Enrichment of a heterotrophic nitrifying and aerobic denitrifying bacterial consortium: Microbial community succession and nitrogen removal characteristics and mechanisms

This study cultivated a bacterial consortium (S60) from landfill leachate that exhibited effective heterotrophic nitrification and aerobic denitrification (HN-AD) properties. Under aerobic conditions, the removal of NH₄⁺-N reached 100 % when the S60 consortium utilised NH₄⁺-N either as the sole nitrogen source or in combination with NO₂^--N and NO₃^--N. Optimal HN-AD performance was achieved with sodium acetate as a carbon source and a pH of 7.0-8.0, dissolved oxygen concentration of 4.0-5.0 mg/L, and a C/N ratio of 10. Furthermore, the presence of functional genes (amoA, hao, napA, nirK, nirS, nosZ), hydroxylamine oxidase, nitrate reductase, and nitrite reductase was confirmed in the S60 consortium. Drawing from these findings, two HN-AD pathways were delineated: NH₄⁺-N → NH₂OH → NO₂^--N → NO₃^--N → NO₂^--N → NO → N₂O → N₂ and NH₄⁺-N → NH₂OH → N₂O → N₂. Metagenomic binning analysis of the S60 consortium uncovered complete pathways for dissimilatory nitrate reduction and denitrification within Halomonas, Zobellella, Stutzerimonas, Marinobacter, and Pannonibacter. These findings offer new insights into the application of HN-AD bacteria and their collaborative nitrogen removal in environments with varying nitrogen sources.