FIG. 3.

Kinetics of initiation of Ti plasmid conjugative transfer. Donors harboring pCMA1ΔtraI (traM) (□, ▪), pTiC58ΔaccRΔtraI (▵, ▴), or pKMA1ΔtraI (accR traM) (○, •) were grown to early exponential phase; at zero time, 3-oxo-C8-HSL was added to give a concentration of 25 nM, and growth was continued. Samples were collected at intervals and assayed for conjugative transfer (A) and TraR activity as assessed by activation of the traCDG::lacZ reporter on pH4I41 (B). Open symbols show conjugative transfer efficiency, expressed as numbers of transconjugants obtained per input donor, or β-galactosidase activity, expressed as numbers of units per 10⁹ cells. Closed symbols show growth of the cultures as measured by OD₆₀₀. Samples of cells harboring pCMA1ΔtraI (1), pTiC58ΔaccRΔtraI (2), or pKMA1ΔtraI (3) grown with (+) or without (−) 25 nM 3-oxo-C8-HSL for 12 h were assayed for TraR levels by immunoblot analysis (C). Proteins in the soluble fractions were separated by sodium dodecyl sulfate-polyacrylamide gel electrophoresis, and TraR was detected by immunoblotting as described in Materials and Methods. The arrow indicates the position of the TraR protein. Matings shown in panels A and B were repeated once, with similar patterns of results, and data from one experiment are shown.