Bioadsorption of cadmium ion by cell surface-engineered yeasts displaying metallothionein and hexa-His

The Cd²⁺-chelating abilities of yeast metallothionein (YMT) and hexa-His displayed on the yeast-cell surface were compared. Display of YMT and hexa-His by -agglutinin-based cell-surface engineering was confirmed by immunofluorescent labeling. Surface-engineered yeast cells with YMT and hexa-His fused in tandem showed superior cell-surface adsorption and recovery of Cd²⁺ under EDTA treatment on the cell surface than hexa-His-displaying cells. YMT was demonstrated to be more effective than hexa-His for the adsorption of Cd²⁺. Yeast cells displaying YMT and/or hexa-His exhibited a higher potential for the adsorption of Cd²⁺ than Escherichia coli cells displaying these molecules. In order to investigate the effect of the displayed YMT and hexa-His on sensitivity to toxic Cd²⁺, growth in Cd²⁺-containing liquid medium was monitored. Unlike hexa-His-displaying cells, cells displaying YMT and hexa-His fused in tandem induced resistance to Cd²⁺ through active and enhanced adsorption of toxic Cd²⁺. These results indicate that YMT-displaying yeast cells are a unique bioadsorbent with a functional chelating ability superior to that of E. coli.     

Heavy metal uptake capacities by the common freshwater green alga Cladophora fracta

Macroalgae have received much attention for heavy metal removal in treatment of domestic wastewater. In this report, the uptake capacity of a common freshwater green alga, Cladophora fracta, for heavy metal ions (copper, zinc, cadmium, and mercury) was evaluated. The equilibrium adsorption capacities were 2.388?mg Cu²⁺, 1.623?mg Zn²⁺, 0.240?mg Cd²⁺, and 0.228?mg Hg²⁺ per gram of living algae at 18°C and pH?5.0. The removal efficiency for Cu²⁺, Zn²⁺, Cd²⁺, and Hg²⁺ were 99, 85, 97, and 98%, respectively. Greater removal efficiency was achieved when the concentrations of metal ions were at very low level. The results indicated that living algae are suitable for removal and recovery of heavy metal ions from aqueous solutions and can be a potential tool to treat industrial wastewater.     

Biosorption of heavy metal ions by brown seaweeds from southern coast of Korea

Heavy metal ions (Pb²⁺, Cd²⁺, Mn²⁺, Cu²⁺, and Cr₂O₇ ^2?) were biosorbed by brown seaweeds (Hizikia fusiformis, Laminaria japonica, and Undaria pinnatifida) collected from the southern coast of South Korea. The biosorption of heavy metal ions was pH-dependent showing a minimum absorption at pH 2 and a maximum biosorption at pH 4 (Pb²⁺, Cd²⁺, Mn²⁺, and Cr₂O₇ ^2?) or pH 6 (Cu²⁺). Biosorption increased most noticeably for pH changes from 2 to 3. In the latter pH range, biosorption increased, because a higher pH decreased the electrostatic repulsion between metal ions and functional groups on the seaweed. In the pH range of 2 ～ 4, biosorption of negatively-charged chromium species (Cr₂O₇ ^?2) followed the pattern of positively-charged metal ions (Pb²⁺, Cd²⁺, Mn²⁺, and Cu²⁺). This suggests that the most prevalent chromium species were positively-charged Cr³⁺, reduced from Cr⁶⁺ in Cr₂O₇ ^?2. Whereas positively-charged heavy metal ions (Pb²⁺, Cd²⁺, Mn²⁺, and Cu²⁺) reached a plateau after the maximum level, biosorption of chromium ions decreased noticeably between pH 5 and 8. Kinetic data showed that biosorption by brown seaweed occurred rapidly during the first 10 min, and most of the heavy metals were bound to the seaweed within 30 min. Equilibrium adsorption data for a lead ion could fit well in the Langmuir and Freundlich isotherm models with regression coefficients (R ²) between 0.93 and 0.98.     

