Acidithiobacillus Sp Research Articles

Community dynamics of attached and free cells and the effects of attached cells on chalcopyrite bioleaching by Acidithiobacillus sp.

The community dynamics of attached and free cells of Acidithiobacillus sp. were investigated and compared during chalcopyrite bioleaching process. In the mixed strains system, Acidithiobacillus ferrooxidans was the dominant species at the early stage while Acidithiobacillus thiooxidans owned competitive advantage from the middle stage to the end of bioprocess. Meanwhile, compared to A. ferrooxidans, more significant effects of attached cells on free biomass with A. thiooxidans were shown in either the pure or mixed strains systems. Moreover, the effects of attached cells on key chemical parameters were also studied in different adsorption-deficient systems. Consistently, the greatest reduction of key chemical ion was shown with A. thiooxidans and the loss of bioleaching efficiency was high to 50.5%. These results all demonstrated the bioleaching function of attached cells was more efficient than the free cells, especially with A. thiooxidans. These notable results would help us to further understand the chalcopyrite bioleaching.

Detection and validation of a small broad-host-range plasmid pBBR1MCS-2 for use in genetic manipulation of the extremely acidophilic Acidithiobacillus sp.

An efficient genetic system for introducing genes into biomining microorganisms is essential not only to experimentally determine the functions of genes predicted based on bioinformatic analysis, but also for their genetic breeding. In this study, a small broad-host-range vector named pBBR1MCS-2, which does not belong to the IncQ, IncW, or IncP groups, was studied for the feasibility of its use in conjugative gene transfer into extremely acidophilic strains of Acidithiobacillus. To do this, a recombinant plasmid pBBR-tac-Sm, a derivative of pBBR1MCS-2, was constructed and the streptomycin resistant gene (Smr) was used as the reporter gene. Using conjugation, pBBR-tac-Sm was successfully transferred into three tested strains of Acidithiobacillus. Then we measured its transfer frequency, its stability in Acidithiobacillus cells, and the level of resistance to streptomycin of the transconjugants and compared this with the IncQ plasmid pJRD215 control. Our results indicate that pBBR1MCS-2 provides a new and useful tool in the genetic manipulation of Acidithiobacillus strains.

Structural Basis for the Thermostability of Sulfur Oxygenase Reductases

The thermostability of three sulfur oxygenase reductases (SORs) was investigated from thermoacidophilic achaea Acidianus tengchongensis (SORAT) and Sulfolobus tokodaii (SORST) as well as the moderately thermophilic bacterium Acidithiobacillus sp. SM-1 (SORSB). The optimal temperatures for catalyzing sulfur oxidation were 80 °C (SORAT), 85 °C (SORST), and 70 °C (SORSB), respectively. The half-lives of the three SORs at their optimal catalytic conditions were 100 min (SORAT), 58 min (SORST), and 37 min (SORSB). In order to reveal the structural basis of the thermostability of these SORs, three-dimensional structural models of them were generated by homology modeling using the previously reported high-resolution X-ray structure of SORAA (from Acidianus ambivalens) as a template. The results suggest that thermostability was dependent on: (a) high number of the charged amino acid glutamic acid and the flexible amino acid proline, (b) low number of the thermolabile amino acid glutamine, (c) increased number of ion pairs, (d) decreased ratio of hydrophobic accessible solvent surface area (ASA) to charged ASA, and (e) increased volumes of the cavity. The number of cavities and the number of hydrogen bonds did not significantly affect the thermostability of SORs, whereas the cavity volumes increased as the thermal stability increased.

Isolation and characterization of Acidithiobacillus caldus from a sulfur-oxidizing bacterial biosensor and its role in detection of toxic chemicals

A novel toxicity detection methodology based on sulfur-oxidizing bacteria (SOB) has been developed for the rapid and reliable detection of toxic chemicals in water. The methodology exploits the ability of SOB to oxidize sulfur particles in the presence of oxygen to produce sulfuric acid. The reaction results in an increase in electrical conductivity (EC) and a decrease in pH. The assay is based on the inhibition of SOB in the presence of toxic chemicals by measuring changes in EC and pH. We found that SOB biosensor can detect toxic chemicals, such as heavy metals and CN−, in the 5–2000 ppb range. One bacterium was isolated from an SOB biosensor and the 16S rRNA gene of the bacterial strain has 99% and 96% sequence similarity to Acidithiobacillus sp. ORCS6 and Acidithiobacillus caldus DSM 8584, respectively. The isolate was identified as A. caldus SMK. The SOB biosensor is ideally suited for monitoring toxic chemicals in water having the advantages of high sensitivity and quick detection.

The effect of ferrous and ferric iron on sphalerite bioleaching with Acidithiobacillus sp.

Bioleaching has gained increased interest as an alternative for processing zinc sulfide ores without the generation of SO 2. The bioleaching of sphalerite with mesophile microorganisms at 1% pulp density has been studied. Batch experiments were carried out at 34 °C and 200 rpm. The effects of pH, concentration of Fe(II), as well as the presence of Fe(III) in the zinc extraction were assessed. Fast zinc dissolution can be achieved working with Acidithiobacillus sp. The best pH for bioleaching is in the 1.75–2.00 range and the presence of Fe(III) has a strong influence in zinc extraction, increasing the rate of dissolution and does not adversely affect the growth of the Acidithiobacillus population.

Microbial desulfurization of different coals.

Coal is the most important nonrenewable energy source of fossil origin. It is also the most common fuel in thermal power plants. However, during coal incineration in power plants, high sulfur content of coal poses serious environmental problems owing to sulfur dioxide emission. We studied the application of microbial methods for removal of sulfur from three types of high sulfur coals-two samples collected from Assam and Rajasthan in India and one from Libiaz, Poland. These coal samples were desulfurized using indigenous Acidithiobacillus sp. After investigation of the effect of various parameters, the conditions optimized for the maximum removal of total sulfur (91.87% for lignite, 63.13% for Polish coal, and only 9.44% for Assam coal) were as follows: initial pH of 1.5 (2.5 in the case of Assam coal), particle size of 45 micro, pulp density of 2% (w/v), incubation period of 30 d at -35 degrees C in presence of 44.2 g/L of ferrous sulfate in the media with shaking at 140 rpm. Poor removal of sulfur in the case of Assam coal was owing to extensive precipitation of jarosites. In addition, the sulfur in Assam coal is mostly found in organic form, which is difficult to remove with Acidithiobacillus sp. The removal of sulfur from the three coal samples was demonstrated with photomicrographic studies.