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1.
Mary-Rus Martínez-Cuenca Domingo J. Iglesias M. Angeles Forner-Giner Eduardo Primo-Millo Francisco Legaz 《Acta Physiologiae Plantarum》2013,35(9):2833-2845
This work studies the effect of bicarbonate on plant performance and the iron acquisition system of Forner-Alcaide 5 (FA-5) seedlings, a citrus genotype known for its tolerance to calcareous soils. Plants were irrigated for 6 weeks with or without 10 mM NaHCO3. Treatment significantly decreased shoot growth, photosynthetic levels and iron concentration in shoots and roots. o,o-57FeEDDHA experiments indicated that 57Fe uptake by roots was inhibited in treated plants. Moreover, those seedlings accumulated more 57Fe in roots, and enhanced mRNA accumulation of ferric reductase genes FRO1 and FRO2 and FC-R activity in roots. H+-ATPase activity and HA1 gene expression were also increased, while HA2 was not affected. In addition, expression of the iron transporter gene IRT1 was increased, while IRT2 was not significantly affected. Finally, according to PEPC enzymatic activity, PEPC1 gene expression was higher in treated roots. In conclusion, it appears that bicarbonate prevents medium acidification by roots, thus reducing Fe2+ uptake. Accordingly, Fe deficiency enhanced the expression of some genes related with the Fe acquisition system (IRT1, FRO1, FRO2, HA1 and PEPC1) and the activity of the corresponding enzymes, which appear to constitute an adaptive mechanism of FA-5 in these soils. 相似文献
2.
Bicarbonate blocks iron translocation from cotyledons inducing iron stress responses in Citrus roots
Mary-Rus Martínez-Cuenca Francisco LegazM. Ángeles Forner-Giner Eduardo Primo-MilloDomingo J. Iglesias 《Journal of plant physiology》2013
The effect of bicarbonate ion (HCO3−) on the mobilization of iron (Fe) reserves from cotyledons to roots during early growth of citrus seedlings and its influence on the components of the iron acquisition system were studied. Monoembryonic seeds of Citrus limon (L.) were germinated “in vitro” on two iron-deprived media, supplemented or not with 10 mM HCO3− (−Fe+Bic and −Fe, respectively). After 21 d of culture, Fe concentration in seedling organs was measured, as well as gene expression and enzymatic activities. Finally, the effect of Fe resupply on the above responses was tested in the presence and absence of HCO3− (+Fe+Bic or +Fe, respectively). −Fe+Bic seedlings exhibited lower Fe concentration in shoots and roots than −Fe ones but higher in cotyledons, associated to a significative inhibition of NRAMP3 expression. HCO3− upregulated Strategy I related genes (FRO1, FRO2, HA1 and IRT1) and FC-R and H+-ATPase activities in roots of Fe-starved seedlings. PEPC1 expression and PEPCase activity were also increased. When −Fe+Bic pre-treated seedlings were transferred to Fe-containing media for 15 d, Fe content in shoots and roots increased, although to a lower extent in the +Fe+Bic medium. Consequently, the above-described root responses became markedly repressed, however, this effect was less pronounced in +Fe+Bic seedlings. In conclusion, it appears that HCO3− prevents Fe translocation from cotyledons to shoot and root, therefore reducing their Fe levels. This triggers Fe-stress responses in the root, enhancing the expression of genes related with Fe uptake and the corresponding enzymatic activities. 相似文献
3.
