Mechanism of pyrite dissolution in the presence of Thiobacillus ferrooxidans

Shifts in the Microbial Populations of Bioleach Reactors Are Determined by Carbon Sources and Temperature

In the present study, the effect of additional carbon sources (carbon dioxide and molasses) on the bio-oxidation of a pyrite-arsenopyrite concentrate at temperatures of 40-50 °C was studied, and novel data regarding the patterns of the bio-oxidation of gold-bearing sulfide concentrates and the composition of the microbial populations performing these processes were obtained. At 40 °C, additional carbon sources did not affect the bio-oxidation efficiency. At the same time, the application of additional carbon dioxide improved the bio-oxidation performance at temperatures of 45 and 50 °C and made it possible to avoid the inhibition of bio-oxidation due to an increase in the temperature. Therefore, the use of additional carbon dioxide may be proposed to prevent the negative effect of an increase in temperature on the bio-oxidation of sulfide concentrates. 16S rRNA gene profiling revealed archaea of the family Thermoplasmataceae (Acidiplasma, Ferroplasma, Cuniculiplasma, and A-plasma group) and bacteria of the genera Leptospirillum, with Sulfobacillus and Acidithiobacillus among the dominant groups in the community. Temperature influenced the composition of the communities to a greater extent than the additional sources of carbon and the mode of operation of the bioreactor. Elevating the temperature from 40 °C to 50 °C resulted in increases in the shares of Acidiplasma and Sulfobacillus and decreases in the relative abundances of Ferroplasma, Leptospirillum, and Acidithiobacillus, while Cuniculiplasma and A-plasma were more abundant at 45 °C. A metagenomic analysis of the studied population made it possible to characterize novel archaea belonging to an uncultivated, poorly-studied group of Thermoplasmatales which potentially plays an important role in the bio-oxidation process. Based on an analysis of the complete genome, we propose describing the novel species and novel genus as "Candidatus Carboxiplasma ferriphilum" gen. nov., spec. nov.

Precipitation of greigite and pyrite induced by Thermococcales: an advantage to live in Fe- and S-rich environments?

Thermococcales, a major order of archaea inhabiting the iron- and sulfur-rich anaerobic parts of hydrothermal deep-sea vents, have been shown to rapidly produce abundant quantities of pyrite FeS₂ in iron-sulfur-rich fluids at 85°C, suggesting that they may contribute to the formation of 'low temperature' FeS₂ in their ecosystem. We show that this process operates in Thermococcus kodakarensis only when zero-valent sulfur is directly available as intracellular sulfur vesicles. Whether in the presence or absence of zero-valent sulfur, significant amounts of Fe₃ S₄ greigite nanocrystals are formed extracellularly. We also show that mineralization of iron sulfides induces massive cell mortality but that concomitantly with the formation of greigite and/or pyrite, a new generation of cells can grow. This phenomenon is observed for Fe concentrations of 5 mM but not higher suggesting that above a threshold in the iron pulse all cells are lysed. We hypothesize that iron sulfides precipitation on former cell materials might induce the release of nutrients in the mineralization medium further used by a fraction of surviving non-mineralized cells allowing production of new alive cells. This suggests that biologically induced mineralization of iron-sulfides could be part of a survival strategy employed by Thermococcales to cope with mineralizing high-temperature hydrothermal environments.

One-Year In Situ Incubation of Pyrite at the Deep Seafloor and Its Microbiological and Biogeochemical Characterizations

In this study, we performed a year-long in situ incubation experiment on a common ferrous sulfide (Fe-S) mineral, pyrite, at the oxidative deep seafloor in the hydrothermal vent field in the Izu-Bonin arc, Japan, and characterized its microbiological and biogeochemical properties to understand the microbial alteration processes of the pyrite, focusing on Fe(II) oxidation. The microbial community analysis of the incubated pyrite showed that the domain Bacteria heavily dominated over Archaea compared with that of the ambient seawater, and Alphaproteobacteria and Gammaproteobacteria distinctively codominated at the class level. The mineralogical characterization by surface-sensitive Fe X-ray absorption near-edge structure (XANES) analysis revealed that specific Fe(III) hydroxides (schwertmannite and ferrihydrite) were locally formed at the pyrite surface as the pyrite alteration products. Based on the Fe(III) hydroxide species and proportion, we thermodynamically calculated the pH value at the pyrite surface to be pH 4.9 to 5.7, indicating that the acidic condition derived from pyrite alteration was locally formed at the surface against neutral ambient seawater. This acidic microenvironment at the pyrite surface might explain the distinct microbial communities found in our pyrite samples. Also, the acidity at the pyrite surface indicates that the abiotic Fe(II) oxidation rate was much limited at the pyrite surface kinetically, 3.9 × 103- to 1.6 × 105-fold lower than that in the ambient seawater. Moreover, nanoscale characterization of microbial biomolecules using carbon near-edge X-ray absorption fine-structure (NEXAFS) analysis showed that the sessile cells attached to pyrite excreted the acidic polysaccharide-rich extracellular polymeric substances at the pyrite surface, which can lead to the promotion of biogenic Fe(II) oxidation and pyrite alteration. IMPORTANCE Pyrite is one of the most common Fe-S minerals found in submarine hydrothermal environments. Previous studies demonstrated that the Fe-S mineral can be a suitable host for Fe(II)-oxidizing microbes in hydrothermal environments; however, the details of microbial Fe(II) oxidation processes with Fe-S mineral alteration are not well known. The spectroscopic and thermodynamic examination in the present study suggests that a moderately acidic pH condition was locally formed at the pyrite surface during pyrite alteration at the seafloor due to proton releases with Fe(II) and sulfidic S oxidations. Following previous studies, the abiotic Fe(II) oxidation rate significantly decreases with a decrease in pH, but the biotic (microbial) Fe(II) oxidation rate is not sensitive to the pH decrease. Thus, our findings clearly suggest that the pyrite surface is a unique microenvironment where abiotic Fe(II) oxidation is limited and biotic Fe(II) oxidation is more prominent than that in neutral ambient seawater.

Bioleaching of iron from laterite soil using an isolated Acidithiobacillus ferrooxidans strain and application of leached laterite iron as Fenton's catalyst in selective herbicide degradation

A novel isolated strain Acidithiobacillus ferrooxidans BMSNITK17 has been investigated for its bioleaching potential from lateritic soil and the results are presented. System conditions like pH, feed mineral particle size, pulp density, temperature, rotor speed influences bioleaching potential of Acidithiobcillus ferrooxidans BMSNITK17 in leaching out iron from laterite soil. Effect of sulfate addition on bioleaching efficiency is studied. The bioleached laterite iron (BLFe's) on evaluation for its catalytic role in Fenton's oxidation for the degradation of ametryn and dicamba exhibits 94.24% of ametryn degradation and 92.45% of dicamba degradation efficiency. Fenton's oxidation performed well with the acidic pH 3. The study confirms the role of Acidithiobacillus ferrooxidans in leaching iron from lateritic ore and the usage of bioleached lateritic iron as catalyst in the Fenton's Oxidation.

