Role of the flagellum in cell-cycle-dependent expression of bacteriophage receptor activity in Caulobacter crescentus

The rate of adsorption of Caulobacter bacteriophage phi CbK to Caulobacter crescentus is dependent on the structural integrity of the flagellum. Cells lacking part or all of the flagellum because of either mutation or mechanical shear were defective in adsorption, and the extent of the defect in adsorption reflected the amount of flagellar structure missing. Maximal adsorption rates were also dependent on cellular motility and energy metabolism, since adsorption to cells with paralyzed flagella was slower than adsorption to motile cells and inhibition of cellular energy metabolism with azide also reduced adsorption rates, even for nonmotile cells. Nevertheless, the flagellum is not the receptor for phage phi CbK, since flagellumless mutants adsorbed phi CbK at detectable rates. While some portion of the fluctuation in the phi CbK receptor activity during the C. crescentus cell cycle can be ascribed to the periodicity of flagellar loss and reappearance, the phage receptor activity remaining in flagellumless mutants was periodic in the cell cycle. Therefore, the periodic expression of phage receptor activity is an intrinsic property of the C. crescentus cell cycle, although the amplitude of the oscillation may be altered by the periodic expression of flagellar motility.