Enhancing aerobic nitrate removal by amino acid supplementation: Metabolic flexibility of Pseudomonas sp. DE6 in polluted environments

A strain exhibiting high nitrate-removal efficiency under anaerobic conditions was isolated and taxonomically identified as Pseudomonas sp. DE6. Subsequent investigations revealed that supplementation with specific amino acids, including L -asparagine and glycine, substantially enhanced its nitrate-removal capacity under aerobic conditions. The results indicated that when sodium succinate was used as the carbon source at a carbon-to-nitrogen ratio of 4 (mass basis), and the culture was maintained at 30°C, pH 7.0, and 160 rpm under anaerobic tube-incubation conditions, strain DE6 removed 620 mg/L KNO₃ (equivalent to 85.87 mg/L nitrate nitrogen) within 12 h, achieving a removal rate of 1.37 mg N/(g DCW·h) and nearly complete removal of total inorganic-nitrogen within 24 h. However, under aerobic conditions, the nitrate-nitrogen removal rate was substantially lower. Complete removal was achieved only after 24 h with the addition of 0.4 g/L amino acids, yielding a nitrate-nitrogen removal rate of 0.87 mg N/(g DCW·h) and a final total inorganic-nitrogen removal efficiency of 80.94 %. RT-qPCR analysis indicated that nitrate-nitrogen removal was mainly achieved by denitrification and nitrogen assimilation. Following supplementation with amino acids, the expression levels of genes involved in the nitrate assimilation and partial denitrification pathways were significantly upregulated under aerobic conditions. This suggests that amino acid metabolism enhances both denitrification and assimilation by strain DE6 under aerobic conditions, thereby improving the removal efficiency of nitrate nitrogen. These findings highlight the potential for the flexible application of the nitrate-removal mechanism of the amino-acid-coordinated strain DE6 across diverse wastewater-treatment contexts. • A strain of nitrogen-removing bacteria, Pseudomonas sp. DE6, was isolated. • The strain degrades inorganic nitrogen in wastewater at 20℃ room temperature. • Strain DE6 has higher nitrogen removal efficiency than the reported strain. • The strain removed 80.94–100 % of the inorganic nitrogen within 48 h. • Denitrification and assimilation are main nitrogen metabolism modes of strain DE6.