Uptake Of Other Metals Research Articles

Trace Metal Requirements and Interactions in Symbiodinium kawagutii.

Photosynthetic organisms need trace metals for various biological processes and different groups of microalgae have distinctive obligate necessities due to their respective biochemical requirements and ecological niches. We have previously shown that the dinoflagellate Symbiodinium kawagutii requires high concentrations of bioavailable Fe to achieve optimum growth. Here, we further explored the trace metal requirements of S. kawagutii with intensive focus on the effect of individual metal and its interaction with other divalent metals. We found that low Zn availability significantly decreases growth rates and results in elevated intracellular Mn, Co, Ni, and Fe quotas in the dinoflagellate. The results highlight the complex interaction among trace metals in S. kawagutii and suggest either metal replacement strategy to counter low Zn availability or enhanced uptake of other metals by non-specific divalent metal transporters. In this work, we also examined the Fe requirement of S. kawagutii using continuous cultures. We validated that 500 pM of Fe′ was sufficient to support maximum cell density during steady state growth period either at 26 or 28°C. This study shows that growth of S. kawagutii was limited by metal availability in the following order, Fe > Zn > Mn > Cu > Ni > Co. The fundamental information obtained for the free-living Symbiodinium shall provide insights into how trace metal availability, either from ambient seawater or hosts, affects growth and proliferation of symbiotic dinoflagellates and the interaction between symbiont and their hosts.

Characterization of the effects of binary metal mixtures on short-term uptake of Ag, Cu, and Ni by rainbow trout (Oncorhynchus mykiss)

Single metal Biotic Ligand Models (BLMs) have been developed for a number of metals and model organisms. While these BLMs improve our ability to regulate metals in the aquatic environment, in reality, organisms are often simultaneously exposed to metal mixtures. Recently, several attempts have been made to develop mixture BLMs (mBLMs). Some of these models assume competitive interactions between all metals, while others assume only metals with a similar mode of action (e.g., Na+ or Ca2+ antagonists) will competitively interact. To begin testing these assumptions in the mBLM framework, standard 3-h gill metal binding assays with Ag, Cu, and Ni (primary metals), were performed in vivo on freshwater rainbow trout. Fish were exposed across a range of concentrations encompassing the 96-h LC50 for that metal to characterize uptake kinetics for each of these three primary metals (radiolabelled) in the presence and absence of a secondary metal (Ag, Cd, Cu, Ni, Pb, or Zn; not radiolabelled). We observed a complex series of interactions in binary mixtures that frequently contradicted theoretical expectations. Metals with similar modes of action did competitively interact in some instances, but not others, and when they did compete the competition was not necessarily reciprocal (e.g., Cu inhibited Ag uptake but Ag did not inhibit Cu uptake). We also observed examples of interactions between metals with dissimilar modes of action and several examples of metals stimulating the uptake of other metals. The underlying mechanisms for these unexpected interactions are unclear, but suggest that many of the current assumptions in mBLMs regarding the number and types of metal uptake sites and corresponding metal interactions are not correct. Careful characterization of metal mixture interactions is clearly needed before a reliable mBLM can be developed.

Uptake of metals and metalloids by Conyza canadensis L. from a thermoelectric power plant landfill

Fourteen metals and metalloids were determined in Conyza canadensis L. harvested from the fly ash landfill of the thermoelectric power plant ?Kolubara? (Serbia). Fly ash samples were collected together with the plant samples and subjected to sequential extraction according to the three-step sequential extraction scheme proposed by the Community Bureau of Reference (BCR; now the Standards, Measurements and Testing Program). The contents of metals and metalloids were determined by inductively coupled plasma optical emission spectrometry (ICP-OES) in plant root and the aboveground part and correlated with their contents in the fly ash samples. The bioconcentration factor (BCF) and translocation factors (TF) were calculated to access uptake of metals from fly ash and their translocation to the aboveground part. Results regarding As revealed that fly ash samples in the proximity of the active cassette had higher amounts of the element. Principal component analysis (PCA) showed that As had no impact on the classification of plant parts. BCF for As ranged from 1.44 to 23.8 and varied, depending on the investigated area; TF for As ranged from 0.43 to 2.61, indicating that the plant translocated As from root to shoot. In addition to As, Conyza canadensis L. exhibited efficient uptake of other metals from fly ash. According to the calculated BCF and TF, the plant retained Al, Fe and Cr in the root and translocated Zn, Cd, Cu and As from root to shoot in the course of the detoxifying process.

