Extracellular synthesis of antibacterial silver nanoparticles using psychrophilic bacteria

Cell-free culture supernatants of five psychrophilic bacteria Pseudomonas antarctica, Pseudomonas proteolytica, Pseudomonas meridiana, Arthrobacter kerguelensis and Arthrobacter gangotriensis and two mesophilic bacteria Bacillus indicus and Bacillus cecembensis have been used to synthesize silver nanoparticles (AgNPs). The AgNPs were characterized using UV-Visible spectroscopy, transmission electron microscopy and atomic force microscopy. The sizes of the AgNPs ranged from 6 to 13 nm and were stable for 8 months in the dark. The synthesis and stability of AgNPs appears to depend on the temperature, pH or the species of bacteria (P. antarctica or A. kerguelensis) from which the supernatant is used. It was observed that the A. kerguelensis supernatant could not produce AgNPs at the temperature where the P. antarctica could synthesize AgNPs. Thus the study provides evidence that the factors in the cell-free culture supernatants that facilitate synthesis of AgNPs vary from bacterial species to species. The AgNPs were bacteriocidal. This report presents for the first time data on the generation of AgNPs using culture supernatants of psychrophilic bacteria and also demonstrates that culture supernatants of species of Arthrobacter, a genus which has never been investigated earlier, can also synthesize AgNPs.