Figure 4.

An overview of siderophore cycling in a generic organism. Typically, iron-loaded siderophores are imported through TonB-dependent transporters (TBDT) in the outer membrane, with power supplied by a TonB-ExbB-ExbD-complex in the inner membrane. Further transport is done by ABC-transporters. Export of siderophores can happen by a variety of transporter types. Note that the iron is reduced to Fe²⁺ at some point during this cycle, but the timing and location of this is often not clear. Created with Biorender.com.