2.6.4. Siderophore Productions Assay
CAS (chrome azurol S) agar medium devoid of nutrients was used as an indicator of siderophore production. The components needed for a liter of the overlay medium were: 0.5 M MOPS buffer, 10 g MgSO4.7H2O, 1 g CaCl2.2H2O, 50 mL of Solution I (CAS) (0.065 g in 50 mL H2O), 10 mL of Solution II (0.135 g FeCl3.2H2O in 500 mL H2O), 40 mL of Solution III (0.0729 g CTAB in 40 mL H2O) and 9 g Bacto-Agar [38]. Ten mL of the overlay medium was spread on culture plates of selected strains grown at 37 ℃ for 4 days on solid MGM medium. After a maximum period of 15 min, a color change in the blue medium was considered positive for siderophore production. The experiment was repeated three times.