Characterization of biosynthesized silver nanoparticles from Streptomyces aqueous extract and evaluation of surface-capping proteins involved in the process

Abstract

Microbial mineralization offers an efficient alternative to obtain metallic nanoparticles. The aim of this work was to synthesize green silver nanoparticles (AgNPs) using the metal resistant strain Streptomyces sp. M7. In addition, molecular modeling and docking studies were performed in order to understand how stabilizing proteins interact with the nanoparticle's surface. The production of AgNPs was influenced by the incubation time. AgNPs showed a moderate polydispersity of size and spherical shape. The hydrodynamic diameter was determined by Dynamic Light Scattering (DLS). Fourier Transform Infrared Spectroscopy (FTIR) and Raman analysis showed that organic molecules such as oxide-reduction enzymes coated the AgNPs surface. Molecular modeling and docking studies indicated that actually different enzymes may be simultaneously bound to the nanoparticle surface forming a layer capping-protein with different affinities. Thermogravimetric analysis (TGA) showed high thermal resistance of AgNPs, probably by the presence of organic residues on the surface. The green synthesized AgNPs showed antimicrobial activity against several multidrug-resistant bacteria, particularly Serratia marcescens SmCR371. This strain belongs to a cluster with epidemic behavior, harboring an extended spectrum of β-lactamases and carbapenemase. AgNPs produced by Streptomyces sp. M7 could be considered as a new line of defense against microbial resistance or as a complement of traditional antibiotics.