Kinetic study of sulfide leaching by galvanic interaction between chalcopyrite, pyrite, and sphalerite in the presence of T. ferrooxidans (30 degrees C) and a thermophilic microorganism (55 degrees C)

A systematic, kinetic study and comparison of the leaching of mixed metal sulfides by galvanic conversion and in the presence of bacteria has been carried out for the first time using both powder (-100 to -400 mesh) and larger (bulk) specimen systems. The rates of dissolution of copper from chalcopyrite and zinc from sphalerite as single, electrically isolated (separate) systems were compared with electrically contacting (galvanically coupled) systems involving CuFeS(2)/FeS(2) and ZnS/FeS(2), with and without bacteria and at temperatures of 30 and 55 degrees C. The dissolution of Cu was observed to increase by a factor of 4.6 when the galvanic leaching of CuFeS(2)/FeS(2) was compared to CuFeS(2) leaching at 30 degrees C. When bacteria were present, Cu dissolution increased by an additional factor of 2.1 in the CuFeS(2)/FeS(2) system. At 55 degrees C, the corresponding ratios for Cu were 4.3 and 2.7, respectively. The galvanic leaching of Zn in the ZnS/FeS(2) system compared to ZnS leaching increased by a factor of 2 at 30 degrees C; in the presence of bacteria the dissolution of Zn from the ZnS/FeS(2) system increased by an additional factor of 1.3 at the same temperature. By comparison, the ratio of Cu dissolution from CuFeS(2) in acid-bacterial medium and sterile controls (without bacteria) was 5.5. The corresponding ratio for Zn from ZnS was 2.2 at both 30 and 55 degrees C. The order of reaction was found to be essentially first order for the leaching of powder systems at both 30 and 55 degrees C (with T. Ferrooxidans and thermophilic microorganisms, respectively). The corresponding reaction rate constants were observed to be 12.6 and 22.9 for T. ferrooxidans and the thermophilic microorganisms, respectively. Activation energies for the various systems were also determined.     

A new look at microbial leaching patterns on sulfide minerals

Leaching patterns on sulfide minerals were investigated by high-resolution scanning electron microscopy (SEM). Our goal was to evaluate the relative contributions of inorganic surface reactions and reactions localized by attached cells to surface morphology evolution. Experiments utilized pyrite (FeS(2)), marcasite (FeS(2)) and arsenopyrite (FeAsS), and two iron-oxidizing prokaryotes in order to determine the importance of cell type, crystal structure, and mineral dissolution rate in microbially induced pit formation. Pyrite surfaces were reacted with the iron-oxidizing bacterium Acidithiobacillus ferrooxidans (at 25 degrees C), the iron-oxidizing archaeon 'Ferroplasma acidarmanus' (at 37 degrees C), and abiotically in the presence of Fe(3+) ions. In all three experiments, discrete bacillus-sized (1-2 μm) and -shaped (elliptical) pits developed on pyrite surfaces within 1 week of reaction. Results show that attaching cells are not necessary for pit formation on pyrite. Marcasite and arsenopyrite surfaces were reacted with A. ferrooxidans (at 25 degrees C) and 'F. acidarmanus' (at 37 degrees C). Cell-sized and cell-shaped dissolution pits were not observed on marcasite or arsenopyrite at any point during reaction with A. ferrooxidans, or on marcasite surfaces reacted with 'F. acidarmanus'. However, individual 'F. acidarmanus' cells were found within individual shallow (<0.5 μm deep) pits. The size and shape (round rather than elliptical) of the pits conformed closely to the shape of F. acidarmanus (cells) pits on arsenopyrite. We infer these pits to be cell-induced. We attribute the formation of pits readily detectable (by SEM) to the higher reactivity of arsenopyrite compared to pyrite and marcasite under the conditions the experiment was conducted. These pits contributed little to the overall surface topographical evolution, and most likely did not significantly increase surface area during reaction. Our results suggest that overall sulfide mineral dissolution may be dominated by surface reactions with Fe(3+) rather than by reactions at the cell-mineral interface.     

