Impulse responses in bacterial chemotaxis

Steven M. Block, Jeffrey E. Segall, Howard C. Berg

Research output: Contribution to journalArticlepeer-review

212 Scopus citations


The chemotactic behavior of Escherichia coli has been studied by exposing cells tethered by a single flagellum to pulses of chemicals delivered iontophoretically. Normally, wild-type cells spin alternately clockwise and counterclockwise, changing their direction on the average approximately once per second. When cells were exposed to a very brief diffusive wave of attractant, the probability of spinning counterclockwise quickly peaked, then fell below the prestimulus value, returning to baseline within a few seconds; repellent responses were similar but inverted. The width of the response indicates that cells integrate sensory inputs over a period of seconds, while the biphasic character implies that they also take time derivates of these inputs. The sensory system is maximally tuned to concentration changes that occur over a span of approximately 2 sec, an interval over which changes normally occur when cells swim in spatial gradients; it is optimized to extract information from signals subject to statistical fluctuation. Impulse responses of cells defective in methylation were similar to those of wild-type cells, but did not fall as far below the baseline, indicating a partial defect in adaptation. Impulse responses of cheZ mutants were aberrant, indicating a serious defect in excitation.

Original languageEnglish (US)
Pages (from-to)215-226
Number of pages12
Issue number1
StatePublished - Nov 1982
Externally publishedYes

ASJC Scopus subject areas

  • Biochemistry, Genetics and Molecular Biology(all)


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