To test bacterial ability in solubilizing P, 1 mL of spent medium
from the 7 ARB was incubated with 0.1 g of phosphate rock (PR),
0.01 g of FePO4 (FP) or 0.04 g phytate (PA) for 24 h at 30 C under
200 rpm shaking condition. The amounts of insoluble P were used
to ensure sufficient surface exposure with the spent growth medium
for effective P solubilization. To test whether P was solubilized
by siderophores via Fe chelation, we used 1 mL of the filter-sterilized
spent medium of wild type and mutants PchA and PchC
(Hartney et al., 2011) and incubated it with 0.01 g FePO4 for 24 h
at 30 C. The water soluble P was measured using modified molybdenum
blue method (Ghosh et al., 2011).