Distribution of iron, cobalt, zinc and selenium in macrofungi

Samples of wild growing ectomycorrhizal and terrestrial saprobic macrofungi (mushrooms) were collected from unpolluted areas and analyzed for their iron, cobalt, zinc and selenium content. Trace elements were determined using long-term instrumental neutron activation analysis. In total, 217 samples, including 87 species of ectomycorrhizal fungi and 43 species of terrestrial saprobes, were examined. Distribution of trace element contents in ectomycorrhizal and saprobic macrofungi was investigated; results are thoroughly compared with previously published data. Doubtful literature data and ability of macrofungi to accumulate/concentrate investigated elements are discussed. Hygrophoropsis aurantiaca was found to concentrate Fe and Russula atropurpurea was confirmed as an effective Zn-accumulating species. Distribution of Se in ectomycorrhizal species was obviously different from that in saprobic species; selenium contents were higher in saprobic species (mostly above 2 ppm).     

Translocation of manganese, iron, cobalt, and zinc in tomato

Tomato plants in solution culture were treated with 0 to 50 μm Mn, Co, or Zn in the presence of 5 μm Fe. Stem exudates were analyzed to determine quantities and forms of the metals translocated.     

Radioprotective activity of complexes of copper, cobalt and zinc with substituted acylhydrazones

Acylhydrazone metal complexes belong to a new class of radioprotective agents that have a cytostatic effect increasing, in some cases, the survival rate of irradiated animals by 40-60 per cent compared to irradiated controls. The most active drugs are hypotoxic and applied in much lower doses than ordinary S-containing radioprotective agents to achieve the same protective effect.     

Resistance to cadmium, cobalt, zinc, and nickel in microbes.

The divalent cations of cobalt, zinc, and nickel are essential nutrients for bacteria, required as trace elements at nanomolar concentrations. However, at micro- or millimolar concentrations, Co2+, Zn2+, and Ni2+ (and "bad ions" without nutritional roles such as Cd2+) are toxic. These cations are transported into the cell by constitutively expressed divalent cation uptake systems of broad specificity, i.e., basically Mg2+ transport systems. Therefore, in case of a heavy metal stress, uptake of the toxic ions cannot be reduced by a simple down-regulation of the transport activity. As a response to the resulting metal toxicity, metal resistance determinants evolved which are mostly plasmid-encoded in bacteria. In contrast to that of the cation Hg2+, chemical reduction of Co2+, Zn2+, Ni2+, and Cd2+ by the cell is not possible or sensible. Therefore, other than mutations limiting the ion range of the uptake system, only two basic mechanisms of resistance to these ions are possible (and were developed by evolution): intracellular complexation of the toxic metal ion is mainly used in eucaryotes; the cadmium-binding components are phytochelatins in plant and yeast cells and metallothioneins in animals, plants, and yeasts. In contrast, reduced accumulation based on an active efflux of the cation is the primary mechanism developed in procaryotes and perhaps in Saccharomyces cerevisiae. All bacterial cation efflux systems characterized to date are plasmid-encoded and inducible but differ in energy-coupling and in the number and types of proteins involved in metal transport and in regulation. In the gram-positive multiple-metal-resistant bacterium Staphylococcus aureus, Cd2+ (and probably Zn2+) efflux is catalyzed by the membrane-bound CadA protein, a P-type ATPase. However, a second protein (CadC) is required for full resistance and a third one (CadR) is hypothesized for regulation of the resistance determinant. The czc determinant from the gram-negative multiple-metal-resistant bacterium Alcaligenes eutrophus encodes proteins required for Co2+, Zn2+, and Cd2+ efflux (CzcA, CzcB, and CzcC) and regulation of the czc determinant (CzcD). In the current working model CzcA works as a cation-proton antiporter, CzcB as a cation-binding subunit, and CzcC as a modifier protein required to change the substrate specificity of the system from Zn2+ only to Co2+, Zn2+, and Cd2+.     

