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1.
Growth Kinetics of Thiobacillus ferrooxidans Isolated from Arsenic Mine Drainage 总被引:6,自引:5,他引:1
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Thiobacillus ferrooxidans is found in many Alaskan and Canadian drainages contaminated by metals dissolved from placer and lode gold mines. We have examined the iron-limited growth and iron oxidation kinetics of a T. ferrooxidans isolate, AK1, by using batch and continuous cultures. Strain AK1 is an arsenic-tolerant isolate obtained from placer gold mine drainage containing large amounts of dissolved arsenic. The steady-state growth kinetics are described with equations modified for threshold ferrous iron concentrations. The maximal specific growth rate (μmax) for isolate AK1 at 22.5°C was 0.070 h−1, and the ferrous iron concentration at which the half-maximal growth rate occurred (Kμ) was 0.78 mM. Cell yields varied inversely with growth rate. The iron oxidation kinetics of this organism were dependent on biomass. We found no evidence of ferric inhibition of ferrous iron oxidation for ferrous iron concentrations between 9.0 and 23.3 mM. A supplement to the ferrous medium of 2.67 mM sodium arsenite did not result in an increased steady-state biomass, nor did it appear to affect the steady-state growth kinetics observed in continuous cultures. 相似文献
2.
Abdel Gaffar Elhag Said Toshio Murashige 《In vitro cellular & developmental biology. Plant》1979,15(8):593-602
Summary Initial trials with tomato-root cultures disclosed the desirability of employing a gently agitated liquid medium containing
iron in the chelated form. For the normal cultivars “Ace” and “Tropic”, subcultures were best achieved by utilizing sectors
that possessed one or more newly emerged laterals. Continuous cultures of a nonlateral-forming tomato mutant, “Diageotropica”,
and of citron were accomplished by subculturing tips of the elongating primary roots. The tomato roots were cultured in White's
medium with the Fe2(SO4)3 replaced by 0.03 mM NaFeEDTA. Sustained growth of citron-root tips necessitated the use of a medium containing Murashige
and Skoog salts, 7.5% sucrose, 100 mg per I each of citric acid and thiamine HCl, and 5000 mg per li-inositol. The success with citron-root cultures was extendable to all cultivars ofC. medica L., but not to otherCitrus species relatives. Both citron and “Diageotropica” root cultures manifested undiminished elongation through repeated subcultures;
but neither produced laterals in response to any cultural treatments.
Research was supported in part by National Science Foundation Grant OIP75-10390 and Elvenia J. Slosson Fellowship in Ornamental
Horticulture. 相似文献
3.
Enrichment-based methods targeted at uranium-tolerant populations among the culturable, aerobic, chemo-heterotrophic bacteria
from the subsurface soils of Domiasiat (India’s largest sandstone-type uranium deposits, containing an average ore grade of
0.1 % U3O8), indicated a wide occurrence of Serratia marcescens. Five representative S. marcescens isolates were characterized by a polyphasic taxonomic approach. The phylogenetic analyses of 16S rRNA gene sequences showed
their relatedness to S. marcescens ATCC 13880 (≥99.4% similarity). Biochemical characteristics and random amplified polymorphic DNA profiles revealed significant
differences among the representative isolates and the type strain as well. The minimum inhibitory concentration for uranium
U(VI) exhibited by these natural isolates was found to range from 3.5–4.0 mM. On evaluation for their uranyl adsorption properties,
it was found that all these isolates were able to remove nearly 90–92% (21–22 mg/L) and 60–70% (285–335 mg/L) of U(VI) on
being challenged with 100 μM (23.8 mg/L) and 2 mM (476 mg/L) uranyl nitrate solutions, respectively, at pH 3.5 within 10 min
of exposure. his capacity was retained by the isolates even after 24 h of incubation. Viability tests confirmed the tolerance
of these isolates to toxic concentrations of soluble uranium U(VI) at pH 3.5. This is among the first studies to report uranium-tolerant
aerobic chemoheterotrophs obtained from the pristine uranium ore-bearing site of Domiasiat. 相似文献
4.
