Thermophilic acidophilic Archaea were enriched from samples collected from geothermally active sites in Papua New Guinea. Pure cultures (JP2 and JP3) were obtained from mixed culture enrichments and were characterised and tested for their bioleaching ability. All cultures possessed Sulfolobus-like morphology, and the presence of distinctive cyclized tetraether lipids. The two pure cultures were identified by their 16S rRNA gene sequences as being most closely related to Sulfolobus solfataricus. Each isolate was able to oxidise both Fe2+ and sulphur, and grow on both pyrite and chalcopyrite under autotrophic conditions. Leaching experiments showed that the isolates were capable of rapidly leaching a chalcopyrite concentrate (up to 91% Cu release in 108 h). Optimal temperatures for growth and chalcopyrite leaching were determined for each strain. Chalcopyrite dissolution rates for JP2 at different temperatures were determined using a previously described kinetic model. An Arrhenius plot to investigate the relationship between dissolution rate and temperature, showed that for JP2, an increase in temperature from 70 to 83 °C resulted in a 6.6-fold rate increase. Studies with both mixed and pure cultures showed that these cultures were capable of rapidly leaching a chalcopyrite concentrate at very high temperatures (up to 90 °C), but also were capable of bioleaching at 50 °C. These thermophilic acidophiles possess the ability to bioleach over a wide range of temperatures. They are potentially well suited to industrial leaching applications where considerable temperature fluctuations limit the growth of other non-thermophilic bioleaching microorganisms.
"However, despite this advantage, thermophiles appear more susceptible to the physicochemical stresses caused by the harsh operating environment. This sensitivity displayed by thermophiles to mineral solids has been studied with the model thermophilic microorganism Sulfolobus metallicus (Nemati and Harrison, 2000; Nemati et al., 2000; Plumb et al., 2002; Rubio and Garcia Frutos, 2002; Harrison et al., 2003; Sissing and Harrison, 2003; Stott et al., 2003; Raja, 2005; Astudillo and Acevedo, 2009; Valencia and Acevedo, 2009; Vilcaez et al., 2009). The fundamental mechanisms whereby microbial stress is caused by increasing pulp density or decreasing particle size, hence increasing particle surface area loading, have been explored, but have not to date been explained adequately. "
[Show abstract][Hide abstract] ABSTRACT: The generation of Reactive Oxygen Species (ROS), H2O2 and OH, has been observed from sulfide mineral containing particles in acidic solutions. The implications of this phenomenon, as a potential microbial stress-causing effect, have been studied previously with respect to thermophilic bioleaching performance in the presence of finely milled pyrite and chalcopyrite concentrates. In this study, the effect of sulfide mineralogy on ROS generation in the absence of microbes under physicochemical conditions typical for the bioleach environment was investigated. The mineralogical and elemental composition of eleven different samples containing sulfide mineral was obtained. These Au, Cu and other base metal-containing sulfide mineral concentrates as well as a milled whole ore of low Cu grade were tested for ROS generation. The whole ore sample and two refractory Au concentrates containing approximately 50% pyrite, generated significantly less ROS compared to the base metal-containing concentrates when compared on a constant surface area loading basis. Sulfide mineral-related variables were correlated with ROS generation. A significant difference was observed between FeS2 and CuFeS2 grades separately, whereas a combined measure of both minerals present in samples showed a consistently strong correlation to ROS generation. The Cu grade, total Cu-containing sulfides and the chalcopyrite content of Cu-containing samples correlated well with ROS generation. However, a common deterministic variable with a strong association to increased ROS generation was not found. A sub-set of samples were subjected to QEMSCAN® for textural analysis. Results suggested that a decrease in sulfide mineral liberation, caused by gangue silicate mineral occlusion to solution, resulted in decreased reactivity as shown in one of the Au-containing samples. Well-liberated chalcopyrite and pyrite phases corresponded to increased reactivity of samples. Pyrite, which was present in all of the reactive samples, was shown to be associated with other sulfide minerals, implicating its importance in galvanic interactions. Micro-analysis of chalcopyrite and pyrite phases from highly reactive samples showed an abundance of particles with extensive cracking and the possible presence of secondary transformation phases (szomolnokite). These results suggest that sulfide mineralogy, liberation and extent of physical processing affect sulfide mineral concentrate reactivity in acidic solutions.