Inhibition of mugineic acid-ferric complex uptake in barley by copper, zinc and cobalt

The interfering effects of copper, zinc, and cobalt on the uptake of mugineic acid-ferric complex were studied in barley ( Hordeum vulgare , cv. Minorimugi) grown in nutrient solution. Short-term uptake experiments of 3 h were performed utilizing both ionic and mugineic acid-complex forms of each metal at two different concentrations. Copper was most effective in decreasing iron uptake when added in an ionic form at either concentration. The inhibition order at higher concentrations followed Cu(II) > Zn(II) ≥ Co(II), Co(III), which is consistent with the stability constants of these metal complexes with mugineic acid. The displacement of iron from its mugineic acid complex by these metals is suggested as a probable explanation for the decreased iron uptake. The inhibitory effect of metal complexes with mugineic acid on iron uptake was only found in cases with higher concentrations of Cu(II) and Zn(II) complexes. Deformation of the specific iron transport system in the plasma membrane due to their adsorption may be responsible for this effect.     

Bioleaching of cobalt and zinc from pyrite ore in relation to calcitic gangue content

Bioleaching of a pyrite ore containing high concentrations of cobalt (0.1%) and zinc (0.065%) was affected by small amounts of calcitic gangue (from 0.01 to 1.01%). Results from an air-lift percolator and from Erlenmeyer flask experiments show that a small percentage of calcite raises the pH and arrests the growth of the acidophilic bacterium Thiobacillus ferrooxidans. In percolator experiments, when calcite is completely removed by the continuous addition of small quantities of acid, and the pH of the liquor becomes acid, the micro-organism begins to grow and to bio-oxidize the pyrite ore. The growth of T. ferrooxidans shows different lag phase spans (from 13 to 190 days) depending on carbonate dissolution. The metals Fe, Zn and Co are released into the leaching solution together at different rates after a lag-time which depends on calcite concentrations in pyrite gangue. Metal ratios in the mineral bulk are different from those in the liquor, Zn dissolving 5 times more readily than Co. Bioleaching rates for metal removal from pyrite are higher in percolator (for Fe, from 5 to 15 mg/l/h) than in flask experiments (from 0.5 to 2 mg/l/h), but the lag phases are shorter (from 2 to 65 days). The differences between the two systems are related to calcite dissolution and gypsum precipitation.F. Baldi is with the Università di Siena, Dipartimento di Biologia Ambientale, via P. A. Mattioli, 4, I-53100 Siena. A. Bralia, F. Riccobono and G. Sabatini are with the Università di Siena, Istituto di Mineralogia I-53100 Siena, Italy.     

Effect of nutritional regime on accumulation of cobalt, manganese and zinc by green microalgae

Abstract Accumulation of cobalt, manganese and zinc by the algae Chlorella emersonii, Chlamydomonas reinhardtii and Scenedesmus obliquus has been characterized under photoautotrophic, photoheterotrophic and chemoheterotrophic nutritional regimes. All three species accumulated smaller amounts of Co²⁺, Mn²⁺ and Zn²⁺ under chemoheterotrophic and photoheterotrophic conditions than under photoautotrophic conditions except in the case of cobalt accumulation by C. reinhardtii where there was little difference in the amount of cobalt accumulated under any of the nutritional regimes. Decreased accumulation of the three metals by C. emersonii and C. reinhardtii largely resulted from a decrease in the initial biosorptive phase of uptake whereas the decrease in Mn²⁺ and Zn²⁺ accumulation by C. reinhardtii under chemoheterotrophic and photoheterotrophic conditions was due to a decrease in the slow energy-dependent phase of uptake.     

Structural and electronic mimics of the active site of cobalt(II)-substituted zinc metalloenzymes

Complexes of cobalt(II) and zinc(II) which involve monodentate coordination of two alkyl carboxylate and two imidazole ligands in a slightly distorted tetrahedral fashion have visible and magnetic circular dichroism spectra remarkably similar to the cobalt(II)-substituted proteolytic enzymes thermolysin and carboxypeptidase A. Single crystal x-ray structure determinations on [Co(C₂H₅COO)₂Im₂], Im = imidazole, and its zinc counterpart reveal only minor structural differences between the cobalt and zinc species. Electron paramagnetic resonance spectra of cobalt(II) doped into zinc(II) complexes with known structures demonstrate the extreme sensitivity of the g-values to minor structural differences.     

