Figure 1.

Determination of the upper limit of the thermal niches of two E. coli strains. Bacterial cells were heat shocked to different temperatures ranging from 42 to 54°C. Cell survival of the strains (A) E. coli DPD3084 and (B) E. coli K12-TG1 was measured after a 1-and 2-h plateau phase at the desired temperature. The relative percentage of cell count was defined as the ratio of the number of CFU in the heat-shocked sample divided by the number of CFU in the corresponding unshocked sample (i.e., the control = 100%) multiplied by 100. The upper limit of the thermal niche corresponds to the maximal temperature at which 100% bacterial survival is recorded whereas survival rate higher and lower than 100% correspond, respectively, to cell growth and cell death. Note that no points are represented for 54°C because no cell survived. The means of at least three independent measurements were calculated and the 95% confidence intervals of the means are presented.