George E. Cutsail III Peter E. Doan Brian M. Hoffman Jacques Meyer Joshua Telser 《Journal of biological inorganic chemistry》2012,17(8):1137-1150
We have employed EPR and a set of recently developed electron nuclear double resonance (ENDOR) spectroscopies to characterize a suite of [2Fe?C2S] ferredoxin clusters from Aquifex aeolicus (Aae Fd1, Fd4, and Fd5). Antiferromagnetic coupling between the FeII, S?=?2, and FeIII, S?=?5/2, sites of the [2Fe?C2S]+ cluster in these proteins creates an S?=?1/2 ground state. A complete discussion of the spin-Hamiltonian contributions to g includes new symmetry arguments along with references to related FeS model compounds and their symmetry and EPR properties. Complete 57Fe hyperfine coupling (hfc) tensors for each iron, with respective orientations relative to g, have been determined by the use of ??stochastic?? continuous wave and/or ??random hopped?? pulsed ENDOR, with the relative utility of the two approaches being emphasized. The reported hyperfine tensors include absolute signs determined by a modified pulsed ENDOR saturation and recovery (PESTRE) technique, RD-PESTRE??a post-processing protocol of the ??raw data?? that comprises an ENDOR spectrum. The 57Fe hyperfine tensor components found by ENDOR are nicely consistent with those previously found by M?ssbauer spectroscopy, while accurate tensor orientations are unique to the ENDOR approach. These measurements demonstrate the capabilities of the newly developed methods. The high-precision hfc tensors serve as a benchmark for this class of FeS proteins, while the variation in the 57Fe hfc tensors as a function of symmetry in these small FeS clusters provides a reference for higher-nuclearity FeS clusters, such as those found in nitrogenase. 相似文献
4.
The pea (Pisum sativum L.) mutant, E107 (brz, brz) accumulated extremely high concentrations of Fe in its older leaves when grown in light rooms in either defined nutrient media or potting mix, or outdoors in soil. Leaf symptoms (bronze color and necrosis) were correlated with very high Fe concentrations. When E107 plants were grown in nutrient solutions supplied 10 μm Fe, as the Fe(III)-N,N′-ethylenebis[2-(2-hydroxyphenyl)glycine] chelate, their roots released higher concentrations of Fe(III) reducing substances to the nutrient media than did roots of the normal parent cv, `Sparkle.' Reciprocal grafting experiments demonstrated that the high concentrations of Fe in the shoot was controlled by the genotype of the root. In short-term 59Fe uptake studies, 15-day-old E107 seedlings exhibited higher rates of Fe absorption than did `Sparkle' seedlings under Fe-adequate growth conditions. Iron deficiency induced accelerated short-term Fe absorption rates in both mutant and normal genotypes. Iron-treated E107 roots also released larger amounts of both protons and Fe(III) reductants into their nutrient media than did iron-treated `Sparkle' roots. Furthermore, the mutant translocated proportionately more Fe to its shoot than did the parent regardless of Fe status. 相似文献
5.
The Role of Iron-Deficiency Stress Responses in Stimulating
Heavy-Metal Transport in Plants 总被引:30,自引:0,他引:30
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Plant accumulation of Fe and other metals can be enhanced under Fe deficiency. We investigated the influence of Fe status on heavy-metal and divalent-cation uptake in roots of pea (Pisum sativum L. cv Sparkle) seedlings using Cd2+ uptake as a model system. Radiotracer techniques were used to quantify unidirectional 109Cd influx into roots of Fe-deficient and Fe-sufficient pea seedlings. The concentration-dependent kinetics for 109Cd influx were graphically complex and nonsaturating but could be resolved into a linear component and a saturable component exhibiting Michaelis-Menten kinetics. We demonstrated that the linear component was apoplastically bound Cd2+ remaining in the root cell wall after desorption, whereas the saturable component was transporter-mediated Cd2+ influx across the root-cell plasma membrane. The Cd2+ transport system in roots of both Fe-deficient and Fe-sufficient seedlings exhibited similar Michaelis constant values, 1.5 and 0.6 μm, respectively, for saturable Cd2+ influx, whereas the maximum initial velocity for Cd2+ uptake in Fe-deficient seedlings was nearly 7-fold higher than that in Fe-grown seedlings. Investigations into the mechanistic basis for this response demonstrated that Fe-deficiency-induced stimulation of the plasma membrane H+-ATPase did not play a role in the enhanced Cd2+ uptake. Expression studies with the Fe2+ transporter cloned from Arabidopsis, IRT1, indicated that Fe deficiency induced the expression of this transporter, which might facilitate the transport of heavy-metal divalent cations such as Cd2+ and Zn2+, in addition to Fe2+. 相似文献
6.
