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1.
New insights into the metal specificity of the Pseudomonas aeruginosa pyoverdine–iron uptake pathway
Armelle Braud Françoise Hoegy Karine Jezequel Thierry Lebeau Isabelle J. Schalk 《Environmental microbiology》2009,11(5):1079-1091
Pyoverdine (PvdI) is the major siderophore secreted by Pseudomonas aeruginosa PAOI in order to get access to iron. After being loaded with iron in the extracellular medium, PvdI is transported across the bacterial outer membrane by the transporter, FpvAI. We used the spectral properties of PvdI to show that in addition to Fe3+ , this siderophore also chelates, but with lower efficiencies, all the 16 metals used in our screening. Afterwards, FpvAI at the cell surface binds Ag+ , Al3+ , Cd2+ , Co2+ , Cu2+ , Fe3+ , Ga3+ , Hg2+ , Mn2+ , Ni2+ or Zn2+ in complex with PvdI. We used Inductively Coupled Plasma-Atomic Emission Spectrometry to monitor metal uptake in P. aeruginosa : TonB-dependent uptake, in the presence of PvdI, was only efficient for Fe3+ . Cu2+ , Ga3+ , Mn2+ and Ni2+ were also transported into the cell but with lower uptake rates. The presence of Al3+ , Cu2+ , Ga3+ , Mn2+ , Ni2+ and Zn2+ in the extracellular medium induced PvdI production in P. aeruginosa . All these data allow a better understanding of the behaviour of the PvdI uptake pathway in the presence of metals other than iron: FpvAI at the cell surface has broad metal specificity at the binding stage and it is highly selective for Fe3+ only during the uptake process. 相似文献
2.
Abstract Plasmid-encoded copper (Cu2+ ) resistance in Escherichia coli was due to decreased uptake of Cu2+ . The Cu2+ -resistant E. coli Rtsl strain contained a 60 MDa plasmid which is known to encode for both Cu2+ and kanamycin resistance. A plasmid-free derivative of the same organism exhibited a greater uptake of Cu2+ , and sensitivity to Cu2+ in both respiration and growth studies than the E. coli Rtsl strain. 相似文献
3.
Abstract: The activities mediated by the N -methyl-D-aspartate (NMDA) receptor were studied in cultured rat cerebellar granule cells. Micromolar concentrations of the metal binding compounds, EDTA, cysteine, and histidine, as well as serum albumin strongly potentiated receptor activity in the presence of millimolar concentrations of Ca2+ and Mg2+ . The findings indicated that these agents remove an endogenous metal, probably Zn2+ , which attenuates NMDA receptor-mediated 45 Ca uptake and toxicity. Several added metal ions were therefore tested at low micromolar concentrations. Zn2+ was found to be the most potent inhibitor of NMDA-induced 45 Ca uptake, followed by Cu2+ and Fe2+ . Co2+ , Cd2+ , Fe3+ , and AI3+ had no significant effect, whereas Ni2+ potentiated the 45 Ca uptake but inhibited at much higher concentrations. The potentiating agents that remove the endogenous metal had a particularly dramatic effect in the presence of Mg2+ , the voltage-dependent suppressor of the NMDA receptor. Mg2+ also played an important role in the inhibitory effect of added Zn2+ . Much lower concentrations of Zn2+ were needed to achieve inhibition of NMDA-induced 45 Ca uptake in the presence of Mg2+ . Under a variety of conditions, a very good correlation was found between NMDA receptor-mediated 45 Ca uptake and the magnitude of acute neurotoxicity. 相似文献
4.