Geochemical signatures of lignite mining products in sediments downstream a fluvial-lacustrine system

As a result of the open-cast lignite mining in the Lusatian region of north-eastern Germany, large amounts of iron, sulphate, trace metals, and aluminium are fed into the groundwater and small streams that discharge into the River Spree, which ultimately flows through urban Berlin. In this study, we examined whether the input of these mining products leads to longitudinal gradients in element compositions and mineral formations in the riverine sediments. The signatures of fluvial and interconnected lacustrine sediments along a 190-km flow section were evaluated via principal component analysis to define the impact range of the open-cast products. These products clearly showed a sediment impact range of at least ~90 km downstream of the mining area. In particular, nickel and cobalt readily co-precipitate with iron, while sedimentary sulphur initially increases and therefore shows a longer impact range than amorphous iron oxy-hydroxides. These findings further demonstrate that sulphur and iron have different transport mechanisms. Although sulphate concentrations in the river waters of Berlin are still high, sedimentary iron and sulphur contents at the city border are only slightly higher than at the reference point close to the source of River Spree. The strongly diminished but still present mining signature in urban Berlin is replaced by an urban signature characterised by high levels of zinc, chromium, lead, and copper.

Simultaneously enhance iron/sulfur metabolism in column bioleaching of chalcocite by pyrite and sulfur oxidizers based on joint utilization of waste resource

In chalcocite (Cu₂S) bioleaching, the lack of iron metabolism is a key restricting factor. As the most common sulfide mineral, pyrite (FeS₂) can release Fe(Ⅱ) and compensate for the iron metabolism deficiency in chalcocite bioleaching. The bioleaching of chalcocite in an imitated industrial system was improved by enhancing the iron-sulfur metabolism simultaneously using pyrite and sulfur oxidizers based on the joint utilization of waste resources, while the bioleaching performance and community structure in the leachate were systematically investigated. Due to the active sulfur/iron metabolism, the pH reached 1.2, and Fe³⁺ was increased by 77.78%, while the biomass of planktonic cells was improved to 2.19 × 10⁷ cells/mL. Fourier transform infrared reflection (FTIR) and X-ray diffraction (XRD) analysis results showed that more iron-sulfur crystals were produced due to more active iron-sulfur metabolism. Scanning electron microscopy (SEM) revealed that many derivative particles and corrosion marks appeared on the surface of the ore, implying that the mineral-microbe interaction was strengthened. Confocal laser scanning microscopy (CLSM) showed the accumulation of cells and extracellular polymeric substances (EPS) on the ore surface, indicating a stronger contact leaching mechanism. Furthermore, the community structure and canonical correspondence analysis (CCA) demonstrated that the introduction of sulfur-oxidizing bacteria and pyrite could maintain the diversity of dominant leaching microorganisms at a high level. Sulfobacillus (27.75%) and Leptospirllillum (20.26%) were the dominant sulfur-oxidizing and iron-oxidizing bacteria during the bioleaching process. With the accumulation of multiple positive effects, the copper ion leaching rate was improved by 44.8%. In general, this new type of multiple intervention strategy can provide an important guide for the bioleaching of low-grade ores.

Contributions of Microbial “Contact Leaching” to Pyrite Oxidation under Different Controlled Redox Potentials

The function of microbial contact leaching to pyrite oxidation was investigated by analyzing the differences of residue morphologies, leaching rates, surface products, and microbial consortia under different conditions in this study. This was achieved by novel equipment that can control the redox potential of the solution and isolate pyrite from microbial contact oxidation. The morphology of residues showed that the corrosions were a little bit severer in the presence of attached microbes under 750 mV and 850 mV (vs. SHE). At 650 mV, the oxidation of pyrite was undetectable even in the presence of attached microbes. The pyrite dissolution rate was higher with attached microbes than that without attached microbes at 750 mV and 850 mV. The elemental sulfur on the surface of pyrite residues with sessile microorganisms was much less than that without attached microbes at 750 mV and 850 mV, showing that sessile acidophiles may accelerate pyrite leaching by reducing the elemental sulfur inhibition. Many more sulfur-oxidizers were found in the sessile microbial consortium which also supported the idea. The results suggest that the microbial “contact leaching” to pyrite oxidation is limited and relies on the elimination of elemental sulfur passivation by attached sulfur-oxidizing microbes rather than the contact oxidation by EPS-Fe.

Sources and mixing of sulfate contamination in the water environment of a typical coal mining city, China: evidence from stable isotope characteristics

To explore the sources and distribution characteristics of SO₄^2- in the surface waters of the Linhuan mining area in Huaibei, river and surface water samples in subsidence and mine drainage locations in the study area were collected at different times. The conventional hydrochemical indexes and the eigenvalues of sulfur and oxygen isotopes were tested and analyzed. The results suggested the following: (1) The SO₄^2- content showed seasonal changes: low-flow seasons > mid-flow seasons > high-flow seasons. (2) Based on δ³⁴S_SO4 and δ¹⁸O_SO4 isotope analyses, the main source of SO₄^2- was the dissolution of evaporite salt rocks in the stratum of the upstream area. The SO₄^2- in the subsidence area was mainly from the river water supply, mine drainage and coal gangue leaching. The high concentration of SO₄^2- in the mine drainage was mainly from the dissolution of evaporative salt rocks. (3) The calculation results of the ternary mixing model showed that the SO₄^2- in the subsidence area water was affected by mine drainage and gangue leaching to different degrees. The results showed that the sulfate contribution proportion of the river water source to the subsidence area water was 35.8-65.9%; the sulfate contribution proportion of the mine drainage source to the subsidence area water was 2.0-26.6%; and the sulfate contribution proportion of the gangue leaching end source ranged from 16.3% to 56.9%. Coal mining activities had an important impact on the sulfate in the subsidence area water.

