How the Presence of Hemin Affects the Expression of the Different Iron Uptake Pathways in Pseudomonas aeruginosa Cells

Iron is an essential nutriment for
almost all organisms, but this
metal is poorly bioavailable. During infection, bacteria access iron
from the host by importing either iron or heme. Pseudomonas
aeruginosa, a gram-negative pathogen, secretes two
siderophores, pyoverdine (PVD) and pyochelin (PCH), to access iron
and is also able to use many siderophores produced by other microorganisms
(called xenosiderophores). To access heme, P. aeruginosa uses three distinct uptake pathways, named Has, Phu, and Hxu. We
previously showed that P. aeruginosa expresses the Has and Phu heme uptake systems and the PVD- and PCH-dependent
iron uptake pathways in iron-restricted growth conditions, using proteomic
and RT-qPCR approaches. Here, using the same approaches, we show that
physiological concentrations of hemin in the bacterial growth medium
result in the repression of the expression of the proteins of the
PVD- and PCH-dependent iron uptake pathways, leading to less production
of these two siderophores. This indicates that the pathogen adapts
its phenotype to use hemin as an iron source rather than produce PVD
and PCH to access iron. Moreover, the presence of both hemin and a
xenosiderophore resulted in (i) the strong induction of the expression
of the proteins of the added xenosiderophore uptake pathway, (ii)
repression of the PVD- and PCH-dependent iron uptake pathways, and
(iii) no effect on the expression levels of the Has, Phu, or Hxu systems,
indicating that bacteria use both xenosiderophores and heme to access
iron.