Defining the Roles of the Cation Diffusion Facilitators in Fe(2+)/Zn(2+) Homeostasis and Establishment of Their Participation in Virulence in Pseudomonas aeruginosa

Transporters of the cation diffusion facilitator (CDF) family form dimers that export transition metals from the cytosol. The opportunistic pathogen Pseudomonas aeruginosa encodes three homologous CDF genes, czcD (PA0397), aitP (PA1297), and yiiP (PA3963). The three proteins are required for virulence in a plant host model. Disruption of the aitP gene leads to higher Fe(2+) and Co(2+) sensitivity together with an intracellular accumulation of these ions and to a decreased survival in presence of H(2)O(2). Strains lacking czcD and yiiP showed low Zn(2+) sensitivity. However, in iron-rich media and in the presence of Zn(2+) these strains secreted higher levels of the iron chelator pyoverdine. Disruption of czcD and yiiP in a non-pyoverdine producer strain and lacking the Zn(2+)-transporting ATPase, increased the Zn(2+) sensitivity and the accumulation of this ion. Most importantly, independent of the pyoverdine production strains lacking CzcD or YiiP, presented lower resistance to imipenem, ciprofloxacin, chloramphenicol, and gentamicin. These observations correlated with a lower survival rate upon EDTA-lysozyme treatment and overexpression of OprN and OprD porins. We hypothesize that while AitP is an Fe(2+)/Co(2+) efflux transporter required for Fe(2+) homeostasis, and ultimately redox stress handling, CzcD, and YiiP export Zn(2+) to the periplasm for proper Zn(2+)-dependent signaling regulating outer membrane stability and therefore antibiotic tolerance.