A comparative study on the micro-surface characteristics at black shale initial oxidation stage

The pyrite oxidation is crucial to the overall black shale oxidation process. A. ferrooxidans was documented an effective oxidation ability on pure pyrite, but its role in black shale oxidation is unclear. In this study, a comparative study of acid solution and A. ferrooxidans on the micro-surface characteristics at the initial stage (7 days) was conducted on black shale slices, a comprehensive approach combining the micro-morphologies, micro-structures, micro-environmental pH and micro-surface elemental content were investigated by using polarizing microscopies, SEM, fluorescent staining and EDX line scan analysis. The pyrite oxidation rate was employed to the index for black shale oxidation degree, and analyzed by XRD, aqueous pH, oxidation-reduction potential (ORP), ferrous and ferric ions concentrations measurement. The results show that the micro-surface characteristics are different in acid solution and A. ferrooxidans groups, which significantly impact the pyrite oxidation rate. A. ferrooxidans promote the jarosite formation and elemental C accumulation on the rocks micro-surface, which is assumed to inhibit further reactions. Two reaction phases named “pyrite oxidized phase” and “jarosite formation phase” are proposed to occur in the initial stage of A. ferrooxidans oxidizing black shale. These findings provide experimental data to evaluate the micro-surface reactions during black shale oxidation process.

Triple oxygen isotope insight into terrestrial pyrite oxidation

The mass-independent minor oxygen isotope compositions (Δ'¹⁷O) of atmospheric O₂ and [Formula: see text] are primarily regulated by their relative partial pressures, [Formula: see text]/[Formula: see text] Pyrite oxidation during chemical weathering on land consumes [Formula: see text] and generates sulfate that is carried to the ocean by rivers. The Δ'¹⁷O values of marine sulfate deposits have thus been proposed to quantitatively track ancient atmospheric conditions. This proxy assumes direct [Formula: see text] incorporation into terrestrial pyrite oxidation-derived sulfate, but a mechanistic understanding of pyrite oxidation-including oxygen sources-in weathering environments remains elusive. To address this issue, we present sulfate source estimates and Δ'¹⁷O measurements from modern rivers transecting the Annapurna Himalaya, Nepal. Sulfate in high-elevation headwaters is quantitatively sourced by pyrite oxidation, but resulting Δ'¹⁷O values imply no direct tropospheric [Formula: see text] incorporation. Rather, our results necessitate incorporation of oxygen atoms from alternative, ¹⁷O-enriched sources such as reactive oxygen species. Sulfate Δ'¹⁷O decreases significantly when moving into warm, low-elevation tributaries draining the same bedrock lithology. We interpret this to reflect overprinting of the pyrite oxidation-derived Δ'¹⁷O anomaly by microbial sulfate reduction and reoxidation, consistent with previously described major sulfur and oxygen isotope relationships. The geologic application of sulfate Δ'¹⁷O as a proxy for past [Formula: see text]/[Formula: see text] should consider both 1) alternative oxygen sources during pyrite oxidation and 2) secondary overprinting by microbial recycling.

Semiconductor-Microbial Mechanism of Selective Dissolution of Chalcocite in Bioleaching

Chalcocite-dominant secondary copper ore with a high pyrite content had a rapidly increased iron concentration in the middle and later periods of bioleaching, which increased the difficulty of separating copper and iron ions in the leaching solution. In the two aspects of microbial community succession and energy band theory, the selective dissolution mechanism of chalcocite in this type of copper ore was analyzed and illustrated using experiments and first-principles calculations. The results showed that controlling the solution potential at a lower level was beneficial to the selective leaching of chalcocite, while bacteria promoted the leaching of pyrite and chalcocite simultaneously by oxidizing Fe²⁺ to Fe³⁺ in the solution. Below 700 mV of solution potential, the bacterial community, mainly consisting of Acidithiobacillus and Sulfobacillus, had a stronger promotion on the selective dissolution of chalcocite. The solution energy level of bioleaching was higher than ideal pyrite but lower than ideal chalcocite, which resulted in the accumulation of electrons on the surface of pyrite and the formation of holes at the top of the chalcocite valence band. When bacteria assisted the oxidation of Fe²⁺ to Fe³⁺ and caused the raise of the solution potential, the difference between the solution energy level and the top of the pyrite valence band would be smaller than the width of the pyrite energy gap. Below 700 mV, the assistance of Acidithiobacillus and Sulfobacillus on the oxidation of Fe²⁺ was weak. Chalcocite would be selectively dissolved by oxygen and a small amount of Fe³⁺ in the solution. Because of the existence of Fe, Cu, and S vacancies in real minerals, the atomic activity in the Cu-S bond and the Fe-S bond enhanced, and the reaction difficulty between chalcocite, pyrite, and electron acceptors in the solution reduced. The solution potential should be controlled at 600 mV or less to ensure the selective dissolution of chalcocite.

Can Sulfate Be the First Dominant Aqueous Sulfur Species Formed in the Oxidation of Pyrite by Acidithiobacillus ferrooxidans?

According to the literature, pyrite (FeS₂) oxidation has been previously determined to involve thiosulfate as the first aqueous intermediate sulfur product, which is further oxidized to sulfate. In the present study, pyrite oxidation by Acidithiobacillus ferrooxidans was studied using electrochemical and metabolic approaches in an effort to extend existing knowledge on the oxidation mechanism. Due to the small surface area, the reaction rate of a compact pyrite electrode in the form of polycrystalline pyrite aggregate in A. ferrooxidans suspension was very slow at a spontaneously formed high redox potential. The slow rate made it possible to investigate the oxidation process in detail over a term of 100 days. Using electrochemical parameters from polarization curves and levels of released iron, the number of exchanged electrons per pyrite molecule was estimated. The values close to 14 and 2 electrons were determined for the oxidation with and without bacteria, respectively. These results indicated that sulfate was the dominant first aqueous sulfur species formed in the presence of bacteria and elemental sulfur was predominantly formed without bacteria. The stoichiometric calculations are consistent with high iron-oxidizing activities of bacteria that continually keep the released iron in the ferric form, resulting in a high redox potential. The sulfur entity of pyrite was oxidized to sulfate by Fe³⁺ without intermediate thiosulfate under these conditions. Cell attachment on the corroded pyrite electrode surface was documented although pyrite surface corrosion by Fe³⁺ was evident without bacterial participation. Attached cells may be important in initiating the oxidation of the pyrite surface to release iron from the mineral. During the active phase of oxidation of a pyrite concentrate sample, the ATP levels in attached and planktonic bacteria were consistent with previously established ATP content of iron-oxidizing cells. No significant upregulation of three essential genes involved in energy metabolism of sulfur compounds was observed in the planktonic cells, which represented the dominant biomass in the pyrite culture. The study demonstrated the formation of sulfate as the first dissolved sulfur species with iron-oxidizing bacteria under high redox potential conditions. Minor aqueous sulfur intermediates may be formed but as a result of side reactions.

