Solubilization of insoluble inorganic phosphates by a novel salt- and pH-tolerant Pantoea agglomerans R-42 isolated from soybean rhizosphere

To develop environment-friendly biofertilizer solubilizing insoluble phosphates, salt- and pH-tolerant, insoluble inorganic phosphate-solubilizing bacterium was isolated from soybean rhizosphere. On the basis of its physiological characteristics and Vitek analysis, this bacterium was identified as Pantoea agglomerans. The optimal medium composition and cultural conditions for the solubilization of insoluble phosphate by P. agglomerans R-42 were 3% (w/v) of glucose, 0.1% (w/v) of NH4NO3, 0.02% (w/v) of MgSO4 • 7H2O, and 0.06% (w/v) of CaCl2 • 2H2O along with initial pH 7.5 at 30 °C. The soluble phosphate production under optimal condition was around 900 mg/l, which was approximately 4.6-fold higher than the yield in the MPVK medium. The solubilization of insoluble phosphate was associated with a drop in the pH of the culture medium. P. agglomerans R-42 showed resistance against different environmental stresses like 5–45 °C temperature, 1–5% salt concentration and 3–11 pH range. Insoluble phosphate solubilization was highest from CaHPO4 (1367 mg/l), hydroxyapatite (1357 mg/l) and Ca3(PO4)2 (1312 mg/l). However, the strain produced soluble phosphate to the culture broth with the concentrations of 28 mg/l against FePO4, and 19 mg/l against AlPO4, respectively.