Search

The influence of sodium chloride on dissolution of chalcopyrite and surface sulfur speciation during bioleaching of chalcopyrite with the extreme thermophile Acidianus manzaensis YN-25 was studied. The addition of sodium chloride accelerated the dissolution of chalcopyrite by reducing the accumulation of elemental sulfur layers on the mineral surface, resulting in an increase in the concentration of copper ions from 2.37g/L to 2.67g/L. Jarosite and elemental sulfur were found in the bioleached residues, while the amount of elemental sulfur accumulating on the mineral surface decreased drastically from 25.4% to 3.0% when 0.66g/L of sodium chloride was present during bioleaching. Therefore, the accumulation of elemental sulfur on the mineral surface is likely mainly responsible for the slowdown in the dissolution rate. The results indicated that bioleaching chalcopyrite with extreme thermophiles possessing high sulfur oxidation activity likely enhances dissolution of chalcopyrite by effectively removing elemental sulfur accumulating on the mineral surface., (Copyright © 2012 Elsevier Ltd. All rights reserved.)

The structure of a 14 kDa structural protein from Acidianus two-tailed virus (ATV) was solved by single-wavelength anomalous diffraction (SAD) phasing using X-ray data collected at 2.0 A wavelength. Although the anomalous signal from methionine sulfurs was expected to suffice to solve the structure, one chloride ion turned out to be essential to achieve phasing. The minimal data requirements and the relative contributions of the Cl and S atoms to phasing are discussed. This work supports the feasibility of a systematic approach for the solution of protein crystal structures by SAD based on intrinsic protein light atoms along with associated chloride ions from the solvent. In such cases, data collection at long wavelengths may be a time-efficient alternative to selenomethionine substitution and heavy-atom derivatization.

Metal centres play an important structural role in maintaining the native conformation of a protein. Here we use biophysical methods to investigate what is the relative contribution of iron-sulfur clusters in respect to ionic interactions in a thermophilic di-cluster ferredoxin model. Changes in protonation affect both the stability and the conformational dynamics of the protein fold. In the pH 5.5-8 interval, the protein has a high melting temperature (T(m) approximately 120 degrees C), which decreases towards pH extremes. Acidification triggers events in two steps: down to the isoelectric point (pH 3.5) the Fe-S clusters remain unchanged, the secondary structure content increases and the single Trp becomes more solvent shielded, denoting a more compact fold. Further acidification down to pH 2 sets off exposure of the hydrophobic core and Fe-S cluster disintegration, yielding a molten globule state. The relative stabilising contribution of the clusters becomes evident when stabilising ionic interactions are switched off as a result of poising the protein at pH 3.5, at an overall null charge: under these conditions, the Fe-S clusters disassemble at T(m)=72 degrees C, whereas the protein unfolds at T(m)=52 degrees C. Overall, this ferredoxin denotes a considerable structural plasticity around its native conformation, a property which appears to depend more on the integrity of its metal clusters rather than on the status of its stabilising electrostatic interactions. The latter however play a relevant role in determining the protein thermal stability.