Silver and gold nanoparticles synthesized from Streptomyces sp. isolated from acid forest soil with special reference to its antibacterial activity against pathogens

Biological systems such as bacteria, fungi or plants for synthesis of noble nanoparticles (NPs) are easy, inexpensive and eco-friendly. Obtained bioparticles due to its physico-chemical nature possess biologically active properties such as antimicrobial activity. In this study, the biological synthesis of silver (Ag) and gold (Au) nanoparticles using Streptomyces sp. strain NH21 isolated from acidic soil and its antibacterial activity against bacteria is presented. The physico-chemical properties of obtained particles were characterized. UV–Vis showed broad peak at 404 and 424 nm for AgNPs and 564 nm for AuNPs. Transmission electron microscopy studies showed small sized nanoparticles of 44 nm for supernatant and 8.4 nm for biomass synthesized AgNPs, and 10 nm for supernatant synthesized AuNPs, which was confirmed by nanoparticle tracking analyses. Fourier transform infrared spectroscopy revealed the presence of capping agents over metal-NPs. The negative Zeta potential values of metal-NPs indicated stability of biosynthesized particles. In vitro antibacterial activity and minimal inhibitory concentration of NPs was assessed against Gram-positive and Gram-negative bacteria. Unlike to gold-NPs, silver-NPs showed reliable antibacterial activity. Atomic force microscopy analysis recorded changes in cell morphology of tested bacterial strains after treatment with nanoparticles.