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。     

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.     

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.     

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.     

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.     

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.     

Anaerobes into heavy metal: Dissimilatory metal reduction in anoxic environments

Within the last decade, a novel form of microbial metabolism of major environmental significance has been elucidated. In this process, known as dissimilatory metal reduction, specialized microorganisms, living in anoxic aquatic sediments and ground water, oxidize organic compounds to carbon dioxide with metals serving as the oxidant. Recent studies have demonstrated that this metabolism explains a number of important geochemical phenomena in ancient and modern sedimentary environments, affecting not only the cycling of metals but also the fate of organic matter. Furthermore, this metabolism may have practical application in remediation of environments contaminated with toxic metals and/or organics.     

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.     

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.     

Heavy metal tolerance by ectomycorrhizal fungi and metal amelioration by Pisolithus tinctorius

Five ectomycorrhizal fungi, Pisolithus tinctorius, Thelephora terrestris, Cenococcum geophilum, Hymenogaster sp. and Scleroderma sp., which were demonstrated previously to be capable of forming ectomycorrhizas with some pine, eucalypt and fagaceous tree species were grown in vitro in liquid cultures for 3 weeks at six different concentrations of nine heavy metals, aluminium, iron, copper, zinc, nickel, cadmium, chromium, lead and mercury. Measurements of mean mycelial dry weight yields indicated that the local isolates of Hymenogaster sp. and Scleroderma sp., as well as the introduced fungal species P. tinctorius, were able to withstand high concentrations of Al, Fe, Cu and Zn and might, therefore, have potential for revegetation schemes in metal-contaminated soils. The metal amelioration mechanism in the metal-tolerant fungal species P. tinctorius was observed to involve extrahyphal slime and, as demonstrated by energy-dispersive X-ray spectrometry, was achieved by polyphosphate linkage of Cu and Zn.     

EDTA enhanced heavy metal phytoextraction: metal accumulation,leaching and toxicity

Synthetic chelates such as ethylene diamine tetraacetic acid (EDTA) have been shown to enhance phytoextraction of some heavy metals from contaminated soil. In a soil column study, we examined the effect of EDTA on the uptake of Pb, Zn and Cd by Chinese cabbage (Brassica rapa), mobilization and leaching of heavy metals and the toxicity effects of EDTA additions on plants. The most effective was a single dose of 10 mmol EDTA kg^–1 soil where we detected Pb, Zn and Cd concentrations that were 104.6, 3.2 and 2.3-times higher in the aboveground plant biomass compared to the control treatments. The same EDTA addition decreased the concentration of Pb, Zn and Cd in roots of tested plants by 41, 71 and 69%, respectively compared to concentrations in the roots of control plants. In columns treated with 10 mmol kg^–1 EDTA, up to 37.9, 10.4 and 56.3% of initial total Pb, Zn and Cd in soil were leached down the soil profile, suggesting high solubility of heavy metals-EDTA complexes. EDTA treatment had a strong phytotoxic effect on the red clover (Trifolium pratense) in bioassay experiment. Moreover, the high dose EDTA additions inhibited the development of arbuscular mycorrhiza. The results of phospholipid fatty acid analyses indicated toxic effects of EDTA on soil fungi and increased environmental stress of soil microfauna.     

High-valent corrole metal complexes

This commentary concentrates on corrole complexes with the three metal ions that are most relevant to oxidation catalysis: chromium, manganese, and iron. Particular emphasis is devoted to the only recently introduced meso-triarylcorroles and a comparison with the traditionally investigated beta-pyrrole-substituted corroles. Based on a combination of spectroscopic methods, electrochemistry, and X-ray crystallography, it is concluded that in most high-valent metallocorroles the corrole is not oxidized. Both experimental (for (oxo)chromium(V) corrole) and computational (for (oxo)manganese(V) corrole) evidence indicate that the stabilization of high-valent metal ions by corroles originates from a combination of short metal-nitrogen bonds and large metal out-of-plane displacements in the corrole, which lead to quite unexpected interactions of the oxo-metal pi* orbitals with the in-plane orbitals of the corrole.     

High-valent transition metal corrolazines

High-valent metalloporphyrin intermediates have been implicated as key players in numerous mechanistic proposals for both biological (e.g., heme protein) and synthetic porphyrin mediated transformations. However, the direct observation of these species is quite challenging because of the inherently short lifetimes of many of these metalloporphyrin intermediates. This review focuses on our own efforts to synthesize and study a new class of porphyrinoid compounds called corrolazines, which are designed to stabilize high-valent species for direct analysis. These compounds are related to corroles, which also exhibit the unusual ability to stabilize high oxidation states, and the reactivity and physical properties of relevant corrole and porphyrin analogs are compared with the appropriate corrolazines. The chemistry of Cu, Co, V, and Mn are highlighted, with a particular emphasis on the reactivity of high-valent manganese-oxo complexes.     

Thermophilic microbial metal reduction

Thermophilic microorganisms can reduce Fe(III), Mn(IV), Cr(VI), U(VI), Tc(VII), Co(III), Mo(VI), Au(I, III), and Hg(II). Ferric iron and Mn(IV) can be used as electron acceptors during growth; the physiological role of the reduction of the other metals is unclear. The process of microbial dissimilatory reduction of Fe(III) is the most thoroughly studied. Iron-reducing prokaryotes have been found in virtually all of the recognized types of terrestrial ecosystems, from hot continental springs to goethermally heated subsurface sediments. Thermophilic iron reducers do not belong to a phylogenetically homogenous group and include representatives of many bacterial and archaeal taxa. Iron reducing thermophiles can couple Fe(III) reduction with oxidation of a wide spectrum of organic and inorganic compounds. In the thermophilic microbial community, they can fulfil both degradative and productive functions. Thermophilic prokaryotes probably carried out global reduction of metals on Earth in ancient times, and, at the same time, they are promising candidates for use in modern biotechnological processes.     

Put the metal to the petal: metal uptake and transport throughout plants

Compared to other organisms, plants have expanded families of transporters that are involved in the uptake and efflux of metals. Fortunately, in many cases, the examination of double mutants has been sufficient to overcome the challenge of studying functionally redundant gene families. Plants that lack two heavy-metal-transporting P-type ATPase family members (HMA2 and HMA4) reveal a function for these transporters in Zn translocation from roots to shoots. Likewise, the phenotype of plants that lack two natural resistance associated macrophage protein (NRAMP) homologs (NRAMP3 and NRAMP4) implicate these metal uptake proteins in the mobilization of vacuolar Fe stores during seed germination. Most families of metal transporters are ubiquitous but the Yellow Stripe1-Like (YSL) family is plant specific and YSL family members have been implicated in the transport of metals that are complexed with a plant specific chelator called nicotianamine (NA).