Acidithiobacillus Ferrooxidans Strain Research Articles

Development of Technology for the Bioleaching of Uranium in a Solution of Bacterial Immobilization

This study presents findings regarding the kinetics of ferrous iron oxidation in solution mediated by Acidithiobacillus ferrooxidans bacteria within a continuous-flow bioreactor employing diverse types of immobilizers. The objective is to augment the rate of ferrous iron oxidation in solutions utilizing an immobilizer for Acidithiobacillus ferrooxidans strains. Immobilization represents a promising avenue for enhancing the efficiency of Fe2⁺ oxidation via acidophilic ferrooxidizing bacteria, leading to a several-fold increase in oxidation rate. A comparative analysis was conducted to evaluate the efficacy of different types of immobilizer in facilitating iron oxidation within a continuous-flow bioreactor, including the application of wood chips coated with Fe(OH)3. The results indicate that wood chips coated with iron hydroxide serve as effective type of immobilizer, facilitating the robust attachment of Acidithiobacillus ferrooxidans via electrostatic interactions between negatively charged bacteria and positively charged surfaces. Experimental investigations were conducted using novel immobilization matrices in pilot-scale tests simulating the underground borehole leaching (UBL) of uranium. The bioactivation of leaching solutions enhances the efficiency and environmental compatibility of UBL compared to conventional chemical oxidation methods. The relationships between redox potential and ferric iron content in bioactivated solutions during the UBL of uranium were delineated. The significance of this study lies in its elucidating the pivotal role of Fe2⁺ oxidation in uranium extraction processes, particularly in the context of UBL. By employing bioactivation mediated by Acidithiobacillus ferrooxidans, the study demonstrates not only enhanced uranium extraction efficiency, but also markedly improved environmental sustainability compared to traditional chemical oxidation methods. The findings reveal crucial correlations between redox potential and ferric iron concentration in bioactivated solutions.

Bioleaching of chalcopyrite using native Acidithiobacillus ferrooxidans isolated in a mining area in Kitwe Zambia

This study aimed to assess the influence of the physical-chemical factors (particle size, shake flask speed, starting pH, and pulp density) in bioleaching of Zambian chalcopyrite using a novel native isolated Acidithiobacillus ferrooxidans strain DJN1 2021 from samples collected within mining area at Copper Nkana slag dump also known as the Black Mountain in Kitwe, Copperbelt Province in Zambia. The bacterium isolation was done using the modified 9 K selective media and was identified as A. ferrooxidans by using conventional procedures and 16S rRNA gene sequencing. The resulting sequences were analyzed by trimming and generating consensus sequences using Bio-edit software. Blasting results produced a significant alignment of 99.6% similarity with the corresponding sequences of A. ferrooxidans in GenBank. The phylogenetic analysis entails that the isolated strain was identified as A. ferrooxidans and named A. ferrooxidans strain DJN1 2021 with accession number MZ713091. Bioleaching of chalcopyrite (CuFeS2) by A. ferrooxidans (DJN1 2021) was conducted in shake flasks (100 ml) with a 9 K medium. The experiments were tested to optimize the initial pH, particle size, pulp density, and shake flask speed in the recovery of copper from its ore. The results revealed that all of the factors significantly influence the bioleaching process. When the initial pH was 1.8, copper was extracted at the rate of 30.6% within 30 bioleaching days. This was the maximum dissolution observed. The effect of revolution speed in the three different shake flask speeds (i.e. 50 rpm, 90 rpm, and 150 rpm) showed a significant difference in the rate of copper dissolution. A marked difference was observed between shake flask speeds of 50 rpm and 90 rpm with dissolutions of 29.4% and 30.0% respectively. In experiments to look into the effect of particle size, two size fractions were subjected to bioleaching on a shake flask, i.e. (<45 and 45-<63) µm. Results showed that the (45-<63) µm size fraction gave the highest copper extraction of 29.2%. A pulp density of 6% produced the highest extraction of 32.6%. These findings reveal that this novel native A. ferrooxidans strain DJN1 2021 has the potential to bioleaching of copper from chalcopyrite upon optimization in a bioreactor.