The speciation of a particular element in any given matrix is a prerequisite to understanding its solubility and leaching properties. In this context, speciation of uranium in lanthanum zirconate pyrochlore (La2Zr2O7 = LZO), prepared by a low‐temperature combustion route, was carried out using a simple photoluminescence lifetime technique. The LZO matrix is considered to be a potential ceramic host for fixing nuclear and actinide waste products generated during the nuclear fuel cycle. Special emphasis has been given to understanding the dynamics of the uranium species in the host as a function of annealing temperature and concentration. It was found that, in the LZO host, uranium is stabilized as the commonly encountered uranyl species (UO22+) up to a heat treatment of 500 °C at the surface. Above 500 °C, the uranyl ion is diffused into the matrix as the more symmetric octahedral uranate species (UO66–). The uranate ions thus formed replace the six‐coordinated ‘Zr’ atoms at regular lattice positions. Further, it was observed that concentration quenching takes place beyond 5 mol% of uranium doping. The mechanism of the quenching was found to be a multipolar interaction. Copyright © 2016 John Wiley & Sons, Ltd. 相似文献
5.
The ferrous iron oxidation kinetics of Thiobacillus ferrooxidans in batch cultures was examined, using on-line off-gas analyses to measure the oxygen and carbon dioxide consumption rates
continuously. A cell suspension from continuous cultures at steady state was used as the inoculum. It was observed that a
dynamic phase occurred in the initial phase of the experiment. In this phase the bacterial ferrous iron oxidation and growth
were uncoupled. After about 16 h the bacteria were adapted and achieved a pseudo-steady state, in which the specific growth
rate and oxygen consumption rate were coupled and their relationship was described by the Pirt equation. In pseudo-steady
state, the growth and oxidation kinetics were accurately described by the rate equation for competitive product inhibition.
Bacterial substrate consumption is regarded as the primary process, which is described by the equation for competitive product
inhibition. Subsequently the kinetic equation for the specific growth rate, μ, is derived by applying the Pirt equation for bacterial substrate consumption and growth. The maximum specific growth rate,
μ
max, measured in the batch culture agrees with the dilution rate at which washout occurs in continuous cultures. The maximum
oxygen consumption rate, q
O2,max, of the cell suspension in the batch culture was determined by respiration measurements in a biological oxygen monitor at
excess ferrous iron, and showed changes of up to 20% during the course of the experiment. The kinetic constants determined
in the batch culture slightly differ from those in continuous cultures, such that, at equal ferric to ferrous iron concentration
ratios, biomass-specific rates are up to 1.3 times higher in continuous cultures.
Received: 8 February 1999 / Accepted: 17 February 1999 相似文献
6.
Four growth regulators incorporated into Murashige and Skoog's basal medium were tested for their effect on the rate of tillering
ofLolium multiforum plantlets in culture. Tillering was stimulated in the presence of 1–2 mg l−1 6-benzylaminopurine, but 1 mg l−1 gave less plantlet distortion and the tillers could be separated easily. Small shoot tips were considered to be best for
establishing aseptic cultures for propagation, but individual tillers were best for transferring to the tiller inducing medium,
both initially and at subculturing. Tillering rate was affected by culture vessel, temperature and light intensity. Of the
variations tested, the optimum conditions were to culture whole tillers onto a medium containing 1 mg l−1 BAP in 30-ml universal tubes at 20°C with continuous white fluorescent light at 12,000 lx for 4–5 weeks. Rates in excess
of 40 tillers per month were obtained in culture compared with 5–12 in the glasshouse. 相似文献
7.
