Dimensional rearrangement of rod-shaped bacteria following nutritional shift-up. II. Experiments with Escherichia coli B/r

The dimensions of Escherichia coli B/r (strain H266) in transition between two states of balanced growth, were determined from electron micrographs of fixed cells by sampling the culture at various times following nutritional shift-up from a doubling time of 72 min to one of 24 min. Mean cell length rises immediately and overshoots its final steady-state value, cell diameter increases monotonically; both approach their asymptotic levels only after several hours. The results are compared with the dimensions predicted by each of two models of cell growth and morphogenesis in rod-shaped bacteria. The first attributes cell elongation to circular zones that double in number at a particular time during the cell cycle and which act at rates proportional to the growth rate; the second is similar, except that it considers surface growth rather than length extension as the active process, length being determined passively. Two possibilities are examined, that the zonal growth rate adjusts immediately to the new growth conditions, and that it does so gradually. The experimental data appear consistent with the gradual response version of the surface growth model.