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1.
A detailed investigation of nanostructured iron oxides/(oxy)hydroxides gathered after cultivation of bacteria from the genus Leptothrix as iron (II) oxidizers is presented. A specific type of medium is selected for the cultivation of the bacteria. Results for sediment powder and bio-film on glass substrate samples from the same media are discussed. XRD, Raman spectroscopy, SEM, and TEM images and PPMS measurements are used to prove the exact composition of the biogenic products and to interpret the oxidation process. Analysis of the data collected shows that around 80 % of the iron (II) from the growth medium has been transformed into iron (III) in the form of different (oxy)hydroxides, with the rest found to be in a mixed 2,5 valence in magnetite. Our investigation shows that the bio-film sample has a phase content different from that of the powdered biomass and that lepidocrocite (γ-FeOOH) is the predominant and the initial biogenic phase in both samples. Magnetite nanoparticles are a secondary product in the bio-film, part of which possesses a defective quasi-maghemite surface layer. In the powdered biomass, the oxidation steps are not fully completed. The initial products are non-stoichiometric and due to the mixed ferric and ferrous ions present, they develop into: (i) lepidocrocite (γ-FeOOH) as a basic sediment, (ii) magnetite (Fe 3O 4) and (iii) goethite (α-FeOOH) in small quantities. The average size of all iron-bearing particles is found to be below 30 nm. The magnetic measurements performed show a superparamagnetic behavior of the material at room temperature. 相似文献
2.
Dithionite has been found to reduce directly (without mediators) the Escherichia coli R2 subunit of ribonucleotide reductase. With dithionite (∼10 mM) in large excess, the reaction at 25 °C is complete in ∼10 h.
Preparations of E. coli R2 have an Fe III
2 (met-R2) component in this work at ∼40% levels, alongside the fully active enzyme Fe III
2 . . . Tyr*, which has a tyrosyl radical at Tyr-122. In the pH range studied (7–8) the kinetics are biphasic. Rate laws for
both phases give [S 2O 4
2–] and not [S 2O 4
2–] 1/2 dependencies, and saturation kinetics are observed for the first time in R2 studies. No dependence on pH was detected. The
kinetics (25 °C) of the first phase are reproduced in separate experiments using only met-R2, with association of S 2O 4
2– to met-R2, K=330 M –1, occurring prior to electron transfer, k
et=4.8×10 –4 s –1, I=0.100 M (NaCl). The second phase assigned to the reaction of Fe III
2 . . . Tyr* with S 2O 4
2– gives K=800 M –1 and k
et=5.6×10 –5 s –1. Bearing in mind the substantially smaller reduction potential for Fe III
2 compared to Tyr*, this is a quite remarkable finding, with implications similar to those already reported for the reaction
of R2 with hydrazine, but with additional information provided by the saturation kinetics. The similarity in rates for the
two phases (∼fourfold difference) suggests that reduction of Fe III
2 is occurring in both cases, and since S 2O 4
2– is involved a two-equivalent change is proposed with the formation of Fe II
2 . . . Tyr* in the case of active R2. As a sequel to the second phase, intramolecular reduction of the strongly oxidising
Tyr* by the Fe II
2 is rapid, and further decay of Fe IIFe III is also fast. There is no stable mouse met-R2 form, and the single-phase reaction with dithionite gives saturation kinetics
with K=208 M –1 and k
et=1.7±10 –3 s –1. Mechanistic implications, including the applicability of a pathway for electron transfer via Fe A, are considered.
Received: 25 February 1998 / Received: 20 August 1998 相似文献
3.
Bacterial biomass collected from sheath-forming bacteria of the genera Sphaerotilus and Leptothrix was collected from a high-mountain natural stream water source. The elemental constitution and oxide phases of the products after selective cultivation of the bacteria on two different elective media using neutron activation analysis (NAA), electron microscopy (SEM, TEM), and X-ray diffraction (XRD) were studied. A high enrichment level of iron was revealed by the NAA technique in cultivated isolates as compared to the reference sample from nature. Three types of iron oxide compounds were established after cultivation in Adler’s medium: lepidocrocite (γ-FeOOH), magnetite (Fe 3O 4), and goethite (α-FeOOH). The cultivation in the Isolation medium yielded a single phase, that of goethite, excluding one sample with a distinguishable amount of lepidocrocite. XRD and EM investigations show that the biogenic oxides are nanosized. Our study exemplifies the possibilities of the biotechnology approach for obtaining, under artificial conditions, large quantities of iron-containing by-products that could be of further used in appropriate nano- and biotechnologies. 相似文献
4.
