SULFATE REQUIREMENT FOR IRON OXIDATION BY THIOBACILLUS FERROOXIDANS

Effects of chloride acclimation on iron oxyhydroxides and cell morphology during cultivation of Acidithiobacillus ferrooxidans

Iron oxyhydroxides as the efficient scavengers for heavy metals have been extensively investigated in iron-rich acid sulfate waters in the presence of Acidithiobacillus ferrooxidans (A. ferrooxidans, an especially important chemolithoautotroph for bioleaching and desulfurization of coal). In this study, we observed the morphology and elemental composition of cells in stationary phase and examined the dynamic variation of iron oxyhydroxides produced in cultures of A. ferrooxidans incubated in modified 9K medium initially including 0.15 M of ferrous iron, in the absence/presence of 0.2 M of chloride (NaCl/FeCl(2)). Results showed that chloride acclimation had little effect on cellular morphology and elemental uptake that was mainly related to culture medium. Furthermore, schwertmannite with the typical morphology of aggregated spheres covered by some "pincushions" was precipitated first in bacterial cultures in the favorable pH range of 2.9 ± 0.1 to 2.6 ± 0.1. Some of schwertmannite could be transformed to lozenge-shaped jarosite, due to a successively decreasing of pH values. However, the jarosite transformation represented a lag period of 5 and 4 days in the chloride-rich cultures with sulfate at a low level, compared to the cultures with sulfate at a high level, which could be attributed to the influence of sulfate requirement and chloride acclimation.

Iron Oxidation and Precipitation of Ferric Hydroxysulfates by Resting Thiobacillus ferrooxidans Cells

The oxidation of ferrous ions, in acid solution, by resting suspensions of Thiobacillus ferrooxidans produced sediments consisting of crystalline jarosites, amorphous ferric hydroxysulfates, or both. These products differed conspicuously in chemical composition and infrared spectra from precipitates formed by abiotic oxidation under similar conditions. The amorphous sediments, produced by bacterial oxidation, exhibited a distinctive fibroporous microstructure when examined by scanning electron microscopy. Infrared spectra indicated outer-sphere coordination of Fe(III) by sulfate ions, as well as inner-sphere coordination by water molecules and bridging hydroxo groups. In the presence of excess sulfate and appropriate monovalent cations, jarosites, instead of amorphous ferric hydroxysulfates, precipitated from bacterially oxidized iron solutions. It is proposed that the jarositic precipitates result from the conversion of outer-sphere (T(d)) sulfate, present in a soluble polymeric Fe(III) complex, to inner-sphere (C(3v)) bridging sulfate. The amorphous precipitates result from the further polymerization of hydroxo-linked iron octahedra and charge stabilized aggregation of the resulting iron complexes in solution. This view was supported by observations that bacterially oxidized iron solutions gave rise to either amorphous or jarositic sediments in response to ionic environments imposed after oxidation had been completed and the bacteria had been removed by filtration.

The Characterization of Salt Tolerance in Biomining Microorganisms and the Search for Novel Salt Tolerant Strains

In this study an acidic saline drain in the Western Australian wheat belt was sampled and enriched for salt tolerant chemolithotrophic microorganisms in acidic media containing up to 100 gL-1 NaCl. A mixed consortium was obtained which grows at pH 1.8 and oxidises iron (II) in the presence of up to 30 gL-1 NaCl. In comparative tests (growth rates and iron (II) oxidation rates) it was found that NaCl concentrations >3.5 gL-1 generally cause reduced growth and iron (II) oxidation rates in known biomining organisms. The results help to set a benchmark for NaCl tolerance in known biomining microorganisms and will lead to the generation of a consortium of microorganisms that can oxidise iron (II) effectively in saline process water.

