Potential application of aerobic denitrifying bacterium Pseudomonas aeruginosa PCN-2 in nitrogen oxides (NOx) removal from flue gas

[Display omitted] •High-efficient aerobic denitrifier with extremely low NO accumulation was isolated.•Coordinate expressions of denitrification gene napA, nirS, and cnorB were revealed.•Less NO was accumulated under higher O2 concentration during nitrate reduction.•Efficient NO and NO2 removal was realized by immobilized bacteria in batch test.•NOx removal efficiency of 91–96% was achieved in biotrickling filter with PCN-2. 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 O2 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 cd1 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 O2 concentration of 0–10%. A biotrickling filter established with present strain achieved high NOx removal efficiencies of 91.94–96.74% at inlet NO concentration of 100–500ppm and O2 concentration of 0–10%, which implied promising potential applications in purifying NOx contaminated flue gas.