Solubilization of rock phosphate by phosphate solubilizing bacteria isolated from effluent treatment plant sludge of a fertilizer plant.

This study evaluates the efficiency of Phosphate solubilizing bacteria isolated from Effluent Treatment Plant sludge of Paradeep Phosphate Limited, Odisha, India, to solubilize rock phosphate (RP) and the mechanism and structural changes during solubilization investigated by scanning electron microscopy (SEM), X-ray diffraction (XRD), and Fourier-transform infrared spectroscopy (FTIR). Out of 13 bacterial isolates, Bacillus cereus S0B4, Solibacillus isronensis S0B8, and Bacillus amyloliquefaciens S0B17 strains were found to be the best RP solubilizers. This is the first report on S. isronensis S0B8 with the ability to solubilize RP. In particular, the potent strain B. cereus S0B4 showed maximum soluble P (338.5 mg/L) on the 7th day. Negative correlations (r = -0.70; p ≤ 0.01) were observed between soluble P concentration and pH, whereas positive correlation exists with the growth of B. cereus S0B4 (r = 0.91, p ≤ 0.01), S. isronensis S0B8 (r = 0.75, p ≤ 0.01), and B. amyloliquefaciens S0B17 (r = 0.77, p ≤ 0.01) respectively. The P release kinetics followed the 1st order model well (R2 = 0.8001-0.8503). It seems that H+ ions and organic anions released from the organic acids are major factors responsible for RP solubilization. The SEM observations demonstrate that B. cereus S0B4 corroded the RP surface significantly due to the proton attack. The XRD analysis confirms that the intensity of all mineral peaks decreases after treatment with B. cereus S0B4. The FTIR analysis indicated a significant decrease of calcite and fluorapatite's vibrational bands with the disappearance of quartz.