FIG 1.
Effects of oxygen on protein interactions between V. cholerae virulence regulators in a bacterial two-hybrid system. The E. coli cAMP-based two-hybrid system was used in this study (25). See Materials and Methods for details. The BTH101 strains containing different combinations of T25-T18 fusion pairs were grown aerobically, microaerophilically, and anaerobically at 37°C until mid-log phase, and β-galactosidase activity was measured and recorded in Miller units (29). (A) Effects of oxygen on AphB-AphB and AphBC235S-AphBC235S interactions. (B) Effects of oxygen on positive controls (leucine zipper of GCN4) and negative controls (empty vectors). (C) ToxR-ToxR, TcpP-TcpP, and ToxT-ToxT interactions. The ratios of β-galactosidase units from cultures grown anaerobically and aerobically are presented. (D) ToxR-TcpP interactions. The results are the mean of three experiments ± the standard deviation. β-gal, β-galactosidase; WT, wild type; NS, not significantly different.