Novel alkali-resistant nitrogen and phosphorus removal strain I4: Performance evaluation and molecular mechanism

• Strain I4 had high simultaneously nitrogen and phosphorus removal ability with a wide alkali tolerance range. • Unraveling the metabolic pathways of carbon, nitrogen and phosphorus of strain I4. • A noticeable variation in the expression of functional genes across various media was detected. • The activities of key enzymes in nitrogen and phosphorus metabolism were determined. The highly alkali-tolerant strain Pseudomonas sediminis I4, isolated from a brackish-water pond, demonstrates both nitrification-aerobic denitrification and aerobic phosphorus removal capabilities. The optimal conditions for nitrogen and phosphorus removal were determined to include a carbon-to-nitrogen ratio of 10, a phosphorus-to-nitrogen ratio of 0.2, a temperature of 30°C, and sodium citrate as the carbon source. The strain exhibited a salinity tolerance range of 0–2 % and an optimal pH range of 7–11. The nitrogen and phosphorus removal efficiencies reached 93–100 % and 100 % in 24 h, respectively. Genomic analysis revealed complex nitrogen assimilation and dissimilation processes, transport proteins, and predicted pathways for nitrogen and phosphorus removal. Enzyme activity assays indicated that nitrogen- and phosphorus-related enzymes exhibited higher activity at pH 11, enhancing the strain’s nutrient removal efficiency. Strain I4′s strong alkali resistance and nutrient removal capacity underscore its applicability in brackish and saline-alkaline environments.