Microbial and geochemical controls on waste rock weathering and drainage quality

Bacteria can adversely affect the quality of drainage released from mine waste by catalyzing the oxidation of sulfide minerals and thereby accelerating the release of acidity and metals. However, the microbiological and geochemical controls on drainage quality from unsaturated and geochemically heterogeneous waste rock remain poorly understood. Here, we identified coexisting neutrophilic and acidophilic bacteria in different types of waste rock, indicating that robust endemic consortia are sustained within pore-scale microenvironments. Subsequently, natural weathering was simulated in laboratory column experiments with waste rock that contained either in-situ microbial consortia or suppressed populations with up to 1000 times smaller abundance and reduced phenotypic diversity after heating and drying. Drainage from waste rock with in-situ populations was up to two pH units lower and contained up to 16 times more sulfate and heavy metals compared to drainage from waste rock bearing treated populations, indicating significantly higher sulfide-oxidation rates. The drainage chemistry was further affected by sorption and formation of secondary-mineral phases (e.g., gypsum and hydroxy-carbonates). This study provides direct evidence for the existence of diverse microbial communities in waste rock and their important catalytic role on weathering rates, and illustrates the mutual controls of microbiology and geochemistry on waste-rock drainage quality.

Effect of initial pH, operating temperature, and dissolved oxygen concentrations on performance of pyrite-fuel cells in the presence of Acidithiobacillus ferrooxidans

Fuel cell technology can be applied to remove pyrite from pyrite containing mine waste (PCMW) and to generate electricity. This study investigated the effect of pH, presence of Acidithiobacillus ferrooxidans, operating temperature, and dissolved oxygen (DO) concentration on the performance of pyrite-fuel cells (PFCs). These factors affect the pyrite dissolution rate, which affects the electron movement for electricity generation, hence electrical performance. The PFCs performance based on the maximum power density and maximum current density, obtained on the 28th day, was better at pH 2.2 (0.74 mW m^-2, 28 mA m^-2) than at pH 4.3 and pH 6.5 and in the presence of A. ferrooxidans (i.e., biotic PFCs) than in the abiotic PFCs. The biotic PFCs showed more consistent performance regardless of the operating temperature than the abiotic PFCs. The PFCs performance was better at higher DO concentrations (30-33 mg L^-1) than at lower DO concentrations (8-9 and 0-2 mg L^-1); however, gas purging used to adjust DO concentrations could adversely affect the biotic PFCs performance. This study demonstrates that PCMW treatment and electricity generation can be achieved using the fuel cell-based technology, and the PFCs performance can be optimized by adjusting the operating conditions.

Wastes generated by mineral extraction industries

Mineral extraction industries at each mining step generate large volume of waste, and most of them represent potentially sources of crucial metals. This chapter describes extraction and main mining processes, principal classifications of the generated wastes, as well as the chemical properties of the waste material, their disposal and further treatment to recover metals. Most of the presented technological solutions are or have been tested in real processes or using real waste materials.

Limited role of sessile acidophiles in pyrite oxidation below redox potential of 650 mV

Pyrite oxidation by mixed mesophilic acidophiles was conducted under conditions of controlled and non-controlled redox potential to investigate the role of sessile microbes in pyrite oxidation. Microbes attached on pyrite surfaces by extracellular polymeric substances (EPS), and their high coverage rate was characterized by scanning electron microscopy (SEM), confocal laser scanning microscopy (CLSM) and atomic force microscopy (AFM). The dissolution of pyrite was negligible if the redox potential was controlled below 650 mV (near the rest potential of pyrite), even though the bacteria were highly active and a high coverage rate was observed on pyrite surfaces. However, with un-controlled redox potential the rate of pyrite oxidation increased greatly with an increasing redox potential. This study demonstrates that sessile microbes play a limited role in pyrite oxidation at a redox potential below 650 mV, and highlight the importance of solution redox potential for pyrite oxidation. This has implications for acid mine drainage control and pyrite oxidation control in biometallurgy practice.

Electrochemical Applications in Metal Bioleaching

Biohydrometallurgy comprises the recovery of metals by biologically catalyzed metal dissolution from solids in an aqueous solution. The application of this kind of bioprocessing is described as "biomining," referring to either bioleaching or biooxidation of sulfide metal ores. Acidophilic iron- and sulfur-oxidizing microorganisms are the key to successful biomining. However, minerals such as primary copper sulfides are recalcitrant to dissolution, which is probably due to their semiconductivity or passivation effects, resulting in low reaction rates. Thus, further improvements of the bioleaching process are recommendable. Mineral sulfide dissolution is based on redox reactions and can be accomplished by electrochemical technologies. The impact of electrochemistry on biohydrometallurgy affects processing as well as analytics. Electroanalysis is still the most widely used electrochemical application in mineralogical research. Electrochemical processing can contribute to bioleaching in two ways. The first approach is the coupling of a mineral sulfide to a galvanic partner or electrocatalyst (spontaneous electron transfer). This approach requires only low energy consumption and takes place without technical installations by the addition of higher redox potential minerals (mostly pyrite), carbonic material, or electrocatalytic ions (mostly silver ions). Consequently, the processed mineral (often chalcopyrite) is preferentially dissolved. The second approach is the application of electrolytic bioreactors (controlled electron transfer). The electrochemical regulation of electrolyte properties by such reactors has found most consideration. It implies the regulation of ferrous and ferric ion ratios, which further results in optimized solution redox potential, less passivation effects, and promotion of microbial activity. However, many questions remain open and it is recommended that reactor and electrode designs are improved, with the aim of finding options for simplified biohydrometallurgical processing. This chapter focuses on metal sulfide dissolution via bioleaching and does not include other biohydrometallurgical processes such as microbial metal recovery from solution.

Analysis of the microbial community in moderately acidic drainage from the Yanahara pyrite mine in Japan

Acid rock drainage (ARD) originating from the Yasumi-ishi tunnel near the main tunnel of the Yanahara mine in Japan was characterized to be moderately acidic (pH 4.1) and contained iron at a low concentration (51 mg/L). The composition of the microbial community was determined by sequence analysis of 16S rRNA genes using PCR and denaturing gradient gel electrophoresis. The analysis of the obtained sequences showed their similarity to clones recently detected in other moderately acidic mine drainages. Uncultured bacteria related to Ferrovum- and Gallionella-like clones were dominant in the microbial community. Analyses using specific primers for acidophilic iron- or sulfur-oxidizing bacteria, Acidithiobacillus ferrooxidans, Leptospirillum spp., Acidithiobacillus caldus, Acidithiobacillus thiooxidans, and Sulfobacillus spp. revealed the absence of these bacteria in the microbial community in ARD from the Yasumi-ishi tunnel. Clones affiliated with a member of the order Thermoplasmatales were detected as the dominant archaea in the ARD microbial population.

