Papers by Keyword: Acidithiobacillus ferrooxidans

Abstract: Extracellular polymeric substances (EPS) play an important role in the attachment of bacteria to sulphide minerals, biofilm formation and efficiency of the bioleaching process. Previous studies have suggested a potential connection between galactose and EPS formation. In this context, the influence of exogenous galactose on EPS formation during the bioleaching of pyrite was studied. In order to fully adapt the microorganism to bioleaching conditions it was performed a total of five consecutive sub cultures, one every fifteen days, taking for each one inocula from previous culture in shake flasks with 200 ml of fermentation medium at 30°C, 200 rpm, 40 gL^-1 mineral and an initial pH of 1,8. Assays were performed in a medium supplemented with exogenous galactose (0.25% w/v) and without exogenous galactose (control), both with an initial concentration of ferric sulphate in the first three sub cultures of 5 gL^-1, decreasing in the last two sub cultures to 2.5 gL^-1. Samples of three cultures in both conditions were analyzed using confocal laser scanning microscopy (CLSM) labelling the cells with propidium iodide and EPS carbohydrates with Wheat Germ Agglutinin (WGA). Samples obtained on the last day of the fifth culture showed that the EPS layer on the particle surface was 5.00 μm³/μm² in the case of the control condition and 6.10 μm³/μm² when bioleaching was carried out in the presence of exogenous galactose. Also it was observed that in the fifth sub culture the volumetric productivity of total iron in the control experiment was 0.0065 gL^-1.h^-1 compared with 0.0076 gL^-1.h^-1 obtained in presence of galactose. The results reveal that the presence of galactose in the bioleaching solution stimulates EPS's formation and apparently also favour the pyrite bioleaching process.

Abstract: Valuable metals as well as ferrous iron and sulfur compounds are released from ore by ferric iron and sulfuric acid chemical attack. Biomining microorganisms allow the recycling of these products by oxidizing ferrous iron and/or sulfur compounds. The energy released from the oxidation of these substrates is used for the growth of the acidophilic chemolithoautotrophic bacterium Acidithiobacillus ferrooxidans. The respiratory pathways involved in these respiratory processes have been deciphered and the expression of the genes encoding these redox proteins is dependent on the electron donor present in the medium. Furthermore, in the presence of both ferrous iron and sulfur, the genes involved in iron oxidation are expressed before those involved in sulfur oxidation. We propose that the global redox responding two component system RegBA is responsible for this regulation since (i) the redox potential increases during iron oxidation but remains stable during sulfur oxidation and (ii) the transcriptional regulator RegA binds the regulatory region of a number of genes/operons involved in iron and sulfur oxidation. To understand the mechanism of the At. ferrooxidans RegBA system, the regA gene and the DNA corresponding to the DNA binding domain of RegA were cloned in an expression plasmid in Escherichia coli. The recombinant proteins, RegA and RegA-HTH respectively, were purified. The binding of RegA-HTH, phosphorylated and unphosphorylated RegA on the regulatory region of some target operons have been compared by gel shift mobility assay.

Abstract: Iron-sulfur (Fe-S) proteins are ubiquitous and participate in multiple essential functions of life. However, little is currently known about the mechanisms of iron-sulfur biosynthesis and transfer in acidophilic microorganisms. In this study, the IscS, IscU and IscA proteins from Acidithiobacillus ferrooxidans were successfully expressed in Escherichia coli and purified by affinity chromatography. The IscS was a cysteine desulfurase which catalyzes desulfurization of L-cysteine and transfer sulfur for iron-sulfur cluster assembly. Purified IscU did not have an iron-sulfur cluster but could act as a scaffold protein to assemble the [2Fe-2S] cluster in vitro. The IscA was a [4Fe-4S] cluster binding protein, but it also acted as an iron binding protein. Further studies indicated that the iron sulfur clusters could be transferred from pre-assembled scaffold proteins to apo-form iron sulfur proteins, the reconstituted iron sulfur proteins could restore their physiological activities.

Abstract: The presence of extracellular polymeric substances (EPS) is important in the building of biofilms on mineral surfaces, increasing the bioleaching activity, as well as protecting the cells from adverse environmental conditions. The objective of this work was to study the effect of galactose in EPS production by Acidithiobacillus ferrooxidans. The experiences were performed in shake flask of 250 mL at 30 °C, 200 rpm and at an initial pH of 1.8. In order to establish the natural tolerance of the strain, its growth behaviour was evaluated at high ferric iron concentrations by adding consecutively the equivalent of 9 g/L of ferrous iron each time it was depleted in the broth. Cell growth stopped once ferric iron concentration increased up to 38 g/L. In order to determine the optimal conditions for EPS production, experiments were run in a chemostat of 0.5 L, operated at a constant dilution rate of 0.03 h^-1. Different steady states were obtained varying feeding concentrations of galactose (0.15%; 0.25% and 0.35%) and carbon dioxide (180 ppm and 360 ppm). , Cells grown in the chemostat at optimum operation conditions were used as inoculum to determine oxidative capacity of the microorganisms overproducing EPS. The EPS was quantified using confocal laser scanning microscopy (CLSM), labelling the cells with propidium iodide and EPS carbohydrates with wheat germ agglutinin (WGA). The higher volume production of EPS was observed in cells grown using 360 ppm of CO₂ and 0.35% of galactose. Also it was observed a size increment of cells, compared to cells grown in culture medium having 9 g/L of ferrous iron where presence of EPS was no detected. The results revealed that EPS overproducing A. ferrooxidans showed a tolerance to ferric iron concentration almost 9.5 g/L higher than the natural tolerance of cells grown in absence of galactose. Presence of galactose in culture medium stimulated the EPS production.