Rhizofiltration of Heavy Metals from Eutrophic Water Using Pistia Stratiotes in a Controlled Environment

The remediation of waters polluted with heavy metals using Pistia stratiotes was studied with the aim of assessing the potential of P.stratiotes as a rhizofiltration agent. Wild plants of P. stratiotes were grown in various high concentration solutions of Chromium(Cr), Lead(Pb) and Nickel(Ni). The plants were allowed to grow for twenty one days before harvesting. Metal concentrations were then determined using Atomic Absorption Spectrophotometry. The data generated from the analysis was subjected to analysis of variance (ANOVA) to determine if there is any significant difference between the treatments and the rate of multiplication of the plants. Different concentrations of the metals that were over 300 times what is obtainable in normal plants were observed. The uptake of Ni by P. stratiotes is higher than the uptake of other metals in this study. The uptake of metals was greater in the 2000 ppm treatment than in the other treatments. The plant is able to tolerate the high concentration of heavy metals without showing any visible symptoms. It is also capable of growing past and reproducing within the shortest possible time. P. stratiotes is an excellent candidate for rhizofiltration of heavy metal from polluted waters.

Trace metal complexation by the triscatecholate siderophore protochelin: structure and stability

Although siderophores are generally viewed as biological iron uptake agents, recent evidence has shown that they may play significant roles in the biogeochemical cycling and biological uptake of other metals. One such siderophore that is produced by A. vinelandii is the triscatecholate protochelin. In this study, we probe the solution chemistry of protochelin and its complexes with environmentally relevant trace metals to better understand its effect on metal uptake and cycling. Protochelin exhibits low solubility below pH 7.5 and degrades gradually in solution. Electrochemical measurements of protochelin and metal-protochelin complexes reveal a ligand half-wave potential of 200 mV. The Fe(III)Proto(3-) complex exhibits a salicylate shift in coordination mode at circumneutral to acidic pH. Coordination of Mn(II) by protochelin above pH 8.0 promotes gradual air oxidation of the metal center to Mn(III), which accelerates at higher pH values. The Mn(III)Proto(3-) complex was found to have a stability constant of log β(110) = 41.6. Structural parameters derived from spectroscopic measurements and quantum mechanical calculations provide insights into the stability of the Fe(III)Proto(3-), Fe(III)H(3)Proto, and Mn(III)Proto(3-) complexes. Complexation of Co(II) by protochelin results in redox cycling of Co, accompanied by accelerated degradation of the ligand at all solution pH values. These results are discussed in terms of the role of catecholate siderophores in environmental trace metal cycling and intracellular metal release.

Efficient Purification of Heavy-Metal-Contaminated Water by Microalgae-Activated Pine Bark

Batch experiments were performed to study metal sorption by pine bark and algae-treated bark. The biosorption of copper (Cu), lead (Pb), zinc (Zn), cadmium (Cd), cobalt (Co), and nickel (Ni) in synthetic multimetal aqueous solutions was studied as a function of metal content in solution, and amount and size of bark particles used for sorption. Influence of water hardness (Ca2+ only was tested) on the metal sorption process was also evaluated. Metal uptake from solutions with high heavy metal content (i.e. 10× the limit for leachate from landfills) was found to be independent of Ca2+ concentration. At low metal content in solution (i.e. 1× the limit for leachate from landfills), uptake of Cu, Zn, Ni, and Cd decreased with increasing Ca2+ content in water. Microalgae-treated bark was found to increase the metal sorption efficiency. Air-drying of bark-entrapped algae was shown to be the best method for sorbent drying. In general, the green algae, Chlorella sp. and Pseudokirchneriella subcapitata showed the best results in metal uptake. Sorption of Co, Zn, Ni, and Cd from solution with high levels of both heavy metals and calcium increased by almost 50% with algae treatment of bark was applied. At low levels of metals and calcium content, 100% uptake of Cu and Pb in water was observed. Uptake of other metals from solution with low metal and Ca content was relatively high (50–60%). Low pH (pH 3.0) had no influence on metal sorption from solutions with high metal content. For solutions with low metal content a decrease of metal uptake by 10–15% was observed for all the metals but Pb. Thus, the treatment of bark with microalgae was successful and influenced positively the uptake capacity of the bark.