Bioleaching of metals from printed circuit boards supported with surfactant-producing bacteria

This study has evaluated the possibility of bioleaching zinc, copper, lead, nickel, cadmium and chromium from printed circuit boards by applying a culture of sulphur-oxidising bacteria and a mixed culture of biosurfactant-producing bacteria and sulphur-oxidising bacteria. It was revealed that zinc was removed effectively both in a traditional solution acidified by a way of microbial oxidation of sulphur and when using a microbial culture containing sulphur-oxidising and biosurfactant-producing bacteria. The average process efficiency was 48% for Zn dissolution. Cadmium removal was similar in both media, with a highest metal release of 93%. For nickel and copper, a better effect was obtained in the acidic medium, with a process effectiveness of 48.5% and 53%, respectively. Chromium was the only metal that was removed more effectively in the bioleaching medium containing both sulphur-oxidising and biosurfactant-producing bacteria. Lead was removed from the printed circuit boards with very low effectiveness (below 0.5%). Aerating the culture medium with compressed air increased the release of all metals in the medium with sulphur and biosurfactant, and of Ni, Cu, Zn and Cr in the acidic medium. Increasing the temperature of the medium (to 37°C) had a more significant impact in the acidic environment than in the neutral environment.

Comparative genomics in acid mine drainage biofilm communities reveals metabolic and structural differentiation of co-occurring archaea

Background

Metal sulfide mineral dissolution during bioleaching and acid mine drainage (AMD) formation creates an environment that is inhospitable to most life. Despite dominance by a small number of bacteria, AMD microbial biofilm communities contain a notable variety of coexisting and closely related Euryarchaea, most of which have defied cultivation efforts. For this reason, we used metagenomics to analyze variation in gene content that may contribute to niche differentiation among co-occurring AMD archaea. Our analyses targeted members of the Thermoplasmatales and related archaea. These results greatly expand genomic information available for this archaeal order.

Results

We reconstructed near-complete genomes for uncultivated, relatively low abundance organisms A-, E-, and Gplasma, members of Thermoplasmatales order, and for a novel organism, Iplasma. Genomic analyses of these organisms, as well as Ferroplasma type I and II, reveal that all are facultative aerobic heterotrophs with the ability to use many of the same carbon substrates, including methanol. Most of the genomes share genes for toxic metal resistance and surface-layer production. Only Aplasma and Eplasma have a full suite of flagellar genes whereas all but the Ferroplasma spp. have genes for pili production. Cryogenic-electron microscopy (cryo-EM) and tomography (cryo-ET) strengthen these metagenomics-based ultrastructural predictions. Notably, only Aplasma, Gplasma and the Ferroplasma spp. have predicted iron oxidation genes and Eplasma and Iplasma lack most genes for cobalamin, valine, (iso)leucine and histidine synthesis.

Conclusion

The Thermoplasmatales AMD archaea share a large number of metabolic capabilities. All of the uncultivated organisms studied here (A-, E-, G-, and Iplasma) are metabolically very similar to characterized Ferroplasma spp., differentiating themselves mainly in their genetic capabilities for biosynthesis, motility, and possibly iron oxidation. These results indicate that subtle, but important genomic differences, coupled with unknown differences in gene expression, distinguish these organisms enough to allow for co-existence. Overall this study reveals shared features of organisms from the Thermoplasmatales lineage and provides new insights into the functioning of AMD communities.

The pyrite iron cycle catalyzed by Acidithiobacillus ferrooxidans

In this paper, we study a model of the biotic pyrite iron cycle catalyzed by bacteria Acidithiobacillus ferrooxidans, in mining activity sites waste dumps. Chemical reactions, reaction rates and the population growth model are mostly taken from the existing literature. Analysis of the corresponding dynamical system shows the existence of up to four non-trivial steady state solutions. The stability of the equilibria solutions is determined, finding up to two coexisting stable solutions. Two Hopf bifurcations and a region of parameter space in which there are stable periodic solutions are found. In addition, we find a homoclinic bifurcation which gives rise to a stable periodic orbit of large period. The existence of these stable oscillatory solutions gives a possible explanation for the oscillations of bacteria concentration and pH for the iron cycle, described in Jaynes et al. (Water Resour Res 20:233-242, 1984).

Gene identification and substrate regulation provide insights into sulfur accumulation during bioleaching with the psychrotolerant acidophile Acidithiobacillus ferrivorans

The psychrotolerant acidophile Acidithiobacillus ferrivorans has been identified from cold environments and has been shown to use ferrous iron and inorganic sulfur compounds as its energy sources. A bioinformatic evaluation presented in this study suggested that Acidithiobacillus ferrivorans utilized a ferrous iron oxidation pathway similar to that of the related species Acidithiobacillus ferrooxidans. However, the inorganic sulfur oxidation pathway was less clear, since the Acidithiobacillus ferrivorans genome contained genes from both Acidithiobacillus ferrooxidans and Acidithiobacillus caldus encoding enzymes whose assigned functions are redundant. Transcriptional analysis revealed that the petA1 and petB1 genes (implicated in ferrous iron oxidation) were downregulated upon growth on the inorganic sulfur compound tetrathionate but were on average 10.5-fold upregulated in the presence of ferrous iron. In contrast, expression of cyoB1 (involved in inorganic sulfur compound oxidation) was decreased 6.6-fold upon growth on ferrous iron alone. Competition assays between ferrous iron and tetrathionate with Acidithiobacillus ferrivorans SS3 precultured on chalcopyrite mineral showed a preference for ferrous iron oxidation over tetrathionate oxidation. Also, pure and mixed cultures of psychrotolerant acidophiles were utilized for the bioleaching of metal sulfide minerals in stirred tank reactors at 5 and 25°C in order to investigate the fate of ferrous iron and inorganic sulfur compounds. Solid sulfur accumulated in bioleaching cultures growing on a chalcopyrite concentrate. Sulfur accumulation halted mineral solubilization, but sulfur was oxidized after metal release had ceased. The data indicated that ferrous iron was preferentially oxidized during growth on chalcopyrite, a finding with important implications for biomining in cold environments.