Abstract: The volumetric oxygen transfer coefficient (k_La) was used to define the conditions necessary for minimum aeration and to eliminate potential oxygen limitation in bioleaching cultures of Acidithiobacillus ferrooxidans. The Michaelis constants for oxygen were 1.07 and 0.71 μmol O₂ l^-1 for the oxidation of ferrous iron and elemental sulphur, respectively. The critical oxygen concentration, below which oxygen limitation occurred, was determined to be 6.25 and 3.125 μmol O₂ l^-1 for the oxidation of ferrous iron and elemental sulphur, respectively. The (k_La)_crit values required to maintain oxygen-unlimited substrate oxidation for ferrous iron and elemental sulphur were 7.70 and 4.88 h^-1, respectively.

Abstract: An acidophilic strain was isolated from drainage in Shanxi coal mine, after 16SrDNA amplification and sequencing analysis, it was identified to be Acidithiobacillus ferrooxidans. The ferrous ion oxidation rate of At.f and pH value were studied during its growth, the results showed that, the strain entering into the exponential growth phase needed about 30 hours, and the oxidation rate was more than 99% after 60 hours. The pH value increased from 2.08 to 2.64 at first 30 hours and then decreased to 2.0, and finally maintained at 2.0 in the whole growth process. The isolated strain provided a potential alternative method to handle the steel-picking sulfuric acid waste liquor.

Abstract: Acidithiobacillus ferrooxidans (A. ferrooxidans) was used to leach the hard cobalt white alloy in this study. The optimum pH and temperature in the presence of A. ferrooxidans was 2.0 and 30°C respectively. Three methods of treating the bacteria, which are directly inoculated with 10⁷ cell.ml^-1 in 9K culture medium, collected bacteria by centrifugation and dispersed to 10⁷ cell.ml^-1in the iron-free 9K culture medium, and beforehand adapted by the alloy and collected by centrifugation, were employed. The result showed that for the first mode, it took 6ds to finish the leaching of cobalt and 8d for copper with decrease in the number of the bacteria in leaching. For the second one, it needs 3d and 7d to dissolve cobalt and copper, and also accompanied decrease in the bacteria. And for the third one, the modified A. ferrooxidans could increase to10⁸ cell.ml^-1, and the leaching of two metals was, respectively, for 2d and 5d with the extracting rate of them being 99.50% and 99.0%.

Abstract: Strains of Acidithiobacillus ferrooxidans (At.f) were separated and purified from water sample collected from a hot spring and bioleaching a low grade phosphate ore. The results indicated that bioleaching phosphorus rate increasing sharply was starting at the ending of pH value decreasing, and ascend velocity had slowed down after linear regression of pH was at its second peak. In the environment of ultraviolet mutagenesis, the initial growth of At.f (r) was decreased by illumination time increased, but the maximum rate of bioleaching phosphate ore (ηm) was increased. In the condition of ultrasonic vibration, r was increased by vibration time added, and ηm was almost increased, except 20 min, owing to the modificatory coefficient was large enough. In circumstances of low temperature treatment, r was decreased by treatment time raised; ηm was more increase than the sample of un-treatment (CK).

Abstract: Microbial leaching was used to mobilize copper from two kinds of waste electronic scraps used as raw materials for printed wire boards. Both of Acidithiobacillus ferrooxidans and Acidithiobacillus thiooxidans used to solubilize copper from the samples. The experimental results demonstrated that the percentages of copper basically increased with decrease of sieve fraction of the samples. The green non-conductive coating of the waste electronic scraps was proved to have little effect on the leaching efficiency of both of the pure culture of Acidithiobacillus ferrooxidans and Acidithiobacil thiooxidans or their mixed culture. Acidithiobacillus ferrooxidans has larger solubilizing capability for copper than Acidithiobacillus thiooxidans.

Abstract: A strain of Acidithiobacillus ferrooxidans designated S t1 was isolated and identified from the acid mine drainage of Tianmashan Coal Mine, Tongling county, Anhui province. Its morphological, physiological and biochemical characters, growth conditions of pH value and temperature, 16S rDNA sequence and the phylogenetic tree was studied. Results showed that the bacteria strains from different sites have divergence at the curve of pH and Eh values during the enriching culture. The isolated strain S t1 grew in a pH rang from 2.0 to 3.0 and temperature 25 to 35°C with over 98％similarity to Acidithiobacillus ferrooxidans in 16S rDNA sequence.