Raman spectroscopic and laser scanning confocal microscopic analysis of sulfur in living sulfur-precipitating marine bacteria

Laser Raman microprobe spectroscopy and laser scanning confocal microscopy were used to determine the presence and speciation of sulfur in sulfur-oxid izing, marine bacteria from Monterey Bay, CA. The bacteria studied include: large, filamentous Thioploca and Beggiatoa, endosymbionts in the vesicomyi d clam Calyptogena kilmeri, and a filamentous bacterium of undetermined spe cies. All of these bacteria were shown spectroscopically to store elemental sulfur in submicrometer to several micrometer diameter vesicles. More deta iled Raman spectroscopic study of the vesicles in Thioploca and Beggiatoa p rovided further chemical and structural characterization of the elemental s ulfur. The sulfur is bonded in the common, stable S. ring configuration and is of an extremely fine-grained microcrystalline form. No additional (orga no) sulfur compounds were detected spectroscopically in the vesicles under the low laser powers required to preserve the molecular structure of the su lfur. The present spectroscopic and optical data stand in contrast to repor ts and inferences of liquid-like elemental sulfur or homogeneous, complex s ulfur compounds in other sulfur-oxidizing bacteria. The findings of this st udy are compatible with a model of sulfur vesicles as dominated by microcry stalline solid elemental sulfur, perhaps embedded in a matrix and/or confin ing membrane of organic material. The high reactivity and solubility observ ed in these vesicles is attributed to the extremely fine grain size of the solid elemental sulfur. (C) 2001 Elsevier Science B.V. All rights reserved.