Influence of chloride and sulfate on formation of akaganéite and schwertmannite through ferrous biooxidation by Acidithiobacillus ferrooxidans cells

Iron (oxyhydr)oxides play important roles in the fixation of toxic elements and also in the distribution of nutrients for plants in soils. Akaganéite and schwertmannite, as the iron oxyhydroxides having an analogous tunnel structure, have been widely recognized in Fe-rich environments. The objective of this study was to examine the formation of akaganéite/ schwertmannite via biooxidation of 0.1 M of ferrous solution containing only Cl-, SO4(2-) or both the anions with a Cl-/SO4(2-) mole ratio of 1, 3, 6, and 10 by chloride-acclimated Acidithiobacillus ferrooxidans cells. Results showed that ferrous iron in chloride/sulfate-containing solutions could be easily biooxidized to ferric iron, and subsequent Fe(III)-hydrolysis/precipitation could result in the formation of large quantity of akaganéite/schwertmannite precipitates. The resulting precipitates were identified to be the pure akaganéite (Fe8O8(OH)7.1(Cl)0.9, the pure schwertmannite (Fe8O8(OH)4.42(SO4)1.79, and the main schwertmannite phase (Fe8O8(OH)(8-2x)(SO4)x, with 1.09 < or = x < or = 1.73), respectively, under different Cl-/SO4(2-) mole ratio conditions. Obviously, sulfate inhibited drastically the bioformation of akaganéite but facilitated schwertmannite phase occurrence in the ferrous solution containing both sulfate and chloride. However, the presence of chloride ion in initial ferrous solution containing sulfate and Acidithiobacillus ferrooxidans cells would affect the morphology and other characteristics of schwertmannite generated.

Biosynthesis of nanocrystal akaganéite from FeCl2 solution oxidized by Acidithiobacillus ferrooxidans cells

Akaganéite (beta-FeOOH) is a major iron oxyhydroxide component in some soils, marine concretions, and acid mine drainage environments. Recently, synthetic beta-FeOOH has been found to be a promising absorbent in the treatment of metal-contaminated water. It has been recognized in previous study that akaganéite could be formed via FeCl2 chemical oxidation under specific conditions. Here we report a novel and simple method for akaganéite bioformation from FeCl2 solution oxidized by Acidithiobacillus ferrooxidans LX5 cells at 28 degrees C. After acclimation in modified 9K medium containing 0.2 M chloride, Acidithiobacillus ferrooxidans cells had great potential for oxidization of Fe2+ as FeCl2 solution, and then resulted in the formation of precipitates. The resulting precipitates were identified by powder X-ray diffraction and transmission FT-IR analyses to be akaganéite. Scanning electron microscopy images showed the akaganéite was spindle-shaped, approximately 200 nm long with an axial ratio of about 5, and the spindles had a rough surface. X-ray energy-dispersive spectral analyses indicated the chemical formula of the crystalloid akaganéite could be expressed as Fe8O8(OH)7.1(Cl)0.9 with Fe/Cl molar ratio of 8.93. The biogenetic akaganéite had a specific surface area of about 100 m2 g(-1) determined by BET method.

Microbial leaching of metals from sulfide minerals

Microorganisms are important in metal recovery from ores, particularly sulfide ores. Copper, zinc, gold, etc. can be recovered from sulfide ores by microbial leaching. Mineral solubilization is achieved both by 'direct (contact) leaching' by bacteria and by 'indirect leaching' by ferric iron (Fe(3+)) that is regenerated from ferrous iron (Fe(2+)) by bacterial oxidation. Thiobacillus ferrooxidans is the most studied organism in microbial leaching, but other iron- or sulfide/sulfur-oxidizing bacteria as well as archaea are potential microbial agents for metal leaching at high temperature or low pH environment. Oxidation of iron or sulfur can be selectively controlled leading to solubilization of desired metals leaving undesired metals (e.g., Fe) behind. Microbial contribution is obvious even in electrochemistry of galvanic interactions between minerals.

Selective inhibition of the oxidation of ferrous iron or sulfur in Thiobacillus ferrooxidans

The oxidation of either ferrous iron or sulfur by Thiobacillus ferrooxidans was selectively inhibited or controlled by various anions, inhibitors, and osmotic pressure. Iron oxidation was more sensitive than sulfur oxidation to inhibition by chloride, phosphate, and nitrate at low concentrations (below 0.1 M) and also to inhibition by azide and cyanide. Sulfur oxidation was more sensitive than iron oxidation to the inhibitory effect of high osmotic pressure. These differences were evident not only between iron oxidation by iron-grown cells and sulfur oxidation by sulfur-grown cells but also between the iron and sulfur oxidation activities of the same iron-grown cells. Growth experiments with ferrous iron or sulfur as an oxidizable substrate confirmed the higher sensitivity of iron oxidation to inhibition by phosphate, chloride, azide, and cyanide. Sulfur oxidation was actually stimulated by 50 mM phosphate or chloride. Leaching of Fe and Zn from pyrite (FeS(2)) and sphalerite (ZnS) by T. ferrooxidans was differentially affected by phosphate and chloride, which inhibited the solubilization of Fe without significantly affecting the solubilization of Zn.

