Toxic metal biosorption by macrocolonies of cyanobacterium <Emphasis Type="Italic">Nostoc sphaeroides</Emphasis> Kützing

The cyanobacterium Nostoc sphaeroides Kützing is expected to be effective in toxic metal adsorption as it produces abundant exopolysaccharides with functional groups. Therefore, the adsorption properties of Cu²⁺, Cd²⁺, Cr³⁺, Pb²⁺, Ni²⁺, and Mn²⁺ on fresh macrocolonies and algal powder of N. sphaeroides were compared at pH 5 and 25 °C. The adsorption capacity of fresh biomass for Pb²⁺ and of algal powder for Pb²⁺ and Cr³⁺ were highest in single metal solutions. Compared to the fresh biomass, the metal adsorption capacities of algal powder were similar for Ni²⁺, Cd²⁺, and Pb²⁺ and slightly greater for Cr³⁺, but they were markedly smaller for Mn²⁺ and Cu²⁺. Coexisting ions (in tap water or in multiple solutions) significantly decreased the metal adsorption capacity, except for Cr³⁺ in tap water. The Pb²⁺ and Cr³⁺ adsorption dynamic process fitted the pseudo-second-order model well, showing fast adsorption at the first stage in 10 and 20 min, respectively. Higher pH in acidic ranges favored the adsorption greatly. The Langmuir isotherm model was suitable for explaining the adsorption, and the maximum adsorption capacities were 116.28 and 22.37 mg g^?1 for Pb²⁺ and Cr³⁺, respectively. The adsorption process was endothermic, confirmed by the significantly higher adsorption capability at higher temperature. Hydroxyl, amino, and carboxyl groups were the main functional groups based on Fourier transform infrared spectroscopy analysis, and they bind to metal ions via ion exchange. The results suggest that fresh macrocolonies of N. sphaeroides can be used as an effective biosorbent for metal ion removal, especially for Pb²⁺ and Cr³⁺.     

Biosorption of Heavy Metals (Cd2+, Cu2+, Co2+, and Mn2+) by Thermophilic Bacteria,Geobacillus thermantarcticus and Anoxybacillus amylolyticus: Equilibrium and Kinetic Studies

ABSTRACT

Two strains of thermophilic bacteria, Geobacillus thermantarcticus and Anoxybacillus amylolyticus, were employed to investigate the biosorption of heavy metals including Cd²⁺, Cu²⁺, Co²⁺, and Mn²⁺ ions. The effects of different biosorption parameters such as pH (2.0–10.0), initial metal concentrations (10.0–300.0 mg L^?1), amount of biomass (0.25–10 g L^?1), temperature (30–80°C), and contact time (15–120 min) were investigated. Concentrations of metal ions were determined by using an inductively coupled plasma optical emission spectrometry (ICP-OES). Optimum pHs for Cd²⁺, Cu²⁺, Co²⁺, and Mn²⁺ biosorption by Geobacillus thermantarcticus were found to be 4.0, 4.0, 5.0, and 6.0, respectively. For Anoxybacillus amylolyticus, the optimum pHs for Cd²⁺, Cu²⁺, Co²⁺, and Mn²⁺ biosorption were found to be 5.0, 4.0, 5.0, and 6.0, respectively. The Cd²⁺, Cu²⁺, Co²⁺, and Mn²⁺ removals at 50 mg L^?1 in 60 min by 50 mg dried cells of Geobacillus thermantarcticus were 85.4%, 46.3%, 43.6%, and 65.1%, respectively, whereas 74.1%, 39.8%, 35.1%, and 36.6%, respectively, for Anoxybacillus amylolyticus. The optimum temperatures for heavy metal biosorption were near the optimum growth temperatures for both strains. Scatchard plot analysis was employed to obtain more compact information about the interaction between metal ions and biosorbents. The plot results were further studied to determine if they fit Langmuir and Freundlich models.     