Z.T. Xing J.H. Cheng Q. Tan Y.J. Pan 《World journal of microbiology & biotechnology》2006,22(8):799-806
Summary Extracellular laccase in cultures of Grifola frondosa grown in liquid culture on a defined medium was first detectable in the early/middle stages of primary growth, and enzyme activity continued to increase even after fungal biomass production had peaked. Laccase production was significantly increased by supplementing cultures with 100–500 (M Cu over the basal level (1.6 mM Cu) and peak levels observed at 300 mM Cu were ∼
∼7-fold higher than in unsupplemented controls. Decreased laccase activity similar to levels detected in unsupplemented controls, as well as an adverse effect on fungal growth, occurred with further supplementation up to and including 0.9 mM Cu, but higher enzyme titres (2- to 16-fold compared with controls) were induced in cultures supplemented with 1–2 mM Cu2+. SDS-PAGE combined with activity staining revealed the presence of a single protein band (M
r ∼
∼70 kDa) exhibiting laccase activity in control culture fluids, whereas an additional distinct second laccase protein band (M
r␣∼
∼45 kDa) was observed in cultures supplemented with 1–2 mM Cu. Increased levels of extracellular laccase activity, and both laccase isozymes, were also detected in cultures of G. frondosa supplemented with ferulic, vanillic, veratric and 4-hydroxybenzoic acids, and 4-hydroxybenzaldehyde. The optimal temperature and pH values for laccase activity were 65 °C and pH 2.2 (using 2,2′-azinobis(3-ethylbenzthiazoline-6-sulfonate) {ABTS} as substrate), respectively, and the enzyme was relatively heat stable. In solid-state cultures of G. frondosa grown under conditions adopted for industrial-scale mushroom production, extracellular laccase levels increased during the substrate colonization phase, peaked when the substrate was fully colonized, and then decreased sharply during fruit body development. 相似文献
8.
Abundance and structure of the communities of neutrophilic lithotrophic iron-oxidizing bacteria (FeOB) inhabiting four low-mineralized
ferruginous springs of the Marcial Waters Resort (South Karelia, Russia) and the brackish chalybeate spring of the Staraya
Russa Resort (Novgorod region, Russia), were investigated, as well as the physicochemical conditions of these environments.
In fresh iron-containing precipitates collected near the spring outlets and within the spring-discharge areas, as well as
along the spring watercourses, the numbers of unicellular FeOB enumerated on nutrient media ranged from 105 to 107 cells per 1 mL of sediments irrespective of the initial Fe(II) concentration (11–126 mg L−1). In the spring waters and along the spring watercourses inhabited by iron-oxidizing bacteria, the concentration of dissolved
oxygen did not exceed 0.05–0.1 mg L−1. Unicellular FeOB were predominant in three springs, while in the springs with relatively low Fe(II) concentrations (11–22
mg L−1), various morphological forms of Gallionella and uncultured forms of the iron-oxidizing bacterium Toxothrix trichogenes prevailed. In the model experiments with the water samples collected in the ferruginous springs and bogs under controlled
conditions, the fractionation of stable iron isotopes and the rate of iron oxidation were found to depend on the oxygen regime
and, to a lesser extent, on the initial Fe(II) concentration. The maximum enrichment of the iron oxides formed during the
simulation experiments with the light 54Fe isotope was observed during bacterial oxidation under microaerobic conditions at O2 concentrations of 0.1–0.3 mg L−1 and in the cultures of iron-oxidizing bacteria. During the abiogenic oxidation of Fe(II), the extent of stable isotope fractionation
was 1.5–2 times lower. Enrichment of Fe(III) oxides with the light 54Fe isotope (3- to 5-fold) was considerably lower at high rates of both the biogenic and abiogenic processes of iron oxidation
under aerobic conditions; however, it was more intense during the bacterial processes. Comparison of the rates of enrichment
of Fe(III) oxides with the light isotope during the model experiments with pure and enrichment cultures of iron-oxidizing
bacteria from the sediments of ferruginous springs and bogs revealed that the biogenic factor plays a key role in the oxidation
processes of the iron cycle, as well as in the differentiation of the composition of stable iron isotopes in the studied ecosystems. 相似文献
9.
