Soluble Fe2 Research Articles

Chemically modified nanoparticles surface for sensing bacterial loading—experimental study based on fluorescence stimulation by iron ions

The influence of iron ions supplied from magnetite nanoparticles with chemically modified surface on Pseudomonas aeruginosa germ was aimed—with experimental and theoretical approach of the intensity of the fluorescent signal emitted by the pyoverdine like siderophores. As the coated magnetic nanoparticles could function as probes, the possibility of designing a chemical device was considered based on the sensing of iron reduction from Fe3+ into the more soluble Fe2+, for detecting various levels of contamination (10÷108 cell/ml) of biological specimens and environmental samples. The proposed mathematical model estimated the fluorescence intensity due to siderophore synthesized by Pseudomonas, considering that the parameter describing the ion–bacteria interaction depends differently on the cell density for different magnetite nanoparticle coatings: linear dependence was found in the case of sodium oleate coating while power function was revealed for tetramethyl ammonium coating of magnetite nanocores, in both cases magnetite suspension being supplied in the same concentration (0.1μl/ml). The calculated values of fluorescence intensity fitted the experimental data corresponding to magnetite supplied bacteria with graph slopes close to the unit and correlation coefficients of 0.999 and 0.996, while for the control samples, where that parameter was zeroed, correlation coefficient was found of 0.999.

Arsenic mobilization in alluvial soils of Punjab, North–West India under flood irrigation practices

A laboratory investigation was carried out to examine the mechanism of arsenic (As) mobilization under flooded conditions (24 and 240 h) in 18 alluvial soils of Punjab, North–West India. Total dissolved As increased from a range of 3–16 μg L−1 (mean 9 μg L−1) to a range of 33–1,761 μg L−1 (mean 392 μg L−1) with the increase in flooding period from 24 to 240 h. The amount of As mobilization varied depending upon redox potential (pe) created by flooding conditions. After 24 h of flooded conditions, pe of soil water suspension ranged from −1.75 to 0.77 (mean −0.24). Increasing the flooding period to 240 h, pe of soil water suspension decreased in the range of −4.49 to −2.74 (mean −3.29). Pourbaix diagram identified arsenate (HAsO4 2−) as predominant species in most of the alluvial soil–water suspensions under oxidized conditions, after 24 h of equilibration period, which ultimately transformed to arsenite (H3AsO3 0) after 240 h of anaerobic condition due to more reduced status. The solid phase identified was orpiment (As2S3). Identification of iron and manganese species in alluvial soil water suspension by Pourbaix diagram indicated decline in both soluble Fe2+ and SO4 2− concentration due to the formation of iron sulfide mineral phase after 240 h under anaerobic conditions. In these soils, decline in soluble Fe was also due to the precipitation of vivianite [Fe3(PO4)2·8H2O]. Elevated arsenic content and low pe value were measured in aquifers located in paddy growing fields comparative to aquifers of other sites. Large degree of variability in As concentrations was recorded in aquifers located at same sites. Thus, it is better to analyze each aquifer for their As content rather than to depends on the prediction on As content of neighbouring wells. The present investigation elucidates that flood irrigation practices in Punjab for growing paddy crop could induce the geochemical conditions favorable to mobilize arsenic from surface soils which could eventually elevate its content in the underlying shallow aquifers. Water abstracted from these aquifers by hand pumps or tube wells for drinking purposes could create hazards for local population due to loading with arsenic concentration above the safe limits. Thus, to avoid further contamination of shallow aquifers with arsenic, it is advisable to shift the flooded rice cultivation to other upland crops having lesser water requirement.

