metal ion concentrations ranged from 10(-6) to 10(-9)  M, except in the case of Fe(III), which was effective at 10(-18)  M. These metal concentrations did not affect algal photosynthesis. Therefore, a slightly enhanced ROS production is a general and early response to elevated, environmentally relevant metal concentrations.

Effect of copper intoxication on rat liver proteasome activity: relationship with oxidative stress

Copper toxicity is associated with formation of reactive oxygen species, which are capable to oxidize proteins. The selective removal of the latter by the 20S proteasome is considered an essential part of the cell antioxidant defense system. The aim of the present study was to investigate whether peptidase activities of rat liver proteasomes were affected by chronic (40 mg CuSO(4)/rat/daily with the drinking water for 2 weeks) and acute (20 mg/kg CuSO(4), s.c.) copper treatment. To evaluate the role of proteasome, its inhibitor MG132 was also used. The degree of copper-induced oxidative stress (OS), established by measuring lipid peroxidation, protein oxidation, and cellular glutathione level, as well as activities of antioxidant enzymes--catalase, superoxide dismutase, and gultathionine peroxidase, depended on the mode of copper administration. Chronic copper administration (mild oxidative stress) did not affect proteasome activities, whereas acute copper treatment (severe oxidative stress) caused a decline in chymotryptic- and tryptic-like activities. The treatment of copper-loaded animals with MG132 did not change copper-induced alterations in the tested indices, except an additional increase in protein oxidation and inhibition of glutathionine peroxidase activity. The results suggested that the in vivo copper-induced oxidative stress was associated with changes in the catalytic activity of proteasome.

Biomarkers in aquatic plants: selection and utility

This review emphasizes the predictive ability, sensitivity and specificity of aquatic plant biomarkers as biomonitoring agents of exposure and effect. Biomarkers of exposure are those that provide functional measures of exposure that are characterized at a sub-organism level. Biomarkers of effect require causal linkages between the biomarker and effects, measured at higher levels of biological organization. With the exception of pathway specific metabolites, the biomarkers assessed in this review show variable sensitivity and predictive ability that is often confounded by variations in growth conditions, rendering them unsuitable as stand alone indicators of environmental stress. The use of gene expression for detecting pollution has been, and remains immature; this immaturity derives from inadequate knowledge on predictive ability, sensitivity and specificity. Moreover, the ability to the detect mode of action of unknown toxicants using gene expression is not as clear-cut as initially hypothesized. The principal patterns in gene expression is not as clear-cut as initially hypothesized. The principal patterns in gene expression are generally derived from stress induced genes, rather than on ones that respond to substances with known modes of action (Baerson et al. 2005). Future developments in multivariate statistics and chemometric methods that enhance pattern analyses in ways that could produce a "fingerprint", may improve methods for discovering modes of action of unknown toxicants. Pathway specific metabolites are unambiguous, sensitive, correlate well to growth effects, and are relatively unaffected by growth conditions. These traits make them excellent biomarkers under both field and laboratory conditions. Changes in metabolites precede visible growth effects; therefore, measuring changes in metabolite concentrations (Harring et al. 1998; Shaner et al. 2005). The metabolic phase I enzymes (primarily associated with P-450 activity) are non-specific biomarkers, and few studies relate them to growth parameters. P-450 activity both increases and decreases in response to chemical stress, often confounding interpretation of experimental results. Alternatively, phase II metabolic enzymes (e.g., glutathione S-transferases; GST's) appear to be sensitive biomarkers of exposure, and potentially effect. Some GST's are affected by growth factors, but others may only be induced by xenobiotics. Measuring xenobiotic-induced GST's, or their gene expression patterns, are good candidates for future biomarkers of the cumulative load of chemical stress, both in the laboratory and under field conditions. Phytochelatins respond to some but not all metal ions, and may therefore be used as biomarkers of exposure to identify the presence and bioavailability of ions to which they respond. However, more data on their specificity to, and interactions with growth factors, in more species are needed. The flavenoids are only represented by one heavy metal exposure study; therefore their use as biomarkers is currently difficult to judge. Stress proteins tend to be specific for toxicants that affect protein function. Growth factors are known to affect the level of stress proteins; hence, the use of stress proteins as biomarkers will be confined to experiments performed under controlled growth conditions, where they can be excellent indicators of proteotoxicity. Reactive oxygen species (ROS), ROS scavenging enzymes, changes in pigment content, photosynthesis and chlorophyll fluorescence are all affected by growth factors, particularly light and nutrient availability. Therefore, these biomarkers are best suited to investigate the mode of action of toxicants under controlled growth conditions. These biomarkers are sensitive to xenobiotic stressors that affect various processes in the photosynthetic apparatus, and can be used to diagnose which photosynthetic process or processes are primarily affected. Chlorophyll fluorescence is a non-destructive measure, and is thereby well suited for repeated measures of effect and recovery (Abbaspoor and Streibig 2005; Abbaspoor et al. 2006; Cedergreen et al. 2004). Bi-phasic responses (over time and with dose) are probably major sources of variation in sensitivity for many biomarkers. Metabolic enzymes, stress proteins, ROS and their corresponding scavenging enzymes increase in a time-frame and at doses in which plant cell damage is still repairable. However, when toxicity progresses to the point of cell damage, the concentration/activity of the biomarker either stabilizes or decreases. Examples of this response pattern are given in Lei et al. (2006); Pflugmacher et al. (2000b); Teisseire et al. (1998); and Teisseire and Guy (2000). Gene expression is also a time-dependent phenomenon varying several fold within a few hour. Therefore, bi-phasic response patterns make timing and dose-range, within which the biomarkers can be used as measures of both exposure and effect, extremely important. As a result, most biomarkers are best suited for situations in which the time and dose dependence of the biomarker, in the investigated species, are established. Notwithstanding the previously mentioned limitations, all assessed biomarkers provide valuable information on the physiological effects of specific stressors, and are valuable tools in the search for understanding xenobiotic modes of action. However, the future use of aquatic plant biomarkers will probably be confined to laboratory studies designed to assess toxicant modes of action, until further knowledge is gained regarding the time, dose and growth-factor dependence of biomarkers, in different species. No single biomarker is viable in gaining a comprehensive understanding of xenobiotic stress. Only through the concomitant measurement of a suite of appropriate biomarkers will our diagnostic capacity be enhanced and the field of ecotoxicology, as it relates to aquatic plants, advanced.

