Nitrogen removal characteristics and underlying mechanisms by a heterotrophic nitrification-aerobic denitrification Pseudomonas stutzeri strain 4-3

AIMS: A heterotrophic nitrification-aerobic denitrification bacterial strain that could effectively remove nitrogen from wastewater was identified, and its nitrogen removal characteristics and possible mechanism underlying were investigated. METHODS AND RESULTS: A nitrogen-removing strain was isolated from produced water of Changqing oilfield in the Ordos Basin and identified as Pseudomonas stutzeri 4-3 by physiological and biochemical characteristics as well as the phylogenetic analysis. Nitrification and denitrification capabilities were tested under different nitrogen sources, showing that strain 4-3 possessed heterotrophic nitrification and aerobic denitrification capabilities, with a maximum total nitrogen removal rate of 91.345%. Comparative studies under aerobic and anoxic conditions revealed that this strain effectively removed nitrogen sources, and the total nitrogen removal rates were slightly higher under aerobic conditions than those in anoxic conditions, achieving an ammonia nitrogen removal rate of 10.603 mg·L-1·h-1. The extracellular polymeric substances secreted by strain 4-3 could enhance nitrogen removal capacity, and the removal efficiency was increased by 23.5% with the increase of exogenous EPS concentration. CONCLUSIONS: The newly isolated P. stutzeri strain 4-3 was a facultative anaerobic bacterium that carried functional genes of denitrification and exhibited efficient heterotrophic nitrification and aerobic denitrification capabilities. Moreover, EPS secreted by this strain played an auxiliary role in the denitrification process.