Fig. 2.

Thermotolerance assays were performed at 50°C (a) and 4°C (b). E. coli P (with pET-28a) and E. coli H (with pET-28a-S.so-HSP20) were cultured as described and subjected to 50°C treatment for up to 60 min and 4°C treatment for up to 4 days. After heat or cold treatment, samples were taken at the time indicated, diluted, and immediately plated on LB plates with kanamycin. Survival of E. coli H cells (black boxes) and E. coli P cells (open boxes) are shown, and are expressed as a percentage of the survival obtained in LB plates. Data are representative of three trials and were expressed as the mean±SEM. Statistical significance was performed using the two-tailed paired Student's t test. (*p < 0.05; **p < 0.01)