Chemotaxis away from thiocyanic and isothiocyanic esters in Pseudomonas aeruginosa

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.