FIG. 4.

ToxR-dependent ompU transcription is increased in the presence of bile or DC. V. cholerae classical biotype strains KKV598 (wild type [wt]), KKV62 (ΔtoxR), and KKV163 (ΔtoxT), and El Tor biotype strains KKV557 (wt), KKV555 (ΔtoxR), and KKV556 (ΔtoxT) carrying the ompUp-lacZ transcriptional fusion plasmid pAL144 were grown in LB (open bars) alone or supplemented with 0.4% bile (shaded bars) or 0.1% DC (solid bars) and then assayed for β-galactosidase as described in the text. Media also contained 100 μg of ampicillin per ml. Results are the average of three samples. The β-galactosidase activity of each strain harboring the vector pTL61T (21) alone grown under these conditions (ca. 500 Miller U), which can be considered background activity, has been subtracted out.