A novel and efficient facultative anaerobic denitrifying bacterium was isolated and identified as Pseudomonas citronellolis WXP-4. The strain WXP-4 could achieve 100% nitrate and nitrite removal efficiency utilizing sodium succinate as a carbon source, C/N ratio 7, pH 7.0, and temperature 40 °C under both aerobic and anaerobic conditions. The bacterium could tolerate a wide range of NO3--N concentrations from 100 to 1000 mg/L with a maximum nitrogen removal rate of 32.05 mg/(L h). An interesting phenomenon was found that no N2O emission occurred during the denitrifying process under anaerobic conditions, while there was 0.06 mg/L under aerobic conditions. This phenomenon had been confirmed by fluorescence quantitative PCR and the results showed that the relative abundance of nosZ gene increased by 17-fold based on the ratio of anaerobic to aerobic, and thus, nosZ gene could encode more nitrous oxide reductase to accelerate the conversion of N2O under anaerobic conditions. Moreover, the narG, nirK, and norB genes were also identified in the denitrifying pathway of the strain WXP-4. This investigation has demonstrated enormous potential for the future application in wastewater treatment systems.
Keywords: Denitrification genes; Fluorescence quantitative PCR; Metabolic pathway; Nitrogen removal; Nitrous oxide; Pseudomonas citronellolis.