RNA Folding and Catalysis Mediated by Iron (II)

Mg2+ shares a distinctive relationship with RNA, playing important and specific roles in the folding and function of essentially all large RNAs. Here we use theory and experiment to evaluate Fe2+ in the absence of free oxygen as a replacement for Mg2+ in RNA folding and catalysis. We describe both quantum mechanical calculations and experiments that suggest that the roles of Mg2+ in RNA folding and function can indeed be served by Fe2+. The results of quantum mechanical calculations show that the geometry of coordination of Fe2+ by RNA phosphates is similar to that of Mg2+. Chemical footprinting experiments suggest that the conformation of the Tetrahymena thermophila Group I intron P4–P6 domain RNA is conserved between complexes with Fe2+ or Mg2+. The catalytic activities of both the L1 ribozyme ligase, obtained previously by in vitro selection in the presence of Mg2+, and the hammerhead ribozyme are enhanced in the presence of Fe2+ compared to Mg2+. All chemical footprinting and ribozyme assays in the presence of Fe2+ were performed under anaerobic conditions. The primary motivation of this work is to understand RNA in plausible early earth conditions. Life originated during the early Archean Eon, characterized by a non-oxidative atmosphere and abundant soluble Fe2+. The combined biochemical and paleogeological data are consistent with a role for Fe2+ in an RNA World. RNA and Fe2+ could, in principle, support an array of RNA structures and catalytic functions more diverse than RNA with Mg2+ alone.

Chemical oxidation of ibuprofen in the presence of iron species at near neutral pH

The objective of this work was to evaluate the removal of ibuprofen (IBP) using the oxidants hydrogen peroxide (H2O2) and sodium persulfate (Na2S2O8). The ability of magnetite (Fe3O4) to activate persulfate (PS) and H2O2 for the oxidation of IBP at near neutral pH was evaluated as well. The use of soluble Fe2+ to activate H2O2 and Na2S2O8 was also investigated. H2O2 and Na2S2O8 were inactive during the sixty-minute experiments when used alone. However, activation using Fe2+ increased the removal to 95% in the presence of H2O2 (Fenton reaction) and 63% in the presence of Na2S2O8 at pH 6.6. Chemical oxygen demand (COD) removal was also greater for Fenton oxidation (65%) than for iron-activated PS oxidation (25%). Activation of H2O2 and PS by Fe3O4 was only observed at a high oxidant concentration and over 48h of reaction time. A second order rate kinetic constant was determined for H2O2 (3.0∗10−3M−1s−1) and Na2S2O8 (1.59∗10−3M−1s−1) in the presence of Fe3O4. Finally, several of the degradation products formed during oxidation of IBP in the presence of H2O2 and Na2S2O8 (activated by Fe2+) were identified. These include oxalic acid, pyruvic acid, formic acid, acetic acid, 4-acetylbenzoic acid, 4-isobutylacetophenone (4-IBAP) and oxo-ibuprofen.

Biotransformation of Heavy Metals from Soil in Synthetic Medium Enriched with Glucose and Shewanella sp. HN-41 at Various pH

The biotransformation of heavy metals from contaminated soil was examined using a facultative anaerobic bacterium Shewanella sp. HN-41. The experiments were carried out to assess the influence of glucose at various pH on the transformation of heavy metals from soil thorough solubilization. A preliminary study on the transformation of heavy metals from soil was first performed using a defined medium supplemented with glucose at 10, 20, and 30 mM to select the effective concentration. Among the three concentrations examined, glucose at 30 mM leached a highest level of metal ions. Therefore, 30 mM glucose was used as the representative carbon source for the subsequent experiments in a defined medium at various pH (5, 6, 7, 8, and 9). The organism HN-41 was not influenced by pH ranging from acidic to neutral and was able to metabolize all the metal elements from contaminated soil. The level of Fe, Cr, As, Mn, Pb, and Al solubilization ranged from 3 to 7664 mg kg−1 at various initial pH. The rate of metal solubilization was found to be low at neutral pH compared with acidic and alkaline. These results are expected to assist in the development of heavy metal transformation processes for the decontamination of heavy metal-contaminated soil.

