共查询到20条相似文献,搜索用时 15 毫秒
1.
Summary The plasmid-borne czc operon ensures for resistance to Cd 2+, Zn 2+ and Co 2+ ions through a tricomponent export pathway and is associated to various conjugative plasmids of A. eutrophus strains isolated from metal-contaminated industrial areas. The czc region of pMOL30 was reassessed especially for the segments located upstream and downstream the structural genes czc CBA. In cultures grown with high concentrations of heavy metals, czc-mediated efflux of cations is followed by a process of metal bioprecipitation. These observations led to the development of bioreactors designed for the removal of heavy metals from polluted effluents. 相似文献
2.
Exogenous plasmid isolation was used to assess the presence of mobilizing plasmids in several soils and activated sludges. Triparental matings were performed with Escherichia coli (a member of the γ subgroup of the Proteobacteria) as the donor of an IncQ plasmid (pMOL155, containing the heavy metal resistance genes czc: Co r, Zn r, and Cd r), Alcaligenes eutrophus (a member of the β subgroup of the Proteobacteria) as the recipient, and indigenous microorganisms from soil and sludge samples as helper strains. We developed an assay to assess the plasmid mobilization potential of a soil ecosystem on the basis of the number of transconjugants obtained after exogenous isolations. After inoculation into soil of several concentrations of a helper strain ( E. coli CM120 harboring IncP [IncP1] mobilizing plasmid RP4), the log numbers of transconjugants obtained from exogenous isolations with different soil samples were a linear function of the log numbers of helper strain CM120(RP4) present in the soils. Four soils were analyzed for the presence of mobilizing elements, and mobilizing plasmids were isolated from two of these soils. Several sludge samples from different wastewater treatment plants yielded much higher numbers of transconjugants than the soil samples, indicating that higher numbers of mobilizing strains were present. The mobilizing plasmids isolated from Gent-O sludge and one plasmid isolated from Eislingen soil hybridized to the repP probe, whereas the plasmids isolated from Essen soil did not hybridize to a large number of rep probes (repFIC, repHI1, repH12, repL/M, repN, repP, repT, repU, repW, repX). This indicates that in Essen soil, broad-host-range mobilizing plasmids belonging to other incompatibility groups may be present. 相似文献
3.
Protoplasts prepared from yeast-like cells, hyphae and chlamydospores of Aureobasidium pullulans can take up heavy metals such as Zn 2+, Co 2+, Cd 2+ and Cu 2+. In relation to intact cells, the sensitivity of protoplasts to Cu 2+ and Cd 2+ was increased although chlamydospore protoplasts were more tolerant than yeast-like cell protoplasts. Surface binding of metals was reduced in protoplasts as compared with intact cells and this reduction was particularly evident for chlamydospore protoplasts. At the highest concentrations used, uptake of Zn 2+, Co 2+ and Cd 2+ by yeast-like cell protoplasts was greater than that observed in intact cells which may have been due to toxicity, especially for Cd 2+, resulting in increased membrane permeability, though for Zn 2+ and Co 2+ some barrier effect of the cell wall could not be completely discounted. Chlamydospore protoplasts were capable of intracellular metal uptake, unlike intact chlamydospores, and for Zn 2+, uptake appeared to be via a different system less specific than that of the other cell types. For chlamydospores, the use of protoplasts confirmed the importance of the cell wall in preventing entry of metal ions into the cell. 相似文献
4.