Multi-metal biosorption and bioaccumulation by Exiguobacterium sp. ZM-2

The present work deals with the biosorption performance of dried and non-growing biomasses of Exiguobacterium sp. ZM-2, isolated from soil contaminated with tannery effluents, for the removal of Cd²⁺, Ni²⁺, Cu²⁺, and Zn²⁺ from aqueous solution. The metal concentrations studied were 25 mg/l, 50 mg/l, 100 mg/l, 150 mg/l and 200 mg/l. The effect of solution pH and contact time was also studied. The biosorption capacity was significantly altered by pH of the solution. The removal of metal ions was conspicuously rapid; most of the total sorption occurred within 30 min. The sorption data have been analyzed and fitted to the Langmuir and Freundlich isotherm models. The highest Q_max value was found for the biosorption of Cd²⁺ at 43.5 mg/g in the presence of the non-growing biomass. Recovery of metals (Cd²⁺, Zn²⁺, Cu²⁺ and Ni²⁺) was found to be better when dried biomass was used in comparison to non-growing biomass. Metal removal through bioaccumulation was determined by growing the bacterial strain in nutrient broth amended with different concentrations of metal ions. This multi-metal resistant isolate could be employed for the removal of heavy metals from spent industrial effluents before discharging them into the environment.     

Uptake of Metal Ions by Rhizopus arrhizus Biomass

Rhizopus arrhizus biomass was found to absorb a variety of different metal cations and anions but did not absorb alkali metal ions. The amount of uptake of the cations was directly related to ionic radii of La³⁺, Mn²⁺, Cu²⁺, Zn²⁺, Cd²⁺, Ba²⁺, Hg²⁺, Pb²⁺, UO₂²⁺, and Ag⁺. The uptake of all the cations is consistent with absorption of the metals by sites in the biomass containing phosphate, carboxylate, and other functional groups. The uptake of the molybdate and vanadate anions was strongly pH dependent, and it is proposed that the uptake mechanism involves electrostatic attraction to positively charged functional groups.     

Metal resistance and removal by two strains of the green alga, <Emphasis Type="Italic">Chlorella vulgaris</Emphasis> Beijerinck,isolated from Laguna de Bay,Philippines

Two strains of Chlorella vulgaris Beijerinck isolated from two different sites in Laguna de Bay, Philippines, were studied for their resistance and ability to remove four metal ions, i.e., Cu²⁺, Cr⁶⁺, Pb²⁺, and Cd²⁺ added separately in BG-11 growth medium. The growth of the two strains was severely inhibited at 2 mg.L⁻¹ of Cu²⁺, 5 mg.L⁻¹ of Cr⁶⁺, 8 mg.L⁻¹ of Pb²⁺, and 10 mg.L⁻¹ of Cd²⁺. However, the two strains exhibited different EC₅₀ values for the same metal ion. The WB strain had a significantly higher resistance (p < 0.01) for Cd²⁺ and Cr⁶⁺ compared with the SB strain, while the SB strain had significantly higher resistance (p < 0.01) for Cu²⁺ compared with the WB strain. On the other hand, the two strains behaved differently in their capacity to remove the metal ions in BG-11 medium containing 1.0 mg.L⁻¹ of the three metal ions, except for Cu²⁺, which was added at 0.1 mg.L⁻¹. The WB strain showed the highest removal of Cd²⁺ at 70.3% of total, followed by Pb²⁺ at 32%, while the SB strain exhibited the highest removal of Pb²⁺ at 48.7% followed by Cd²⁺ at 40.7% of the total. Both strains showed the least removal of Cr⁶⁺ at 28% and 20.8% of the total for the WB and SB strains respectively. The percentage removal for Cu²⁺ was 50.7% and 60.8% for the WB and SB strains respectively. After 12 days of incubation, both strains showed that a greater percentage of the metal ions removed were accumulated intracellularly than adsorbed at a ratio of at least 2:1. Both strains manifested the same cytological deformities, like a loss of pyrenoids at 10 mg.L⁻¹ in all four metal ions. Discoloration and disintegration of chloroplasts were observed at 1.0 mg.L⁻¹ in Cu²⁺ and 5 mg.L⁻¹ in Cr⁶⁺. The nonrelease of autospores from the mother cells was observed at 10 mg.L⁻¹ in Cu²⁺ and Cr⁶⁺. Presented at the 6th Meeting of the Asian Pacific Society of Applied Phycology, Manila, Philippines.     

