Two chemotaxis-defective mutants of Pseudomonas aeruginosa, designated PC1 and PC2, were selected by the swarm plate method after N-methyl-N-nitro-N-nitrosoguanidine mutagenesis. These mutants were fully motile but incapable of swarming, suggesting that they had a defect in the intracellular signalling pathway. Computerassisted capillary assays confirmed that they failed to show behavioral responses to chemical stimuli, including peptone, methyl thiocyanate, and phosphate. Two chemotaxis genes were cloned by phenotypic complementation of PC1 and PC2. From nucleotide sequence analysis, one gene was found to encode a putative polypeptide that was homologous to the enteric CheZ protein, while the other gene was cheY, which had been previously reported (M. N. Starnbach and S. Lory, Mol. Microbiol. 6:459-469, 1992). Deletion and complementation analysis showed that PC1 was a cheY mutant, whereas PC2 had a double mutation in the cheY and cheZ genes. A chromosomal cheZ mutant, constructed by inserting a kanamycin resistance gene cassette into the wild-type gene, changed its swimming direction much more frequently than did wild-type strain PAO1. In contrast, cheY mutants were found to rarely reverse their swimming directions.Chemotaxis is the movement of an organism toward chemical attractants and away from chemical repellents (1). Pseudomonas aeruginosa is attracted to various amino acids (6) and is less strongly responsive to sugars and organic acids (15, 16). The taxis toward several amino acids is subject to control by nitrogen availability in a manner similar to the control of various enzymes of nitrogen metabolism (6) and is mediated by methylation and demethylation of methyl-accepting proteins analogous to those of the enteric bacteria (5). The strengths of the chemotactic responses to glucose and to citrate are also dependent on prior growth of the bacterial cells on those carbon sources (16). The glucose-binding protein has been identified as the glucose chemoreceptor in this organism (28). However, virtually nothing is known about the other chemoreceptors of P. aeruginosa. Our previous work demonstrated that P. aeruginosa is attracted to P i (10). This chemotactic response is induced by P i limitation. The P i -starved cells are also attracted to arsenate (11). Since P i competitively inhibits the response to arsenate, both P i and arsenate are likely to be detected by the same chemoreceptor. Genetic evidence showed that P i taxis in P. aeruginosa is not regulated by the phoB and phoR gene products but requires the phoU gene (12). P. aeruginosa is also repelled by thiocyanic and isothiocyanic esters, including allyl isothiocyanate, ethyl thiocyanate, methyl isothiocyanate, and methyl thiocyanate (19).The molecular mechanisms that underlie bacterial chemotaxis have been studied intensively with the enteric bacteria Escherichia coli (20) and Salmonella typhimurium (30) and to a lesser extent with the gram-positive bacterium Bacillus subtilis (4). However, little is known about the chemotaxis genes in the bacteri...

Negative chemotaxis, the movement of organisms away from chemicals, was investigated in Pseudomonas aeruginosa using a rapid videotape method. Digital image processing was used to detect changes in bacterial numbers near the mouth of a capillary containing a test chemical. P. aeruginosa was found to be repelled by thiocyanic and isothiocyanic esters including allyl isothiocyanate, ethyl thiocyanate, methyl isothiocyanate and methyl thiocyanate. Particularly, the movement of bacteria away from methyl thiocyanate was so drastic that bacterial numbers near the mouth of the capillary decreased by approximately 80% within 30 s after the start of observation. Mutant strains, fully motile but lacking positive chemotaxis, did not escape away from the esters, suggesting a common mechanism between positive and negative chemotaxes in this organism.

Negative chemotaxis, the movement of organisms away from chemicals, was investigated in Pseudomonas aeruginosa using a rapid videotape method. Digital image processing was used to detect changes in bacterial numbers near the mouth of a capillary containing a test chemical. P. aeruginosa was found to be repelled by thiocyanic and isothiocyanic esters including allyl isothiocyanate, ethyl thiocyanate, methyl isothiocyanate and methyl thiocyanate. Particularly, the movement of bacteria away from methyl thiocyanate was so drastic that bacterial numbers near the mouth of the capillary decreased by approximately 80% within 30 s after the start of observation. Mutant strains, fully motile but lacking positive chemotaxis, did not escape away from the esters, suggesting a common mechanism between positive and negative chemotaxes in this organism.