Analysis of the surface proteins of Acidithiobacillus ferrooxidans strain SP5/1 and the new, pyrite-oxidizing Acidithiobacillus isolate HV2/2, and their possible involvement in pyrite oxidation

Two strains of rod-shaped, pyrite-oxidizing acidithiobacilli, their cell envelope structure and their interaction with pyrite were investigated in this study. Cells of both strains, Acidithiobacillus ferrooxidans strain SP5/1 and the moderately thermophilic Acidithiobacillus sp. strain HV2/2, were similar in size, with slight variations in length and diameter. Two kinds of cell appendages were observed: flagella and pili. Besides a typical Gram-negative cell architecture with inner and outer membrane, enclosing a periplasm, both strains were covered by a hitherto undescribed, regularly arranged 2-D protein crystal with p2-symmetry. In A. ferrooxidans, this protein forms a stripe-like structure on the surface. A similar surface pattern with almost identical lattice vectors was also seen on the cells of strain HV2/2. For the surface layer of both bacteria, a direct contact to pyrite crystals was observed in ultrathin sections, indicating that the S-layer is involved in maintaining this contact site. Observations on an S-layer-deficient strain show, however, that cell adhesion does not strictly depend on the presence of the S-layer and that this surface protein has an influence on cell shape. Furthermore, the presented data suggest the ability of the S-layer protein to complex Fe3+ ions, suggesting a role in the physiology of the microorganisms.

Nanominerals and nanoparticles in feed coal and bottom ash: implications for human health effects

Environmental and human health risk assessments of nanoparticle effects from coal and bottom ash require thorough characterisation of nanoparticles and their aggregates. In this manuscript, we expand the study of human exposure to nanosized particles from coal combustion sources (typically <100 nm in size), characterising the complex micromineralogy of these airborne combustion-derived nanomaterials. Our study focuses on bottom ash generated in the Santa Catarina power station (Brazil) which uses coal enriched in ashes, many potential elements (e.g. Cr and Ni) and pyrite. Transmission electron microscope data reveal nanoscale C deposits juxtaposed with and overgrown by slightly larger aluminosilicate (Al-Si) glassy spheres, oxides, silicates, carbonated, phosphates and sulphates. Iron oxides (mainly hematite and magnetite) are the main bottom ash products of the oxidation of pyrite, sometimes via intermediate pyrrhotite formation. The presence of iron oxide nanocrystals mixed with silicate glass particles emphasises the complexity of coal and bottom ash micromineralogy. Given the potentially bioreactive nature of such transition metal-bearing materials, there is likely to be an increased health risk associated with their inhalation.

Insights into the dynamics of bacterial communities during chalcopyrite bioleaching

The microbial ecology of the bioleaching of chalcopyrite ores is poorly understood and little effort has been made to handle the microbiological components of these processes. In this study, the composition and structure of microbial communities in acid mineral bioleaching systems have been studied using a PCR-based cloning approach. Denaturing gradient gel electrophoresis (DGGE) analysis of PCR-amplified 16S rRNA gene fragments from bacteria was used to evaluate the changes in the bacterial community in the process of chalcopyrite bioleaching in a shaken flask system. The results revealed that the bacterial community was disturbed after the addition of chalcopyrite. Phylogenetic analyses of 16S rRNA gene fragments revealed that the retrieved sequences clustered together with the genera Acidithiobacillus, Leptospirillum, and Acidovorax. Multidimensional scaling analysis of DGGE banding patterns revealed that the process of chalcopyrite bioleaching in 46 days was divided into four stages. In the first stage, Leptospirillum were dominant. In the second stage, Leptospirillum and Acidithiobacillus groups were mainly detected. In the third and fourth stages, the bacterial community was relatively stable and was dominated by Leptospirillum and Acidithiobacillus. These results extend our knowledge on the microbial dynamics in chalcopyrite bioleaching, a key issue required to improve commercial applications.

Microbial communities in acid mine drainage

The dissolution of sulfide minerals such as pyrite (FeS2), arsenopyrite (FeAsS), chalcopyrite (CuFeS2), sphalerite (ZnS), and marcasite (FeS2) yields hot, sulfuric acid-rich solutions that contain high concentrations of toxic metals. In locations where access of oxidants to sulfide mineral surfaces is increased by mining, the resulting acid mine drainage (AMD) may contaminate surrounding ecosystems. Communities of autotrophic and heterotrophic archaea and bacteria catalyze iron and sulfur oxidation, thus may ultimately determine the rate of release of metals and sulfur to the environment. AMD communities contain fewer prokaryotic lineages than many other environments. However, it is notable that at least two archaeal and eight bacterial divisions have representatives able to thrive under the extreme conditions typical of AMD. AMD communities are characterized by a very limited number of distinct species, probably due to the small number of metabolically beneficial reactions available. The metabolisms that underpin these communities include organoheterotrophy and autotrophic iron and sulfur oxidation. Other metabolic activity is based on anaerobic sulfur oxidation and ferric iron reduction. Evidence for physiological synergy in iron, sulfur, and carbon flow in these communities is reviewed. The microbial and geochemical simplicity of these systems makes them ideal targets for quantitative, genomic-based analyses of microbial ecology and evolution and community function.

Application of clone library analysis and real-time PCR for comparison of microbial communities in a low-grade copper sulfide ore bioheap leachate

The microbial communities of leachate from a bioleaching heap located in China were analyzed using the 16S rRNA gene clone library and real-time quantitative PCR. Both methods showed that Leptospirillum spp. were the dominant bacteria, and Ferroplasma acidiphilum were the only archaea detected in the leachate. Clone library results indicated that nine operational taxonomic units (OTUs) were obtained, which fell into four divisions, the Nitrospirae (74%), the gamma-Proteobacteria (14%), the Actinobacteria (6%) and the Euryarchaeota (6%). The results obtained by real-time PCR in some ways were the same as clone library analysis. Furthermore, Sulfobacillus spp., detected only by real-time PCR, suggests that real-time PCR was a reliable technology to study the microbial communities in bioleaching environments. It is a useful tool to assist clone library analysis, to further understand microbial consortia and to have comprehensive and exact microbiological information about bioleaching environments. Finally, the interactions among the microorganisms detected in the leachate were summarized according to the characteristics of these species.

Biofilm bacterial community structure in streams affected by acid mine drainage

We examined the bacterial communities of epilithic biofilms in 17 streams which represented a gradient ranging from relatively pristine streams to streams highly impacted by acid mine drainage (AMD). A combination of automated ribosomal intergenic spacer analysis with multivariate analysis and ordination provided a sensitive, high-throughput method to monitor the impact of AMD on stream bacterial communities. Significant differences in community structure were detected among neutral to alkaline (pH 6.7 to 8.3), acidic (pH 3.9 to 5.7), and very acidic (pH 2.8 to 3.5) streams. DNA sequence analysis revealed that the acidic streams were generally dominated by bacteria related to the iron-oxidizing genus Gallionella, while the organisms in very acidic streams were less diverse and included a high proportion of acidophilic eukaryotes, including taxa related to the algal genera Navicula and Klebsormidium. Despite the presence of high concentrations of dissolved metals (e.g., Al and Zn) and deposits of iron hydroxide in some of the streams studied, pH was the most important determinant of the observed differences in bacterial community variability. These findings confirm that any restoration activities in such systems must focus on dealing with pH as the first priority.

