Ferroplasma Acidiphilum Research Articles

Characterisation of growth parameters for the extremely acidophilic archaeon Ferroplasma acidiphilum DSM 12658 using a two-step turbidimetric growth measurement method

The acidophilic archaeon Ferroplasma acidiphilum exhibits remarkable adaptations to life in highly acidic environments. Nevertheless, the investigation of its molecular biology is challenging because of the slow growth of the organism, low biomass yield, and limitations of standard growth measurement techniques caused by iron oxidation.•A novel two-step turbidimetric growth measurement (2TGM) method was developed to address the shortcomings associated with iron precipitation in culture media. The method comprises two distinct preparation steps.•The initial 2TGM step involves centrifuging culture samples at high speed to remove F. acidiphilum cells and iron precipitates, thus preparing a blank.•The second 2TGM step involves centrifuging the culture at a lower speed with the objective of selectively removing iron precipitates, thus allowing F. acidiphilum cells to remain suspended in the supernatant. This preparation enables subsequent measurement of cell density.A study on the growth of F. acidiphilum showed a standard logistic pattern with a 35-h lag phase, approximately 9-h doubling time, and 0.042 OD carrying capacity. A new two-step turbidimetric growth measurement (2TGM) method overcomes limitations of existing approaches, enabling further investigation of F. acidiphilum.

Kinetic, electrochemical and spectral characterization of bacterial and archaeal rusticyanins; unexpected stability issues and consequences for applications in biotechnology

Motivated by the ambition to establish an enzyme-driven bioleaching pathway for copper extraction, properties of the Type-1 copper protein rusticyanin from Acidithiobacillus ferrooxidans (AfR) were compared with those from an ancestral form of this enzyme (N0) and an archaeal enzyme identified in Ferroplasma acidiphilum (FaR). While both N0 and FaR show redox potentials similar to that of AfR their electron transport rates were significantly slower. The lack of a correlation between the redox potentials and electron transfer rates indicates that AfR and its associated electron transfer chain evolved to specifically facilitate the efficient conversion of the energy of iron oxidation to ATP formation. In F. acidiphilum this pathway is not as efficient unless it is up-regulated by an as of yet unknown mechanism. In addition, while the electrochemical properties of AfR were consistent with previous data, previously unreported behavior was found leading to a form that is associated with a partially unfolded form of the protein. The cyclic voltammetry (CV) response of AfR immobilized onto an electrode showed limited stability, which may be connected to the presence of the partially unfolded state of this protein. Insights gained in this study may thus inform the engineering of optimized rusticyanin variants for bioleaching processes as well as enzyme-catalyzed solubilization of copper-containing ores such as chalcopyrite.

Pool bio-oxidation and fitting analysis of low-grade arsenic-containing refractory gold ore

To overcome the limitations of geography, climate, and ore characteristics on the ore beneficiation process, bio-oxidation studies on low-grade arsenic-bearing refractory gold ore by pool leaching were carried out, as well as process fitting analysis. The gold particles are encapsulated by pyrite and arsenopyrite. After 60 days of bio-oxidation, the oxidation rates of arsenic, sulfur, and gold were 39%∼69%, 24%∼41%, and 49%∼83%, respectively. The inoculated Acidithiobacillus ferrooxidans, Ferroplasma acidiphilum, and Leptospirillum ferrodiazotrophum could all mediate the initial pyrite/arsenopyrite oxidation and the Fe2+ oxidation reaction, but only the former could mediate the subsequent sulfur compound oxidation. When compared to daily bacterial circulation and bacterial replacement every ten days, aeration improved the gold leaching rate by 14%∼22%. The Boltzmann model could fit both the arsenic and sulfur bio-oxidation, with model fit variances greater than 0.98. Based on the experimental and fitting results, the bio-oxidation cycle was determined to be 60 days, and the bio-oxidation mechanisms are summarized. This study has significant practical implications for the rational utilization of gold resources and provides theoretical and practical guidance for similar gold ores.

