Thermophilic Iron Research Articles

Deferrivibrio essentukiensis sp. nov., gen. nov., a Representative of Deferrivibrionaceae fam. nov., Isolated from the Subsurface Aquifer of Caucasian Mineral Drinking Waters

The Yessentukskoye deposit of Caucasian mineral waters contains balneologically valuable drinking mineral water, which is extracted from the Upper Cretaceous 1 km subsurface aquifer and is almost unexplored by microbiologists. We have sampled this water via continuously operating production wells, characterized the phylogenetic diversity of its microbial community, and obtained enrichments of thermophilic iron reducers from the source aquifer. From the enrichments, a novel anaerobic thermophilic bacterium, reducing Fe(III) in the mineral ferrihydrite with acetate as the electron donor, was isolated into a pure culture. The novel isolate, designated as strain Es71-Z0220T belonging to Deferribacterales order, is thermophilic, neutrophilic, halotolerant, motile vibrio. It utilizes synthesized ferrihydrite, fumarate, nitrate or elemental sulfur as the electron acceptors with organic acids as the electron donors. The strain is incapable of soluble Fe(III) complexes reduction and fermentative growth. The draft genome assembly of strain Es71-Z0220T resulted in 65 contigs with a total size of ca. 2.3 Mb. On the basis of whole-genome phylogenetic reconstruction and physiological characterization, the novel isolate was considered to represent a novel family, genus and species for which the name Deferrivibrio essentukiensis gen. nov., sp. nov. is proposed. Genome analysis revealed key determinants of anaerobic respiration and carbon substrate utilization pathways in the organism with peculiarities related to putative Fe(III)-reducing electron transfer chain. Considering the revealed metabolic features of Deferrivibrio essentukiensis, the involvement of the organism in its subsurface environment in biogeochemical by carbon cycling by coupling the organic matter oxidation with Fe(III) minerals reduction is discussed.

Thermophilic iron containing type superoxide dismutase from Cohnella sp. A01

Superoxide dismutases (SODs) (EC 1.15.1.1) are well known antioxidant enzymes that play critical roles in cellular defenses of living organisms against harmful superoxide radicals during oxidative stress. This study details on cloning, biochemical and functional characterization of an iron containing type superoxide dismutase (SOD) from a novel thermophilic bacteria Cohnella sp. A01 (CaSOD). The secondary and three dimensional structure of the protein were predicted. CaSOD gene was subsequently cloned into pET-26b(+) expression vector and expression of the recombinant protein (rCaSOD) was optimized in E. coli BL21 (DE3) and the purified recombinant SOD showed a single band with an apparent molecular weight of 26 kDa by SDS-PAGE. The half-life and thermodynamic parameters including ΔH⁎, ΔS⁎, and ΔG⁎ were 187 min at 60 °C, 7.3 kJ.mol−1, −76.8 kJ.mol−1.°K−1, and 84.1 kJ.mol−1, respectively. The rCaSOD exhibited catalytic activity in a very broad range of pH (6.0–10.0) and temperatures (35–75 °C), as well as stability in a broad pH range, from 3.0 to 11.0, and wide range of temperature, different concentrations of detergent agents, metal ions, organic solvents and other chemicals. The results suggest that this novel enzyme could be used for various industrial applications in cosmetic, food, and pharmaceutical industries.

Sequential pretreatment of double refractory gold ore (DRGO) with a thermophilic iron oxidizing archeaon and fungal crude enzymes

Double refractory gold ore was sequentially pretreated to oxidize sulfides by thermophilic archaeon Acidianus brierleyi and then to decompose carbonaceous matters using the cell-free spent medium (CFSM) from white-rot fungus Phanerochaete chrysosporium. The pretreatment by A. brierleyi significantly improved the gold recovery from 25% to 77%. Additionally, the crude lignin-degrading enzymes in the CFSM converted the carbonaceous matters into more easily degradable substances, which were removed by alkaline washing, leading to a final gold recovery of 92%. These mineralogical alterations were confirmed by differential thermogravimetric analysis and quantitative evaluation of minerals with scanning electron microscopy. Based on the results, gold grains were mostly liberated after bio-oxidation of sulfides, and in following CFSM treatment, large particles of carbonaceous aluminosilicate were formed from the aggregation of clay minerals, gold grains and with partially decomposed carbonaceous matters acting as binders.

