Green Synthesis Of Chitosan Coated SeNPs From Rosa Roxbunghii Extract And Study On Its Antibacterial Properties And Mechanism

Selenium is an important trace element in human body.It mainly exists in three forms,namely inorganic selenium,organic selenium and nano-selenium.Nano-selenium（SeNPs）has the characteristics of high bioactivity,low toxicity,easy to be absorbed by organisms,and is a reliable selenium source for human supplement.Biosynthesis is a SeNPs preparation method which has attracted much attention in recent years.It has many advantages such as simple operation,fast synthesis speed,green reaction process and no pollution.More importantly,bioactive ingredients such as organic acids,reducing sugars and proteins used in this method can also make SeNPs have better biocompatibility,which is attractive for development and application.In view of this,a novel SeNPs coated with phenolic modified chitosan（RC-SeNPs）was successfully synthesized in this study using Na₂Se O_3,roxroth juice and chitosan as selenium source,reducing agent and stabilizer respectively.On this basis,the bacteriostatic properties of RC-SeNPs against common human,animal and plant pathogens were further studied.In addition,the antioxidant activity of RC-SeNPs was also investigated.Finally,the antibacterial mechanism of the novel RC-SeNPs against Staphylococcus aureus,a typical pathogen,was systematically studied at the cell level and DNA level.The research results mainly include the following aspects:（1）Phenolic modified chitosan coated new SeNPs were successfully synthesized.At room temperature,stirring speed of 600 RPM and chitosan concentration of 0.02%,the optimal volume ratio of Rosa roxbunghii extract to 2.15 m M Na₂Se O₃solution（supplemental concentration）was 4:1.Under these conditions,RC-SeNPs prepared were uniform in size and spherical,covered with chitosan and phenols on the surface,with an average particle size of 123.9 nm.The polydispersion index（PDI）is 0.265,and the average Zeta potential is-25.6 m V.In addition,EDX results show that Se is the dominant element of SeNPs,and the atomic percentage of C,N and O is significantly lower than Se.The XRD pattern is basically consistent with that of SeNPs standard data card（JCPDS card No.06-0362）.FTIR results show that THE SURFACE of RC-SeNPs has a variety of reductive stable functional groups.（2）RC-SeNPs has excellent bacteriostasis against a variety of common human,animal and plant pathogens.The bacteriostasis performance of RC-SeNPs against four common pathogenic bacteria in descending order:Physalospora piricola>Bacillus subtilis>S.aureus>Escherichia coli.The inhibition zone diameters of RC-SeNPs against P.Piricola,B.Subtili,S.aureus and E.coli were 18±0.67 mm,16±0.32 mm,12±0.13 mm and 9±0.93 mm,respectively.The minimum inhibitory concentration（MIC）value of PC-Se NP sagainst S.aureus was 5 mg/m L,the MIC value against E.coli and B.Subtilis was 0.75 mg/m L,and the MIC value against P.Piricola was 0.5 mg/m L.In addition,the results of in vivo bacteriostatic experiment（apple drilling experiment）showed that RC-SeNPs could significantly inhibit the growth of P.Piricola in apple fruits,which was a relatively ideal candidate preparation for P.Piricola disease control in apple.（3）RC-SeNPs has excellent antioxidant activity.It was found that RC-SeNPs could scavenge 96.02%DPPH free radical and 98.92%ABTS+free radical,indicating that RC-SeNPs had excellent antioxidant activity and could be used as a free radical scavant in the treatment of related diseases in the future.（4）The bacteriostatic mechanism of RC-SeNPs against S.aureus at the cellular and DNA levels was studied.The results of biological electron microscopy showed that RC-SeNPs could directly affect the biofilm,cell wall and nucleus of S.aureus,causing serious damage to the above microstructure.In addition,transcriptome experiment results showed that there were 362 differentially expressed genes in RC-SeNPs compared with conventional cultured cells,including 286 up-regulated genes and 76 down-regulated genes,which were enriched by GO pathway and analyzed by KEEG functional annotation.These genes are mainly involved in physiological and biochemical processes such as fatty acid metabolism,amino acid metabolism,protein transcription and translation,and DNA replication,proving that RC-SeNPs ultimately leads to the growth inhibition and even death of S.aureus bacteria by affecting the above processes.