FIG. 1.

EDF is a signal molecule that can trigger mazEF-mediated cell death. We used strains MC4100relA⁺/pBAD (Cam^r), and MC4100relA⁺/pQE30 (Cam^s). Each strain was grown separately in M9 minimal medium containing the relevant antibiotic. When the cultures reached mid-logarithmic phase (OD₆₀₀ of 0.4), they were washed and resuspended in M9 minimal medium. (A) A mixture of two strains was prepared in M9 medium such that the final concentrations were 10⁸ cells/ml of a “donor” Cam^r culture (carrying Cam^r/pBAD) and 10⁴ cells/ml of “recipient” Cam^s Amp^r culture (WT or ΔmazEF carrying Amp^r pQE30). (B) Both “donor” Cam^r culture (carrying Cam^r/pBAD) and the “recipient” Cam^s Amp^r culture (carrying Amp^r pQE30) were diluted in M9 medium; a mixture of the two was prepared in which the final concentration of each strain was 10⁴ cells/ml. At various times, samples were removed and preincubated without shaking at 37°C for 10 min, after which chloramphenicol (45 μg/ml) was added to induce cell death. A culture to which no chloramphenicol was added served as a control. The cultures were washed and resuspended in preheated (37°C) saline. CFU were determined by plating on LB medium plates with either chloramphenicol or ampicillin that were then incubated at 37°C for 12 h. Here, we present only the Amp^r Cam^s subculture survivors, which we determined by comparing the number of chloramphenicol-induced Amp^r colonies versus the number of uninduced control colonies on LB medium plates with ampicillin. In this figure and in all the following figures, the results are the averages from three independent experiments that were carried out in triplicate.