The growth of P. luminescens in the presence of 2'2'-dipyridyl. The sensitivity of each mutant to iron levels was assayed by determining the ability of each mutant to grow in the presence of increasing concentrations of 2'2'-dipyridyl. The OD600 of overnight cultures of each strain was adjusted to 1 and 10 μl of the cell suspension was spotted onto the surface of an LB agar plate supplemented with the indicated concentration of 2'2'-diyridyl. The plates were incubated at 30°C for 48 h before a digital photograph of each agar plate was taken. The final image was assembled by cutting and pasting the appropriate colony from each photograph using Adobe Photoshop 7. It is important to highlight that the photographs were not manipulated in any other way. The data shown is a representative example and the experiment was repeated in triplicate.