Abstracts of Some Notable Papers Presented at the 2008 Meeting of the Junior Kentucky Academy of Science

Abstracts of Some Notable Papers Presented at the 2008 Meeting of the Junior Kentucky Academy of Science

Lichen Substances Prevent Lichens from Nutrient Deficiency

The dibenzofuran usnic acid, a widespread cortical secondary metabolite produced by lichen-forming fungi, was shown to promote the intracellular uptake of Cu(2+) in two epiphytic lichens, Evernia mesomorpha and Ramalina menziesii, from acidic, nutrient-poor bark. Higher Cu(2+) uptake in the former, which produces the depside divaricatic acid in addition to usnic acid, suggests that this depside promotes Cu(2+) uptake. Since Cu(2+) is one of the rarest micronutrients, promotion of Cu(2+) uptake by lichen substances may be crucial for the studied lichens to survive in their nutrient-poor habitats. In contrast, study of the uptake of other metals in E. mesomorpha revealed that the intracellular uptake of Mn(2+), which regularly exceeds potentially toxic concentrations in leachates of acidic tree bark, was partially inhibited by the lichen substances produced by this species. Inhibition of Mn(2+) uptake by lichen substances previously has been demonstrated in lichens. The uptake of Fe(2+), Fe(3+), Mg(2+), and Zn(2+), which fail to reach toxic concentrations in acidic bark at unpolluted sites, although they are more common than Cu(2+), was not affected by lichen substances of E. mesomorpha.

Uptake and Translocation of Heavy Metals in Salt Marsh Sediments by Spartina patens

The Hackensack Meadowlands is a coastal marsh system in northeastern New Jersey, located approximately 10 km west of New York City. Within the Meadowlands, twelve destructed or degraded estuarine wetland sites are currently part of ecological restoration projects that are in various phases of development from planning to completion (http:// www.meadowlands.state.nj.us/naturalresources/wetlands/ Wetlands.cfm). A completed restoration site is Harrier Meadow (North Arlington, NJ) where mitigation work included the creation of channels, impoundments, low marsh habitat and upland habitat islands. Important salt marsh plant species such as salt-meadow grass (Spartina patens), and spike grass (Distichlis spicata) dominate portions of the marsh. The sediments of Harrier Meadow contain heavy metals at concentrations that are below regulatory action limits (e.g., cadmium (Cd) 0–1 ppm; chromium (Cr) 10–18 ppm; copper (Cu) 13–60 ppm; nickel (Ni) 7–15 ppm; lead (Pb) 0–87 ppm; zinc (Zn) 28–94 ppm) (http:// www.meri.njmeadowlands.gov/ecorisk/), but above those typically found in uncontaminated environments (van Driel et al. 1995; Swaileh et al. 2004). Since Spartina species have been shown to take up heavy metals into roots and translocate them into aboveground parts (see Weis and Weis (2004) for review), we had investigated the fate and the effects of selected heavy metals (i.e., Cd, Cr, Cu, Ni, Pb, and Zn) in sediment cores that were densely covered with Spartina patens in a recent short-term study (Suntornvongsagul et al. 2007). Since levels of metals taken up and translocated had been shown to vary depending on the metal concentration in the substrate (Vogel-Mikus et al. 2005), and to be affected by the presence of other metals (McKenna et al. 1993; Podar et al. 2004), half of these cores were artificially amended with Ni in order to increase its availability, and to assess potential effects on uptake of other metals. Ni was chosen since it was the most accumulated metal in shoots from a mixture containing Cd(II), Cu(II), Ni(II) and Zn(II) in identical concentrations (Peralta-Videa et al. 2002), and was assumed to persist in hydrated form in pore water. We demonstrated that Ni-amendment had no significant effect on the fate of other metals in sediments, however, observed increased root-uptake of certain metals. Although translocation of Ni into shoots reflected the 10-fold higher concentrations in sediments and roots in Ni-amended cores, metal translocation into shoots was generally small for all metals (Suntornvongsagul et al. 2007). The goal of the current study was to extend the observations beyond the first growing season, and to assess whether Ni-amendment had effects on metal uptake and translocation after three growing seasons.