Fe uptake in dicotyledonous plants is mediated by a root plasma membrane-bound ferric reductase that reduces extracellular Fe(III)-chelates, releasing Fe2+ ions, which are then absorbed via a metal ion transporter. We previously showed that Fe deficiency induces an increased capacity to absorb Fe and other micronutrient and heavy metals such as Zn2+ and Cd2+ into pea (Pisum sativum L.) roots [Cohen et al. (1998) Plant Physiol 116:1063–1072). To investigate the molecular basis for this phenomenon, an Fe-regulated transporter that is a homologue of the Arabidopsis IRT1 micronutrient transporter was isolated from pea seedlings. This cDNA clone, designated RIT1 for root iron transporter, encodes a 348 amino acid polypeptide with eight putative membrane-spanning domains that is induced under Fe deficiency and can functionally complement yeast mutants defective in high- and low-affinity Fe transport. Chelate buffer techniques were used to control Fe2+ in the uptake solution at nanomolar activities representative of those found in the rhizosphere, and radiotracer methodologies were employed to show that RIT1 is a very high-affinity 59Fe2+ uptake system (K
m =54–93 nM). Additionally, radiotracer (65Zn, 109Cd) flux techniques were used to show that RIT can also mediate a lower affinity Zn and Cd influx (K
m of 4 and 100 M, for Zn2+ and Cd2+, respectively). These findings suggest that, in typical agricultural soils, RIT1 functions primarily as a high-affinity Fe2+ transporter that mediates root Fe acquisition. This is consistent with recent findings with Arabidopsis IRT1 knockout mutants that strongly suggest that this transporter plays a key role in root Fe uptake and nutrition. However, the ability of RIT1 to facilitate Zn and Cd uptake when these metals are present at elevated concentrations suggests that RIT1 may be one pathway for the entry of toxic metals into the food chain. Furthermore, the finding that plant Fe deficiency status may promote heavy metal uptake via increased expression of this transporter could have implications both for human nutrition and also for phytoremediation, the use of terrestrial plants to sequester toxic metals from contaminated soil. 相似文献
7.
Reduction and transport of Fe from siderophores 总被引:1,自引:0,他引:1
Soils contain siderophores produced by bacteria and fungi; however, the role of siderophores in Fe nutrition of plants is uncertain. The Strategy I plant cucumber (Cucumis sativus L.) was used in an investigation of ferric chelate reduction activity and uptake and transport of Fe from ferric hydroxyethylethylenetriacetic acid (FeHEDTA) and ferric N,N–di–(2–hydroxybenzoyl)–ethylenediamine– N,N-diacetic acid (FeHBED) and the hydroxamate siderophores, ferric rhodotorulic acid (FeRA) and ferric ferrioxime B (FeFOB). Cucumber seedlings were grown in a hydroponic medium without Fe or supplied with 10 M FeHEDTA. Iron-deficient cucumber roots readily reduced FeHEDTA, while Fe-sufficient roots had low levels of ferric chelate reduction activity. The siderophore FeRA was reduced by Fe-deficient roots at 8% of the rate of FeHEDTA, while FeFOB was not reduced. The highly stable synthetic chelate FeHBED was reduced at 16% the rate of FeHEDTA. Fe transport to shoots by Fe-deficient seedlings from the slowly reducible complexes 59FeRA and 59FeHBED was, respectively, 74% and 73% of that transported from 59FeHEDTA. The ferrous complexing agent, bathophenanthrolinedisulfonic acid (BPDS), had a strong inhibitory effect on uptake and transport of Fe from 59FeHEDTA or 59FeRA into shoots. An average of 11% as much Fe was transported to shoots of Fe-deficient seedlings from 59FeFOB as from 59FeHEDTA. Neither the Fe nutritional status of the seedlings nor the presence of BPDS influenced the uptake and transport of Fe from 59FeFOB. It is concluded that cucumber roots may take up substantial amounts of Fe from FeRA and FeHBED following reduction, while small amounts of Fe may be taken up from FeFOB by a mechanism not involving reduction of the ferric siderophore at the root surface. 相似文献
8.
