Fig. 3.
Microscopic examination of morphological changes upon toxin induction in E. coli. (A-D) Light micrographs representing crystal violet-stained E. coli Bl21(DE3) cells with the dual promoter plasmid pBAD18-cptA-cptB-PT7. (A) Uninduced cells serve as control; (B) cells induced with 1 mM IPTG; (C) cells induced with 0.2% L-arabinose after ten hours of induction; and (D) same cells as in (C) after 24 h of 0.2% L-arabinose induction. L-arabinose-induced cells, expressing toxin but no antitoxin, appear (C) filamented and (D) lemon-shaped. Both control (A) and antitoxin-expressing cells (B) kept the typical rod-shaped form of E. coli. (E-F) Electron micrographs of uninduced and L-arabinose induced cells. (E) Uninduced cells serve as control with rod-shaped cells showing two copies of DNA as a step towards binary fission; (F, both panels) 0.2% L-arabinose induced cells in which cells tend to filament under the effect of toxin induction with no signs of cell division, but with (F, right panel) some lemon-shaped cells instead of dividing rods.