Display of lead-binding proteins on Escherichia coli surface for lead bioremediation

Cell surface display of heavy metal-binding proteins has been used to enhance the adsorption capacity of heavy metals and the engineered microbial cells can be potentially used for the bioremediation of heavy metals. In this study, the proteins PbrR, PbrR691, and PbrD from the Cupriavidus metallidurans strain CH34 were displayed on the extracellular membrane of Escherichia coli BL21 cells, with the N-domain of ice-nucleation protein as the anchor protein to achieve specific adsorption of lead ions (Pb²⁺) and bioremediation of lead in the soil. The localization of fusion proteins was confirmed by western blot analysis. We investigated the effects of fusion pattern, expression level, heavy metal concentration, and the presence of other heavy metal ions on the adsorption of Pb²⁺ by these engineered bacteria, and the optimal linker peptide (flexible linker) and inducer concentration (0.5 mM) were obtained. The engineered bacteria showed specific selectivity and strong adsorption capacity for Pb²⁺. The maximum Pb²⁺ adsorption capacity of strains displaying the three proteins (PbrR, PbrR691, and PbrD) were 942.1-, 754.3-, and 864.8-μmol/g cell dry weight, respectively, which was the highest reported to date. The engineered E. coli bacteria were also applied to Pb²⁺-contaminated soil and the detoxification effects were observed via the seed germination test and the growth of Nicotiana benthamiana in comparison with the control BL21, which provides the proof-of-concept for in situ remediations of Pb²⁺-contaminated water or soil.     

Using pretreated chestnut endothelium to adsorb lead and cadmium ions from water

The nature chestnut endothelium, as waster source from chestnut (Castaneamollissima) has pigment effecting the process of adsorbing heavy metalions, and the decolorized endothelium has low adsorption capacity. In order to raise the adsorption capacity of heavy metal ions, the discolor endothelium was pretreated by acidic formaldehyde, cis-butenedioic acid and irradiation. Thermodynamic and kinetics model was fitted to the adsorption of Pb (II) and Cd(II) ions onto modified chestnut endothelium by cis-butenedioic acid. Three independent variables including pH, adsorption time and contact temperature were selected as affecting factors to Response Surface. The modified experiment results showed adsorption rate of Pb(II) and Cd(II) ions on the chestnut endothelium modified by 0.5?mol/L cis-butenedioic acid was higher than other modified methods. Thermodynamic and kinetics model was fitted with Langmuir and Pseudo-second-order kinetic model, respectively. 59.23?°C of the adsorption temperature, the 5.72?h of adsorption time and the 6.16 of pH are the optimized conditions of the adsorption rate of Pb²⁺ on modified chestnut endothelium. 55.93?°C of the adsorption temperature, the 4.43?h of adsorption time and the 6.06 of pH are the optimized adsorption conditions of Cd²⁺. Under the optimized condition, the experiment value of the adsorption of Pb²⁺ and Cd²⁺ was 99.76% and 98.90%, respectively, which are close to the predicted value. The FTIR indicated that CO, OH and CH involved in the adsorption process of Pb²⁺ and Cd²⁺.     

Accumulation of cadmium by hairy-root cultures of Solanum nigrum

Summary Cadmium uptake by cultures of transformed hairy-roots of Solanum nigrum was studied. The effect of pH, buffer type, temperature, exposure time and Cd²⁺ content ranging from 0.2 to 2000 ppm was measured. Cd²⁺ uptake was dependent on increasing metal concentration and it was time dependent. From the variety of buffers tested, MES buffer and borate ions were found to be beneficial for the Cd²⁺ uptake. The high effectivness of Cd²⁺ accumulation in the roots decreased significantly after increasing the Cd²⁺ content in the buffer over 2 ppm.     

