Production of extracellular silver nanoparticles by radiation-resistant Deinococcus wulumuqiensis R12 and its mechanism perspective

Recently, rapid progress has been made in the utilization of microbes for green synthesis of metal nanoparticles. We found that the cell-free supernatant of the extremophile Deinococcus wulumuqiensis R12 contains silver nanoparticles (AgNPs) when grown in media with different concentrations of AgNO₃. The microbially synthesized AgNPs were then systematically characterized by UV/Vis spectroscopy (UV/Vis), X-ray diffraction (XRD), fourier transform infrared spectroscopy (FTIR), scanning electron microscopy (SEM), transmission electron microscopy (TEM), energy-dispersive spectroscopy (EDS), dynamic light scattering (DLS) and zeta potential measurements. The microbial AgNPs had an absorption peak at 430 nm and had a face-centered cubic structure. They were spherical with a uniform size of 5–16 nm, which was smaller than most reported AgNPs. The mechanism of nanoparticle synthesis by D. wulumuqiensis R12 was then briefly investigated. A previously unknown NADPH-dependent oxidoreductase of 28.29 kDa was identified, which might play the main role in the biosynthesis of AgNPs by strain R12. The concentration of the oxidoreductase in the supernatant increased 4-fold after the addition of AgNO₃. Furthermore, the addition of NADPH significantly improved the production of AgNPs.