Potential of single and designed mixed cultures to enhance the bioleaching of chalcopyrite by oxidation-reduction potential control

Biomining is the extraction of target metals from ores or wastes such as the dissolution of chalcopyrite for copper recovery. A key outstanding topic of study is to improve the rate and total copper released from chalcopyrite that can become ‘passivated’ by surface layers, which hinders oxidative attack on the metal sulfide bond. One strategy to increase chalcopyrite bioleaching is to control of the oxidation-reduction potential in the desired range by using ‘weak’ iron oxidizers. In this study, 15 acidophilic species were evaluated for their ability to catalyze chalcopyrite dissolution that resulted in the addition of Acidithiobacillus ferrianus, Sulfobacillus thermotolerans, and Metallosphaera sedula to the known ‘weak’ iron oxidizing species. Based upon these data, four microbial consortia were designed including mesophiles (25° and 37 °C), moderate thermophiles (49 °C), and thermophiles (70 °C) that increased copper recoveries by up to 32% compared to abiotic controls. The best performing consortium was the moderate thermophiles Sulfobacillus thermotolerans, Sulfobacillus acidophilus, and Ferroplasma acidiphilum that maintained the oxidation-reduction potential in the desired range. However, the consortia also showed evidence of synergistic interactions between ‘weak’ iron oxidizers that increased the efficiency of ferrous iron oxidation that resulted in oxidation-reduction potentials above the desired range and lower copper release. Therefore, while designing microbial consortia is a promising strategy to improve the performance of chalcopyrite bioleaching, care must be taken to ensure synergistic effects do not result in high oxidation-reduction potentials.

Rates of iron(III) reduction coupled to elemental sulfur or tetrathionate oxidation by acidophilic microorganisms and detection of sulfur intermediates

Bioleaching processes and acid mine drainage (AMD) generation are mainly driven by aerobic microbial iron(II) and inorganic sulfur/compound oxidation. Dissimilatory iron(III) reduction coupled to sulfur/compound oxidation (DIRSO) by acidophilic microorganisms has been described for anaerobic cultures, but iron reduction was observed under aerobic conditions as well. Aim of this study was to explore reaction rates and mechanisms of this process. Cell-specific iron(III) reduction rates for different Acidithiobacillus (At.) strains during batch culture growth or stationary phase with iron(III) (∼40 mM) as electron acceptor and elemental sulfur or tetrathionate as electron donor (1% or 5 mM, respectively) were determined. The rates were highest under anaerobic conditions for the At. ferrooxidans type strain with 6.8 × 106 and 1.1 × 107 reduced iron(III) ions per second per cell for growth on elemental sulfur and tetrathionate, respectively. The iron(III) reduction rates were somehow lower for the anaerobically sulfur grown archaeon Ferroplasma acidiphilum, and lowest for the sulfur grown At. caldus type strain under aerobic conditions (1.7 × 106 and 7.3 × 104 reduced iron(III) ions per second per cell, respectively). The rates for five strains of At. thiooxidans (aerobe) were in between those for At. ferrooxidans (anaerobe) and At. caldus (aerobe). There was no pronounced pH dependence of iron(III) reduction rates in the range of pH 1.0–1.9 for the type strains of all species but rates increased with increasing pH for four other At. thiooxidans strains. Thiosulfate as sulfur intermediate was found for At. ferrooxidans during anaerobic growths on tetrathionate and iron(III) but not during anaerobic growths on elemental sulfur and iron(III), and a small concentration was measured during aerobic growths on tetrathionate without iron(III). For the At. thiooxidans type strain thiosulfate was found with tetrathionate grown cells under aerobic conditions in presence and absence of iron(III), but not with sulfur grown cells. Evidence for hydrogen sulfide production at low pH was found for the At. ferrooxidans as well as the At. thiooxidans type strains during microaerophilic growth on elemental sulfur and for At. ferrooxidans during anaerobic growths on tetrathionate and iron(III). The occurrence of sulfur compound intermediates supports the hypothesis that chemical reduction of iron(III) ions takes place by sulfur compounds released by the microbial cells.

