The toxicities of sodium perfluorononyloxy-benzenesulfonate (OBS) to animals and plants are similar to those of perfluorooctane sulfonate.However,the mechanism of its toxicity to aerobic denitrifying bacteria is still unclear.In the present study,the ecotoxicity of OBS on an aerobic denitrifying strain,Pseudomonas stutzeri,was evaluated.The results showed that a dosage of OBS clearly affected the growth and aerobic denitrification of P.stutzeri.When compared with an unamended control,the degradation efficiency of the total nitrogen decreased by 30.13％ during exposure to 200 mg/L of OBS,and the complete degradation time of nitrate-nitrogen was delayed by 4 h.The lactate dehydrogenase and superoxide dismutase produced by the bacteria increased with the concentration of OBS,and reactive oxygen species were also detected by confocal laser scanning microscope imaging.Transmission electron microscope imaging revealed chromosome deformation of the cells and damage to cell content;moreover,outer membrane vesicles were secreted from the bacteria,which was the important detoxification mechanism of P.stutzeri to OBS.Expression of the genes involved in aerobic nitrification and oxidative stress were also changed under OBS stress,which further confirmed the toxicity of OBS to P.stutzeri.This study reveals the environmental exposure risk of OBS from the perspective of microorganisms.