Continuous flow 70 °C archaeal bioreactor for iron oxidation and jarosite precipitation

This study is the first demonstration of a continuous culture bio-catalysed iron oxidation and jarosite precipitation reactor using thermophilic archaea, for use in hydrometallurgical process flow sheets to oxidize and partially remove iron from solution while minimizing valuable base metal (i.e. Ni and Cu) losses. A two-stage continuous stirred tank reactor (CSTR) system comprised of two CSTRs, each with its own settler, was operated to achieve biological iron oxidation and precipitation at 70°C. The two-stage reactor configuration was used to allow the growth of microorganisms that prefer different redox regimes. The bioreactors were inoculated with a mixed culture of extreme thermophilic iron oxidisers from genera Acidianus, Metallosphaera and Sulfolobus. The influent (pH1.5) contained (gL−1): 15 Fe2+, 1.5 Cu, 1.5 Ni (all as sulfates), nutrients and trace elements. The system demonstrated efficient iron oxidation and precipitation of the oxidised iron in the form of well settling jarosite with only minor losses of Cu and Ni via co-precipitation. At a total hydraulic retention time (HRT) of 13–14h in the two reactors, the overall iron oxidation rate was up to 1.0gL−1h−1 and conversion extent of >95%. During this time, the pH values were 1.3–1.6 and 1.3–1.6, and redox potentials (Ag/AgCl reference) were 440–530mV and 510–610mV, in the first and second reactor, respectively. The extent of Fe and sulfate removal, was relatively high, 52 and 25% respectively, while valuable Cu and Ni losses were low, i.e. 0.46% and 0.03%, respectively. The precipitates were exclusively jarosite, with potassium jarosite being the dominant form (38–51%), followed by hydronium (30–35%), ammonium (13–18%) and sodium jarosites (6–9%). The precipitates had good settling properties facilitating effective solid–liquid separation. Bioreactor performance was, however, found to be sensitive to instantaneous exposure to high concentrations of typical contaminants in hydrometallurgical processing streams, when added simultaneously. The addition of (gL−1) 2.0 Al, 0.05 As, 0.05F, 0.2 Co, 5.0 Mg and 0.4 Mn to the influent solution decreased iron oxidation and jarosite content in precipitates.

Iron Oxidation and Jarosite Precipitation in a Continuous Two-Stage 70°C Archaeal Bioreactor

This study is the first demonstration of a continuous culture bio-catalysed iron oxidation and jarosite precipitation reactor using thermophilic archea, for use in hydrometallurgical process flow sheets. A two-stage continuous stirred tank reactor (CSTR) system comprised of two CSTRs, each with its own settler, was operated for biological iron oxidation and precipitation at 70°C. The two-stage design was to allow the growth of microorganisms that prefer various redox regimes. The bioreactors were inoculated with a mixed culture of extreme thermophilic iron oxidisers from genera Acidianus, Metallosphaera and Sulfolobus. The influent (pH 1.5) contained (g L-1) 15 Fe2+, 1.5 Cu, 1.5 Ni (all as sulfates), nutrients and trace elements. At a hydraulic retention time (HRT) of 6-7 h in each CSTR, the overall iron oxidation rate was 1.0±0.1 g L-1 h-1 and percent 97±2%. The pH values were 1.38±0.16 and 1.57±0.05, and redox potentials (Ag/AgCl reference) were474±47 mV and 575±1 mV, in CSTR1 and CSTR2, respectively. The percentages of influent Fe, Cu and Ni removed as precipitates from settlers were 52%, 0.46% and 0.03%, respectively. The precipitates were comprised of jarosite (100%), potassium jarosite being the dominant form (38-51%), followed by hydronium (30-35%), ammonium (13-18%) and sodium jarosites (6-9%). The precipitates had a sludge volume index of 5.8-19 mL g-1, indicating good settling properties facilitating easy removal through settling. The simultaneous and instantaneous addition of contaminants (g L-1: 2.0 Al, 0.05 As, 0.05 F, 0.2 Co, 5.0 Mg and 0.4 Mn), potentially contained in hydrometallurgical processing streams, into the influent decreased the iron oxidation (50% overall oxidation with HRT of 26-29 h in each CSTR) and jarosite content in precipitates (85-87%). In conclusion, the two-stage high-temperature CSTR system allowed iron oxidation and precipitation of the oxidised iron in the form of well settling jarosite with only minor loss of Cu and Ni via co-precipitation. However, the bioreactor performance was hampered by the introduction of other transition metals, fluoride and arsenic.

