Fig. 2.

Expression of heterologous sitAI cassettes results in traA-dependent target cell death. (A) CFU time course of target cells from agar plates when competed against SitAI-expressing inhibitors. Open circles and dashed lines indicate that target cells are ∆traA; closed circles and solid lines indicate that target cells are traA⁺. Adjacent image shows the morphology (filamentation) of fluorescently labeled traA⁺ target cells after coincubation with SitA⁺ inhibitor cells. (Scale bar, 5 μm.) (B) (Left) Results of swarm inhibition coculture experiments in which a nonmotile inhibitor strain expresses a unique sitAI cassette and susceptible motile target cells are traA⁺, ∆traA, or SitI⁺. Strains were mixed at a 1:1 ratio with the exception of SitA6^Mf1 inhibitors, which were mixed at 5:1. (Right) Results of swarm inhibition cocultures of SitAI-expressing nonmotile and SitAI-expressing motile strains at an 8:1 cell ratio. SitAI6^Mf1-expressing nonmotile inhibitors were excluded because they were always killed by the opposing motile strain and never caused swarm inhibition. SI Appendix, Fig. S1, provides micrographs of these results. All strain, plasmid, and primer details are given in SI Appendix, Tables S1–S3.