[Show abstract][Hide abstract] ABSTRACT: The extreme acid conditions required for scorodite (FeAsO4·2H2O) biomineralization (pH below 1.3) are suboptimal for growth of most thermoacidophilic Archaea. With the objective to develop a continuous process suitable for biomineral production, this research focuses on growth kinetics of thermoacidophilic Archaea at low pH conditions. Ferrous iron oxidation rates were determined in batch-cultures at pH 1.3 and a temperature of 75°C for Acidianus sulfidivorans, Metallosphaera prunea and a mixed Sulfolobus culture. Ferrous iron and CO2 in air were added as sole energy and carbon source. The highest growth rate (0.066 h−1) was found with the mixed Sulfolobus culture. Therefore, this culture was selected for further experiments. Growth was not stimulated by increase of the CO2 concentration or by addition of sulphur as an additional energy source. In a CSTR operated at the suboptimal pH of 1.1, the maximum specific growth rate of the mixed culture was 0.022 h−1, with ferrous iron oxidation rates of 1.5 g L−1 d−1. Compared to pH 1.3, growth rates were strongly reduced but the ferrous iron oxidation rate remained unaffected. Influent ferrous iron concentrations above 6 g L−1 caused instability of Fe2+ oxidation, probably due to product (Fe3+) inhibition. Ferric-containing, nano-sized precipitates of K-jarosite were found on the cell surface. Continuous cultivation stimulated the formation of an exopolysaccharide-like substance. This indicates that biofilm formation may provide a means of biomass retention. Our findings showed that stable continuous cultivation of a mixed iron-oxidizing culture is feasible at the extreme conditions required for continuous biomineral formation.
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"In recent years, some studies (Goebel and Stackebrandt 1994; Norris et al. 2000; Rawlings et al. 1999; Hawkes et al. 2006) have suggested that Leptospirillum spp., At. caldus, Sufobacillus spp., and Ferroplasma cupricumulans play significant roles in the dissolution of mineral ores at bioleaching systems operated at 45–50 °C. A number of studies also have shown that, at high temperature, the solubilization of copper from mineral ore proceeds much more efficiently (Dew et al. 2000; Plumb et al. 2002). Nowadays, there has been an increasing interest in the application of mixed cultures leaching mineral sulfides at 40–50 °C and microbial community analysis (Okibe et al. 2003; Okibe and Johnson 2004). "
[Show abstract][Hide abstract] ABSTRACT: To compare oxidative dissolution rates of chalcopyrite by different consortia of moderately thermophilic acidophiles, various defined mixed cultures of three bacteria Acidithiobacillus caldus s2, Leptospirillum ferriphilum YSK, and Sulfobacillus sp. LN and one archaeon Ferroplasma thermophilum L1 were studied in batch shake flask cultures incubated at 45 degrees C. Chalcopyrite dissolution was determined by measuring variations of soluble copper, ferric iron, and pH. Microbial population dynamics involved in bioleaching process were monitored using real-time quantitative polymerase chain reaction (PCR) technology. The complex consortia containing both chemoautotrophic (L. ferriphilum and At. caldus) and chemomixotrophic (Sulfobacillus LN and F. thermophilum) moderate thermophiles were found to be the most efficient in all of those tested. Mutualistic interactions between physiologically distinct moderately thermophilic acidophiles, involving transformations of iron and sulfur and transfer of organic compound, were considered to play a critical role in promoting chalcopyrite dissolution. The real-time PCR assay was reliable to analyze population dynamics of moderate thermophiles in bioleaching systems, and the analysis results were consistent with physiological characteristics of these strains.
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