FIG 3.

Calcium effects on TcpP induction of virulence. (A) Effect of Ca²⁺ on TcpP-mediated tcpA expression. The expression of tcpA with controlled levels of TcpP (ΔtcpPH; ΔtoxR with pBAD-tcpPH) when exposed to 0.1 mM TC, 10 mM CaCl₂, or both together in the presence or absence of the calcium-specific chelator, EGTA, at the final concentrations indicated was assessed. (B) Activation of ToxT by TcpP and its cysteine mutant derivatives. The expression of toxT by wild-type (WT) TcpP and mutants with TcpP^C207S (null activity) or TcpP^218S (constitutive activity) was evaluated in the presence of 0.1 mM TC, 10 mM CaCl₂, or both together. Cells were grown at 37°C microaerobically until reaching mid-log phase, and the luminescence was measured. The data shown are from three independent experiments. *, P < 0.05 (Student t test).