Purification and reconstitution of the methyl-accepting chemotaxis proteins from Bacillus subtilis

Diversity in chemotaxis mechanisms among the bacteria and archaea

The study of chemotaxis describes the cellular processes that control the movement of organisms toward favorable environments. In bacteria and archaea, motility is controlled by a two-component system involving a histidine kinase that senses the environment and a response regulator, a very common type of signal transduction in prokaryotes. Most insights into the processes involved have come from studies of Escherichia coli over the last three decades. However, in the last 10 years, with the sequencing of many prokaryotic genomes, it has become clear that E. coli represents a streamlined example of bacterial chemotaxis. While general features of excitation remain conserved among bacteria and archaea, specific features, such as adaptational processes and hydrolysis of the intracellular signal CheY-P, are quite diverse. The Bacillus subtilis chemotaxis system is considerably more complex and appears to be similar to the one that existed when the bacteria and archaea separated during evolution, so that understanding this mechanism should provide insight into the variety of mechanisms used today by the broad sweep of chemotactic bacteria and archaea. However, processes even beyond those used in E. coli and B. subtilis have been discovered in other organisms. This review emphasizes those used by B. subtilis and these other organisms but also gives an account of the mechanism in E. coli.

Effect of loss of CheC and other adaptational proteins on chemotactic behaviour in Bacillus subtilis

Bacillus subtilis has a more complex mechanism of chemotaxis than does the paradigm organism, Escherichia coli. In order to understand better the role of the novel chemotaxis proteins--CheC, CheD and CheV--mutants in which increasing numbers of the corresponding genes had been deleted were studied as tethered cells and their biases and sometimes durations of counterclockwise (CCW) and clockwise (CW) flagellar rotations in response to addition and removal of the attractant asparagine were observed. The cheC mutant was found to have considerably reduced switching frequency (that is, prolonged CCW and CW rotations) without a significantly different prestimulus CCW bias, compared with wild-type. This result may indicate that in absence of CheC the switch might be in a conformation less resembling the transition state than in presence of CheC. Conversely, the cheB (methylesterase) mutant showed considerably increased switching frequency without affecting CCW bias, compared with wild-type. Removal of all known adaptation systems--the methylation, CheC and CheV systems--resulted in a mutant (cheRBCDV) that still retained some adaptation following the addition of attractant.