Green Synthesis of Silver Nanoparticles with Culture Supernatant of a Bacterium and Their Antibacterial Activity against Soft Rot Pathogen .

Bacterial stem and root rot disease of sweet potato caused by recently broke out in major sweet potato planting areas in China and calls for effective approaches to control the pathogen and disease. Here, we developed a simple method for green synthesis of silver nanoparticles (AgNPs) using bacterial culture supernatants. AgNPs synthesized with the cell-free culture supernatant of a bacterium displayed the characteristic surface plasmon resonance peak at 420-430 nm and as nanocrystallites in diameters of 20-100 nm determined by transmission electron microscopy, scanning electron microscopy, and X-ray diffraction spectroscopy. Functional groups associated with proteins in the culture supernatant may reduce silver ions and stabilize AgNPs. The AgNPs showed antibacterial activities against growth, swimming motility, biofilm formation, and maceration of sweet potato tubers whereas the culture supernatant of did not. AgNPs (12 µg∙ml) and AgNO (50 µg∙ml) showed close antibacterial activities. The antibacterial activities increased with the increase of AgNP concentrations. The green-synthesized AgNPs can be used to control the soft rot disease by control of pathogen contamination of sweet potato seed tubers.