FIG. 4.

Flagellin expression is shut down in the absence of Cl⁻. Cells were pregrown in the presence of 1 M NaCl, flagella were sheared off, and cells were transferred to medium containing NO₃⁻ or Cl⁻. At four different time points (see the legend to Fig. 2A), samples were taken and analyzed for motility by light microscopy and for flagellin content by Western blot analyses. pc, preculture.