Chalcopyrite concentrate leaching with biologically produced ferric sulphate

Biological ferric iron production was combined with ferric sulphate leaching of chalcopyrite concentrate and the effects of pH, Fe3+, temperature and solids concentration on the leaching were studied. The copper leaching rates were similar at pH of 1.0-1.8 and in the presence of 7-90 g L-1 Fe3+ despite massive iron precipitation with 90 g L-1 Fe3+. Increase of the leaching temperature from 50 degrees C to 86 degrees C and solids concentration from 1% to 10% increased the copper leaching rate. Increase in solids concentration from 1% to 10% decreased the copper yields from 80% to 40%. Stepwise addition of ferric iron did not improve the copper yields. CuFeS2, Ag and Cu1.96S potentials indicated the formation of a passivating layer, which consisted of jarosite and sulphur precipitates and which was responsible for the decreased leaching rates.     

Biooxidation capacity of the extremely thermoacidophilic archaeon metallosphaera sedula under bioenergetic challenge

The biooxidation capacity of an extremely thermoacidophilic archaeon Metallosphaera sedula (DSMZ 5348) was examined under bioenergetic challenges imparted by thermal or chemical stress in regard to its potential use in microbial bioleaching processes. Within the normal growth temperature range of M. sedula (70-79 degrees C) at pH 2.0, upward temperature shifts resulted in bioleaching rates that followed an Arrhenius-like dependence. When the cells were subjected to supraoptimal temperatures through gradual thermal acclimation at 81 degrees C (Han et al., 1997), cell densities were reduced but 3 to 5 times faster specific leaching rates (Fe3+ released from iron pyrite/cell/h) could be achieved by the stressed cells compared to cells at 79 degrees C and 73 degrees C, respectively. The respiration capacity of M. sedula growing at 74 degrees C was challenged by poisoning the cells with uncouplers to generate chemical stress. When the protonophore 2,4-dinitrophenol (5-10 μM) was added to a growing culture of M. sedula on iron pyrite, there was little effect on specific leaching rates compared to a culture with no protonophore at 74 degrees C; 25 μM levels proved to be toxic to M. sedula. However, a significant stimulation in specific rate was observed when the cells were subjected to 1 μM nigericin (+135%) and 2 μM (+63%); 5 μM levels of the ionophore completely arrested cell growth. The ionophore effect was further investigated in continuous culture growing on ferrous sulfate at 74 degrees C. When 1 μM nigericin was added as a pulse to a continuous culture, a 30% increase in specific iron oxidation rate was observed for short intervals, indicating a potential positive impact on leaching when periodic chemical stress is applied. This study suggests that biooxidation rates can be increased by strategic exposure of extreme thermoacidophiles to chemical or thermal stress, and this approach should be considered for improving process performance. Copyright 1998 John Wiley & Sons, Inc.     

Phosphate ester hydrolysis is catalyzed by a bacterial transferrin: potential implications for in vivo iron transport mechanisms

Two synergistic anions, p-nitrophenyl phosphate ester (NPP) and SO(4)(2-), were found to form new stable assemblies with Fe(3+) and a bacterial transferrin, FbpA (FbpA=ferric binding protein). Fe(3+)FbpA-SO(4) undergoes rapid anion exchange in the presence of NPP to form Fe(3+)FbpA-NPP. Formation of Fe(3+)FbpA-NPP was found to accelerate the rate of hydrolysis of the bound phosphate ester (k(hyd)=1.6 x 10(-6) s(-1) at 25 degrees C and pH 6.5) by >10(3) fold over the uncatalyzed reaction. These findings suggest a dual function for FbpA in vivo: transport of Fe(3+) across the periplasmic space to the inner membrane in certain gram-negative bacteria and hydrolysis of periplasmic polyphosphates.     

