Biosynthesis and characterization of gold nanoparticles from plant growth promoting rhizobacteria

Gold nanoparticles have unique properties that make them applicable in different fields of science and technology. Thirty PGPR isolates were screened individually for their ability to synthesize gold nanoparticles which was denoted by color change from pale yellow to purple/red wine colour. Only ten were selected for further studies on the basis of maximum gold nanoparticles synthesis activity, which were further investigated for morphological and biochemical characters. PG-4 PGPR isolate showed 98% similarity with Bacillus thuringiensis strain KUDC1746, 16S ribosomal RNA, partial sequence. Phylogenetic analysis based on nucleotide sequences using NJ method show high boot strap value of 87%. These gold nanoparticles were characterized by FTIR spectrum which showed the presence of the functional groups, XRD results confirmed that these nanoparticles were originally gold nanoparticles, Scanning electron microscope results confirmed that gold nanoparticles were spherical in nature and monodispersed along with some clusters. Antibacterial activity of biosynthesized gold nanoparticles was assessed against five pathogenic bacteria and maximum inhibiton was found against Agrobacterium tumefaciens under in vitro conditions.