Acclimation of Daphnia magna to environmentally realistic copper concentrations

It may be hypothesised that as the bioavailable background concentration of an essential metal increases (within natural limits), the natural tolerance (to the metal) of the acclimated/adapted organisms and communities will increase. In this study the influence of acclimation to different copper concentrations on the sensitivity of the freshwater cladoceran Daphnia magna Straus was investigated. D. magna was acclimated over three generations to environmentally relevant copper concentrations ranging from 0.5 to 100 microg Cu/l (copper activity: 7.18 x 10(-15) to 3700 x 10(-12) M Cu2+). A modified standard test medium was used as culture and test medium. Medium modifications were: reduced hardness (lowered to 180 mg CaCO3/l) and addition of Aldrich humic acid at a concentration of 5 mg DOC/l (instead of EDTA). The effects of acclimation on these organisms were monitored using acute mortality assays and long-term assays in which life table parameters, copper body concentrations and energy reserves were used as test endpoints. Our results showed a two-fold increase in acute copper tolerance with increasing acclimation concentration for second and third generation organisms. Copper acclimation concentrations up to 35 microg Cu/l (80 pM Cu2+) did not affect the net reproduction and the intrinsic growth rate. The energy reserves of the acclimated daphnids revealed an Optimal Concentration range (OCEE) and concentrations between 5 and 12 microg Cu/l (0.5-4.1 pM Cu2+) and 1 and 35 microg Cu/l (0.023-80 pM Cu2+) seemed to be optimal for first and third generation daphnids, respectively. Lower and higher copper concentrations resulted in deficiency and toxicity responses. It was also demonstrated that up to 35 microg Cu/l, third generation daphnids were able to regulate their total copper body concentration. These results clearly indicate that bioavailable background copper concentrations present in culture media have to be considered in the evaluation of toxicity test results, especially when the toxicity data are used for water quality guideline derivation and/or ecological risk assessment for metals.     

Development of Tolerance for Copper in Cyanobacteria Repeatedly Exposed to Its Toxic Effect

Experiments on cyanobacterial cultures showed that initial exposure to copper at concentrations of 0.01–0.05 mg/l not only has a direct toxic effect, but also significantly modifies the copper tolerance of cyanobacteria for repeated exposure. The response to repeated exposure and the mechanism of tolerance depend on the strength of the initial effect of copper and the extent of heterogeneity of the initial cyanobacterial population.     

Proline improves copper tolerance in chickpea (Cicer arietinum)

The present study suggests the involvement of proline in copper tolerance of four genotypes of Cicer arietinum (chickpea). Based on the data of tolerance index and lipid peroxidation, the order for copper tolerance was as follows: RSG 888?>?CSG 144?>?CSG 104?>?RSG 44 in the selected genotypes. The basis of differential copper tolerance in chickpea genotypes was characterized by analyzing, antioxidant enzymes (superoxide dismutase, ascorbated peroxidase and catalase), phytochelatins, copper uptake, and proline accumulation. Chickpea genotypes showed stimulated superoxide dismutase activity at all tested concentrations of copper, but H₂O₂ decomposing enzymes especially; ascorbate peroxidase did not increase with 25 and 50 μM copper treatments. Catalase activity, however, increased at lower copper concentrations but failed to stimulate at 50 μM copper. Such divergence in responses of these enzymes minimizes their importance in protecting chickpea against copper stress. The sensitive genotypes showed greater enhancement of phytochelatins than that of tolerant genotypes. Hence, the possibility of phytochelatins in improving copper tolerance in the test plant is also excluded. Interestingly, the order of proline accumulation in the chickpea genotypes (RSG 888?>?CSG 144?>?CSG 104?>?RSG 44) was exactly similar to the order of copper tolerance. Based on hyperaccumulation of proline in tolerant genotype (RSG 44) and the reduction and improvement of lipid peroxidation and tolerance index, respectively, by proline pretreatment, we conclude that hyperaccumulation of proline improves the copper tolerance in chickpea.     