ENERGY SUPPLY FOR THE CHEMOAUTOTROPH FERROBACILLUS FERROOXIDANS

Dugan, Patrick R. (Syracuse University, Syracuse, N.Y.), and Donald G. Lundgren. Energy supply for the chemoautotroph Ferrobacillus ferrooxidans. J. Bacteriol. 89:825-834. 1965.-A working model is proposed to explain dissimilatory ferrous iron oxidation by Ferrobacillus ferrooxidans, that is, oxidation linked to an energy source. The model is supported by experimental evidence reported here as well as in the literature. Polarographic assays of the culture medium demonstrated an iron "complex" involving oxygen. The initial "complex" would be oxygenated, but not oxidized because no electron transport has taken place. The "complex" is formed in solution or on the cell surface and is somehow reacted with iron oxidase (or oxygenase), resulting in the release of an electron. Either sulfate or a flavoprotein is suggested as involved in the initial electron-transfer link between iron and the cell. The electron is transported in the cell through a typical electron-transport system involving coenzyme Q(6), cytochrome c, and cytochrome a; oxygen is the final electron acceptor. Electron micrographs of intact and sectioned cells are included to show structural detail in support of the model.

Direct 5S rRNA Assay for Monitoring Mixed-Culture Bioprocesses

This study demonstrates the efficacy of a direct 5S rRNA assay for the characterization of mixed microbial populations by using as an example the bacteria associated with acidic mining environments. The direct 5S rRNA assay described herein represents a nonselective, direct molecular method for monitoring and characterizing the predominant, metabolically active members of a microbial population. The foundation of the assay is high-resolution denaturing gradient gel electrophoresis (DGGE), which is used to separate 5S rRNA species extracted from collected biomass. Separation is based on the unique migration behavior of each 5S rRNA species during electrophoresis in denaturing gradient gels. With mixtures of RNA extracted from laboratory cultures, the upper practical limit for detection in the current experimental system has been estimated to be greater than 15 different species. With this method, the resolution was demonstrated to be effective at least to the species level. The strength of this approach was demonstrated by the ability to discriminate between Thiobacillus ferrooxidans ATCC 19859 and Thiobacillus thiooxidans ATCC 8085, two very closely related species. Migration patterns for the 5S rRNA from members of the genus Thiobacillus were readily distinguishable from those of the genera Acidiphilium and Leptospirillum. In conclusion, the 5S rRNA assay represents a powerful method by which the structure of a microbial population within acidic environments can be assessed.

Molecular aspects of the electron transfer system which participates in the oxidation of ferrous ion by Thiobacillus ferrooxidans

The enzymes and redox proteins, which participate in the oxidation of ferrous ion by the acidophilic iron-oxiding bacterium Thiobacillus ferrooxidans, have been isolated and characterized. They are Fe(II)-cytochrome c oxidoreductase, cytochromes c-552(s), c-552(m) and c-550(m), rusticyanin, and cytochrome c oxidase. On the basis of the interactions of these components, an electron transfer system has been proposed which seems to function in the oxidation of ferrous ion by the bacterium.

Respiratory enzymes of Thiobacillus ferrooxidans. Kinetic properties of an acid-stable iron:rusticyanin oxidoreductase

