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Chemotactic‐like response of Escherichia coli cells lacking the known chemotaxis machinery but containing overexpressed CheY

We describe a chemotactic‐like response of Escherichia coli strains lacking most of the known chemotaxis machinery but containing high levels of the response regulator CheY. The bacteria accumulated in aspartate‐containing capillaries, they formed rings on tryptone‐containing semisolid agar, and the probability of counterclockwise flagellar rotation transiently increased in response to stimulation with aspartate (10−10–10−5 M; the response was inverted at > 10−4 M). The temporal response was partial and delayed, as was the response of a control wild‐type strain having a high CheY level. α‐Methyl‐DL‐aspartate, a non‐metabolizable analogue of aspartate as well as other known attractants of E. Coli, glucose and, to a lesser extent, galactose, maltose and serine caused a similar response. So did low concentrations of acetate and benzoate (which, at higher concentrations, act as repellents for wild‐type E. coli ). Other tested repellents such as indole, Ni2+ and Co2+ increased the clockwise bias. These observations raise the possibility that, at least when the conventional signal transduction components are missing, a non‐conventional chemotactic signal transduction pathway might be functional in E. coli. Potential molecular mechanisms are discussed.