Structure and size of gold nanoparticles formed on cells and S-layers of Bacillus sphaericus JG-A12

The strain Bacillus sphaericus JG-A12, isolated from a uranium mining waste pile near the town of Johanngeorgenstadt, is capable of selective and reversible accumulation of U, Cu, Pb, Al, and Cd from uranium waste waters. The cells of this strain are enveloped by a surface layer protein (S-layer). The highly regular structure of this S-layer with many pores of identical size offers good binding sites for different kinds of molecules and provides nucleation sites for the formation of metal nanoclusters or minerals. In this study we demonstrate that B. sphaericus JG-A12 cells and their purified S-layer protein sheets were capable to reduce Au to metallic nanoclusters in the presence of reducing agents such as molecular H2. The gold nanoparticles were regularly distributed and sized according to the pores of the S-layer lattice. The metallic nature of the clusters was confirmed by different techniques such as extended X-ray absorption fine structure (EXAFS) and X-ray absorption near edge (XANES) spectroscopy, UV-vis spectroscopy, X-ray powder diffraction (XRD), and transmission electron microscopic (TEM) analysis. The size of the gold nanoparticles was estimated to be almost 1 nm. Our results demonstrate that B. sphaericus JG-A12 can be used to prepare gold nanoparticles for industrial applications.