重金属Cd2+和Cu2+胁迫下泥蚶消化酶活性的变化

为了探讨重金属Cd²⁺和Cu²⁺胁迫对泥蚶消化酶活性的影响,运用酶学分析的方法,按《渔业水质标准》（GB 11607）规定的Cd²⁺、Cu²⁺最高限量值的1、2、5、10倍设置重金属离子Cd²⁺、Cu²⁺浓度及其组合,研究了在重金属Cd²⁺、Cu²⁺胁迫下,30d内泥蚶3种消化酶活性的变化规律。结果表明：与空白对照组相比,在重金属Cd²⁺、Cu²⁺或其组合的胁迫下,较低浓度组泥蚶的淀粉酶活性实验前期增强（即被诱导）,实验后期减弱（即被抑制）,较高浓度组泥蚶的淀粉酶活性从实验一开始就减弱,并保持在较低水平,毒性比较,同一重金属高浓度 > 低浓度,不同重金属及其组合Cu²⁺ > （Cd²⁺+Cu²⁺）组合 > Cd²⁺;泥蚶脂肪酶的活性实验前期增强,实验后期转为微减弱或减弱,毒性比较,同一重金属高浓度 > 低浓度,不同重金属及其组合（Cd²⁺+Cu²⁺）组合 > Cu²⁺ > Cd²⁺;泥蚶胃蛋白酶的活性实验前期增强,且活性呈现升高-降低-再升高-再降低的变化,实验后期分别表现微增强、微减弱和减弱,毒性比较,同一重金属高浓度 > 低浓度,不同重金属及其组合（Cd²⁺+Cu²⁺）组合 > Cu²⁺ > Cd²⁺。可见：环境中的Cd²⁺和Cu²⁺对泥蚶的消化酶活性起着明显的影响作用。     

Compartments for the Management of Municipal Solid Waste

Despite technological developments and improved liner-material applications, heavy metals in landfill leachate still penetrate the soil profile, polluting the soil and ground-water. An alternative approach therefore must be explored to reduce heavy-metal migration in soil-bentonite landfill liners. By considering the interaction of different heavy metals and their synergetic and antagonistics behaviors, such an approach could be developed. Low mobility metals such as Cu²⁺, and Pb²⁺ inhibit the adsorption of Cd²⁺ which is a moderate-mobility metal and Cu²⁺ sorption is decreased by the presence of Zn²⁺ and Cd²⁺. Therefore, Zn²⁺, a low-mobility metal, cannot be grouped with Cu²⁺. This way, four compatible metal groups have been identified: (1) low mobility: Pb²⁺, Cu²⁺, and Ag, (2) low mobility: Zn²⁺ and Cr³⁺; (3) moderate mobility: As²⁺, Fe²⁺, and Ni²⁺; (4) high mobility: Cd²⁺ and Hg²⁺. Cd²⁺ with a moderate mobility pattern is synergetic to Fe²⁺ and is more mobile with Ni²⁺. Therefore, Cd²⁺ is separated from the moderate-mobility group and is consigned with Hg, a high-mobility metal. The liner materials suitable for Hg²⁺ are assumed to be suitable for Cd²⁺ as well. Based on this concept, and to reduce heavy metal mobility, wastes should be segregated on compatibility basis according to their heavy metal contents before being disposed in different individual compartments. For wastes containing several incompatible heavy metals, sorting should be based on the heavy-metal with the highest concentration. Another solution is the manufacturing of products using compatible heavy metal combinations and then labeling them accordingly. Such waste segregation and landfill compartmentalization lowers risks of groundwater contamination and liner cost.     

Cell Surface Display of MerR on <Emphasis Type="Italic">Saccharomyces cerevisiae</Emphasis> for Biosorption of Mercury

The metalloregulatory protein MerR which plays important roles in mer operon system exhibits high affinity and selectivity toward mercury (II) (Hg²⁺). In order to improve the adsorption ability of Saccharomyces cerevisiae for Hg²⁺, MerR was displayed on the surface of S. cerevisiae for the first time with an α-agglutinin-based display system in this study. The merR gene was synthesized after being optimized and added restriction endonuclease sites EcoR I and Mlu I. The display of MerR was indirectly confirmed by the enhanced adsorption ability of S. cerevisiae for Hg²⁺ and colony PCR. The hydride generation atomic absorption spectrometry was applied to measure the Hg²⁺ content in water. The engineered yeast strain not only showed higher tolerance to Hg, but also their adsorption ability was much higher than that of origin and control strains. The engineered yeast could adsorb Hg²⁺ under a wide range of pH levels, and it could also adsorb Hg²⁺ effectively with Cd²⁺ and Cu²⁺ coexistence. Furthermore, the engineered yeast strain could adsorb ultra-trace Hg²⁺ effectively. The results above showed that the surface-engineered yeast strain could adsorb Hg²⁺ under complex environmental conditions and could be used for the biosorption and bioremediation of environmental Hg contaminants.     

