Nitrogen removal characteristics and predicted conversion pathways of a heterotrophic nitrification-aerobic denitrification bacterium, Pseudomonas aeruginosa P-1

In this study, the heterotrophic nitrification-aerobic denitrification activity of Pseudomonas aeruginosa (P-1) strain was investigated, and the N transformation pathway was revealed. The highest removal rates of NH₄⁺, NO₃^-, and NO₂^- (9.29, 6.12, and 3.72 mg L^-1 h^-1, respectively) by this strain were higher than those by most reported bacteria and were achieved when the carbon source was glucose, C/N ratio was 15, pH was 8, temperature was 30 °C, and shaking speed was 200 rpm. The removal order and characteristics of three N sources were investigated in Pseudomonas aeruginosa for the first time. The results revealed that P-1 preferentially nitrified NH₄⁺ and only began to denitrify NO₂^- and NO₃^- when NH₄⁺ was almost entirely depleted. Isotopic labeling of N sources revealed that P-1 uses both partial and complete nitrification/denitrification pathways that can operate either simultaneously or independently, depending on the availability of different types of N compounds, with N₂ as the final gaseous product and virtually no NO₂^- accumulation. Moreover, the P-1 strain could convert various nitrogen compounds under high salinity (40 g L^-1) and high concentrations of Cu²⁺, Zn²⁺, Cr⁶⁺, Pb²⁺, and Cd²⁺ (50 mg L^-1). Therefore, P-1 could be used as an alternative of inorganic N-removal bacteria in practical applications.