Tn situ analysis of sulfur in the sulfur globules of phototrophic sulfur bacteria by X-ray absorption near edge spectroscopy

During the oxidation of sulfide and thiosulfate purple and green sulfur bac teria accumulate globules of 'elemental' sulfur. Although essential for a t horough understanding of sulfur metabolism in these organisms, the exact ch emical nature of the stored sulfur is still unclear. We applied sulfur K-ed ge X-ray absorption near edge spectroscopy (XANES) to probe the forms of su lfur in intact cells. Comparing XANES spectra of Allochromatium vinosum, Th iocapsa roseopersicina, Marichromatium purpuratum, Halorhodospira halophila and Chlorobium vibrioforme grown photolithoautotrophically on sulfide with reference probes (fingerprint method), we found sulfur chains with the str ucture R-S-n-R. Evidence for the presence of sulfur rings, polythionates an d anionic polysulfides in the sulfur globules of these bacteria was not obt ained. (C) 1999 Elsevier Science B.V. All rights reserved.