J. Xu H. X. Yin X. J. Liu T. Yuan Q. Mi L. L. Yang Z. X. Xie W. Y. Wang 《Biologia Plantarum》2009,53(4):784-788
The possible involvement of nitric oxide in response of Solanum nigrum seedlings to Fe deficiency was investigated. Iron deficiency resulted in decreased shoot height and chlorophyll content and
increased proliferation of root hairs and H2O2, K+ and Ca2+ content. NO donor S-nitrosoglutathione (GSNO) was effective in preventing Fe deficiency-induced increase in content of H2O2 and the ion uptake. The protective effects of GSNO were reversed by cPTIO, an NO scavenger, and tungstate, a nitrate reductase
(NR) inhibitor. 相似文献
9.
Yi-Chieh Chang Mohamed Zouari Yolanda Gogorcena Juan Jos Lucena Javier Abadía 《Plant Physiology and Biochemistry》2003,41(11-12):999-1005
The effects of the heavy metals Cd and Pb on the activity of the enzyme ferric chelate reductase (FC-R, E.C. 1.6.99.13) have been studied in excised sugar beet root tips. The activity of this enzyme is markedly increased by iron deficiency. Metals were used as chloride salts or chelated with EDTA, and chemical speciation was carried out to predict the metal chemical species in equilibrium both in the ferric reductase assay and in the nutrient solutions. Three different heavy metal treatments were used. First, effects of Cd and Pb on the functioning of the FC-R were assessed in Fe-deficient plants, by including metals in the enzyme assay medium only. Results indicate that 50 μM CdCl2 or Cd-EDTA did not affect FC-R activities even when assay time was as long as 2 h, whereas Pb slightly decreased enzyme activity only at concentrations of 2 mM. Second, short-time Cd and Pb pre-treatments (30–60 min) were imposed on intact Fe-deficient plants before carrying out the assay of FC-R activity. These short-term treatments induced significant decreases in the FC-R activities previously induced by Fe deficiency. With Cd, effects were more pronounced at higher concentrations, and they were stronger when Cd was in the free ion form than when present in the form of Cd-EDTA chelate. Third, prolonged Cd and Pb treatments were imposed on plants grown on 45 μM Fe-EDTA to assess the long-term effects of heavy metals on the induction of the FC-R enzyme. These long-term heavy metal treatments caused a significant increase in the root FC-R activities, indicating that Cd and Pb induce a deficiency in Fe in sugar beet that in turn elicits FC-R activity. The increases, however, are not as large as those found in total absence of Fe. 相似文献
10.
Tarek Slatni Gianpiero ViganiImen Ben Salah Saber KouasMarta Dell’Orto Houda GouiaGraziano Zocchi Chedly Abdelly 《Plant science》2011,181(2):151-158
Iron is an important nutrient in N2-fixing legume nodules. The demand for this micronutrient increases during the symbiosis establishment, where the metal is utilized for the synthesis of various iron-containing proteins in both the plant and the bacteroid. Unfortunately, in spite of its importance, iron is poorly available to plant uptake since its solubility is very low when in its oxidized form Fe(III). In the present study, the effect of iron deficiency on the activity of some proteins involved in Strategy I response, such as Fe-chelate reductase (FC-R), H+-ATPase, and phosphoenolpyruvate carboxylase (PEPC) and the protein level of iron regulated transporter (IRT1) and H+-ATPase proteins has been investigated in both roots and nodules of a tolerant (Flamingo) and a susceptible (Coco blanc) cultivar of common bean plants. The main results of this study show that the symbiotic tolerance of Flamingo can be ascribed to a greater increase in the FC-R and H+-ATPase activities in both roots and nodules, leading to a more efficient Fe supply to nodulating tissues. The strong increase in PEPC activity and organic acid content, in the Flamingo root nodules, suggests that under iron deficiency nodules can modify their metabolism in order to sustain those activities necessary to acquire Fe directly from the soil solution. 相似文献
11.