Investigation of the basis for Ni tolerance conferred by the expression of TjZnt1 and TjZnt2 in yeast strains

Introduction of ZIP family transporter gene homologues TjZnt1 and TjZnt2 (metal ion transporters) into yeast strains conferred increased Ni(II) tolerance in that species. The action of ZIP family transporter homologues, however, could not explain the Ni resistance of yeast strains transformed with TjZnt1 and TjZnt2. To elucidate the mechanism of Ni tolerance conferred by TjZnt1 and TjZnt2 in yeast strains, we made a series of investigations based upon three hypotheses, including (1) cellular Ni efflux, (2) exclusion of Ni due to competitive uptake of other metals, and (3) Ni binding to histidine-rich domains (chelation). The critical Ni tolerance level of TjZnt2 expressing yeast strains was 1.4 mM, whereas, the TjZnt1 expressing yeast strains were tolerant of Ni concentrations as high as 2.0 mM. The TjZnt1 expressing yeast strain had significantly lower Ni content and significantly higher Zn content than the control and TjZnt2 expressing yeast strain. Effects of the deletion of histidine-rich domain HRD1 or HRD2, or deletion of the region from HRD1 to HRD2, resulted in the same or slightly less Ni(II) tolerance in the TjZnt1 expressing yeast strain. These data indicate that Ni tolerance of the TjZnt2 expressing yeast strain is not correlated with binding to HRDs (Hypothesis 3). Ni tolerance of TjZnt1 expressing yeast strain was, however, partially correlated with Zn influx, which suppressed Ni influx, therefore Ni influx (Hypothesis 1) and competitive inhibition of Ni influx by other metals (Hypothesis 2), remain viable hypotheses which will be subject to further testing.

Identification of a Crucial Histidine Involved in Metal Transport Activity in the Arabidopsis Cation/H+ Exchanger CAX1

In plants, yeast, and bacteria, cation/H+ exchangers (CAXs) have been shown to translocate Ca2+ and other metal ions utilizing the H+ gradient. The best characterized of these related transporters is the plant vacuolar localized CAX1. We have used site-directed mutagenesis to assess the impact of altering the seven histidine residues to alanine within Arabidopsis CAX1. The mutants were expressed in a Saccharomyces cerevisiae strain that is sensitive to Ca2+ and other metals. By utilizing a yeast growth assay, the H338A mutant was the only mutation that appeared to alter Ca2+ transport activity. The CAX1 His338 residue is conserved among various CAX transporters and may be located within a filter for cation selection. We proceeded to mutate His338 to every other amino acid residue and utilized yeast growth assays to estimate the transport properties of the 19 CAX mutants. Expression of 16 of these His338 mutants could not rescue any of the metal sensitivities. However, expression of H338N, H338Q, and H338K allowed for some growth on media containing Ca2+. Most interestingly, H338N exhibited increased tolerance to Cd2+ and Zn2+. Endomembrane fractions from yeast cells were used to measure directly the transport of H338N. Although the H338N mutant demonstrated 25% of the wild type Ca2+/H+ transport, it showed an increase in transport for both Cd2+ and Zn2+ reflected in a decrease in the Km for these substrates. This study provides insights into the CAX cation filter and novel mechanisms by which metals may be partitioned across membranes.

