Cadmium accumulation by a Citrobacter sp. immobilized on gel and solid supports: Applicability to the treatment of liquid wastes containing heavy metal cations

Polyacrylamide gel-immobilized cells of a Citrobacter sp. removed cadmium from flows supplemented with glycerol 2-phosphate, the metal uptake mechanism being mediated by the activity of a cell-bound phosphatase that precipitates liberated inorganic phosphate with heavy metals at the cell surface. The constraints of elevated flow rate and temperature were investigated and the results discussed in terms of the kinetics of immobilized enzymes. Loss in activity with respect to cadmium accumulation but not inorganic phosphate liberation was observed at acid pH and was attributed to the pH-dependent solubility of cadmium photsphate. Similarly high concentrations of chloride ions, and traces of cyanide inhibited cadmium uptake and this was attributed to the ability of these anions to complex heavy metals, especially the ability of CN(-) to form complex anions with Cd(2+). The data are discussed in terms of the known chemistry of chloride and cyanide-cadmium complexes and the relevance of these factors in the treatment of metal-containing liquid wastes is discussed. The cells immobilized in polyacrylamide provided a convenient small-scale laboratory model system. It was found that the Citrobacter sp. could be immobilized on glass supports with no chemical treatment or modification necessary. Such cells were also effective in metal accumulation and a prototype system more applicable to the treatment of metal-containing streams on a larger scale is described.     

Enzymically accelerated biomineralization of heavy metals: Application to the removal of americium and plutonium from aqueous flows

Abstract: A biological process for the removal of heavy metals from the aqueous flows is described. Metals are precipitated on the surface of immobilized cells of a Citrobacter sp. as cell-bound metal phosphates. This uses phosphate liberated by the activity of a cell-bound phosphatase. Some radionuclides (e.g. 241americium) form metal phosphates readily; efficient removal of ²⁴¹Am on a continuous basis is demonstrated. At low phosphatase activities, the efficiency of uranium removal correlates with enzyme activity. High phosphatase activities are not realised as an increase in metal removal, suggesting that chemical events become rate-limiting. Studies have suggested that maximal metal uptake occurs only after nucleation and the formation of precipitation foci. A model is presented to illustrate how nucleation and crystallization processes could enhance the removal of plutonium and neptunium from dilute solutions.     

Effect of substrate concentration and nitrate inhibition on product release and heavy metal removal by a Citrobacter sp

A Citrobacter sp. accumulates heavy metals as cell-bound metal phosphates, utilizing phosphate released by the enzymatic cleavage of a phosphomonoester substrate. The effect of increased substrate (glycerol 2-phosphate, G2P) concentration on phosphate release and heavy metal accumulation was evaluated using a stirred tank reactor (STR) and a plug flow reactor (PFR). A significant improvement in metal removal was achieved with increased substrate concentration using immobilized Citrobacter cells in the PFR, which was not observed using free cells in the STR. Nitrate is an inhibitor of the Citrobacter phosphatase. This inhibition was concentration dependent and reversible. The rate of product release was restored by increasing the concentration of substrate (G2P). The ratio of rates of phosphate release under two different conditions (different nitrate and G2P concentrations) can be described by a equation developed from Michaelis-Menten kinetics. The concentration of substrate required for restoration of maximum velocity, V(max), in a batch and continuous-flow system can be predicted by substitution and calculation; this was confirmed by an experiment in model systems using cell suspensions and polyacrylamide gel immobilized cells in a flow-though column. For use in industrial situations it may be uneconomical or infeasible to supply additional substrate. Bioreactor activity was also restored by increasing the flow residence time, in accordance with a Michaelis-Menten-based model to describe removal of lanthanum from nitrate-supplemented flow in a PFR. (c) 1997 John Wiley & Sons, Inc. Biotechnol Biotechnol Bioeng 55:821-830, 1997.     

