Analysis of nonmotile mutants of the dimorphic bacterium Caulobacter crescentus

A total of 69 spontaneous nonmotile mutants were isolated from the dimorphic bacterium Caulobacter crescentus. The majority of the mutants were unable to assemble a flagellar filament (Fla-), although eight were able to synthesize a short stub of a flagellum. A third mutant class assembled flagella of normal morphology but were nonmotile (Mot-). Genetic analysis by phiCr30-mediated transduction revealed 27 linkage groups for the fla and stub-forming mutations, and three linkage groups for the mot mutations. Intracellular flagellin detected by immunodiffusion was at the limit of detectability in most of the Fla- and stub-forming mutants but normal in the Mot- mutants. The Fla- and stub-forming mutants also showed decreased sensitivity to the swarmer-specific phages phiCbK and phiCb5 and phiCr40. One additional strain was totally resistant to phiCbK, and the mutation in this strain has been designated pleA. Each of the mutants containing mot mutations showed wild-type sensitivity to all of the phages tested.