Iron (II) distribution and oxidation kinetics in hydrothermal plumes at the Kairei and Edmond vent sites, Indian Ocean

Deep-sea hydrothermal activity cycles the entire volume of the global ocean through deep-sea hydrothermal plumes at least every 4–8 × 10 3 a, a rapid timescale that is comparable to global deep-ocean mixing. An important process within hydrothermal plumes is the oxidation of dissolved iron discharged with vent fluids, leading to the co-precipitation of many other vent-sourced metals, thus, modifying gross hydrothermal fluxes to the deep ocean, and acting as a net sink in the ocean chemical budgets of certain key tracers. Here, we report direct measurements of dissolved Fe(II) oxidation rates from two recently discovered Indian Ocean vent sites that are intermediate between Pacific and Atlantic values, thus demonstrating that the rate of iron oxidation and formation of scavenging Fe(III) solid phases, in hydrothermal plumes varies systematically along the global deep-ocean “conveyor.” The average pseudo first-order rate constant for the oxidation reaction is 0.303 h −1 and the corresponding half-life 2.31 h. The rate plots show some curvature, however, indicating additional processes, possibly interactions with organic matter, may also influence the net oxidation/removal rate. Different rates of oxidation of iron in hydrothermal plumes in different ocean basins have important implications for the dispersion of produced oxide phases, which in turn may impact on uptake of other metals from seawater and deposition into underlying ridge-crest and ridge flank sediments.

The Effect of pH and Plaque on the Uptake of Cu and Mn in Phragmites australis(Cav.) Trin ex. Steudel

The physico-chemical properties of iron oxyhydroxide plaques formed on the roots of Phragmites australis under field and laboratory conditions were determined using electron microscopy and energy dispersive spectrometry (EDS) analysis. Plaques were present as an amorphous coating on roots with an uneven distribution. They were shown to be composed of iron in both the field and laboratory, and phosphorus was found to be adsorbed onto the surface of plaques formed in the laboratory. The uptake of copper and manganese in the presence and absence of plaque was investigated under two different pH regimes. Concentrations of Cu were lower in the shoots of P. australis in the presence of plaque (565mg kg−1) than when it was absent (1400mg kg−1), under growth conditions of higher pH (6.0). The adsorption of Cu and Mn onto the plaque surface was not the mechanism by which plaque reduced the uptake of other metals. Alternatively, the plaque may simply act as a physical barrier. Under conditions of lower pH (3.5) the activity of hydrogen ions at the root surface interfered with the movement of metals into the root and masked any potential effect of iron plaque.

Effective regulation of iron acquisition in graminaceous plants. The role of mugineic acids as phytosiderophores

Discovery of mugineic acids as phytosiderophores has shown that some graminaceous monocotyledonous plants have a different iron acquisition strategy (strategy II) from dicotyledonous and nongraminaceous monocotyledonous plants (strategy I). The process of iron acquisition by strategy II plants can be divided into four main steps: biosynthesis, secretion, solubilization, and uptake, all of which are effectively regulated by different systems. The biosynthesis of mugineic acids is controlled by an on‐off system which is operated under the control of iron demand in the plant. All mugineic acids share the same biosynthetic pathway from L‐methionine to 2′‐deoxymugineic acid, but the subsequent steps differ among plant species and even cultivars. The biosynthesis of mugineic acids is associated with the methionine recycling pathway. The secretion of mugineic acids shows a distinct diumal rhythm. Mugineic acids solubilize sparingly soluble inorganic iron by chelation and possess a high chelation affinity for iron, but not for other polyvalent ions such as Ca2+, Mg2+ and Al3+. The iron uptake process is regulated by a specific uptake system that transports the mugineic acid‐Fe(III) complex as an intact molecule. This system specifically recognizes the mugineic acid‐Fe(III) complexes, but not other mugineic acid‐metal or synthetic chelator‐Fe(III) complexes, suggesting that binding sites with strict recognition for stereostructure of the complex are located on the plasma membrane. All these regulatory systems are considered to represent an efficient strategy to acquire adequate amounts of iron and to avoid factors unfavorable for iron acquisition such as high pH, high concentrations of bicarbonate, Ca2‐ and Mg2+, microbial degradation, and uptake of other metals that are common in calcareous soils.