Mineral and iron oxidation at low temperatures by pure and mixed cultures of acidophilic microorganisms

An enrichment culture from a boreal sulfide mine environment containing a low-grade polymetallic ore was tested in column bioreactors for simulation of low temperature heap leaching. PCR-denaturing gradient gel electrophoresis and 16S rRNA gene sequencing revealed the enrichment culture contained an Acidithiobacillus ferrooxidans strain with high 16S rRNA gene similarity to the psychrotolerant strain SS3 and a mesophilic Leptospirillum ferrooxidans strain. As the mixed culture contained a strain that was within a clade with SS3, we used the SS3 pure culture to compare leaching rates with the At. ferrooxidans type strain in stirred tank reactors for mineral sulfide dissolution at various temperatures. The psychrotolerant strain SS3 catalyzed pyrite, pyrite/arsenopyrite, and chalcopyrite concentrate leaching. The rates were lower at 5 degrees C than at 30 degrees C, despite that all the available iron was in the oxidized form in the presence of At. ferrooxidans SS3. This suggests that although efficient At. ferrooxidans SS3 mediated biological oxidation of ferrous iron occurred, chemical oxidation of the sulfide minerals by ferric iron was rate limiting. In the column reactors, the leaching rates were much less affected by low temperatures than in the stirred tank reactors. A factor for the relatively high rates of mineral oxidation at 7 degrees C is that ferric iron remained in the soluble phase whereas, at 21 degrees C the ferric iron precipitated. Temperature gradient analysis of ferrous iron oxidation by this enrichment culture demonstrated two temperature optima for ferrous iron oxidation and that the mixed culture was capable of ferrous iron oxidation at 5 degrees C.     

Volatilization of mercury under acidic conditions from mercury-polluted soil by a mercury-resistant Acidithiobacillus ferrooxidans SUG 2-2.

Volatilization of mercury under acidic conditions from soil polluted with mercuric chloride (1.5 mg Hg/kg soil) was studied with resting cells of a mercury-resistant strain, Acidithiobacillus ferrooxidans SUG 2-2. When resting cells of SUG 2-2 (0.01 mg of protein) were incubated for 10 d at 30 degrees C in 20 ml of 1.6 mM sulfuric acid (pH 2.5) with ferrous sulfate (3%) and mercury-polluted soil (1 g), which contained 7.5 nmol of Hg, approximately 4.1 nmol of mercury was volatilized, indicating that 54% of the total mercury in the soil was volatilized. The amount of mercury volatilized from the soil was dependent on the concentration of Fe2+ added to the medium. When elemental sulfur, sodium tetrathionate, and pyrite were used as an electron donor for the mercury reduction, 16, 2.4 and 0.84%, respectively, of the total mercury added to the solution were volatilized. The optimum pH and temperature for mercury volatilization were 2.5 and 30 degrees C. Approximately 92% of the total mercury in a salt solution (pH 2.5) with resting cells of SUG 2-2 (0.01 mg of protein), ferrous sulfate (3%) and mercury-polluted soil (1 g) was volatilized by further addition of both resting cells and Fe2+ and by incubating for 30 d at 30 degrees C.     

Relative contributions of biological and chemical reactions to the overall rate of pyrite oxidation at temperatures between 30 degrees C and 70 degrees C

The stoichiometry and kinetics of the spontaneous, chemical reaction between pyrite and ferric iron was studied at 30, 45, and 70 degrees C in shake flasks at pH 1.5 by monitoring the ferrous iron, total iron, elemental sulfur, and sulfate concentration profiles in time. It was found that the sulfur moiety of pyrite was oxidized completely to sulfate. Elemental sulfur was not produced in detectable amounts. The iron moiety of pyrite was released as ferrous iron. All observed initial reaction rates could be fitted into an empirical equation. This equation includes the concentrations of ferric iron and pyrite, and a constant which is dependent on the temperature and the nature of the main anion present. It was observed that ferrous iron formed during the reaction slowed down the oxidation of pyrite by ferric iron. The extent of this effect decreased with increasing temperature. With the aid of the empirical equation, the contribution of the chemical oxidation of pyrite by ferric iron to the overall oxidation in a hypothetical plug-flow reactor, in which biologically mediated oxdidation of pyrite and ferrous iron by oxygen also takes place, can be assessed. At 30, 45, and 70 degrees C, respectively, 2, 8-17, and 43% of the pyrite was oxidized chemically by ferric iron. Therefore, it is expected that only in reactors operating at high temperatures with extremely thermophilic bacteria, will chemical oxidation cause a significant deviation from the apparent first order overall kinetics of biological pyrite oxidation.     