The uptake of Cd2+ by excised roots of Tamarix aphylla (L.) Karst, was investigated using roots of hydroponically grown plants. The concentration isotherm of Cd2+ uptake approached saturation with a single phase hyperbola. The time course of Cd2+ absorption was generally hyperbolic, with an apparent linear section between 2 and 30 min. The temperature response varied among different temperature ranges: a Q10 of approximately 1.9 was found between 10 and 20°C, but at higher and lower temperatures Q10 values were only 1–1.3. It is concluded that Cd2+ uptake by the roots of T. aphylla at moderate temperatures is mediated by a metabolic process, combined with a passive influx component that becomes dominant at higher and lower temperatures. The distribution of the absorption sites for Cd2+ and for Fe2+ along the roots of T. aphylla was also investigated. Cadmium uptake showed no apparent pattern, whereas a distinct pattern of uptake was observed for Fe2+ , with the highest rates at the root tip. Iron absorption was stimulated in the presence of nutrients, whereas that of Cd2+ was inhibited. Adsorption and absorption of Cd2+ were strongly inhibited by Ca2+ and by Mg2+ , but were unaffected by Fe2+ . Monovalent ions (Na+ , K+ , Li+ ) also reduced Cd2+ absorption, but to a lesser extent than Ca2+ and Mg2+ . Uptake of Cd+ was reduced at lower pH of the medium. The importance of interfering cations for Cd2+ tolerance of T. aphylla is emphasized. 相似文献
5.
Mechanism of iron uptake by plants 总被引:5,自引:0,他引:5
JOHN C. BROWN 《Plant, cell & environment》1978,1(4):249-257
Abstract. Green plants require a continuous supply of Fe as they grow, because Fe does not not move from the older to the newer leaves. Soils do not lack Fe per se , but it may not be available to plants grown in alkaline soils. Plants are classed 'Fe-efficient' if they respond to Fe-deficiency stress by inducing biochemical reactions that make Fe available in a useful form, and 'Fe-inefficienT' if they do not. Iron uptake induced in response to Fe stress involves release of hydrogen ions and reductants by the root. The lowered pH and presence of reductant at the root zone, along with reduction of Fe3+ to Fe2+ at the root surface, enables Fe2+ to be taken up primarily through the young lateral roots. Ferrous iron is present throughout the protozylem and may or may not have entered the root by a carrier. The root-absorbed Fe2+ is oxidized to Fe3+ at the junction of the protoxylem and the metaxylem, chelated by citrate, and then transported in the metaxylem to the plant top. In the plant, the chemical reactions injuced by Fe-deficiency stress may affect nitrate reductase activity, use of Fe from Fe3+ phosphate and chelating agents, and tolerance to heavy metals. An efficient mechanism for Fe uptake in roots appears to be important for the efficient use of Fe in plant tops. 相似文献
6.
Jocelyn K. Middlemiss rea M. Anderson Chad W. Stratilo Harold G. Weger 《Journal of phycology》2001,37(3):393-399
Plasma membrane ferric reductase activity was enhanced 5-fold under iron limitation in the unicellular green alga Chlorella kessleri Fott et Nováková. Furthermore, ferric reductase activity in iron-limited cells was approximately 50% higher in the light than in the dark. In contrast, iron uptake rates of iron-limited cells were unaffected by light versus dark treatments. Rates of iron uptake were much lower than rates of ferric reduction, averaging approximately 2% of the dark ferric reduction rate. Ferric reduction was associated with an increased rate of O2 consumption in both light and dark, the increase in the light being approximately 1.5 times as large as in the dark. The increased rate of O2 consumption could be decreased by half by the addition of catalase, indicating that H2 O2 is the product of the O2 consumption and that the increased O2 consumption is nonrespiratory. The stimulation of O2 consumption was almost completely abolished by the addition of bathophenanthroline disulfonate, a strong chelator of Fe2 + . Anaerobic conditions or the presence of exogenous superoxide dismutase affected neither ferric reduction nor iron uptake. We suggest that the O2 consumption associated with ferric reductase activity resulted from superoxide formation from the aerobic oxidation of Fe2 + , which is the product of ferric reductase activity. At saturating concentrations of Fe3 + chelates, ferric reductase activity is much greater than the iron uptake rate, leading to rapid oxidation of Fe2 + and superoxide generation. Therefore, O2 consumption is not an integral part of the iron assimilation process. 相似文献
7.