The influence of physicochemical parameters on the bioleaching of zinc sulfide concentrates using a mixed culture of moderately thermophilic microorganisms

This work investigates the extraction of zinc from Bama zinc sulfide concentrate (Isfahan, Iran) using a mixed culture of moderately thermophilic iron- and sulfur-oxidizing microorganisms including Leptospirillum ferriphilum, Acidithiobacillus caldus, Sulfobacillus sp. and Ferroplasma sp. The effects of some physicochemical parameters, namely pH, nutrient medium type, temperature, and the external addition of ferrous iron on the zinc extraction, redox potential and iron mobilization were investigated in shake flasks. Experiments were carried out at the pulp density of 5% (w/v) and a stirring rate of 150rpm. The highest zinc extraction (91%) was achieved at 45°C, leaching time of 18days, initial pH of 1.8 and Norris nutrient medium. The zinc extraction was 3.7-fold higher in the bioleaching compared to chemical leaching. The leaching rate of the sphalerite concentrate tended to decrease with decreasing pH from 1.8 to 1.2. It was also found that the increasing of ferrous iron addition from 0.02 to 0.05M led to a decrease both in the zinc extraction and bacterial activity indicating the inhibitory effect of increased iron on the microorganisms. SEM-EDX analyses revealed both poorly crystallized iron hydroxyl sulfates and well-crystallized jarosites on the surface of the solid residues.

Bioleaching of a Marine Hydrothermal Sulfide Ore with Mesophiles, Moderate Thermophiles and Thermophiles

Marine hydrothermal polymetallic sulfide ores contain high amounts of valuable metals such as Cu, Pb, Zn, Au, Ag, as well as In, Ge, Bi, and Se. Samples from a site in the Indian Ocean were taken during a BGR ship cruise, crushed and sieved for bioleaching experiments to reveal the extraction of the various metals. Chalcopyrite was the main mineral, the total copper content was 38.5 %wt. Comparative bioleaching with mesophilic, moderate thermophilic and thermophilic acidophilic iron- and sulfur-oxidizing bacteria and archaea was investigated. Batch culture experiments were conducted at 2% (w/v) pulp density in shake flasks in the presence of Acidithiobacillus ferrooxidans, Acidiphilium sp. and Acidithiobacillus thiooxidans as mesophiles (30°C), a mixed culture of moderate thermopilic iron- and sulfur oxidizing bacteria (50°C) and the thermophile Acidianus brierleyi (70°C). The results after four weeks showed most effective dissolution of copper in the presence of A. brierleyi (up to 4.3 g/l), compared with moderate thermophiles and mesophiles (3.3 g/l and 2.5 g/l, respectively). Furthermore, the bioleaching performance was approved with dissolved iron concentrations. Conclusively, an increase in temperature from 30 °C to 70 °C had a major impact on bioleaching efficiency. Copper and iron extraction efficiency occurred in the order thermophiles, moderate thermophiles, mesophiles.

Microbial community dynamics during a demonstration-scale bioheap leaching operation

In the present work the microbial community of a low grade nickel ore demonstration-scale bioheap was examined under varying weather (outside air temperature between +30 and −39°C) and operational conditions over a period of three years in Talvivaara, Finland. After the start-up of heap irrigation, oxidation of pyrrhotite and pyrite increased the heap temperature up to 90°C. Leach liquor temperatures varied between 60 and 15°C over the operation period, affecting the progress of sulfide ore oxidation.The microbial communities were profiled by polymerase chain reaction (PCR) — denaturing gradient gel electrophoresis (DGGE) followed by partial sequencing of 16S rRNA gene. Large temperature gradients prevailed resulting in the simultaneous presence of active mesophilic and thermophilic iron- and/or sulfur-oxidisers in the heap. As mineral oxidation progressed microbial diversity decreased and Acidithiobacillus ferrooxidans became increasingly dominant. The number of bacteria in the leach liquors was in the range of 105–107cellsmL−1. After one year of bioheap operation several ore samples were drilled from the heap and A. ferrooxidans, Acidithiobacillus caldus, an uncultured bacterium clone H70 related organism, Ferrimicrobium acidiphilum and a bacterium related to Sulfobacillus thermosulfidooxidans were found. Cell counts from the ore samples varied between 105 and 107cellsg−1 ore sample. The archaeal species present in leach liquors were novel and related to uncultivated species. During the secondary leaching phase the leaching community remained steady. A. ferrooxidans dominated, and an uncultured bacterium clone H70-related organism and Leptospirillum ferrooxidans were present.

