Simultaneous removal of nitrogen and phosphorous by heterotrophic nitrification-aerobic denitrification of a metal resistant bacterium Pseudomonas putida strain NP5

A novel strain NP5 with efficient heterotrophic nitrification, aerobic denitrification and phosphorus accumulation ability was isolated and identified as Pseudomonas putida strain NP5. The removed ammonium and phosphate were mainly converted into intracellular components by assimilation, and negligible nitrification intermediates and N2O were accumulated during heterotrophic nitrification. In addition, the optimal conditions for nutrient removal were: succinate as carbon source, C/N 10, P/N 0.2, temperature 30 degrees C, salinity 0% and shaking speed 160 rpm. Besides, strain NP5 possessed an exceptional heavy metal and nanoparticles resistance. Cr6+ was found to be the most toxic among the tested metals, and it could be removed simultaneously. Moreover, an obvious phosphorus release was observed under anaerobic condition, and repeated exposure to the anaerobic/aerobic conditions could significantly improve the nutrient removal. Furthermore, the successful expression of key enzymes for nitrogen and phosphorous removal provided additional evidence for possibility of simultaneous nitrification, denitrification and phosphorus removal.