Nitrogen Removal Characteristics and Application by a Novel Cold-Resistant Bacterium

Biological nitrogen removal is often inhibited under low-temperature conditions due to reduced microbial activity and impaired metabolic processes. A novel cold-resistant bacterium, Acinetobacter pragensis FX1, was isolated and exhibited efficient nitrogen removal capacity across a broad temperature range of 5–30 °C. Notably, strain FX1 remained metabolically active at 5 °C, with a specific growth rate of 0.04 h−1 and a generation time of 18.09 h, demonstrating excellent cold-resistant capability. Under ideal operating conditions (sodium citrate as carbon source, C/N ratio of 10, pH 7, and a shaking speed of 150 rpm) at 10 °C, removal efficiencies of NH4+-N, NO3−-N, and NO2−-N reached 99.39%, 81.30%, and 99.78%, respectively. Nitrogen balance analysis, combined with genome annotation, revealed that nitrogen assimilation was the predominant pathway, thereby avoiding the potential for greenhouse gas (N2O) generation. Genes associated with cold shock response and fatty acid biosynthesis supported the maintenance of membrane stability and the sustainability of metabolic activity under cold stress. Furthermore, bioaugmentation with strain FX1 successfully improved nutrient removal performance at 10 °C, driven by synergistic interactions with indigenous microbial communities. Overall, these results demonstrate the potential of strain FX1 as a promising candidate for enhancing biological nitrogen removal performance in cold-region wastewater treatment.