Tolerance to Copper and to Salinity in Daphnia longispina: Implications within a Climate Change Scenario

Considering IPPC climate change scenarios, it is pertinent to predict situations where coastal ecosystems already impacted with chemical contamination became exposed to an additional stressor under a future scenario of seawater intrusion. Accordingly, the present study aimed at evaluating if a negative association between tolerance to a metal and to saltwater exists among genotypes of a freshwater organism. For this, five clonal lineages of the cladoceran Daphnia longispina O.F. Müller, exhibiting a differential tolerance to lethal levels of copper, were selected. Each clonal lineage was exposed to lethal and sublethal concentrations of sodium chloride (assumed as a protective surrogate to evaluate the toxicity of increased salinity to freshwater organisms). Mortality, time to release the first brood and total number of neonates per female were monitored and the somatic growth rate and intrinsic rate of natural increase were computed for each clonal lineage. Data here obtained were compared with their lethal responses to copper and significant negative correlations were found. These results suggest that genetically eroded populations of D. longispina, due to copper or salinity, may be particularly susceptible to a later exposure to the other contaminant supporting the multiple stressors differential tolerance.     

Modulation of Antioxidant Attributes and Grain Yield in Fragrant Rice by Exogenous Cu Application

Journal of Plant Growth Regulation - Despite copper (Cu) being an essential nutrient for the growth and development of all living organisms, the yield and tolerance mechanisms of fragrant rice...     

Surface chemical studies of Thiobacillus ferrooxidans with reference to copper tolerance

A strain of Thiobacillus ferrooxidans was adapted to grow at higher concentrations of copper by single step culturing in the presence of 20 g/L (0.314 mol/L) cupric ions added to 9K medium. Exposure to copper results in change in the surface chemistry of the microorganism. The isoelectric point of the adapted strain (pI=4.7) was observed to be at a higher pH than that of the wild unadapted strain(pI=2.0). Compared to the wild strain, the copper adapted strain was found to be more hydrophobic and showed enhanced attachment efficiency to the pyrite mineral. The copper adsorption ability of the adapted strain was also found to be higher than that of the wild strain. Fourier transform infrared spectroscopy of adapted cells suggested that a proteinaceous new cell surface component is synthesized by the adapted strain. Treatment of adapted cells with proteinase-K, resulted in complete loss of tolerance to copper, reduction in copper adsorption and hydrophobicity of the adapted cells. These observations strongly suggest a role played by cell surface modifications of Thiobacillus ferrooxidans in imparting the copper tolerance to the cells and bioleaching of sulphide minerals.     

Influence of sludge retention time on tolerance of copper toxicity for polyphosphate accumulating organisms linked to polyhydroxyalkanoates metabolism and phosphate removal

This study explored the influence of sludge retention time (SRT) on tolerance of copper invasion for polyphosphate accumulating organisms (PAOs) in an enhanced biological phosphorus removal (EBPR). The experimental data showed the anaerobic polyhydroxyalkanoates (PHA) storage for the sludge at 10d SRT was less influenced by copper invasion than those at 5d and 15d SRTs. The reaction of PAOs aerobically taking up phosphate for the sludge at 5d or 15d SRT almost ceased at 2 mg Cu L⁻¹, whereas PAOs in the sludge at 10d SRT retained half of the ability to take up phosphate. Both the PHAs degradation and synthesis rates decreased with increasing copper concentration, regardless of the SRTs. However, the copper inhibition of the former was greater than that of the later.     

Stability of copper tolerance inThiobacillus ferrooxidans

A strain ofThiobacillus ferrooxidans MAL-4-1 was adapted to grow at higher concentrations of copper by repeated subculturing in the presence of increasing levels of added cupric ions in 9K medium. The strains adapted to copper were found to be more efficient in bioleaching of copper from concentrates. When copper tolerant strains were back cultured repeatedly in 9K medium without cupric ions, the initially developed metal tolerance was observed to be lost. This indicates that the copper tolerance developed is stress-dependent and not a permanent trait of the adapted strain.     

