Effect And Mechanism Of Silver Nanoparticles On The Removal Of Norfloxacin By Phanerochaete Chrysosporium

Norfloxacin(NOR),as a typical fluoroquinolones antibiotic,remains in the water environment.It has toxic effect on microorganism in wastewater treatment process,so the treatment efficiency is not high.Silver Nanoparticles(AgNPs)is also widely used because of many excellent characteristics,which inevitably enters the water environment,and also has an impact on environmental microorganisms.In this study,the typical strain of white rot fungus,Phanerochaete Chrysosporium(P.Chrysosporium),was used as the experimental fungus to study its activity and biodegradation of NOR under the stress of the coexistence system of AgNPs and NOR.The migration and transformation behavior of AgNPs was monitored,and the response mechanism of microorganisms under the stress of toxic substances was revealed.In this study,two kinds of AgNPs with polyvinylpyrrolidone as surface stabilizer were synthesized,which were 48.70 nm,-12.70 mV and 76.41 nm,-17.77 mV,respectively.AgNPs can inhibit the cell activity and the biodegradation of NOR in high concentration and promote it in low concentration.At the concentration of 0.01 ?M and 0.12 ?M,the cell activity of P,Chrysosporium was increased by 1.29 and 1.51 times,respectively,while at the stimulation of 12 ?M,the cell activity was decreased by 64%.Under the stimulation of 0.1 ?M AgNPs,the biological removal rate of NOR was 73%,1.3 times of the control group,while the removal rate of 10 ?M was only 50%of the control group.At the same time,48 nm AgNPs can remove NOR faster than 76 nm AgNPs under low concentration stimulation,and the inhibition effect is more obvious under high concentration.The toxic excitation effect of AgNPs has nothing to do with the Ag+released by oxidation.The higher the concentration of Ag+,the more obvious the inhibition effect.Low concentration of AgNPs can migrate between the solution phase and the biological phase,trigger the change of biological characteristics of cells,and stimulate cells to produce more extracellular proteins in the face of NOR stress to reduce toxicity inhibition.It can also improve the activity of SOD and CAT enzymes,indicating that they can induce more antioxidant enzymes to enhance the ability of antioxidant stress,so as to achieve the biodegradation of NOR.The functional groups such as hydroxyl,aldehyde,ketone and mercapto on the surface of mycelium participate in the biodegradation of NOR and can reduce Ag+to AgCl-NPs and AgS-NPs,which can aggregate on the cell surface.