Efficient phosphate accumulation in the newly isolated Acinetobacter junii strain LH4

Phosphate (PO₄^3-) accumulation associated with bacteria contributes to efficient remediation of eutrophic waters and has attracted attention due to its low cost, high removal efficiency and environmental friendliness. In the present study, we isolated six strains from sludge with high concentrations of chemical oxygen demand, total nitrogen and total phosphorus levels. Among them, strain LH4 exhibited the greatest PO₄^3- removal ability. Strain LH4 is typical of Acinetobacter junii based on physiological, biochemical, and molecular analyses and is a PO₄^3--accumulating organism (PAO) based on toluidine blue staining. The strain grew quickly when subjected to aerobic medium after pre-incubation under anaerobic condition, with a maximum OD₆₀₀ of 1.429 after 8 h and PO₄^3- removal efficiency of 99%. Our data also indicated that this strain preferred utilizing the carbon (C) sources sodium formate and sodium acetate and the nitrogen (N) sources NH₄Cl and (NH₄)₂SO₄ over other compounds. To achieve optimal PO₄^3- removal efficiency, a C:N ratio of 5:1, inoculation concentration of 3%, solution pH of 6, incubation temperature of 30 °C, and shaking speed of 100 rpm were recommended for A. junii strain LH4. By incubating this strain with different concentrations of PO₄^3-, we calculated that its relative PO₄^3- removal capacity ranged from 0.67 to 3.84 mg L^-1 h^-1, ranking in the top three among reported PAOs. Our study provided a new PO₄^3--accumulating bacterial strain that holds promise for remediating eutrophic waters, and its potential for large-scale use warrants further investigation.