Copper and cobalt uptake byHaumaniastrum species

Summary Herbarium specimens of the genus Haumaniastrum (mainly from Shaba Province Zaïre) were analysed for copper and cobalt.H. homblei showed elevated copper levels and indicated its tolerance to mineralized ground.H. robertii (previously-known as a copper flower) showed the expected high copper concentrations, but contained abnormally high concentrations of cobalt (av. 4304 g/g dry weight) far exceeding those of copper. This species has the highest cobalt content of any phanerogam and its distribution may be controlled by cobalt rather than by copper. re]19761220     

INTER- AND INTRASPECIFIC VARIATION OF MOSSES IN TOLERANCE TO COPPER AND ZINC

Bryophytes are often viewed as slowly evolving with little genetic variation within and among populations. A study of heavy-metal tolerance was initiated to test the capacity of bryophytes to undergo genetic differentiation in response to natural selection. Tolerance of Funaria hygrometrica to copper and zinc was greater in populations that originated on soil with high concentrations of these metals. Protonemal growth was more inhibited by the metals than was germination, and copper was more toxic than zinc. Zinc and copper tolerances were correlated, but so were the zinc and copper concentrations of native substrates. The pattern of population differentiation for heavy-metal tolerance in this species is much like that of flowering plants. Five populations of Physcomitrium pyriforme, which does not occur on metal-contaminated soil, were all highly tolerant of zinc but extremely intolerant of copper. This species seems to have an inherent tolerance to the former. Significant variation in tolerance to copper and zinc occurred among populations, but tolerance did not correlate with metal contents in native substrates. This pattern differs from that of flowering plants. Normal populations of species that colonize contaminated sites tended to be more tolerant than populations of species that do not colonize such sites. The extensive population differentiation in Funaria hygrometrica augments the evidence from electrophoretic data that there is genetic variation among populations of mosses and liverworts.     

The tonoplast copper transporter COPT5 acts as an exporter and is required for interorgan allocation of copper in Arabidopsis thaliana

Copper is an essential micronutrient for all organisms because it serves as a cofactor of several proteins involved in electron transfer. Elevated copper concentrations can cause toxic effects and organisms have established suitable mechanisms to regulate the uptake and internal distribution of copper to balance the content at an optimal concentration. In recent studies, a family of copper transporters (COPT) with high homology to other eukaryotic copper transporters (Ctr) has been identified in Arabidopsis thaliana. In this study we clarified the physiological function of COPT5. This carrier is located in the tonoplast and functions as a vacuolar copper exporter. Mutants lacking this transporter have altered copper contents in different organs when compared with wild-type plants. We were able to detect copper accumulation in the root and a decreased copper content in siliques and seeds when the COPT5 gene is mutated by T-DNA insertion. Vacuoles purified from copt5 T-DNA-insertion mutants show remarkably increased copper concentrations compared with wild-type organelles. We assume that on the cellular level COPT5 is important for copper export from the vacuole and on the level of the whole plant it is involved in the interorgan reallocation of copper ions from the root to reproductive organs.     

Phytoprotective Effect of Ammonium Humate at High Copper Concentrations in the Environment

The influence of ammonium humate obtained from peat on the tolerance of wheat plants to high CuSO₄ concentrations (100, 250, 500, and 1000 μM/L) has been studied. Seeds were germinated on a copper sulfate solution with and without the humate. Then the plants were grown on Hoagland’s solution in an artificial climate chamber. The coefficient of protective action by humate was estimated in the following two ways: by dry weight changes and by the copper ion content in comparison with the plants grown without humate. The protective role of the humate at 100 and 250 μM has been established, which is due to reduction of copper accumulation in the plants. It has been found that the humate at higher concentrations enhances the toxic effect of copper.     