Influence of mobile genetic elements and insertion sequences in long- and short-term adaptive processes of Acidithiobacillus ferrooxidans strains

The recent revision of the Acidithiobacillia class using genomic taxonomy methods has shown that, in addition to the existence of previously unrecognized genera and species, some species of the class harbor levels of divergence that are congruent with ongoing differentiation processes. In this study, we have performed a subspecies-level analysis of sequenced strains of Acidithiobacillus ferrooxidans to prove the existence of distinct sublineages and identify the discriminant genomic/genetic characteristics linked to these sublineages, and to shed light on the processes driving such differentiation. Differences in the genomic relatedness metrics, levels of synteny, gene content, and both integrated and episomal mobile genetic elements (MGE) repertoires support the existence of two subspecies-level taxa within A. ferrooxidans. While sublineage 2A harbors a small plasmid related to pTF5, this episomal MGE is absent in sublineage 2B strains. Likewise, clear differences in the occurrence, coverage and conservation of integrated MGEs are apparent between sublineages. Differential MGE-associated gene cargo pertained to the functional categories of energy metabolism, ion transport, cell surface modification, and defense mechanisms. Inferred functional differences have the potential to impact long-term adaptive processes and may underpin the basis of the subspecies-level differentiation uncovered within A. ferrooxidans. Genome resequencing of iron- and sulfur-adapted cultures of a selected 2A sublineage strain (CCM 4253) showed that both episomal and large integrated MGEs are conserved over twenty generations in either growth condition. In turn, active insertion sequences profoundly impact short-term adaptive processes. The ISAfe1 element was found to be highly active in sublineage 2A strain CCM 4253. Phenotypic mutations caused by the transposition of ISAfe1 into the pstC2 encoding phosphate-transport system permease protein were detected in sulfur-adapted cultures and shown to impair growth on ferrous iron upon the switch of electron donor. The phenotypic manifestation of the △pstC2 mutation, such as a loss of the ability to oxidize ferrous iron, is likely related to the inability of the mutant to secure the phosphorous availability for electron transport-linked phosphorylation coupled to iron oxidation. Depletion of the transpositional △pstC2 mutation occurred concomitantly with a shortening of the iron-oxidation lag phase at later transfers on a ferrous iron-containing medium. Therefore, the pstII operon appears to play an essential role in A. ferrooxidans when cells oxidize ferrous iron. Results highlight the influence of insertion sequences and both integrated and episomal mobile genetic elements in the short- and long-term adaptive processes of A. ferrooxidans strains under changing growth conditions.

Bioleaching of tellurium from mine tailings by indigenous Acidithiobacillus ferrooxidans.

Tellurium (Te) is a scarce and valuable metalloid, which can be found in some mine tailings. In this work, an indigenous Acidithiobacillus ferrooxidans strain was used to leach Te from mine tailings collected in the Shimian Te mine region, China. Under the optimized conditions of initial pH of 2·0, pulp density of 4% and temperature of 30°C, 47·77% of Te can be dissolved after 24 days of bioleaching. The leaching of Te by different systems such as bioleaching, Ferric ion (Fe(III)) leaching and acid leaching was compared. The results showed that the leaching behaviour of Te is similar to that of sulphur in sulphide minerals, that is, Fe(III) first oxidizes telluride (Te(-II)) in minerals to elemental Te, and then elemental Te can be oxidized by bacteria to Te(IV) and Te(VI). Besides, it was also showed by scanning electron microscope observation and Fourier transform infrared spectroscopy analysis of the ore sample before and after bioleaching that some bedded structure covered on the surface of the ore after bioleaching acting as a reaction compartment, and the changing of active groups indicated a possible attachment between bacteria and ore. There is an indirect mechanism involved in bioleaching of Te.

Characterization and genomic analysis of two novel psychrotolerant Acidithiobacillus ferrooxidans strains from polar and subpolar environments.

