Molecular analysis of the phosphate-specific transport (pst) operon of Pseudomonas aeruginosa

The organization of the phosphate-specific transport (pst) operon in Pseudomonas aeruginosa has been determined. The gene order of the pst operon is pstC, 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 known Escherichia coli pst operon is the lack of the pstS gene encoding a periplasmic phosphate (Pi)-binding protein. Even though the three pst genes were absolutely required for P(i)-specific transport, expression of the pst operon at high levels did not increase P(i) uptake in P. aeruginosa. DNA sequences for the pstB and phoU genes have been determined previously. The newly identified pstC and pstA 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 their E. coli counterparts. A chromosomal deletion of the entire pst operon rendered P. aeruginosa unable to repress P(i) taxis under conditions of P(i) excess. The phoU and pstB genes are essential for repressing P(i) taxis. However, mutants lacking either PstC or PstA alone were able to repress P(i) taxis under conditions of P(i) excess.