BIOKINETIC CHARACTERIZATION OF FERROPLASMA ACIDIPHILUM

Abstract. Recently a mixed culture dominated by the iron-oxidizing microorganisms Leptospirillum and Ferroplasma has been used in a large-scale microbial fuel cell for electrical power generation. There are many factors that affect the kinetics of iron oxidation by the mixotroph Ferroplasma acidiphilum. This study investigated the effects of pH, temperature, and substrate and yeast extract concentrations in order to arrive at kinetically favorable operating conditions with minimal jarosite precipitation. Furthermore, F. acidiphilum was cultured with Leptospirillum sp. in order to determine its viability as a species capable of limiting the organic by-products of chemolithotrophic microbial growth. Bacterial characterization in the culture was accomplished using fluorescent in situ hybridization (FISH). It was found that the ferrous iron oxidation was most favorable at yeast extract concentration of 0.02% (w/v), pH of 1.6, temperature of 35 oC and an initial ferrous iron concentration of 1 g/L yielding a maximum specific growth rate of 0.0351-0.042 h-1. Moreover, F. acidiphilum displayed a symbiotic relationship with its chemolithotrophic counterpart, Leptospirillum sp. in that they were able to utilize the metabolic organic products of the chemolithotroph and limit the organic concentration to ~20 ppm total organic carbon (TOC), well below the threshold concentration of 250 ppm for chemolithotroph activity.

Extracellular polymeric substances overproduction strategy in Ferroplasma acidiphilum growth for biooxidation of low-grade gold bearing ore: Role of monosaccharides

The adhesion of microorganisms to surfaces and the affecting factors is important in biomining pretreatment. In this research, the novelty is focused on studying the monosaccharide's impact on the adaptability and adhesivity of Ferroplasma acidiphilum for oxidization of sulfide-bearing ore containing pyrite harboring 98 % of gold in its crystal lattice. d-sucrose increased EPS production with the highest amount of pyrite dissolution (69 %) as compared to the other types of monosaccharides (d-galactose and d-fructose). Addition of 0.8 wt% d-sucrose enhanced the production of ferric ions 65 % for the ore load of 20 wt% while for the addition of 0.4 wt%, the ferric ions concentration was maximum up to 95 %. The results indicated that the addition of both yeast extract and d-sucrose with the concentration of 0.4 wt% enhanced the EPS (Extracellular Polymeric Substances) biovolume fraction from 7.5 to 32.5 v/v %.

Bulk flotation followed by selective leaching with biogenic ferric iron is a promising solution for eco-friendly processing of complex sulfidic ores.

The development of cost-effective environmentally friendly technologies is of current importance for the intensification of metal recovery. Here, we propose a new direction in the use of a two-step process for the treatment of complex sulfidic ores. In the first step, ore flotation allows the obtainment of a bulk copper-zinc concentrate and low-toxicity waste. In the second step, zinc is selectively extracted by chemical leaching with a biogenic ferric iron solution, while copper is accumulated in the leach residue. Importantly, the efficiency of this step depends on the chemical and mineralogical composition of polymetallic concentrates. Four samples of the copper-zinc sulfide concentrate with various contents of copper and zinc have been leached in multiple cycles at 80°C, 10% of pulp density, and pH 1.3-1.5. The leaching of the concentrate that contained 14.7% of copper and 5.0% of zinc for three leaching cycles (total duration, 5.75h) allowed the obtainment of a leach residue containing 15.3 and 0.14% of copper and zinc, respectively. At the same time, the leaching of another concentrate that contained 19.2% of copper and 2.64% of zinc after one leaching cycle (total duration, 0.67h) led to copper and zinc contents of 19.1 and 0.72%, respectively, in the leach residue. Therefore, the treatment of only two concentrates allowed the obtainment of high-grade copper concentrates containing low amounts of zinc. Ferric iron, the oxidant of sulfide minerals, was fully regenerated in leachate within 30-35h at 40°C using an acidophilic microbial community dominated by Leptospirillum ferriphilum, Sulfobacillus spp., and Ferroplasma acidiphilum. The loss of copper and zinc in solid waste of the bioregeneration did not exceed 1.0% and 1.8%, respectively. The proposed flowsheet of bulk concentrate processing has several important advantages over conventional technologies, including short duration of leaching, formation of low-toxicity solid waste, and pyrometallurgical processing of only high-grade copper concentrates. This approach can be a promising solution for the efficient processing of polymetallic bulk concentrates.