Activated carbon-containing alginate adsorbent for the simultaneous removal of heavy metals and toxic organics

By combining two functions of alginate gel and activated carbon, an activated carbon-containing alginate bead (AC-AB) adsorbent was developed and successfully used to simultaneously remove heavy metal ions and toxic organics. Quantitative analysis showed that almost all of the adsorption of toxic organics, such as p-toluic acid, is caused by the activated carbon in the AC-AB adsorbent, whereas the alginate component has a major role in the removal of heavy metals. A 50-L solution containing eight heavy metals (Pb²⁺, Mn²⁺, Cd²⁺, Cu²⁺, Zn²⁺, Fe²⁺, Al³⁺ and Hg²⁺) and four mineral ions was run continuously through a filter cartridge packed with 160 g of the AC-AB adsorbent. The adsorbent showed a high capacity to remove heavy metals completely from the water, while allowing essential minerals, such as K⁺, Na⁺, Mg²⁺ and Ca²⁺, to pass through the filter. The adsorbent could be regenerated using eluents, such as HNO₃, and reused repeatedly without considerable loss of its metal uptake capacity through 10 subsequent cycles of adsorption and desorption. With its high capacity and high selectivity for toxic heavy metals, the AC-AB adsorbent has enormous potential for application in drinking water treatment technologies.     

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.     

Cd2+和Pb2+对花翅摇蚊(Chironomus kiiensis)幼虫生长发育的影响及富集效应

河流、湖泊等水生环境中普遍存在的重金属污染破坏水生生态系统并间接威胁人类健康。为探究重金属胁迫下水生昆虫花翅摇蚊（Chironomus kiiensis）生态毒理,测定了重金属Cd²⁺和Pb²⁺胁迫对花翅摇蚊化蛹率和羽化率的影响,检测了摇蚊的口器致畸与富集效应。研究结果表明,Cd²⁺和Pb²⁺影响摇蚊幼虫化蛹和羽化过程,单一重金属离子处理14 d Pb²⁺处理组的化蛹率和羽化率分别为22.22%和8.89%,低于Cd²⁺的化蛹率（25.56%）和羽化率（11.11%）,表现出更强的抑制效应。混合离子1：2和2：1配比处理组化蛹率和羽化率均为11.11%和4.44%,显著低于单一重金属离子胁迫下的化蛹率和羽化率。单一重金属离子及混合离子处理均能导致花翅摇蚊幼虫口器致畸,表现为上颚前齿断裂,中齿和基齿磨损、缺失,下唇板齿部不规则,下唇板边缘齿与中央齿磨损、断裂、增生、缺失。不同重金属离子处理下幼虫口器致畸率不同,并与暴露时间呈正相关,其中1：2配比处理14 d致畸率达到40.61%。重金属离子在摇蚊幼虫体内产生生物富集效应,单一重金属离子处理下的Pb²⁺富集含量7 d至14 d由11.46 mg/kg上升至31.32 mg/kg,不同配比混合离子处理下Pb²⁺富集含量均呈增加趋势,其中1：2配比处理组由15.48 mg/kg上升至42.50 mg/kg,而Cd²⁺在单一重金属与1：1混合离子处理组7 d至14 d的富集含量无显著性变化,2：1配比处理组由14.20 mg/kg下降至9.52 mg/kg,1：2配比由5.85 mg/kg上升至20.99 mg/kg。这些研究结果表明Cd²⁺和Pb²⁺胁迫影响花翅摇蚊幼虫生长发育且口器出现畸型,与重金属在幼虫体内的富集密切相关,为研究重金属对水生生态系统多重效应提供了理论依据。     

Cr3+和Cd2+对普通小球藻生长及抗氧化酶活性的影响

[目的] 为探究重金属对淡水绿藻生长的影响。[方法] 选取对水质检测具有明显指示作用的普通小球藻（Chlorella vulgaris）为实验材料,CdCl₂·2H₂O和CrCl₃·7H₂O提供重金属离子,探究不同浓度Cr³⁺和Cd²⁺在单一和复合胁迫下对藻细胞浓度、叶绿素a及相关抗氧化酶活性的影响。[结果] 随着Cr³⁺和Cd²⁺浓度不断增加,藻细胞浓度呈先增长后下降趋势;叶绿素a含量呈现先下降后升高再下降的现象,浓度为1 mg/L的单一和复合胁迫下有最大值,且毒性作用表现为Cr³⁺ < Cd²⁺ < Cr³⁺+Cd²⁺;与藻细胞膜相关的丙二醛（MDA）和过氧化氢（H₂O₂）含量随着重金属离子浓度的增大而增长;重金属离子浓度低于10 mg/L时对藻细胞内抗氧化酶系统中的超氧化物歧化酶（SOD）、过氧化氢酶（CAT）和过氧化物酶（POD）表现为促进作用,而大于10 mg/L时具有抑制作用。[结论] 结果表明在单一或复合重金属胁迫下,普通小球藻会充分调动与抗逆性相关的酶来维持自身的正常生长。     

