FIG. 5.

Activation of the rrnB-lac hybrid promoter by FIS as a function of growth phase in batch cultures grown in LB (A and B), M9 with glucose (C), and M9 with glycerol (D). In panel B, the cultures were kept at low density for several hours by dilution with prewarmed LB medium at 30-min intervals. Fold activation by FIS is the ratio of the β-galactosidase activities of strains RLG1816 and RLG1817 (Table 1) carrying the FIS-activated rrnB-lac and the non-FIS-activated rrnB-Δ72-lac promoter-lacZ fusions, respectively. Activity was measured after 15 min of induction by IPTG at various times after dilution of cells from stationary phase into fresh medium. Points on the graphs correspond to the end of the 15-min induction period. Peak levels of activation varied less than 15% in different experiments. Strains were isogenic and grew identically within the experiments illustrated in each panel; only one growth curve is presented for the sake of clarity. The growth rates (μ; doublings/hour) for both strains in each medium are indicated.