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.
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