The occurrence of sulfur and phosphorus within bacterially derived crystalline and pseudocrystalline octahedral gold formed in vitro

A temperature study (4 degrees C, room temperature, 60 degrees C and 90 degrees C) employing a bacterial in vitro model (Southam and Beveridge, 1994) revealed a role for S and P in octahedral Au 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 degrees C or 90 degrees C enhanced formation of the crystalline octahedral gold. This crystalline octahedral Au generated an electron diffraction pattern consistent with synthetic Au.