Figure 3.

LuxO represses tcpP expression. (A) toxR, tcpP, and toxT were cloned into the expression vector pBAD24 (33), and the plasmids were introduced into the V. cholerae luxO mutant. Subsequently, the strains were grown under AKI-inducing conditions in the presence of 0.01% arabinose. CT production was quantitated after 5 h incubation at 37°C with aeration. The data are presented as the percentage of CT production of the wild-type bearing the same plasmids. (B) tcpP-lacZ expression was assayed in the wild type, the luxO mutant, and the wild-type strain constitutively expressing a cloned hapR gene (denoted phapR). β-galactosidase activity assays (39) were conducted after growth with aeration for 5 h at 37°C in AKI medium.