Bioremediation of organic and metal contaminants with dissimilatory metal reduction

PCR fingerprinting offers a practical molecular means to quickly and reliably differentiate bacteria for microbial products screening. A combination of low resolution and high resolution PCR fingerprinting provides a hirarchical system which allows the discrimination of bacteria at species and subspecies level within 7 h. DNA was extracted from cells by incubating them in water at 95°C for 30 min. A sample of 1 l of the cell-free aqueous extract then was used as a source of template DNA in the PCR. The PCR products were separated by electrophoresis on an acrylamide gel and visualized by ethidium bromide staining. The band patterns generated for each different culture were unique, reproducible, and independent of cultivation conditions. Band patterns may be compared visually or by using imaging and pattern matching software. In our laboratory, bacteria such as actinomycetes, Gram-negative and Gram-positive soil eubacteria, and photosynthetic non-sulfur bacteria have been differentiated using PCR fingerprinting.     

细菌金属离子外排系统及金属稳态调控

铁、铜、锌、锰等金属离子是各类生物体生存和增殖所必需的微量元素,可影响生物体内蛋白酶活性、免疫反应、生理过程和抗感染机制。细菌感染过程中,宿主可通过限制或提高体内环境中金属离子的浓度来抑制细菌增殖,与此同时,细菌进化出各种转运系统以适应宿主体内金属离子水平的变化。由于不同细菌的金属离子外排系统在结构和生化特性上存在变异,它们呈现出独特的金属离子外排模式。本文根据现有文献报道及本团队研究结果,对铁、铜、锌和锰离子的细菌外排系统进行讨论和总结,旨在综述目前对细菌金属离子稳态调控机制研究进展的认识,为深入理解细菌金属稳态调控相关机制提供参考。     

The role of metal on imide hydrolysis: metal content and pH profiles of metal ion-replaced mammalian imidase

Imidase catalyzes the hydrolysis of a variety of imides. The removal of metal from imidase eliminates its activity but does not affect its tetrameric and secondary structure. The reactivation of the apoenzyme with transition metal ions Co(2+), Zn(2+), Mn(2+), and Cd(2+) shows that imidase activity is linearly dependent on the amount of metal ions added. Ni(2+) and Cu(2+) are also inserted, one per enzyme subunit, into the apoimidase, but do not restore imidase activity. Enzyme activity with different metal replaced imidase varies significantly. However, the changes of the metal contents do not appear to affect the pK(a)s obtained from the bell-shaped pH profiles of metal reconstituted imidase. The metal-hydroxide mechanism for imidase action is not supported based on the novel findings from this study. It is proposed that metal ion in mammalian imidase functions as a Lewis acid, which stabilizes the developing negative charge of imide substrate in transition state.     

Ligand and metal X-ray absorption in transition metal complexes

The ligand K edges and metal L edges of transition metal complexes are discussed within the perspective of recent progress in calculations on bulk transition metal oxides. Similarities and differences between bulk transition metal systems and coordination complexes are discussed. It is argued that the core hole effect reduces the amount of ligand p-states in the 3d-band (the β² value) by approximately 10-20%. It is suggested that matrix elements do not have to be included in XAS calculations if one calculates the projected DOS in the area of the core state radius. In case of metal L edge spectra, the additional effects of multiplets and charge transfer are discussed and compared with DFT calculations.     

Mechanisms of metal carcinogenesis

Experimental observations that pertain to mechanisms of metal carcinogenesis are summarized, with emphasis upon (a) interactions of metals with nucleic acids in vitro; (b) impairment by metals of the fidelity of DNA replication by DNA polymerase in vitro; (c) mutagenicity of metals in microorganisms; (d) cytogenetic aberrations induced by metals in tissue culture cells; (e) induction by metals of neoplastic transformation of tissue culture cells; and (f) nuclear uptake of metals in vivo and concomitant inhibitory effects of metals on synthesis of nucleic acids. Considered in toto, the experimental data support the somatic mutation hypothesis of chemical carcinogenesis. Sufficient experimental evidence is available regarding four carcinogenic metals (As, Be, Cr, and Ni) to permit speculations about the molecular reactions whereby these metals may induce somatic mutations. This article is an updated outgrowth of a review presented at the A. O. Beckman Conference on the Biochemistry of Cancer that was held in San Antonio, Texas, on September 6–8, 1978. The earlier draft of this article is being published in the proceedings volume.     

Rhizosphere bacteria affect growth and metal uptake of heavy metal accumulating willows

A variety of plants growing on metalliferous soils accumulate metals in their harvestable parts and have the potential to be used for phytoremediation of heavy metal polluted land. There is increasing evidence that rhizosphere bacteria contribute to the metal extraction process, but the mechanisms of this plant–microbe interaction are not yet understood. In this study ten rhizosphere isolates obtained from heavy metal accumulating willows affiliating with Pseudomonas, Janthinobacterium, Serratia, Flavobacterium, Streptomyces and Agromyces were analysed for their effect on plant growth, Zn and Cd uptake. In plate assays Zn, Cd and Pb resistances and the ability of the bacteria to produce indole-3-acetic acid (IAA), 1-amino-cyclopropane-1-carboxylic acid deaminase (ACC deaminase) and siderophores were determined. The isolates showed resistance to high Zn concentrations, indicating an adaptation to high concentrations of mobile Zn in the rhizosphere of Salix caprea. Four siderophore producers, two IAA producers and one strain producing both siderophores and IAA were identified. None of the analysed strains produced ACC deaminase. Metal mobilization by bacterial metabolites was assessed by extracting Zn and Cd from soil with supernatants of liquid cultures. Strain Agromyces AR33 almost doubled Zn and Cd extractability, probably by the relase of Zn and Cd specific ligands. The remaining strains, immobilized both metals. When Salix caprea plantlets were grown in γ-sterilized, Zn/Cd/Pb contaminated soil and inoculated with the Zn resistant isolates, Streptomyces AR17 enhanced Zn and Cd uptake. Agromyces AR33 tendentiously promoted plant growth and thereby increased the total amount of Zn and Cd extracted from soil. The IAA producing strains did not affect plant growth, and the siderophore producers did not enhance Zn and Cd accumulation. Apparently other mechanisms than the production of IAA, ACC deaminase and siderophores were involved in the observed plant–microbe interactions.     