The hydrated iron(III) oxide limonite is reported for the first time as a biomineral. In situ laser Raman spectra of the tooth cores from major lateral teeth of the chiton Plaxiphora albida are compared with those of synthetic and mineral iron phosphates and iron oxides. Raman spectra measured on iron phosphate and iron oxide standard materials are shown to be easily distinguishable from one another. The central tooth cores of mature P. albida teeth do not show any evidence for the presence of a separate iron phosphate mineral. Rather, in each tooth a narrow band of the hydrated iron(III) oxide limonite is shown to separate the magnetite of the tooth surface from a central core region comprising both lepidocrocite and limonite. The high concentration of phosphorus in P. albida tooth cores, previously observed by energy dispersive spectroscopy, is not associated with a separate iron phosphate mineral, indicating that this element may be adsorbed onto the surface of the iron oxide minerals present. The failure to detect a separate iron(III) phosphate is discussed with reference to other chiton species that display high levels of iron and phosphorus in the cores of their mature major lateral teeth. 相似文献
5.
Magnetotactic bacteria orient and migrate along geomagnetic field lines. This ability is based on intracellular magnetic
structures, the magnetosomes, which comprise nanometer-sized, membrane-bound crystals of the magnetic iron minerals magnetite
(Fe 3O 4) or greigite (Fe 3S 4). Magnetosome formation is achieved by a mineralization process with biological control over the accumulation of iron and
the deposition of the mineral particle with specific size and orientation within a membrane vesicle at specific locations
in the cell. This review focuses on the current knowledge about magnetotactic bacteria and will outline aspects of the physiology
and molecular biology of the biomineralization process. Potential biotechnological applications of magnetotactic bacteria
and their magnetosomes as well as perspectives for further research are discussed.
Received: 2 December 1998 / Received revision: 2 March 1999 / Accepted: 5 March 1999 相似文献
6.
Raman spectroscopic investigations of the major lateral teeth of the chitons Acanthopleura rehderi and Acanthopleura curtisiana indicate that, in addition to the magnetite of the cutting surface and a carbonated hydroxyapatite in the central tooth core, these species deposit limonite in place of the lepidocrocite reported for other members of the genus Acanthopleura. A comparison of the spectra from these species with those of Onithochiton quercinus, which also deposits limonite, indicates that the current assignment of these species to Acanthopleura may not be appropriate. Biomineralization of the major lateral teeth may be a useful parameter to include in the taxonomic classification of chiton species. 相似文献
7.
We purified two catechol oxidases from Lycopus europaeus and Populus nigra which only catalyze the oxidation of catechols to quinones without hydroxylating tyrosine. The molecular mass of the Lycopus enzyme was determined to 39 800 Da and the mass of the Populus enzyme was determined to 56 050 Da. Both catechol oxidases are inhibited by thiourea, N-phenylthiourea, dithiocarbamate, and cyanide, but show different pH behavior using catechol as substrate. Atomic absorption
spectroscopic analysis found 1.5 copper atoms per protein molecule. Using EPR spectroscopy we determined 1.8 Cu per molecule
catechol oxidase. Furthermore, EPR spectroscopy demonstrated that catechol oxidase is a copper enzyme of type 3. The lack
of an EPR signal is due to strong antiferromagnetic coupling that requires a bridging ligand between the two copper ions in
the met preparation. Addition of H 2O 2 to both enzymes leads to oxy catechol oxidase. In the UV/Vis spectrum two new absorption bands occur at 345 nm and 580 nm. In accordance with the oxy forms of hemocyanin and tyrosinase the absorption band at 345 nm is due to an O 2
2– (π σ*)→Cu(II) ( d
x2–y2
) charge transfer (CT) transition. The absorption band at 580 nm corresponds to the second O 2
2– (π v*)→Cu(II) ( d
x2–y2
) CT transition. The UV/Vis bands in combination with the resonance Raman spectra of oxy catechol oxidase indicate a μ-η 2 : η 2 binding mode for dioxygen. The intense resonance Raman peak at 277 cm –1, belonging to a Cu-N (axial His) stretching mode, suggests that catechol oxidase has six terminal His ligands, as known for
molluscan and arthropodan hemocyanin.
