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

Abstract During the oxidation of sulfide and thiosulfate purple and green sulfur bacteria accumulate globules of ‘elemental’ sulfur. Although essential for a thorough understanding of sulfur metabolism in these organisms, the exact chemical nature of the stored sulfur is still unclear. We applied sulfur K-edge X-ray absorption near edge spectroscopy (XANES) to probe the forms of sulfur in intact cells. Comparing XANES spectra of Allochromatium vinosum , Thiocapsa roseopersicina , Marichromatium purpuratum , Halorhodospira halophila and Chlorobium vibrioforme grown photolithoautotrophically on sulfide with reference probes (fingerprint method), we found sulfur chains with the structure R-S n -R. Evidence for the presence of sulfur rings, polythionates and anionic polysulfides in the sulfur globules of these bacteria was not obtained.