Figure 1

Addiction modules. A,B,C: A bacterium containing a plasmid secrets a long-lived toxin and a short lived antidote (A). Loss of the plasmid (B) results in loss of the antidote before loss of the toxin and this causes cell death (C); D,E,F,G,H: A bacterium secreting a toxin and producing an antidote (D) will kill a bacterium that does not have the addiction module (E) and (F) whilst being protected itself (G). It is unable to kill a bacterium with the addiction module (H); I,J,K,L: A bacterium housing a plasmid with an addiction module divides (I) and a daughter cell containing the plasmid survives (J) whereas one without the plasmid (K) is killed by remaining toxin (L); a process known as post-segregational killing.