Screening Of Naproxen-degrading Bacteria And Study On Degradation Pathways

Naproxen is a synthetic non-steroidal anti-inflammatory drug(NSAID).It is mainly used in the form of its sodium salt for medical care.It has small side effects and is well tolerated.It can be used as a treatment for arthritis and rheumatism.Effective anti-inflammatory drug.However,its heavy use has caused severe drug residues and caused significant toxicity to aquatic organisms.At present,the removal of naproxen in the water environment is mainly divided into physical and chemical methods and biological methods,and biological methods have been widely used due to their outstanding advantages such as low cost and environmental friendliness.However,naproxen has been reported to degrade microbial strain resources.It is scarce and the degradation pathway is not clear.Therefore,screening naproxen degrading bacteria with high degrading activity is of great significance for the study of naproxen's microbial degradation.In this study,a strain of naproxen-degrading bacteria G1 was screened out from activated sludge in a sewage treatment plant.The influencing factors and growthdegradation kinetics of naproxen degradation by G1 were investigated.Activated sludge acclimation can make mature sewage treatment plant activated sludge gradually have the ability to remove naproxen.Naproxen is gradually added to the activated sludge according to the proportion.After long-term domestication,the naproxen-degrading bacteria in the activated sludge become the dominant flora,thereby achieving the purpose of domestication.When the concentration of naproxen in activated sludge was 50 mg / L,the degradation rate of naproxen by activated sludge was 57.80%;when the concentration of naproxen in activated sludge was 100 mg / L,The degradation rate of naproxen is 65.38%.When the concentration of naproxen in activated sludge is 150 mg / L,the degradation rate of naproxen by activated sludge can reach 86.65%.During the domestication,through highthroughput sequencing of the activated sludge,it was found that as the acclimation of the activated sludge progressed,the high concentration of naproxen screened the flora in the activated sludge,and the richness of the community in the activated sludge was obvious.The diversity of the community is gradually reduced.Subsequently,the distribution of the community structure at the level of naproxen-degrading bacteria was obtained,and the community structure of activated sludge during domestication was determined.It can be observed that Rhodanobacter and Microbacterium became dominant species.After domestication,a naproxen-efficient strain was selected from the dominant genera and named G1.Combining physiological and biochemical identification,Biolog identification and 16S rRNA sequencing analysis,the strain G1 was identified as Microbacterium xylanilyticum.The best growth and degradation conditions of strain G1 were obtained through experiments: temperature 30 ?,pH = 7,inoculation amount 5.0%,and shaking speed 150 r /min.The enzyme that degrades NPX in strain G1 is an inducing enzyme.Strain G1 is capable of degrading ibuprofen,3-amino-5 methylisoxazole and carbamazepine.The mathematical equation was used to construct the growth kinetics model of strain G1,and the maximum specific growth rate of strain G1 was 0.044h-1.A degradation kinetic model of strain G1 was constructed using the Haldane equation.The half-saturation constant of strain G1 was Ks =167.37 mg / L,and the maximum specific degradation rate ?max = 0.245 h-1.GC-MS analysis was performed on the degradation solution at different periods,and combined with the change in the concentration of TOC in the degradation solution,a possible degradation pathway of naproxen was speculated: the carboxyl group on naproxen was deoxidized to remove carbon dioxide to generate 2-ethenyl-6-methoxy-Naphthalene,2-ethenyl-6-methoxy-Naphthalene is oxidized by water to generate 2-Acetyl-6-methoxynaphthalene,which is oxidized again to naphthalene ring opening,Change to 3,4-dimethoxy-benzalcohol.It can be known that naproxen was partially mineralized during the degradation process.