Induction of the manganese-containing superoxide dismutase in Escherichia coli by nalidixic acid and by iron chelators 总被引:1,自引:0,他引:1
Abstract Nalidixic acid caused a significant increase in the Mn-containing superoxide dismutase (MnSOD) of Escherichia coli . The maximum stimulatory effect of nalidixic acid on MnSOD biosynthesis was observed at 0.1 mM. The stimulatory effect of nalidixic acid was not due to increases in the intracellular flux of O− 2 , but rather to its ability to chelate Fe2+ . Furthermore, 2,2'-dipyridyl and 1,10-phenanthroline were shown to cause a 7- to 20-fold increase in the MnSOD of E. coli . It is proposed that the repressor for MnSOD is an iron-containing protein. 相似文献
8.
Indispensability of Iron for the Growth of Cultured Chick Cells 总被引:1,自引:0,他引:1
KOJI SAITO YASUKO HAGIWARA TAKAYUKI HASEGAWA EIJIRO OZAWA 《Development, growth & differentiation》1982,24(6):571-580
In order to clarify the role of iron in the growth promoting effect of transferrin (Tf), the effects of the following substances were examined in cultured chick skeletal myogenic cells: transition metal ions (Fe2+ , Fe3+ , Cr3+ , Cu2+ , Mn2+ , Co2+ , Cd2+ , Zn2+ and Ni2+ ), Tf complexes with these metals and metal-free apoTf.
The cells did not grow well when incubated in a culture medium composed of Eagle's minimum essential medium and horse serum. But they grew well in the presence of Fe2+ or Fe3+ (10–100 μM) or iron-bound Tf (10–500 nM) in the medium. None of the transition metal ions other than iron was effective. Neither apoTf nor Tf complexes with these metals showed the growth promoting effect. The generality of the requirement of iron for cell growth was ascertained in the primary culture of other types of chick embryonic cells: fibroblasts, cardiac myocytes, retinal pigment cells and spinal nerve cells.
The results show that iron is one of the indispensable substances for cell growth and suggest that Tf protein plays a role in facilitating the transport of iron into the cells. 相似文献
The cells did not grow well when incubated in a culture medium composed of Eagle's minimum essential medium and horse serum. But they grew well in the presence of Fe
The results show that iron is one of the indispensable substances for cell growth and suggest that Tf protein plays a role in facilitating the transport of iron into the cells. 相似文献
9.
Physiological and biochemical modifications induced by Fe-deficiency have been studied in cucumber ( Cucumis sativus L. cv. Marketer) roots, a Strategy I plant that initiates a rapid acidification of the medium and an increase in the electric potential difference when grown under Fe-deficiency. Using the aqueous two-phase partitioning method, a membrane fraction which has the plasmalemma characteristics was purified from roots of plants grown in the absence and in the presence of iron. The plasma membrane vesicles prepared from Fe-deficient plants showed an H+ -ATPase activity (EC 3.6.1.35) that is twice that of the non-deficient control. Furthermore, membranes from Fe-deficient plants showed a higher capacity to reduce Fe3+ -chelates. The difference observed in the reductase activity was small with ferricyanide (only 30%) but was much greater with Fe3 -EDTA and Fe3 -citrate (210 and 250%, respectively). NADH was the preferred electron donor for the reduction of Fe3+ compounds. Fe3+ reduction in plasma membrane from cucumber roots seems to occur with utilisation of superoxide anion, since addition of superoxide dismutase (SOD; EC 1.15.1.1) "in vitro" decreased Fe3+ reduction by 60%.
The response and the difference induced by iron starvation on these two plasma membrane activities together with a possible involvement of O2 in controlling the Fe3+ /Fe2+ ratio in the rhizosphere are discussed. 相似文献
The response and the difference induced by iron starvation on these two plasma membrane activities together with a possible involvement of O
10.
