Biotransformation Of Gold And Silver Ions Into Nanoparticles By Deinococcus Bacteria

Nanomaterial is a new kind of material,which is in the range of 0.1 to 100 nm in at least one dimension of its three-dimensional space.Nanomaterials are generally synthesized using a variety of methods,including physical,chemical and biological methods.The physical and chemical methods are usually high energy consumption and easy to cause pollution,while biosynthesis is a green synthesis method based on biological matrix.Because of their rapid growth,easy cultivation and low cost,microorganisms have become an important biological source for the biosynthesis of nanoparticles.Many bacteria are able to reduce metal ions,making them suitable for synthesis of metal nanoparticles.Deinococcus bacteria are extreme microorganisms,known for their strong resistance to ionizing radiation,ultraviolet light,strong oxidant and some chemical mutagens.They also have strong ability of reducing heavy metal ions.So,they have been paid special attention in the fields of biology,medicine and environmental engineering.However,the metal nanoparticles biosynthesis ability and mechanism of Deinococcus bacteria are far from clear.In our study,three species of Deinococcus bacteria were selected to investigate their biosynthesis of gold and silver nanoparticles.The main research contents and results were as follows:1.We investigated the synthesis of gold nanoparticles and silver nanoparticles by D.radiodurans,D.geohermalis and D.radiopugnans using gold and silver ions in solution,respectively.The results showed that all the three species were able to synthesize gold and silver nanoparticles.Under the same experimental conditions,D.geothermalis and D.radiodurans spent relatively less time to reach reaction equilibrium of nanoparticle formation(approximately 10 h for gold nanoparticles and 25 h for silver nanoparticles).We chose D.geothermalis with high synthesis rate and wider growth temperature range(25?60?)for further study.2.The gold nanoparticles(AuNPs)and silver nanoparticles(AgNPs)synthesized by D.geothermalis were characterized by scanning electron microscopy(SEM),energy dispersive X-ray spectroscopy(EDX),transmission electron microscopy(TEM),X-ray diffraction(XRD)and dynamic light scattering(DLS).Nanoparticles mainly distributed on cell surface,and some in extracellular space or inside the cells.The nanoparticles were mainly spherical or ellipsoid,while a minority of them were irregular.The gold nanoparticles exhibited a strong characteristic peak at 2.2 keV in the EDX spectrum,with an average particle size of 99.12 nm.And silver nanoparticles had a strong characteristic peak at 3 keV,and the average particle size of AgNPs was 40.3 7nm.Moreover,the nanocrystalline nature of synthesized gold and silver nanoparticles was determined using XRD,and the lattice type was a face-centered cubic structure.Effects of reaction conditions on the biosynthesis of AuNPs and AgNPs,including metal ion concentration,temperature and pH of the reaction system,were also analyzed.3.A preliminary study on the biosynthesis mechanism of gold and silver nanoparticles was carried out using Fourier transform infrared spectroscopy(FTIR)and analysis of mutant deficient in a surface layer protein.The results of FTIR showed that some functional groups,such as C-O groups,amide and carboxyl groups from polypeptides or proteins might be involved in metal ion reduction and formation of AuNPs/AgNPs.The protein and other biological molecules might be used as the capping agents on the surface of nanoparticles to prevent aggregation,thus leading to stabilization of the AuNPs/AgNPs.In addition,gene deletion of SlpA from S-layer of the cell envelope resulted in the decrease of nanoparticles synthetic ability of the bacterial cells,indicating that S-layer protein might be involved in the biosynthesis process of AuNPs/AgNPs.In this study,we investigated the ability of Deinococcus bacteria for biotransformation of gold and silver ions into AuNPs and AgNPs,characterized the synthesized nanoparticles,analyzed the biosynthesis conditions,and made a preliminary study on the biosynthesis mechanism of gold/silver nanoparticles.The results provided a basis for further research of nanomaterials synthesis and biosynthesis mechanism using extreme microorganisms.