FIG. 1.

Adaptive response of E. coli to selenite and H₂O₂ stresses. Exponentially growing cells (E. coli MC4100, GC4468, or BW829) were pretreated or not with 30 μM H₂O₂, 100 μM paraquat, 500 μM SeO₄²⁻, or 250 μM SeO₃²⁻ in the presence or absence of 100 μg of chloramphenicol/ml. After 60 min of treatment, 25 mM selenite (A, B, and C) or 5 mM H₂O₂ (D) was added to the cultures. At intervals, samples were diluted and plated onto LB agar to monitor cell viability. The data are mean values from at least three experiments, with essentially similar results. (A) MC4100 strain. Symbols: •, not pretreated; ▪, pretreated SeO₃²⁻; ▴, pretreated SeO₄²⁻; ○, pretreated chloramphenicol plus SeO₃²⁻. (B) GC4468 strain (symbols: •, not pretreated; ○, pretreated SeO₃²⁻) and BW829 strain (symbols: ▪, not pretreated; □, pretreated SeO₃²⁻). (C) MC4100 strain. Symbols: •, not pretreated; ▪, pretreated H₂O₂; ▴, pretreated paraquat. (D) MC4100 strain. Symbols: •, not pretreated; ▪, pretreated H₂O₂; ▴, pretreated SeO₃²⁻; ○, pretreated SeO₄²⁻.