Bacterial plasmids encode resistance systems for toxic metal ions, including Ag +, AsO 2-, AsO 43-, Cd 2+, Co 2+, CrO 42-, Cu 2+ Hg 2+, Ni 2+, Pb 2+, Sb 3+, TeO 32-, Tl + and Zn 2+. The function of most resistance systems is based on the energy-dependent efflux of toxic ions. Some of the efflux systems are ATPases and others are chemiosmotic cation/proton antiporters. The Cd 2+-resistance ATPase of Gram-positive bacteria (CadA) is membrane cation pump homologous with other bacterial, animal and plant P-type ATPases. CadA has been labeled with 32P from [ α- 32p]ATP and drives ATP-dependent Cd 2+ (and Zn 2+) uptake by inside-out membrane vesicles (equivalent to efflux from whole cells). Recently, isolated genes defective in the human hereditary diseases of copper metabolism, namely Menkes syndrome and Wilson's disease, encode P-type ATPases that are more similar to bacterial CadA than to other ATPases from eukaryotes. The arsenic resistance efflux system transports arsenite [As(III)], alternatively using either a double-polypeptide (ArsA and ArsB) ATPase or a single-polypeptide (ArsB) functioning as a chemiosmotic transporter. The third gene in the arsenic resistance system, arsC, encodes an enzyme that converts intracellular arsenate [As(V)] to arsenite [As(III)], the substrate of the efflux system. The triple-polypeptide Czc (Cd 2+, Zn 2+ and Co 2+) chemiosmotic efflux pump consists of inner membrane (CzcA), outer membrane (CzcC) and membrane-spanning (CzcB) proteins that together transport cations from the cytoplasm across the periplasmic space to the outside of the cell. 相似文献
5.
Through subcultivations of Thiobacillus thiooxidans WU-79A in autotrophic media in which the concentrations of Cd 2+ and Zn 2+ were increased successively, Cd 2+-resistant (CDR) and Zn 2+-resistant strains (ZNR) were obtained. The growth of WU-79A was inhibited by the addition of 25 mM Cd 2+ as well as Zn 2+. However, CDR and ZNR could grow without any lag phase in media containing 200 mM Cd 2+ and 250 mM Zn 2+, respectively. CDR and ZNR were able to grow even in media containing up to 400 mM Cd 2+ and 600 mM Zn 2+, respectively, although they exhibited lag phases. CDR could grow in medium containing up to 250 mM Zn 2+, as could ZNR in medium containing up to 200 mM Cd 2+. Cd 2+-binding and Zn 2+-binding proteins were isolated from CDR and ZNR, respectively, by gel filtration and ion exchange chromatography. The molecular weights of both proteins were estimated to be approximately 13,000 by gel filtration. The fact that there was no strong absorption at 280 nm of the proteins suggested that they had few aromatic amino acids. Broad absorption bands which are typical of mercaptide (metal thiolate) complexes were detected. The properties of the proteins were spectrophotometrically similar to those of metallothionein. 相似文献
6.
We express the effective Hamiltonian of an ion-binding site in a protein as a combination of the Hamiltonian of the ion-bound site in vacuum and the restraints of the protein on the site. The protein restraints are described by the quadratic elastic network model. The Hamiltonian of the ion-bound site in vacuum is approximated as a generalized Hessian around the minimum energy configuration. The resultant of the two quadratic Hamiltonians is cast into a pure quadratic form. In the canonical ensemble, the quadratic nature of the resultant Hamiltonian allows us to express analytically the excess free energy, enthalpy, and entropy of ion binding to the protein. The analytical expressions allow us to separate the roles of the dynamic restraints imposed by the protein on the binding site and the temperature-independent chemical effects in metal-ligand coordination. For the consensus zinc-finger peptide, relative to the aqueous phase, the calculated free energy of exchanging Zn 2+ with Fe 2+, Co 2+, Ni 2+, and Cd 2+ are in agreement with experiments. The predicted excess enthalpy of ion exchange between Zn 2+ and Co 2+ also agrees with the available experimental estimate. The free energy of applying the protein restraints reveals that relative to Zn 2+, the Co 2+, and Cd 2+-site clusters are more destabilized by the protein restraints. This leads to an experimentally testable hypothesis that a tetrahedral metal binding site with minimal protein restraints will be less selective for Zn 2+ over Co 2+ and Cd 2+ compared to a zinc finger peptide. No appreciable change is expected for Fe 2+ and Ni 2+. The framework presented here may prove useful in protein engineering to tune metal selectivity. 相似文献
7.
