Figure 1

The engineered bacteria used in this study. (A) The gene circuit consists of two modules: a killing module (red shading) and a rescue module (green shading). The killing module contains an IPTG inducible (P _lac promoter) ccdB gene from the CcdA/CcdB toxin-antitoxin system. The rescue module contains an IPTG inducible (P _lac/ara-1 promoter) luxR/luxI quorum-sensing (QS) system from Vibrio fischeri ⁸ and an AHL inducible (P _lux promoter) ccdA from the CcdA/CcdB toxin-antitoxin system. Induction with IPTG (1 mM) causes expression of luxR/luxI and ccdB. ccdB causes cell death⁴⁴. However, ccdA can inhibit ccdB if luxI synthesizes a sufficient amount of AHL (yellow circles), which is dependent upon the initial density of bacteria in the population. (B) Final density of engineered bacteria (CFU/mL) in cultures incubated for 48 hours starting from different initial densities (see Methods for details) Green bars = no IPTG, circuit off. Blue bars = IPTG, circuit on. An OD₆₀₀ of 0 indicates that no CFUs were detectable in the medium. Standard deviation (SD) from a minimum of three biological replicates.