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

Abstract

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.