Fig. 4.
Different levels of the CptB antitoxin showed diversity in its protection effect against the CptA toxin. Growth curves and percentage of surviving viable cells of E. coli Bl21(DE3) harboring the dual promoter plasmid pBAD18-cptA-cptB-PT7 vs. uninduced cells (control) at the following conditions. (A) antitoxin induction using different concentrations of IPTG (0.01, 0.1, 1, 5 and 10 mM), followed by toxin induction (0.2% L-arabinose) vs cells with L-arabinose induction only, (B) induction by either 0.2% L-arabinose (CptA inducer), 5 mM IPTG (CptB inducer), or both. OD600nm was measured every hour for 10 h. (C) Percentage of surviving viable cells upon simultaneous induction of both toxin (with 0.2% L-arabinose) and antitoxin (with either 1 or 5 mM IPTG). Percent survival was calculated using viable count assays, and plotted against time. The data represent the means of three independent experiments. Error bars represent the standard error of the means. Asterisks (*) indicate statistically significant differences (at p < 0.05), as determined by ANOVA followed by post hoc t-test.