Leucine aminopeptidase (bovine lens). The relative binding of cobalt and zinc to leucine aminopeptidase and the effect of cobalt substitution on specific activity.

Prolonged incubation of zinc-zinc leucine aminopeptidase (bovine lens) (EC 3.4.1.1) with 0.05 M CoCl2 and M KCl in 0.2 M N-ethylmorpholine-HCl at pH 7.5 and 37 degrees yields an active enzyme in which 2 g atoms of Co2+ per 54,000 dalton subunit have replaced the Zn2+. Incubation of cobalt-cobalt leucine aminopeptidase with various AnCl2 concentrations or zinc-zinc leucine aminopeptidase with various CoCl2 concentrations in M KCl and 0.2 M N-ethylmorpholine-HCl at pH 7.5 and 37 degrees demonstrates that Co2+ and Zn2+ compete reversibly for two independent binding sites per subunit for which the ratio of the association constants for Zn2+ and Co2+ (1KZn:1KCo = 1KZn/Co; 2KZn:2KCo = 2KZn/Co) are 115 and 15.9 for sites 1 and 2, respectively. The specific activities of the various species of enzyme with 2 mM L-leucine p-nitroanilide as substrate in 0.2 M N-ethylmorpholine-HCl and 0.01 M NaHCO3 at pH 7.5 are estimated to be (in micromoles per min per mg) 0.043 for the zinc-zinc. 0.039 for the zinc-cobalt, 0.541 for the cobalt-zinc, and 0.536 for the cobalt-cobalt forms, which implies that activity is affected only when cobalt is substituted at site 1, the "activation site." The site, at which cobalt substitution has no effect on activity, is designated the "structural site." The value of Km for cobalt-cobalt leucine aminopeptidase with L-leucine p-nitroanilide as substrate in 0.2 M N-ethylmorpholine-HCl at pH 7.5 containing 0.01 M NaHCO3 at 30 degrees is 0.52 mM while Vmax is 0.90 mumol per min per mg. In the additional presence of 1 M KCl, Km is 0.19 mM while Vmax is 0.68 mumol per min per mg.     

Influence of silicon on cobalt, zinc, and magnesium in baker's yeast, Saccharomyces cerevisiae

Silicon (Si, as silicate) is involved in numerous important structure and function roles in a wide range of organisms, including man. Silicate availability influences metal concentrations within various cell and tissue types, but, as yet, clear mechanisms for such an influence have been discovered only within the diatoms and sponges. In this study, the influence of silicate on the intracellular accumulation of metals was investigated in baker's yeast (Saccharomyces cerevisiae). It was found that at concentrations up to 10 mM, silicate did not influence the growth rate of S. cerevisiae within a standard complete medium. However, an 11% growth inhibition was observed when silicate was present at 100 mM. Intracellular metal concentrations were investigated in yeast cultures grown without added silicate (−Si) or with the addition of 10 mM silicate (+Si). Decreased amounts of Co (52%), Mn (35%), and Fe (20%) were found within +Si-grown yeast cultures as compared to −Si-grown ones, whereas increased amounts of Mo (56%) and Mg (38%) were found. The amounts of Zn and K were apparently unaffected by the presence of silicon. +Si enhanced the yeast growth rate for low-Zn²⁺ medium, but it decreased the growth rate under conditions of a low Mg²⁺ medium and did not alter the growth rates in high Zn²⁺ and Co²⁺ media. +Si doubled the uptake rate of Co²⁺ but did not influence that of Zn²⁺. We propose that a possible explanation for these results is that polysilicate formation at the cell wall changes the cell wall binding capacity for metal ions. The toxicity of silicate was compared to germanium (Ge, as GeO₂), a member of the same group of elements as Si (group 14). Hence, Si and Ge are chemically similar, but silicate starts to polymerize to oligomers above 5 mM, whereas Ge salts remain as monomers at such concentrations. Ge proved to be far more toxic to yeast than Si and no influence of Si on Ge toxicity was found. We propose that these results relate to differences in cellular uptake.