PHOSPHORUS is second only to Nitrogen as the most limiting element for plant growth. The concentration of soluble P in soil is usually very low, however, more than 80% of P becomes immobile and unavailable for plant uptake. The development of a biological alternative to chemical fertilizers is of great importance for the improvement of agriculture as well as the protection of the environment. The present study investigated thirteen efficient inorganic-phosphate solubilizing bacteria (PSB) isolated from various rhizospheric soil samples collected from El-Bekaa, Lebanon. Two isolates (Pseudomonas sp. HD and Escherichia sp. HD), exhibited the highest phosphate solubilization percentages of 76.60 and 88.21%, respectively. Application of the Plackett-Burman design resulted in phosphate solubilization efficiency of 79.08 and 93.77% for Pseudomonas sp. HD and Escherichia sp. HD, respectively. In vitro cultivation of different plants was applied to reflect the relative importance of Pseudomonas sp. HD and Escherichia sp. HD as biofertilizers on growth parameter of melon (Cucumis melo var. inodorus), horse-bean (Vicia faba), cucumber (Cucumis sativus), Armenian cucumber (Cucumis melo var. flexuosus), bean (Phaseolus vulgaris) and squash (Cucurbita pepo). The best growth parameters of the studied plants where observed where seeds were soaked in water and Ca3(PO4)2 with Pseudomonas sp. HD and Escherichia sp. HD.