Growth models of the continuous bacterial leaching of iron pyrite by Thiobacillus ferrooxidans

The leaching of iron pyrite by Thiobacillus ferrooxidans was studied in a continuous stirred tank reactor at a variety of dilution rates (0.012-0.22 h(-1)), pyrite surface areas (18-194 m(2)/L), and inlet soluble substrate (Fe(2+)) concentrations (0-3000 ppm). The bacterial leaching rate was found to increase with increasing pyrite surface area, dilution rate, and inlet Fe(2+) concentration. The concentration of bacteria in solution was related to the concentration of bacteria attached to the pyrite surface by a Langmuir-type adsorption-desorption relation. Fitting the experimental data to this relation yielded a value for the area occupied per bacterium of 86 mum(2). This result is consistent with the concept of preferential bacterial attachment of certain sites on the solid. A bacterial growth model was developed that included both bacterial growth in solution and growth of bacteria attached to the pyrite surface. The specific growth rate of the attached bacteria was calculated from this model and was found to increase with increasing solid dilution rate and to decrease with increasing pyrite surface area and soluble substance concentration. An explanation of these results based on an active-inactive site mechanisms was also developed.     

The effect of temperature on the continuous ferrous-iron oxidation kinetics of a predominantly Leptospirillum ferrooxidans culture.

The ferrous-iron oxidation kinetics of a bacterial culture consisting predominantly of Leptospirillum ferrooxidans were studied in continuous-flow bioreactors. The bacterial culture was fed with a salts solution containing 12 g/L ferrous-iron, at dilution rates ranging from 0.01 to 0.06 l/h, and temperatures ranging from 30 to 40 degrees C, at a pH of 1.75. The growth rate, and the oxygen and ferrous-iron utilization rates of the bacteria, were monitored by means of off-gas analysis and redox-potential measurement. The degree-of-reduction balance was used to compare the theoretical and experimental values of r(CO(2)), -r(O(2)) and -r(Fe(+2)), and the correlation found to be good. The maximum bacterial yield on ferrous-iron and the maintenance coefficient on ferrous-iron, were determined using the Pirt equation. An increase in the temperature from 30 to 40 degrees C did not appear to have an effect on either the maximum yield or maintenance coefficient on ferrous-iron. The average maximum bacterial yield and maintenance coefficient on ferrous-iron were found to be 0.0059 mmol C/mmol Fe(2+) and 0.7970 mmol Fe(2+)/mmol C)/h, respectively. The maximum specific growth rate was found to be 0.077 l/h. The maximum specific ferrous-iron utilization rate increased from 8.65 to 13.58 mmol Fe(2+)/mmol C/h across the range from 30 to 40 degrees C, and could be described using the Arrhenius equation. The kinetic constant in bacterial ferrous-iron oxidation increased linearly with increasing temperature. The ferrous-iron kinetics could be accurately described in terms of the ferric/ferrous-iron ratio by means of a Michaelis-Menten-based model modified to account for the effect of temperature. A threshold ferrous-iron level, below which no further ferrous-iron utilization occurred, was found at a ferric/ferrous-iron ratio of about 2500. At an overall iron concentration of 12 g/L, this value corresponds to a threshold ferrous-iron concentration of 78.5 x10(-3) mM.     