PROKARYOTIC DIVERSTY OF ACID MINE DRAINAGE PONDS IN ORE ENRICHMENT PLANT

The biodiversity of acidophilic prokaryotes was determined in three AMD ponds (pH 2.7-6.5) in Turkey (İzmir-Halıköy antimony ore enrichment plant) using 16S rRNA cloning and denaturing gradient gel electrophoresis methods. Water samples were taken two times in March 2014 and June 2015. The microbial diversity identified includes species such as Acidiphilium angustum, Acidocella sp., Ferroplasma acidiphilum, Acidithiobacillus ferriphilus, Acidithiobacillus ferrivorans, Acidiphilium rubrum, Thiomonas sp., Acidiphilium multivorum, Acidiphilium cryptum, Ferrovum myxofaciens, Acidocella aluminiidurans with the used techniques. In addition to, it has been determined that biodiversity is variable in the operating mine pools. Aciditihobacillus ferriphilus, Acidiphilium angustum, and Acidiphilium rubrum are new records for Turkey.

Distinct Roles of Acidophiles in Complete Oxidation of High-Sulfur Ferric Leach Product of Zinc Sulfide Concentrate.

A two-step process, which involved ferric leaching with biologically generated solution and subsequent biooxidation with the microbial community, has been previously proposed for the processing of low-grade zinc sulfide concentrates. In this study, we carried out the process of complete biological oxidation of the product of ferric leaching of the zinc concentrate, which contained 9% of sphalerite, 5% of chalcopyrite, and 29.7% of elemental sulfur. After 21 days of biooxidation at 40 °C, sphalerite and chalcopyrite oxidation reached 99 and 69%, respectively, while the level of elemental sulfur oxidation was 97%. The biooxidation residue could be considered a waste product that is inert under aerobic conditions. The results of this study showed that zinc sulfide concentrate processing using a two-step treatment is efficient and promising. The microbial community, which developed during biooxidation, was dominated by Acidithiobacillus caldus, Leptospirillum ferriphilum, Ferroplasma acidiphilum, Sulfobacillus thermotolerans, S. thermosulfidooxidans, and Cuniculiplasma sp. At the same time, F. acidiphilum and A. caldus played crucial roles in the oxidation of sulfide minerals and elemental sulfur, respectively. The addition of L. ferriphilum to A. caldus during biooxidation of the ferric leach product proved to inhibit elemental sulfur oxidation.

Effect of Graphite on Copper Bioleaching from Waste Printed Circuit Boards

The efficient extraction of copper as a valuable metal from waste printed circuit boards (WPCBs) is currently attracting growing interest. Here, we systematically investigated the impact of bacteria on the efficiency of copper leaching from WPCBs, and evaluated the effect of graphite on bioleaching performance. The HQ0211 bacteria culture containing Acidithiobacillus ferrooxidans, Ferroplasma acidiphilum, and Leptospirillum ferriphilum enhanced Cu-leaching performance in either ferric sulfate and sulfuric acid leaching, so a final leaching of up to 76.2% was recorded after 5 days. With the addition of graphite, the percentage of copper leaching could be increased to 80.5%. Single-factor experiments confirmed the compatibility of graphite with the HQ0211 culture, and identified the optimal pulp density of WPCBs, the initial pH, and the graphite content to be 2% (w/v), 1.6, and 2.5 g/L, respectively.

Two-step biohydrometallurgical technology of copper-zinc concentrate processing as an opportunity to reduce negative impacts on the environment

