Figure 2. A “Point of No Return” in E. coli after the Induction of the (A) Plasmid Borne or (B) Chromosomally Borne E. coli mazF Gene.

(A) E. coli cells growing in minimal medium were cotransformed with two plasmids, one carrying mazE and the other one carrying mazF, each regulated by different promoters: mazF can be induced by arabinose and repressed by glucose, and mazE can be induced by IPTG. At time zero, mazF expression was induced by the addition of arabinose. Samples of the induced culture were withdrawn at various time points and spread on plates containing glucose and IPTG (shown in blue on the graph) or glucose without IPTG (shown in yellow on the graph). Based on data in [54].

(B) E. coli cells growing in minimal medium were transformed with a single plasmid-carrying mazE that can be induced by IPTG. At the logarithmic phase, stress was induced by the addition of a transcription inhibitor. After the cells were incubated at 37 ^°C for a short period of time, the transcription inhibitor was removed. Samples of the induced culture were withdrawn at various time points and spread on plates containing IPTG (shown in blue on the graph) or without IPTG (shown in yellow on the graph). The percentage of survivors was calculated by comparing the number of colony forming units (CFUs) of the MazF-induced culture to the number of CFUs of the uninduced culture at time zero. Based on data in [55].