Early stage toxicity of excess copper to photosystem II of Chlorella pyrenoidosa-OJIP chlorophyll a fluorescence analysis

Acute toxicity of excess Cu on the photosynthetic performance of Chlorella pyrenoidosa was examined by using chlorophyll a fluorescence transients and JIP-test after exposure to elevated Cu concentrations for a short time period. High Cu concentration resulted in a significant suppression in photosynthesis and respiration. The absorption flux (ABS/RC) per PSII reaction center increased with increasing Cu concentration, but the electron transport flux (ET0/RC) decreased. Excess Cu had an insignificant effect on the trapping flux (TR0/RC). The decline in the efficiency, with which a trapped exciton can move an electron into the electron transport chain further than Q(A)-(Psi0), the maximal quantum yield of primary photochemistry (Phi0), and the quantum yield of electron transport (Phi(E)0) were also observed. The amount of active PSII reaction centers per excited cross section (RC/CS) was also in consistency with the change of photosynthesis when cells were exposed to excess Cu concentration. JIP-test parameters had a good linear relationship with photosynthetic O2 evolution. These results suggested that the decrease of photosynthesis in exposure to excess Cu may be a result of the inactivation of PSII reaction centers and the inhibition of electron transport in the acceptor side.

Mechanisms of copper toxicity in Saccharomyces cerevisiae determined by microarray analysis

The effect of the heavy metal copper on the expression of a wide spectrum of genes was analyzed by using a DNA microarray. The gene expression profile of baker's yeast Saccharomyces cerevisiae grown in a medium containing a sublethal concentration of cupric sulfate was compared with that of yeast grown in a normal medium. Among approximately 6000 yeast ORFs, 143 ORFs were induced more than twofold to resist copper toxicity after exposure to copper. Copper metallothionein CUP1-1 and CUP1-2 were induced more than 20-fold. Some genes related to sulfur metabolism and oxidative stress response were also up-regulated. This DNA microarray analysis identified several molecular targets of copper toxicity.

The peroxiredoxin and glutathione peroxidase families in Chlamydomonas reinhardtii

Thiol/selenol peroxidases are ubiquitous nonheme peroxidases. They are divided into two major subfamilies: peroxiredoxins (PRXs) and glutathione peroxidases (GPXs). PRXs are present in diverse subcellular compartments and divided into four types: 2-cys PRX, 1-cys PRX, PRX-Q, and type II PRX (PRXII). In mammals, most GPXs are selenoenzymes containing a highly reactive selenocysteine in their active site while yeast and land plants are devoid of selenoproteins but contain nonselenium GPXs. The presence of a chloroplastic 2-cys PRX, a nonselenium GPX, and two selenium-dependent GPXs has been reported in the unicellular green alga Chlamydomonas reinhardtii. The availability of the Chlamydomonas genome sequence offers the opportunity to complete our knowledge on thiol/selenol peroxidases in this organism. In this article, Chlamydomonas PRX and GPX families are presented and compared to their counterparts in Arabidopsis, human, yeast, and Synechocystis sp. A summary of the current knowledge on each family of peroxidases, especially in photosynthetic organisms, phylogenetic analyses, and investigations of the putative subcellular localization of each protein and its relative expression level, on the basis of EST data, are presented. We show that Chlamydomonas PRX and GPX families share some similarities with other photosynthetic organisms but also with human cells. The data are discussed in view of recent results suggesting that these enzymes are important scavengers of reactive oxygen species (ROS) and reactive nitrogen species (RNS) but also play a role in ROS signaling.