New insights into heterotrophic nitrification-aerobic denitrification during efficient pyridine degradation by
Nuo Wang1, Hui Zhang1, Xianya Liu1
1College of Environmental Science and Engineering, Beijing Forestry University, Beijing 100083, China; Beijing Key Laboratory for Source Control Technology of Water Pollution, Engineering Research Center for Water Pollution Source Control and Eco-remediation, Beijing Forestry University, Beijing 100083, China.
None:
Pyridine, a typical N-heterocyclic compound, poses both carbon and nitrogen pollution. Biodegradation is cost-effective and eco-friendly for treating industrial pyridine wastewater. However, highly efficient pyridine-degrading strain is warranted, and the associated nitrogen conversion mechanisms remain elusive. Herein, a high pyridine-tolerant strain Rhodococcus pyridinivorans WN2 was isolated, which exhibited positive responses to a broad range of pyridine concentrations, with superior growth and degradation at a high-strength pyridine up to 3000 mg/L. Strain WN2 showed favorable adaptability to salinity (1.5 % NaCl) and superior degradation under neutral to alkaline conditions (pH 7.0-10.0), DO of 1.8-3.7 mg/L and mesophilic temperatures (30-40 °C). During pyridine metabolism, mass balance analysis revealed a significant portion of carbon and nitrogen from pyridine was assimilated into biomass C (20.1 %) and biomass N (19.2 %). Isotope labeling evidence (15N2, 4.1 %) confirmed that a portion of the released ammonium underwent dissimilatory conversion via heterotrophic nitrification-aerobic denitrification (HNAD) process during pyridine degradation. Combined with transcriptomic analysis, an efficient nitrogen removal pathway via direct ammonia oxidation (NH4+→NH2OH → N2) mediated by dnf gene cluster was identified, and an efficient pyridine degradation pathway via direct pyridine ring cleavage mediated by pbd gene cluster was revealed. Furthermore, carbon metabolic pathways including tricarboxylic acid (TCA) cycle and glyoxylate cycle, as well as energy generation pathways including respiratory electron transport chain (ETC) and ATP synthase, were coordinately up-regulated under pyridine stimulation, which collectively provided sufficient energy for growth and metabolism of strain WN2. This study provides new insights into nitrogen conversion metabolism during efficient biological pyridine degradation.
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