Adaptive strategies of Parietaria diffusa (M.&K.) to calcareous habitat with limited iron availability*

The study of native plants growing in hostile environments is useful to understand how these species respond to stress conditions. Parietaria diffusa (M.&K.) is able to survive in highly calcareous soils and extreme environments, such as house walls, without displaying any chlorotic symptoms. Here, we have investigated the existence of Strategy I complementary/alternative mechanism(s) involved in Fe solubilization and uptake and responsible for Parietaria's extraordinary efficiency. After assessing the specific traits involved in a calcicole-behaviour in the field, we have grown plants in conditions of Fe deficiency, either direct (-Fe) or induced by the presence of bicarbonate (+FeBic). Then, the growth performance, physiological and biochemical responses of the plants were investigated. The study shows that in Parietaria+FeBic, the classical responses of Strategy I plants are activated to a lower extent than in -Fe. In addition, there is a greater production of phenolics and organic acids that are both exuded and accumulated in the roots, which in turn show structures similar to 'proteoid-like roots'. We suggest that in the presence of this constraint, Parietaria undergoes some metabolic rearrangements that involve PEP-consuming reactions and an enhancement of the shikimate pathway.

Treatment of underground water in open flow and closed-loop fixed bed systems by utilizing the natural minerals clinoptilolite and vermiculite

Abstract Iron and manganese are found naturally in several soil and rock minerals while in the same time they are used as raw material in steel manufacture and products. Both metals can reach ground water reserves easily by rain or other means and while surface water does not usually contain high concentrations of iron or manganese because the oxygen-rich water enables both minerals to settle out as sediments, in anaerobic conditions, like in ground water deposits, iron and manganese are reduced to their soluble oxidation states Fe2+ and Mn2+. The problem of groundwater contaminated with these metals has become evident the last decades and several methods have been tested in the related literature. Ion exchange and adsorption are inexpensive and simple methods, especially when natural minerals are used, as zeolites and clays, however, the relevant studies of simultaneous removal of Fe and Mn from natural samples in the literature are few. In the present study natural clinoptilolite (zeolite) and vermiculi...

Tribological Behavior among Piston Ring -Hydrorefined Mineral Oil- Cylinder Liner for Diesel Engine

With a piston ring reciprocating liner test rig, the tribological behavior at top dead center of diesel engine was evaluated between hydrorefined mineral oil (HMO) and two kinds of cylinder liner/piston ring, chromium-plated+honing/physical vapor deposition (CP/PVD) and boron-phosphrous alloy cast iron+honing/physical vapor deposition (CI/PVD). Friction coefficient vs. temperature at different loads was used to discriminate the principal function of tribofilm. The analysis shows that the interface between CP/PVD and HMO was subject to thin film lubrication with stearic acid at 70-150°C. When the temperature exceeds 150°C, zinc dialkyl dithiophosphate (ZDDP) began to change the friction status of interface. However, the steady boundary lubrication of CI/PVD exists from 50—250°C at different loads and can not distinguish the scope of additives effects. The reason can be attributed to the chemical reactivity of chromium and iron with the HMO. The soluble Fe2+ or Fe3+ of CI/PVD maybe played an important role in the tribofilm activation level. The understanding provides friction pairs selection at definite lubrication oil and a design guideline for boundary films.

The role of rice phenolics efflux transporter in solubilizing apoplasmic iron

Iron (Fe) is an essential micronutrient for plants whose deficiency presents a major worldwide agricultural problem. Moreover, Fe is not easily available in neutral to alkaline soils, rendering plants deficient in Fe despite its abundance. Plants secrete phenolics, such as protocatechuic acid (PCA) and caffeic acid (CA), to take up and utilize apoplasmic precipitated Fe, but despite the rapid progress in understanding cellular and subcellular Fe transport, the molecular mechanisms of phenolics synthesis and secretion are not clear. Recently, we isolated and characterized a phenolics efflux transporter in rice by characterizing a mutant in which the amount of PCA and CA in the xylem sap was dramatically reduced, which we hence named phenolics efflux zero 1 (pez1). PEZ1 is a plasma membrane protein that transports PCA when expressed in Xenopus laevis oocytes, and characterization of PEZ1 knockdown and overexpressing plants revealed that it plays an essential role in solubilizing precipitated apoplasmic Fe. The identification of PEZ1 will increase our understanding of apoplasmic Fe solubilization as well as promote research on phenolics efflux mechanisms in different organisms.

