Synthesis And Reduction Mechanism Of Noble Metal Nanoparticles By Burkholderia Contaminans ZCC

Noble metal nanoparticles have been widely used in various fields such as electronics,industrial catalysis and biomedicine due to their unique physical and chemical properties.Compared with traditional physical and chemical synthesis methods,the microbial method has attracted widespread attention from researchers in the synthesis of noble metal nanoparticles due to its advantages of being green,non-toxic,and environmentally friendly.Studying the process mechanisms of microbial synthesis of noble metal nanoparticles is of great significance for the recovery of precious metals and revealing the interaction between microorganisms and noble metal ions.In this process,microorganisms can evolve multiple mechanisms to resist the toxicity of noble metal ions including reduction of noble metal ions.Previous studies have only focus on the ability of microorganisms to synthesize noble metal nanoparticles,such as gold and silver nanoparticles(AuNPs,AgNPs),however,the process mechanisms are not fully explored.Therefore,in this thesis,Burkholderia contaminans strain ZCC,which has multiple heavy metal resistance,is used as the research material.By combining with various characterization techniques such as physics,chemistry,transcriptomics,and proteomics,the reaction mechanisms of ZCC in synthesizing AuNPs and AgNPs are systematically studied,and the main conclusions are as follows:(1)B.contaminans strain ZCC has the ability to reduce Au(Ⅲ)to AuNPs on the cell surface.During this reduction process,significant changes occur in the functional groups of surface proteins for ZCC cells,with approximately 11.1%of(C-C/C-H)bonds being converted to C=O bonds(8.1%)and C-OH bonds(3.0%),while 29.4%of C=O bonds are converted to(C-OH/C-O-C/P-O-C)bonds.After reduction of the Au(Ⅲ)ions,strain ZCC display the ability of extracellular electron transfer via membrane proteins and can produce reduced riboflavin,but does not do so without Au(Ⅲ)being present.The addition of exogenous riboflavin can increase the rate of AuNPs synthesis driven by ZCC.Transcriptomic analysis of the genes rib BDEFH supports the above conclusion.That is,under Au(Ⅲ)stress,the expression of the gene rib B encoding3,4-dihy-droxy 2-butanone 4-phosphate synthase is significantly down regulated while a significant up-regulation of the gene rib D encoding the enzyme that generates 5-amino-6-ribitylaminouracil from the reduction of 5-amino-6-(5-phos-phoribosylamino)uracil is observed in ZCC cells.However,the expression of the gene rib H encoding enzymes involved in the biosynthesis of 6,7-dimethyl-8-ribityl-lumazine is significantly down regulated.Most importantly,no significant change is observed in the gene expression of rib E encoding enzymes catalyzing the synthesis of riboflavin.Furthermore,the gene expression of rib F encoding RF kinase and flavin mononucleotide adenylyl-transferase was also down regulated.All of these results indicate that ZCC can utilize indirect electron transfer pathway via riboflavin to enhance the reduction of Au(Ⅲ)and further demonstrate the importance of riboflavin in the biological reduction of Au(Ⅲ).(2)B.contaminans strain ZCC can reduce Ag~+to AgNPs with a diameter of approximately 10±5 nm inside the cell.During this process,there are significant changes in the functional groups of surface proteins for ZCC cells,with approximately 5.72%of C-OH bonds being converted to C-C/C-H bonds(3.61%)and C=O bonds(2.11%),while4.52%of C=O(carbonyl)bonds are converted to C-OH bonds.The presence of Ag~+and AgNPs can also induce the ability of extracellular electron transfer through specific membrane proteins and extracellular riboflavin in ZCC cells,but this does not occur in the absence of Ag~+ions.Proteomic analysis reveals that significant changes are observed in the expression of proteins related to heavy metal efflux systems,protein secretion systems,oxidative phosphorylation,intracellular electron transfer chains,glutathione synthesis and metabolism pathways after ZCC cells exposure to Ag~+.Among them,glutathione S-transferase and ferredoxin-dependent cytochrome c reductase iron-sulfur subunit play important roles in the biosynthesis of AgNPs.