Biosorption of chromium to fungi

Eighteen fungal strains were isolated from water and soil samples and tested for their ability to enrich chromium. The microorganism with the highest enrichment capacity, a zygomycete (Mucor hiemalis MP/92/3/4), was chosen for detailed investigations. Some basic tests such as the pH-dependence, the kinetics of the enrichment and the metal selectivity were carried out with the two most frequent oxidation states of chromium, the trivalent cation (Cr³⁺) and the hexavalent anion (CrO₄ ^2–). With Cr³⁺ the enrichment showed a saturation kinetic reaching 70% of the maximum capacity after about 30 min, whereas with CrO₄ ^2– a linear time course with a much lower metal enrichment was observed. The highest level of enrichment for Cr³⁺ was observed at pH 5.5 (21.4 mg/g dry wt), and for CrO₄ ^2– at pH 1 (4.3 mg/g dry wt). Investigations concerning the metal enrichment selectivity resulted in the following series of decreasing ion uptake: Cr³⁺ > Cu²⁺ > Pb²⁺ > Ag⁺ > Al³⁺ > Co²⁺ > Zn²⁺ > Ni²⁺ > Fe²⁺ > Mo⁵⁺ > Cd²⁺ > ^2– > CrO₄ ^2– > VO^3–, calculated on a molar basis. Trivalent chromium caused a staining of the outer cell wall region in transmission electron microscopy. The localization of chromium in the stained outer layers of the cell wall could be verified by electron energy loss spectroscopy. The enrichment of Cr³⁺ by M. hiemalis seemed to be mainly a passive biosorption to the cell wall, whereas for the uptake of CrO₄ ^2– intracellular accumulation as well as biosorption is possible.     

Heavy metal resistant <Emphasis Type="Italic">Distigma proteus</Emphasis> (Euglenophyta) isolated from industrial effluents and its possible role in bioremediation of contaminated wastewaters

Summary The alga, Distigma proteus, isolated from industrial wastewater showed tolerance against Cd²⁺ (8.0 μg/ml), Cr⁶⁺ (12 μg/ml), Pb²⁺ (15 μg/ml) and Cu²⁺ (10 μg/ml). The metal ions slowed down the growth of the organism after 4–5 days of exposure. The reduction in cell population was 90% for Cu²⁺, 84% for Cd²⁺, 71% for Cr⁶⁺, and 63% for Pb²⁺ after 8 days of metal stress. The order of resistance to heavy metal, in terms of reduction in the cellular population, was Cu²⁺ > Cd²⁺ > Cr⁶⁺ > Pb²⁺. Chromium- and cadmium-processing capabilities of the alga were worked out for its potential use as a bioremediator of wastewater. The reduction in the amount of Cr⁶⁺ after 2, 4, 6 and 8 days of algal culture containing 5.0 μg Cr⁶⁺ ml⁻¹ of culture medium was 77, 85, 92 and 97%, respectively. Distigma could also remove 48% Cd²⁺after 2 days, 68% after 4 days, 80% after 6 days and 90% after 8 days from the medium. The heavy metal uptake ability of Distigma can be exploited for metal detoxification and environmental clean-up operations.     

Naked Eye Detection of Cr3+ and Co2+ Ions by Gold Nanoparticle Modified with Azomethine

This paper reports the synthesis of azomethine-modified gold nanoparticles with azomethine (azomethine-AuNPs) in aqueous media, which were characterized by FT-IR spectroscopy, ultraviolet–visible spectroscopy (UV-Vis), dynamic light scattering (DLS), thermogravimetric analysis (TGA), and transmission electron microscopy (TEM). The azomethine-AuNPs were employed as colorimetric for Cr³⁺ and Co²⁺ ions at pH 6.2–7.5 and 8.1–9.1, at room temperature in aqueous solution. In the presence of Cr³⁺ and Co²⁺, the azomethine-AuNPs induce aggregation of the nanoparticles. Upon aggregation, the surface plasmon absorption band red-shifts so that the nanoparticle solution appears a blue color. The sensitivity of azomethine-AuNPs towards other metal ions, Mg²⁺, Mn²⁺, Cr⁶⁺, Na⁺, Ni²⁺, Ag⁺, Al³⁺, Ca²⁺, Cd²⁺, Cu²⁺, Fe²⁺, Fe³⁺, Hg²⁺, Cd²⁺, K⁺, Co³⁺, Ni²⁺, Pb²⁺, and Zn²⁺ are negligible. This highly selective sensor allows a direct quantitative assay of Co²⁺ and Cr³⁺ with colorimetric detection limits of 83.22 and 108 nM, respectively.