Ultrastructural localization of calcium, byelectron-probe X-ray microanalysis, in the small intestine of suckling rats

The subcellular distribution of calcium has been investigated in samples, from the intestinal mucosa of 10-day-old rats, prepared for X-ray microanalysis by various techniques designed to minimize the loss of this element. Calcium retention and its threshold of detection was most satisfactory in freeze-dried frozen thin sections. In resin-embedded samples the best retention of calcium was found in specimens fixed in absolute ethanol, embedded without osmication, and sectioned onto glycerol. The results of this investigation indicate the presence of calcium in the supranuclear vacuole of enterocytes in the distal intestine of the neonatal rat. This calcium is probably taken up during the endocytosis of material from the intestinal lumen. The same mechanism may also be important in the uptake of other metals by suckling animals.

Species associations and metal contents of algae from rivers polluted by heavy metals

SUMMARY. The algal flora of the Rivers Hayle and Gannel. whieh drain copper and lead mining regions of Cornwall, are described and compared. Although fluctuations in the rarer members of the algal communities were observed, the dominant filamentous algae at most sites did not change over the year of study. Both the total algal abundance and the number of species were depressed at high metal sites. Associations of species that were evident in field samples were confirmed and correlated with water metal levels by principal component analysis. The close similarity between the flora of similar sites on the copper‐polluted River Hayle and the lead‐polluted River Gannei implies that the degree of metal pollution, rather than the polluting metal per se, determines the species present. All mine sites were characterized by a Microspora ‐community whereas a Zygnemales community of Spirogyra and Mougeotia species was typical of low metal pollution. Moderately polluted sites downsteam of the mines had an intermediate flora of Zygnemaies, Microsporales. Ulotrichales and gelatinous Volvocales and Tetrasporales species. No species could be said to invariably indicate metal pollution; the most abundant species at highly contaminated sites were also those with the widest distributions.Field samples of filamentous algae (mainly Spirogyra, Zygogonium, Mougeotia and Microspora species) contained metal concentrations several orders of magnitude greater than ambient levels. For copper and iron, both algal metal contents and concentration ratios (μg g‐1 algae/μg ml‐1 water) were positive functions of water metal levels, although algal iron appeared to plateau at water concentrations of about 1 mg ml‐1. Algal lead concentrations, but not the concentration ratios, also were positively correlated with water lead levels. Thus, for these three metals, the algal metal contents were indicative of ambient conditions. In contrast, algal zinc concentrations were nearly constant and consequently the concentration ratios for this metal were inversely related to water levels. This result suggests that unlike the uptake of other metals, uptake of zinc by these aigae may be strictly regulated.

Species of dissolved metals derived from oligotrophic hard water

By fractioning of dissolved organic carbon (DOC) and of associated metals Na, K, Mg, Ca, Al, Fe, Mn, Ni, Cr, Cu, Pb, Cd, and Zn according to the molecular sizes by means of gel chromatography in several stages, it could be shown that all metals, even the alkaline and alkaline earth metals, are, to a measurable degree, present in chelated form. This type of association covers 97.3% with Pb, 94.6% with Al, 91.5% with Cr, 82.2% with Fe of the total concentrations of each metal mentioned. About 69% of all metal chelates are represented by Mg-compounds. This may be caused by pre-treatment procedures, nevertheless the Mg-concentrations of the different DOC-fractions indicating to be one regulating factor for the uptake of other metals in the studied hard water. The chelated form was also obtained with Mn, Cd, Zn, and Mg, while with Cu, Ni, Na, Ca, and K there is an abundance of ionic forms. The metal distribution within the different molecular size fractions of the DOC proves the existence of specific distribution pattern for Pb and Mn: Pb is preferably chelated by macromolecular substances, whereas Mn combines mainly with minor ones. Cr seems to behave similar as Pb. Regulation' mechanisms for the different metal distribution patterns within the DOC-fractions as well as ecophysiological aspects of the results are discussed.