Bacterial sorption of heavy metals

Four bacteria, Bacillus cereus, B. subtilis, Escherichia coli, and Pseudomonas aeruginosa, were examined for the ability to remove Ag+, Cd2+, Cu2+, and La3+ from solution by batch equilibration methods. Cd and Cu sorption over the concentration range 0.001 to 1 mM was described by Freundlich isotherms. At 1 mM concentrations of both Cd2+ and Cu2+, P. aeruginosa and B. cereus were the most and least efficient at metal removal, respectively. Freundlich K constants indicated that E. coli was most efficient at Cd2+ removal and B. subtilis removed the most Cu2+. Removal of Ag+ from solution by bacteria was very efficient; an average of 89% of the total Ag+ was removed from the 1 mM solution, while only 12, 29, and 27% of the total Cd2+, Cu2+, and La3+, respectively, were sorbed from 1 mM solutions. Electron microscopy indicated that La3+ accumulated at the cell surface as needlelike, crystalline precipitates. Silver precipitated as discrete colloidal aggregates at the cell surface and occasionally in the cytoplasm. Neither Cd2+ nor Cu2+ provided enough electron scattering to identify the location of sorption. The affinity series for bacterial removal of these metals decreased in the order Ag greater than La greater than Cu greater than Cd. The results indicate that bacterial cells are capable of binding large quantities of different metals. Adsorption equations may be useful for describing bacterium-metal interactions with metals such as Cd and Cu; however, this approach may not be adequate when precipitation of metals occurs.     

Bacterial resistance and detoxification of heavy metals

Microbial cells have resistances to essentially all of the toxic heavy metals of the Periodic Table. In bacterial cells, the genetic determinants of these resistances are frequently found on small extrachromosomal plasmids and transposons. Sometimes the resistances are associated with detoxifying enzymes. This is true for the Hg²⁺ → Hg⁰ reductase, the As³⁺ → As⁵⁺ oxidase and the Cr⁶⁺ → Cr³⁺ reductase. In other cases, such as As⁵⁺, Ag⁺ and Cd²⁺, no change in redox state occurs but, rather, uptake and transport differences accompany resistance determinants. This article summarizes what is known of bacterial metal resistances for which enzymatic detoxification is known to be the mechanism of resistance. The characteristics and functions of the enzymes are described, as well as a summary of the newer DNA sequence analysis (basic science) and bench-scale efforts (applied science) for the mercuric resistance system.     

Bacterial resistance mechanisms for heavy metals of environmental concern

Summary Bacterial species have genetically-determined systems for resistances to toxic heavy metals. Those for metals of environmental concern including mercury cadmium, arsenic and others are briefly summarized, considering the genes of the systems and the biochemical mechanisms by which the resistance proteins function.     

Preparation of cation exchanger from lemon and sorption of divalent heavy metals

A cation exchanging material was developed from lemon by modifying the pectic-cellulosic substances in the lemon peel by lemon juice having citric acid. For this purpose, chopped lemon removed from seeds and yellow skin was heated in two stages, firstly at 50 degrees C for 24h and subsequently at 120 degrees C for 2h. The material obtained was ground, repeatedly washed with water and dried. Lemon peel and lemon resin obtained were characterized through physicochemical analyses and FTIR spectroscopy. Heavy metal binding performance of this material was determined by removal tests conducted by using 10mM solutions of divalent metals. Experimental results show that the resin prepared from lemon is effective especially for Pb and Cu removals. For a lemon resin dosage of 10 g l(-1), sorption affinity of divalent metal ions is found to be in an order of Pb>Cu>Ni>Fe>Cd>Zn>Co>Mn. Typically, sorption capacities are about 0.87 and 0.43 mmol g(-1) for Pb and Mn, respectively.     

Bacterial metal-resistance proteins and their use in biosensors for the detection of bioavailable heavy metals

We have expressed and purified metal-resistance and metal regulatory proteins from the bacterial determinants of resistance to heavy metals and utilised these in the development of biosensors for heavy metals. Both the metallothionein from the cyanobacterium Synechococcus PCC 7942 and the MerR regulatory protein from transposon Tn501 allow the detection of non-specific metal binding down to 10(-15) M concentrations of Hg(II), Cu(II), Zn(II) and Cd(II) in pure solution. Differential effects of the metals can be detected at both low and high concentrations, and the shape of the capacitance curves may reflect biologically relevant responses of the proteins to metals. Further work is required to establish the relationship between the detected binding of metal and the biological response of the protein, or to provide biosensors of use in the natural environment.     

重金属对土壤微生物的生态效应

通过分析重金属对土壤微生物生化过程与数量、种群及群落的影响、影响重金属对土壤微生物毒性的因素、重金属对土壤微生物毒性的评价指标、微生物对重金属的耐性与适应性以及重金属毒性的差异 ,综合评述了重金属对土壤微生物的生态效应 .     