A novel acidophilic, thermophilic iron and sulfur-oxidizing archaeon isolated from a hot spring of tengchong, yunnan, China

A novel acidophilic, thermophilic iron and sulfur-oxidizing archaeon isolated from a hot spring of tengchong, yunnan, China

A novel acidophilic, thermophilic iron and sulfur-oxidizing archaeon isolated from a hot spring of tengchong, yunnan, China.

A novel thermoacidophilic iron and sulfur-oxidizing archaeon, strain YN25, was isolated from an in situ enriched acid hot spring sample collected in Yunnan, China. Cells were irregular cocci, about 0.9–1.02 µm × 1.0–1.31 µm in the medium containing elemental sulfur and 1.5–2.22 µm × 1.8–2.54 µm in ferrous sulfate medium. The ranges of growth and pH were 50–85 (optimum 65) and pH 1.0–6.0 (optimum 1.5–2.5). The acidophile was able to grow heterotrophically on several organic substrates, including various monosaccharides, alcohols and amino acids, though the growth on single substrate required yeast extract as growth factor. Growth occurred under aerobic conditions or via anaerobic respiration using elemental sulfur as terminal electron acceptor. Results of morphology, physiology, fatty acid analysis and analysis based on 16S rRNA gene sequence indicated that the strain YN25 should be grouped in the species Acidianus manzaensis. Bioleaching experiments indicated that this strain had excellent leaching capacity, with a copper yielding ratio up to 79.16% in 24 d. The type strain YN25 was deposited in China Center for Type Culture Collection (=CCTCCZNDX0050).

Conventional and electrochemical bioleaching of chalcopyrite concentrates by moderately thermophilic bacteria at high pulp density

Conventional and electrochemical bioleaching were investigated to extract copper from Sarcheshmeh chalcopyrite concentrate at high pulp densities. Experiments were conducted in the presence and absence of a mixed culture of moderately thermophilic iron- and sulphur oxidizing bacteria using a 2-L stirred electro-bioreactor at 20% (w/v) pulp density, an initial pH of 1.4–1.6, a temperature of 50 °C, a stirring rate of 600 rpm and Norris nutrient medium with 0.02% (w/w) yeast extract addition. The results of 10 day leaches showed that, when using electrochemical bioleaching in an ORP range of 400 to 430 mV, copper recovery reaches about 80% which is 3.9, 1.5 and 1.17 times higher than that achieved in abiotic electrochemical leaching, conventional bioleaching, and electrochemical bioleaching at 440–480 mV ORP, respectively. It appears that applying current directly to the slurry optimises both, the biological and chemical subsystems, leading to an increase in both, the dissolution rate and the final recovery of copper from the concentrate. Mineralogical analysis of the solid residues of electrochemical leaching in both, biotic and abiotic media, showed the formation of chalcocite and covellite minerals on the surface of not leached chalcopyrite. It is postulated that the reduction of refractory chalcopyrite to more soluble minerals such as chalcocite and covellite is achieved through both, electron transfer upon electrode contact and by ferrous reduction at the low ORP of the slurry. These secondary minerals are then rapidly dissolved through bioleaching, while at the same time a formation of a passive layer of jarosites is minimised. This process also appears to promote an increased bacteria–solid ratio due to favourable growth conditions.

HPLC inorganic arsenic speciation analysis of samples containing high sulfuric acid and iron levels

To monitor the oxidation of arsenite to arsenate in oxidizing and bioleaching reactors, speciation analysis of the inorganic arsenic compounds is required. Existing arsenic speciation analysis techniques are based on the use of liquid chromatography columns coupled to detector equipment such as inductively coupled plasma optical emission spectrometry (ICP-OES). These techniques are fairly complex and expensive. Therefore, for analysis of arsenic speciation in our studies on thermophilic iron and arsenic oxidation, we developed a simple (and inexpensive) method based on anionic ion exclusion chromatography using sulfuric acid as mobile phase, followed by UV detection. The detection limit was 0.1 mg L−1 of arsenite (As3+) and 0.1 mg L−1 of arsenate (As5+). The method was validated with samples from an iron-oxidizing bioreactor containing 0.12 mol L−1 H2SO4, 1 g L−1 arsenic, and 3 g L−1 iron. Samples from arsenopyritic gold concentrates by partial bio-oxidation and leaching samples were analyzed, showing the usefulness of the method for arsenic contained in environmental compartments. We also describe the apparent effect of the arsenic valence state on ICP-OES detection for total arsenic.

