Biosynthesis Mechanism And Properties Of Functionalized Gold Nanoparticles Using The Extremophile Deinococcus Radiodurans

Gold nanoparticles(AuNPs)are the tiny particles of gold in any dimension between 1 and 100 nm and have significantly novel physicochemical properties.AuNPs have been widely applied in various fields,including biosensing and nanomedicine.Biosynthesis of AuNPs using microorganisms is economic,safe,and environmentally friendly,which has attracted much attention from researchers.However,the biosynthesis mechanisms and functions of AuNPs have not been clearly described to date and the efficiency of the biosynthesis of nanomaterials using common organisms is another challenge due to the low cell viability under extreme environments.The extremophile Deinococcus radiodurans is well known for its exceptional resistance to stresses including radiation and oxidants,which possesses abundant biological resources tolerating stresses of adverse conditions.Hence,studies of efficient biosynthesis mechanisms and properties of functionalized nanomaterials using D.radiodurans are of great significance.In this work,we detailed the ability and process of reducing Au(?)to biosynthesize the functionalized AuNPs using D.radiodurans and evaluated the functional properties of formed nanoparticles based on biochemistry,nanomaterial science,molecular biology,cellular biology,and transcriptomic techniques.We revealed the molecular mechanism of biosynthesis of AuNPs formed by D.radiodurans and evaluated the functional mechanism of the AuNPs.The main results were as follows:1.Compared with the common microorganism,such as Escherichia coli,D radiodurans cells have a relatively efficient ability to tolerate and reduce Au(?)for the biosynthesis of gold nanoparticles(Dr-AuNPs).The Dr-AuNPs exhibited spherical morphology with a Zeta potential value of-20.01±0.17 mV and were distributed in the cell envelope,across the cytosol,and in the extracellular space.It was found that upon binding to cellular biomolecules through interactions with carboxyl,amine,phospho,and hydroxyl groups,Au(?)was reduced to Au(I),which was further reduced to Au(0)with the capping groups to stabilize the Dr-AuNPs.The purified Dr-AuNPs exhibited antibacterial activity against bacteria by damaging their cell envelope and were not significantly cytotoxic to normal mammalian cell lines MCF-10A and NRK,which can be used as an antibacterial agent.2.Proteins coated on the surface of Dr-AuNPs were identified,indicating that proteins from the bacterium were involved in the formation of functional AuNPs.The biosynthesized AuNPs using the cellular proteins from D.radiodurans(Drp-AuNPs)appeared to have spherical morphology with an average size of 51.7217.38 nm and good stability.During the synthesis process,Au(?)was reduced to Au(?)and further to Au(0)by interactions with the hydroxyl,amine,carboxyl,phospho,and sulfhydryl groups of proteins and was subsequently stabilized by these groups.The different AuNP's biosynthetic ability using purified protein CrtI or Dps2,which were involved in the resistance to oxidants in D.radiodurans,might be determined by the amino acid composition and reducing capability of the proteins.Compared with sodium citrate-AuNPs(SC-AuNPs),Drp-AuNPs exhibited little cytotoxic to normal cells MCF-10A and NRK.The high stability and biocompatibility of Drp-AuNPs could be attributed to the presence of the stabilizing agent(proteins)on the surface of nanoparticles.The stable and noncytotoxic Drp-AuNPs may be applicable in the biosensing and drug delivery fields.3.The molecular mechanism of the effective synthesis of DX-AuNPs functionalized with the oxidation products of deinoxanthin(DX),a special hydroxylated tetraterpenoid in D.radiodurans,was elucidated and detailed.It was demonstrated that Au(?)was rapidly reduced to Au(?)and subsequently reduced to Au(0)by the donation of hydrogen atoms from the hydroxyl groups of DX.The oxidized form DX3(deprotonated 2-ketodeinoxanthin)acted as a surface-capping agent to stabilize the AuNPs.The formed DX-AuNPs were spherical with a Zeta potential value of-24.95±0.38 mV.Compared with SC-AuNPs,the functionalized DX-AuNPs demonstrated significantly stronger inhibitory activity against cancer cell lines MCF-7 and ACHN,but are not toxic to normal cell line NRK.DX-AuNPs accumulated in the cytoplasm,organelles and nuclei and induced autophagy,ROS generation,DNA damage and apoptosis within MCF-7 cancer cells.The data from transcriptome analysis showed the expression levels of genes related to cell growth,metabolism,oxidative stress,and apoptosis were significantly up-regulated or down-regulated in the MCF-7 cells treated with DX-AuNPs.The induction of apoptosis by DX-AuNPs could be mainly attributed to the alteration of above gene expression levels.In conclusion,the extremophile D.radiodurans with tolerance to the stress of Au(?)has an efficient ability to reduce Au(?)to biosynthesize functionalized gold nanoparticles coated by different functional groups using the cells,their cellular proteins and special metabolite(tetraterpenoid).These results revealed bioactive molecules and their functional groups involved in the synthesis of AuNPs using D.radiodurans,and demonstrated the biosynthesis mechanism of functionalized AuNPs using the extremophile and the functional properties of these nanoparticles.These results provide a foundation and an effective material for the biosynthesis of functionalized AuNPs using biological source.This study also provides significant insight into the biosynthesis mechanism of metallic nanomaterials and the functionalized modifications of nanomaterials.In addition,the results will facilitate the applications of the functional AuNPs or other nanomaterials biosynthesized by D.radiodurans in the fields of biology and medicine.