Reaction intermediates and single turnover rate constants for the oxidation of heme by human heme oxygenase-1

Heme oxygenase converts heme to biliverdin, iron, and CO in a reaction with two established intermediates, alpha-meso-hydroxyheme and verdoheme. Transient kinetic studies show that the conversion of Fe(3+)-heme to Fe(3+)-verdoheme is biphasic. Electron transfer to the heme (0.11 s(-1) at 4 degrees C and 0.49 s(-1) at 25 degrees C) followed by rapid O(2) binding yields the ferrous dioxy complex. Transfer of an electron (0.056 s(-1) at 4 degrees C and 0.21 s(-1) at 25 degrees C) to this complex triggers the formation of alpha-meso-hydroxyheme and its subsequent O(2)-dependent fragmentation to Fe(3+)-verdoheme. The conversion of Fe(3+)-verdoheme to Fe(3+)-biliverdin is also biphasic. Thus, reduction of Fe(3+) to Fe(2+)-verdoheme (0.15 s(-1) at 4 degrees C and 0.55 s(-1) at 25 degrees C) followed by O(2) binding and an electron transfer produces Fe(3+)-biliverdin (0.025 s(-1) at 4 degrees C and 0.10 s(-1) at 25 degrees C). The conversion of Fe(3+)-biliverdin to free biliverdin is triphasic. Reduction of Fe(3+)-biliverdin (0.035 s(-1) at 4 degrees C and 0.15 s(-1) at 25 degrees C), followed by rapid release of Fe(2+) (0.19 s(-1) at 4 degrees C and 0.39 s(-1) at 25 degrees C), yields the biliverdin-enzyme complex from which biliverdin slowly dissociates (0.007 s(-1) at 4 degrees C and 0.03 s(-1) at 25 degrees C). The rate of Fe(2+) release agrees with the rate of Fe(3+)-biliverdin reduction. Fe(2+) release clearly precedes biliverdin dissociation. In the absence of biliverdin reductase, biliverdin release is the rate-limiting step, but in its presence biliverdin release is accelerated and the overall rate of heme degradation is limited by the conversion of Fe(2+)-verdoheme to the Fe(3+)-biliverdin.     

Mechanism of Bacterial Pyrite Oxidation

The oxidation by Ferrobacillus ferrooxidans of untreated pyrite (FeS(2)) as well as HCl-pretreated pyrite (from which most of the acid-soluble iron species were removed) was studied manometrically. Oxygen uptake was linear during bacterial oxidation of untreated pyrite, whereas with HCl-pretreated pyrite both a decrease in oxygen uptake at 2 hr and nonlinear oxygen consumption were observed. Ferric sulfate added to HCl-pretreated pyrite restored approximately two-thirds of the decrease in total bacterial oxygen uptake and caused oxygen uptake to revert to nearly linear kinetics. Ferric sulfate also oxidized pyrite in the absence of bacteria and O(2); recovery of ferric and ferrous ions was in excellent agreement with the reaction Fe(2)(SO(4))(3) + FeS(2) = 3FeSO(4) + 2S, but the elemental sulfur produced was negligible. Neither H(2)S nor S(2)O(3) (2-) was a product of the reaction. It is probable that two mechanisms of bacterial pyrite oxidation operate concurrently: the direct contact mechanism which requires physical contact between bacteria and pyrite particles for biological pyrite oxidation, and the indirect contact mechanism according to which the bacteria oxidize ferrous ions to the ferric state, thereby regenerating the ferric ions required for chemical oxidation of pyrite.     

Identification and characterization of a novel ferric reductase from the hyperthermophilic Archaeon Archaeoglobus fulgidus

Archaeoglobus fulgidus, a hyperthermophilic sulfate-reducing Archaeon, contains high Fe(3+)-EDTA reductase activity in its soluble protein fraction. The corresponding enzyme, which constitutes about 0.75% of the soluble protein, was purified 175-fold to homogeneity. Based on SDS-polyacrylamide gel electrophoresis, the ferric reductase consists of a single subunit with a M(r) of 18,000. The M(r) of the native enzyme was determined by size exclusion chromatography to be 40,000 suggesting that the native ferric reductase is a homodimer. The enzyme uses both NADH and NADPH as electron donors to reduce Fe(3+)-EDTA. Other Fe(3+) complexes and dichlorophenolindophenol serve as alternative electron acceptors, but uncomplexed Fe(3+) is not utilized. The purified enzyme strictly requires FMN or FAD as a catalytic intermediate for Fe(3+) reduction. Ferric reductase also reduces FMN and FAD, but not riboflavin, with NAD(P)H which classifies the enzyme as a NAD(P)H:flavin oxidoreductase. The enzyme exhibits a temperature optimum of 88 degrees C. When incubated at 85 degrees C, the enzyme activity half-life was 2 h. N-terminal sequence analysis of the purified ferric reductase resulted in the identification of the hypothetical gene, AF0830, of the A. fulgidus genomic sequence. The A. fulgidus ferric reductase shares amino acid sequence similarity with a family of NAD(P)H:FMN oxidoreductases but not with any ferric reductases suggesting that the A. fulgidus ferric reductase is a novel enzyme.     