The ferric-chelate reductase (FC-R) activity of mesophyll protoplasts isolated from Fe-sufficient (control) and Fe-deficient sugar beet (Beta vulgaris L.) leaves has been characterized. Measurements were made in an ionic environment similar to that in the apoplastic space of the sugar beet mesophyll cells. The FC-R activity of Fe-sufficient and Fe-deficient protoplasts was dependent on light. Fe deficiency decreased markedly the FC-R activity per protoplast surface unit. The optimal pH for the activity of the FC-R in mesophyll protoplasts was in the range 5.5 to 6.0, typical of the apoplastic space. Beyond pH 6.0, the activity of the FC-R in mesophyll protoplasts decreased markedly in both Fe-sufficient and Fe-deficient protoplasts. These data suggest that both the intrinsic decrease in FC-R activity per protoplast surface and a possible shift in the pH of the apoplastic space could lead to the accumulation of physiologically inactive Fe pools in chlorotic leaves. 相似文献
12.
Nicholas E. Hoffman Harish C. Chandramoorthy Santhanam Shanmughapriya Xueqian Q. Zhang Sandhya Vallem Patrick J. Doonan Karthik Malliankaraman Shuchi Guo Sudarsan Rajan John W. Elrod Walter J. Koch Joseph Y. Cheung Muniswamy Madesh 《Molecular biology of the cell》2014,25(6):936-947
Emerging findings suggest that two lineages of mitochondrial Ca2+ uptake participate during active and resting states: 1) the major eukaryotic membrane potential–dependent mitochondrial Ca2+ uniporter and 2) the evolutionarily conserved exchangers and solute carriers, which are also involved in ion transport. Although the influx of Ca2+ across the inner mitochondrial membrane maintains metabolic functions and cell death signal transduction, the mechanisms that regulate mitochondrial Ca2+ accumulation are unclear. Solute carriers—solute carrier 25A23 (SLC25A23), SLC25A24, and SLC25A25—represent a family of EF-hand–containing mitochondrial proteins that transport Mg-ATP/Pi across the inner membrane. RNA interference–mediated knockdown of SLC25A23 but not SLC25A24 and SLC25A25 decreases mitochondrial Ca2+ uptake and reduces cytosolic Ca2+ clearance after histamine stimulation. Ectopic expression of SLC25A23 EF-hand–domain mutants exhibits a dominant-negative phenotype of reduced mitochondrial Ca2+ uptake. In addition, SLC25A23 interacts with mitochondrial Ca2+ uniporter (MCU; CCDC109A) and MICU1 (CBARA1) while also increasing IMCU. In addition, SLC25A23 knockdown lowers basal mROS accumulation, attenuates oxidant-induced ATP decline, and reduces cell death. Further, reconstitution with short hairpin RNA–insensitive SLC25A23 cDNA restores mitochondrial Ca2+ uptake and superoxide production. These findings indicate that SLC25A23 plays an important role in mitochondrial matrix Ca2+ influx. 相似文献
13.
