Conventional biological removal of nitrogen oxides (NOx) from flue gas has been severely restricted by the presence of oxygen. This paper presents an efficient alternative for NOx removal at varying oxygen levels using the newly isolated bacterial strain Pseudomonas aeruginosa PCN-2 which was capable of aerobic and anoxic denitrification. Interestingly, nitric oxide (NO), as the obligatory intermediate, was negligibly accumulated during nitrate and nitrite reduction. Moreover, normal nitrate reduction with decreasing NO accumulation was realized under O-2 concentration ranging from 0 to 100%. Reverse transcription and real-time quantitative polymerase chain reaction (RT-qPCR) analysis revealed that high efficient NO removal was attributed to the coordinate regulation of gene expressions including napA (for periplasmic nitrate reductase), nirS (for cytochrome cd(1) nitrite reductase) and cnorB (for NO reductase). Further batch experiments demonstrated the immobilized strain PCN-2 possessed high capability of removing NO and nitrogen dioxide (NO2) at O-2 concentration of 0-10%. A biotrickling filter established with present strain achieved high NO. removal efficiencies of 91.94-96.74% at inlet NO concentration of 100-500 ppm and O-2 concentration of 0-10%, which implied promising potential applications in purifying NO. contaminated flue gas. (C) 2016 Elsevier B.V. All rights reserved.