Pyrite formation in marshes during early diagenesis

Pyrite was removed from peat cores by draining the sediments and allowing the pyrite to oxidize. Then the peat cores were placed back into intertidal salt marsh sediments to incubate. Pyrite accumulated rapidly in peat incubated in situ. A greater accumulation of pyrite was observed in peat that contained living grass than peat in which the grass had been killed.

Resin‐imbedded samples of peat from nearby sediments showed that small single crystals of pyrite were abundant, supporting the idea that pyrite in marshes forms rapidly through direct precipitation. Pyrite was also observed filling vascular channels in roots. It had been proposed that pyrite fills root channels in freshwater environments where the primary sulfur source used by sulfate‐reducing bacteria is organic sulfur rather than sulfate. The widespread occurrence of pyrite filling vascular channels in salt marsh peat makes it unlikely that pyrite morphology can be used to infer the salinity of the overlying water.

Marsh sediments are characterized by higher carbon/sulfur ratios and pyritization (Fe‐pyritel(Fe‐pyrite + Fe‐HCl)) indices than marine subtidal sediments. Within wide ranges these indices do not seem to be very sensitive to salinity of flooding water or carbon concentrations in sediments. Oxidation and iron availability appear to be the major controls on pyrite accumulation in marshes. While pyrite concentrations in submerged sediments can be used as indicators of relative rates of sulfate reduction, sulfur storage in intertidal marsh sediments is not as tightly linked to this microbial process.     

Kinetics of iron oxidation by Leptospirillum ferriphilum dominated culture at pH below one

The kinetics of ferrous iron oxidation by Leptospirillum ferriphilum (L. ferriphilum) dominated culture was studied in the concentration range of 0.1-20 g Fe(2+)/L and the effect of ferric iron (0-60 g Fe(3+)/L) on Fe(2+) oxidation was investigated at pH below one. Denaturing gradient gel electrophoresis of PCR amplified 16S rRNA genes followed by partial sequencing confirmed that the bacterial community was dominated by L. ferriphilum. In batch assays, Fe(2+) oxidation started without lag phase and the oxidation was completed within 1 to 60 h depending on the initial Fe(2+) concentration. The specific Fe(2+) oxidation rates increased up to around 4 g/L and started to decrease at above 4 g/L. This implies substrate inhibition of Fe(2+) oxidation at higher concentrations. Haldane equation fitted the experimental data reasonably well (R(2) = 0.90). The maximum specific oxidation rate (q(m)) was 2.4 mg/mg VS . h, and the values of the half saturation (K(s)) and self inhibition constants (K(i)) were 413 and 8,650 mg/L, respectively. Fe(2+) oxidation was competitively inhibited by Fe(3+) and the competitive inhibition constant (K(ii)) was 830 mg/L. The time required to reach threshold Fe(2+) concentration was around 1 day and 2.3 days with initial Fe(3+) concentration of 5 and 60 g/L, respectively. The threshold Fe(2+) concentration, below which no further Fe(2+) oxidation occurred, linearly increased with increasing initial Fe(2+) and Fe(3+) concentrations. Fe(2+) oxidation proceeds by L. ferriphilum dominated culture at pH below 1 even in the presence of 60 g Fe(3+)/L. This indicates potential of using and biologically regenerating concentrated Fe(3+) sulfate solutions required, for example, in indirect tank leaching of ore concentrates.     

