Study On Bio-removal Of Ciprofloxacin And Norfloxacin By Activated Sludge

Fluoroquinolone is a broad-spectrum bactericide that inhibits DNA synthesis,which has been attracted great attention since it has been widely distributed in the environment and has potential to induce antibiotic resistance.The activated sludge process is widely applied to remove antibiotics.In this study,the removal efficiencies and biotransformation pathways of fluoroquinolone antibiotics（e.g.ciprofloxacin（CIP）and norfloxacin（NOR））by the activated sludge after acclimation with CIP or NOR.The main findings are as follows:An activated sludge（AS）consortium with high bio-removal capability to CIP and NOR was obtained by acclimating with 5.0 mg·L^-1 CIP and NOR for 10 d.The removal efficiencies of CIP and NOR were around 93.1%and 83.9%by the AS consortium within 24 h,respectively.Meanwhile,a CIP-and NOR-transforming bacterial strain（S5）,which is highly homologous to the 16S r RNA gene sequence of Enterobacter sp.,was isolated from the acclimated AS.The bio-removal efficiency of CIP under the acclimated AS consortium was higher than that under the pure culture of Enterobacter sp.S5（93.1%vs.89.3%）,while the bio-removal efficiency of NOR under the acclimated AS consortium was lower than that under the pure culture of Enterobacter sp.S5（83.9%vs.89.8%）.Meanwhile,it was also found that the biotransformation and bio-adsorption were two main ways to bio-remove CIP and NOR.However,the CIP and NOR biotransformation efficiencies of the acclimated AS were higher than under the pure culture of Enterobacter sp.S5,while the CIP and NOR adsorption of acclimated AS were lower than that under the pure culture of Enterobacter sp.S5.Additionally,the transformation products and pathways of CIP and NOR under the acclimated AS consortium were identified and analyzed by the HPLC-Q-TOF MS.It was found that the N-acetylciprofloxacin and N-acetylnorfloxacin were the main biotransformation products of CIP and NOR.It is possible that acetyltransferase may be involved in the biotransformation process under the acclimated AS consortium.Whether under the pure culture of Enterobacter sp.S5 or the acclimated AS consortium,the cytotoxicity of CIP and NOR transformation products to gram-negative bacteria was alleviated.Finally,the high-throughput sequencing technology was used to analyze the changes of microbial community structure and diversity.It was demonstrated that the CIP or NOR reduced significantly the richness of the acclimated AS microbial communities,and that Proteobacteria became the dominant bacteria in the acclimated AS.The relative abundance of Klebsiella,Escherichia,and Pseudomonas were increased after acclimated with CIP or NOR in the acclimated AS.It also found that the abundances of genes involved in carbohydrate transport and metabolism,membrane transport,energy metabolism,and energy production and conversion functions were significantly up-regulated by the CIP or NOR acclimation.Take together,these results provide new stratigies for the bio-removal of fluoroquinolones in environments,and in degree provide theoretical basis for understading the potential biotransformation pathway during the CIP or NOR degration.