Sulfide Mineral Induced Oxidative Stress as a Limiting Factor in Tank Bioleaching Performance

In tank bioleaching, decreasing particle size of milled concentrates has been shown to improve leaching performance owing to increased mineral surface area and mechanical activation effects of fine mineral particles. However, evidence suggests a critical lower limit of particle size distribution exists below which the performance of the thermophilic iron and sulfur oxidizer Sulfolobus metallicus is compromised and complete culture death may result. This paper proposes an explanation for these observations at fine fractions through identifying a relationship between mineral composition of six sulfide concentrates, their extent of milling and the generation of the reactive oxygen species (ROS) hydrogen peroxide (H2O2) and hydroxyl radicals (•OH) in slurries. The effect of oxidative stress induced in the absence of minerals on growth and bioleaching performance of S. metallicus is studied.

Bioleaching of high grade Pb–Zn ore by mesophilic and moderately thermophilic iron and sulphur oxidizers

The purpose of this study was to test the feasibility of using iron and sulphur oxidizing bacteria for the acid leaching of a high grade Pb–Zn ore material. Three strains (ATCC 13661, NCIMB 13537 and C2-TF) of Acidithiobacillus ferrooxidans and two strains (MT-TH1 and MT-13) of Sulfobacillus thermosulfidooxidans were tested in this study. The bioleaching was monitored by measuring the dissolved metals and by X-ray diffraction analysis of leach residues. The bioleaching efficiency varied between 0.014 and 0.35. The maximum dissolution of lead was achieved with the mesophilic At. ferrooxidans (NCIMB 13537) at 30 °C. The maximum recovery of zinc was achieved with moderately thermopilic S. thermosulfidooxidans (MT-TH1) at 45 °C.

Microbial reduction of structural Fe3+ in nontronite by a thermophilic bacterium and its role in promoting the smectite to illite reaction

The illitization process of Fe-rich smectite (nontronite NAu-2) promoted by microbial reduction of structural Fe3+ was investigated by using a thermophilic metal-reducing bacterium, Thermoanaerobacter ethanolicus , isolated from the deep subsurface. T. ethanolicus was incubated with lactate as the sole electron donor and structural Fe3+ in nontronite as the sole electron acceptor, and anthraquinone-2, 6-disulfonate (AQDS) as an electron shuttle in a growth medium (pH 6.2 and 9.2, 65 °C) with or without an external supply of Al and K sources. With an external supply of Al and K, the extent of reduction of Fe3+ in NAu-2 was 43.7 and 40.4% at pH 6.2 and 9.2, respectively. X-ray diffraction and scanning and transmission electron microscopy revealed formation of discrete illite at pH 9.2 with external Al and K sources, while mixed layers of illite/smectite or highly charged smectite were detected under other conditions. The morphology of biogenic illite evolved from lath and flake to pseudo-hexagonal shape. An external supply of Al and K under alkaline conditions enhances the smectite-illite reaction during microbial Fe3+ reduction of smectite. Biogenic SiO2 was observed as a result of bioreduction under all conditions. The microbially promoted smectite-illite reaction proceeds via dissolution of smectite and precipitation of illite. Thermophilic iron reducing bacteria have a significant role in promoting the smectite to illite reaction under conditions common in sedimentary basins.

Zinc extraction from Iranian low-grade complex zinc–lead ore by two native microorganisms: Acidithiobacillus ferrooxidans and Sulfobacillus

A mesophilic iron oxidizing bacterium, Acidithiobacillus ferrooxidans, has been isolated (33 °C) from a typical, chalcopyrite concentrate of the Sarcheshmeh copper mine in the region of Kerman located in the south of Iran. In addition, a thermophilic iron oxidizing bacterium, Sulfobacillus, has been isolated (60 °C) from the sphalerite concentrate of Kooshk lead and zinc mine near the city of Yazd in the center point of Iran. Variation of pH, ferrous and ferric concentration on time and effects of some factors such as temperature, cell growth, initial ferrous concentration and pH on bioleaching of low-grade complex zinc–lead ore were investigated. The results obtained from bioleaching experiments indicate that the efficiency of zinc extraction is dependent on all of the mentioned variables; especially the temperature and initial Fe(II) concentration have more effect than other factors for these microorganisms. In addition, results show that the maximum zinc recovery was achieved using a thermophilic culture. Zinc dissolution reached 58% with Sulfobacillus while it was 51% with A. ferrooxidans at pH = 1.5, initial Fe(II) concentration = 7 and 9 g/L for A. ferrooxidans and Sulfobacillus, respectively, after 30 days .