The involvement of Ca 2+ in the response to high Mn 2+, Co 2+, Ni 2+, Cu 2+, Zn 2+, Cd 2+, and Hg 2+ was investigated in Saccharomyces cerevisiae. The yeast cells responded through a sharp increase in cytosolic Ca 2+ when exposed to Cd 2+, and to a lesser extent to Cu 2+, but not to Mn 2+, Co 2+, Ni 2+, Zn 2+, or Hg 2+. The response to high Cd 2+ depended mainly on external Ca 2+ (transported through the Cch1p/Mid1p channel) but also on vacuolar Ca 2+ (released into the cytosol through the Yvc1p channel). The adaptation to high Cd 2+ was influenced by perturbations in Ca 2+ homeostasis. Thus, the tolerance to Cd 2+ often correlated with sharp Cd 2+-induced cytosolic Ca 2+ pulses, while the Cd 2+ sensitivity was accompanied by the incapacity to rapidly restore the low cytosolic Ca 2+. 相似文献
8.
The passive sorption of Pb +2, Cd +2, Zn +2, Co +2, Ni +2, and Mn +2 by isolated corn mitochondria was determined, and, except for Pb +2, the maximum sorption for each cation was about 58 nmol per milligram of protein. Sorption of Pb +2 was apparently ten times greater, but precipitation may have been the cause of this larger value. The effects of Pb +2, Cd +2, Zn +2, Co +2, and Ni +2 on acceptorless rates of electron transport for three substrates were determined. Greater than 50% inhibitions of oxidation were observed for succinate after additions of >0.1 m M Cd +2, Zn +2, or Pb +2: for NADH after additions of >0.5 m M Cd +2 or Zn +2; and for malate + pyruvate after additions of >0.1 m M Cd +2. Some inhibition of the rate of substrate oxidation was observed for most cations at higher concentrations. Coupling, as measured by ADP/O ratios, was inhibited at lowest concentrations by Cd +2 or Zn +2 and at higher concentrations by Co +2 or Ni +2. Substantial swelling of mitochondria oxidizing succinate was observed following additions of O.1 m M Cd +2 or Pb +2, Correlations are drawn between the effects of Pb +2, Cd +2, Zn +2, Co +2, and Ni +2 and their sorption to mitochondrial membranes. 相似文献
9.
Bacterial chromosomes have genes for transport proteins for inorganic nutrient cations and oxyanions, such as NH 4
+, K +, Mg 2+, Co 2+, Fe 3+, Mn 2+, Zn 2+ and other trace cations, PO 4
3-, SO 4
2- and less abundant oxyanions. Together these account for perhaps a few hundred genes in many bacteria. Bacterial plasmids
encode resistance systems for toxic metal and metalloid ions including Ag + AsO 2
-, AsO 4
3-, Cd 2+, Co 2+, CrO 4
2−, Cu 2+, Hg 2+, Ni 2+, Pb 2+, TeO 3
2−, TI + and Zn 2+. Most resistance systems function by energy-dependent efflux of toxic ions. A few involve enzymatic (mostly redox) transformations.
Some of the efflux resistance systems are ATPases and others are chemiosmotic ion/proton exchangers. The Cd 2+-resistance cation pump of Gram-positive bacteria is membrane P-type ATPase, which has been labeled with 32P from [γ- 32P]ATP and drives ATP-dependent Cd 2+ (and Zn 2+) transport by membrane vesicles. The genes defective in the human hereditary diseases of copper metabolism, Menkes syndrome
and Wilson’s disease, encode P-type ATPases that are similar to bacterial cadmium ATPases. The arsenic resistance system transports
arsenite [As(III)], alternatively with the ArsB polypeptide functioning as a chemiosmotic efflux transporter or with two polypeptides,
ArsB and ArsA, functioning as an ATPase. The third protein of the arsenic resistance system is an enzyme that reduces intracellular
arsenate [As(V)] to arsenite [As(III)], the substrate of the efflux system. In Gram-negative cells, a three polypeptide complex
functions as a chemiosmotic cation/protein exchanger to efflux Cd 2+, Zn 2+ and Co 2+. This pump consists of an inner membrane (CzcA), an outer membrane (CzcC) and a membrane-spanning (CzcB) protein that function
together.
Received 08 August 1997/ Accepted in revised form 01 November 1997 相似文献
10.
