FIGURE 4.

Sublethal treatment with the antibiotic A22 causes cell width to increase without altering peptidoglycan composition or density. A, cell width reaches a new steady-state value after 2.5 h of A22 treatment at sublethal concentrations, and increases approximately linearly as a function of A22 concentration. Average width and length were calculated from phase-contrast images (n = 195–549 cells). Shown are the cells from each population with the smallest sum of squared deviation in length and width from the average. B, relative abundances of each muropeptide moiety remain essentially unchanged under sublethal A22 treatment. C, the ratio of integrated absorbance of the baseline-subtracted chromatogram to the concentration of protein decreases with increasing A22 concentration (c). A fit to the function A/(1 + Bc) (blue dashed line) exhibits a trend similar to that of the inverse of the average cell width ⟨w⟩ (black dotted line), indicating that the ratio is proportional to the surface area-to-volume ratio, as expected for cylinders with constant peptidoglycan density. The standard errors of the estimates of A and B are 0.055 and 0.063, respectively. n denotes the number of samples contributing to each data point.