Synthesis Of Extracellular Stable Gold Nanoparticles By Cupriavidus metallidurans CH34 Cells

Abstract

The biogenic synthesis of metallic nanoparticles is of increasing interest. In this report, synthesis of gold nanoparticles by the model heavy metal-resistant strain Cupriavidus metallidurans CH34 and Escherichia coli strain MG1655 was studied. For the synthesis of AuNPs, bacterial cells and secretomes were incubated with Au(III) ions, revealing that only CH34 cells can produce dispersions of AuNPs. Comparative bioinformatic analysis of proteomes from both strains showed potential CH34 proteins that may be electron donors during reduction of extracellular Au(III) ions and for the biosynthesis of gold nuggets in nature. Powder X-ray diffraction demonstrated that biogenic AuNPs are composed of face-centered cubic gold with a crystallinity biased towards {111} planes. Transmission electron microscopy images showed that AuNPs morphology was dominated by triangular and decahedral nanostructures. EDX and FT-IR spectra showed the presence of sulfur and vibrations associated to the biogenic AuNPs. Based on these results, and analyses of previous genomic and proteomic data, a mechanism for extracellular gold reduction and synthesis of AuNPs by strain CH34 is proposed. Average AuNPs diameter was obtained by nanoparticle tracking analysis, dynamic light scattering and analysis of electron microscopy images. DLS studies showed that biogenic AuNPs colloids are stable after exposure to ultrasound, high ionic strength and extreme pH conditions, and revealed the presence of basic groups associated to the AuNPs surface. Electrophoretic and dynamic light scattering indicated that biogenic dispersions of AuNPs are stabilized by a steric mechanism. The AuNPs produced by C. metallidurans CH34 are not cytotoxic towards bacterial cells, in contrast to biogenic AgNPs. These stable non-toxic biogenic AuNPs have potential clinical applications including development of topic delivery formulations and optical biosensors.