The bioleaching process is carried out by aerobic acidophilic iron-oxidizing bacteria that are mainly mesophilic or moderately thermophilic. However, many mining sites are located in areas where the mean temperature is lower than the optimal growth temperature of these microorganisms. In this work, we report the obtaining and characterization of two psychrotolerant bioleaching bacterial strains from low-temperature sites that included an abandoned mine site in Chilean Patagonia (PG05) and an acid rock drainage in Marian Cove, King George Island in Antarctic (MC2.2). The PG05 and MC2.2 strains showed significant iron-oxidation activity and grew optimally at 20°C. Genome sequence analyses showed chromosomes of 2.76 and 2.84 Mbp for PG05 and MC2.2, respectively, and an average nucleotide identity estimation indicated that both strains clustered with the acidophilic iron-oxidizing bacterium Acidithiobacillus ferrooxidans. The Patagonian PG05 strain had a high content of genes coding for tolerance to metals such as lead, zinc, and copper. Concordantly, electron microscopy revealed the intracellular presence of polyphosphate-like granules, likely involved in tolerance to metals and other stress conditions. The Antarctic MC2.2 strain showed a high dosage of genes for mercury resistance and low temperature adaptation. This report of cold-adapted cultures of the At. ferrooxidans species opens novel perspectives to satisfy the current challenges of the metal bioleaching industry.

Attempts to Stimulate Leaching Activity of Acidithiobacillus ferrooxidans Strain TFBk

Autotrophic acidophilic bacteria Acidithiobacillus ferrooxidans is a model species for studying metal bioleaching from low-grade sulfide ores and concentrates. Arsenopyrite gold-bearing concentrates are refractory and often processed using biohydrometallurgical approaches; therefore, it is important to develop methods to improve arsenopyrite bioleaching. In the present work, we have studied the possibility of improving arsenopyrite concentrate bioleaching by the strain of A. ferrooxidans. For this purpose, we have analyzed the genome of the strain A. ferrooxidans TFBk to reveal the genes potentially important in the bioleaching process. Genes determining resistance to arsenic, as well genes involved in the utilization of C1-compounds and resistance to oxidative stress, were revealed. Therefore, the possibility of increasing the rate of arsenopyrite concentrate bioleaching using C1-compounds (methanol and formate) was studied. Formate was able to increase both the biomass yield of the strain A. ferrooxidans TFBk as well as the bioleaching rate. In addition, the effect of redox potential increase by means of the addition of sodium persulfate in the medium on arsenopyrite concentrate bioleaching was studied. It was shown that the addition of 0.1% sodium persulfate stimulated strain growth, while a higher concentration inhibited it. Despite this, the rate of concentrate bioleaching increased in the presence of 0.5–1.0% of persulfate, which may be explained by the interactions of added oxidizer with concentrate components.

Sewage Sludge Ash-Based Biofertilizers as a Circular Approach to Phosphorus: The Issue of Fe and Al in Soil and Wheat and Weed Plants

Sewage sludge management for fertilizer purposes can be a step in the circular phosphorus (P) economy. Using microbial solubilization in manufacturing fertilizers from recycled materials is an innovative approach with the potential to increase P compounds’ bioavailability, and fertilizers from sewage sludge ash and P-solubilizing bacteria are promising products of this technology. In addition to P and a range of macronutrients, these fertilizers contain small amounts of micronutrients and potentially toxic elements. This paper discusses the effects of fertilizer on iron (Fe) and aluminum (Al) content in soil, test plants (spring or winter wheat; grain and straw), weeds and post-harvest residues, based on field experiments. Treatments with conventional P fertilizers (superphosphate, phosphorite) and without P fertilization provided references. The tested biofertilizers containing the Bacillus megaterium or Acidithiobacillus ferrooxidans strain had no effect on total Fe and Al content in the soil or on the concentration of these elements in plant biomass when applied at P doses up to 35.2 kg ha–1. Fe and Al levels in grain did not suggest a potential risk to consumers.

