GENETIC IDENTIFICATION OF CHEMOTACTIC TRANSDUCERS FOR AMINO-ACIDS IN PSEUDOMONAS-AERUGINOSA

Two chemotactic transducer genes (termed pctB and pctC) and an open re ading frame (orf1) were found in the pctA-flanking region which was pr eviously identified as a chemotactic transducer gene in Pseudomonas ae ruginosa. The pctB and pctC genes encode predicted polypeptides of 629 and 632 amino acids, respectively. Overall, PctB and PctC had 81 and 75% amino acid identities with PctA, respectively. A null mutant strai n PCT2, which contained a deletion in the entire pctC, orf1, pctA and pctB genes, did not show chemotaxis towards all 20 commonly occurring L-amino acids. This mutant strain also failed to respond to amino acid catabolites (cadaverine, 4-aminobutyrate and putrescine) that are str ong attractants for the wild-type strain PAO1. To study the role of ea ch gene product in L-amino acid taxis, plasmids harbouring the pctC, o rf1, pctA, or pctB genes were constructed and introduced into strain P CT2 by transformation. The orf1 gene did not complement the defect in chemotaxis of strain PCT2. The pctA gene restored the ability of strai n PCT2 to respond to 18 L-amino acids, suggesting that PctA plays a ma jor role in detecting L-amino acids in P. aeruginosa. The pctB and pct C genes complemented the defect in chemotaxis to only seven (Ala, Arg, Glu, Lys, Met, Tyr, Gln) and two (His, Pro) L-amino acids, respective ly.