     

Gellan gel beads containing magnetic nanoparticles: An effective biosorbent for the removal of heavy metals from aqueous system

This study describes an efficient adsorbent consisting of magnetic Fe₃O₄ and gellan gum, which couples magnetic separation with ionic exchange for heavy metal removal. Adsorption kinetics analysis showed that the adsorption capacities were in an order of Pb²⁺ > Cr³⁺ > Mn²⁺. Different experimental parameters studies indicated that adsorbent dosage, initial metal concentration, temperature and initial pH played important roles in adsorption process. Additionally, the Freundlich model gave a better fit to the experimental data than the Langmuir model. Chemical analysis of calcium ions released into the bulk solutions demonstrated that carboxyl group is critical for binding Pb²⁺, Mn²⁺ and Cr³⁺. Furthermore, a high desorption efficiency was obtained by sodium citrate.     

Effect of heavy metal ions on growth and biochemical characteristics of photosynthesis of barley and maize seedlings

The effects of Cu²⁺, Zn²⁺, Cd²⁺ and Pb²⁺ on growth and the biochemical characteristics of photosynthesis were more expressed in barley (Hordeum vulgare L.) than in maize (Zea mays L.) seedlings. The barley and maize seedlings exhibited retardation in shoot and root growth after exposure of Cu²⁺, Cd²⁺ and Pb²⁺. The Zn²⁺ions practically did not influence these characteristics. The total protein content of barley and maize roots declined with an increase in heavy metal ion concentrations. The protein content of barley shoots was only slighly decreased with an increase in heavy metal ion concentrations, but the protein content in maize shoots was increased under the same conditions. The chlorophyll content was decreased in barley shoots and increased in maize. The ribulose-l,5-bisphosphate carboxylase (RuBPC, EC 4.1.1.39) and phosphoenolpyruvate carboxylase (PEPC, EC 4.1.1.31) activities were decreased drastically by Cu²⁺, Cd²⁺ and Pb²⁺ in thein vivo experiments. The tested heavy metal ions affect photosynthesis probably mainly by inhibition of these key carboxylating enzymes: this mechanism was studied in thein vitro experiments.     

Characterization of cadmium removal by Rhodotorula sp. Y11

Experiments were conducted studying the removal of Cd²⁺ from water via biosorption using Rhodotorula sp. Y11. The effects of temperature and initial pH of the solution on biosorption were studied. Caustic and heat treatments showed different influences on the biosorption capacity, and the highest metal uptake value (19.38 mg g⁻¹) was obtained by boiling treated yeast cells. The presence of competing cations, such as Ag⁺, Cu²⁺, and Mg²⁺, except Na⁺ ions, significantly interfered with the metal uptake. Results indicate that the Langmuir model gave a better fit to the experimental data than the Freundlich equation. The q ₁₀ value was 11.38 mg g⁻¹ for Cd²⁺ uptake by Y11. Chemical modifications of the biomass demonstrated that carboxyl and amide groups play an important role in Cd²⁺ biosorption.     

A multinuclear nmr relaxation study of the interaction of divalent metal ions with l-aspartic acid

