THE OCCURRENCE OF SULFUR AND PHOSPHORUS WITHIN BACTERIALLY DERIVED CRYSTALLINE AND PSEUDOCRYSTALLINE OCTAHEDRAL GOLD FORMED IN VITRO

Abstract

A temperature study (4°C, room temperature, 60°C and 90°C) employing a bacterial in vitro model (Southam and Beveridge, 1994) revealed a role for S and P in octahedral An formation. Ionic Au immobilized by Bacillus subtilis 168 was first precipitated as colloidal Au. During diagenesis, these colloids were transformed into spherical pseudocrystalline gold particles composed of 74.56 ± 2.60 at% Au, 8.56 ± 1.71 at% S, and 13.94 ± 1.48 at% P. These minerals then aggregated as roughly shaped noncrystalline octahedral Au which was subsequently transformed into crystalline octahedral Au containing 85.37 ± 0.16 at% Au (the maximum detected[, 0.77 ± 1.33 at% S, and 10.27 ± 0.88 at% P. The strong P signals (13.39 ± 2.01 average at%[ obtained from the Au minerals examined by energy-dispersive X-ray spectroscopy suggest that organic phosphate compounds also play a role in the in vitro development of octahedral Au, possibly as bacteria-Au-complexing agents. Increasing the time to 4 weeks at room temperature or the temperature to either 60°C or 90°C enhanced formation of the crystalline octahedral gold. This crystalline octahedral Au generated an electron diffraction pattern consistent with synthetic Au.