Cadmium accumulation by immobilized cells of a Citrobacter sp. using various phosphate donors

Immobilized cells of a Citrobacter species scavenge cadmium with high efficiency from challenge flows containing Cd(2+). Metal uptake by the cells in mediated by a cellbound phosphatase which liberates inorganic phosphate from an organic phosphate to precipitate cadmium as cell-bound metal phosphate. Hitherto glycerol 2-phosphate has served as the phosphate donor, but for an economic large scale process an inexpensive and readily available phosphate donor is required and the use of alkyl phosphates was investigated. This was limited due to interference by the alcohol simultaneously liberated. An alternative, pulsed process is described whereby alkyl phosphate-supplemented main pulses interspersed with short alkyl phosphate-free "recovery" pulses greatly reduced the requirement for glycerol 2-phosphate. Wider aspects of phosphate donor utilization were also investigated to compare this strain of Citrobacter with a strain previously reported to accumulate lead but not cadmium.     

Isolation and characterization of endophytic bacterium LRE07 from cadmium hyperaccumulator Solanum nigrum L. and its potential for remediation

Valuable endophytic strains facilitating plants growth and detoxification of heavy metals are required because the application of plant–endophyte symbiotic system is a promising potential technique to improve efficiency of phytoremediation. In this study, endophytic bacterium LRE07 was isolated from cadmium hyperaccumulator Solanum nigrum L. It was identified as Serratia sp. by 16S rRNA sequence analysis. The endophytic bacterium LRE07 was resistant to the toxic effects of heavy metals, solubilized mineral phosphate, and produced indoleacetic acid and siderophore. The heavy metal detoxification was studied in growing LRE07 cells. The strain bound over 65% of cadmium and 35% of zinc in its growing cells from single metal solutions 72 h after inoculation. Besides the high removal efficiencies in single-ion system, an analogous removal phenomenon was also observed in multi-ions system, indicating that the endophyte possesses specific and remarkable heavy metal remediation abilities.     

Screening of plant growth promoting traits in heavy metals resistant bacteria: Prospects in phytoremediation

Phytoremediation is considered as a novel environmental friendly technology, which uses plants to remove or immobilize heavy metals. The use of metal-resistant plant growth-promoting bacteria (PGPB) constitutes an important technology for enhancing biomass production as well as tolerance of the plants to heavy metals. In this study, we isolated twenty seven (NF1-NF27) chromium resistant bacteria. The bacteria were tested for heavy metals (Cr, Zn, Cu, Ni, Pb and Co) resistance, Cr(VI) reduction and PGPB characters (phosphate solubilization, production of IAA and siderophores). The results showed that the bacterial isolates resist to heavy metals and reduce Cr(VI), with varying capabilities. 37.14% of the isolates have the capacity of solubilizing phosphate, 28.57% are able to produce siderophores and all isolates have the ability to produce IAA. Isolate NF2 that showed high heavy metal resistance and plant growth promotion characteristics was identified by 16S rDNA sequence analysis as a strain of Cellulosimicrobium sp.. Pot culture experiments conducted under greenhouse conditions showed that this strain was able to promote plant growth of alfalfa in control and in heavy metals (Cr, Zn and Cu) spiked soils and increased metal uptake by the plants. Thus, the potential of Cellulosimicrobium sp. for both bioremediation and plant growth promotion has significance in the management of environmental pollution.     

Phosphotransferase activity of acid phosphatases of a Citrobacter sp.

The acid phosphatase of an atypical Citrobacter sp. was purified in two isoforms, designated CPI and CPII, which had different K_m values for glycerol 1-phosphate and glycerol 2-phosphate The enzyme was not inhibited by the end-product glycerol. Enzyme activity was increased in the presence of phosphate acceptor molecules having free hydroxyl groups (glycerol, methanol, ethanol). ³¹P-nuclear magnetic resonance spectroscopy indicated transfer of the liberated phosphate onto the alcohol, with the de novo production of (e.g.) glycerol 1-phosphate by enzyme supplemented with phosphomonoester substrate and glycerol.     

