Characterization and Mechanisms of Biosolubilization of Rock Phosphate by Microbes Isolated from Mahanadi Estuary, Odisha, India

Microbial solubilization of rock phosphate (RP) considered being an alternative to chemical phosphorous (P) fertilizer, causing high costs and environmental pollution. This work aimed to isolate efficient phosphate solubilizing strains from the estuary region of the Mahanadi river to check their RP solubilizing efficiency, and the mechanisms were discussed. Two strains of bacteria (Bacillus thuringenesis P0B11 and Lysinobaccillus fusiformis P0B28) and a fungus (Aspergillus aculeatus P0F3) were the most effective strain solubilizing RP. This is the first report of RP solubilization by L. fusiformis P0B28 and the first report of in vitro stearic acid production during RP solubilization. In particular, the potent strain A. aculeatus P0F3 produced the highest soluble P (345.6 mg/l) on 5th day. The soluble P concentration showed a significant negative correlation (r = − 0.88, p ≤ 0.01) with the pH, while it is positively correlated with the growth of B. thuringenesis P0B11 (r = 0.87, p ≤ 0.01), L. fusiformis P0B28 (r = 0.55, p ≤ 0.01) and A. aculeatus P0F3 (r = 0.96, p ≤ 0.01), respectively. The P release process from rock phosphate fit the first-order kinetics model well (R2 = 0.8046–0.8401). Organic acids produced by the isolates found to be the major mechanism for RP solubilization by supplying H+ ions and organic anions. High P concentration was related to the high corroded structure formation on the RP surface, reduction in all mineral peak intensities and a large decrease in the intensity of vibrational bands of calcite and fluorapatite confirmed by SEM, XRD, and FTIR, respectively.