FIG 1.

Activation of the Cpx pathway regulates ToxR. (A) qRT-PCR analysis of toxS and toxR transcript levels. RNA was isolated from cultures of V. cholerae C6706, carrying the overexpression plasmid pCpxR, in the absence (noninduced; black bars) or presence of 0.1% arabinose (induced; gray bars) and converted to cDNA. The cDNA was subjected to qRT-PCR analysis as described in Materials and Methods. (B) Luminescence activity of V. cholerae C6706 carrying the overexpression plasmid pCpxR, transformed with the vector control (pJW15), cpxP-lux, or toxR-lux reporter. CpxR was overexpressed by adding 0.1% arabinose (induced). Reporter gene expression was measured as described in Materials and Methods and is reported as CPS corrected for cell density (OD₆₀₀). Time zero represents the time when cells were shifted to shaking conditions and induced after the culture first was statically grown for 6 h. The overall averages and standard deviations resulting from two separate experiments performed in quintuplicate are shown. The asterisks indicate a statistically significant difference between induced and noninduced treatments for the toxR-lux reporter (P < 0.0001 by two-way ANOVA with Sidak's multiple-comparison test).