Bioleaching of pyrite by acidophilic thermophile Acidianus brierleyi

The kinetics of bioleaching of pyrite (FeS(2)) by the acidophilic thermophilic bacterium Acidianus brierleyi was studied in a well-mixed batch reactor. Experiments were done at 65 degrees C and pH 1.5 on adsorption of A. brierleyi onto pyrite particles, liquid-phase oxidation of ferrous iron by A. brierleyi, and microbial leaching of pyrite. The adsorption of A. brierleyi was a fast process; equilibrium was attained within the first 30 min of exposure to pyrite. The adsorption equilibrium data were well correlated with the Langmuir isotherm. The oxidation of ferrous iron was markedly accelerated in the presence of A. brierleyi, and the growth yield on ferrous iron was determined. The bioleaching of pyrite by A. brierleyi was found to take place with a direct attack by adsorbed cells on the surface of pyrite, the chemical leaching of pyrite by ferric iron being insignificant. Rate data collected under a wide variety of operating variables were analyzed to determine kinetic and stoichiometric parameters for the microbial pyrite leaching. The specific growth rate on pyrite for A. brierleyi was about four times that for the mesophilic bacterium, Thiobacillus ferrooxidans, whereas the growth yields on pyrite for the two microbes were approximately equal to one another in magnitude. A comparison of A. brierleyi with T. ferrooxidans for pyrite leachability demonstrated the thermophile to be much more effective. (c) 1995 John Wiley & Sons, Inc.     

Cross-bridge kinetics modeled from myoplasmic [Ca2+] and LV pressure at 17 degrees C and after 37 degrees C and 17 degrees C ischemia

We modeled changes in contractile element kinetics derived from the cyclic relationship between myoplasmic [Ca(2+)], measured by indo 1 fluorescence, and left ventricular pressure (LVP). We estimated model rate constants of the Ca(2+) affinity for troponin C (TnC) on actin (A) filament (TnCA) and actin and myosin (M) cross-bridge (A x M) cycling in intact guinea pig hearts during baseline 37 degrees C perfusion and evaluated changes at 1) 20 min 17 degrees C pressure, 2) 30-min reperfusion (RP) after 30-min 37 degrees C global ischemia during 37 degrees C RP, and 3) 30-min RP after 240-min 17 degrees C global ischemia during 37 degrees C RP. At 17 degrees C perfusion versus 37 degrees C perfusion, the model predicted: A x M binding was less sensitive; A x M dissociation was slower; Ca(2+) was less likely to bind to TnCA with A x M present; and Ca(2+) and TnCA binding was less sensitive in the absence of A x M. Model results were consistent with a cold-induced fall in heart rate from 260 beats/min (37 degrees C) to 33 beats/min (17 degrees C), increased diastolic LVP, and increased phasic Ca(2+). On RP after 37 degrees C ischemia vs. 37 degrees C perfusion, the model predicted the following: A x M binding was less sensitive; A x M dissociation was slower; and Ca(2+) was less likely to bind to TnCA in the absence of A. M. Model results were consistent with reduced myofilament responsiveness to [Ca(2+)] and diastolic contracture on 37 degrees C RP. In contrast, after cold ischemia versus 37 degrees C perfusion, A x M association and dissociation rates, and Ca(2+) and TnCA association rates, returned to preischemic values, whereas the dissociation rate of Ca(2+) from A x M was ninefold faster. This cardiac muscle kinetic model predicted a better-restored relationship between Ca(2+) and cross-bridge function on RP after an eightfold longer period of 17 degrees C than 37 degrees C ischemia.     