Jiangxia Li Jun Zhang Steven L. Larson John H. Ballard Kai Guo Zikri Arslan 《International journal of phytoremediation》2019,21(12):1197-1204
AbstractElectrokinetic-enhanced phytoremediation is an effective technology to decontaminate heavy metal contaminated soil. In this study, we examined the effects of electrokinetic treatments on plant uptake and bioaccumulation of U from soils with various U sources. Redistribution of uranium in soils as affected by planting and electrokinetic treatments was investigated. The soil was spiked with 100?mg kg–1 UO2, UO3, and UO2(NO3)2. After sunflower and Indian mustard grew for 60 days, 1 voltage of direct-current was applied across the soils for 9 days. The results indicated that U uptake in both plants were significantly enhanced by electrokinetic treatments from soil with UO3 and UO2(NO3)2. U was more accumulated in roots than in shoots. Electrokinetic treatments were effective on lowering soil pH near the anode region. Overall, uranium (U) removal efficiency reached 3.4–4.3% from soils with UO3 and uranyl with both plants while that from soil with UO2 was 0.7–0.8%. Electrokinetic remediation treatment significantly enhanced the U removal efficiency (5–6%) from soils with UO3 and uranyl but it was 0.8–1.3% from soil with UO2, indicating significant effects of U species and electrokinetic enhancement on U bioaccumulation. This study implies the potential feasibility of electrokinetic-enhanced phytoremediation of U soils with sunflower and Indian mustard. 相似文献
10.
The kinetics of continuous oxidation of ferrous iron by immobilized cells of Thiobacillus ferrooxidans was studied in a packed-bed bioreactor. Polyurethane foam biomass support particles were used as carriers for cell immobilization.
Effects of ferrous iron concentration and its volumetric loading on the kinetics of the reaction were investigated. Media
containing different concentrations of ferrous iron in the range 5–20 kg m-3 were tested. For each medium the kinetics of the reaction at different volumetric loadings of ferrous iron, at a constant
temperature of 30°C, were determined. With media containing 5 kg m-3 and 10 kg m-3 Fe2+, the fastest oxidation rates of 34.25 kg m-3 h-1 and 32 kg m-3 h-1 were achieved at a dilution rate of around 6 h-1, which represents a residence time of 10 min. Employing a higher concentration of ferrous iron (20 kg m-3) in the medium resulted in lower oxidation rates, with a maximum value of 10 kg m-3 h-1, indicating an inhibitory effect of ferrous iron on growth and activity of T. ferrooxidans. The reliable performance of the bioreactor during the course of the experiments confirmed the suitability of polyurethane
foam biomass support particles as carriers for T. ferrooxidans immobilization.
Received: 5 December 1995/Received revision: 21 April 1996/Accepted: 29 April 1996 相似文献
11.
Anaerobic and aerobic oxidation of ferrous iron at neutral pH by chemoheterotrophic nitrate-reducing bacteria 总被引:11,自引:0,他引:11
Nine out of ten anaerobic enrichment cultures inoculated with sediment samples from various freshwater, brackish-water, and
marine sediments exhibited ferrous iron oxidation in mineral media with nitrate and an organic cosubstrate at pH 7.2 and 30° C.
Anaerobic nitrate-dependent ferrous iron oxidation was a biological process. One strain isolated from brackish-water sediment
(strain HidR2, a motile, nonsporeforming, gram-negative rod) was chosen for further investigation of ferrous iron oxidation
in the presence of acetate as cosubstrate. Strain HidR2 oxidized between 0.7 and 4.9 mM ferrous iron aerobically and anaerobically
at pH 7.2 and 30° C in the presence of small amounts of acetate (between 0.2 and 1.1 mM). The strain gained energy for growth
from anaerobic ferrous iron oxidation with nitrate, and the ratio of iron oxidized to acetate provided was constant at limiting
acetate supply. The ability to oxidize ferrous iron anaerobically with nitrate at approximately pH 7 appears to be a widespread
capacity among mesophilic denitrifying bacteria. Since nitrate-dependent iron oxidation closes the iron cycle within the anoxic
zone of sediments and aerobic iron oxidation enhances the reoxidation of ferrous to ferric iron in the oxic zone, both processes
increase the importance of iron as a transient electron carrier in the turnover of organic matter in natural sediments.
