The Screening, Identification, and Efficient Nitrogen Removal Performance of a Novel Heterotrophic Nitrifying–Aerobic Denitrifying <i>Pseudomonas</i> sp. L5

ABSTRACT A novel bacterium with heterotrophic nitrification–aerobic denitrification (HN– AD ) capability, designated Pseudomonas sp. L5, was isolated from the activated sludge of an aerobic denitrification reactor in our laboratory and subsequently identified. This strain can efficiently conduct nitrogen metabolism using NH 4 + –N, NO 3 − –N and NO 2 − –N as nitrogen sources. Single‐factor experiments combined with response surface methodology (RSM) were used to optimize the culture conditions of strain L5. The predicted optimal conditions for growth and nitrogen removal were a C/N ratio of 31.29, sodium acetate as the carbon source, a temperature of 31.18°C, and an initial pH of 7.25. Notably, even under mildly alkaline conditions (pH 9.0), the strain maintained high aerobic denitrification efficiency, with a NO 3 − –N removal rate of 86.236%. The nitrogen metabolism pathway of strain L5 was elucidated through a combined analysis of the expression of key HN– AD genes and enzyme activities. The denitrification capacity of strain L5 under alkaline conditions provides a theoretical basis and technical support for the application of aerobic denitrifying bacteria in high‐pH wastewater treatment.