Rusticyanin is an acid-stable, soluble blue copper protein found in abundance in the periplasmic space of Thiobacillus ferrooxidans, an acidophilic bacterium capable of growing autotrophically on soluble ferrous sulfate. An acid-stable iron:rusticyanin oxidoreductase activity was partially purified from cell-free extracts of T. ferrooxidans. The enzyme-catalyzed, iron-dependent reduction of the rusticyanin exhibited three kinetic properties characteristic of aerobic iron oxidation by whole cells. (i) A survey of 14 different anions indicated that catalysis by the oxidoreductase occurred only in the presence of sulfate or selenate, an anion specificity identical to that of whole cells. (ii) Saturation with both sulfatoiron(II) and the catalyst produced a concentration-independent rate constant of 3 s-1 for the reduction of the rusticyanin, which is an electron transfer reaction sufficiently rapid to account for the flux of electrons through the iron respiratory chain. (iii) Values for the enzyme-catalyzed pseudo-first-order rate constants for the reduction of the rusticyanin showed a hyperbolic dependence on the concentration of sulfatoiron(II) with a half-maximal effect at 300 microM, a value similar to the apparent KM for iron shown by whole cells. On the basis of these favorable comparisons between the behavior patterns of isolated biomolecules and those of whole cells, this iron:rusticyanin oxidoreductase is postulated to be the primary cellular oxidant of ferrous ions in the iron respiratory electron transport chain of T. ferrooxidans.

Two membrane-bound c-type cytochromes of Thiobacillus ferrooxidans: purification and properties

Membrane-bound cytochrome c, cytochrome c-552 (m) was purified from Thiobacillus ferrooxidans. It showed an absorption peak at 410 nm in the oxidized form, and peaks at 552, 523 and 416 nm in the reduced form. Its molecular mass, Em,7 and isoelectric point were 22,300, +0.336 volt and 9.1, respectively. Another membrane-bound cytochrome c, cytochrome c-550 (m) was also purified. It showed an absorption peak at 408 nm in the oxidized form, and peaks at 550, 523 and 418 nm in the reduced form. Its molecular mass was estimated to be 51,000. Ferrocytochromes c-552 (m) and c-550 (m) were oxidized by cytochrome c oxidase of the bacterium. The reactivity with the oxidase of cytochrome c-550 (m) was higher than that of cytochrome c-552 (s) (soluble cytochrome) of the bacterium, while the reactivity of cytochrome c-552 (m) was greatly lower than that of cytochrome c-552 (s).

Kinetics of Iron Oxidation by Thiobacillus ferrooxidans

A statistical relationship between the rate of ferric ion production by a strain of Thiobacillus ferrooxidans and various levels of cell concentration, Fe 2+ concentration, Na + concentration, and temperature was studied by a direct colorimetric method at 304 nm. The relationship was linear (90 to 93%), cross-product (3 to 4%), and quadratic (1 to 2%). The levels of cell concentration and Fe 2+ concentration and their respective interactions with one another and the other factors had the most significant effects on the regression models. The solution of the quadratic response surface for optimum oxidation was a saddle point, and the predicted critical levels of temperature, cell concentration, Fe 2+ concentration, and Na + concentration ranged between −6 and 2°C, 0.43 and 0.62 mg/ml, 72 and 233 mM, and 29.6 mM, respectively.

Sulfate-dependent iron oxidation by Thiobacillus ferrooxidans: characterization of a new EPR detectable electron transport component on the reducing side of rusticyanin

Iron(II) oxidation by pH 2.5 HCl-washed cells of Thiobacillus ferrooxidans is known to be sulfate dependent. Sulfate dependence of the autooxidation of a novel component in the electron transport pathway is demonstrated. This component exhibits an electron paramagnetic resonance (EPR) signal in the oxidized state at g = 2.005 distinguishable from the g = 2.08 signal attributed to rusticyanin. The novel component is proposed to be a three-iron-sulfur cluster based upon the g value, lineshape, and temperature dependence. Oxyanion specificity for the EPR signal has the same dependence on sulfate as does iron(II) oxidation. By using azide to inhibit electron transfer to oxygen, sulfate was shown to be involved in electron transfer from the g = 2.005 component to the copper of rusticyanin.

Use of the respiration activity of Thiobacillus ferrooxidans for the specific determination of iron(II, III)

A method is described for the determination of Fe2+ and Fe3+ after its reduction to Fe2+ on the basis of oxygen uptake rate as a function of Fe2+ concentration. By using substrate-specific Thiobacillus ferrooxidans in combination with the standard addition method a specific determination of iron(II, III) is possible with the determination limit of 3 mumol/L.

