Phosphate solubilization of Paenibacillus polymyxa and Paenibacillus macerans from mycorrhizal and non-mycorrhizal cucumber plants

The phosphate-solubilizing ability of sixteen Paenibacillus strains, which previously were isolated from rhizosphere, hyphosphere or bulk soil, respectively, from mycorrhizal and non-mycorrhizal cucumber plants, were examined. Result from this study showed that seven strains could solubilize both Ca-3(PO4)(2) and CaHPO4, while inositol hexaphosphate could be solubilized by two strains in National Botanical Research Institute's phosphate growth medium. However, none of the Paenibacillus strains produced clear solubilization halos in National Botanical Research Institute's phosphate growth medium with AlPO4 or FePO4 as phosphate source. Quantitative estimation of phosphate solubilization in National Botanical Research Institute's phosphate growth broth with inorganic and organic phosphate sources showed that all 16 strains solubilized CaHPO4, 12 strains solubilized Ca-3(PO4)(2), 6 strains solubilized AlPO4, 10 strains solubilized FePO4 and 7 strains solubilized inositol hexaphosphate, which showed that screening of phosphate solubilizing bacteria should be done by quantifying their potential of phosphate solubilization in liquid growth medium. Overall, our results show that the Paenibacillus strains have a potential in phosphate solubilization, however, the efficacy of phosphate solubilization did not seem to differ between strains of Paenibacillus originating from either mycorrhizal or non-mycorrhizal systems.