3. Results and discussion
3.1. Bacterial solubilization of phosphate rock and FePO4
The spent medium was collected after growing bacteria for 24 h, which contained bacterial exudates without bacteria including organic acids, siderophore and phytase. Since those bacteria were isolated from an arsenic-rich soil with low Fe and P availability, it was expected that those bacteria have better ability to solubilize Fe and P compared to typical bacteria. To determine bacterial ability in solubilizing insoluble P mineral phosphate rock, we measured the P concentration in the spent media with and without addition of P mineral. The spent media without phosphate rock contained 0.08–0.74 mg L−1 P (data not shown). Among the 7 ARB tested, only 5 strains (PG4, 5, 9, 10, and 12) solubilized more P than the control bacterium PC (Table 1). PC was used a control because its P solubilization would be similar to other rhizosphere pseudomonad. The strains PG5 and PG12 were the most efficient in solubilizing P from phosphate rock (1.36–2.40 mg L−1) while PG16 and PG6 were unable to solubilize P (Table 1).