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The Gradient-Sensing Mechanism in Bacterial Chemotaxis

Robert M. Macnab and D. E. Koshland
Proceedings of the National Academy of Sciences of the United States of America
Vol. 69, No. 9 (Sep., 1972), pp. 2509-2512
Stable URL: http://www.jstor.org/stable/61804
Page Count: 4
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Since scans are not currently available to screen readers, please contact JSTOR User Support for access. We'll provide a PDF copy for your screen reader.
The Gradient-Sensing Mechanism in Bacterial Chemotaxis
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Abstract

A ``temporal gradient apparatus'' has been developed that allows the motility of bacteria to be studied after they have been subjected to a sudden change from one uniform concentration of attractant to another. A sudden decrease elicits the tumbling response observed with spatial gradients; it was found, however, that a sudden increase also elicits a response, namely supercoordinated swimming. This demonstrates that chemotaxis is achieved by modulation of the incidence of tumbling both above and below its steady-state value. The initial responses gradually revert to the steady-state motility pattern characteristic of a uniform distribution of attractant. The apparent detection of a spatial gradient by the bacteria therefore involves an actual detection of a temporal gradient experienced as a result of movement through space. Potential models for the chemotactic response based on some ``memory'' mechanism are discussed.

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