Summary Studying metal ion resistances gives us important insights into environmental processes and provides an understanding of basic living processes. This review concentrates on bacterial efflux systems for inorganic metal cations and anions, which have generally been found as resistance systems from bacteria isolated from metal-polluted environments. The protein products of the genes involved are sometimes prototypes of new families of proteins or of important new branches of known families. Sometimes, a group of related proteins (and presumedly the underlying physiological function) has still to be defined. For example, the efflux of the inorganic metal anion arsenite is mediated by a membrane protein which functions alone in Gram-positive bacteria, but which requires an additional ATPase subunit in some Gram-negative bacteria. Resistance to Cd 2+ and Zn 2+ in Gram-positive bacteria is the result of a P-type efflux ATPase which is related to the copper transport P-type ATPases of bacteria and humans (defective in the human hereditary diseases Menkes' syndrome and Wilson's disease). In contrast, resistance to Zn 2+, Ni 2+, Co 2+ and Cd 2+ in Gram-negative bacteria is based on the action of proton-cation antiporters, members of a newly-recognized protein family that has been implicated in diverse functions such as metal resistance/nodulation of legumes/cell division (therefore, the family is called RND). Another new protein family, named CDF for cation diffusion facilitator has as prototype the protein CzcD, which is a regulatory component of a cobalt-zinc-cadmium resistance determinant in the Gram-negative bacterium Alcaligenes eutrophus. A family for the ChrA chromate resistance system in Gram-negative bacteria has still to be defined. 相似文献
11.
Apoenzyme, containing ⩽0.1 zinc atoms and ⩽0.2 Fe atoms per subunit and with ⩽3% of the phosphatase activity, has been prepared from native red kidney bean purple phosphatase. Treatment of this apoenzyme with Fe 3+ or Zn 2+ separately gave very little recovery of activity, whereas treatment with both Fe 3+ and Zn 2+ resulted in complete restoration of activity, indicating that both metal ions are essential. ZnFe enzyme with close to one iron and one zinc atom per subunit has been reconstituted by this procedure. Essentially full reactivation was also achieved by addition of Fe 3+ together with Fe 2+ or Co 2+ to the apoenzyme; Fe 3+ and Cd 2+ gave 27% restoration of activity, whereas Fe 3+ with Mn 2+, Cu 2+, Ni 2+ or Hg 2+ gave little or no increase in activity. Kinetic parameters for the hydrolysis of p-nitrophenyl phosphate and ATP by the FeFe derivative are reported. 相似文献
12.
Bacterial biosensors can measure pollution in terms of their actual toxicity to living organisms. A recombinant bacterial biosensor has been constructed that is known to respond to toxic levels of Zn 2+, Cd 2+ and Hg 2+. The zinc regulatory gene zntR and zntA promoter from znt operon of E. coli have been used to trigger the expression of GFP reporter protein at toxic levels of these ions. The sensor was induced with 3–800?ppm of Zn 2+, 0.005–4?ppm of Cd 2+ and 0.001–0.12?ppm of Hg 2+ ions. Induction studies were also performed in liquid media to quantify GFP fluorescence using fluorimeter. To determine the optimum culture conditions three different incubation periods (16, 20 and 24?h) were followed. Results showed an increased and consistent fluorescence in cells incubated for 16?h. Maximum induction for Zn 2+, Cd 2+ and Hg 2+ was observed at 20, 0.005 and 0.002?ppm, respectively. The pPROBE-zntR-zntA biosensor reported here can be employed as a primary screening technique for aquatic heavy metal pollution. 相似文献
13.
Cultures of Aspergillus parasiticus produce the polyketide versicolorin A in response to elevation of the Zn 2+ content of the growth medium. With suboptimal Zn 2+ (0.8 μ M) mycelial growth is about half maximal, and versicolorin synthesis is essentially zero. Inclusion of Cd 2+ (1–100 μ M) in the Zn 2+-limiting growth medium allows optimal growth and stimulates full versicolorin synthesis. Cd 2+, like Zn 2+, will stimulate versicolorin sysnthesis only when added within the first 30 h after conidial inoculation. The transport system for Cd 2+ uptake may be the same as that for Zn 2+, as judged by in vivo competition studies. Cd 2+ is a competitive inhibitor of Zn 2+ uptake, with Ki = 20 μM. 相似文献
14.