In situ monitoring of lepidocrocite bioreduction and magnetite formation by reflection Mossbauer spectroscopy

The miniaturized Mössbauer spectrometer (MIMOS II) was used to monitor in situ the mineralogical transformation of lepidocrocite (γ-FeOOH) in a Shewanella putrefaciens culture under anaerobic conditions using methanoate as the electron source. Magnetite was the only biogenic mineral formed during the course of the incubation. The analysis of the biogenic mineral by transmission electron microscopy (TEM) revealed cubic-shaped crystals with a relatively homogeneous grain size of about 50 nm. After one day of incubation, the departure from stoichiometry, δ, of the biogenerated magnetite was very low (δ ~ 0.025) and rapidly reached values close to zero. Such low values of δ were not obtained for magnetite synthesized inorganically when Fe3+ in the form of γ-FeOOH was reacted with stoichiometric quantities of soluble Fe2+ and OH-. The experimental setup used in this study could be replicated in field experiments when assessing the formation of magnetite in modern geological settings as its formation is suspected to be caused by a strong bacterial activity.

Chemistry of rainwater and aerosols over Bay of Bengal during CTCZ program

For the first time, simultaneous study on physical and chemical characteristics of PM10, PM2.5, and rainwater chemistry was attempted over the Bay of Bengal in monsoon season of 2009. The aerosols and rainwater samples were collected onboard ship ‘SK-261, ORV Sagar Kanya’ during Oceanographic Observations in the Northern Bay of Bengal under the Continental Tropical Convergence Zone (CTCZ) program conducted during 16 July to 19 Aug 2009. Aerosol samples collected by PM10 and PM2.5 were analyzed for various water soluble (Na+, K+, Ca2+, Mg2+, NH4+, Cl−, SO42− and NO3− and acid soluble (Fe2+, Al3+, Zn2+, Mn3+ and Ni2+) ionic constituents. The pH of rainwater varied from 5.10 to 7.04. Chloride ions contributed most to the total ion concentration in aerosol and rainwater, followed by Na+. Significant contributions of SO42−, NO3− and NH4+ found in PM2.5, PM10 and high concentrations of TSP and non sea-salt SO42− over the mid-ocean is attributed to the long range transport of anthropogenic pollution from the Indian continent. The scavenging ratio was maximum for coarse particles such as Ca2+ and minimum for fine particles like NH4+.

Siderophores Are Not Involved in Fe(III) Solubilization during Anaerobic Fe(III) Respiration by Shewanella oneidensis MR-1

Shewanella oneidensis MR-1 respires a wide range of anaerobic electron acceptors, including sparingly soluble Fe(III) oxides. In the present study, S. oneidensis was found to produce Fe(III)-solubilizing organic ligands during anaerobic Fe(III) oxide respiration, a respiratory strategy postulated to destabilize Fe(III) and produce more readily reducible soluble organic Fe(III). In-frame gene deletion mutagenesis, siderophore detection assays, and voltammetric techniques were combined to determine (i) if the Fe(III)-solubilizing organic ligands produced by S. oneidensis during anaerobic Fe(III) oxide respiration were synthesized via siderophore biosynthesis systems and (ii) if the Fe(III)-siderophore reductase was required for respiration of soluble organic Fe(III) as an anaerobic electron acceptor. Genes predicted to encode the siderophore (hydroxamate) biosynthesis system (SO3030 to SO3032), the Fe(III)-hydroxamate receptor (SO3033), and the Fe(III)-hydroxamate reductase (SO3034) were identified in the S. oneidensis genome, and corresponding in-frame gene deletion mutants were constructed. DeltaSO3031 was unable to synthesize siderophores or produce soluble organic Fe(III) during aerobic respiration yet retained the ability to solubilize and respire Fe(III) at wild-type rates during anaerobic Fe(III) oxide respiration. DeltaSO3034 retained the ability to synthesize siderophores during aerobic respiration and to solubilize and respire Fe(III) at wild-type rates during anaerobic Fe(III) oxide respiration. These findings indicate that the Fe(III)-solubilizing organic ligands produced by S. oneidensis during anaerobic Fe(III) oxide respiration are not synthesized via the hydroxamate biosynthesis system and that the Fe(III)-hydroxamate reductase is not essential for respiration of Fe(III)-citrate or Fe(III)-nitrilotriacetic acid (NTA) as an anaerobic electron acceptor.

