Abstract
Among a collection of gold nanoparticles (AuNPs) synthesizing bacteria isolated from soil samples from high altitude metal-rich dump sites near industrial city, Taif, KSA (Lat 99o44' and 79o45' E), the strain G10 was selected based on their high-ability to synthesize gold nanoparticles. The morphological, physiological and phylogenetic studies indicated that strain G10 belonged to the Alcaligenes sp. and identified as Alcaligenes faecalis. In this study, the bacteria Alcaligenes faecalis was screened and found to extracellularly produce gold nanoparticles of different sizes and shapes by reduction of gold (Au3+) ions. Therefore, biosynthesis of gold nanoparticles (AuNPs) from Alcaligenes faecalis bacterium is considered to be a novel, effective and eco-friendly method. The AuNPs were characterized using UV-visible spectroscopy and Transmission Electron Microscopy (TEM). The nanoparticles exhibited maximum absorbance at 532 nm in UV-Vis spectroscopy. TEM micrographs revealed the extracellular formation of spherical nanoparticles in the size range of 5 to 55 nm. The particle size histograms of gold nanoparticles show that the average particles sizes decreases with increasing reaction temperature. The results also indicate that the size of AuNPs can be modulated by pH. The corresponding selected area electron diffraction (SAED) and X-ray diffraction (XRD) pattern showed the characteristic Bragg peaks of (111), (200), (220) and (311) of pure face-centered cubic (fcc) gold structure. Interestingly, the colloidal suspensions of gold nanoparticles are stable for several months. Fourier transform infrared (FTIR) spectroscopy analysis proved that, the proteins released to the medium by the bacteria, are probably responsible for the formation and stabilization of the AuNPs The size and stability of AuNPs appears to depend on the temperature, pH, and supernatant concentrations.