In this study, bioaccumulation and heavy metal resistance of Cd 2+, Cu 2+, Co 2+ and Mn 2+ ions by thermophilic Geobacillus thermantarcticus and Anoxybacillus amylolyticus was investigated. The bacteria, in an order with respect to metal resistance from the most resistant to the most sensitive, was found to be Mn 2+ > Co 2+ > Cu 2+ > Cd 2+ for both G. thermantarcticus and A. amylolyticus. It was determined that the highest metal bioaccumulation was performed by A. amylolyticus in Mn 2+ (28,566 μg/g dry weight), and the lowest metal bioaccumulation was performed by A. amylolyticus in Co 2+ (327.3 μg/g dry weight). The highest Cd 2+ capacities of dried cell membrane was found to be 36.07 and 39.55 mg/g membrane for G. thermantarticus and A. amylolyticus, respectively, and the highest Cd 2+ capacities of wet cell membrane was found to be 14.36 and 12.39 mg/g membrane for G. thermantarcticus and A. amylolyticus, respectively. 相似文献
15.
Summary A total of 107 bacterial strains were isolated from rhizosphere soil of Diplachne fusca naturally grown in industrial metal-contaminated soils. All the isolates were examined for their ability to tolerate Cd 2+, Cr 3+, Co 2+, Cu 2+, Pb 2+, Ni 2+ and Zn 2+ in their growth medium, in addition, three related phenotypic characters, the ability to produce acids and siderophores and/or
calcium phosphate solubilization, were tested. The resistance patterns, expressed as MICs, for all bacterial isolates to seven
different metal ions were surveyed by using the agar dilution method. A great proportion of the isolates were resistant to
Cr (99%), Pb (93%), Cu (87%) and Zn (86%). On the other hand, 77, 49 and 45% were sensitive to Co, Ni and Cd, respectively.
The majority of the strains tested (98%) were multiple metal-resistant, with hexametal resistance as the major pattern (24.2%).
The increase in metal ion uptake (especially Cr, Pb, Zn and Ni) by D. fusca was correlated with higher numbers of siderophore-producing, phosphate-solubilizing and acid-producing bacteria 95, 81 and
64%, respectively. 相似文献
16.
Complexes formed by reduced glutathione (GSH) with metal cations (Cr 2+, Mn 2+,Fe 2+,Co 2+,Ni 2+,Cu 2+,Zn 2+,Cd 2+,Hg 2+) were systematically investigated by the density functional theory (DFT). The results showed that the interactions of the metal cations with GSH resulted in nine different stable complexes and many factors had an effect on the binding energy. Generally, for the same period of metal ions, the binding energies ranked in the order of Cu 2+>Ni 2+>Co 2+>Fe 2+>Cr 2+>Zn 2+>Mn 2+; and for the same group of metal ions, the general trend of binding energies was Zn 2+>Hg 2+>Cd 2+. Moreover, the amounts of charge transferred from S or N to transition metal cations are greater than that of O atoms. For Fe 2+,Co 2+,Ni 2+,Cu 2+,Zn 2+,Cd 2+ and Hg 2+ complexes, the values of the Wiberg bond indices (WBIs) of M-S (M denotes metal cations) were larger than that of M-N and M-O; for Cr 2+ complexes, most of the WBIs of M-O in complexes were higher than that of M-S and M-N. Furthermore, the changes in the electron configuration of the metal cations before and after chelate reaction revealed that Cu 2+, Ni 2+,Co 2+ and Hg 2+ had obvious tendencies to be reduced to Cu +,Ni +,Co + and Hg + during the coordination process. 相似文献
17.
