EXPRESSION OF THE FERRIC ENTEROBACTIN RECEPTOR (PFEA) OF PSEUDOMONAS-AERUGINOSA - INVOLVEMENT OF A 2-COMPONENT REGULATORY SYSTEM

Expression of the ferric enterobactin receptor in Pseudomonas aerugino sa 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 read ing frames (ORFs), pfeR and pfeS, which appeared to comprise an operon . The predicted products of pfeR and pfeS (molecular weight 26796 and 50597, respectively) exhibited a high degree of homology to response-r egulator and sensor components, respectively, of the superfamily of pr okaryotic environmentally responsive protein pairs. Consistent with an apparent role in regulating expression of pfeA in response to enterob actin, introduction of pfeR/pfeS into P. aeruginosa on a high-copy-num ber vector enhanced enterobactin-dependent expression of pfeA. Further more, a pfeR mutant obtained by in vitro mutagenesis and gene replacem ent 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 l ocation for PfeS.