Biological nitrogen removal and metabolic characteristics of a novel cold-resistant heterotrophic nitrification and aerobic denitrification Rhizobium sp. WS7

For improving the poor de-nitrogen efficiency and effluent quality faced by wastewater treatment plants in winter, a novel cold-resistant strain, Rhizobium sp. WS7 was isolated. Strain WS7 presented dramatic de-nitrogen efficiencies including 98.73 % of NH4+-N, 99.98 % of NO3--N, 100 % of NO2--N and approximately 100 % of mixed nitrogen (NH4+-N and NO3--N) at 15 °C. Optimum parameters of WS7 for aerobic denitrification were determined. Additionally, functional genes (amoA, napA, nirK, norB, and nosZ) and key enzymes (nitrate reductase and nitrite reductase) activities were determined. Nitrogen balance analysis suggested that assimilation played a dominant role in de-nitrogen by WS7, the NH4+-N metabolic pathway was deduced as NH4+-N → NH2OH → NO → N2O → N2, and the NO3--N/NO2--N metabolic pathway was deduced as NO3--N → NO2--N → NO → N2O → N2. The cold-resistant Rhizobium sp. WS7 has great application feasibility in cold sewage treatment.