Characterization of <i>Pseudomonas stutzeri</i> strain AY4 with nitrogen removal and application in wastewater treatment

A new strain capable of removing ammonium and nitrate nitrogen from animal farm wastewater was isolated and identified as <i>Pseudomonas stutzeri</i> strain AY4. Nitrogen balance analysis showed 52.9% and 63.2% of NH₄⁺-N and NO₃^--N conversion to gaseous nitrogen, respectively, in laboratory conditions. Strain AY4 was also able to remove 92.7%, 95.8%, and 91.4% of total nitrogen, NH₄⁺-N, and NO₃^--N in the real farm wastewater, which was significantly greater than that of the uninoculated control group. The quantitative real-time PCR experiment showed that the transcript levels of <i>glnA</i>, <i>glnE</i>, <i>amtB</i>, <i>napA</i>, <i>narI</i>, <i>nirB</i>, and <i>nirD</i> genes related to nitrogen metabolism were significantly upregulated during wastewater treatment. Strain AY4 showed high potential working in low carbon-to-nitrogen ratio and wide range of temperature adaptability, which makes it suitable for wastewater treatment in various environmental conditions. In addition, the study of transcript levels of genes related to nitrogen metabolism is important for revealing the mechanism of action of <i>P. stutzeri</i> in wastewater treatment.IMPORTANCEThe heterotrophic nitrifying-aerobic denitrifying bacterium <i>Pseudomonas stutzeri</i> strain AY4, isolated in this study, simultaneously removed ammonium nitrogen and nitrate nitrogen from wastewater. Upregulation of the transcript levels of <i>glnA</i>, <i>glnE</i>, <i>amtB</i>, <i>napA</i>, <i>narI</i>, <i>nirB</i>, and <i>nirD</i> genes associated with nitrogen metabolism favored the removal of nitrogen from actual wastewater. The isolation of novel strains with nitrogen removal ability has positively contributed to the treatment of nitrogen-containing farm wastewater.