Received: 24 April 1997 / Accepted: 22 September 1997 相似文献
12.
《Inorganica chimica acta》1986,119(2):227-232
Interaction between D-glucuronic acid and hydrated uranyl salts has been studied in aqueous solution and solid complexes of the type UO2(D- glucuronate)X·2H20 and UO2(D-glucuronate)2·2H2O, where X = CI−, Br− or NO3−, are isolated and characterized by means of FT-IR and proton-NMR spectroscopy.On comparison with the structurally identified Ca(D-glucuronate)Br·3H2O compound, it is concluded that the UO22+ cation binds to two D- glucuronate moieties in uranylsugar complexes via O6, O5 oxygen atoms (ionized carboxyl group) of the first and O6′, 04 (non-ionized carboxyl group) of the second sugar moiety, whereas in the UO2(D- glucuronate)2·2H2O salt the uranyl ion is bonded to two sugar anions through O6, O6′ oxygen atoms of the ionized carboxyl group, resulting in a six- coordination geometry around the uranium ion. The strong intermolecular hydrogen bonding network of the free acid is rearranged upon sugar metalation and the sugar moiety showed β-anomer conformation both in the free acid and in these uranylsugar complexes. 相似文献
13.
Gonzalez-Contreras P Weijma J Buisman CJ 《Applied microbiology and biotechnology》2012,93(3):1295-1303
The extreme acid conditions required for scorodite (FeAsO4·2H2O) biomineralization (pH below 1.3) are suboptimal for growth of most thermoacidophilic Archaea. With the objective to develop
a continuous process suitable for biomineral production, this research focuses on growth kinetics of thermoacidophilic Archaea
at low pH conditions. Ferrous iron oxidation rates were determined in batch-cultures at pH 1.3 and a temperature of 75°C for
Acidianus sulfidivorans, Metallosphaera prunea and a mixed Sulfolobus culture. Ferrous iron and CO2 in air were added as sole energy and carbon source. The highest growth rate (0.066 h−1) was found with the mixed Sulfolobus culture. Therefore, this culture was selected for further experiments. Growth was not stimulated by increase of the CO2 concentration or by addition of sulphur as an additional energy source. In a CSTR operated at the suboptimal pH of 1.1, the
maximum specific growth rate of the mixed culture was 0.022 h−1, with ferrous iron oxidation rates of 1.5 g L−1 d−1. Compared to pH 1.3, growth rates were strongly reduced but the ferrous iron oxidation rate remained unaffected. Influent
ferrous iron concentrations above 6 g L−1 caused instability of Fe2+ oxidation, probably due to product (Fe3+) inhibition. Ferric-containing, nano-sized precipitates of K-jarosite were found on the cell surface. Continuous cultivation
stimulated the formation of an exopolysaccharide-like substance. This indicates that biofilm formation may provide a means
of biomass retention. Our findings showed that stable continuous cultivation of a mixed iron-oxidizing culture is feasible
at the extreme conditions required for continuous biomineral formation. 相似文献
14.
The biodegradation of tributyl phosphate (Bu3-P, TBP), releasing phosphate at a high enough concentration locally to precipitate uranium from solution, was demonstrated
by a mixed culture consisting primarily of pseudomonads. The effect of various parameters on Bu3-P biodegradation by growing cells is described. Growth at the expense of Bu3-P as the carbon and phosphorus source occurred over a pH range from 6.5 to 8, and optimally at pH 7. Bu3-P biodegradation was optimal at 30 °C, reduced at 20 °C and negligible at 4 °C and 37 °C. Incorporation of Cu or Cd inhibited,
and Ni, Co and Mn reduced its degradation. Inorganic phosphate (above 10 mM) and kerosene (up to 1 g/l) reduced Bu3-P biodegradation significantly, but nitrate had no effect. Sulphate (10–100 mM) was inhibitory. When pregrown biomass was used
the fastest rates of tributyl and dibutyl phosphate biodegradation were 25 μmol h−1 mg protein−1 and 37 μmol h−1 mg protein−1 respectively. Microcarrier-immobilised biomass decontaminated uranium-bearing acid mine waste water by uranium phosphate
precipitation at the expense of Bu3-P hydrolysis in the presence of 35 mM SO4
2−. At pH 4.5, 79% of the UO2
2+ was removed at a flow rate of 1.4 ml/h on a 7-ml test column.
