Removal of nitrate nitrogen by Pseudomonas JI-2 under strong alkaline conditions: Performance and mechanism

[Display omitted] •Strain JI-2 could effectively remove nitrate nitrogen at pH 11 (11.05 mg N/(L·h)).•JI-2 secreted PS and acidic groups to alleviate the adverse effects of alkalinity.•JI-2 contains complex genes and metabolic mechanisms for alkali tolerance.•JI-2 responds to a strong alkaline environment by complex regulatory mechanisms. The nitrate nitrogen removal characteristics of Pseudomonas JI-2 under strong alkaline conditions and the composition and functional groups of extracellular polymeric substance were analyzed. Furthermore, nontargeted metabonomics and bioinformatics technology were used to investigate the alkaline tolerance mechanism. JI-2 removed 11.05 mg N/(L·h) of nitrate with the initial pH, carbon to nitrogen ratio and temperature were 11.0, 8 and 25 °C respectively. Even when the pH was maintained at 11.0, JI-2 could still effectively remove nitrate. JI-2 contains a large number of Na+/H+ antiporters, such as Mrp, Mnh (mnhACDEFG) and Pha (phaACDEFG), which can stabilize the intracellular acid–base environment, and SlpA can enable quick adaptation to alkaline conditions. Moreover, JI-2 responds to the strong alkaline environment by secreting more polysaccharides, acidic functional groups and compatible solutes and regulating key metabolic processes such as pantothenate and CoA biosynthesis and carbapenem biosynthesis. Therefore, JI-2 can survive in strong alkaline environments and remove nitrate efficiently.