Figure 8. Schematic of the pyoverdine secretion pathways in P. taiwanensis.

Pyoverdine precursors are synthesized in the cytoplasm and secreted into the periplasm by the inner membrane transporter PvdE, and then form mature fluorescent pyoverdine in the periplasmic space⁷,⁴⁴,⁴⁵. There are three possibilities that can explain the secretory pathways of pyoverdine: (1) pyoverdine adheres to T6SS tube structure and secretes into the culture medium after pushing the Hcp tube with the VgrG spike; (2) pyoverdine secretes into medium through passive diffusion after T6SS punches a hole in the outer-membrane; (3) pyoverdine is secreted via an unknown export system.