Abstract: Nations were found to inhibit the uptake of L-tryptophan into synaptosomes with a shallow dose-response curve. Almost maximal inhibition was obtained with 10 mM-Na+ . The divalent cations Ca2+ and Mg2+ were shown to be responsible for the increased uptake of L-tryptophan in the absence of Na+ ions. Other divalent cations also promoted tryptophan uptake under this condition (Ca2+ < Mg2+ < Mn2+ < Fe2+ < Zn2+ < Cu2+ ). It was concluded that monovalent chelate complexes were responsible for this enhancing effect. The measured L-tryptophan uptake was the net product of membrane bound and unbound tryptophan. Both bound and unbound tryptophan were increased in the presence of divalent cations. If no divalent cations were added to the incubation medium, Na+ ions decreased the unbound tryptophan but were without effect on bound tryptophan. Under these circumstances D-tryptophan had no effect on binding of the L-isomer and affected the transport of 1.-tryptophan only at very high does (100 x conc. L-tryptophan). These results suggest that I -tryptophan binds to a stereospecific transport carrier located in the synaptosomal membrane and that Na+ ions prevent the translocation of this carrier amino acid complex from the outer to the inner site of the neuronal membrane. 相似文献
11.
12.
Jonas Rubikas Daumantas Matulis Arunas Leipus Daiva Urbaitiene 《FEMS microbiology letters》1997,155(2):193-198
Strain Escherichia coli V38 resistant to 4 mM NiCl2 was isolated from the city sewage sludge. It showed low nickel accumulation by cells and nickel ion efflux. Cells were pregrown (induced) overnight in the presence of Ni2+ , then the culture was kept on ice for 20–30 min and transferred to 37°C for further incubation. When the Ni2+ concentration during growth was the same as during incubation, there was no noticeable accumulation of Ni2+ . When the Ni2+ concentration during incubation was higher than that used for induction, uptake of 63 Ni2+ and delayed efflux were seen. The uptake and delay of both efflux and growth were directly proportional to the difference between the concentrations used for induction and incubation. Active nickel ion uptake was seen in cells taken from cultures in the delayed efflux period. 相似文献
13.
Harald Kosegarten Bernd Hoffmann Evan Rroco Franz Grolig Karl-Heinz Glüsenkamp Konrad Mengel 《Physiologia plantarum》2004,122(1):95-106
The relationship between the apoplastic pH in young sunflower roots ( Helianthus annuus L.) and the plasmalemma ferric chelate reductase (FC-R; EC 1.16.1.7) activity in roots was investigated. The hypothesis was tested that a high apoplastic pH depresses FC-R activity, thereby restricting the uptake of Fe2+ into the cytosol. Until recently, little has been known about this relationship, because pH and redox reaction measurements are difficult to perform within the confines of the root apoplast. We recorded the apoplastic pH by means of the fluorescence ratio in conjunction with video microscopy by covalently tagging fluorescein boronic acid to OH groups of the root cell wall. FeIII reduction was measured using a similar approach by tagging ferrozine diboronic acid with OH groups of the cell wall. Ferrozine forms an Fe2+ complex, thus indicating the reduction of ferric iron. In roots bathing in buffered outer solutions of different pH, a high pH sensitivity of apoplastic FeIII reduction was found, with the highest ferric iron reduction rates at an apoplastic pH of 4.9; above an apoplastic pH of 5.3, no reduction was observed. Nitrate in the bathing solution increased the apoplastic pH and hence depressed the FeIII reduction; ammonium had the reverse effect. Nitrate together with HCO3 – , a combination which is typical of calcareous soils, had the strongest depressing effect. From the results, it can be concluded that the main reason for the frequently occurring iron deficiency chlorosis of plants grown on calcareous soils is the inhibition of FeIII reduction in the apoplast, and hence Fe2+ uptake into the cytosol. 相似文献
14.
