Soil extract calcium phosphate media for screening of phosphate-solubilizing bacteria

Media development for screening bacteria capable of solubilizing inorganic complex forms of phosphorous to a soluble form is a major concern in agricultural research. This study formulated an effective, alternative solid and liquid media to the currently available Pikovskaya (PVK) medium, which relies on the use of calcium phosphate and numerous inorganic components for the screening of phosphate-solubilizing bacteria. In this present study, soil extract calcium phosphate (SECP) broth was formulated with simple medium requirements. SECP broth performed better than PVK broth as evidenced by its ability to support a higher bacterial population, higher reduction in broth pH and higher organic acid production and ultimately a better phosphate solubilization, based on the zone of clearance using bromocresol green or congo red in addition to bromothymol blue. Apart from calcium phosphate, rock phosphate and aluminum phosphate were also used as phosphate sources for the screening of different phosphate-solubilizing strains. This solid SECP medium could be used effectively with other phosphorous sources such as rock phosphate and aluminum phosphate. A high correlation between solid-based assay and broth-based assay for screening of phosphate-solubilizing bacteria was observed in the study.