Dissolved Organic Matter Sources and Consequences for Iron and Arsenic Mobilization in Bangladesh Aquifers

Iron (Fe) and dissolved organic matter (DOM) cycling have been implicated in arsenic mobilization via microbially mediated Fe oxide reduction. To evaluate the sources and multiple roles of DOM in Bangladesh aquifers, we conducted spectroscopic analyses on various types of surface water and groundwater samples from a site representative of aquifer chemistry and hydrology. Surface water contained humic substances with oxidized quinone-like moieties and high concentrations of labile microbially derived DOM. In contrast, in shallow groundwater where dissolved iron and arsenic concentrations were high, the quinone-like moieties of humic substances were more reduced, with less abundant labile DOM than that of surface water. Instead, DOM at these depths was characterized by terrestrial (plant/soil) signatures. A sediment microcosm experiment demonstrated that Fe(II) and terrestrially derived DOM were released from sediment over time. The results provide new evidence to support a dual role of natural DOM in Bangladesh aquifers (1) as a labile substrate for Fe- and humic-reducing bacteria and (2) as an electron shuttle via humic substances to enhance microbial iron reduction. Fluorescence index, amino acid-like fluorescence, and redox index may serve as useful indicators of the type of DOM likely to be involved in Fe solubilization and potentially As mobilization reactions.

Ferrous and Ferric Ion Generation During Iron Electrocoagulation

Our research on arsenate removal by iron electrocoagulation (EC) produced highly variable results, which appeared to be due to Fe2+ generation without subsequent oxidation to Fe3+. Because the environmental technology literature is contradictory with regard to the generation of ferric or ferrous ions during EC, the objective of this research was to establish the iron species generated during EC with iron anodes. Experimental results demonstrated that Fe2+, not Fe3+, was produced at the iron anode. Theoretical current efficiency was attained based on Fe2+ production with a clean iron rod, regardless of current, dissolved-oxygen (DO) level, or pH (6.5-8.5). The Fe2+ remaining after generation and mixing decreased with increasing pH and DO concentration due to rapid oxidation to Fe3+. At pH 8.5, Fe2+ was completely oxidized, which resulted in the desired Fe(OH)3(s)/ FeOOH(s), whereas, at pH 6.5 and 7.5, incomplete oxidation was observed, resulting in a mixture of soluble Fe2+ and insoluble Fe(OH)3(s)/FeOOH(s). When compared with Fe2+ chemical coagulation, a transient pH increase during EC led to faster Fe2+ oxidation. In summary, for EC in the pH 6.5-7.5 range and at low DO conditions, there is a likelihood of soluble Fe2+ species passing through a subsequentfiltration process resulting in secondary contamination and inefficient contaminant removals.

Iron availability affects the function of mitochondria in cucumber roots

* In Strategy-I-plants, iron (Fe) deficiency induces processes leading to increased Fe solubilization in the rhizosphere, including reduction by ferric reductases and active proton extrusion. These processes require active respiration to function. In this work we investigated the effect of Fe deficiency on respiratory activities of cucumber (Cucumis sativus) roots. * We compared oxygen consumption rate and the activities of the respiratory chain complexes on purified mitochondria from roots grown in the presence or absence of Fe using biochemical and molecular approaches. * Oxygen consumption rate in apex roots was increased under Fe deficiency that was mostly resistant to KCN and salycilichydroxamic acid (SHAM) inhibitors, indicating other oxygen-consuming reactions could be present. Indeed, enzyme assays revealed that lack of Fe induced a decrease in the activities of respiratory complexes that was proportional to the number of Fe atoms in each complex. A decrease of cyt c, Rieske and NAD9 proteins was also observed. Transmission electron microscopy (TEM) analysis showed that mitochondria undergo structural changes under Fe deficiency. * Our data show that mitochondria and the electron transport chain are an important target of Fe limitation and that mitochondria modify their function to meet higher demands for organic acids while restricting the activity of enzymes with Fe cofactors.

