FIG 2.

Population cell size and C period measurements in B. subtilis and E. coli. (A) Cell size increases with respect to growth rate in B. subtilis and E. coli under conditions of nutrient limitation. The relationship is not as clearly exponential for B. subtilis as it is for E. coli (dotted lines are linear regression fits of logarithm-transformed data, the dashed line is a linear regression fit). Representative images of cells during division show change in aspect ratio as a function of growth rate. Length and width measurements are presented in Fig. S2. (B) C period measurements with respect to growth rate in B. subtilis and E. coli under conditions of nutrient limitation. For E. coli, C is approximately constant at 39 min (horizontal dotted line) for doubling times faster than 60 min (λ = 0.69). The two-sided P value to reject the null hypothesis that the slope of C on growth rate is zero is 0.55 using the Wald test. The constancy is less clear for B. subtilis, with a P value of 0.13 for the same test. Though lower, it is still not enough to reject the null hypothesis that the slope is zero. However, single-cell data show that C + D is proportional to generation time (Fig. S5). B. subtilis growth media are colored as described for Fig. 1B, with additional LB data in gray. The E. coli data are from previously published work (3). Red, synthetic rich; orange, glucose with 12 amino acids; yellow; glucose with 6 amino acids; green, glucose; blue, glycerol. Additional conditions are indicated in gray.