Bioaccumulation of metal cations by Saccharomyces cerevisiae

Yeast cells are capable of accumulation of various heavy metals, preferentially accumulating those of potential toxicity and also those of value. They retain their ability to accumulate heavy metals under a wide range of ambient conditions. In the present study it was shown that yeast cells in suspension accumulate heavy metal cations such as Cu²⁺, Co²⁺. The level of copper accumulation was dependent on the ambient metal concentration and was markedly inhibited by extremes of ambient pH. Temperature (5–40°C) and the presence of the alkali metal sodium had much smaller effects on the level of copper accumulation. This suggests that in waste-waters of pH 5.0–9.0, yeast biomass could provide an effective bioaccumlator for removal and/or recovery of the metal. During bioaccumulation and subsequent processes it is necessary to retain the biomass. It was shown in the present study that this could be achieved by cell immobilization. Immobilization allowed for complete removal of Cu²⁺, Co²⁺, and Cd²⁺ from synthetic metal solutions. The immobilized material could be freed of metals by use of the chelating agent ethylenediamine tetraacetic acid (EDTA) and recycled for further bioaccumulation events with little loss of accumulation capacity.Correspondence to: J. R. Duncan     

Cell surface display of synthetic phytochelatins using ice nucleation protein for enhanced heavy metal bioaccumulation.

Synthetic phytochelatins (ECs) composed of (Glu-Cys)nGly are protein analogs of phytochelatin that exhibit improved metal-binding capacity over metallothioneins (MTs). Expression of EC20 on the surface of E. coli using the Lpp-OmpA anchor resulted in improved bioaccumulation of cadmium and mercury, providing a new method for treating heavy metal contamination. To further improve the whole-cell accumulation of heavy metals, EC20 was expressed on the surface of Moraxella sp., a bacterium known to survive in contaminated environments, using the truncated ice nucleation protein (INPNC) anchor. Production of EC20 was approximately three-fold higher in Moraxella sp. than E. coli. As a consequence, the mercury-binding capacity of the recombinant Moraxella sp. was increased by more than 10-fold. Owing to the very high level of surface expression, the use of Moraxella sp. and INPNC anchor may prove to be useful for the remediation of other environmental contaminants.     

铜锈环棱螺对沉积物中重金属的生物积累及其与重金属赋存形态的关系

以铜锈环棱螺（Bellamya aeruginosa）为测试生物,采用28 d沉积物生物积累试验研究铜锈环棱螺对污染河流沉积物中重金属的生物积累,并探讨其与重金属赋存形态的关系.结果表明：铜锈环棱螺肝胰脏对Cd、Pb、Cu、Cr、Zn和Mn均具有较强的积累作用.不同重金属的积累量存在较大差别,Zn的积累量最多,占重金属总积累量的84.32%±4.36%,其次为Cu,占7.67%±2.84%;Pb、Cr和Mn的比例相对较少,分别为3.62%±1.84%、2.22%±1.03%和1.33%±0.15%;Cd所占比例最少,为0.83%±0.53%.肝胰脏中重金属元素之间的相关性均不显著.肝胰脏金属污染指数与沉积物污染综合指数具有显著的正相关关系,铜锈环棱螺可以作为沉积物重金属污染的监测生物.不同沉积物Cd、Cr、Zn和Mn的生物-沉积物积累因子（BSAF）具有较大的差异,Cu和Pb的BSAF比较稳定.Cd的生物积累与沉积物中Cd的可交换的与酸可溶态及可氧化态显著相关;Pb的生物积累与Pb的可还原态显著相关;Cu的生物积累与Cu的可氧化态显著相关;Mn的生物积累与Mn的可交换的与酸可溶态和可还原态显著相关;Cr和Mn的生物积累与其不同形态和总量均不相关.BSAF不宜作为衡量铜锈环棱螺对沉积物中重金属生物积累能力的指标.     