Biosensors for heavy metals

A biosensor is an analytical device that consists of an immobilized biocomponent in conjunction with a transducer, and represents a synergistic combination of biotechnology and microelectronics. This review summarizes the use of biosensors for detecting and quantifying heavy metal ions. Heavy metal contamination is of serious concern to human health since these substances are non-biodegradable and retained by the ecological system. Conventional analytical techniques for heavy metals (such as cold vapour atomic absorption spectrometry, and inductively coupled plasma mass spectrometry) are precise but suffer from the disadvantages of high cost, the need for trained personnel and the fact that they are mostly laboratory bound. Biosensors have the advantages of specificity, low cost, ease of use, portability and the ability to furnish continuous real time signals. The analysis of heavy metal ions can be carried out with biosensors by using both protein (enzyme, metal-binding protein and antibody)-based and whole-cell (natural and genetically engineered microorganism)-based approaches.Published online: March 2005     

Histochemical demonstration of heavy metals

Summary The three steps of the sulphide silver method have been examined: 1) Transformation of metals to metal sulphides; 2) Fixation and embedding or freezing of the tissue for sectioning; and 3) Deposition of metallic silver on the metal sulphides in a physical developer. Based on the results, a revised method is described and discussed. It is particularly important 1) To maintain a sufficient but low concentration of sulphide ions during the perfusion; 2) To avoid using oxidating or acid fixatives; 3) To ensure low temperatures while embedding in paraffin or during polymerization of Epon; and 4) to use a slow-acting physical developer. Examples of the metal sulphide pattern from various tissues are presented.     

重金属污染可能改变稻田土壤团聚体组成及其重金属分配

采集了太湖地区污染与非污染稻田表土,采用原状土低能量分离-分散技术提取土壤团聚体粒组,分析土壤中不同粒径团聚体颗粒组质量组成和Pb、Cd、Hg、As等重金属元素的含量, 讨论重金属污染下土壤团聚体组成和重金属团聚体分配的变化.结果表明：在重金属污染下,供试水稻土砂粒级团聚体减少,而较细粒径团聚体相对增多;4种重金属元素在不同粒径团聚体颗粒组中的含量存在差异,但随粒径的变化趋势基本一致,即在<0.002 mm粒径的颗粒组中最高, 其次是0.2～2 mm粒径的颗粒组,而在0.02～0.2 mm和0.002～0.02 mm粒径的团聚体中呈现亏缺现象（富集系数为0.56～0.96）.表明重金属污染可能减弱了较大土壤团聚体的形成,导致细粒径团聚体相对增多,从而明显提高了重金属元素在粉砂和粘粒组团聚体中的分配,这可能进一步提高了污染农田重金属的水迁移和大气颗粒物迁移的风险.对于重金属污染对稻田土壤生物物理和生物化学过程的影响及其机制还需要进一步研究.     

Phytoremediation potential of Lemna minor L. for heavy metals

Phytoremediation potential of L. minor for cadmium (Cd), copper (Cu), lead (Pb), and nickel (Ni) from two different types of effluent in raw form was evaluated in a glass house experiment using hydroponic studies for a period of 31 days. Heavy metals concentration in water and plant sample was analyzed at 3, 10, 17, 24, and 31 day. Removal efficiency, metal uptake and bio-concentration factor were also calculated. Effluents were initially analyzed for physical, chemical and microbiological parameters and results indicated that municipal effluent (ME) was highly contaminated in terms of nutrient and organic load than sewage mixed industrial effluent (SMIE). Results confirmed the accumulation of heavy metals within plant and subsequent decrease in the effluents. Removal efficiency was greater than 80% for all metals and maximum removal was observed for nickel (99%) from SMIE. Accumulation and uptake of lead in dry biomass was significantly higher than other metals. Bio-concentration factors were less than 1000 and maximum BCFs were found for copper (558) and lead (523.1) indicated that plant is a moderate accumulator of both metals. Overall, L. minor showed better performance from SMIE and was more effective in extracting lead than other metals.     

Interactions of lichens with heavy metals

Recent developments in knowledge about the interactions between lichens and heavy metals at different levels, from populations to cells and from ecology to molecular biology are reviewed. Sources of heavy metals, mechanisms of heavy metal accumulation and detoxification by lichens are discussed. Special emphasis is placed on ultrastructural changes as well as physiological parameters such as membrane integrity, pigment composition, chlorophyll a fluorescence, photosynthesis, respiration, contents of ATP, amino acids, ergosterol, ethylene, non-protein thiols, activity of antioxidant enzymes and expression of stress proteins.     

