Figure 5.

Potential methods of Ton-independent iron acquisition. (A) The type IV secretion system could secrete a factor that either binds iron or stimulates iron release by the host, thereby facilitating iron uptake by gonococci. (B) The T4SS apparatus may act as a pore for iron to pass into either the periplasm or the cytosol. The T4SS pore is represented in a simplified fashion by the outer membrane protein complex (blue rectangle), the transmembrane proteins (green rectangle), and the inner membrane protein complex (orange rectangle). (C) The T4SS could affect gonococcal trafficking within host epithelial cells so that gonococci expressing a T4SS (diplococcus with green box) go to an iron-rich niche. OM, outer membrane; PP, periplasm; IM, inner membrane.