An electrochemical method of measuring the oxidation rate of ferrous to ferric iron with oxygen in the presence of Thiobacillus ferrooxidans

The oxidation of Fe(2+) with oxygen in sulfate solutions was studied in the presence of T. ferrooxidans. To measure the chemical activity of bacteria, and the oxidation rate of iron, the redox potentials of solutions were continuously monitored during the experiments. The redox potentials were simultaneously monitored on the platinum and pyrite indicator electrodes. The redox potential versus time curves were further used to calculate the basic kinetic parameters, such as the reaction orders, the activation energy, and the frequency factor. It was found that under atmospheric conditions, and at Fe(2+) < 0.001M, T < 25 degrees C, and at pH above 2.2, the oxidation of iron is governed by the following rate expression: \documentclass{article}\pagestyle{empty}\begin{document}$$ - \frac{{d[{\rm Fe};{2 + }]}}{{dt}} = 1.62 \times 10;{11} C_{{\rm bact}} [{\rm H}; + ][{\rm Fe};{2 + }]p{\rm O}_2 e;{ - (58.77/RT)} $$\end{document} Below pH = 2.2, the oxidation rate is independent of H(+) Concentration.     

Bacterial sensors based on Acidithiobacillus ferrooxidans Part I. Fe2+ and S2O32- determination

An amperometric bacterial sensor with current response to Fe(2+) and S(2)O(3)(2-) ions has been designed by immobilizing an acidophilic biomass of Acidithiobacillus ferrooxidans on a multi disk flat-front oxygen probe. The bacterial layer was located between the oxygen probe and a membrane of cellulose. A filtration technique was used to yield the bacterial membranes having reproducible activity. The decrease of O(2) flow across the bacterial layer is proportional to the concentration of the dosed species. The dynamic range appeared to be linear for the Fe(2+) ions up to 2.5 mmol L(-1) with a detection limit of 9 x 10(-7) mol L(-1) and a sensitivity of 0.25 A L mol(-1). The response of the biosensor is 84 s for a determination of 2 x 10(-4) mol L(-1) Fe(2+). Optimizing the Fe(2+) determination by A. ferrooxidans sensor was carried out owing to Design of Experiments (DOE) methodology and empirical modelling. The optimal response was thus obtained for a pH of 3.4, at 35 degrees C under 290 rpm solution stirring. S(2)O(3)(2-) concentration was determined at pH 4.7, so avoiding its decomposition. The concentration range was linear up to 0.6 mmol L(-1). Sensitivity was 0.20 A L mol(-1) with a response time of 207 s for a 2 x 10(-4) mol L(-1) S(2)O(3)(2-) concentration.     

High-rate ferric sulfate generation by a Leptospirillum ferriphilum-dominated biofilm and the role of jarosite in biomass retention in a fluidized-bed reactor

The aims of this work were to develop a high-rate fluidized-bed bioprocess for ferric sulfate production, to characterize biomass retention, and to determine the phylogeny of the enrichment culture. After 7 months of continuous enrichment and air aeration at 37 degrees C, the iron oxidation rate of 8.2 g Fe(2+) L(-1)h(-1) (4.5.10(-12) g Fe(2+) cell(-1) h(-1)) was obtained at a hydraulic retention time (HRT) of 0.6 h. However, oxygen supply became the rate-limiting factor. With gas mixture (99.5% O(2)/0.5% CO(2) (vol/vol)) aeration and HRT of 0.2 h, the iron oxidation rate was 26.4 g Fe(2+) L(-1)h(-1) (1.0.10(-11) g Fe(2+) cell(-1) h(-1)). Leptospirillum sp. was predominant in the mesophilic fluidized-bed reactor (FBR) enrichment culture as determined by fluorescent in situ hybridization, while Acidithiobacillus ferrooxidans was not detected. Denaturing gradient gel electrophoresis (DGGE) of the amplified partial 16S rDNA showed only three bands, indicating a simple microbial community. DGGE fragment excision and sequencing showed that the populations were related to L. ferriphilum (100% similarity in sequence) and possibly to the genus Ferroplasma (96% similarity to F. acidiphilum). Jarosite precipitates accumulated on the top of the activated carbon biomass carrier material, increasing the rate of iron oxidation. The activated carbon carrier material, jarosite precipitates, and reactor liquid contained 59% (or 3.71.10(9) cells g(-1)), 31% (or 3.12.10(10) cells g(-1)) and 10% (or 1.24.10(8) cells mL(-1)) of the total FBR microbes, respectively, demonstrating that the jarosite precipitates played an important role in the FBR biomass retention.