Complete Genome Sequence of a Chemolithoautotrophic Iron-Oxidizing Bacterium, Acidithiobacillus ferrooxidans Strain NFP31, Isolated from Volcanic Ash Deposits on Miyake-Jima, Japan.

ABSTRACTThe genome sequence of Acidithiobacillus ferrooxidans strain NFP31, which is a chemolithoautotrophic iron-oxidizing bacterium that inhabits acidified volcanic deposits on Mount Oyama, Miyake Island (Miyake-jima), Japan, was determined to identify the genetic characteristics associated with pioneer microbes in newly placed pyroclastic deposits.

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.

A Biotechnological Strategy for Molybdenum Extraction Using Acidithiobacillus ferrooxidans.

Biosorption is a potential tool for the extraction of metals from contaminated water and recovery of precious metals, which is a convenient alternative to conventional processes. In the present study, molybdenum recovery by Acidithiobacillus ferrooxidans strain ZT-94 was evaluated. Additionally, the effects of pH initial concentration of molybdenum, contact time, adsorbent concentration, and temperature on the biosorption were investigated. As revealed by the results, the greatest amount of molybdenum sorption was achieved at pH 5. By increasing the concentration of molybdenum from 2 to 45mg/l, the molybdenum removal increases from 71.13 to 150mg/g dry weight of biomass, but biosorption efficiency decreased. Also, increasing the dry weight of biomass from 0.008 to 0.06g/l degreased the biosorption efficiency from 20.68 to 85.69%. The results of molybdenum biosorption were evaluated by Langmuir and Freundlich adsorption isotherm. The maximum biosorption capacity for molybdenum extraction was 150.497mg/g and amount which is very suitable for a biosorbent. The biosorption was examined by scanning electron microscopy-energy-dispersive X-ray spectroscopy. Because of the elevated biosorption properties of molybdenum by this biosorbent, it can be concluded that Acidithiobacillus ferrooxidans strain ZT-94 is a promising candidate for the removal and recovery of molybdenum from aqueous systems.

Поліморфізм штамів Acidithiobacillus ferrooxidans, ізольованих із відходів вугільної та енергетичної промисловості України

The results of Acidithiobacillus ferrooxidans strains genetic variability studies that were first isolated from waste by coal and energy industries of Ukraine are reported in this article. These strains, according to the results of previous studies, are fully consistent with the biological properties of A. ferrooxidans bacteria given in Bergey’s Manual of Determinative Bacteriology and other original works [8, 10, 12, 18] also strains studied, regardless of habitat, were resistant to temperature and pH, had a mixed type of food, similar energy sources used by strains, etc. [1, 10, 11]. Using PCR was confirmed the affiliation of isolated from different of origin dumps of acidophilic chemolithotrophic strains with A. ferrooxidans. Genetic polymorphism of the strains was studied by RAPD-PCR using universal primer M13. It was shown that strains of A. ferrooxidans that were isolated from various dumps have a wide genetic diversity. By PCR, their affiliation with the species A. ferrooxidans was confirmed. Comparison analysis of the obtained RAPD profiles showed the variability of the strains which coincides with their main phenotypic properties, as described earlier [11]. The most heterogeneous profiles were characteristic of A. ferrooxidans DTV 1, A. ferrooxidans Lad 5 and A. ferrooxidans Lad 27. The obtained RAPD profiles served as the basis for the generation of the dendrogram constructed using the Neighbor-Joining method and calcula­ting the similarity matrix, based on the coefficient of similarity of Nei &amp; Li. Based on the obtained dendrogram, the formation of two clusters that combine similar strains is shown. The obtained indicators of the probability of formation of nodes of the constructed dendrogram range from 65.0 to 76.0 %%, which confirms the high degree of similarity between strains grouped by clusters. It is also shown that the first of the cluster includes strains that were isolated from coal and waste from its enrichment, and the second cluster includes strains that were isolated from coal waste. The obtained data confirm that the genetic variability of the strains depends on the primary location of isolation of the strains, and the coefficients of similarity between them varies from 0.182 to 0.80.