Bioremediation of Heavy Metals in Liquid Media Through Fungi Isolated from Contaminated Sources

Wastewater particularly from electroplating, paint, leather, metal and tanning industries contain enormous amount of heavy metals. Microorganisms including fungi have been reported to exclude heavy metals from wastewater through bioaccumulation and biosorption at low cost and in eco-friendly way. An attempt was, therefore, made to isolate fungi from sites contaminated with heavy metals for higher tolerance and removal of heavy metals from wastewater. Seventy-six fungal isolates tolerant to heavy metals like Pb, Cd, Cr and Ni were isolated from sewage, sludge and industrial effluents containing heavy metals. Four fungi (Phanerochaete chrysosporium, Aspegillus awamori, Aspergillus flavus, Trichoderma viride) also were included in this study. The majority of the fungal isolates were able to tolerate up to 400 ppm concentration of Pb, Cd, Cr and Ni. The most heavy metal tolerant fungi were studied for removal of heavy metals from liquid media at 50 ppm concentration. Results indicated removal of substantial amount of heavy metals by some of the fungi. With respect to Pb, Cd, Cr and Ni, maximum uptake of 59.67, 16.25, 0.55, and 0.55 mg/g was observed by fungi Pb3 (Aspergillus terreus), Trichoderma viride, Cr8 (Trichoderma longibrachiatum), and isolate Ni27 (A. niger) respectively. This indicated the potential of these fungi as biosorbent for removal of heavy metals from wastewater and industrial effluents containing higher concentration of heavy metals.     

鄱阳湖北段白鹭和苍鹭重金属富集特征比较

水鸟对重金属的富集水平及特征是了解湿地生态系统健康状况、水鸟生境安全的重要渠道。2016年通过非损伤取样方式采集了鄱阳湖北段白鹭Egretta garzetta和苍鹭Ardea cinerea各20个卵壳样品,并收集了2种鹭鸟觅食地的土壤样品9份,利用电感耦合等离子体质谱仪对卵壳和土样中铬(Cr)、铜(Cu)、镍(Ni)、锌(Zn)、砷(As)、铅(Pb)、镉(Cd)、汞(Hg)8种重金属的残留量进行了测量,分析了重金属在2种鹭鸟卵壳中的残留量,在此基础上分析了该区域2种鹭鸟对土壤重金属富集特征。研究结果表明,8种重金属中,白鹭和苍鹭卵壳重金属残留量均以Zn最高、Cd最低。苍鹭的Pb残留量极显著高于白鹭(P<0.01)。白鹭和苍鹭卵壳对Hg的生物富集系数最高,As的最低,而苍鹭对Pb的生物富集系数极显著高于白鹭(P<0.01)。     

Genetic engineering of Escherichia coli for enhanced uptake and bioaccumulation of mercury.

Synthetic phytochelatins (ECs) are a new class of metal-binding peptides with a repetitive metal-binding motif, (Glu-Cys)(n)Gly, which were shown to bind heavy metals more effectively than metallothioneins. However, the limited uptake across the cell membrane is often the rate-limiting factor for the intracellular bioaccumulation of heavy metals by genetically engineered organisms expressing these metal-binding peptides. In this paper, two potential solutions were investigated to overcome this uptake limitation either by coexpressing an Hg(2+) transport system with (Glu-Cys)(20)Gly (EC20) or by directly expressing EC20 on the cell surface. Both approaches were equally effective in increasing the bioaccumulation of Hg(2+). Since the available transport systems are presently limited to only a few heavy metals, our results suggest that bioaccumulation by bacterial sorbents with surface-expressed metal-binding peptides may be useful as a universal strategy for the cleanup of heavy metal contamination.     

Seasonal variation of metal accumulation and translocation in yellow pond-lily (Nuphar lutea)

Abstract

Heavy metal bioaccumulation and translocation properties of aquatic plants are interesting because of their potential use in phytoextraction. However, there is not enough knowledge about the seasonal changes of the metal distribution properties of aquatic plants. Our study focused on seasonal variation of some heavy metals in relation to their bioaccumulation and translocation in Nuphar lutea, a floating leaved, widespread plant that is important to wildlife. In this study, N. lutea, corresponding sediment and water samples were collected at different seasons from Lake Abant (Turkey) and analysed for their heavy metal content (Pb, Cr, Cu, Mn, Ni, Zn and Cd). Accumulation and translocation of heavy metal ratios were calculated seasonally. It was found that Cr and Zn were actively transported from sediment to the root, where they accumulated especially in summer; it was also shown that Cu, Mn and Zn were not only taken up from the sediment but also from the surrounding water. The investigations suggested that translocation ratios for leaf/root of Pb, Cr, Mn and Zn reached their highest levels in spring. It was found that the bioaccumulation and translocation of heavy metals at different parts of N. lutea changes with respect to season and the type of heavy metal.     