The Exclusion of D 2 O from the Hydration Sphere of FeSO 4 · 7H 2 O Oxidized by Thiobacillus ferrooxidans

Infrared spectra demonstrate that neither FeSO(4) . 7H(2)O nor its bacterial or abiotic hydrated oxidation products incorporate deuterium in acid D(2)O solutions. Deuterium exchange occurred as bridging OD when bacterially oxidized iron was precipitated from D(2)O solutions as ferric hydroxysulfates. The exclusion of deuterium depended upon the stabilization of aquated Fe(II) and Fe(III) complexes by sulfate ions in outer-sphere coordination and is consistent with the requirement and postulated role of sulfate in iron oxidation by Thiobacillus ferrooxidans.

Direct method for continuous determination of iron oxidation by autotrophic bacteria

A method for direct, continuous determination of ferric ions produced in autotrophic iron oxidation, which depends upon the measurement of ferric ion absorbance at 304 nm, is described. The use of initial rates is shown to compensate for such changes in extinction during oxidation, which are due to dependence of the extinction coefficient on the ratio of complexing anions to ferric ions. A graphical method and a computer method are given for determination of absolute ferric ion concentration, at any time interval, in reaction mixtures containing Thiobacillus ferrooxidans and ferrous ions at known levels of SO(4) (2+) and hydrogen ion concentrations. Some examples are discussed of the applicability of these methods to study of the rates of ferrous ion oxidation related to sulfate concentration.

Kinetic studies of iron oxidation by whole cells of Ferrobacillus ferrooxidans

A colorimetric assay was developed for studying the kinetics of iron oxidation with whole cells of the chemoautotroph, Ferrobacillus ferrooxidans. The assay was more advantageous than the conventional method of Warburg manometry because of its simplicity, rapidity, and the small amount of cells required. The assay measured Fe(3+) as a chloride complex which absorbs at 410 nm. Kinetic analysis showed the apparent K(m) for iron oxidation to be 5.4 x 10(-3)m in an unbuffered system and 2.2 x 10(-3)m in the presence of beta-alanine-SO(4) (2-) buffer. Glycine and beta-alanine buffers were used in the measurement of the pH optimum for iron oxidation; the optimum ranged from 2.5 to 3.8. The effect of pH was primarily on the V(max) while the K(m) remained constant. Added SO(4) (2-) was found to stimulate iron oxidation by increasing the V(max) of iron oxidation by whole cells, but it did not affect the K(m). Results of assays of iron oxidation in systems containing various mole percentages of SO(4) (2-) and Cl(-) indicated that Cl(-) did not inhibit iron oxidation but that SO(4) (2-) was required. Sulfate could be partially replaced by HPO(4) (2-) and HAsO(4) (2-) but not by BO(3) (-), MoO(4) (2-), NO(3) (-), or Cl(-); formate and MoO(4) (2-) inhibited iron oxidation.

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.

Ferrous iron oxidation by Ferrobacillus ferrooxidans. Purification and properties of Fe++-cytochrome c reductase

The electron transport chain and Fe++-cytochrome c reductase of Ferrobacillus ferrooxidans were studied to elucidate the mechanism of iron oxidation by this autotrophic bacterium.The iron oxidation involved the cytochrome c and a type cytochrome of F. ferrooxidans in the electron transport system. The initial enzyme of the oxidation system was found to be Fe++-cytochrome c reductase. The iron oxidase system was labile to freezing or sonication; either treatment disrupted some link between the cellular cytochromes c and a. Fe++-cytochrome c reductase and cytochrome oxidase retained their individual activities after either treatment.Fe++-cytochrome c reductase was purified 60-fold to 70-fold. The enzyme was judged to be approximately 90% pure by disc electrophoresis, sedimentation, and DEAE-cellulose chromatography. A suitable assay system with a veronal–acetate buffer was developed for the determination of enzyme activity. The effects of inhibitors and potential activators were studied. No specific inhibitor or cofactor was found, although the enzyme was inhibited by various ionic compounds.Fe++-cytochrome c reductase was dissociated into two subunits, one protein and the other ribonucleic acid (RNA). Neither of the subunits had enzymatic activity and efforts to reconstitute the holoenzyme from the two subunits were unsuccessful. The molecular weights of the holoenzyme, protein subunit, and RNA subunit were determined as 100,000–110,000, 27,000–30,000, and 315,000–330,000, respectively. The protein subunit contained one non-heme iron atom per protein molecule. It was concluded that RNA is an essential component of the enzyme and the failure to recover the activity from subunits is due to the aggregation of RNA after dissociation.

