Sulfur Species Investigation in Extra- and Intracellular Sulfur Globules of Acidithiobacillus ferrooxidans and Acidithiobacillus caldus

The sulfur chemical speciation in extracellular and intracellular sulfur globules of Acidithiobacillus ferrooxidans and Acidithiobacillus caldus were investigated with an integrated approach including scanning electron microscopy, transmission electron microscopy, energy dispersive spectroscopy and sulfur K-edge X-ray absorption near edge structure spectroscopy (XANES). The results indicated that both strains can accumulate extracellular sulfur globules when grown on thiosulfate, and the major sulfur chemical speciation of which were S8 for A. ferrooxidans and mixture of ring sulfur and polythionate for A. caldus, respectively. In contrast, A. ferrooxidans can accumulate both linear sulfur and S8 internally when grown with sulfur powder and thiosulfate, whereas A. caldus did not accumulate intracellular sulfur globules. In addition, the fitted results of sulfur K-edge XANES spectra indicated that the reduced glutathione (containing thiols groups) were involved in sulfur bio-oxidation of both strains and the tetrathionate were the intermediate products during thiosulfate metabolism by two strains.