Evaluation of nitrogen removal performance and metabolic mechanism of a novel salt-tolerant strain Pseudomonas aeruginosa SH3

High salinity impedes efficient nitrogen removal from mariculture wastewater, which inhibits the colonization and nitrogen removal capabilities of nitrogen-removing microbes. This study aimed to isolate and characterize a salt-tolerant heterotrophic nitrification-aerobic denitrification bacterial strain. We evaluated 30 bacterial strains isolated from Portunus trituberculatus aquaculture ponds, among which Pseudomonas aeruginosa SH3 exhibited superior nitrogen removal efficiencies (99 % of NH₄⁺-N, 71 % of NO₂^--N, and 85 % fof NO₃^--N at a salinity of 30 ‰) than the other strains. Single-factor experiments demonstrated that SH3 effectively removed either NH₄⁺-N or NO₂^--N across various C/N ratios (10-20), pH levels (7-9), salinity levels (15-35 ‰), and temperatures (25-35 °C), highlighting its promising nitrogen removal capabilities under conditions suitable for mariculture. Genomic analysis showed that SH3 removes NH₄⁺-N through ammonia assimilation and nitrification and converts NO₂^--N and NO₃^--N via denitrification and assimilatory nitrate reduction. Bioaugmentation with SH3 reduced the startup period by 14 d, addressing a common challenge of prolonged startup times in a moving-bed biofilm reactor used for nitrogen removal in marine recirculating aquaculture systems. Meanwhile, bioaugmentation maintained minimal fluctuations in nitrogen levels throughout the operational period, resulting in consistently low concentrations of NO₂^--N and NH₄⁺-N, both below 1 mg/L. Therefore, strain SH3 exhibits robust nitrogen removal capabilities, demonstrating its practicality and reliability in mariculture wastewater treatment along with providing robust data support for industrial-scale applications.