沉水植物菹草在低温条件下对重金属Cu、Pb、Zn的吸附和富集

在10℃的较低温度条件下,研究了冬春季节生长旺盛的沉水植物菹草(Potamogeton crispus L.)对重金属离子Cu²⁺,Pb²⁺,Zn²⁺的生物吸附特征及解吸情况,对不同初始浓度重金属水体中的重金属离子去除率情况,以及在此过程中菹草各器官(叶、茎、根茎、根)对重金属离子的富集情况。结果表明,菹草对Cu²⁺,Zn²⁺的吸附在20 min内达到平衡,对Pb²⁺的吸附在50 min内达到平衡,吸附动力学结果符合伪二级动力学方程,决定系数分别达1,1,0.997 8。Freundlich等温线可较好地拟合菹草吸附Cu²⁺,Pb²⁺,Zn²⁺的过程,Cu²⁺,Pb²⁺,Zn²⁺的吸附容量分别达到66.900 6,26.543 0,30.371 8 mg·L^-1。以去离子水作洗脱剂,解吸液中3种重金属离子浓度均低于仪器检出限(0.01 mg·L^-1),解吸程度微弱。投放菹草后,随着初始处理浓度的升高,水体Cu²⁺的去除率先降低后升高,Pb²⁺的去除率的变化趋势与Cu²⁺类似。Zn²⁺去除率则随水体Zn²⁺初始浓度的升高而逐渐升高。菹草各器官对水体3种重金属离子的富集能力不同,排序为Cu²⁺＞Zn²⁺＞Pb²⁺。不同器官对同一种重金属离子的富集量差异显著,叶是富集重金属离子的主要器官。水体重金属离子的初始浓度会影响菹草各器官富集重金属离子的能力,一般随水体重金属初始浓度升高,菹草各器官的重金属离子富集量虽有不同程度的增加但富集系数持续减小。     

Fungal assisted bio-treatment of environmental pollutants with comprehensive emphasis on noxious heavy metals: Recent updates

In the present time of speedy developments and industrialization, heavy metals are being uncovered in aquatic environment and soil via refining, electroplating, processing, mining, metallurgical activities, dyeing and other several metallic and metal based industrial and synthetic activities. Heavy metals like lead (Pb), mercury (Hg), cadmium (Cd), arsenic (As), Zinc (Zn), Cobalt (Co), Iron (Fe), and many other are considered as seriously noxious and toxic for the aquatic environment, human, and other aquatic lives and have damaging influences. Such heavy metals, which are very tough to be degraded, can be managed by reducing their potential through various processes like removal, precipitation, oxidation–reduction, bio-sorption, recovery, bioaccumulation, bio-mineralization etc. Microbes are known as talented bio-agents for the heavy metals detoxification process and fungi are one of the cherished bio-sources that show noteworthy aptitude of heavy metal sorption and metal tolerance. Thus, the main objective of the authors was to come with a comprehensive review having methodological insights on the novel and recent results in the field of mycoremediation of heavy metals. This review significantly assesses the potential talent of fungi in heavy metal detoxification and thus, in environmental restoration. Many reported works, methodologies and mechanistic sights have been evaluated to explore the fungal-assisted heavy metal remediation. Herein, a compact and effectual discussion on the recent mycoremediation studies of organic pollutants like dyes, petroleum, pesticides, insecticides, herbicides, and pharmaceutical wastes have also been presented.     