The Consequence of Selection for Copper Tolerance on the Uptake and Accumulation of Copper inMimulus guttatus

Previous research has shown that copper tolerance inMimulusguttatusFischer ex DC. is controlled by a single major geneand can be enhanced by a number of minor genes (or modifiers).Here we report the uptake of copper by three lines which allpossessed the major tolerance gene but differed in the modifiergenes: the major gene only (IT), the major gene plus increased(HT6) and decreased (LT6) modifiers. HT6 showed the highestcopper tolerance and IT the lowest. Copper uptake was investigatedat five copper concentrations and over 30 d to analyse the concentrationof copper accumulated in roots and shoots and the partitioningof apoplastic and symplastic root copper. Significant differenceswere found for root copper concentration with the IT line accumulatingthe highest levels. Fifty-two per cent of the root copper inthe IT line is symplastic and this increases to 60% in LT6 and64% in HT6. Significant differences were recorded for shootcopper concentration with HT6 accumulating the highest and ITthe lowest. At the highest external copper concentration theHT line accumulated nearly 800 µg g^-1in its shoot, approachinglevels reported for copper hyperaccumulation.Copyright 1997Annals of Botany Company Copper tolerance; copper uptake; copper minor genes; Mimulus guttatus     

Increased resistance to copper-induced damage of the root cell plasmalemma in copper tolerant Silene cucubalus

The relation between copper tolerance and the sensitivity of plants with respect to the effect of copper on the plasmalemma of root cells was studied using plants from one copper sensitive and two copper tolerant populations of Silene cucubalus Wib. In each population, the external copper concentration needed to induce ion leakage (a measure of damage to the permeability barrier) was similar to the highest no-effect-concentration of copper for root growth in that population. At higher concentrations, the degree of root growth inhibition paralleled the rate of ion leakage, the degree of trypan blue staining (a measure of plasmalemma integrity) and the accumulation of lipid peroxidation products. The amount of copper taken up by the plants was inversely related to their level of copper tolerance. Compared to copper sensitive plants, copper tolerant plants showed no increased resistance to either the sulfhydryl reagent N-ethylmaleimide or the free radical-producing compound cumene hydroperoxide.
These results indicate that damage to the permeability barrier of root cells constitutes the primary effect of copper toxicity in both sensitive and tolerant plants, and that copper tolerance is coupled to the ability of the plants to prevent such damage. This ability might depend on exclusion of copper by the root cell plasmalemma.     

Copper tolerance in bacteria requires the activation of multiple accessory pathways

Copper is a required micronutrient for bacteria and an essential cofactor for redox-active cuproenzymes. Yet, excess copper is extremely toxic, and is exploited as a bacteriocide in medical and biotechnological applications and also by the mammalian immune system. To evade copper toxicity, bacteria not only control intracellular copper homeostasis, but they must also repair the damage caused by excess copper. In this review, we summarize the bacterial cell-wide response to copper toxicity in Enterobacteria. Tapping into the abundant research data on two key organisms, Escherichia coli and Salmonella enterica, we show that copper resistance requires both the direct copper homeostatic response and also the indirect accessory pathways that deal with copper-induced damage. Since patterns of copper response are conserved through the Proteobacteria, we propose a cell-wide view of copper detoxification and copper tolerance that can be used to identify novel targets for copper-based antibacterial therapeutics.     

Unusual Cu(I)/Ag(I) coordination of Escherichia coli CusF as revealed by atomic resolution crystallography and X-ray absorption spectroscopy

Elevated levels of copper or silver ions in the environment are an immediate threat to many organisms. Escherichia coli is able to resist the toxic effects of these ions through strictly limiting intracellular levels of Cu(I) and Ag(I). The CusCFBA system is one system in E. coli responsible for copper/silver tolerance. A key component of this system is the periplasmic copper/silver-binding protein, CusF. Here the X-ray structure and XAS data on the CusF-Ag(I) and CusF-Cu(I) complexes, respectively, are reported. In the CusF-Ag(I) structure, Ag(I) is coordinated by two methionines and a histidine, with a nearby tryptophan capping the metal site. EXAFS measurements on the CusF-Cu(I) complex show a similar environment for Cu(I). The arrangement of ligands effectively sequesters the metal from its periplasmic environment and thus may play a role in protecting the cell from the toxic ion.     