Microbial communities in acid water environments of two mines, China

To understand the compositions and structures of microbial communities in different acid-aqueous environments, a PCR-based cloning approach was used. A total of five samples were collected from two mines in China. Two samples, named as G1 and G2, were acid mine drainage (AMD) samples and from Yunfu sulfide mine in Guangdong province, China. The rest of the three samples named as D1, DY and D3, were from three sites undertaking bioleaching in Yinshan lead-zinc mine in Jiangxi province, China. Phylogenetic analysis revealed that bacteria in the five samples fell into six putative divisions, which were alpha-Proteobacteria, beta-Proteobacteria, gamma-Proteobacteria, Firmicutes, Actinobacteria and Nitrospira. Archaea was only detected in the three samples from Yinshan lead-zinc mine, which fell into two phylogenentic divisions, Thermoplsma and Ferroplasma. In addition, the results of principal component analysis (PCA) suggested that more similar the geochemical properties in samples were, more similar microbial community structures in samples were.

Microbial populations in acid mineral bioleaching systems of Tong Shankou Copper Mine, China

AIMS

To understand the composition and structure of microbial communities in different acid mineral bioleaching systems, and to present a more complete picture of microbially mediated acid mine drainage production.

METHODS AND RESULTS

In Tong Shankou Copper Mine, China, two samples (named K1 and K2) from two different sites with bioleaching were studied. A bacterial 16S rDNA library and an archaeal 16S rDNA library of the sample from each site were constructed by 16S rDNA polymerase chain reaction (PCR), restriction fragment length polymorphism (RFLP) and sequencing. A total of 18 bacterial representative sequences and 12 archaeal representative sequences were obtained. Phylogenetic analysis indicated that 77.09% of the total bacterial clones were affiliated with Proteobacteria, and 21.22% of the total bacterial clones were closely related to Nitrospira. The rest of the bacterial clones were related to Firmicutes (1.68%). Sequences affiliated with the archaea of the Thermoplasma and Ferroplasma lineages were detected abundantly in the two samples. Unexpectedly, sequences affiliated with Sulfolobales and Methanothermus genera were also detected.

CONCLUSIONS

The molecular studies appear to be consistent with the environmental conditions existing at the sites, which coincides with previous studies. High concentrations of some elements (such as copper, iron and sulfur) seemed to be the key factors resulting in the diverse distribution of typical iron-oxidizing bacteria such as Leptospirillum species and Acidithiobacillus ferrooxidans.

SIGNIFICANCE AND IMPACT OF THE STUDY

Research on micro-organisms present in bioleaching systems especially archaea is not abundant. The acidophiles in the two bioleaching sites obtained from Tong Shankou Copper Mine, China, have not been reported until now. These results may expand our knowledge of the microbial diversity in the acid mineral bioleaching systems.

Modeling of ferrous iron oxidation by a Leptospirillum ferrooxidans-dominated chemostat culture

The objective of this study was to evaluate a direct classical bioengineering approach to model data generated from continuous bio-oxidation of Fe(2+) by a Leptospirillum ferrooxidans-dominated culture fed with either 9 g or 18 g Fe(2+) L(-1) under chemostat conditions (dilution rates were between 0.051 and 0.094 h(-1)). The basic Monod and Pirt equations have successfully been integrated in an overall mass balance procedure, which has not been previously presented in this detail for Fe(2+) oxidation. To ensure chemostat conditions, it was found that the range of the dilution rates had to be limited. A too long retention time might cause starvation or non-negligible death rate whereas, a too short retention time may cause a significant alteration in solution chemistry and culture composition. Modeling of the experimental data suggested that the kinetic- and yield parameters changed with the overall solution composition. However, for respective feed solutions only minor changes of ionic strength and chemical speciation can be expected within the studied range of dilution rates, which was confirmed by thermodynamic calculations and conductivity measurements. The presented model also suggests that the apparent Fe(3+) inhibition on specific Fe(2+) utilization rate was a direct consequence of the declining biomass yield on Fe(2+) due to growth uncoupled Fe(2+) oxidation when the dilution rate was decreased. The model suggested that the maintenance activities contributed up to 90% of the maximum specific Fe(2+) utilization rate, which appears close to the critical dilution rate. Biotechnol. Bioeng. 2008;99: 378-389. (c) 2007 Wiley Periodicals, Inc.

Microbial diversity in acid mineral bioleaching systems of dongxiang copper mine and Yinshan lead-zinc mine

To understand the composition and structure of microbial communities in acid mineral bioleaching systems, the molecular diversity of 16S rDNA genes was examined using a PCR-based cloning approach. A total of 31 Operational Taxonomic Units (OTUs) were obtained from the four samples taken from four different bioleaching sites in Yinshan lead-zinc mine and Dongxiang copper mine in Jiangxi Province, China. The percentages of overlapping OTUs between sites ranged from 22.2 to 50.0%. Phylogenetic analysis revealed that the bacteria present at the four bioleaching sites fell into six divisions, alpha-Proteobacteria (1.1%), beta-Proteobacteria (2.3%), gamma-Proteobacteria (30.8%), Firmicutes (15.4%), Actinobacteria (0.3%) and Nitrospira (50.1%). Organisms of genera Leptospirillum, Acidithiobacillus, and Sulfobacillus, which were in Nitrospira, gamma-Proteobacteria, and Firmicutes divisions, respectively, were the most dominant. The results of principal component analysis based on the six phylogenetic divisions and biogeochemical data indicated that the microbial community structure of a site was directly related to the biogeochemical characteristic of that site. It follows therefore that sites with similar biogeochemical characteristics were comprised of similar microbial community structures. The results in our study also suggest that the elements copper and arsenic appear to be the key factors affecting the compositions and structures of microbial community in the four bioleaching sites.