Iron oxidation by washed cell suspensions of the chemoautotroph, Thiobacillus ferrooxidans

Experimental variables in the manometric study of iron oxidation by washed cell suspensions of the obligate chemoautotroph Thiobacillus ferrooxidans have been examined. To obtain maximum respiration rates, extremely low cell concentrations (11–15 μg nitrogen) must be used, the substrate level must be between 400 arid 800 μmoles Fe++in the form of ferrous sulfate, and physiologically young cells must be employed. With this procedure, Qo2(N) values range from 19,000 to 22,500, nearly double any previously reported results. Optimum pH and temperature for iron oxidation are 1.75 and 40 C, respectively. Water-soluble vitamins and surfactants have no effect on the rate of respiration, Two basal salts of the growth medium (9K), i.e., potassium chloride and potassium phosphate, inhibit iron oxidation if added individually; however, concurrent addition of all the basal salts stimulates respiration significantly. Addition of small amounts of ferric iron reduces the lag and stimulates iron oxidation, whereas larger quantities inhibit respiration. During the first 5 minutes of exposure of resting cells to ferrous sulfate, ferric iron production is twice the amount predicted on the basis of oxygen consumption. Subsequently, ferric iron production levels off to approximate theoretical calculations.

EFFECT OF PHOSPHATE ION AND 2,4-DINITROPHENOL ON THE ACTIVITY OF INTACT CELLS OF THIOBACILLUS FERROOXIDANS

Beck, Jay V. (Brigham Young University, Provo, Utah), and Fred M. Shafia . Effect of phosphate ion and 2,4-dinitrophenol on the activity of cell suspensions of Thiobacillus ferrooxidans . J. Bacteriol. 88: 850–857. 1964.—The rate of oxidation of ferrous salts or elemental sulfur by aged cell suspensions, phosphate-depleted cells, or 2,4-dinitrophenol (DNP)-treated cells of Thiobacillus ferrooxidans was increased by addition of orthophosphate salts. The effect was found to be transitory, with the rate gradually approaching that observed prior to phosphate ion addition. The total increased oxygen uptake was observed to be roughly proportional to the amount of phosphate salt added. The efficiency of CO 2 fixation accompanying oxidation of ferrous salts was found to be about 1.7 μmoles of CO 2 fixed per 100 μmoles of O 2 absorbed, in contrast to a value of about 8.0 μmoles of CO 2 fixed per 100 μmoles of O 2 uptake during sulfur oxidation. The rate of oxidation did not affect the CO 2 fixation efficiency. Whereas addition of phosphate salts to aged or phosphate-depleted cells increased slightly the already high efficiency of CO 2 fixation, it did not affect the complete inhibition of CO 2 fixation observed in the presence of 10 -5 m DNP. The results indicate that the phosphate ion is essential for oxidation of the ferrous ion, and that dinitrophenol and other so-called upcoupling agents interfere with phosphate metabolism. The latter may be a result of action at the site of assimilation of the ferrous ion or it may be an effect on the electron-transport system. In any event, it seems obvious that the phosphate ion is converted into a nonactive form in the presence of dinitrophenol-treated cells, because additional quantities of orthophosphate salts cause an immediate, marked restoration of oxidative activity.

Leaching of Chalcopyrite with Thiobacillus ferrooxidans : Effect of Surfactants and Shaking

The rate of leaching of chalcopyrite by Thiobacillus ferrooxidans has been greatly accelerated by using shaken flasks in place of stationary bottles or percolators. A further increase in rate and extent of leaching was obtained by the use of Tween 20, 40, 60, and 80, Triton X-100, Quaker TT 5386, and Hyamine 2389. Tween 20 was the most effective surfactant. No individual component of the Tween molecule was responsible for the improved leaching. The Tween-to-chalcopyrite ratio is more important than the Tween-to-medium ratio. The effect of the surfactants is probably due to increased contact between the mineral surface and the organism, and shaking provides the necessary oxygen. Rates and yields obtained by use of surfactants and shaking as aids to microbiological leaching approach those obtained with acidified erric sulfate leaching.