Optimization of nitrogen removal performance and metabolic pathway of a heterotrophic nitrifying-aerobic denitrifying bacterial strain Acinetobacter johnsonii sp. N26

Abstract:

[Background] The accumulation of nitrogenous substances in water bodies will cause problems such as eutrophication and death of aquatic organisms, which seriously threatens the aquatic environment and restricts the environmental protection for the sustainable development of China. [Objective] To study the nitrogen removal performance and metabolic pathway of Acinetobacter johnsonii sp. N26, a bacterial strain with heterotrophic nitrifying-aerobic denitrifying function and screened out from sheep manure compost, for the removal of nitrogen pollutants in domestic sewage. [Methods] The growth and nitrogen removal curves of N26 in the media with ammonia nitrogen and nitrate nitrogen were established. The nitrogen removal performance of the strain was optimized by single factor experiment, and the metabolic pathway was studied by nitrogen balance analysis and functional gene identification. [Results] The growth and nitrogen removal curves illustrated that N26 rapidly removed ammonia nitrogen and nitrate nitrogen (initial concentration of 50 mg/L) with high efficiency. For the removal of ammonia nitrogen, the strain showed the removal efficiency of 95.5% and the maximum removal rate of 5.330 mg/(L·h) within 9 h. For the removal of nitrate nitrogen, the strain showed the removal efficiency of 93.6% and the maximum removal rate of 3.147 mg/(L·h) within 15 h, and only a small amount of nitrate and nitrite were accumulated in the end. The strain had the optimum nitrogen removal performance in the medium with ammonium chloride as the nitrogen source and sodium succinate as the carbon source at 30 ℃, the inoculum amount of 15%, pH 8.0–9.0, C/N ratio of 15, rotating speed of 120 r/min, and nitrogen load ≤300 mg/L (ammonia nitrogen). The results of nitrogen balance analysis and functional gene identification indicated that the nitrogen removal process of this strain was not only in line with heterotrophic nitrification-aerobic denitrification but also a short-range nitrification-denitrification process. The metabolic pathways of this strain for nitrogen removal were NH₄⁺-N→NO₂^--N→NO→N₂O→N₂ and NO₃^--N→NO₂^--N→NO→ N₂O→N₂. [Conclusion] A. johnsonii sp. N26 has excellent performance of heterotrophic nitrification-aerobic denitrification and application potential in the treatment of ammonia nitrogen pollution in water bodies. The results can provide a theoretical basis for the application of heterotrophic nitrifying-aerobic denitrifying microorganisms to the biological removal of nitrogen in domestic sewage.