Effects of ygiU overexpression on persister formation. E. coli MG1655 cells were grown in LB medium to mid-exponential phase (~5 × 107 cells/ml) at 37°C with aeration. (A) ygiU expression was induced (squares) from pTOX at T = 0 by the addition of 1 mM arabinose, and MG1655 with a blank vector (pBAD33) served as the control (diamonds). (B) Cells were cultured, and ygiU expression was induced as described in (A). After 2 h of ygiU induction, samples were removed and treated with either cefotaxime (100 μg/ml), mitomycin C (10 μg/ml), ofloxacin (5 μg/ml), or tobramycin (20 μg/ml) for 3 h at 37°C with aeration. The control (MG1655/pBAD) (red bars) was challenged at a cell density similar to that of the ygiU induced cells (blue bars).