Biodismantling, a Novel Application of Bioleaching in Recycling of Electronic Wastes

Electronic components (EC) from waste electrical and electronic equipment (WEEE) such as resistors, capacitors, diodes and integrated circuits are a subassembly of printed circuit boards (PCB). They contain a variety of economically valuable elements e.g., tantalum, palladium, gold, and rare earth elements. However, until recently there has been no systematic dismantling and recycling of the EC to satisfy the demand for raw materials. A problem connected with the recycling of the EC is the removal of the components (dismantling) in order to recover the elements in later processing steps. The aim of the present study was to develop a new technique of dismantling using bioleaching technology to lower costs and environmental impact. In triplicate batch experiments, used PCBs were treated by bioleaching using an iron-oxidizing mixed culture largely dominated by Acidithiobacillus ferrooxidans strains supplemented with 20 mM ferrous iron sulfate at pH 1.8 and 30 °C for 20 days. Abiotic controls were treated by similar conditions in two different variations: 20 mM of Fe2+ and 15 mM of Fe3+. After 20 days, successful dismantling was obtained in both the bioleaching and the Fe3+ control batch. The control with Fe2+ did not show a significant effect. The bioleaching condition presented a lower rate of dismantling which can partially be explained by a constantly higher redox potential leading to a competition of solder leaching and copper leaching from the printed copper wires. The results showed that biodismantling—dismantling using bioleaching—is possible and can be a new unit operation of the recycling process to maximize the recovery of valuable metals from PCBs.

Acidophilic biodesulphurization of calcined pet coke and coal samples in iron and iron-free leaching media

Mineralogically distinct coal samples respond differently to microbial attack. In the present study, a mixed meso-acidophilic bacterial consortium predominantly comprising of Acidithiobacillus ferrooxidans strain was investigated for its biodesulphurization abilities for three distinct sulphur bearing samples (Goa CPC, Rajasthan Lignite, Assam Coal) of Indian origin in iron (9K+) and iron-free (9K−) media. A media devoid of Fe (II) iron was more effective for sulphur removal with maximum desulphurization of 45.19% for Assam coal followed by 36.8% for Rajasthan Lignite and 23.38% for CPC respectively. The proximate analysis, FTIR patterns and XRD analysis of the samples provided better insights into understanding the mineralogical and compositional changes in the coal matrix. Owing to the higher efficiency, Assam coal was additionally subjected to further optimization studies and characterization of the treated coal through TGA. The study indicated that the gross calorific values for all the samples increased following microbial treatment in 9K−media thereby providing a scope for further scale-up studies.

Bioleaching of iron from fly ash using a novel isolated Acidithiobacillus ferrooxidans strain and evaluation of catalytic role of leached iron in the Fenton's oxidation of Cephelaxin

Bioleaching of iron from fly ash using a novel isolated Acidithiobacillus ferrooxidans strain and evaluation of catalytic role of leached iron in the Fenton's oxidation of Cephelaxin

Microbial clean-up of uranium in the presence of molybdenum using pretreated Acidithiobacillus ferrooxidans

The present study is an attempt to optimize the uranium biosorption by pretreated Acidithiobacillus ferrooxidans strain ZT-94. The influences of pH, contact time, biomass dose, uranium concentration and temperature were investigated. In optimal conditions, uranium biosorption capacity was 204.44 mg/g dry weight at pH 4 during 60 min. The biosorbent was characterized by SEM microscope. The equilibrium data was fitted well by the Freundlich model with R2 = 0.8978. In the presence of molybdenum, pretreated biosorbent is tendency to adsorption of uranium. Finally, this study suggests that new biosorbent can be a potential candidate for uranium bioremediation in dual contamination with molybdenum.