Carbon-13 spin-lattice relaxation times, T₁, have been measured for aqueous solutions of L-aspartic acid, L-alanine, O-phospho-L-serine, and 2-mercapto-L-succinic acid in the presence of the paramagnetic metal ions, Cu²⁺ and Mn²⁺, and Mg²⁺ as a diamagnetic control, at ambient temperature and neutral pH. Nitrogen-15, oxygen-17 and proton relaxation times were also obtained for L-aspartic acid and phosphorus-31 relaxation times for O-phospho-L-serine under similar conditions. The structures of these complexes in solution were determined from the various metal ion-nuclei distances calculated from the paramagaetically-induced relaxation. These results indicate that the Cu²⁺ interaction with L-aspartic acid is through α-amino and β-carboxyl groups while Mn²⁺ coordinates most strongly through α-and β-carboxyl groups, with the possibility of a weak interaction through the amino group.An examination of the coordination of these divalent metal ions to an analog of L-aspartic acid in which the β-carboxyl group is replaced by a phosphate group (O-phospho-L-serine) indicated that Cu²⁺ coordination is now probably through the α-amino and phosphate groups, while this analog is a monodentate ligand for Mn²⁺ coordinating through the phosphate group. Removal of the β-carboxyl group (L-alanine) also results in Cu²⁺ coordination through the α-carboxyl and α-amino groups, and the same ligand interactions are observed with Mn²⁺. Replacement of the α-amino group of L-aspartic acid with an - SH group (2-mercapto-L-succinate) is sufficient to eliminate any specific coordination with either Cu²⁺ or Mn²⁺.     

Probing the coordination properties of glutathione with transition metal ions (Cr2+,Mn2+,Fe2+,Co2+, Ni2+,Cu2+,Zn2+,Cd2+,Hg2+) by density functional theory

Complexes formed by reduced glutathione (GSH) with metal cations (Cr²⁺, Mn²⁺,Fe²⁺,Co²⁺,Ni²⁺,Cu²⁺,Zn²⁺,Cd²⁺,Hg²⁺) were systematically investigated by the density functional theory (DFT). The results showed that the interactions of the metal cations with GSH resulted in nine different stable complexes and many factors had an effect on the binding energy. Generally, for the same period of metal ions, the binding energies ranked in the order of Cu²⁺>Ni²⁺>Co²⁺>Fe²⁺>Cr²⁺>Zn²⁺>Mn²⁺; and for the same group of metal ions, the general trend of binding energies was Zn²⁺>Hg²⁺>Cd²⁺. Moreover, the amounts of charge transferred from S or N to transition metal cations are greater than that of O atoms. For Fe²⁺,Co²⁺,Ni²⁺,Cu²⁺,Zn²⁺,Cd²⁺ and Hg²⁺ complexes, the values of the Wiberg bond indices (WBIs) of M-S (M denotes metal cations) were larger than that of M-N and M-O; for Cr²⁺ complexes, most of the WBIs of M-O in complexes were higher than that of M-S and M-N. Furthermore, the changes in the electron configuration of the metal cations before and after chelate reaction revealed that Cu²⁺, Ni²⁺,Co²⁺ and Hg²⁺ had obvious tendencies to be reduced to Cu⁺,Ni⁺,Co⁺ and Hg⁺ during the coordination process.     

Effect of heavy metals on the glutathione status in different ectomycorrhizal <Emphasis Type="Italic">Paxillus involutus</Emphasis> strains

The glutathione (GSH) status and heavy metal tolerance were investigated in four Paxillus involutus strains isolated from different heavy-metal-polluted and non-polluted regions of Europe. The heavy metal burden in the habitats did not affect significantly either the heavy metal (Cr₂O₇²⁻, Cd²⁺, Hg²⁺, Pb²⁺, Zn²⁺, Cu²⁺) tolerance and accumulation or the GSH production of the strains tested. Exposures to heavy metals increased the intracellular GSH concentrations in 12 from 24 experimental arrangements (four strains exposed to six heavy metals) independently of the habitats of the strains. The importance of GSH in heavy metal tolerance (high MIC values, ability to accumulate heavy metals and to grow in the presence of heavy metals) was thus demonstrated in this ectomycorrhizal fungus.     

pH effects on the removal of Cu2+, Cd2+ and Pb2+ from aqueous solution by waste brewery biomass

