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. 1978 Sep;75(9):4150–4154. doi: 10.1073/pnas.75.9.4150

Inversion of a behavioral response in bacterial chemotaxis: Explanation at the molecular level

Shahid Khan *, Robert M Macnab *, Anthony L DeFranco †, D E Koshland Jr †
PMCID: PMC336069  PMID: 360210

Abstract

Certain cheU mutants of Salmonella show inverted chemotactic behavior, being repelled by attractants and attracted by repellents. Such a dramatic change in behavioral pattern would seem at first glance to require drastic and complex alterations in the sensory processing system. In fact, the behavior can be explained by a simple shift in the level of a response regulator and the subtle effects of this shift on flagellar function. Flagella can exist in either a left-handed or a right-handed structure depending on applied torsion. Wild-type cells swim smoothly by counterclockwise rotation of a left-handed helical bundle and tumble when the motors briefly reverse to clockwise rotation (normal random motility). The cheU mutation causes a shift in response regulator level relative to the critical threshold value, resulting in extended clockwise operation so that the flagella are fully converted to the right-handed helical form. These cells therefore swim smoothly by clockwise rotation of a right-handed bundle and tumble when the motor briefly reverses to counterclockwise rotation (inverse random motility). Thus, tumbling is associated with brief reversals and not with a particular sense of rotation. A wild-type cell, with its steady-state response regulator level placing it initially in normal random motility, will swim smoothly on addition of attractant, whereas a cheU mutant with inverse random motility will tumble given the same stimulus. The phenomenon illustrates the profound behavioral consequences that can result from a single mutation in a key gene.

Keywords: flagella, polymorphism, cheU gene, response regulator

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These references are in PubMed. This may not be the complete list of references from this article.

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