Figure 3.

Effect of (p)ppGpp overproduction on the tolerance of E. coli against various abiotic stresses

(A) Hyperosmotic shock triggered by extra 2 M NaCl. The small photo shows the overnight culture after hyperosmotic shock. Large amounts of agglomerated debris appeared in the overnight liquid culture of wild-type strain while the overnight liquid culture of RelA∗ OE strain was still normal.

(B) Acid stress trigged by transition to EG medium (pH: 2.5).

(C) Oxidative stress trigged by addition of a lethal dose (20 mM) of hydrogen peroxide.

(D) Treatment by a lethal dose (20 ng/mL) of ciprofloxacin.

(E) Treatment by a lethal dose (100 μg/mL) of streptomycin. For the cases above, the viability at 0 h is set as 1. Data are represented as mean ± SD.