Expression of the ferric enterobactin receptor (PfeA) of Pseudomonas aeruginosa: involvement of a two-component regulatory system.

Expression of the ferric enterobactin receptor in Pseudomonas aeruginosa is inducible by enterobactin and requires sequences upstream of the structural gene (pfeA). Nucleotide sequencing of a 2.5 kilobase pair (kb) region of DNA immediately upstream of pfeA revealed two open reading frames (ORFs), pfeR and pfeS, which appeared to comprise an operon. The predicted products of pfeR and pfeS (molecular weight 26,796 and 50,597, respectively) exhibited a high degree of homology to response-regulator and sensor components, respectively, of the superfamily of prokaryotic environmentally responsive protein pairs. Consistent with an apparent role in regulating expression of pfeA in response to enterobactin, introduction of pfeR/pfeS into P. aeruginosa on a high-copy-number vector enhanced enterobactin-dependent expression of pfeA. Furthermore, a pfeR mutant obtained by in vitro mutagenesis and gene replacement failed to express PfeA despite the presence of enterobactin in the culture medium. Analysis of the hydropathy profiles of PfeR and PfeS supported a cytoplasmic location for PfeR and a cytoplasmic membrane location for PfeS.