Wissal M’Sehli Sabah Youssfi Silvia Donnini Marta Dell’Orto Patricia De Nisi Graziano Zocchi Chedly Abdelly Mohamed Gharsalli 《Plant and Soil》2008,312(1-2):151-162
The main objective of this work was to compare the tolerance to lime-induced Fe deficiency of two lines of Medicago ciliaris (TN11.11 and TN8.7). We studied the effects of Fe deficiency on: (1) root biomass and rhizosphere acidification, (2) accumulation in the roots and the exudation into the rhizosphere of organic compounds (citric acid, malic acid and phenols), (3) changes under Fe deficient conditions in the activities of two enzymes, the first related to organic acid metabolism (malate dehydrogenase: MDH) and the other to proton extrusion (H+-ATPase activity). After a pre-treatment of one week, plants were transferred into hydroponic culture under three treatments: +Fe, ?Fe and +Fe +lime. Iron deficiency led to 40% increase in root biomass in TN11.11 line in the presence of lime. Both the omission of Fe and the addition of lime to the nutrient solution increased the H+-ATPase activity more in TN11.11 than in TN8.7. In addition, Fe deficiency increased accumulation of organic acids as well as phenols in roots, and stimulated the MDH activity more in TN11.11 than in TN8.7 (+75% and +41% in TN11.11 and TN8.7, respectively). Iron deficiency also increased the amounts of citrate, malate and phenols in root exudates. Our data allowed us to note that the TN11.11 line is more effective in overcoming Fe deficiency than TN8.7. 相似文献
14.
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16.
Mitochondrial Iba57p is required for Fe/S cluster formation on aconitase and activation of radical SAM enzymes 总被引:2,自引:0,他引:2
Gelling C Dawes IW Richhardt N Lill R Mühlenhoff U 《Molecular and cellular biology》2008,28(5):1851-1861
A genome-wide screen for Saccharomyces cerevisiae iron-sulfur (Fe/S) cluster assembly mutants identified the gene IBA57. The encoded protein Iba57p is located in the mitochondrial matrix and is essential for mitochondrial DNA maintenance. The growth phenotypes of an iba57Δ mutant and extensive functional studies in vivo and in vitro indicate a specific role for Iba57p in the maturation of mitochondrial aconitase-type and radical SAM Fe/S proteins (biotin and lipoic acid synthases). Maturation of other Fe/S proteins occurred normally in the absence of Iba57p. These observations identify Iba57p as a novel dedicated maturation factor with specificity for a subset of Fe/S proteins. The Iba57p primary sequence is distinct from any known Fe/S assembly factor but is similar to certain tetrahydrofolate-binding enzymes, adding a surprising new function to this protein family. Iba57p physically interacts with the mitochondrial ISC assembly components Isa1p and Isa2p. Since all three proteins are conserved in eukaryotes and bacteria, the specificity of the Iba57/Isa complex may represent a biosynthetic concept that is universally used in nature. In keeping with this idea, the human IBA57 homolog C1orf69 complements the iba57Δ growth defects, demonstrating its conserved function throughout the eukaryotic kingdom. 相似文献
17.
18.
Alessio Aghemo Eleonora Grassi Maria Grazia Rumi Roberta D'Ambrosio Enrico Galmozzi Elisabetta Degasperi Davide Castaldi Roberta Soffredini Massimo Colombo 《PloS one》2014,9(4)
Background
Severe anemia is a common side effect of Pegylated Interferon + Ribavirin (PR) and Telaprevir (TVR) in hepatitis C virus (HCV) genotype 1 patients with advanced fibrosis or cirrhosis (F3–F4). Inosine triphosphatase (ITPA) genetic variants are associated with RBV- induced anemia and dose reduction.Aim
To test the association of ITPA polymorphisms rs1127354 and rs7270101 with hemoglobin (Hb) decline, need for RBV dose reduction (RBV DR), erythropoietin (EPO) support and blood transfusions during the first 12 weeks of TVR triple therapy.Materials and Methods
69 consecutive HCV-1 patients (mean age 57 years) with F3-F4 who received PR and TVR were genotyped for ITPA polymorphisms rs1127354 and rs7270101. Estimated ITPA deficiency was graded on severity (0–3, no deficiency/mild/moderate/severe).Results
ITPA deficiency was absent in 48 patients (70%), mild in 12 (17%) and moderate in 9 patients (13%). Mean week 4 Hb decline was higher in non ITPA deficient patients (3,85 g/dL) than in mildly or moderately ITPA deficient patients (3,07 g/dL and 1,67 g/dL, p<0.0001). Grade 3–4 anemia developed in 81% non ITPA deficient patients versus 67% mild deficient and 55% moderate deficient patients (p = ns). Grade of ITPA deficiency was not associated with RbvDR (no deficiency: 60%, mild: 58%, moderate: 67%; p = ns), EPO use (no deficiency: 65%, mild: 58%, moderate:56%; p = ns) or need for blood transfusion (no deficiency: 27%, mild: 17%, moderate: 33%; p = ns).Conclusions
In patients with F3–F4 chronic hepatitis C receiving TVR based therapy, ITPA genotype does not impact on the management of early anemia. 相似文献19.
