Figure 3. Expression of virulence determinants is dependent on the common virulence regulators under in vitro conditions.

(A) Simplified overview of the regulatory cascade that is involved in virulence gene expression in V. cholerae. toxT expression occurs upon activation by the regulatory proteins ToxR and TcpP (complexed with ToxS and TcpH, respectively) as indicated by the arrows (solid lines). Next, the synthesized ToxT protein (dashed arrow) induces the expression of the tcp cluster and the ctxAB operon, which ultimately leads to the production of TCP and CT. Elements acting upstream tcpPH and toxRS are excluded for sake of simplicity. Scheme is based on [13]. (B+C) Relative expression of the genes tcpA, tcpB, ctxA, and ctxB in diverse V. cholerae strains, which were grown under virulence-inducing conditions in the presence of lactate (lac) or glucose (glc). Strains tested as indicated above the graphs: panel B: wild type V. cholerae strain (WT; A1552-TntfoX) and its toxR and tcpP-negative derivatives (ΔtoxR and ΔtcpP). panel C: wild type (WT; A1552) and ΔtoxT (A1552ΔtoxT). (D) As in panels B and C except that the V. cholerae wild-type strain was grown under glucose-containing virulence-inducing conditions in the presence of DMSO (gray bars) or virstatin (50 µM dissolved in DMSO; red bars). The values shown in panels B, C, and D represent averages of at least three independent biological replicates (± SD) Statistics were applied on pairwise comparisons using Student's t-test (ns, non-significant; *, P≤0.05; **, P≤0.01; ***, P≤0.001).