Solubilization of organic and inorganic phosphates by three highly efficient soil bacterial isolates

Screening soil samples collected from a diverse range of slightly alkaline soil types, we have isolated 22 competent phosphate solubilizing bacteria (PSB). Three isolates identified as Pantoea agglomerans strain P5, Microbacterium laevaniformans strain P7 and Pseudomonas putida strain P13 hydrolyzed inorganic and organic phosphate compounds effectively. Bacterial growth rates and phosphate solubilization activities were measured quantitatively under various environmental conditions. In general, a close association was evident between phosphate solubilizing ability and growth rate which is an indicator of active metabolism. All three PSB were able to withstand temperature as high as 42°C, high concentration of NaCl upto 5% and a wide range of initial pH from 5 to 11 while hydrolyzing phosphate compounds actively. Such criteria make these isolates superior candidates for biofertilizers that are capable of utilizing both organic and mineral phosphate substrates to release absorbable phosphate ion for plants.