Siderophore-mediated iron transport in Bacillus subtilis and Corynebacterium glutamicum

Hexadentate bacillibactin is the siderophore of Bacillus subtilis and is structurally similar to the better known enterobactin of Gram-negative bacteria such as Escherichia coli. Although both are triscatecholamide trilactones, the structural differences of these two siderophores result in opposite metal chiralities, different affinity for ferric ion, and dissimilar iron transport behaviors. Bacillibactin was first reported as isolated from Corynebacterium glutamicum and called corynebactin. However, failure of iron-starved C. glutamicum to transport 55Fe bacillibactin and lack of required bacillibactin biosynthetic genes suggest that bacillibactin is not the siderophore produced by this organism. Iron transport mediated by siderophores in B. subtilis occurs through a transport process that is specific for the iron chelating moiety, with parallel pathways for catecholates and hydroxamates. For bacillibactin, enterobactin, and their analogs, neither chirality nor presence of an amino acid spacer affects the uptake and transport process, but alteration of the net charge and size of the molecule impedes the recognition.