Mechanism Of Fluoxetine Degradation By Shewanella MR-1 Under Different Oxygen Concentrations

In recent years,the incidence rate of depression has been continuously increasing,and the use of antidepressants has also increased year by year.Since the human body cannot fully digest and absorb the antidepressants,most of the antidepressants and their metabolites are excreted in the urine and feces.However,the existing sewage treatment technologies cannot effectively remove antidepressants from the water,resulting in a large amount of active antidepressants ingredients entering natural water bodies every year,seriously endangering the aquatic ecological security.Therefore,developing new sewage treatment technologies to effectively remove antidepressants from water bodies has become a key concern of researchers.Microbial treatment technology is one of the commonly used technologies in sewage treatment,which is widely used due to its advantages of simple process,low treatment cost and easy scal-up.As a new type of sewage treatment technology,microbial Fenton technology has the advantages of high efficiency and low cost,and has been widely used in the degradation and transformation research of organic pollutants in recent years.In this paper,Shewanella MR-1 was selected for fluoxetine degradation,and the effect of different oxygen concentrations on fluoxetine degradation by Shewanella MR-1 driven Fenton reaction was studied,also the association between relevant degradation factors and oxygen concentration was analyzed.Finally,transcriptomics was used to analyze the intrinsic molecular mechanism of fluoxetine degradation by Shewanella MR-1.This study provides basic genetic data for Shewanella MR-1-driven fluoxetine degradation,and also provides a reference for microbial remediation of antidepressants in water environment.1.The experimental results of physiological characteristics showed that the concentration of fluoxetine had no significant effect on Shewanella MR-1 at 1～5 mg/L under different oxygen concentration conditions,and the bacteria entered the logarithmic growth period from 4 to 16 h and entered the stable period at 16 to 20 h.At concentrations of 10 mg/L,fluoxetine significantly inhibited the physiological activity of the bacteria,resulting in a slower bacterial growth rate.During the transformation process of fluoxetine degradation,Fenton reaction will destroy the cell membrane structure of Shewanella MR-1,and fold and break on the bacterial cell surface.Moreover,according to the results of bacterial fluorescence staining,the proportion of dead bacteria increased significantly under the nitrogen to oxygen concentration ratio of 8:2 and 7:3.2.The experimental results of degradation characteristics show that different oxygen concentration has obvious effects on the concentration of Eh and valent iron in the system.The lower the oxygen concentration,the lower the Eh of the system and the higher the concentration of valent iron is,indicating that the lower the oxygen concentration,the stronger the reducing ability of bacteria.In addition,oxygen concentration can significantly affect the rate of fluoxetine degradation by Shewanella MR-1 driven Fenton reaction.For fluoxetine with a ratio of 8:2,fluoxetine was as high as 0.98 mg/(L·h),and the degradation rate of fluoxetine reached 95.92%.Meanwhile,according to the results of the free radical quenching experiment,fluoxetine degradation mainly depends on the hydroxyl radical produced in the Fenton reaction.3.The results of transcriptomic analysis showed that the oxygen concentration has a significant effect on the gene expression of Shewanella MR-1,the strong oxidative substances produced during the degradation of fluoxetine can change the gene expression in the bacteria,spy/CpxP family proteins,envelope stress response membrane proteins and ABC transporter,flagellin and oxidative stress defense.Related genes controlling electron transport and oxidoreductase in bacteria determine the degradation rate of fluoxetine.Through the differential expression of related genes at different oxygen concentrations,it is found that lactate utilization protein,iron-sulfur binding protein and cytochrome C play a main role in the electron transport of Shewanella MR-1;dihydroxy acid dehydratase,sulfite reductase and formic acid dehydrogenase genes are related to the degradation and transformation of fluoxetine.