Fig. 4

Roles of phoPQ TCS in stress adaptation. a Roles of phoPQ TCS in H₂O₂ susceptibility. LB agar was uniformly spread with the bacterial cell suspension tested. Sterile filter paper soaked in 15 μl of 20% H₂O₂ was placed onto the center of agar. The diameter of growth inhibition zone was measured after 24-h incubation at 37 °C. Bars represent the average values from three independent experiments. Error bars represent the standard error of the mean. *, P < 0.01, significance calculated by Student’s t test. b Roles of phoPQ TCS in MD susceptibility. The logarithmic-phase bacterial culture was adjusted to an OD_450nm of 1.0 and serially diluted 10-fold. Five-microliter suspensions were applied onto the LB agar containing 50 μg/ml MD. After 24-h incubation at 37 °C, cell viability was imaged. c Roles of phoPQ TCS in SDS susceptibility. The logarithmic-phase bacterial culture was adjusted to an OD_450nm of 1.0 and serially diluted 10-fold. Five-microliter suspensions were applied onto the LB agar containing 0.01% SDS. After 24-h incubation at 37 °C, cell viability was imaged. d Roles of phoPQ TCS in iron depletion tolerance. The logarithmic-phase bacterial culture was adjusted to OD_450nm of 1.0 and serially diluted 10-fold. Five-microliter suspensions were applied onto the LB agar containing 45 μg/ml DIP. After 24-h incubation at 37 °C, cell viability was imaged