Evaluation of the Biotechnological Potential of Pure and Mixture of Indigenous Iron-Oxidizing Bacteria to Dissolve Trace Metals from Cu Bearing Ore

This study aimed to investigate the ability of pure and consortia of indigenous iron-oxidizing bacteria to enhance the dissolution of trace metals from Cu and Zn-bearing ore. Three bacterial strains Acidithiobacillus ferrooxidans strain WG101, Leptospirillum ferriphilum strain WG102, Leptospirillum ferrooxidans strain WG103 isolated from Baiyin copper mine, China were used in this study. The biotechnological potential of these indigenous isolates was evaluated both in pure and in consortia to extract cobalt, chromium, and lead from the copper and zinc bearing ore. The sulfur and iron-oxidizing bacterial isolate Acidithiobacillus ferrooxidans strain WG101 exhibited efficient dissolution compared to sole iron-oxidizing Leptospirillum ferriphilum strain WG102, and Leptospirillum ferrooxidans strain WG103. Initial medium pH, pulp density, and temperature were studied as influential parameters in bioleaching carried out by bacterial consortia. The achieved optimum conditions were; initial pH of 1.5, 10% of pulp density, and temperature 30 °C with 68.7 ± 3.9% cobalt, 56.6 ± 3.9% chromium, and 36 ± 3.7% lead recovery. Analytical study of oxidation-reduction potential and pH fluctuation were observed during this whole process that shows the metal dissolution efficiency of bacterial consortia. Alterations in spectral bands of processed residues were reported through FTIR analysis compared with control ore sample. Mössbauer spectroscopy analysis showed the influence of bacterial consortia on iron speciation in bioleached samples. The findings confirm that the indigenous acidophilic iron-oxidizing bacterial strains are highly effective in the dissolution of trace elements present in ore samples. This study not only supports the notion that indigenous bacterial strains are highly effectual in metal dissolution but provides the basic vital conditions to upscale the bioleaching technique for metals dissolution.

Culture-dependent hunt and characterization of iron-oxidizing bacteria in Baiyin Copper Mine, China, and their application in metals extraction.

The exploration of microbial diversity in extremely acidic habitats has provided a vital base for the progression of minerals biotechnology. Three indigenous iron-oxidizing acidophilic bacterial strains were isolated through serial dilution of enriched bacterial culture from Baiyin Copper Mine Stope, China. The morphological, biochemical, physiological, and phylogenetic characteristics of isolates were investigated. These isolates were motile, Gram-negative, and curved shape with pleomorphism except isolate WG101 that was a straight rod. The optimum growth pH and temperature for all isolates were 1.5 and 30 °C, respectively, and showed extreme acidophilic nature. All the isolates showed obligate chemoautotrophic nature and used ferrous iron and pyrite as an energy source, however, isolates WG102 and WG103 were unable to use sulfur, while isolate WG101 could use elemental sulfur and reduced inorganic sodium thiosulfate as an energy source. The phylogenetic analyses based on 16S rRNA sequences revealed that the isolates WG101, WG102, and WG103 were homologous with Acidithiobacillus ferrooxidans strain AS2 (99%), Leptospirillum ferriphilum strain YSK (98%), and Leptospirillum ferrooxidans strain L15 (98%), respectively. These bacterial isolates showed efficient copper and zinc dissolution from the ore. The metals dissolution rate of At. ferrooxidans strain WG101 was 54.5 ± 4.33% (copper) and 49.6 ± 5% (zinc). The metals recovery rate of L. ferriphilum strain WG102 was 45.7 ± 3.5% (copper) and 40.5 ± 2.5% (zinc). The recovery rate of copper and zinc was 49.6 ± 4% and 46.5 ± 3% respectively in the case of L. ferrooxidans strain WG103. The findings of this study are consistent with the notion that the indigenous bacteria are more efficient in minerals dissolution.

