Percentage of PI staining and CFUs under different toxin inductions.

lacI-Phsp or lacI-Phspζ cells bearing plasmid pCB799 (xylR-PXylAε) were grown in MMS7 containing 0.005% Xyl to allow limiting expression of ε2 antitoxin, ε(+), to titrate basal expression of the wt ζ toxin.bExpression of the wt ζ toxin for 120 min was induced by addition of IPTG (1 mM).cThe cells were grown in the presence of 1 mM IPTG and 0.1% Xyl that partially induced the expression of the ε2 antitoxin for 120 min.dxylR-PXylA or xylR-PXylAζY83C were grown in MMS7, which contains 5 mM or 150 mM KCl.eWhen indicated expression of the ζY83C toxin was induced by addition of 0.5% Xyl and the culture incubated for 120 min.fThe presence or the absence of induction of ζ, ζY83C or ε2 are indicated by + or − superscript, respectively.gNumber of cells analyzed are shown in parentheses.hColonies forming units (CFUs) were measured after 120 min of toxin induction by plating appropriate dilutions on LB plates, except in the BG1125 control that was plated in LB containing 0.5% Xyl plates and the condition where both IPTG and Xylc were added that was plated in LB plates containing 0.1% Xyl. The results are the average of at least three independent experiments and are within a 10% standard error.