The ZnuABC high-affinity zinc uptake system and its regulator Zur in Escherichia coli 总被引:6,自引:4,他引:2
In Escherichia coli , lacZ operon fusions were isolated that were derepressed under iron repletion and repressed under iron depletion. Two fusions were localized in genes that formed an operon whose gene products had characteristics of a binding protein-dependent transport system. The growth defect of these mutants on TY medium containing 5 mM EGTA was compensated for by the addition of Zn2+ . In the presence of 0.5 mM EGTA, only the parental strain was able to take up 65 Zn2+ . This high-affinity transport was energized by ATP. The genes were named znuACB (for zinc uptake; former name yebLMI ) and localized at 42 min on the genetic map of E. coli . At high Zn2+ concentrations, the znu mutants took up more 65 Zn2+ than the parental strain. The high-affinity 65 Zn2+ uptake was repressed by growth in the presence of 10 μM Zn2+ . A znuA–lacZ operon fusion was repressed by 5 μM Zn2+ and showed a more than 20-fold increase in β-galactosidase activity when Zn2+ was bound to 1.5 μM TPEN [tetrakis-(2-pyridylmethyl) ethylenediamine]. To identify the Zn2+ -dependent regulator, constitutive mutants were isolated and tested for complementation by a gene bank of E. coli . A complementing gene, yjbK of the E. coli genome, was identified and named zur (for zinc uptake regulation). The Zur protein showed 27% sequence identity with the iron regulator Fur. High-affinity 65 Zn2+ transport of the constitutive zur mutant was 10-fold higher than that of the uninduced parental strain. An in vivo titration assay suggested that Zur binds to the bidirectional promoter region of znuA and znuCB . 相似文献
15.
Abstract Phosphate interference in the production of cephalosporins by Streptomyces clavuligerus had been associated with repression of expandase (desacetoxycephalosporin C synthetase) and inhibition of both expandase and cyclase (isopenicillin N synthetase). The present work shows that inhibition of enzyme action could be prevented by increasing the Fe2+ added to the cell-free reactions or to resting cells incubated with chloramphenicol. Since excess Fe2+ could not reverse phosphate interference of antibiotic synthesis in complete fermentations, it is clear that the major cause of the phosphate effect in fermentations is phosphate repression, rather than phosphate inhibition caused by Fe2+ deprivation. 相似文献
16.
Zinc is an essential micronutrient, and yet it can be toxic when present in excess. Zinc acquisition and distribution are dependent on tightly controlled transport of Zn2+ ions. Schizosaccharomyces pombe represents a second eukaryotic model to study cellular metal homeostasis. In several ways its micronutrient metabolism is fundamentally different from Saccharomyces cerevisiae . We identified the first Zn2+ -uptake system in S. pombe and named it SpZrt1. Knock-out strains for all three ZIP (Zrt, Irt-like protein) transporters in fission yeast were constructed. Only zrt1 Δ cells were unable to grow at low Zn2+ and showed reduced 65 Zn2+ uptake. Elemental profiles revealed a strong decrease in zinc accumulation. Cd2+ ions inhibited uptake but Fe2+ or Mn2+ did not. Both mRNA abundance and protein amount are tightly regulated. Zrt1 activity is rapidly shut down upon transfer of zinc-deficient cells to zinc-replete conditions. In cells lacking Zhf, a transporter mediating endoplasmic reticulum storage of zinc, this response is about 100-fold more sensitive. Thus, removal of excess of zinc from the cytosol is largely Zhf dependent. Moreover, cells deficient for both transporters are no longer able to adjust to changing external Zn2+ concentrations. Optimal growth is restricted to a narrow range of Zn2+ concentrations, illustrating the fine balance between micronutrient deficiency and toxicity. 相似文献
17.
