Nitrogen metabolic characteristics and adaptive mechanisms of Paracoccus sp. QD-21 under complex nitrogenous environments

A novel strain of Paracoccus sp. QD-21, which is capable of simultaneous heterotrophic nitrification and aerobic denitrification, was isolated and investigated for the potential in removal of nitrogen in wastewater treatment. The strain exhibited nitrogen removal rates of 5.55, 3.35, and 2.78 mg/(L·h) for NH ₄ ⁺ -N (100 mg/L), NO ₂ ⁻ -N (100 mg/L), and NO ₃ ⁻ -N (100mg/L), respectively. Notably, QD-21 maintained substantial nitrogen removal efficiency under high concentrations of inorganic nitrogen, highlighting its remarkable tolerance to complex nitrogenous conditions. Optimal nitrogen removal occurred with sodium succinate as carbon source, C/N 7:1, pH 8.41, 140 rpm, 38.41°C, and inoculum size 4.56%. Analysis using molecular biology techniques revealed the presence of genes associated with the nitrification process, such as amo and hao , in QD-21. This confirms the nitrification pathway of strain: NH ₄ ⁺ -N → NH ₂ OH → NO ₂ ⁻ -N → NO ₃ ⁻ -N. Additionally, the presence of nir K, nor B, and nos Z confirms the denitrification pathway in QD-21: NO ₃ ⁻ -N → NO ₂ ⁻ -N → NO → N ₂ O → N ₂ . Meanwhile, the presence of nir BD, nar k, gln L, gln A, glt B, and nas A indicates that a portion of nitrogen enters ammonia assimilation, providing energy for the strain's growth and reproduction. Furthermore, in practical wastewater tests QD-21 achieved removal efficiencies of 75.5% for NH ₄ ⁺ -N and 55.8% for COD. Such findings demonstrate the great potential of strain QD-21 in treating nitrogen pollution from diverse sources.