Figure 1.
E. coli Activates the Colicin Operon in Response to a Competitor Causing DNA Damage
(A) Overview of the colicin operon as encoded on plasmid pColE2-P9 in E. coli. In response to DNA damage, the PcolE2 promoter is activated and the genes encoding colicin E2 (ce2a) and its cognate immunity protein (ce2i) are expressed. To ensure sufficient levels of immunity protein, ce2i is additionally transcribed from a second, constitutively active promoter (Pimm) located within the ce2a gene. A transcriptional terminator (T) after the immunity gene ce2i ensures that the downstream gene encoding the lysis protein (ce2l) is only expressed at very high levels of PcolE2 activation. Adapted from [1].
(B) The response of the E. coli colicin E2 promoter to a foreign DNase colicin (colicin E8). E. coli BZB1011 colonies producing colicin E2 were grown next to competitor colonies overnight and then imaged by stereomicroscopy (left) and confocal microscopy (right). In the colicin E2 producer, the colicin E2 promoter also drives the expression of GFP on a reporter plasmid (pUA66-PcolE2::gfp).
(C) Absence of response of the E. coli colicin E2 promoter to the pore-forming colicin E1 made by E. coli BZB1011 carrying the colicin E1 plasmid.
(D) Wild-type control where the left-hand strain (BZB1011) lacks any colicin plasmid and so does not produce colicins. Scale bars, 2 mm (left) and 50 μm (right).