Received: 2 June 1997 / Received revision: 15 September 1997 / Accepted: 19 September 1997 相似文献
15.
Extracellular laccase in cultures of Grifola frondosa grown in liquid culture on a defined medium was first detectable in the early/middle stages of primary growth, and enzyme activity continued to increase even after fungal biomass production had peaked. Laccase production was significantly increased by supplementing cultures with 100–500 μM Cu over the basal level (1.6 μM Cu) and peak levels observed at 300 μM Cu were 7-fold higher than in unsupplemented controls. Decreased laccase activity similar to levels detected in unsupplemented controls, as well as an adverse effect on fungal growth, occurred with further supplementation up to and including 0.9 mM Cu, but higher enzyme titres (2- to 16-fold compared with controls) were induced in cultures supplemented with 1–2 mM Cu2+. SDS-PAGE combined with activity staining revealed the presence of a single protein band (M
r 70 kDa) exhibiting laccase activity in control culture fluids, whereas an additional distinct laccase protein band (M
r 45 kDa) was observed in cultures supplemented with 1–2 mM Cu. Increased levels of extracellular laccase activity, and both laccase isozymes, were also detected in cultures of G. frondosa supplemented with ferulic, vanillic, veratric and 4-hydroxybenzoic acids, and 4-hydroxybenzaldehyde. Using 2,2′-azino-bis(ethylbenzothiazoline-6-sulfonate) (ABTS) as substrate, the optimal temperature and pH values for laccase activity were 65°C and pH 2.2, respectively, and the enzyme was relatively heat stable. In solid-state cultures of G. frondosa grown under conditions adopted for industrial-scale mushroom production, extracellular laccase levels increased during the substrate colonization phase, peaked when the substrate was fully colonized, and then decreased sharply during fruit body development. 相似文献
16.
Soluble ammonia monooxygenase (AMO) from Nitrosomonas
europaea was purified to homogeneity and metals in the active sites of the enzyme (Cu, Fe) were analyzed by electron paramagnetic
resonance (EPR) spectroscopy. EPR spectra were obtained for a type 2 Cu(II) site with g|| = 2.24, A|| = 18.4 mT and g⊥ = 2.057 as well as for heme and non heme iron present in purified soluble AMO from N. europaea. A second type 2 Cu(II) EPR signal with g|| = 2.29, A|| = 16.1 mT and g⊥ = 2.03 appeared in the spectrum of the ferricyanide oxidized enzyme and was attributed to oxidation of cuprous sites. Comparison
of EPR-detectable Cu2+ with total copper determined by inductively coupled plasma-mass spectrometry (ICP-MS) suggests that there are six paramagnetic
Cu2+ and three diamagnetic Cu1+ per heterotrimeric soluble AMO (two paramagnetic and one diamagnetic Cu per αβγ-protomer). A trigonal EPR signal at g = 6.01,
caused by a high-spin iron, indicative for cytochrome bound iron, and a rhombic signal at g = 4.31, characteristic of specifically
bound Fe3+ was detectable. The binding of nitric oxide in the presence of reductant resulted in a ferrous S = 3/2 signal, characteristic
of a ferrous nitrosyl complex. Inactivation of soluble AMO with acetylene did neither diminish the ferrous signal nor the
intensity of the Cu2+-EPR signal. 相似文献
17.
《Luminescence》2002,17(5):293-298
The reaction of the tetravalent uranium [U(IV)] with dimethyldioxirane (DMD) in strongly acidic water–acetone solutions is accompanied by chemiluminescence (CL) in the visible (Vis) and infra‐red (IR) regions. At least three independent reaction pathways are involved in the U(IV)–DMD oxidation: the first entails the non‐chemiluminescent oxidation of U(IV) to the uranyl ion (UO22+); the second involves the catalytic decomposition of DMD by U(IV) to afford singlet oxygen, as manifested by its characteristic IR‐CL; and in the third process, slow Vis‐CL (510–540 nm) is emitted, following DMD consumption. Copyright © 2002 John Wiley & Sons, Ltd. 相似文献
18.
