Isolation and Screening of Mineral Phosphate Solubilizing Microorganisms

Phosphorus is abundant in soil but its availability is limited due to its immobilization and complexation with mineral ions. The sources of phosphate are sustainable only when they are in receipt of solubilized by rhizospheric microorganisms. Phosphate solubilizing microorganisms (PSMs) such as rhizospheric or endophytic bacteria, free-living fungi, or vesicular -arbuscular mycorrhiza (VAM) have potency to solubilize mineral phosphate source by secretion of acids, enzymes, chelation of metal ions, and H+ ion extrusion. The isolation and screening of these PSMs is done on Pikovskaya medium, NBRIP medium, or Tris minimal agar medium with application of different sources of phosphate like tricalcium phosphate, apatite, or rock phosphate and detected by either zone of solubilization or color of zone around the colony. The amount of released phosphate in the solution is determined by measuring the reduction of phosphomolybdate or vanadomolybdate complex in acidic condition. The amount of reduced complex is directly proportional to soluble phosphate.