An Ecological Risk Assessment of Air Emissions of Trace Metals from Copper and Zinc Production Facilities

Trace metals are components of releases to air emitted by copper and zinc production facilities in Canada. Six metals (copper, zinc, nickel, lead, cadmium, and arsenic) are examined as part of an overall environmental assessment of these releases. Estimates of metal deposition rates to soils and surface waters were derived from monitoring data in the vicinity of the production facilities and also through dispersion modelling studies. Fate and transport modelling of the metals deposited allowed an estimation of critical loads. Estimated annual deposition rates were compared with 25^th-percentile critical loads typically representative of effects on sensitive organisms under 25% of conditions in sandy soils or circumneutral to acidic lake waters. The results of the comparison suggest that there is a potential for adverse effects on aquatic and/or soil-dwelling organisms from exposure to steadystate concentrations of metals in the vicinity of copper and zinc production facilities. Approaches of particular significance in these assessments include probabilistic estimation of critical loads for metals, allowance for the speciation of metals defining the bioavailable fraction and limiting critical effect levels to the high end of natural background metal concentrations.     

The independent cue and cus systems confer copper tolerance during aerobic and anaerobic growth in Escherichia coli

Copper is essential but can be toxic even at low concentrations. Coping with this duality requires multiple pathways to control intracellular copper availability. Three copper-inducible promoters, controlling expression of six copper tolerance genes, were recently identified in Escherichia coli. The cue system employs an inner membrane copper transporter, whereas the cus system includes a tripartite transporter spanning the entire cell envelope. Although cus is not essential for aerobic copper tolerance, we show here that a copper-sensitive phenotype can be observed when cus is inactivated in a cueR background. Furthermore, a clear copper-sensitive phenotype for the cus system is revealed in the absence of O(2). These results indicate that the cue pathway, which includes a copper exporter, CopA, and a periplasmic oxidase, CueO, is the primary aerobic system for copper tolerance. During anaerobic growth, however, copper toxicity increases, and the independent cus copper exporter is also necessary for full copper tolerance. We conclude that the cytosolic (CueR) and periplasmic (CusRS) sensor systems differentially regulate copper export systems in response to changes in copper and oxygen availability. These results underscore the increased toxicity of copper under anaerobic conditions and the complex adaptation of copper export in E. coli.     

Excess copper effect on growth, chloroplast ultrastructure, oxygen-evolution activity and chlorophyll fluorescence in Glycine max cell suspensions

The influence of excess copper on soybean photosynthetic cell suspensions was investigated. The cell suspensions grew well in the presence of 5–20 µ M CuSO₄ and developed tolerance to even higher levels of CuSO₄ (i.e. up to 50 µ M ), indicating that copper was not toxic to the cells at that high concentrations. Cu-adapted cell suspensions grew faster than the control in limiting light conditions and had higher content of chlorophyll per dry weight of cells. Copper was accumulated within the cells, and this event was accompanied by (1) increased oxygen evolution activity; (2) increased number of chloroplasts per cell, smaller chloroplasts, increased thylakoid stacking and grana size; (3) higher fluorescence emission of photosystem II antenna complexes and (4) stimulation of plastocyanin protein synthesis compared with untreated cells. Microanalysis of cross-sections revealed an increase of copper content in chloroplasts as well as vacuole, cytoplasm and cell wall in Cu-adapted cells. No antagonist interaction between copper and iron uptake took place in these cell suspensions. On the other hand, copper at subtoxic concentrations stimulated oxygen evolution activity in thylakoids from control cells, but this event did not take place in those from Cu-adapted ones. Furthermore, the loss of activity by copper inhibitory action at toxic concentrations was two-fold slower in thylakoids from Cu-adapted cells compared with the control ones. The data strongly indicate that copper plays a specific positive role on photosynthesis and stimulates the growth and the oxygen evolution activity in soybean cell suspensions.