Isolation, immobilization of salt-tolerant and inorganic phosphate solubilizing bacteria for producing controlled-release inorganic fertilizer in combination with microorganisms

Salt tolerance is one of the characteristics to ensure the viability of microorganisms when combined with chemical fertilizers. This research aimed to isolate bacteria that had both phosphate-solubilizing and salt-tolerant abilities for production of controlled-release inorganic fertilizer-incorporated microorganisms. Of twenty-five phosphate solubilizing bacteria strains isolated from soil samples collected from Ho Chi Minh City, Dong Nai, and Long An provinces on Pikovskaya medium (PVK), there were three strains of bacteria that had both phosphate solubilizing activity and salt tolerance. The analysis results on PVK medium supplemented with 3% and 4% NaCl showed that only PSM54 strain had phosphorusdegrading ring. Species identification based on 16S-rRNA sequence showed that PSM54 was 99.9% similar to Bacillus velezensis. The controlled-release fertilizer was made by coating biodegradable polymers incorporated with PSM54 bacteria that met standards for slow dissolution according to The Association of American Plant Food Control Officials. After 60 days of being immobilized in the membrane of controlled release, the PSM54 bacteria remained at 88.3% compared to the initial density.