General nonchemotactic mutants of Caulobacter crescentus.

We have examined 35 mutants that have defects in general chemotaxis. Genetic analysis of these mutants resulted in the identification of at least eight che genes located at six different positions on the Caulobacter crescentus chromosome. The cheR, cheB and cheT genes appeared to be located in a three-gene cluster. Mutations in these three genes resulted in the inability of the flagellum to reverse the direction of rotation. Defects in the cheR gene resulted in a loss of the ability to methylate the methyl-accepting chemotaxis proteins. In vitro experiments showed that the lack of in vivo methylation in cheR mutants was due to the absence of methyltransferase activity. Defects in the cheB gene resulted in greatly reduced chemotaxis-associated methylation in vivo and a loss of methylesterase activity in vitro. The specific defects responsible for the lack of a chemotactic response have not been determined for the other identified che genes.