Bacteriological synthesis of iron hydroxysulfate using an isolated Acidithiobacillus ferrooxidans strain and its application in ametryn degradation by Fenton's oxidation process

The investigation reports the application of biogenic jarosite, an iron hydroxy sulfate mineral in Fenton's Oxidation process. Ametryn, a herbicide detrimental to aquatic life and also to human is treated by Fenton's oxidation process using synthesized iron mineral, jarosite. The jarosite synthesis was carried out by using an isolated Acidithiobacillus ferrooxidans bacterial strain with ferrous as an iron supplement. The isolated strain was characterized by molecular techniques and biooxidation activity to ferrous to ferric iron was checked. On Fenton's treatment ametryn degradation upto 84.9% and COD removal to the extent of 56.1% was observed within 2 h of treatment and the reaction follows the pseudo first order kinetics with the curve best fit. The slight increase in kinetic rate constant on jarosite loading rate increase from 0.1 g/L to 0.5 g/L with H2O2 dosage of 100 mg/L confirms that jarosite has a catalytic role in the removal of ametryn. Mass spectroscopy analysis of treated synthetic ametryn solution at various intervals reveal the degradation follows dealkylation and hydroxylation pathway with the formation of three major intermediate compounds discussed here.

Bioleaching of copper- and zinc-bearing ore using consortia of indigenous iron-oxidizing bacteria.

Indigenous iron-oxidizing bacteria were isolated on modified selective 9KFe2+ medium from Baiyin copper mine stope, China. Three distinct acidophilic bacteria were isolated and identified by analyzing the sequences of 16S rRNA gene. Based on published sequences of 16S rRNA gene in the GenBank, a phylogenetic tree was constructed. The sequence of isolate WG101 showed 99% homology with Acidithiobacillus ferrooxidans strain AS2. Isolate WG102 exhibited 98% similarity with Leptospirillum ferriphilum strain YSK. Similarly, isolate WG103 showed 98% similarity with Leptospirillum ferrooxidans strain L15. Furthermore, the biotechnological potential of these isolates in consortia form was evaluated to recover copper and zinc from their ore. Under optimized conditions, 77.68 ± 3.55% of copper and 70.58 ± 3.77% of zinc were dissolved. During the bioleaching process, analytical study of pH and oxidation-reduction potential fluctuations were monitored that reflected efficient activity of the bacterial consortia. The FTIR analysis confirmed the variation in bands after treatment with consortia. The impact of consortia on iron speciation within bioleached ore was analyzed using Mössbauer spectroscopy and clear changes in iron speciation was reported. The use of indigenous bacterial consortia is more efficient compared to pure inoculum. This study provided the basic essential conditions for further upscaling bioleaching application for metal extraction.

Physiological and comparative genomic analysis of Acidithiobacillus ferrivorans PQ33 provides psychrotolerant fitness evidence for oxidation at low temperature

Friendly environmental hydrometallurgy at low temperatures is principally promoted by Acidithiobacillus ferrivorans. Until recently, the synergy between cold tolerance and the molecular mechanism of ferrous iron (Fe2+) oxidation was unknown. In the present paper, we conducted a physiological and comparative genomics analysis of the new strain A. ferrivorans PQ33 to elucidate the oxidation mechanism at low temperatures, with emphasis placed on trehalose and the Rus operon. PQ33 exhibited a doubling time of 66.6 h in Fe2+ at pH 1.6 and 63.6 h in CuS at 5 °C. Genomic island (GI) identification and comparative genome analysis were performed with four available genomes of Acidithiobacillus sp. The genome comprised 3,298,172 bp and 56.55% GC content. In contrast to ATCC Acidithiobacillus ferrooxidans strains, the genome of A. ferrivorans PQ33 harbors one GI, which contains a RusB gene. Moreover, five genes of peptidyl-prolyl cis–trans isomerase (PPIases) were observed. Furthermore, comparative analysis of the trehalose operon suggested the presence of a horizontal transfer event. In addition, comparison of rusticyanin proteins revealed that RusB has better intrinsic flexibility than RusA. This comparison suggests psychrotolerant fitness and supports the genetic canalization of A. ferrivorans PQ33 for oxidation at low temperature.