Benzoylhydrazones and semicarbazones derived from 2,6-diacetylpyridine react with common dioxouranium(VI) compounds such as uranyl nitrate or [NBu4]2[UO2Cl4] to form air-stable complexes. 2,6-Diacetylpyridinebis(benzoylhydrazone) (H2L1), 2,6-diacetylpyridinebis(N4-phenylsemicarbazone) (H2L2) and the asymmetric proligand 2,6-diacetylpyridine(benzoylhydrazone)(N4-phenylsemicarbazone) (H2L3) give yellow products of the composition [UO2(L)]. The neutral compounds contain doubly deprotonated ligands and possess uranium atoms with distorted pentagonal-bipyramidal coordination spheres. The equatorial coordination spheres of the metal atoms can be extended by the addition of a monodentate ligand such as pyridine or DMSO. The uranium atoms in the resulting complexes have hexagonal-bipyramidal coordination environments with the oxo ligands in axial positions.X-ray diffraction studies on [UO2(L1)(DMSO)], [UO2(L2)], [UO2(L2)(DMSO)] and [UO2(L3)] show relatively short U-O bonds to the benzoylic oxygen atoms between 2.273(6) and 2.368(5) Å. This suggests a preference of these donor sites of the ligands over their imino and amine functionalities (U-N bond lengths: 2.502(7)-2.671(7) Å). The addition of a sixth ligand to the equatorial coordination sphere results in a lengthening of the metal-pyridine bonds. 相似文献
19.
Acetylene reduction and indoleacetic acid production by Azospirillum isolates from Cactaceous plants
Azospirillum isolates were obtained from rhizosphere soil and roots of three cactaceae species growing under arid conditions.
All Azospirillum isolates from rhizosphere and roots ofStenocereus pruinosus andStenocereus stellatus were identified asA. brasilense; isolates of surface-sterilized roots fromOpuntia ficus-indica were bothA. brasilense andA. lipoferum. Azospirilla per g of fresh root in the three species ranged from 70×103 to 11×103. The most active strains in terms of C2H2 reduction (25–49.6 nmol/h·ml) and indoleacetic acid (IAA) production (36.5–77 μg/ml) were those identified asA. brasilense and isolated from Stenocereus roots.A. lipoferum isolated from Opuntia roots produced low amounts of IAA (6.5–17.5 μg/ml) and low C2H2-reduction activity (17.8–21.2 nmol/h·ml). 相似文献
20.
Due to various activities associated with nuclear industry, uranium is migrated to aquatic environments like groundwater, ponds or oceans. Uranium forms stable carbonate complexes in the oxic waters of pH 7–10 which results in a high degree of uranium mobility. Microorganisms employ various mechanisms which significantly influence the mobility and the speciation of uranium in aquatic environments. Uranyl bioremediation studies, this far, have generally focussed on low pH conditions and related to adsorption of positively charged UO2 2+ onto negatively charged microbial surfaces. Sequestration of anionic uranium species, i.e. [UO2(CO3) 2 2? ] and [UO2(CO3) 3 4? ] onto microbial surfaces has received only scant attention. Marine cyanobacteria are effective metal adsorbents and represent an important sink for metals in aquatic environment. This article addresses the cyanobacterial interactions with toxic metals in general while stressing on uranium. It focusses on the possible mechanisms employed by cyanobacteria to sequester uranium from aqueous solutions above circumneutral pH where negatively charged uranyl carbonate complexes dominate aqueous uranium speciation. The mechanisms demonstrated by cyanobacteria are important components of biogeochemical cycle of uranium and are useful for the development of appropriate strategies, either to recover or remediate uranium from the aquatic environments. 相似文献