Ferritin Contains Less Iron (59Fe) in Cells When the Protein Pores Are Unfolded by Mutation

Ferric minerals in ferritins are protected from cytoplasmic reductants and Fe2+ release by the protein nanocage until iron need is signaled. Deletion of ferritin genes is lethal; two critical ferritin functions are concentrating iron and oxidant protection (consuming cytoplasmic iron and oxygen in the mineral). In solution, opening/closing (gating) of eight ferritin protein pores controls reactions between external reductant and the ferritin mineral; pore gating is altered by mutation, low heat, and physiological urea (1 mm) and monitored by CD spectroscopy, protein crystallography, and Fe2+ release rates. To study the effects of a ferritin pore gating mutation in living cells, we cloned/expressed human ferritin H and H L138P, homologous to the frog open pore model that was unexpressable in human cells. Human ferritin H L138P behaved like the open pore ferritin model in vitro as follows: (i) normal protein cage assembly and mineralization, (ii) increased iron release (t1/2) decreased 17-fold), and (iii) decreased alpha-helix (8%). Overexpression (> 4-fold), in HeLa cells, showed for ferritin H L138P equal protein expression and total cell 59Fe but increased chelatable iron, 16%, p < 0.01 (59Fe in the deferoxamine-containing medium), and decreased 59Fe in ferritin, 28%, p < 0.01, compared with wild type. The coincidence of decreased 59Fe in open pore ferritin with increased chelatable 59Fe in cells expressing the ferritin open pore mutation suggests that ferritin pore gating influences to the amount of iron (59Fe) in ferritin in vivo.

Redox conditions related to interflow in a soil of the Kroonstad form in the Weatherley catchment

The Kroonstad soil form, in the Weatherley catchment, Eastern Cape Province consists of an orthic A / E / G horizon sequence, and is a typical gleyed soil of South Africa. The profile has an uncommon diffuse E / G transition. Water contents from weekly neutron water meter readings and redox response as indicated by dissolved Fe2+ concentration were correlated with daily rainfall data from automated weather stations. Results showed that reducing conditions were more pronounced in the E horizon than in the orthic A or G horizon as indicated by the Fe2+ concentration. This is contradictory to what is normally expected. Response in soluble iron concentration in the orthic A horizon was largely associated with rainfall events. Responses in the E horizon could not be linked to current rain events. A time lag was found to exist between a response in the A and the E horizon. The G horizon responded to seasonal changes. The inability to relate current rainfall events to redox conditions as indicated by soluble Fe2+ response in the E horizon could be attributed to water entering the E horizon laterally through interflow. This would also explain the observed time lag. This is typical of perched water tables. The lack of response in the G-horizon is an indication of a year round flow pattern controlled by seasonal changes and is typical of phreatic water tables. It is postulated that the non-abrupt E / G transition is an indication of the dominant role of the phreatic water table during pedogenesis, with upwards and lateral movement of water into the E horizon. It is further postulated that the nature of the E / G transition could serve as a valuable criterion to distinguish between the wetter and drier soils of the Kroonstad form.

Riboflavin Biosynthesis Is Associated with Assimilatory Ferric Reduction and Iron Acquisition by Campylobacter jejuni

One of the pathways involved in the acquisition of the essential metal iron by bacteria involves the reduction of insoluble Fe(3+) to soluble Fe(2+), followed by transport of Fe(2+) to the cytoplasm. Flavins have been implicated as electron donors in this poorly understood process. Ferrous iron uptake is essential for intestinal colonization by the important pathogen Campylobacter jejuni and may be of particular importance under low-oxygen conditions. In this study, the links among riboflavin biosynthesis, ferric reduction, and iron acquisition in C. jejuni NCTC11168 have been investigated. A riboflavin auxotroph was generated by inactivation of the ribB riboflavin biosynthesis gene (Cj0572), and the resulting isogenic ribB mutant only grew in the presence of exogenous riboflavin or the riboflavin precursor diacetyl but not in the presence of the downstream products flavin adenine dinucleotide and flavin mononucleotide. Riboflavin uptake was unaffected in the ribB mutant under iron-limited conditions but was lower in both the wild-type strain and the ribB mutant under iron-replete conditions. Mutation of the fur gene, which encodes an iron uptake regulator of C. jejuni, resulted in an increase in riboflavin uptake which was independent of the iron content of the medium, suggesting a role for Fur in the regulation of the as-yet-unknown riboflavin transport system. Finally, ferric reduction activity was independent of iron availability in the growth medium but was lowered in the ribB mutant compared to the wild-type strain and, conversely, increased in the fur mutant. Taken together, the findings confirm close relationships among iron acquisition, riboflavin production, and riboflavin uptake in C. jejuni.