Molecular diversity of microbial community in acid mine drainages of Yunfu sulfide mine

Two acid mine drainage (AMD) samples were studied by a PCR-based cloning approach, which were from Yunfu sulfide mine in Guangdong province, China. A total of 15 operational taxonomic units (OTUs) were obtained from the two AMD samples. The percentage of overlapped OTUs in two AMD samples was 42.1%. Phylogenetic analysis revealed that the bacterium in the two samples fell into four putative divisions, which were Nitrospira, alpha-Proteobacteria, beta-Proteobacteria, and gamma-Proteobacteria four families. Organisms of genuses Acidithiobacillus and Gallionella, which were in gamma-Proteobacteria family and beta-Proteobacteria family, respectively, were dominant in two samples. The proportions of clones affiliated with Gallionella in each sample were 47.2% (G2) and 16.9% (G1). The result suggested that organisms of Gallionella were a very important composition in microbial communities of the two AMD samples we studied. In addition, the PCR amplification of archaeal 16S rDNA genes form these two AMD samples have been performed with two sets of archaea-specific primers, but no PCR product found.

Diversity of 16S ribosomal DNA-defined bacterial population in acid rock drainage from Japanese pyrite mine

Four acidophilic bacteria (YARDs1-4) were isolated from an acid rock drainage (ARD) from Yanahara mine, Okayama prefecture, Japan. The physiological and 16S rDNA sequence analyses revealed that YARD1 was closely affiliated with Acidithiobacillus ferrooxidans, YARD2 was an Acidiphilium-like bacterium, and YARD3 and YARD4 were sulfur-oxidizing bacteria with a relatively close relationship to A. ferrooxidans in the phylogenetic analysis. A molecular approach based on the construction of a 16S rDNA clone library was used to investigate the microbial population of the ARD. Small-subunit rRNA genes were PCR amplified, subsequently cloned and screened for variation by a restriction fragment length polymorphism (RFLP) analysis. A total of 284 clones were grouped into 133 operational taxonomic units (OTUs) by the RFLP analysis. Among them, an OTU showing the same RFLP pattern as those of the isolates from the ARD was not detected. The phylogenetic analysis based on the 16S rDNA sequences from 10 major OTUs and their close relatives revealed that 4 OTUs containing 32.1% of the total clones were loosely affiliated with Verrucomicrobia, 2 OTUs containing 6.6% of the total clones were loosely affiliated with Chloribi, and other OTUs were affiliated with Actinobacteria, Nitrospirae, and beta-Proteobacteria.

Modeling and analysis of biooxidation of gold bearing pyrite-arsenopyrite concentrates by Thiobacillus ferrooxidans

The results of modeling the biooxidation of a mixed sulfidic concentrate by Thiobacillus ferrooxidans is reported here. A kinetic model, which accounts for the dissolution of sulfide matrix due to both bacterial attachment onto the mineral surface and indirect leaching, has been proposed. A comprehensive system approach is employed for modeling the complex biooxidation process by (a) the decomposition of the complete system into several subsystems, (b) modeling individual systems, and (c) integrating the subsystems model in a final system model. The model for subsystems was developed by writing mass balance equations for the different species involved. The bacterial balance accounts for its growth, both on solid substrate and in solution, and for the attachment to and detachment from the surface. The kinetic parameters of the model were determined by designing the experiments in such a manner that only one subsystem was operational. This model was tested in both laboratory scale batch and continuous biooxidation processes. The model predictions agreed with the experimental data reasonably well. A further analysis of the model was carried out to predict the conditions for efficient biooxidation. Studies on the effect of residence time and pulp density on steady-state behavior showed that there is a critical residence time and pulp density below which washout conditions occur. Operation at pulp densities lower than 5% and residence times lower than 72 h was found unfavorable for efficient leaching.

Heavy metal mining using microbes

The use of acidiphilic, chemolithotrophic iron- and sulfur-oxidizing microbes in processes to recover metals from certain types of copper, uranium, and gold-bearing minerals or mineral concentrates is now well established. During these processes insoluble metal sulfides are oxidized to soluble metal sulfates. Mineral decomposition is believed to be mostly due to chemical attack by ferric iron, with the main role of the microorganisms being to reoxidize the resultant ferrous iron back to ferric iron. Currently operating industrial biomining processes have used bacteria that grow optimally from ambient to 50 degrees C, but thermophilic microbes have been isolated that have the potential to enable mineral biooxidation to be carried out at temperatures of 80 degrees C or higher. The development of higher-temperature processes will extend the variety of minerals that can be commercially processed.

Comparison of biooxidation with carbon dioxide assimilation during bacterial growth on ferrous ion or elemental sulfur

Biomass and oxygen uptake activity profiles of a mixed bioleaching culture were studied and compared at various temperatures. Bacteria were grown on ferrous ion or elemental sulfur in a Micro-Oxymax respirometer apparatus that allowed measurement of both oxygen consumption and carbon dioxide assimilation. Balanced growth was observed between 10 degrees C and 35 degrees C, with an optimum at 30 degrees C, on both energy sources. No significant growth was observed at the lowest temperature used, 5 degrees C, or at the highest temperature used, 40 degrees C. The oxygen to carbon dioxide molar yield was 50:1 when growing on ferrous ion but only 17:1 when growing on elemental sulfur. Upon transfer from a sulfide ore to a new energy source, greater numbers in the inoculum reduced the duration of the lag phase. Lag phase duration was also reduced by proximity to the optimum growth temperature. A longer lag phase decreased the achievable growth rate of the cells exponentially, significantly affecting biooxidation activity.

Isolation and phylogenetic characterization of acidophilic microorganisms indigenous to acidic drainage waters at an abandoned Norwegian copper mine

The biodiversity of culturable acidophilic microbes in three acidic (pH 2.7-3.7), metal-rich waters at an abandoned subarctic copper mine in central Norway was assessed. Acidophilic bacteria were isolated by plating on selective solid media, and dominant isolates were identified from their physiological characteristics and 16S rRNA gene sequences. The dominant iron-oxidizing acidophile in all three waters was an Acidithiobacillus ferrooxidans-like eubacterium, which shared 98% 16S rDNA identity with the type strain. A strain of Leptospirillum ferrooxidans was obtained from one of the waters after enrichment in pyrite medium, but this iron oxidizer was below detectable levels in the acidic waters themselves. In two sites, there were up to six distinct heterotrophic acidophiles, present at 10(3) ml(-1). These included Acidiphilium-like isolates (one closely related to Acidiphilium rubrum, a second to Acidiphilium cryptum and a third apparently novel isolate), an Acidocella-like isolate (96% 16S rDNA identity to Acidocella facilis) and a bacterium that shared 94.5% 16S rDNA identity to Acidisphaera rubrifaciens. The other numerically significant heterotrophic isolate was not apparently related to any known acidophile, with the closest match (96% 16S rDNA sequence identity) to an acetogen, Frateuria aurantia. The results indicated that the biodiversity of acidophilic bacteria, especially heterotrophs, in acidic mine waters may be much greater than previously recognized.