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Journal of Bacteriology, October 2008, p. 6376-6383, Vol. 190, No. 19
0021-9193/08/$08.00+0     doi:10.1128/JB.00539-08
Copyright © 2008, American Society for Microbiology. All Rights Reserved.

X-Ray Absorption Spectroscopy as a Probe of Microbial Sulfur Biochemistry: the Nature of Bacterial Sulfur Globules Revisited {triangledown}

Graham N. George,1* Manuel Gnida,2 Dennis A. Bazylinski,4 Roger C. Prince,3 and Ingrid J. Pickering2

Department of Geological Sciences, University of Saskatchewan, 114 Science Place, Saskatoon, Saskatchewan S7N 5E2, Canada,1 Department of Pediatrics, Stanford University School of Medicine, 300 Pasteur Drive, Stanford, California 94305,2 ExxonMobil Biomedical Sciences Inc., Annandale, New Jersey 08801,3 School of Life Sciences, University of Nevada at Las Vegas, Las Vegas, Nevada 891544

Received 19 April 2008/ Accepted 21 July 2008

The chemical nature of the sulfur in bacterial sulfur globules has been the subject of controversy for a number of years. Sulfur K-edge X-ray absorption spectroscopy (XAS) is a powerful technique for probing the chemical forms of sulfur in situ, but two groups have used it with very different conclusions. The root of the controversy lies with the different detection strategies used by the two groups, which result in very different spectra. This paper seeks to resolve the controversy. We experimentally demonstrate that the use of transmittance detection for sulfur K-edge XAS measurements is highly prone to spectroscopic distortions and that much of the published work on sulfur bacteria is very likely based on distorted data. We also demonstrate that all three detection methods used for X-ray absorption experiments yield essentially identical spectra when the measurements are carried out under conditions where no experimental distortions are expected. Finally, we turn to the original question—the chemical nature of bacterial sulfur. We examine isolated sulfur globules of Allochromatium vinosum and intact cells of a strain of magnetotactic coccus and show that XAS indicates the presence of a chemical form of sulfur resembling S8.

* Corresponding author. Mailing address: Department of Geological Sciences, University of Saskatchewan, 114 Science Place, Saskatoon, Saskatchewan S7N 5E2, Canada. Phone: (306) 966-5722. Fax: (306) 966-8593. E-mail: g.george{at}usask.ca

{triangledown} Published ahead of print on 1 August 2008.

Journal of Bacteriology, October 2008, p. 6376-6383, Vol. 190, No. 19
0021-9193/08/$08.00+0     doi:10.1128/JB.00539-08
Copyright © 2008, American Society for Microbiology. All Rights Reserved.





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