Received: 30 July 1998 / Accepted: 26 October 1998 相似文献
8.
Abstract The structure, morphology and organisation of the cusps of the major lateral radula teeth of the chiton Plaxiphora albida have been examined using light, transmission and scanning electron microscopy, together with energy dispersive X-ray analysis and Mössbauer spectroscopy. In this chiton species, both the anterior and posterior surfaces of the major lateral teeth are composed of magnetite, which is indicated to be non-stoichiometric and associated with some maghemite, together with small amounts of phosphorus and silicon. This outer layer surrounds an inner core region of the tooth, which only reaches the surface through a small window zone on the anterior surface and which contains large amounts of iron and phosphorus presumably in the form of iron(III) phosphate. The organic matrix, on which the teeth are constructed, consists of a zone of densely packed fine fibres at the surface of the tooth, underlain by larger fibres which become sparser deeper into the cusp. The core region is characterized by the presence of densely packed short fibres. In contrast to the situation found in most other species of chiton, large fibres of the organic matrix extend throughout the region of magnetite mineralization, leading to the suggestion that the matrix exerts more control over the mineralization of magnetite than has previously been thought. 相似文献
9.
Magnetite (Fe IIFe III2O 4) is often considered as a stable end product of the bioreduction of Fe III minerals (e.g., ferrihydrite, lepidocrocite, hematite) or of the biological oxidation of Fe II compounds (e.g., siderite), with green rust (GR) as a mixed Fe II‐Fe III hydroxide intermediate. Until now, the biotic transformation of magnetite to GR has not been evidenced. In this study, we investigated the capability of an iron‐reducing bacterium, Shewanella putrefaciens, to reduce magnetite at circumneutral pH in the presence of dihydrogen as sole inorganic electron donor. During incubation, GR and/or siderite (Fe IICO 3) formation occurred as secondary iron minerals, resulting from the precipitation of Fe II species produced via the bacterial reduction of Fe III species present in magnetite. Taking into account the exact nature of the secondary iron minerals and the electron donor source is necessary to understand the exergonic character of the biotic transformation of magnetite to GR, which had been considered to date as thermodynamically unfavorable at circumneutral pH. This finding reinforces the hypothesis that GR would be the cornerstone of the microbial transformations of iron‐bearing minerals in the anoxic biogeochemical cycle of iron and opens up new possibilities for the interpretation of the evolution of Earth's history and for the understanding of biocorrosion processes in the field of applied science. 相似文献
10.
The coordination state of Fe(III)- and Fe(II)-mimochrome I, a covalent peptide-deuteroheme sandwich involving two nonapeptides
bearing a histidine residue in a central position, was studied by UV-visible, EPR, and resonance Raman spectroscopy. The ferric
and ferrous states of this new iron species mainly exist, at pH 7, in a low-spin hexacoordinate form with two axial histidine
ligands coming from the peptide chains. A minor amount of high-spin form for the ferric state is also present at pH 7. However,
it is mainly high-spin at pH 2 or in DMSO. Fe(II)-mimochrome I binds CO with an affinity comparable to that of myoglobin and
hemoglobin. Fe(III)-mimochrome I reacts with alkylhydroxylamine and arylhydrazines, leading to the corresponding Fe(II)-nitrosoalkyl
and Fe(III)-σ-aryl complexes, respectively. These reactions were greatly dependent on the solvent used and on the pH, and
were much slower than the corresponding reactions performed by deuterohemin in the presence of excess imidazole. All these
results indicate that the reactivity of iron-mimochrome I is controlled by the binding of the peptide chains to the iron.
