Molecular and Biochemical Methods for Studying Chemotaxis in Bacillus subtilis

This chapter discusses molecular and biochemical methods for studying chemotaxis in Bacillus subtilis. Chemotaxis in bacteria is the oldest sensory-motor network in nature and antedates the evolutionary separation of the archaebacteria from the true bacteria (eubacteria). Through chemotaxis, bacteria migrate by a biased random process to high concentrations of attractants or low concentrations of repellent. Unstimulated, peritrichous bacteria, such as Bacillus subtilis and Escherichia coli, exhibit alternating smooth swims (runs) and tumbles and give the appearance of erratic swimming. The purpose of tumbling is to randomly reorient the bacteria for the succeeding run. When in a gradient of chemoeffector (attractant or repellent), the frequency of runs and tumbles is altered. In general, chemoeffectors bind to chemoreceptors (sensory receptors), and thereby initiate a cascade of events involving phosphoryl transfer to affect briefly the direction of the rotation of the flagella. Like many sensory processes in bacteria, most of which involve transcriptional activation, chemotaxis uses the two-component system—the autophosphorylating kinase and the response regulator. The heart of chemotaxis in both B. subtilis and E. coli is excitation mediated by an autophosphorylating kinase (CheA), which monitors the state of the receptors. In B. subtilis, the binding of attractant to the receptors stimulates CheA activity and leads to the phosphorylation of CheY.