Y. L. Song Y. J. Dong X. Y. Tian J. Kong X. Y. Bai L. L. Xu Z. L. He 《Biologia Plantarum》2016,60(2):329-342
Limited information is available on the role of brassinosteroids (BRs) in response of plants to nutrient deficiency. To understand the functions of BRs in response to iron deficiency, we investigated the effect of 24-epibrassinolide (EBR) on activities of ferric-chelate reductase (FCR), H+-ATPase, Ca2+-ATPase, nitrate reductase (NR), antioxidant enzymes, Fe and other minerals content and distribution, chlorophylls, soluble protein, free proline, reactive oxygen species, and malondialdehyde in peanut (Arachis hypogea L.) plants subjected to Fe deficiency (10?5 M Fe(III)-EDTA) with foliar application of EBR (0, 10?8, 5.0×10?8, 10?7, 5.0×10?7, and10?6 M). Results show that EBR increased Fe translocation from roots to shoots and increased Fe content in cell organelles. Activities of antioxidant enzymes increased and so the ability of resistance to oxidative stress was enhanced. As result of enhancement of H+-ATPase and Ca2+-ATPase activities, the inhibition of Fe, Ca, Mg, and Zn uptake and distribution was ameliorated. Chlorophyll, soluble protein, and free proline content also increased and consequently, chlorosis induced by Fe deficiency was alleviated. The results demonstrate that EBR had a positive role in regulating peanut growth and development under Fe deficiency and an optimal concentration appeared to be 10?7 M. 相似文献
20.
Effect of Oxidation Rate and Fe(II) State on Microbial Nitrate-Dependent Fe(III) Mineral Formation
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A nitrate-dependent Fe(II)-oxidizing bacterium was isolated and used to evaluate whether Fe(II) chemical form or oxidation rate had an effect on the mineralogy of biogenic Fe(III) (hydr)oxides resulting from nitrate-dependent Fe(II) oxidation. The isolate (designated FW33AN) had 99% 16S rRNA sequence similarity to Klebsiella oxytoca. FW33AN produced Fe(III) (hydr)oxides by oxidation of soluble Fe(II) [Fe(II)sol] or FeS under nitrate-reducing conditions. Based on X-ray diffraction (XRD) analysis, Fe(III) (hydr)oxide produced by oxidation of FeS was shown to be amorphous, while oxidation of Fe(II)sol yielded goethite. The rate of Fe(II) oxidation was then manipulated by incubating various cell concentrations of FW33AN with Fe(II)sol and nitrate. Characterization of products revealed that as Fe(II) oxidation rates slowed, a stronger goethite signal was observed by XRD and a larger proportion of Fe(III) was in the crystalline fraction. Since the mineralogy of Fe(III) (hydr)oxides may control the extent of subsequent Fe(III) reduction, the variables we identify here may have an effect on the biogeochemical cycling of Fe in anoxic ecosystems. 相似文献