Some metal alloxides

Tetraalloxygermanium(IV), (CH₂·CH·CH₂·O)₄Ge, has been synthesized from germanium tetrachloride, allyl alcohol, and ammonia. The alloxides [(CH₂·CH· CH₂·O)₄Ti]₂and[(CH₂·CH·CH₂O)₅M]₂ (M = Nb and Ta) have been synthesized by reactions of the corresponding metal isopropoxides with allyl alcohol followed by removal of the isopropanol by azeotropic distillation with benzene. These four metal alloxides can be purified by distillation under reduced pressure. The spectroscopic properties of these new compounds are discussed.     

Precious metal economy

The zebrafish is emerging as a system of choice for modeling human disease. In this issue of Cell Metabolism, Mendelsohn et al. (2006) describe a model for Menkes disease, a genetic disorder in copper utilization. Using genetic and chemical screens, the authors highlight the impact of maternal nutrition on embryo development. The work reveals a hierarchy of temporal and dosage-dependent phenotypes for copper nutrition.     

Retromobilization of heavy metal resistance genes in unpolluted and heavy metal polluted soil

Abstract: Retromobilization of the nonconjugative (Tra⁻Mob⁺) IncQ vector, pMOL155, and the non-mobilizable (Tra⁻Mob⁻) vector, pMOL149, by means of the IncP plasmids RP4 and pULB113 (RP4::Mu3A), was studied in plate matings and in soil microcosms, and compared with direct and triparental mobilization. Both vectors harbour the czc genes, originating from Alcaligenes eutrophus , which code for resistance to Co, Zn, and Cd. The donor of the czc genes was Escherichia coli which did not express these genes. The recipient, Alcaligenes eutrophus , expressed the czc genes very well. Retromobilization, direct and triparental mobilization of pMOL155 was observed in sterile soil. Both the addition of nutrients and heavy metals significantly enhanced the number of (retro)transconjugants. Retromobilization was also detected in nutrient amended nonsterile soil, but the presence of the autochthonous soil biota strongly reduced the number of retrotransconjugants and also prevented their increase upon application of heavy metals to the soil. Retromobilization of the czc genes, cloned in pMOL149, by using pULB113 was also observed, yet only in sterile, nutrient amended, heavy metal polluted soil.     

Functional equivalence of industrial metal cleaning processes comparison of metal cleaning processes within LCA

In an LCA case study, the three most frequent industrial metal cleaning technologies were assessed: Cleaning based on aqueous cleaning agents, non-halogenated hydrocarbon solvents and halogenated hydrocarbon solvents. Beside optimisation analysis, the comparison of the cleaning processes was a main goal of the study. The function of metal cleaning processes can be described with a set of parameters called functional parameters. In order to compare different cleaning processes within LCA, it is a precondition that all relevant functional parameters be equivalent. However, metal cleaning processes from different companies normally differ in most of the functional parameters and, thus, are not functionally equivalent. Therefore, it is necessary to calculate the material and energy flows of the processes corresponding to a reference function as a basis for comparison. This can be achieved by simulating the processes according to the functional parameters with the help of a process model. For a general comparison of the technologies, it is also necessary to consider the assessed machines having the same level of optimisation and the same scale.     

环境重金属污染物的生物有效性

利用生态系统研究了白银有色金属冶炼矿区周围环境中重金属的分布及生物有效性。结果表明 ,工厂在冶炼过程中已造成 Pb、Cd、Cu、Zn对周围环境不同程度的污染 ,其含量与距工厂的距离呈负相关 ;重金属在各种生物体内均有不同程度的吸收和累积 ,其吸收累积量随重金属和生物种类的不同而有差异 ;土壤的污染 ,使农作物和牧草中 Pb、Cd含量超过动物的最大耐受量和中毒的临界值 ;动物研究发现 ,肾脏、骨骼和肝脏是机体内重金属蓄积的主要器官。因此 ,放牧动物可作为环境重金属污染状况的标识 ,对评价重金属环境污染对当地人群的危害也有重要意义     

Microbial reporters of metal bioavailability

When attempting to assess the extent and the implications of environmental pollution, it is often essential to quantify not only the total concentration of the studied contaminant but also its bioavailable fraction: higher bioavailability, often correlated with increased mobility, signifies enhanced risk but may also facilitate bioremediation. Genetically engineered microorganisms, tailored to respond by a quantifiable signal to the presence of the target chemical(s), may serve as powerful tools for bioavailability assessment. This review summarizes the current knowledge on such microbial bioreporters designed to assay metal bioavailability. Numerous bacterial metal‐sensor strains have been developed over the past 15 years, displaying very high detection sensitivities for a broad spectrum of environmentally significant metal targets. These constructs are based on the use of a relatively small number of gene promoters as the sensing elements, and an even smaller selection of molecular reporter systems; they comprise a potentially useful panel of tools for simple and cost‐effective determination of the bioavailability of heavy metals in the environment, and for the quantification of the non‐bioavailable fraction of the pollutant. In spite of their inherent advantages, however, these tools have not yet been put to actual use in the evaluation of metal bioavailability in a real environmental remediation scheme. For this to happen, acceptance by regulatory authorities is essential, as is a standardization of assay conditions.