Abstract The effect of bacterial enterotoxins on rat intestinal permeability properties was studied by comparing the effect of toxin-positive and toxin-negative Escherichia coli and Salmonella typhimurium inoculated into a segment of rat small intestine. Fluoresceinated dextran 3000 (FITC-D3; M r 3000) was applied as permeability marker. The E. coli strain C922a-1 producing heat-labile (LT) and heat-stable (ST) enterotoxins and colonising factor CFA/II increased the transmural passage of the dextran probe into portal blood. In contrast, its plasmid-negative variant, a non-toxin producer lacking CFA, caused permeability changes indistinguishable from the bacteria-free nutrient broth control. Another pair of enterotoxigenic E. coli strains, 1628–14 (LT+ , ST+ , CFA/I+ ) and 1628–15 (LT+ , ST− and CFA/I− ) both increased the intestinal permeability. The observations indicate that the LT+ -only E. coli strain 1628–15 has the ability to promote permeability of rat intestine. The toxin-negative, rough S. typhimurium 395MR10 bacteria had a very small effect on the permeability, which was also achieved with culture filtrate only.
It is concluded that enterotoxigenic E. coli (ETEC) can alter the properties of the mucosal barrier towards intermediate-sized molecules that could be of antigenic significance, or which could play a crucial role in the nutritional status of the host organism. 相似文献
It is concluded that enterotoxigenic E. coli (ETEC) can alter the properties of the mucosal barrier towards intermediate-sized molecules that could be of antigenic significance, or which could play a crucial role in the nutritional status of the host organism. 相似文献
18.
Abstract: The role of Ca2+ and Mn2+ in Rhodospirillum rubrum grown under different conditions with respect to nitrogen source has been studied. The results show that this phototroph does not have an absolute requirement for these cations. In vitro studies of one of the enzymes operative in the metabolic regulation of nitrogenase in Rsp. rubrum have shown that Mn2+ or Fe2+ is required for activity. This investigation indicates that Mn2+ is not required in vivo for the function of this enzyme, suggesting that either Fe2+ is functional or that the enzyme has other properties when active in the cell. 相似文献
19.
Hydroxyl Radicals Generated In Vivo Kill Neurons in the Rat Spinal Cord: Electrophysiological, Histological, and Neurochemical Results 总被引:1,自引:0,他引:1
Abstract: We have used microdialysis to establish an experimental model to characterize mechanisms whereby released substances cause secondary damage in spinal cord injury. We use this model here to characterize damaging effects of the hydroxyl radical (OH') in vivo in the spinal cord. OH'was generatad in vivo by pumping H2 O2 and FeCI2 /EDTA through parallel microdialysis fibers inserted into the spinal cord. These agents mixed in the tissue to produce OH'by Fenton's reaction. Two types of control experiments were also conducted, one administering only 5 m M H2 O2 and the other only 0.5 m M FeCI2 /0.82 m M EDTA. During administration of these chemicals, electrical conduction was recorded as one test for deterioration. OH'blocked conduction completely in 2.5-5 h and Fe2+ /EDTA partly blocked conduction, but H2 O2 alone did not cause detectable blockage. Histological examination supported the hypothesis that neurons were killed by OH', as Fe2+ /EDTA and H2 O2 alone did not destroy significant numbers of neurons. OH', H2 O2 , and Fe2+ all caused gradual increases in extracellular amino acid levels. These results are consistent with Fe2+ -catalyzed free radical generation playing a role in tissue damage upon spinal cord injury. 相似文献
20.
Addition of small amounts of Fe2 + , Zn2 + , Cu2 + and thiamine-HCl to the culture medium was required for promoting the galacto-oligosaccharide (Gal-OS)-producing activity of Sterigmatomyces elviae CBS8119, when the concentration of yeast extract in the medium was lowered to 0·1 g l−1 . Galacto-oligosaccharide production using a recycling cell culture was performed in a medium containing 360 mg ml−1 of lactose supplemented with optimal concentrations of Fe2 + (1·5 mg l−1 of FeSO4 .7H2 O), Zn2 + (15 mg l−1 of ZnSO4 .7H2 O), Cu2 + (0·5 mg l−1 of CuSO4 .5H2 O) and thiamine-HCl (1 mg l−1 ) . Galacto-oligosaccharide production was maintained at high levels during six cycles of production, with the amount of Gal-OS produced in each cycle being more than 216 mg ml−1 (weight yield of more than 60%). 相似文献