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Objective The rapid increase in wastewater discharge from animal husbandry has caused severe environmental pollution. Identifying efficient heterotrophic nitrifying-aerobic denitrifying bacteria and investigating their denitrification mechanisms are of great theoretical and practical importance for mitigating nitrogen pollution in the wastewater. Methods A strain exceling in heterotrophic nitrification-aerobic denitrification (HN-AD) was isolated and from activated sludge in pig farms. Culture conditions were optimized by response surface methodology. We evaluated the inorganic nitrogen-transforming capacity of the strain by assessing its utilization efficiency of single and mixed nitrogen sources and through nitrogen balance analysis. The completeness of the denitrification process was confirmed via gas chromatographic measurements of N2 and N2O. Finally, the nitrogen removal pathways and underlying mechanisms were elucidated through whole-genome analysis. Results The successfully isolated strain Klebsiella sp. WH-E exhibited excellent HN-AD capabilities. The growth conditions of the strain were optimized as follows: sodium citrate as the carbon source, 34.18 °C, initial pH 7.1, a C/N ratio of 14.53, and a shaking speed of 159.59 r/min. When the strain was cultured with ammonium, nitrate, or nitrite as the sole nitrogen source, the nitrogen removal rates were 99.80%, 81.54%, and 80.00%, respectively. Furthermore, when ammonium was the sole nitrogen source, 35.84% and 35.91% of nitrogen were converted into cellular nitrogen and gaseous nitrogen, respectively. When ammonia nitrogen was combined with nitrate nitrogen as mixed nitrogen sources, the nitrogen removal rate was 100.00%; When ammonia nitrogen was combined with nitrite nitrogen as mixed nitrogen sources, the ammonia nitrogen removal rate was 100.00%, and the nitrite nitrogen removal rate was 91.97%, respectively. Whole-genome sequencing identified several nitrogen metabolism-related functional genes, including glnB, norVWR, narGHI, nasBC, and nirBD. Conclusion Klebsiella sp. WH-E possesses three nitrogen metabolism pathways: ammonium assimilation, nitrification-denitrification, and nitrate assimilation and dissimilation. This study confirms the applicability of Klebsiella sp. WH-E for nitrogen removal from full-scale piggery wastewater and establishes a solid theoretical foundation for its engineering applications.
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| 科 Family | 属数 Number of genus | 种数 Number of species | 占总种数比例 Percentage of total species (%) | 属 Genus | 种数 Number of species | 占总种数比例 Percentage of total species (%) |
|---|---|---|---|---|---|---|
| 鹅膏菌科Amanitaceae | 2 | 11 | 5.26 | 鹅膏菌属 Amanita | 10 | 4.78 |
| 小菇科 Mycenaceae | 2 | 12 | 5.74 | 丝盖伞属 Inocybe | 5 | 2.39 |
| 多孔菌科 Polyporaceae | 8 | 14 | 6.70 | 蜡蘑属 Laccaria | 5 | 2.39 |
| 红菇科 Russulaceae | 3 | 23 | 11.00 | 小皮伞属 Marasmius | 6 | 2.87 |
| 小菇属 Mycena | 11 | 5.26 | ||||
| 光柄菇属 Pluteus | 5 | 2.39 | ||||
| 红菇属 Russula | 17 | 8.13 | ||||
| 栓菌属 Trametes | 5 | 2.39 |
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