Competitive Adsorption of Copper‐Nickel and Copper‐Cadmium Binaries on SMW

In this study, the technical feasibility of using a low‐cost sorbent, sheep manure waste (SMW), for the removal of copper, nickel and cadmium ions from aqueous solutions containing Cu²⁺ ‐‐Cd²⁺ or Cu²⁺ ‐‐Ni²⁺ binaries is investigated. The scope of the study includes the investigation of the affinity of each metal ion in the presence of the other. Experimental results showed that the SMW has high affinity for the three studied heavy metals, and the affinity of the SMW for these metals is in the order copper > cadmium > nickel. The presence of copper in a solution containing Ni²⁺ or Cd²⁺ reduces significantly the percentage removal of both nickel and cadmium. On the other hand, the percentage removal of copper was not affected significantly by the presence of either nickel or cadmium. The equilibrium adsorption data were fit very well with Langmuir, Freundlich, Redlich‐Peterson, and Sips isotherm equations. The prediction of the binary adsorption from single metal adsorption data was in fair agreement with the experimental results. The role of ion exchange and carboxyl groups in the adsorption process were also studied.     

Adsorption of Cu(II), Cd(II), and Pb(II) from aqueous single metal solutions by mercerized cellulose and mercerized sugarcane bagasse chemically modified with EDTA dianhydride (EDTAD)

This work describes the preparation of new chelating materials derived from cellulose and sugarcane bagasse for adsorption of Cu²⁺, Cd²⁺, and Pb²⁺ ions from aqueous solutions. The first part involved the mercerization treatment of cellulose and sugarcane bagasse with NaOH 5 mol/L. Non- and mercerized cellulose and sugarcane bagasse were then reacted with ethylenediaminetetraacetic dianhydride (EDTAD) in order to prepare different chelating materials. These materials were characterized by mass percent gain, X-ray diffraction, FTIR, and elemental analysis. The second part consisted of evaluating the adsorption capacity of these modified materials for Cu²⁺, Cd²⁺, and Pb²⁺ ions from aqueous single metal solutions, whose concentration was determined by atomic absorption spectroscopy. These materials showed maximum adsorption capacities for Cu²⁺, Cd²⁺, and Pb²⁺ ions ranging from 38.8 to 92.6 mg/g, 87.7 to 149.0 mg/g, and 192.0 to 333.0 mg/g, respectively. The modified mercerized materials showed larger maximum adsorption capacities than modified non-mercerized materials.     

Heavy metal ions affect the activity of DNA glycosylases of the Fpg family

Prokaryotic enzymes formamidopyrimidine-DNA glycosylase (Fpg) and endonuclease VIII (Nei) and their eukaryotic homologs NEIL1, NEIL2, and NEIL3 define the Fpg family of DNA glycosylases, which initiate the process of repair of oxidized DNA bases. The repair of oxidative DNA lesions is known to be impaired in vivo in the presence of ions of some heavy metals. We have studied the effect of salts of several alkaline earth and transition metals on the activity of Fpg-family DNA glycosylases in the reaction of excision of 5,6-dihydrouracil, a typical DNA oxidation product. The reaction catalyzed by NEIL1 was characterized by values K _m = 150 nM and k _cat = 1.2 min⁻¹, which were in the range of these constants for excision of other damaged bases by this enzyme. NEIL1 was inhibited by Al³⁺, Ni²⁺, Co²⁺, Cd²⁺, Cu²⁺, Zn²⁺, and Fe²⁺ in Tris-HCl buffer and by Cd²⁺, Zn²⁺, Cu²⁺, and Fe²⁺ in potassium phosphate buffer. Fpg and Nei, the prokaryotic homologs of NEIL1, were inhibited by the same metal ions as NEIL1. The values of I₅₀ for NEIL1 inhibition were 7 μM for Cd²⁺, 16 μM for Zn²⁺, and 400 μM for Cu²⁺. The inhibition of NEIL1 by Cd²⁺, Zn²⁺, and Cu²⁺ was at least partly due to the formation of metal-DNA complexes. In the case of Cd²⁺ and Cu²⁺, which preferentially bind to DNA bases rather than phosphates, the presence of metal ions caused the enzyme to lose the ability for preferential binding to damaged DNA. Therefore, the inhibition of NEIL1 activity in removal of oxidative lesions by heavy metal ions may be a reason for their comutagenicity under oxidative stress.     

