FIG. 3.

Effect of bile on expression of OmpU and toxR. (A) Production of OmpU in the presence and absence of bile was analyzed using whole-cell lysates of the wild type (NB10). Equal numbers of cells (lanes 3 to 5) from overnight cultures grown in the presence or absence of bile were pelleted, resuspended in loading buffer, applied to an SDS-12.5% PAGE gel, and either stained with Coomassie blue (A) or transferred to nitrocellulose followed by Western blotting using an antiserum raised against OmpU from V. cholerae (B). Lanes 1 to 5 are the same for both A and B. Lane 1, molecular size markers; sizes are indicated at the left. Lane 2, OMPs from the wild-type. Lane 3, wild type grown in the absence of bile. Lane 4, wild type grown in the presence of 0.04% bile. Lane 5, wild type grown in the presence of 0.4% bile. (C) β-Galactosidase activity of the toxR::lacZ transcriptional gene fusion (pDM8-ToxR) was measured in the wild type (NB10) in the presence (0.04 or 0.4%) or absence of bile. Overnight cultures were diluted into fresh TSB medium to an OD₆₀₀ of 0.05 and then incubated with shaking at 24°C. Samples were taken at various times and analyzed for growth (OD₆₀₀, dotted lines) and β-galactosidase expression (Miller units, solid lines). Miller units for the vector control are between 100 and 200 U, and these were subtracted from the results.