Bacterial Chemotaxis: Molecular Genetics of Sensory Transduction and Chemotactic Gene Expression

Abstract

INTRODUCTION
Motile bacteria exhibit locomoter responses to a variety of environmental stimuli. Chemotaxis in the enteric bacteria Escherichia coli and Salmonella typhimurium is the best-studied of these behaviors and is an excellent model system for investigating a wide range of problems in the areas of molecular genetics and sensory transduction. The many individual components of the chemotaxis machinery are produced and assembled in a controlled manner to create an integrated system that functions through a complex set of interactions. These features pose challenging problems in the realm of gene expression and function. Conversely, the existence of a defined sensory-motor system in organisms that are amenable to detailed genetic analysis provides a powerful approach to the study of sensory mechanisms. In this paper we consider some specific aspects of the study of motility and chemotaxis that illustrate these features. Bacterial chemotaxis is a popular subject for reviews, so the interested reader can find additional information and alternative viewpoints (Ordal 1980; Koshland 1981; Taylor and Lazlo 1981) or emphases on flagella and motility (Macnab 1980; Silverman 1980), genetics (Parkinson 1981), chemoreception (Hazelbauer and Parkinson 1977), or transducers and methylation (Springer et al. 1979; Boyd and Simon 1982; Hazelbauer and Harayama 1983).

CHEMOTACTIC BEHAVIOR
In uniform chemical environments, bacteria swim about in a three-dimensional random walk, produced by periods of smooth swimming punctuated by tumbling episodes that reorient the cell in a new, randomly chosen direction (Berg and Brown 1972). In a spatial gradient of an attractant or a repellent compound, the cell...