Acutolysin D, isolated from the venom of Agkistrodon acutus, possesses marked haemorrhagic and proteolytic activities. The molecular weight and the absorption coefficients ( A
1%
280) of acutolyisn D have been determined to be 47,850 ± 8 amu and 9.3 by mass spectrometer and UV spectrum, respectively. The effects of metal ions on the conformation and activity of acutolysin D have been studied by following fluorescence, circular dichroism and biological activity measurements. Acutolysin D contains two Ca 2+-binding sites and two Zn 2+-binding sites determined by atomic absorption spectrophotometer. Zn 2+ is essential for the enzyme activities of acutolysin D, however, the presence of 1 m M Zn 2+ significantly decreases its caseinolytic activity and intrinsic fluorescence intensity at pH 9.0 due to Zn(OH) 2 precipitate formation. Ca 2+ is important for the structural integrity of acutolysin D, and the presence of 1 m M Ca 2+ markedly enhances its caseinolytic activity. Interestingly, the caseinolytic activity which is inhibited partly by Cu 2+, Co 2+, Mn 2+ or Tb 3+ and inhibited completely by Cd 2+, is enhanced by Mg 2+. The fluorescence intensity of the protein decreases in the presence of Cu 2+, Co 2+, Cd 2+ or Mn 2+, but neither for Ca 2+, Mg 2+ nor for Tb 3+. Zn 2+, Ca 2+, Mg 2+, Cu 2+, Mn 2+, Co 2+ and Tb 3+ have slight effects on its secondary structure contents. In addition, Cd 2+ causes a marked increase of antiparallel β-sheet content from 45.5% to 60.2%. 相似文献
18.
The peptidases in clan MH are known as cocatalytic zinc peptidases that have two zinc ions in the active site, but their metal preference has not been rigorously investigated. In this study, the molecular basis for metal preference is provided from the structural and biochemical analyses. Kinetic studies of Pseudomonas aeruginosa aspartyl aminopeptidase (PaAP) which belongs to peptidase family M18 in clan MH revealed that its peptidase activity is dependent on Co 2+ rather than Zn 2+: the kcat (s −1) values of PaAP were 0.006, 5.10 and 0.43 in no-metal, Co 2+, and Zn 2+ conditions, respectively. Consistently, addition of low concentrations of Co 2+ to PaAP previously saturated with Zn 2+ greatly enhanced the enzymatic activity, suggesting that Co 2+ may be the physiologically relevant cocatalytic metal ion of PaAP. The crystal structures of PaAP complexes with Co 2+ or Zn 2+ commonly showed two metal ions in the active site coordinated with three conserved residues and a bicarbonate ion in a tetragonal geometry. However, Co 2+- and Zn 2+-bound structures showed no noticeable alterations relevant to differential effects of metal species, except the relative orientation of Glu-265, a general base in the active site. The characterization of mutant PaAP revealed that the first metal binding site is primarily responsible for metal preference. Similar to PaAP, Streptococcus pneumonia glutamyl aminopeptidase (SpGP), belonging to aminopeptidase family M42 in clan MH, also showed requirement for Co 2+ for maximum activity. These results proposed that clan MH peptidases might be a cocatalytic cobalt peptidase rather than a zinc-dependent peptidase. 相似文献
20.
Essentially all bacteria have genes for toxic metal ion resistances and these include those for Ag+, AsO
−2
, AsO
3−4
, Cd2+, Co2+, CrO
2−4
, Cu2+, Hg2+, Ni2+, Pb2+, TeO
2−3
, Tl+ and Zn2+. The largest group of resistance systems functions by energy-dependent efflux of toxic ions. Fewer involve enzymatic transformations (oxidation, reduction, methylation, and demethylation) or metal-binding proteins (for example, metallothionein SmtA, chaperone CopZ and periplasmic silver binding protein SilE). Some of the efflux resistance systems are ATPases and others are chemiosmotic ion/proton exchangers. For example, Cd2+-efflux pumps of bacteria are either inner membrane P-type ATPases or three polypeptide RND chemiosmotic complexes consisting of an inner membrane pump, a periplasmic-bridging protein and an outer membrane channel. In addition to the best studied three-polypeptide chemiosmotic system, Czc (Cd2+, Zn2+, and Co2), others are known that efflux Ag+, Cu+, Ni2+, and Zn2+. Resistance to inorganic mercury, Hg2+ (and to organomercurials, such as CH3Hg+ and phenylmercury) involve a series of metal-binding and membrane transport proteins as well as the enzymes mercuric reductase and organomercurial lyase, which overall convert more toxic to less toxic forms. Arsenic resistance and metabolizing systems occur in three patterns, the widely-found ars operon that is present in most bacterial genomes and many plasmids, the more recently recognized arr genes for the periplasmic arsenate reductase that functions in anaerobic respiration as a terminal electron acceptor, and the aso genes for the periplasmic arsenite oxidase that functions as an initial electron donor in aerobic resistance to arsenite. 相似文献
|