Gram-negative bacteria iron transport across

IRON TRANSPORT ACROSS THE OUTER MEMBRANES OF GRAM-NEGATIVE BACTERIA... 

The uptake of siderophore-iron complexes by Gram-negative bacteria is energy dependent and occurs via specific outer membrane proteins. In the periplasmic space, it binds to its cognate periplasmic binding protein and is then actively transported across the cytoplasmic membrane by an ATP-trans-porter protein. Three principal mechanisms for transport through the outer membrane have been described ... 

Figure 2 Siderophore-mediated iron-uptake systems in E. coli. Siderophore-iron complexes bind to transporter proteins located in the outer membrane (also known as OM), a barrier that is characteristic of Gram-negative bacteria. The region between the outer and inner is known as the periplasmic space. Specific carrier proteins such as FhuD transport iron fi om the outer membrane to the inner or cytosolic membrane (also known as CM). The TonB/ExbB/ExbD complex spans the inner and outer membranes and interacts with FepA, as shown, as well as all of the outer membrane receptors. The linkage that the TonB/ExbB/ExbD complex provides between the inner or cytosolic membrane to the outer membrane is thought to allow transmission of sufficient energy from the cytosol to drive siderophore-iron uptake across the outer membrane...

---