the comparison of five low cost liquid formulations to preserve two phosphate solubilizing bacteria from the genera pseudomonas and pantoea

background and objectives: phosphorus is one of the low bioavailable macroelements. use of microorganisms in biofertilizers could release phosphorus from insoluble compounds. pseudomonas putida p13 and pantoea agglomerans p5 are well recognized for application as phosphate solubilizing bioinoculants and are used as solid carrier based. liquid bioinoculants are preferred for economizing production process and longer shelf-life. materials and methods: five low cost liquid formulations were examined. formulations 1, 2 and 3, were phosphate buffer, 0.2% and 0.5% kno3 dissolved in phosphate buffer, respectively. formulation 4 was nutrient broth containing 4% glycerol and formulation 5 was diluted nutrient broth containing 4% glycerol. survival (cfu) and phosphate solubilization index ( si ) were evaluated after 3 months. results: considering strain p5, increase in kno3 concentration decreased preserving ability. while using kno3 at 0.2% was accompanied with reaching maximum si level. overall, less nutritious formulations (1 and 5) provided maximum preserving ability without bioactivity loss. in the case of strain p13, maximum survival obtained in formulations 2 and 3, whereas si level decreased. preserving ability in formulations 1, 4 and 5 was similar but less nutritious formulations (1 and 5), improved bioactivity. conclusion: the results introduced two formulations of 1 and 5 as economically efficient liquid bioinoculants for pseudomonas putida and pantoea agglomerans. keywords: phosphate solubilization, pseudomonas putida , pantoea agglomerans