Cloning and characterization of chemotaxis genes in Pseudomonas aeruginosa

Two chemotaxis-defective mutants of Pseudomonas aeruginosa, designated PC3 and PC4, were selected by the swarm plate method after N-methyl-N'-nitro-N- nitrosoguanidine mutagenesis. These mutants were not complemented by the P. aeruginosa cheY and cheZ genes, which had been previously cloned (Masduki et al., J. Bacteriol., 177, 948-952, 1995). DNA sequences downstream of the cheY and cheZ genes were able to complement PC3 but not PC4. Sequence anal ysis of a 9.7-kb region directly downstream of the cheZ gene found three ch emotaxis genes, cheA, cheB, and cheW: and seven unknown open reading frames (ORFs). The predicted translation products of the cheA, cheB, and cheW gen es showed 33, 36, and 31% amino acid identity with Escherichia coil CheA, C heB, and CheW, respectively. Two of the unknown ORFs, ORF1 and ORF2, encode d putative polypeptides that resembled Bacillus subtilis MotA (40% amino ac id identity) and MotB (34% amino acid identity) proteins, respectively. Alt hough P. aeruginosa was found to have proteins similar to the enteric chemo taxis proteins CheA, CheB, CheW, CheY, and CheZ, the gene encoding a CheR h omologue did not reside in the chemotaxis gene cluster. The P. aeruginosa c heR gene could be cloned by phenotypic complementation of the PC4 mutant. T his gene was located at least 1,800 kb away from the chemotaxis gene cluste r and encoded a putative polypeptide that had 32% amino acid identity with E. coli CheR.