**5. Ability of microorganisms to solubilise phosphates and key mechanisms of microbial P Solubilisation**

Phosphorous is available in the soil as a number of organic and inorganic compounds due to its high reactivity, and those are unavailable for plants [54]. PSMs solubilise these insoluble forms of phosphates into soluble by secreting complex compounds such as organic acid anions, protons, exopolysaccharides, siderophores, hydroxyl ions and extracellular enzymes [55]. The phosphate-solubilising mechanism of PSM has two major aspects as inorganic phosphate solubilisation and organic phosphate solubilisation based on the substrate of P [3].