Bioleaching of low-grade sphalerite using a column reactor

The effects of several variables on zinc recovery in column bioleaching have been investigated. The ore contained sphalerite and pyrite as the main sulfide minerals and chalcopyrite and galena as minor minerals. Tests were carried out using a bench-scale column leach reactor which was inoculated with mesophilic ( Acidithiobacillus ferrooxidans) and thermophilic ( Sulfobacillus) iron oxidizing bacteria; initially isolated from the Sarcheshmeh chalcopyrite concentrate (Kerman, Iran) and Kooshk sphalerite concentrate (Yazd, Iran), respectively. In the inoculated column, jarosite and elemental sulfur were formed. The leaching rate of sphalerite tended to increase with dissolved ferric ion concentration. Microscopic counts of bacteria in the solution tended to be higher at lower pH ranges. Furthermore, the effect of a decreasing particle size on the rate of zinc leaching was enhanced at low pH values. Results show that the maximum zinc recovery was achieved using a thermophilic culture. Zinc dissolution reached 72% and 85% for the mesophilic and thermophilic strains, respectively, after 120 days at column temperatures ranging from 28 to 42 °C.

Comparison of bioleaching ability of two native mesophilic and thermophilic bacteria on copper recovery from chalcopyrite concentrate in an airlift bioreactor

A mesophilic iron oxidizing bacterium, Acidithiobacillus ferrooxidans, has been isolated (33 °C) from a typical chalcopyrite copper concentrate of the Sarcheshmeh copper mine in the region of Kerman located in the south of Iran. In addition, a thermophilic iron oxidizing bacterium, Sulfobacillus, has been isolated (60 °C) from the Kooshk lead and zinc mine near the city of Yazd in central Iran. Effects of some variable parameters such as solids concentration, temperature and pH on the bioleaching of chalcopyrite obtained from Sarcheshmeh copper mine were investigated. Bioleaching experiments were carried out in two batch airlift bioreactors with a recycling stream. The results indicate that the efficiency of copper extraction is dependent on all the variables studied for both microorganisms. Maximum copper recovery was achieved using a thermophilic culture. Copper dissolution reached 85% with Sulfobacillus and 70% with Acidithiobacillus ferrooxidans at 10% w/v pulp density, after 10 days .

Thermophilic Microbial Metal Reduction

Thermophilic microorganisms can reduce Fe(III), Mn(IV), Cr(VI), U(VI), Tc(VII), Co(III), Mo(VI), Au(I, III), and Hg(II). Ferric iron and Mn(IV) can be used as electron acceptors during growth; the physiological role of the reduction of the other metals is unclear. The process of microbial dissimilatory reduction of Fe(III) is the most thoroughly studied. Iron-reducing prokaryotes have been found in virtually all of the recognized types of terrestrial ecosystems, from hot continental springs to goethermally heated subsurface sediments. Thermophilic iron reducers do not belong to a phylogenetically homogenous group and include representatives of many bacterial and archaeal taxa. Iron reducing thermophiles can couple Fe(III) reduction with oxidation of a wide spectrum of organic and inorganic compounds. In the thermophilic microbial community, they can fulfil both degradative and productive functions. Thermophilic prokaryotes probably carried out global reduction of metals on Earth in ancient times, and, at the same time, they are promising candidates for use in modern biotechnological processes.

Mössbauer spectroscopy in studying magnetite formed by iron- and sulfate-reducing bacteria

The kinetics of iron mineral formation by thermophilic dissimilatory iron reducing bacteria using Fe(III) amorphous hydroxide and acetate CH3COO− as an electron acceptor and donor, respectively, was investigated by Mossbauer spectroscopy. The effects of various physical and chemical conditions and the presence of an inert organic substance on the formation of biogenic minerals were considered. The production of magnetite due to microbial sulfate reduction by hyperthermophilic dissimilatory sulfate-reducing microorganisms was investigated by Mossbauer spectroscopy methods.