The reactivity shown by this complex at neutral pH is intermediate between that observed for iron porphyrins in the presence
of excess imidazole and that of hemoproteins characterized by a strong bis-histidine axial coordination, such as cytochrome
b
5. Fe(III)-mimochrome I is able to catalyze styrene epoxidation by using a [Fe(III)-mimochrome I]/[H 2O 2]/[stryrene] ratio of 1 : 10 : 2000 in phosphate buffer solution (pH 7.2) containing 2% CTAB both under strictly anaerobic
conditions and in the presence of oxygen, at 0 °C.
Received: 26 May 1998 / Accepted: 20 August 1998 相似文献
11.
Four reductions of the R2 subunit of mouse ribonucleotide reductase have been studied and found to exhibit different behaviour
from that of Escherichia coli R2. An important difference is that there is no stable met-R2 (Fe 2
II I) form of mouse R2. With hydroxyurea, hydrazine and hydroxylamine uniphasic kinetics are observed for the combined reduction
of radical Tyr ˙ and Fe 2
II I components to tyrosine and Fe 2
II respectively. The rate constants, determined at 370 nm (emphasising Fe III decay) and 417 nm (emphasising Tyr ˙ decay), differ by factors of 2–3, allowing some mechanistic features to be defined. The studies with hydrazine are particularly
important. In the case of E. coli R2, a first phase corresponding to two-equivalent reduction of the met-R2 component has been observed [18]. It is likely
that the four times slower second phase reaction of active E. coli R2 also corresponds to the Fe 2
II I → Fe 2
II change and is followed by fast intramolecular Fe 2
II reduction of the higher potential Tyr ˙. The latter changes are believed to hold also for (active) mouse R2. The Fe IIFe III semi forms have been detected at low levels by EPR for mouse R2 (9%) and E. coli (∼5%) in previous studies. Further substrate reduction of Fe IIFe III occurs at a comparable rate to account for the transient behaviour of Fe IIFe III. For mouse R2 the combined Fe III decay processes (which we are unable to separate) give smaller uniphasic rate constants at 370 nm than at 417 nm. A fitted-base-line
(FBL) treatment of absorbance changes at 417 nm targets more closely the Tyr ˙ decay as a means of monitoring the rate-determining step. The FBL method gives rate constants k (M –1 s –1) at 25 °C and pH 7.5 for hydroxyurea (1.46), hydrazine (0.163) and hydroxylamine (4.4). Surprisingly, phenylhydrazine, with
a less strong reduction potential (0.25 V), gives a substantially faster reduction of the Tyr ˙ as the only redox step (rate constant 27 M –1 s –1). In this case a slower second phase at 370 nm is independent of reductant and corresponds to rate-controlling release of
Fe III. Overall the results indicate a more reactive redox centre for mouse R2 and help develop further an understanding of factors
affecting the reactivity of R2.
Received: 11 October 1996 / Accepted: 11 February 1997 相似文献
12.
4 S 4] 3 + and the reduced [Fe 4S 4] 2 + clusters in the high-potential iron protein I from Ectothiorhodospira halophila were measured in a temperature range from 5 K to 240 K. EPR measurements and 57Fe electron-nuclear double resonance (ENDOR) experiments were carried out with the oxidized protein. In the oxidized state
the cluster has a net spin S = 1/2 and is paramagnetic. As common in [Fe 4S 4] 3 + clusters, the M?ssbauer spectrum was simulated with two species contributing equally to the absorption area: two Fe 3 + atoms couple to the “ferric-ferric” pair, and one Fe 2 + and one Fe 3 + atom give the “ferric-ferrous pair”. For the simulation of the M?ssbauer spectrum, g-values were taken from EPR measurements. A-tensor components were determined by 57Fe ENDOR experiments that turned out to be a necessary source of estimating parameters independently. In order to obtain a
detailed agreement of M?ssbauer and ENDOR data, electronic relaxation has to be taken into account. Relaxing the symmetry
condition in a way that the electric field gradient tensor does not coincide with g- and A-tensors yielded an even better agreement of experimental and theoretical M?ssbauer spectra. Spin-spin and spin-lattice relaxation
times were estimated by pulsed EPR; the former turned out to be the dominating mechanism at T = 5 K. Relaxation times measured by pulsed EPR and obtained from the M?ssbauer fit were compared and yield nearly identical
values. The reduced cluster has one additional electron and has a diamagnetic ( S = 0) ground state. All the four irons are indistinguishable in the M?ssbauer spectrum, indicating a mixed-valence state of
Fe 2.5 + for each.
