FIG. 4.
Conditions that confer H2O2 sensitivity. Different E. coli strains and treatments were studied and are grouped in sets of bars. For bars 1 to 3, AB1157 cells were grown to the log phase and treated with iron chelators for 5 min (none [bar 1], 1 mM dipyridyl [bar 2], and 20 mM desferrioxamine [bar 3]) before the addition of 0.5 mM cystine and 2.5 mM H2O2. For bars 4 to 11, AB1157 cells were treated with a 0.5 mM concentration of an alternative sulfur species (cysteine [bar 4], homocystine [bar 5], sulfide [bar 6], thiosulfate [bar 7], sulfite [bar 8], GSH [bar 9], GSSG [bar 10], and DTT [bar 11],) instead of cystine. For bars 12 and 13, AB1157 cells were grown in minimal medium containing cystine until the cells reached early log phase, and then the cells were washed twice and suspended in minimal medium containing sulfate for 1 h. For bar 13, 20 μg of chloramphenicol per μl was present during the period of growth on sulfate. Cystine was then added, and the cells were challenged with H2O2 for 3 min. For bars 14 and 15, BW25113 and SP53 (cysB) cells were grown in minimal medium containing djenkolic acid and tested for cystine-mediated H2O2 sensitivity. JTG10 (gshA) cells (bar 16) and WP840 (gor) cells (bar 17) were grown in minimal medium containing sulfate and tested for cystine-mediated H2O2 sensitivity. Values are the means and standard deviations (error bars) from five samples.