Extracellular Iron-Sulfur Precipitates From Growth ofDesulfovibrio desulfuricans

Abstract

ABSTRACTWe have examined extracellular iron-bearing precipitates resulting from the growth ofDesulfovibrio desuyfuricansin a basal medium with lactate as the carbon source and ferrous sulfate. Black precipitates were obtained whenD. desulfuricanswas grown with an excess of FeSO4. WhenD. desulfuricanswas grown under conditions with low amounts of FeSO4, brown precipitates were obtained. The precipitates were characterized by iron K-edge XAFS (x-ray absorption fine structure),57Fe Mössbauer-effect spectroscopy, and powder x-ray diffraction. Both were noncrystalline and nonmagnetic (at room temperature) solids containing high-spin Fe(III). The spectroscopic data for the black precipitates indicate the formation of an iron-sulfur phase with 6 nearest S neighbors about Fe at an average distance of 2.24(1) Å, whereas the brown precipitates are an iron-oxygen-sulfur phase with 6 nearest O neighbors about Fe at an average distance of 1.95(1) Å.