The Potential of Using Phosphate-Solubilizing Bacteria as a Controlled-Release Biofertilizer Under Salt Stress Conditions.

Phosphorus deficiency in saline soils, despite high total phosphorus content, limits crop productivity due to low bioavailability. This study aimed to evaluate the phosphate-solubilizing potential and salt stress responses of Priestia megaterium PN18, a bacterium isolated from saline-affected soil, and to assess its suitability as a biofertilizer through cell encapsulation. PN18 was examined for biofilm formation, exopolysaccharide (EPS) production, and sodium uptake under NaCl concentrations ranging from 0.0 to 2.0 mol L^-1. Results showed that biofilm formation decreased with increasing salinity, whereas EPS production increased, peaking at 1.2 mol L^-1, in correlation with sodium uptake. Capsules formulated with 0.6% sodium alginate and 2% CaCl₂ had an average diameter of 2.81 mm and maintained phosphate-solubilizing activity under high salinity, with only a slight decline at 2.0 mol L^-1 NaCl. While free PN18 exhibited a higher maximum solubilization (386 mg L^-1) than encapsulated PN18 (292 mg L^-1), its efficiency sharply declined above 0.4 mol L^-1 NaCl. These findings highlight the potential of PN18 capsules as a controlled-release biofertilizer to improve phosphorus availability and soil fertility in saline environments.