Figure 8.

The timing of lactose consumption as a consequence of LacI dosing. A, glycerol is preferentially consumed before lactose in an aerobic growth with the T5-lacI expression plasmid. This result can be contrasted with Figure 7C, where lactose is preferentially consumed before glycerol. B, specific consumption of lactose during auto-induction growth with the indicated expression plasmids. The T7-Luc expression plasmid does not supplement LacI expression. The T7-lacI-Luc and T5-lacI-Luc plasmids contain a plasmid borne copy of the lac repressor gene with a wild-type promoter and give ~20-fold increase in the level of LacI relative to T7-Luc. The T5-lacI^q-Luc plasmid also contains a plasmid borne copy of the lac repressor with a lacI^q promoter that increases the level of LacI by ~10-fold higher than from T7-lacI-Luc and T5-lacI-Luc. With this latter plasmid, only a small amount of lactose was consumed and culture growth was halted at a cell density of 16 (OD₆₀₀ units). In contrast, the other cultures were able to fully consume the lactose and achieved a cell density of ~21.