Phosphate solubilizing bacteria: Isolation of Bacteria and Phosphate Solubilizing Genes, Mechanism and Genetics of Phosphate Solubilization

Phosphorus is one of the major plant nutrients that is least available in the soil. There are two components of P in soil, organic and inorganic phosphate. Plant growth promoting bacteria (PGPR) are soil and rhizosphere bacteria that can benefit plant growth by different mechanisms. The ability of some microorganisms to convert insoluble P to an accessible form, like orthophosphate, is an important trait in a PGPR for increasing plant yields. The use of phosphate solubilizing bacteria as inoculants simultaneously increases P uptake by the plant and crop yield. Strains from the genera Pseudomonas, Bacillus, Pantoea and Rhizobium are among the most powerful phosphate solubilizers. The principal mechanism for mineral phosphate solubilization is the production of organic acids, and acid phosphatases play a major role in the mineralization of organic phosphorous in soil. The main method for isolation PSB is carrying out by using insoluble organic and inorganic phosphate source in solid or liquid media with monitoring of production of free orthophosphate and decreasing pH in liquid media or production halo zone around colonies or production green, blue and yellow colonies in presence of chromogenic substrates in solid media. Although knowledge of the genetics of phosphate solubilization is still scanty, several phosphatase-encoding genes have been cloned and characterized and a few genes involved in mineral phosphate solubilization have been isolated. Molecular biology methods are a benefit approach to access and characterization of improved PGPR. Transfer and expression of phosphate (organic and inorganic phosphate) solvent encoding genes in bacteria or plants, is a new way for improving of microorganism capacitance as an inoculant.