FIG 2.

Effect of Ca²⁺ on the expression of virulence regulatory genes. (A) Schematic of virulence regulation in V. cholerae. AphA and AphB promote expression of TcpPH, which acts coordinately with ToxRS to induce ToxT and activate virulence. (B) Expression of toxT, toxR, aphB, aphA, and tcpP genes. Wild type containing the indicated promoter-lux reporters was grown at 37°C microaerobically until reaching mid-log phase, and the luminescence was measured. When indicated, 10 mM CaCl₂ or 0.1 mM TC was included in the medium. (C and D) ToxR and TcpP. E. coli containing pBAD-toxRS or pBAD-tcpPH when exposed to TC, CaCl₂, or both together. (C) Induction of ctxA by ToxR (pBAD-toxRS) in E. coli when exposed to TC, CaCl₂, or both together. (D) Induction of toxT by TcpP (pBAD-tcpPH) in E. coli when exposed to TC, CaCl₂, or both together. The data shown are from three independent experiments. *, P < 0.05 (Student t test).