Reduction of sulfur by spirillum 5175 and syntrophism with Chlorobium

Abstract

A small spirillum, designated 5175, was isolated from an anaerobic enrichment culture for Desulfuromonas in which the major medium constituents were acetate and elemental sulfur. The organisms grew only under anaerobic or microaerophilic conditions. Elemental sulfur was formed anaerobically in a malate-sulfide medium, and cell densities of 10(8) cells/ml were obtained. Hydrogen and formate were actively oxidized as substrates for growth under anaerobic conditions; S0, S032-, or S2O32-, but not SO42-, served as electron acceptors and were stoichiometrically reduced to sulfide. Malate or fumarate likewise served as electron acceptors and were reduced to succinate. Nutritional requirements were simple, no vitamins or amino acids being required. For growth in inorganic media when carbon dioxide was the only carbon source, the addition of acetate was required as a source of cell carbon. The organism is gram negative. Cells had a diameter of 0.5 mum and a wavelength of 5.0 mum. Cell suspensions exhibited an absorption spectrum indicative of a cytochrome with peaks in the reduced form at 552, 523, and 416 nm. Well growing syntrophic cultures with Chlorobium were established with formate as the substrate.