FIG 7.
The ΔtrhAEC mutant is preadapted to external stressors that perturb charge or ion gradients across the membrane. (A to E) E. coli WT and the ΔtrhAEC mutant cells were grown to the logarithmic phase at 37°C in LB medium at pH 7.0 and then shifted to (A) acid stress at pH 4.5, (B) alkaline stress at pH 9.0, (C) NaCl stress at 0.75 M or 1 M NaCl, (D) KCl stress at 0.5 M or 0.75 M KCl, or (E) sorbitol stress at 1 M or 1.5 M sorbitol. All growth curves are representative of the average and standard deviation of three biological replicates with three technical replicates. (F and G) The membrane potential of E. coli WT and the ΔtrhAEC mutant was measured using (F) ThT during acid stress at pH 4.5 or (G) alkaline stress at pH 9.0. All measurements represent the membrane potential measurements from three biological and three technical replicates. Error bars represent the standard deviation. a, significantly different from E. coli WT control (P < 0.05); b, significantly different from ΔtrhAEC control (P < 0.05); c, significantly different from E. coli WT stress treatment (pH 4.5 or pH 9.0) (P < 0.05).