FIG 3.

CAS assay for siderophore excretion. Five μl of a cell suspension of C. metallidurans cells was transferred onto a CAS agar plate and incubated for 24 h at 30°C. A yellow halo around the droplet of cell suspension indicates excretion of siderophores that sequester Fe(III) away from the chromazurol indicator (21). Wild-type strain CH34 and its plasmid-free derivative AE104 are shown at positions 1 and 2 on each plate, respectively. CH34 mutants are above the line, AE104 mutants are below. Mutants from CH34 or AE104 are ΔiucA-iucC on positions 3 and 4, ΔaleB on 5 and 6, ΔfurB on 7 and 8, and ΔfurA on 9 and 10, respectively.