Received: 15 February 1999 / Accepted: 31 August 1999 相似文献
13.
Electron paramagnetic resonance spectroscopy has been applied for the first time to study the bio-distribution of magnetoliposomes formed with magnetite nanoparticles (Fe3O4) in tumors and organs of Lewis carcinoma-bearing mice in the absence and presence of an external magnetic field. The animals of the experimental group were subjected to an external magnetic field (0.6 T) in the tumor area after intravenous injection of magnetoliposomes at a dose of 7.56 Fe/kg. Analysis of the electron-spin resonance spectra of mouse organs and tissue samples showed that exposure to a magnetic field resulted in a two-fold increase in Fe3O4 accumulation within the tumor (p < 0.05) compared to the control; this makes it possible to recommend the obtained magnetoliposomes for use as a magnetically controlled carriers for targeted delivery of antitumor agents. A high concentration of superparamagnetic magnetite nanoparticles was detected in the liver in the absence and presence of an external magnetic field. The differences in the accumulation of Fe3O4 in the lungs and liver in the presence of a magnetic field were statistically insignificant. 相似文献
14.
Well-supplied and K-deficient 4-year-old clonal Norway spruce trees were exposed to combinations of two levels of ozone (20
and 80 nl l –
1 O 3) and carbon dioxide (350 and 750 μl l –
1 CO 2) to study the effects of possible future climate factors on gas exchange characteristics. The fumigation was performed in
environmental chambers for a complete growing season. After the exposure, plants were cultivated outdoors to investigate possible
recovery and delayed effects. During the exposure 1-year-old needles responded to the 80 nl l –
1 O 3 treatment by a sharp but transient decrease of both apparent carboxylation efficiency (CE) and maximum photosynthetic capacity
(A 2500). Elevated CO 2 also reduced CE and A 2500. The effect became stronger in the course of the exposure and was accompanied by decreases of N and P as well as chlorophyll
contents. In case of K deficiency, the acclimation response of current-year needles was even more pronounced reflecting lower
sink capacities for carbon metabolites. The joint application of elevated O 3 and CO 2 resulted in the lowest values of gas exchange parameters and chlorophyll contents. At the beginning of the growing season
after the exposure and under outdoor conditions, all these treatment effects disappeared in the needles which had developed
during the fumigation. In the course of the development of the new flush, however, the well-supplied 1-year-old needles which
had been treated with 80 nl l –
1 O 3 and 350 μl l –
1 CO 2 in the year before, exhibited a sharp decline of CE and A 2500. Simultaneously, chlorotic mottle and bands developed. These delayed symptoms are discussed in the context of the previously
published “memory” effect for O 3 (Sandermann et al. 1989). Additionally, evidence is presented that shoot development is altered in plants which had been
exposed to elevated O 3.
Accepted: 5 August 1996 相似文献
15.
Mechanisms of inorganic carbon assimilation were investigated in the deep-water alga Phyllariopsis purpurascens (C. Agardh) Henry et South (Laminariales, Phaeophyta). The gross photosynthetic rate as a function of external pH, at a constant
concentration of 2 mM dissolved inorganic carbon (DIC), decreased sharply from pH 7.0 to 9.0, and was not substantially different
from 0 above pH 9.0. These data indicate that P. purpurascens is inefficient in the use of external HCO 3
− as a carbon source in photosynthesis. Moreover, the photosynthetic rate as a function of external DIC and the highest pH
(9.01 ± 0.07) that this species can achieve in a closed system were consistent with a low capacity to use HCO 3
−, in comparison to many other species of seaweeds. The role of external carbonic anhydrase (CA; EC 4.2.1.1) on carbon uptake
was investigated by measuring both the HCO 3
−-dependent O 2 evolution and the CO 2 uptake, at pH 5.5 and 8.0, and the rate of pH change in the external medium, in the presence of selected inhibitors of extra-
and intracellular CA. Photosynthetic DIC-dependent O 2 evolution was higher at pH 5.5 (where CO 2 is the predominant form of DIC) than at pH 8.0 (where the predominant chemical species is HCO 3
−). Both intra- and extracellular CA activity was detected. Dextran-bound sulfonamide (DBS; a specific inhibitor of extracellular
CA) reduced the photosynthetic O 2 evolution and CO 2 uptake at pH 8.0, but there was no effect at pH 5.5. The pH-change rate of the medium, under saturating irradiance, was reduced
by DBS. Phyllariopsis purpurascens has a low efficiency in the use of HCO 3
− as carbon source in photosynthesis; nevertheless, the ion can be used after dehydration, in the external medium, catalyzed
by extracellular CA. This mechanism could explain why the photosynthetic rate in situ was higher than that supported solely
by the diffusion of CO 2 from seawater.