Polymetallic concentrates obtained during ore beneficiation pose a significant problem for the mining and metallurgy industry due to an increase in load on subsequent comminution steps and a high loss of metals in slag during smelting. Storage of such slag can lead to pollution of groundwater due to weathering. Biohydrometallurgy is an option for the processing of sulfidic raw materials that has a low impact on the environment. Processing of sulfidic concentrates of copper-zinc ore via bioleaching techniques was studied in this paper. Three mixed microbial cultures of acidophilic microorganisms were enriched from industrial mining sites: two autotrophic mesophilic cultures containing Acidithiobacillus ferroxidans and Leptospirillum spp. (grown at 30 and 35 °C), and a mixotrophic moderate thermophilic culture containing Sulfobacillus thermotolerans, Leptospirillum ferriphilum, as well as the archaea Ferroplasma acidiphilum and Acidiplasma spp. (grown at 40 °C). The autotrophic microbial culture growing at 30 °C was used to generate an iron-containing biosolution for ferric leaching of a copper-zinc concentrate. Zinc and iron extracted into solution faster than copper during high-temperature (80 °C) ferric leaching of the concentrate due to galvanic interactions between minerals, redox conditions of the medium, and differences between mineral oxidation mechanisms. Weight loss of the leach residue was 34.0%, with relative copper content increased by 1.0%, zinc content decreased by 6.18%, and iron content decreased by 15.1%. Biooxidation of ferrous iron in the pregnant leach solution by three microbial cultures was also studied. The most effective culture was moderate thermophilic. The results of studies on the bioregeneration of leaching solutions are relevant to the development of a two-step biohydrometallurgical technology for processing of copper-zinc concentrate with a closed cycle of technological flows. The ferrous iron biooxidation rate by the moderate thermophilic culture reached 20 g L−1 day−1. The leach residue obtained can be considered a high-grade copper concentrate able to be processed via smelting. This bioleaching process would make it possible to reduce pollution of groundwater by some toxic metals stored in slags. An environmentally friendly technology flow sheet for copper-zinc sulfidic ore processing using two-step bioleaching treatment was proposed.

Effect of Organic Nutrients on the Activity of Archaea of the Ferroplasmaceae Family

The effect of different organic compounds (glucose, fructose, ribose, glycine, alanine, pyruvate, acetate, citrate, and yeast extract) as well as of the wastes of food production (molasses, stillage, sweet whey), on the growth of iron-oxidizing acidophilic microorganisms and biooxidation of ferrous iron was studied. Representatives of the microorganisms predominating in biohydrometallurgical processes—archaea of the family Ferroplasmaceae (A. aeolicum V1T, A. cupricumulans BH2T, Acidiplasma sp. MBA-1, Ferroplasma acidiphilum B-1) and bacteria of the genus Sulfobacillus (S. thermosulfidooxidans SH 10–1, S. thermotolerans Kr1T)—were the subjects of the study. All studied strains most actively grew and oxidized ferrous iron in the presence of yeast extract, which is probably due to the presence of a large number of different growth factors in its composition, while others substrates provided growth of microorganisms and ferrous iron oxidation.

Physiological and Morphological Characteristics of Acidophilic Bacteria Leptospirillum ferriphilum and Acidithiobacillus thiooxidans, Members of a Chemolithotrophic Microbial Consortium

A thermoacidophilic consortium of chemolithotrophic microorganisms oxidizing the concentrate of high-pyrrhotite pyrite−arsenopyrite ore at 38–40°C was isolated. The most active members of the consortium were identified as Leptospirillum ferriphilum, Acidithiobacillus thiooxidans, Ferroplasma acidiphilum, and Sulfobacillus thermotolerans. Leptospirillum and Thiobacillus species were the most numerous members of the consortium and had the highest activity of ferrous iron and sulfur oxidation, respectively. The optimal temperature values for the growth of both isolates were within 35–38°C. The optimal ranges of initial pH were 1.0–1.2 and 1.75–1.85 for leptospirilla and 1.7–3.3 for thiobacilli with the pH optimum of 1.9. Significant polymorphism and specific cyclic growth with formation of vibrios, spirilla, rods with different end shape, spiral filaments, numerous “pseudococci,” and densely packed spiral filaments surrounded by a sheath were revealed for the Leptospirillum isolate. Two latter morphoforms of L. ferriphilum were not previously described. Differences in ability of the morphoforms to oxidize Fe2+ were revealed. For the first time, the possibility of growth in the presence of organic substances was demonstrated for A. thiooxidans. The rates of growth and substrate oxidation, cell size, and the maximal cell yield decreased insignificantly in comparison with the lithoautotrophic strain.