Inhibition of photosynthesis by heavy metals

Inhibition of photosynthesis by heavy metals is well documented. In this review the results are compared between in vitro experiments on isolated systems (chloroplasts, enzymes ­.), experiments on excised leaves and intact plants and algae in vivo. In vitro experiments suggest potential sites of heavy metal interaction with photosynthesis at several levels of organisation, which are not necessarily confirmed in vivo. Analytical data on subcellular heavy metal level are generally missing to discuss their mechanism of action in the intact organism. In the field factors such as soil characteristics and air pollution have to be taken into account for assessing the mechanism of action of heavy metals on photosynthesis in plants, growing in a polluted erea.paper presented at the FESPP meeting in Strasbourg (1984)     

Bacterial leaching of metals from sewage sludge

Summary Thiobacillus thiooxidans is capable of oxidizing sulfur in digested sludge, while decreasing the pH value from about 5.5 to, say, 1.0 to 1.5. Insoluble metal sulfides can be solubilized through this acidification. Thiobacillus ferrooxidans oxidises pyritic ore in the presence of 6% centrifuged sludge if the pH value is adjusted to about 2.5. When mixing T. thiooxidans and T. ferrooxidans with sludge and 1% sulfur, the former acidifies the sludge and the latter oxidizes metal sulfides; together they solubilize more metal than T. thiooxidans alone. The following metals solubilized from their sulfides have been investigated so far: iron, copper, zinc, nickel, and cadmium. The possibility of recycling metals from sewage sludge with this method is discussed.     

Synthesis of a chitosan-linked calix[4]arene chelating polymer and its sorption ability toward heavy metals and dichromate anions

This communication describes preparation, characterization, and the evaluation of sorption properties of a calix[4]arene-based chitosan polymer (C[4]BCP). C[4]BCP was used to sorption studies of some heavy metal cations (Co(2+), Ni(2+), Cu(2+), Cd(2+)(,) Hg(2+) and Pb(2+)) and dichromate anions (Cr(2)O(7)(2-)/HCr(2)O(7)(-)) as sorbent material. Also the supporting material (chitosan) was used for comparison in these experiments. The results for heavy metal cations showed that C[4]BCP was excellent sorbent and the effect of chitosan was low. In the sorption studies of dichromate anions, C[4]BCP was highly effective sorbent at pH 1.5.     

Remobilization of toxic heavy metals adsorbed to bacterial wall-clay composites.

Significant quantities of Ag(I), Cu(II), and Cr(III) were bound to isolated Bacillus subtilis 168 walls, Escherichia coli K-12 envelopes, kaolinite and smectite clays, and the corresponding organic material-clay aggregates (1:1, wt/wt). These sorbed metals were leached with HNO3, Ca(NO3)2, EDTA, fulvic acid, and lysozyme at several concentrations over 48 h at room temperature. The remobilization of the sorbed metals depended on the physical properties of the organic and clay surfaces and on the character and concentration of the leaching agents. In general, the order of remobilization of metals was Cr much less than Ag less than Cu. Cr was very stable in the wall, clay, and composite systems; pH 3.0, 500 microM EDTA, 120-ppm [mg liter-1] fulvic acid, and 160-ppm Ca remobilized less than 32% (wt/wt) of sorbed Cr. Ag (45 to 87%) and Cu (up to 100%) were readily removed by these agents. Although each leaching agent was effective at mobilizing certain metals, elevated Ca or acidic pH produced the greatest overall mobility. The organic chelators were less effective. Lysozyme digestion of Bacillus walls remobilized Cu from walls and Cu-wall-kaolinite composites, but Ag, Cr, and smectite partially inhibited enzyme activity, and the metals remained insoluble. The extent of metal remobilization was not always dependent on increasing concentrations of leaching agents; for example, Ag mobility decreased with some clays and some composites treated with high fulvic acid, EDTA, and lysozyme concentrations. Sometimes the organic material-clay composites reacted in a manner distinctly different from that of their individual counterparts; e.g., 25% less Cu was remobilized from wall- and envelope-smectite composites than from walls, envelopes, or smectite individually in 500 microM EDTA. Alternatively, treatment with 160-ppm Ca removed 1.5 to 10 times more Ag from envelope-kaolinite composites than from the individual components. The particle size of the deposited metal may account for some of the stability changes; those metals that formed large, compact aggregates (Cr and Ag) as seen by transmission electron microscopy were less likely to be remobilized. In summary, it is apparent that remobilization of toxic heavy metals in sediments, soils, and the vadose zone is a complicated issue. Predictions based on single inorganic or organic component systems are too simplistic.     

重金属污染对土壤有机质积累的影响

采用田间采样分析与室内培养试验相结合的方法,研究了不同重金属污染土壤中有机质积累的差异及重金属污染强度对土壤有机质矿化动态变化的影响.结果表明：污染土壤中重金属的大量积累可减弱有机物质的矿化速率,增加土壤有机质的积累.土壤中颗粒态有机质及其占总有机碳的比例随重金属积累的增加而增加;而微生物生物量碳占总碳的比例却随土壤重金属污染水平的提高而下降.污染土壤中颗粒态有机质对重金属有显著的富集,这可能是影响土壤有机物质进一步矿化的原因之一.重金属污染可改变土壤有机质的矿化速率,影响土壤有机质的积累与分配.