Objectives This study choose 4 different strains of Pseudomonas fluorescens(gram-negative bacteria), respectively as CHA0, F113, Phl1c2 and PF5, and one gram-positive bacterium, Bacillus megaterium X14, as phosphate solubilizing bacteria (PSB) to verify how bacteria helps dissolving phosphate to improve the growth of corn.

Methods Soluble phosphate content in each single and double strains of PSB incubated solution was measured to compare the solubization of each strain and combination. Dry weight, height and total phosphorus content of potted corn samples were examined to evaluate the solvency rate of insoluble phosphorus source Ca₃(PO₄)₂and colonization of different single and double strains PSB solution.

Results 1) Under NBRIP broth growth condition, after single strain inoculated, any of the 4 G^- bacteria (Pseudomonas fluorescens CHA0, F113, Phl1c2, PF5) solution dissolved much more phosphate than G⁺ bacteria (Bacillus megaterium X14). The combination of any two G^- bacteria solution showed higher phosphate dissolving than combination with any one G^- bacterium and the G⁺ bacterium combination. 2) There were no significant differences of phosphate solubilizing and plant healthy if corn growth in pot under greenhouse, regardless which single strain was inoculated. 3) The corn inoculated with a double strains with the G⁺ bacteria (Bacillus megateriumX14) and any one of the G^- bacteria (Pseudomonas fluorescen) strains showed higher phosphate absorption and more healthy growth than any of 2 G^- bacteria strains combination.

Conclusions In conclusion, G⁺ and G^- bacteria combination inoculation helps to absorb more phosphate in potted corn growth even the same solution showed less effective to dissolved phosphate in laboratory NBRIP condition. The laboratory absorption experiment should not be the only indicator to select PSB strains. Consideration of both laboratory absorption and potted growth experiments should provide more information for application.