Mechanism of Silver-Catalyzed Bioleaching of Enargite Concentrate

Silver-catalyzed bioleaching of enargite concentrate with three bacteria (Acidimicrobium ferrooxidans ICP, Sulfobacillus sibiricus N1, Acidithiobacillus caldus KU) and one archaeon (Ferroplasma acidiphilum Y) was conducted in order to elucidate the catalytic mechanism of silver sulfide in enargite bioleaching. Whereas Cu recovery remained relatively low (43%) and Fe dissolved completely without silver sulfide, Cu recovery was greatly enhanced (96%) and Fe dissolution was suppressed (29%) in the presence of 0.04% silver sulfide. In the latter case, 52% of the solubilized As was re-immobilized, in contrast to only 14% As re-immobilization in the former. The silver-catalyzed bioleaching (at 0.04% silver sulfide) proceeded at low redox potentials within the optimal range, which likely promoted enargite dissolution via formation of intermediate Cu2S. XAFS analysis revealed that As was mainly immobilized as As (V), which was in agreement with the EPMA results detecting ferric arsenate passivation on some enargite grains. Furthermore, formation of trisilver arsenic sulfide (Ag3AsS4) was detected by XRD and EPMA, covering the surface of enargite particles. An intermediate layer, consisting of (Cu,Ag)3AsS4, was also observed between the enargite grain and trisilver arsenic sulfide layer, implying that Cu in enargite may be gradually substituted by solubilized Ag. The overall mechanism of silver-catalyzed bioleaching of enargite concentrate will be proposed.

Microbial Population of Industrial Biooxidation Reactors

Microbial population performing biooxidation of flotation concentrate of gold bearing sulfide ore containing pyrite, arsenopyrite, and pyrrhotite was studied using cultural and molecular biological (metagenomics sequencing of V3-V4 fragments of 16S rRNA gene) approaches. The biooxidation of the concentrate was conducted at temperatures from 38 to 42°C. Strains of Acidithiobacillus thiooxidans, Acidiphilium multivorum, Leptospirillum ferriphilum, Sulfobacillus thermotolerans, Ferroplasma acidarmanus, and Ferroplasma acidiphilum were isolated from the samples of the pulp from biooxidation reactors. It was shown that optimum temperatures of isolated strains were from 38 to 40°C. Metagenomic analysis demonstrated predominance of the genera Acidiferrobacter, Acidithiobacillus, Acidiphilum, Leptospirillum, and Ferroplasma. According to results of molecular biological analysis, share of the genus Acidithiobacillus was of 0 to 25%, share of the genus Acidiferrobacter was of 7 to 56%, share of the genus Acidiphilum was of 0.03 to 36%, share of the genus Leptospirillum was of 0.7 to 7%, whereas share of the archaea of the genus Ferroplasma was of 33 to 94%. Thus, it was shown that representatives of the genus Ferroplasma can play significant role in bioleach process. Representatives of the genus Acidiferrobacter were previously detected in acid mine drainages, acid soils as well as in bioleach heaps and reactors, whereas data on predominance of the genus in tank bioleach processes have not been presented in the literature. In the present study, strains of the genus Acidiferrobacter were not isolated despite application of the nutrient media recommended for Acidiferrobacter and their properties were not studied. Nevertheless, results of the present study suggest that representatives of the genus Acidiferrobacter have a great impact on industrial bioleach processes.

Linking Microbial Community Dynamics in BIOX<sup>®</sup> Leaching Tanks to Process Conditions: Integrating Lab and Commercial Experience

In the commercial BIOX® process, an acidophilic mixed bacterial and archaeal community dominated by iron and sulphur oxidising microorganisms is used to facilitate the recovery of precious metals from refractory gold-bearing sulphidic mineral concentrates. Characterisation of the microbial communities associated with commercial BIOX® reactors from four continents revealed a significant shift in the microbial community structure compared to that of the seed culture, maintained at SGS (South Africa). This has motivated more detailed study of the microbial community dynamics in the process. Microbial speciation of a subset of the BIOX® reactors at Fairview mines (Barberton, South Africa) and two laboratory maintained reactors housed at Centre for Bioprocess Engineering Research, University of Cape Town, has been performed tri-annually for three years by quantitative real-time polymerase chain reaction. The laboratory BIOX® culture maintained on Fairview concentrate was dominated by the desired iron oxidiser, Leptospirillum ferriphilum, and sulphur oxidiser, Acidithiobacillus caldus, when operated under standard BIOX® conditions. Shifts in the microbial community as a result of altered operating conditions were transient and did not result in a loss of the microbial diversity of the BIOX® culture. The community structure of the Fairview mines BIOX® reactor tanks showed archaeal dominance of these communities by organisms such as the iron oxidiser Ferroplasma acidiphilum and a Thermoplasma sp. for the period monitored. Shifts in the microbial community were observed across the monitoring period and mapped to changes in performance of the commercial process plant. Understanding the effect of changes in the plant operating conditions on the BIOX® community structure may assist in providing conditions that support the desired microbial consortium for optimal biooxidation to maximize gold recovery.

