Shirish S. Pingale1 and Popat S. Virkar2
The use of phosphate solubilizing bacteria as inoculants simultaneously increases Phosphorus uptake by the plant and crop yield. Strains from the genera Pseudomonas, Bacillus 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 vital role in the mineralization of organic phosphorous in soil. Several phosphatase-encoding genes have been cloned and characterized and few genes involved in mineral phosphate solubilization have been isolated. Therefore, genetic manipulation of phosphate-solubilizing bacteria to improve their ability to enhance plant growth may include cloning genes involved in both mineral and organic phosphate solubilization, followed by their expression in selected rhizobacterial strains. The extent to which soil phosphorus (P) status gets affected the incidence of soil phosphate-solubilising bacteria (PSB). Bacteria were isolated from rhizosphere and non-rhizosphere soils differing in Phosphorus status. The P-solubilising phenotype was determined on agar supplemented with sparingly-soluble mineral phosphates (Ca2OH(PO4)3 and CaHPO4). The frequency of Psolubilisation in the bacterial population was significantly greater in soils of low-P status. P-solubilising bacteria from high-P level soils and soils which had not received P fertiliser were identified. The phytogenetic composition of PSB differed significantly (P < 0.05) between sites, however nearly half the families were common across all sites, constituting a ‘core community’ of P-solubilising bacteria. As the abundance and composition of P-solubilising bacteria are under strong selection pressure affected through farm management strategies, better understanding of their ecology provides the opportunity to increase the availability of soil P for plant-uptake.