Shewanella putrefaciens produces an Fe(III)-solubilizing organic ligand during anaerobic respiration on insoluble Fe(III) oxides

The mechanism of Fe(III) reduction was investigated using voltammetric techniques in anaerobic incubations of Shewanella putrefaciens strain 200 supplemented with Fe(III) citrate or a suite of Fe(III) oxides as terminal electron acceptor. Results indicate that organic complexes of Fe(III) are produced during the reduction of Fe(III) at rates that correlate with the reactivity of the Fe(III) phase and bacterial cell density. Anaerobic Fe(III) solubilization activity is detected with either Fe(III) oxides or Fe(III) citrate, suggesting that the organic ligand produced is strong enough to destabilize Fe(III) from soluble or solid Fe(III) substrates. Results also demonstrate that Fe(III) oxide dissolution is not controlled by the intrinsic chemical reactivity of the Fe(III) oxides. Instead, the chemical reaction between the endogenous organic ligand is only affected by the number of reactive surface sites available to S. putrefaciens. This report describes the first application of voltammetric techniques to demonstrate production of soluble organic-Fe(III) complexes by any Fe(III)-reducing microorganism and is the first report of a Fe(III)-solubilizing ligand generated by a metal-reducing member of the genus Shewanella.

English

Sphalerite [(Zn,Fe)S] from Mississippi Valley type (MVT), volcanogenic massive sulfide (VMS), and polymetallic vein (PMV) ore deposits show variable rates of dissolution and resulting aqueous metals concentrations under acid conditions. An important control on dissolution rates is solubilized iron that eventually produces Fe(III), a strong oxidant of sphalerite. VMS (high Fe and Cd) and PMV (high Fe and metals) sphalerite samples showed faster rates of sphalerite dissolution (10 -9 to 10 -10 mol/L/s Zn +2 ) and Fe solubilization (10 -9 to 10 -10 mol/L/s total Fe), and higher aqueous trace metals compared to MVT sphalerite that has low Fe and trace metals; these characteristics are manifested by slower rates of sphalerite dissolution (10 -10 to 10 -11 mol/L/s Zn +2 ) and Fe solubilization (10 -12 mol/L/s total Fe), and low aqueous metals compared to VMS and PMV samples. Aqueous concentrations of major (Fe, Zn) and trace (Cu, Cd, Pb, Mn) elements depended on the original composition and rate of dissolution of sphalerite. Fine-grained, high-Fe VMS sphalerite (6.7 wt.%) leached at pH 2-3 (25° C) produced dissolved Fe and Zn approaching 50 and 180 mg/L, respectively, within 1 week; Cu and Pb were 3 and 250 g/L, respectively. The same sphalerite leached at pH 4.0 or higher took two months to yield comparable concentrations. Coarse-grained VMS sphalerite leached for several months at a pH of 4.0 yielded only 100g/L Fe and 9.2 mg/L Zn. PMV sphalerite (4.2 wt.%) had a Zn solubilization rate and trace metal concentrations similar to the VMS sample, but a faster Fe solubilization rate (10 -8 mol/L/s Fetot). Low-iron sphalerite (0.2-0.3 wt.%) from MVT deposits produced Zn concentrations similar to the VMS sphalerite at pH 2.0 but lower concentrations at pH 4.0. At both pH values, aqueous Fe from the high-Fe VMS sample was 100 times that from the MVT sample. Trace metals showed a range of concentrations that generally depended on their original abundance in the solid and their solubilities in the acid solution. Because sphalerite from different ore deposits can be major sources of aqueous metals that may affect the composition of nearby surface and ground water, the potential metal contribution of non-pyritic minerals such as sphalerite should be a major consideration during all stages of economic development of an ore deposit. Additional