Level of toxin expression and bacterial growth.

lacI-Phspζ cells bearing plasmid pCB799 (xylR-PXylAε) were grown in MMS7 containing 0.005% Xyl to allow limiting ε2 antitoxin expression, ε(+), to titrate basal expression of the wt ζ toxin.aCells grown exponentially in MMS7 to ∼5×107 cells ml−1, a sample was collected (corresponding to 2 ml at an OD560 of 0.4), cells lysed and subjected to immunoblot transfer for toxin detection. Cells grown exponentially in MMS7 to ∼5×107 cells ml−1, 0.5% Xylb or 1 mM IPTGc was added, samples collected at different times.dThe presence or the absence of induction of ζ, ζY83C or ε2 are indicated by + or − superscript, respectively.eSamples were collected after 60 min of induction, equivalent amounts of cells (corresponding to 2 ml at an OD560 of 0.4) were lysed and subjected to immunoblot transfer for toxin detection. Toxin levels are expressed as monomers/per cells.fCell doubling time (in min) was measured by recording the OD560 every 30 min until reaching early stationary phase. NA, not applicable. The results are the average of at least four independent experiments.