Influence of joint application of heavy metals on level of each metal accumulated in the periwinkle Tympanotonus fuscatus (Gastropoda: Potamididae)

Most laboratory assessments of toxicity and bioaccumulation of heavy metals have been concentrated on the accumulation of these metal ions when exposed singly to the test organisms. However, under the natural environmental settings, the metals are never present in isolation and may interact with each other, therefore justifying the need to study the influence of joint application of metals on accumulated levels in exposed animals. In this study, exposure of the periwinkle Tympanotonus fuscatus to sublethal concentrations (equivalent to 0.1 and 0.01 of 96 h LC50) of heavy metals revealed that they were bioaccumulative varying amounts, depending on the type of metal, exposure period and concentration in the test media. While Zn and Pb ion accumulation increased steadily with exposure time, the amounts of Cu accumulated fluctuated regularly over the 30-day experimental period. The levels of Zn, Cu and Cd bioaccumulated over the 30-day experimental period were reduced by over 2-6 folds (with bioaccumulation ratio values ranging from 0.15 to 0.81) when compared to concentrations of the respective metals accumulated during single bioaccumulation studies. However, Pb concentrations accumulated during the joint action studies increased nearly 2-fold (bioaccumulation ratio range 1.36 to 2.0-fold).     

Interaction of Heavy Metals in Multimetal Biosorption by Galerina vittiformis from Soil

ABSTRACT Soil heavy metal contamination, a major threat due to industrialization, can be tackled by an efficient and economical process called bioremediation. Mushrooms are employed to accumulate heavy metals from soil due to their high metal accumulation potential and better adaptability. The bioaccumulation potential of Galerina vittiformis was already reported for individual metals. At natural conditions, since soil consists of more than one polluting metal, more focus has to be given to multimetal systems. In this study, multimetal accumulation potential was analyzed using central composite design, and the responses obtained were analyzed using response surface methodology. Heavy metals such as Cu(II), Cd(II), Cr(VI), Pb(II), and Zn(II) were subjected to biosorption at 10–250 mg/kg concentrations along with pH 5–8. The results showed that the preference of the organism for the five metals under study was in the order Pb(II) > Zn(II) > Cd(II) > Cu(II) > Cr(VI) at pH 6.5 under multimetal condition. The study also indicates that the metal interaction pattern in multimetal interaction is a property of their ionic radii. The response surface methodology clearly explains the effect of interaction of heavy metals on the accumulation potential of the organism using three-dimensional response plots. The present work suggests that the fungus Galerina vittiformis could be employed as a low-cost metal removal agent from heavy metal–polluted soil.     

Identification of structural nif genes in an iron-oxidising moderate thermophile

The effect of 500 mM NaCl on the growth, and phosphatase production of a Citrobacter sp. was investigated. Although growth was retarded, phosphatase production was enhanced by 50%. Relief from osmotic stress using the osmoprotectant glycine betaine gave normal growth, but phosphatase activity was reduced. The Citrobacter sp. ceased to grow following a shift to anaerobic conditions, but anaerobically-incubated cells continued to produce phosphatase after a transient lag.     

Cadmium accumulation by a Citrobacter sp

Cadmium accumulation by a Citrobacter sp. growing in the presence of the metal occurred as a sharp peak during the mid-exponential phase of growth, but cultures showed considerable inhibition of growth compared to cadmium-free controls. This problem was overcome by pregrowing the cells in cadmium-free medium and subsequently exposing them to the metal in the resting state, under which conditions higher concentrations of cadmium were tolerated and metal uptake was enhanced. This ability was retained when the cells were immobilized and then challenged with a flow containing Cd2+; 65% of the metal presented was removed from solution. The influence on uptake of the composition of the exposure buffer and of various cell treatments were investigated and the results are discussed with respect to the anticipated speciation of the cadmium presented to the cells and also with respect to the probable mechanism of metal uptake. This is thought to occur through the activity of a cell-bound phosphatase, induced during pre-growth by the provision of glycerol 2-phosphate as sole phosphorus source. Continued enzyme function in resting cells would then precipitate the metal as cell-bound cadmium phosphate.