An industrial strain of Saccharomyces cerevisiae collected from the waste of a brewing industry was used to remove lead, cadmium and copper from aqueous solutions (1?mm). Metal removal efficiency by using either biomass suspension directly diluted into the metal solutions or biomass previously incubated and washed in distilled water was compared. In all experiments with unwashed biomass a shift in the medium pH from 4.5 to a final value in the 7.0–8.0 range occurred. This pH increase was responsible for a metal precipitation effect associated to the metal biosorption. A very different pH profile was observed when washed biomass was used leading to different removal profiles for Cd²⁺ and Pb²⁺ and a similar one for Cu²⁺. In the absence of biomass, medium components and/or the excreted intracellular products proved to interfere in the metal removal and to be responsible for 80% Pb²⁺ precipitation, in the pH 4.5–5.0 range. To initial metal solution pH, leading to the lowest residual ion concentrations, after 96?h of contact with unwashed biomass and in the absence of pH adjustment, was 4.5–5.0. Continuous or stepwise adjustment of medium pH to this range during the process was unfavourable for metal removal, being the continuous adjustment the worst procedure. In this case, Cd²⁺ was not biosorbed and Cu²⁺ removal decreased from 76 to 33%. However, Pb²⁺ was always extensively removed (89%) and only slightly affected by pH control. The global results suggest different removal mechanisms for each cation. Cu²⁺ was removed by both metal sorption and precipitation, due to the pH shift that occurred during the process, while Cd²⁺ removal showed to be completely dependent of this pH shift. Pb²⁺ was totally and quickly removed, by precipitation, in the presence of the biomass suspension and at pH 4.5. Moreover, the biosorbent changes occurring during the process played an important role in the metal removal when non-viable microbial biomass is used.     

OPTIMIZATION OF SOME HEAVY METALS BIOSORPTION BY REPRESENTATIVE EGYPTIAN MARINE ALGAE1

Marine algae—as inexpensive and renewable natural biomass—have attracted the attention of many investigators to be used to preconcentrate and biosorb many heavy metal ions. Impressed by this concept, the metal uptake capacity of Egyptian marine algae was examined using representatives of green and brown algae, namely, Ulva lactuca L. and Sargassum latifolium (Turner) C. Agardh, respectively. The biosorption efficiencies of Cu²⁺, Co²⁺, Ni²⁺, Cd²⁺, Hg²⁺, Ag²⁺, and Pb²⁺ ions seem to depend on the type of the algae used as well as the conditions under which the uptake processes were conducted. It was demonstrated that a pH range of 7.5–8.8 was optimum for the removal of the tested metals. Similarly, the uptake process was markedly accelerated during the first 2 h using relatively low metal level and sufficient amounts of the dried powdered tested algae.     

Comparison of Rhizopus nigricans in a pelleted growth form with some other types of waste microbial biomass as biosorbents for metal ions

Biosorption of metal ions (Li⁺, Ag⁺, Pb²⁺, Cd²⁺, Ni²⁺, Zn²⁺, Cu²⁺, Sr²⁺, Fe²⁺, Fe³⁺ and Al³⁺) by Rhizopus nigricans biomass was studied. It was shown that metal uptake is a rapid and pH-dependent process, which ameliorates with increasing initial pH and metal concentrations. Different adsorption models: Langmuir, Freundlich, split-Langmuir and combined nonspecific-Langmuir adsorption isotherm were applied to correlate the equilibrium data. The maximum biosorption capacities for the individual metal ions were in the range from 160 to 460 mol/g dry weight. Scatchard transformation of equilibrium data revealed diverse natures of biomass metal-binding sites. The binding of metals was also discussed in terms of the hard and soft acids and bases principle. The maximum biosorption capacities and the binding constant of R. nigricans were positively correlated with the covalent index of metal ions.The following types of waste microbial biomass originating as by-products from industrial bioprocesses were tested for biosorption of metal ions: Aspergillus terreus, Saccharomyces cerevisiae, Phanerochaete chrysosporium, Micromonospora purpurea, M. inyoensis and Streptomyces clavuligerus. The determined maximum biosorption capacities were in the range from 100 to 500 mol/g dry weight. The biosorption equilibrium was also represented with Langmuir and Freundlich sorption isotherms.     