Interactions of the extremely acidophilic archaeon Ferroplasma acidiphilum with acidophilic bacteria during pyrite bioleaching

Interactions of the extremely acidophilic archaeon Ferroplasma acidiphilum with acidophilic bacteria during pyrite bioleaching

Interactions of the extremely acidophilic archaeon Ferroplasma acidiphilum with acidophilic bacteria during pyrite bioleaching

Bioleaching has been applied as a successful technique for metal recovery from various mineral sources like low-grade ores, waste materials and tailings. Mixed cultures of bioleaching microorganisms have a high performance in mineral dissolution. Thus far, microbial interactions in bioleaching communities are poorly understood. In this paper, the acidophilic archaeon Ferroplasma acidiphilum and the bacteria Leptospirillum ferriphilum and Sulfobacillus thermosulfidooxidans were chosen to study their interactions during pyrite leaching. The initial attachment to pyrite and pyrite leaching efficiency of pure and mixed populations were investigated. The data indicate: (i) attachment and bioleaching efficiency of L. ferriphilum was reduced in the presence of F. acidiphilum. However, the combination of F. acidiphilum and S. thermosulfidooxidans showed increased leaching, although the initial attachment rate was reduced, when compared to pure cultures. Thus, synergistic or antagonistic interactions may exist between F. acidiphilum and S. thermosulfidooxidans or F. acidiphilum and L. ferriphilum, respectively; (ii) pre-established biofilms of L. ferriphilum inhibited initial attachment to pyrite by cells of F. acidiphilum and did not promote pyrite leaching by F. acidiphilum. In contrast, inactivated biofilm cells of S. thermosulfidooxidans enhanced pyrite bioleaching by F. acidiphilum; (iii) adhesion forces of cells to an AFM tip (Si3N4) seemed to be not correlated to attachment and bioleaching capacity; and (iv) lectins were applied to show and distinguish single species in mixed biofilm populations. Physical contact between cells of S. thermosulfidooxidans and F. acidiphilum was visible.

Characterization of Ferroplasma acidiphilum growing in pure and mixed culture with Leptospirillum ferriphilum.

Biomining is defined as biotechnology for metal recovery from minerals, and is promoted by the concerted effort of a consortium of acidophile prokaryotes, comprised of members of the Bacteria and Archaea domains. Ferroplasma acidiphilum and Leptospirillum ferriphilum are the dominant species in extremely acid environments and have great use in bioleaching applications; however, the role of each species in this consortia is still a subject of research. The hypothesis of this work is that F. acidiphilum uses the organic matter secreted by L. ferriphilum for growth, maintaining low levels of organic compounds in the culture medium, preventing their toxic effects on L. ferriphilum. To test this hypothesis, a characterization of Ferroplasma acidiphilum strain BRL-115 was made with the objective of determining its optimal growth conditions. Subsequently, under the optimal conditions, L. ferriphilum and F. acidiphilum were tested growing in each other's supernatant, in order to define if there was exchange of metabolites between the species. With these results, a mixed culture in batch cyclic operation was performed to obtain main specific growth rates, which were used to evaluate a mixed metabolic model previously developed by our group. It was observed that F. acidiphilum, strain BRL-115 is a chemomixotrophic organism, and its growth is maximized with yeast extract at a concentration of 0.04% wt/vol. From the experiments of L. ferriphilum growing on F. acidiphilum supernatant and vice versa, it was observed that in both cases cell growth is favorably affected by the presence of the filtered medium of the other microorganism, proving a synergistic interaction between these species. Specific growth rates were obtained in cyclic batch operation of the mixed culture and were used as input data for a Flux Balance Analysis of the mixed metabolic model, obtaining a reasonable behavior of the metabolic fluxes and the system as a whole, therefore consolidating the model previously developed. © 2016 American Institute of Chemical Engineers Biotechnol. Prog., 32:1390-1396, 2016.