Received: 6 March 1998 / Accepted: 22 June 1998 相似文献
16.
The radula in a group of molluscan invertebrates, the chitons (Polyplacophora), is a ribbon-like apparatus used for feeding and which bears a series of distinctive mineralized teeth called the major lateral teeth. While some chiton species deposit only iron biominerals in these teeth, many others deposit both iron and calcium. In this study, the calcium biomineral in the teeth of one of the latter types of species, the Australian east-coast chiton, Chiton pelliserpentis, has been isolated and examined for the first time. Spectroscopic and crystallographic techniques have identified the biomineral as a carbonate-substituted apatite with significant fluoride substitution also likely. Fourier-transform infrared and laser Raman spectroscopy indicated that the carbonate content was less than that of either bovine tibia cortical bone or human tooth enamel. X-ray diffraction analysis showed the biomineral to be poorly crystalline due to small crystal size and appreciable anionic substitution. The lattice parameters were calculated to be a=9.382?Å and c=6.883?Å, which are suggestive of a fluorapatite material. It is postulated that structural and biochemical differences in the tooth organic matrix of different chiton species will ultimately determine if the teeth become partly calcified or iron mineralized only. 相似文献
17.
Reactions (25 °C) of galactose oxidase, GOase ox from Fusarium NRRL 2903 with five different primary-alcohol-containing substrates RCH 2OH:- D-galactose ( I) and 2-deoxy- d-galactose ( II) (monosaccharides); methyl-β- d-galactopyranoside ( III) (glycoside); d-raffinose ( IV) (trisaccharide); and dihydroxyacetone ( V) have been studied in the presence of O 2. The GOase ox state has a tyrosyl radical coordinated at a square-pyramidal Cu II active site, and is a two-equivalent oxidant. Reactant concentrations were [GOase ox] (0.8–10 μM), RCH 2OH (1.0–6.0 mM), and O 2 (0.14–0.29 mM), with I=0.100 M (NaCl). The reactions, monitored at 450 nm by stopped-flow spectrophotometry, terminated with depletion of the O 2. Each trace was fitted to the competing reactions GOase ox+RCH 2 OH → GOase redH 2+RCHO ( k
1), and GOase redH 2+O 2→ GOase ox+H 2O 2 ( k
2), with GOase redH 2 written as the doubly protonated two-electron-reduced Cu I product. It was necessary to avoid auto-redox interconversion of GOase ox and GOase semi . Information obtained at pH 7.5 indicates a 5 : 95 (ox : semi) "native" mix equilibration complete in ∼3 h. At pH >7.5,
rate constants 10 –4 k
1 / M –1 s –1 for the reactions of GOase ox with ( I) (1.19), ( II) (1.07), ( III) (1.29), ( IV) (1.81), ( V) (2.94) were determined. On decreasing the pH to 5.5, k
1 values decreased by factors of up to a half, and acid dissociation p K
as in the range 6.6–6.9 were obtained. UV-Vis spectrophotometric studies on GOase ox gave an independently determined p K
a of 6.7. No corresponding reactions of the Tyr495Phe variant were observed, and there are no similar UV-Vis absorbance changes
for this variant. The p K
a is therefore assigned to protonation of Tyr-495 which is a ligand to the Cu. The rate constant k
2 (1.01×10 7 M –1 s –1) is independent of pH in the range 5.5–9.0 investigated, suggesting that H + (or H-atoms) for the O 2 → H 2O 2 change are provided by the active site of GOase red . The Cu I of GOase red is less extensively complexed, and a coordination number of three is likely.
Received: 4 February 1997 / Accepted: 16 May 1997 相似文献
18.
