Siderophores detection by blue agar CAS assay

Siderophores were detected using a blue agar CAS medium as described by Schwyn & Neilands (1987). The solid CAS medium was composed of one mL 20% sucrose solution, three mL sterilized 10% casamino acid, 100 µL one mmol/L CaCl₂, five mL CAS dye solution (a mixture of 0.012 g of chrome azurol S in 10 mL of ddH₂O, two mL one mmol/L FeCl_3, and 0.015 g hexadecyltrimethylammonium bromide in eight mL of deionized H₂O), PIPES buffer (pH 6.8–7.0), and 2 g agar powder per 100 mL H₂O.

P. triticisoli BJ-18 was inoculated in 20 mL of liquid LB medium with shaking at 200 rpm at 30 °C for 48 h. one mL of the bacterial solution was centrifuged, washed with sterile deionized water, and then suspended with 200 µL of sterile deionized H₂O. 10 µL of the suspension was inoculated on a CAS plate. The color changed from blue to light orange, indicating the presence of iron carriers.