Studies of biosorption of Pb2+, Cd2+ and Cu2+ from aqueous solutions using Adansonia digitata root powders

The potentials of Adansonia digitata root powders (ADRP) for adsorption of Pb²⁺, Cd²⁺ and Cu²⁺ from aqueous solutions was investigated. Physico-chemical analysis of the adsorbent (ADRP) shows that hydroxyl, carbonyl and amino groups were predominant on the surface of the adsorbent. Scanning Electron Microscope (SEM) image revealed its high porosity and irregular pores in the adsorbent while the Energy Dispersive X-ray Spectrum showed the major element with 53.0% Nitrogen, 23.8% carbon, 9.1% calcium, 7.5% potassium and 6.6% magnesium present. The found optimal conditions were: initial concentration of the metal ions = 0.5 mg/L, pH = 5, contact time = 90 min, adsorbent dose = 0.4 g and particle size = 32 µm. Freundlich isotherm showed good fit for the adsorption of Pb²⁺, Cd²⁺ and Cu²⁺. Dubinin-Radushkevich isotherm revealed that the adsorption processes were physisorption Cd(II) and Cu(II) but chemisorption with respect to Pb(II) ions. The kinetics and thermodynamic studies showed that Pseudo-second order and chemisorptions provided the best fit to the experimental data of Pb (II) ions only. Batch desorption result show that desorption in the acidic media for the metal ions were more rapid and over 90% of the metal ions were recovered from the biomass.     

Comparison of Physiological Changes in Euglena gracilis During Exposure to Heavy Metals of Heterotrophic and Autotrophic Cells

The effect of different concentrations of Hg²⁺, Cd²⁺, and Pb²⁺ on ultrastructure, growth, respiration, photosynthesis, chlorophyll content, and metal accumulation in Euglena gracilis was examined. The toxicity of the heavy metals was dependent on the culture medium used and whether cells were grown in the dark or under illumination. Hg²⁺ was the most toxic metal, which showed effects at a concentration as low as 1.5 μM; Cd²⁺ showed an intermediate toxicity (effects observed above 50 μM); and Pb²⁺ was almost ineffective up to 1 mM. Cells grown for several weeks in the dark, in the presence of 1.5 μM Hg²⁺ showed a reduced sensitivity to subsequent exposure to Cd²⁺ or Pb²⁺. The Hg²⁺-pretreated cells also presented an enhanced capacity to accumulate other metals. In comparison, light-grown cells showed a greater Cd²⁺ accumulation, but a lower Pb²⁺ uptake than Hg²⁺-pretreated dark-grown cells. Pretreatment of light-grown cells with Hg²⁺ did not enhance the accumulation of Cd²⁺. These results suggest that the capacity to tolerate heavy metals by Euglena may have mechanistic differences when cells are grown in the dark or under illumination.     

Heavy metal ions are potent inhibitors of protein folding

Environmental and occupational exposure to heavy metals such as cadmium, mercury and lead results in severe health hazards including prenatal and developmental defects. The deleterious effects of heavy metal ions have hitherto been attributed to their interactions with specific, particularly susceptible native proteins. Here, we report an as yet undescribed mode of heavy metal toxicity. Cd²⁺, Hg²⁺ and Pb²⁺ proved to inhibit very efficiently the spontaneous refolding of chemically denatured proteins by forming high-affinity multidentate complexes with thiol and other functional groups (IC₅₀ in the nanomolar range). With similar efficacy, the heavy metal ions inhibited the chaperone-assisted refolding of chemically denatured and heat-denatured proteins. Thus, the toxic effects of heavy metal ions may result as well from their interaction with the more readily accessible functional groups of proteins in nascent and other non-native form. The toxic scope of heavy metals seems to be substantially larger than assumed so far.