Effects of heavy metal cations on the mitochondrial ornithine/citrulline transporter reconstituted in liposomes

The effect of heavy metal cations on the mitochondrial ornithine/citrulline transporter was tested in proteoliposomes reconstituted with the protein purified from rat liver. The transport activity was measured as [³H]ornithine uptake in proteoliposomes containing internal ornithine (ornithine/ornithine antiport mode) or as [³H]ornithine efflux in the absence of external substrate (ornithine/H⁺ transport mode). 0.1 mM Cu²⁺, Pb²⁺, Hg²⁺, Cd²⁺ and Zn²⁺ strongly inhibited (more than 85%) the antiport; whereas Mn²⁺, Co²⁺ and Ni²⁺ inhibited less efficiently (25, 47 and 69%, respectively). The IC₅₀ values of the transporter for the different metal ions ranged from 0.71 to 350 μM. Co²⁺ and Ni²⁺ also inhibited the [³H]ornithine efflux whereas Cu²⁺, Pb²⁺, Hg²⁺, Cd²⁺ and Zn²⁺ stimulated the [³H]ornithine efflux. The stimulation of the [³H]ornithine efflux by Cu²⁺ and Cd²⁺ (as well as by Pb²⁺, Hg²⁺ and Zn²⁺) was not prevented by NEM and was reversed by DTE. These features indicated that the inhibition of the antiport was due to the interaction of the Cu²⁺, Pb²⁺, Hg²⁺, Cd²⁺ and Zn²⁺ with a population of SH groups, of the transporter, responsible for the inhibition of the physiological function; whereas the stimulation of [³H]ornithine efflux was due to the induction of a pore-like function of the transporter caused by interaction of cations with a different population of SH groups. Differently, the inhibition of the ornithine transporter by Ni²⁺, Co²⁺ or Mn²⁺ was caused by interaction with the substrate binding site, as indicated by the competitive or mixed inhibition.     

Substrate Profile and Metal-ion Selectivity of Human Divalent Metal-ion Transporter-1

Divalent metal-ion transporter-1 (DMT1) is a H⁺-coupled metal-ion transporter that plays essential roles in iron homeostasis. DMT1 exhibits reactivity (based on evoked currents) with a broad range of metal ions; however, direct measurement of transport is lacking for many of its potential substrates. We performed a comprehensive substrate-profile analysis for human DMT1 expressed in RNA-injected Xenopus oocytes by using radiotracer assays and the continuous measurement of transport by fluorescence with the metal-sensitive PhenGreen SK fluorophore. We provide validation for the use of PhenGreen SK fluorescence quenching as a reporter of cellular metal-ion uptake. We determined metal-ion selectivity under fixed conditions using the voltage clamp. Radiotracer and continuous measurement of transport by fluorescence assays revealed that DMT1 mediates the transport of several metal ions that were ranked in selectivity by using the ratio I_max/K_0.5 (determined from evoked currents at −70 mV): Cd²⁺ > Fe²⁺ > Co²⁺, Mn²⁺ ≫ Zn²⁺, Ni²⁺, VO²⁺. DMT1 expression did not stimulate the transport of Cr²⁺, Cr³⁺, Cu⁺, Cu²⁺, Fe³⁺, Ga³⁺, Hg²⁺, or VO⁺. ⁵⁵Fe²⁺ transport was competitively inhibited by Co²⁺ and Mn²⁺. Zn²⁺ only weakly inhibited ⁵⁵Fe²⁺ transport. Our data reveal that DMT1 selects Fe²⁺ over its other physiological substrates and provides a basis for predicting the contribution of DMT1 to intestinal, nasal, and pulmonary absorption of metal ions and their cellular uptake in other tissues. Whereas DMT1 is a likely route of entry for the toxic heavy metal cadmium, and may serve the metabolism of cobalt, manganese, and vanadium, we predict that DMT1 should contribute little if at all to the absorption or uptake of zinc. The conclusion in previous reports that copper is a substrate of DMT1 is not supported.     

Removal of copper using marine brown alga, Undaria Pinnatifida modified with oxime

Summary As oxime is selective for Cu²⁺, oxime groups were introduced to the cell wall of alga by glutaraldehyde. Such modified biomass showed high affinity for Cu²⁺, which resulted in the increase of copper sorption capacity about 4.5 times higher than that of natural alga. For pH range from 2.5 to 3.0, only Cu²⁺ were removed by alga biomass modified with oxime, while other heavy metal ions such as Ca²⁺,Cd²⁺,Pb²⁺ were not adsorbed. By changing pH, selective recovery of Cu²⁺ was achieved.