Endophytes Of Ginkgo Biloba Mediated The Biosynthesis And Antibacterial Activity Of Silver Nanoparticles

Silver nanoparticles(AgNPs)have broad-spectrum bactericidal properties and are less susceptible to drug resistance,and have important market prospects as novel antimicrobial agents in food packaging and biopharmaceuticals.With the advantages of many secondary metabolites,rapid reproduction and resistance to adversity,plant endophytes are receiving increasing attention from scholars as novel biomaterials for the synthesis of AgNPs.Ginkgo biloba is a valuable plant herb with traditional medicinal and food origins in China,and its endophytic resources have been reported,but the exploitation of AgNPs is still in its infancy.Based on that,this study explored the application of G.biloba endophytes obtained by isolation and screening in the preparation of AgNPs,and analysed the bacterial inhibition mechanism of AgNPs.The main research results are as follows:1.Screening and identification of synthetic AgNPs endophytesThe 67 endophytic strains of G.biloba isolated were subjected to primary screening,and the endophytic bacteria YP22 and endophytic fungus YJ25 with strong synthetic ability were selected.YP22 had a specific 16S gene sequence length of 1451 bp and was identified as Bacillus zanthoxyli GBE11 with 99.72%homology similarity.YJ25 had a specific ITS gene sequence length of 559 bp and was identified as Colletotrichum cosmi GBE2318 with 99.87%homology similarity.2.Optimization of synthesis conditions and characterization of AgNPsThe AgNPs synthesized by B.zanthoxyli GBE11 and C.cosmi GBE2318 were named Bz-AgNPs and Cc-AgNPs,respectively,and the most suitable conditions for the synthesis of Bz-AgNPs were optimized as follows:inoculum level 1.25%,pH 9.0,fermentation at 30℃ for 72 h,3 mmol/L silver nitrate,reaction at 35℃ for 72 h;Cc-AgNPs were optimized as follows:inoculum level 7%,pH 6.5,fermentation at 28℃ for 48 h,3 mmol/L silver nitrate,reaction at 40℃ for 36 h.In addition,the characterization results showed that:TEM showed subspherical particles;both XRD and EDS spectra confirm the presence of AgNPs,which belongs to the face-centered cubic structure.The zeta potential analysis showed that Bz-AgNPs had superior stability compared with Cc-AgNPs.3.Study on antibacterial properties and mechanism of AgNPsBz-AgNPs inhibited the growth of B.subtilis WB800 with MIC of 7.81 μg/mL and MBC of 15.62 μg/mL,while Cc-AgNPs inhibited the growth of B.subtilis WB800 with MIC and MBC of 31.25 μg/mL.Scanning electron microscopy and DCFH-DA fluorescence techniques showed that AgNPs could achieve the inhibition effect by disrupting the cell membrane structure and inducing intracellular reactive oxygen species production.In summary,this study found for the first time that B.zanthoxyli GBE11 and C.cosmi GBE2318 isolated from G.biloba had the ability to synthesize AgNPs,and optimized the reaction conditions to obtain the most suitable reaction conditions for the formation of AgNPs,and also found that the synthesized AgNPs had certain antibacterial activity.This project provides a new reference and reference for the synthesis of functional AgNPs by G.biloba for biological and medical applications,and enriches the understanding of the antibacterial mechanism of AgNPs.