The formation of hydroxysulphate green rust 2, a Fe(II-III) compound commonly found during corrosion processes of iron-based materials in seawater, has not yet been reported in bacterial cultures. Here we used Shewanella putrefaciens, a dissimilatory iron-reducing bacterium to anaerobically catalyze the transformation of a ferric oxyhydroxide, lepidocrocite (γ-FeOOH), into Fe(II) in the presence of various sulphate concentrations. Biotransformation assays of γ-FeOOH were performed with formate as the electron donor under a variety of concentrations. The results showed that the competitive formation of hydroxycarbonate green rust 1 (GR1(CO 3 2?)) and hydroxysulphate green rust 2 (GR2(SO 4 2 ?)) depended upon the relative ratio ( R) of bicarbonate and sulphate concentrations. When R ≥ 0.17, GR1(CO 3 2 ?) only was formed whereas when R < 0.17, a mixture of GR2(SO 4 2 ?) and GR1(CO 3 2 ?) was obtained. These results demonstrated that the hydroxysulphate GR2 can originate from the microbial reduction of γ-FeOOH and confirmed the preference for carbonate over sulphate during green rust precipitation. The solid phases were characterized by X-ray diffraction, transmission Mössbauer spectroscopy and scanning electron microscopy. Diffuse reflectance infrared Fourier transform spectroscopy confirmed the presence of intercalated carbonate and sulphate in green rust's structure. This study sheds light on the influence of dissimilatory iron-reducing bacteria on microbiologically influenced corrosion. 相似文献
19.
The potentially toxic effects of soluble lanthanide (L) ions, although microbially induced mineralization can facilitate the
formation of tractable materials, has been one factor preventing the more widespread use of L-ions in biotechnology. Here,
we propose a new mixed-L precursor method as compared to the traditional direct addition technique. L (Nd, Gd, Tb, Ho and
Er)-substituted magnetites, L
y
Fe 3 − y
O 4 were microbially produced using L-mixed precursors, L
x
Fe 1 − x
OOH, where x = 0.01–0.2. By combining lanthanides into the akaganeite precursor phase, we were able to mitigate some of the toxicity,
enabling the microbial formation of L-substituted magnetites using a metal reducing bacterium, Thermoanaerobacter sp. TOR-39. The employment of L-mixed precursors enabled the microbial formation of L-substituted magnetite, nominal composition
up to L 0.06Fe 2.94O 4, with at least tenfold higher L-concentration than could be obtained when the lanthanides were added as soluble salts. This
mixed-precursor method can be used to extend the application of microbially produced L-substituted magnetite, while also mitigating
their toxicity. 相似文献
20.
This study examined the effect of mild hypobaria (MH) on the peak oxygen consumption (O 2peak) and performance of ten trained male athletes [ (SEM); O 2peak = 72.4 (2.2) ml · kg −1 · min −1] and ten trained female athletes [O 2peak = 60.8 (2.1) ml · kg −1 · min −1]. Subjects performed 5-min maximal work tests on a cycle ergometer within a hypobaric chamber at both normobaria (N, 99.33
kPa) and at MH (92.66 kPa), using a counter-balanced design. MH was equivalent to 580 m altitude. O 2peak at MH decreased significantly compared with N in both men [− 5.9 (0.9)%] and women [− 3.7 (1.0)%]. Performance (total kJ)
at MH was also reduced significantly in men [− 3.6 (0.8)%] and women [− 3.8 (1.2)%]. Arterial oxyhaemoglobin saturation (S aO 2) at O 2peak was significantly lower at MH compared with N in both men [90.1 (0.6)% versus 92.0 (0.6)%] and women [89.7 (3.1)% versus
92.1 (3.0)%]. While S aO 2 at O 2peak was not different between men and women, it was concluded that relative, rather than absolute, O 2peak may be a more appropriate predictor of exercise-induced hypoxaemia. For men and women, it was calculated that 67–76% of the
decrease in O 2peak could be accounted for by a decrease in O 2 delivery, which indicates that reduced O 2 tension at mild altitude (580 m) leads to impairment of exercise performance in a maximal work bout lasting ≈ 5 min.
Accepted: 30 July 1996 相似文献
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