MOLECULAR ANALYSIS OF THE PHOSPHATE-SPECIFIC TRANSPORT (PST) OPERON OF PSEUDOMONAS AERUGINOSA

The organization of the phosphate-specific transport (pst) operon inPseudomonas aeruginosa has been determined. The gene order of thepst operon ispstC, pstA, pstB, phoU, and a well-conserved Pho box sequence (16/18 bases identical) exists in the promoter region. The most striking difference from the knownEscherichia coli pst operon is the lack of thepstS gene encoding a periplasmic phosphate (Pi)-binding protein. Even though the threepst genes were absolutely required for Pi-specific transport, expression of thepst operon at high levels did not increase Pi uptake inP. aeruginosa. DNA sequences for thepstB andphoU genes have been determined previously. The newly identifiedpstC andpstA genes encode possible integral membrane proteins of 677 amino acids (M r 73 844) and 513 amino acids (M r 56 394), respectively. The amino acid sequences of PstC and PstA predict that these proteins contain a long hydrophilic domain not seen in theirE. coli counterparts. A chromosomal deletion of the entirepst operon renderedP. aeruginosa unable to repress Pi taxis under conditions of Pi excess. ThephoU andpstB genes are essential for repressing Pi taxis. However, mutants lacking either PstC or PstA alone were able to repress Pi taxis under conditions of Pi excess.